Proceedings of the Idaho. Nutrient Management Conference

Transcription

1 Proceedings of the Idaho Nutrient Management Conference Volume 4 Sponsored by the University of Idaho Extension and the College of Agricultural and Life Sciences University of Idaho Nutrient Management Conference Planning Committee Brad Brown, Co-chair Amber Moore, Co-chair and Editor Mireille Chahine Mario de Haro Marti Christi Falen Richard Norell March 4, 28 Best Western Sawtooth Inn and Suites Jerome Idaho

2 Welcome to the 4 th Biennial Idaho Nutrient Management Conference Jerome, Idaho March 4, 28 The purpose of this one day conference is to demonstrate the various research projects that are being conducted by the University of Idaho and USDA ARS, and to identify needs for research in order to fill gaps that may arise. Continued nutrient management education is vital to the state of Idaho. This conference has been, and will remain, a valuable means of providing up-to-date research information to ensure that nutrient management planning will be agronomically and environmentally sound. We would like to thank the speakers, workshop coordinators, and especially our panelists who have graciously agreed to participate in this conference. They have taken time to share their knowledge and expertise for the improvement of nutrient management in the state of Idaho. Once again, welcome to the 4 th Biennial Idaho Nutrient Management Conference. UI Nutrient Management Conference Planning Committee Brad Brown, Cereal Cropping Specialist, Parma, ID Amber Moore, Soil Fertility Specialist, Twin Falls, ID Mireille Chahine, Dairy Specialist, Twin Falls, ID Mario de Haro Marti, Gooding County Extension Educator, Gooding, ID Christi Falen, Lincoln County Extension Educator, Shoshone, ID Richard Norell, Dairy Specialist, Idaho Falls, ID

3 Table of Contents Water and nutrient balances for the Twin Falls irrigation tract, David Bjorneberg, Dale Westermann, and Nathan Nelson... 1 New Findings in Manure/Compost/Soil Phosphorus Relations, April Leytem... 7 Organic waste nitrogen and phosphorus dynamics under dryland agroecosystems, Jim Ippolito and Ken Barbarick Potato variety response to phosphorus fertilizer, Mike Thornton, Deron Beck, Jeff Stark, and Bryan Hopkins Biofuel byproducts as nitrogen sources for potatoes, Amber Moore and Ashok Alva Irrigated small grain residue management effects on soil properties, David Tarkalson, Brad Brown, Hans Kok, and David Bjorneberg... 3 Evaluation of strip-tillage and fertilizer placement in Southern Idaho corn production, David Tarkalson and David Bjorneberg Nitrogen placement, row spacing, and water management for furrowirrigated field corn, Gary Lehrsch, Robert Sojka, and Dale Westermann Nitrogen and water use efficiency in onion production under drip and furrow irrigation, Steve Reddy, Jerry Neufeld, and Jim Klauzer Fall applied nitrogen sources for onions, Brad Brown Slow release nitrogen for irrigated hard red spring wheat yield and protein, Brad Brown Emissions from a dairy wastewater storage pond, manure processing area, and composting yard in South-central Idaho, Mario de Haro Marti, Ron Sheffield, and Mireille Chahine Dairy compost effects on soil test levels, Glenn Shewmaker and Jason Ellsworth Triticale for phosphorus removal, Brad Brown... 84

4 WATER AND NUTRIENT BALANCES FOR THE TWIN FALLS IRRIGATION TRACT D. Bjorneberg 1, D. Westermann 1 and N. Nelson 2 1 USDA ARS, Kimberly, ID 2 Kansas State University ABSTRACT Surface water return flow from the 22,5 acre Twin Falls irrigation tract to the Snake River has been measured since 25 to identify changes in water, salt and nutrient balances as conservation practices have been implemented. Irrigation water diverted from the Snake River was the main hydrologic input to this watershed, supplying 73% of the water in 25 and 83% in 26. Approximately 5% of the total water input was potentially used by crops and 35 to 4% returned to the Snake River. Two years of monitoring have shown that water quality has improved since similar monitoring took place from 1968 to Net loss of suspended sediment was 196 lb acre -1 in 25 and 9 lb acre -1 in 26 compared to 41 lb acre -1 during the 1971 irrigation season. Net loss of nitrate-n decreased from 3 lb acre -1 in 1969 to 9 to 13 lb acre -1 in 25 and 26. INTRODUCTION Monitoring on the Twin Falls irrigation tract was initiated in 25 to assess the effectiveness of conservation practices in an irrigated watershed as part of the Conservation Effects Assessment Project (CEAP), a national effort by NRCS and ARS to quantify impacts of implemented conservation practices. The Twin Falls irrigation tract is a 22,5 acre watershed located along the Snake River in southern Idaho. The Twin Falls Canal Company diverts water from the Snake River and delivers it to farms through 112 miles of main canals and over 99 miles of smaller channels and laterals. Water is typically diverted from mid-april to late- October. Runoff from furrow irrigated fields and unused irrigation water collect in surface drains that flow back to the Snake River if the water cannot be diverted to other fields. Subsurface drains also contribute flow to surface drains, which continue to flow after the irrigation season. Earlier studies showed that the Twin Falls Irrigation tract had a net loss of sediment, nitrate, and soluble salts, and a net gain of soluble phosphorus when the Twin Falls tract was about 95% surface irrigated. The net loss of 2141 lb acre -1 soluble salt (Carter et al., 1971) was a good indication for the sustainability of this irrigated watershed, but the net losses of 3 lb acre -1 nitrate-n (Carter et al., 1971) and 41 lb acre -1 of sediment (Carter et al., 1974) were a concern. The purpose of this paper is to compare the earlier water, salt and nutrient balances with current data when the Twin Falls irrigation tract is approximately 35% sprinkler irrigated. MATERIALS AND METHODS Monitoring sites for calculating water and nutrient balances are categorized as primary, secondary, or tertiary sites. Primary sites have data loggers recording water depth and automatic water samplers collecting time-composite water samples (.2 L (.75 gal.) sub-sample every 5 h in 2 L (.5 gal) bottles). The three or four 2 L composite samples from each primary site are combined into a weekly composite sample during sample processing. The 5 h interval was chosen so samples were not collected at the same time each day. Secondary sites also have data loggers recording flow but a 2 L water sample is only collected once per week. Tertiary sites 1

5 have less flow than primary or secondary sites so flow rate is manually measured once per week when 2 L water samples are collected. Flow rates at primary and secondary sites are measured with weirs or calculated from stage-discharge relationships. Flow rates at tertiary sites are measured by recording water depth from a staff gage on a weir or from a weir stick on a concrete structure. Crop areas and irrigation methods for the entire Twin Falls tract were estimated by a single field survey each year of one randomly chosen section within each of the 17 townships in the tract. Total area surveyed was 1,9 acres or about 5% of the total land area in the Twin Falls tract. The relative area of each crop type identified by the driving survey was multiplied by the total area of the irrigation district to determine the total area of each crop. Potential crop water use was calculated by multiplying crop areas by the potential water use for each crop calculated by AgriMet (USBR, 27) for the Kimberly, ID site. Non-growing season evapotranspiration (ET) was calculated using bare soil ET calculated by Allen and Robison (27). All return flow monitoring sites were visited weekly while water was flowing to collect water samples and measure flow rate or download flow data. Water samples were refrigerated until processed the day after collection. During sample processing, samples were stirred for 1 to 2 min before measuring ph and electrical conductivity (EC). A 5 ml aliquot was taken for total nitrogen (N) and phosphorus (P) analysis. A second 2 ml aliquot was filtered (.45 micron) and analyzed for dissolved nutrients and salts. A third aliquot was used to determine sediment concentration by filtering a known volume (approximately 1 ml) through.45 micron filter paper and weighing the dried filter paper. The filtered water sample was analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES) for P, K, Ca, Mg, Na, Al, Fe, Mn, Zn, and S concentrations, and by flow injection analysis (FIA) for NO 3 -N, NH 4 -N, and Cl concentrations. An aliquot (~25 ml) of the unfiltered water sample was digested with a Kjeldahl procedure (USEPA, 1983) and analyzed by ICP-OES for total P and by FIA for NH 4 -N for total N. The volume of flow at each site was calculated for each sample interval. This volume was multiplied by parameter concentrations from laboratory analysis to calculate mass loads. Loads were summed over appropriate intervals (e.g. yearly or monthly) to determine net input or output of a parameter. Flow-weighted concentrations were calculated by dividing the mass load for a time period by the total flow volume for the same period. Soluble salt concentration was calculated by multiplying EC (μs cm -1 ) by.64. RESULTS AND DISCUSSION Annual water balances and salt and nutrient loads were calculated from May to April rather than the traditional October to September water year because our monitoring began in May 25. Water balances for the first two years of monitoring are shown in table 1. Above normal precipitation in 25 contributed 24% of the total water input compared to 14% in 26. Irrigation water flowing in the Twin Falls Canal Company (TFCC) Main Canal was the main hydrologic input to the watershed, supplying 73% of the water in 25 and 83% in 26. Less water was diverted in 25 due to above normal precipitation in the spring and limited irrigation water supply due to drought. More water was diverted in the 1969 water year (88 in.) and the Main Canal contributed 89% of the total input (Carter et al., 1971). Approximately half of the total water input to the watershed was used by crops and nongrowing season ET. Annual irrigation return flow was 26 in. in 25 and 3 in. in 26, or 37% 2

6 and 43%, respectively, of the total input to the irrigation tract. About 25% to 3% of the measured return flow occurred during the non-irrigation season as a result of subsurface drainage. The positive water balance accounts for all measurement and calculation errors, the quantity of water lost through evaporation or seepage from irrigation canals, and deep percolation that did not flow to subsurface drainage. Alost 8% of the return flow was measured at primary sites (data loggers and automatic samplers). The increase in flow at tertiary sites in 26 occurred because two tertiary sites were added and one primary site was temporarily converted to two tertiary sites while the TFCC constructed new water quality ponds in 26. The Twin Falls irrigation tract still had a net loss of suspended sediment in 25 and 26 (Table 2), although current losses are much less than the 41 lb acre -1 measured by Carter et al. (1974) during the 1971 irrigation season. Converting to sprinkler irrigation, installing sediment ponds, and using polyacrylamide all contribute to reduced sediment loads in return flow streams. The difference in net sediment losses between 25 and 26 was not due to differences in return flow sediment loads but much lower inflow sediment load in 25 compared to 26 (Table 2). Additional monitoring may show that annual net sediment loss is typically less than the 196 lb acre -1 measured in 25. We also must assume that the 1971 water year was not an abnormal year when concluding that sediment loss has decreased. Compared to 1971 data, both inflow and outflow sediment loads have decreased, which is noteworthy because Carter et al. (1974) only collected data from May to September. The net sediment loss from May to September 25 was only 45 lb acre -1. There was a net gain of 116 lb acre -1 of sediment for the same time period in 26. The decreased outflow sediment loads correspond with decreased flow-weighted sediment concentrations for May to September: 3 mg L -1 in 1971, 13 mg L -1 in 25, and 1 mg L -1 in 26. Inflow sediment concentrations also seem to have decreased from 55 mg L -1 in 1971 to 29 mg L -1 in 25 and 43 mg L -1 in 26. Current monitoring indicates a net increase in soluble salts in the watershed (table 2). Data from Carter et al. (1971) indicated that there was a net loss of 2141 lb acre -1 soluble salts from the Twin Falls tract in the 1969 water year, because soluble salt concentrations in subsurface drainage were more than twice the concentration of irrigation inflow. The effects of irrigation diversion and subsurface drainage on soluble salt concentrations are demonstrated in figure 1. Inflow salt concentration was higher during the irrigation season due to higher salt concentrations in the Snake River compared to Rock Creek. Outflow salt concentrations were greater after the irrigation season when subsurface drainage contributed almost all of the flow. The change from losing salts to retaining salts was possibly due to changes in irrigation practices that result in less deep percolation that ultimately becomes subsurface drainage. Also, Carter et al. (1971) considered that the unaccounted for balance of water was subsurface flow. Using that assumption with current data changes the net accumulation of soluble salts to a net loss of about 178 lb acre -1 each year, which is still much less than the loss measured by Carter et al. (1971), indicating that less water may be percolating through the soil and flowing to subsurface drainage. Nitrate-N losses in 25 and 26 (Table 2) were less than half of loss in 1969 (3 lb acre -1 nitrate-n). Estimating the additional contribution to subsurface flow as was done by Carter et al. (1971) increases the nitrate-n loss to about 18 lb acre -1 for both 25 and 26. Decreased nitrate losses could result from less water percolating through the soil to subsurface drains or changes in other factors such as irrigation systems, fertilization practices, and crop types. 3

7 Dissolved P data indicate that there was a net gain of soluble P in the Twin Falls irrigation tract in 25 and 26 (Table 2), which means more dissolved P was removed from the Snake River than returned. The annual net gain varied among years but was always less than 1 lb acre -1. The first two years of monitoring on the Twin Falls irrigation tract indicate that water quality has improved since similar data were collected in 1968 to Exact cause-effect relationships have not been identified in this preliminary analysis, but a major change on agricultural land has been conversion from furrow irrigation to sprinkler irrigation. REFERENCES Allen, R.G. and C.W. Robison. 27. Evapotranspiration and Consumptive Irrigation Water Requirements for Idaho. University of Idaho. Carter, D.L., J.A. Bondurant, and C.W. Robbins Water-soluble NO 3 -nitrogen, PO 4 - phosphorus, and total salt balances on a large irrigation tract. Soil Science Society of American Proceedings 35: Carter, D.L., M.J. Brown, C.W. Robbins, and J.A. Bondurant Phosphorus associated with sediments in irrigation and drainage waters for two large tracts in southern Idaho. Journal of Environmental Quality 3: USBR (US Bureau of Reclamation). 27. AgriMet The Pacific Northwest Cooperative Agricultural Weather Network. USEPA (US Environmental Protection Agency) Methods for Chemical Analysis of Water and Wastes, EPA-6/ Revised March 1983, Method

8 Table 1. Water balances for 25 and 26 for the Twin Falls Irrigation Tract (in.) Inputs Main Canal (in.) Rock Creek 2 2 Total Surface Flow Precipitation 17 1 Total Input Outputs Primary Secondary 3 4 Tertiary 1 3 Total Surface Flow Crop Water Use Total Output Balance (total input total output) Table 2. Suspended sediment, soluble salts and nutrient balances for 25 and 26 for the Twin Falls irrigation tract. Suspended Sediment Soluble Salts Nitrate-N Dissolved P Inputs (lb acre -1 ) Main Canal Rock Creek Total Input Outputs Primary Secondary Tertiary Total Output Balance * * Balance is total input minus total output. 5

9 Flow-weighted Monthly Soluble Salt Conc. (mg/l) 8 6 Irrigation Diversion Irrigation Diversion 4 2 Mar-5 May-5 Aug-5 Nov-5 Feb-6 May-6 Aug-6 Nov-6 Feb-7 May-7 Aug-7 Inflow Outflow Figure 1. Flow-weighted average soluble salt concentrations in watershed inflow and outflow. Watershed inflow is the Main Canal and Rock Creek. Watershed outflow contains subsurface drainage that flows to surface drainage channels. 6

10 NEW FINDINGS IN MANURE/COMPOST/SOIL PHOSPHORUS RELATIONS A. Leytem USDA-ARS, Kimberly, Idaho ABSTRACT Land application of manure and compost can increase phosphorus (P) transfer in runoff, although the risk depends on both the sorption capacity of the soil and the characteristics of the manure and compost. Traditionally, in calcareous soils, P sorption has been thought to be controlled by the calcium carbonate (CaCO3) content. Contrary to this, we have demonstrated that there are two main phases of P reactions in the calcareous soils of southern Idaho. At low to medium P concentrations, P sorption appears to be related to organically complexed iron (Fe) and manganese (Mn), suggesting that such complexes may regulate P sorption in these soils. At high P concentrations, precipitation of (Ca-P) complexes appears to control P solubility. Manure and compost characteristics can also influence the solubility of P in soils which have received application of these materials. When manures containing large amounts of organic P (such as phytate) are added to soils, soil test P is negatively correlated to the percentage of organic P in the manures in the short term. Following longer soil reaction times, soil test P was related to the amount of carbon (C) added with the manures. When manures contain small amounts of organic P, increases in soil test P following manure application are more closely correlated with the manure C:P ratio and soil microbial P concentration rather than the P characteristics of the manures. These results suggest that stimulation of the microbial biomass by added organic C is important in determining soil P solubility following manure application. Comparison of the effects of manures and composts with fertilizer on increases in soil test P demonstrated that the same amount of total P added to a semi-arid calcareous soil resulted in differences in P solubility following the trend fertilizer > manure > compost. Although the P solubility in manure and compost amended soils was less than soils amended with fertilizers, plant production and plant P uptake, in some instances, was greater from manure and compost amended soils than soils treated with fertilizers. The chemistry of P sorption and solubility in calcareous soils is complex, and the addition of both manures and composts to these soils can create greater complexity. A better understanding of long term P cycling in manure/compost amended calcareous soils is necessary in order to better optimize use of these materials as a nutrient source. INTRODUCTION Animal production in the United States is valued at over $1 billion and has significantly consolidated over the past twenty years, with a larger number of animals being produced on an increasingly smaller land base. Such consolidation of animal production can generate regional and farm-scale nutrient surpluses that contribute to non-point source nutrient pollution of water bodies, because nutrient imports in feed and mineral fertilizer can exceed nutrient exports. Recycling manure-derived nutrients to crops not only reduces the need for commercial fertilizers, but can also improve soil physical properties. Unfortunately, the large amounts of manure produced in localized areas and the high cost of implementing effective nutrient utilization strategies in an unbalanced system often favor disposal rather than conservation of manure nutrients. 7

11 Over-application or mismanagement of manure can degrade surface and groundwater quality with excess nutrients. Phosphorus is a particular problem, because it can accumulate in soil to concentrations above those needed for optimum crop production. This is due in part to unfavorable N:P ratios in manures relative to the uptake of these nutrients by most crops, which results in over-application of P when manures are applied to meet the N requirement of the crop. As a result, long-term manure application to agricultural land leads to soil P accumulation, and can accelerate P transfer in runoff to water bodies contributing to eutrophication in freshwater ecosystems. The environmental fate of P in animal manures/composts is determined by the soil sorption characteristics as well as the chemical composition of the materials being land applied. At present, there is little information on the effect of manure/compost applications on P solubility and availability in irrigated calcareous soils of southern Idaho. This is unsatisfactory, because the recent expansion of the dairy industry in southern Idaho means that managing manure nutrients is an urgent priority. The following discussion is a brief summary of published work evaluating both the soil properties affecting P sorption on semi-arid calcareous soils, as well as the effects of manure/compost addition on P solubility and plant P uptake Further details can be obtained from the manuscripts referenced. DISCUSSION Phosphorus sorption in calcareous soils Leytem and Westermann (23) conducted a study to identify soil chemical properties controlling P sorption in semi-arid calcareous soils of the Pacific Northwest. Sorption isotherms of 18 mainly calcareous soils ranging widely in soil physical and chemical properties were constructed by equilibrating 4g soil with 4ml.1M calcium chloride (CaCl 2 ) containing between and 7 mg P L -1 for 24 h. They reported that the dominant P sorption processes in the initial region of the sorption curves was likely associated with variable charged surfaces such as oxides, clay surfaces and organically complexed metals, but there was no indication of an interaction with CaCO 3. This was particularly evident when a discernable inflection point between sorption and probable Ca-P precipitation was present as seen in a subset of 11 soils having similar sorption curve properties (Figure 1). The steep slopes of the isotherms after the inflection point were attributed to the precipitation of Ca-phosphates. Regression analysis of maximum P sorption as well as two measurements of total sorbed P consistently listed organically complexed Fe and Mn as the main factors affecting the P sorption capacity (Figure 2). Although regression does not elucidate actual interactions of soil properties, the continual selection of organically complexed metals does suggest that these metals are an important component of P sorption at low to medium P concentrations. This was attributed to P complexation with organic matter through metal bridges, or possibly organic carbon (OC) interfering with Ca-P and metal oxide precipitation by coating the surfaces of carbonates and retaining P in these surface complexes through metal interactions. 8

12 Sorbed P (mmol P kg -1 ) [Mn nta + Fe nta ] (mg kg -1 ) Figure Figure 2. Inflection point r 2 = Equilibrium P (mg P L -1 ) P Sorbed (mmol P kg -1 ) The value of the threshold concentration (C t ) needed for Ca-P precipitation, was greater in all soils than the corresponding threshold needed for precipitation in pure CaCO 3 systems (> 3 x 1-4 M). In 16 soils evaluated, C t was significantly correlated to OC. The positive correlation of C t to OC suggests that either soluble OC or OC associated with the CaCO 3 surfaces may be interfering with precipitation of Ca-phosphates at low P concentrations in these soils. In summary, both amorphous and organically complexed metals appeared to be more important to P sorption in the soils studied than was CaCO 3 concentration. In addition, these organically complexed and amorphous metals were involved in the inhibition of Ca-P precipitation. What is unclear is the role that organically complexed metals play in the sorption of P and the possible interference with Ca-P precipitation. It is possible that OC-metal complexes in solution interact with soluble P forming a cationic bridge between the OC and P, thus removing it from solution. It is also possible that these OC-metal associations exist on the surfaces of carbonates, clays and possibly even amorphous metals, thereby providing sites for sorption of P. By better understanding what soil properties are affecting P sorption as well as the inflection point at which Ca-P precipitation processes begin to control P solubility, we will be better able to predict the potential P release for plant uptake or loss through surface runoff and leaching. If organic materials are added as a nutrient source, it is beneficial to know at what concentrations they can be applied in order to maximize plant uptake of P while reducing the formation of insoluble Ca-P minerals. On the other hand, when manure or other organic materials containing P are land applied strictly for disposal, we may want to manage their application to promote precipitation of stable P complexes and, therefore, lessen the amount of P potentially lost in runoff and leaching. Phosphorus sorption in manure/compost amended calcareous soils Soluble phosphorus release from manure/compost amended soils varies considerably depending on the source of the manure/compost applied (i.e., animal species, diets fed, manure handling and storage). This is primarily due to differences in the concentrations of total and soluble phosphorus in the manure/compost, but may also in part be due to variability in other manure/compost physical and chemical properties. Inorganic phosphate is relatively soluble in soils compared to phytate (an organic P component of some manures), which is strongly retained and unlikely to be lost as soluble phosphorus in runoff. Therefore, variability of the phosphorus composition of manures/composts, either due to differences in species, manure handling techniques, or through dietary manipulation, could increase phosphorus transport from landapplied manures/composts to water bodies. 9

13 When a variety of materials (swine, dairy, and beef cattle manures having been handled/stored differently) with a range of phytate content (approximately 8% of the total phosphorus) were incorporated into semi-arid calcareous soils, there was no significant correlation between phytate content and soil phosphorus solubility (Leytem and Westermann, 25; Leytem et al., 25). In this instance the small amounts of phytate in the manures were probably insufficient to influence phosphorus solubility in the soil. Instead, phosphorus solubility was clearly influenced by the amount of C added with the manures (Figure 3). When poultry manures with a large range in phytate content (35 8% of the total phosphorus) were added to a similar calcareous soil, the amount of phytate in the manures was strongly negatively correlated with the bicarbonate extractable phosphate concentration following manure application (Leytem et al.; 26, Figure 4). Manures were applied at the same total phosphorus rate, so this correlation was almost certainly due to the greater proportion of water-soluble phosphate added in manure with lower phytate concentrations. This relationship between manure phytate and phosphorus solubility was transient, becoming insignificant after nine weeks of incubation. This demonstrates clearly that when manures are applied on the basis of phosphorus content, the proportion of phytate and, therefore, water-soluble phosphate, has a strong influence on the solubility of the manure phosphorus soon after application. Although phytate is strongly bound in soils, microbes in the semi-arid calcareous soil were able to easily break it down into inorganic phosphate within only nine weeks, increasing soil P solubility to that of manures having low phytate concentrations. Relative Percent Extractable Bicarbonate P (%) Figure 3. 1 MCP y = 78.7e -.1x r 2 =.77*** C:P ratio of source material Manure Phytic Acid (%) The solubility of phosphorus in manure-amended soils seems to be influenced by the characteristics of the manure applied. In the short term, manures with large phytate contents can demonstrate lower phosphorus solubility on calcareous soils. However, due to microbial breakdown of phytate in applied manures and concurrent release of soluble phosphorus, these differences are likely to become insignificant over time. Other manure properties, particularly the C content, seem to exert a large influence on phosphorus solubility in manure-amended calcareous soils, presumably due to stimulation of the microbial biomass and fixation of phosphorus in microbial tissue. This means that the addition of manure may result in a lower soluble phosphorus concentration than would be expected from mineral phosphate fertilizer application. Change in Olsen P (mg kg -1 ) Figure 4. Corn based diet Barley based diet -.12x r 2 =.9 (corn based diets only) 1

14 Soil test phosphorus and plant response to added phosphorus from manures, composts, and fertilizers Leytem and Westermann (25) conducted a growth chamber study to determine the effects of manure, compost, and fertilizers typically land applied on calcareous soils to determine the effects on soil test P and potential plant P availability of these sources. Six manure types (swine solids from low phytate and regular barley diets, swine liquid, dairy liquid, beef solid, and dairy compost) and four fertilizer (mono calcium phosphate, mono ammonium phosphate, Polymer coated mono ammonium phosphate, and ammonium polyphosphate) P amendments were applied to two Portneuf soils at a rate of 6 mg P kg -1, incubated for 2 weeks, then planted with barley grown for 7 weeks. The addition of identical amounts of P from fertilizers or manures/compost to soils did not uniformly increase extractable P concentrations. The greatest initial increases in extractable P were from fertilizer treatments not coated for controlled release (mono ammonium phosphate, mono calcium phosphate, ammonium polyphosphate), and in some cases liquid manure treatments were equally as effective as these fertilizers. When manure treatments were either a solid or composted material, the increase in extractable soil P tended to be smaller. The controlled release fertilizer (polymer coated mono ammonium phosphate) behaved as expected and released small amounts of P over the duration of the experiment due to the protective coating on the fertilizer particles. In general, extractable P in most treatments decreased over the course of the experiment from the combination of continued soil P reaction and plant uptake. Changes in extractable P in these soils were closely associated with the C:P ratio of the materials, as C:P increased relative P extractability decreased. The decrease in extractable P may be due to microbial uptake of P in these amended soils, stimulated by C additions. It is also possible that there was a chemical interaction between C added in the manures and P retention in the soils. The greater the C concentration, the more P that might be retained by the soils, since Leytem and Westermann (23) found that the P sorption maxima was related to the amount of organically complexed Fe and Mn in soils from this region. This strong relationship between increases in soil test P and the C:P ratio of applied manures was also documented on thirteen additional soils collected from the Pacific Northwest region (Leytem et al., 25), as well as in field studies using dairy compost and manures (Leytem, unpublished data). Plant P uptakes were similar or greater when the swine solids and liquid manures were applied compared to the inorganic fertilizer materials. Calculated relative percent extractable P values for shoot-biomass production and shoot P accumulation suggests that all manures and fertilizers, except for beef solids, were generally more effective at increasing plant growth and P uptake than an equivalent rate of P as mono-calcium phosphate. Generally, manures increased soil test P only 5% of that from inorganic mono-calcium phosphate fertilizer, but had a 5% greater impact on plant P uptake, especially the swine manures and dairy liquid. This suggests that some manures may be more effective at supplying plant P than traditional fertilizers at equivalent P application rates. In summary, solubility of P in manure or compost amended soils varies with the type of material applied. These differences affect plant growth as well as the potential for off-site losses of P, as soluble P losses are linked to extractable soil P concentrations. Different P weighing coefficients for manure effects on crop growth or water quality should be used to better predict their potential impact. In cases where manures are incorporated in calcareous soils it appears possible to determine an appropriate weighting coefficient based on an easily measured manure property, such as the C:P ratio. The relationship between C:P ratios in manures and relative soil 11

15 P extractability may also help better predict allowable P loadings when combined with manure application rates and appropriate soil properties. However, additional field studies are needed to further develop it for this use. CONCLUSIONS The processes controlling P solubility in calcareous soil are complex. Phosphorus sorption in these soils is controlled by clays, metal oxides, and organically complexed metals at low P concentrations, while Ca-P precipitation occurs at higher P concentrations. The amount of organic matter in a soil can either enhance P sorption or inhibit P precipitation resulting in enhanced solubility of P added to these soils. When manures and composts are added to calcareous soils, the characteristics of the materials themselves can significantly influence the P solubility. Materials having high organic P concentrations (i.e. phytate) have greater P sorption in the short term, as phytate is sorbed strongly by soils. Over time as phytate degrades in these soils, the soluble P increases and tends to be controlled by the carbon content of the applied materials. Materials that have low organic P concentrations (typical of the manures/composts in southern Idaho) tend to have P solubility controlled by the amount of carbon added with the materials, due to chemical and microbial influences. Although manure amended soils may have a lower soil test P value than soils amended with fertilizers at the same total P rate, the plant P uptake is greater in some instances, suggesting that manure amended soils have good potential to supply plant available P. A better understanding of long term P cycling in manure/compost amended calcareous soils is necessary in order to better optimize use of these materials as a nutrient source. REFERENCES Leytem, A.B. and D.T. Westermann. 23. Phosphorus sorption by Pacific Northwest calcareous soils. Soil Sci. 168: Leytem, A.B. and D.T. Westermann. 25. Phosphorus availability to barley from manures and fertilizers on a calcareous soil. Soil Sci. 17: Leytem, A.B., B.L. Turner, V. Raboy, K. Peterson. 25. Linking manure properties to soil phosphorus solubility: Importance of the carbon to phosphorus ratio. Soil Sci. Soc. Am. J. 69: Leytem, A.B., D.R. Smith, T.J. Applegate, and P.A. Thacker. 26. The influence of manure phytic acid on phosphorus solubility in calcareous soils. Soil Sci. Soc. Am. J. 7:

16 ORGANIC WASTE NITROGEN AND PHOSPHORUS DYNAMICS UNDER DRYLAND AGROECOSYSTEMS J. Ippolito 1 and K. Barbarick 2 1 USDA-ARS, Kimberly, ID 2 Colorado State University, Fort Collins, CO ABSTRACT Organic waste beneficial-use programs effectively recycle plant nutrients when applied at agronomic rates. Our objectives were to determine: biosolids nitrogen (N) fertilizer equivalency; biosolids N mineralization during years of above and below average precipitation and long-term N mineralization; which soil phosphorus (P) phases dominate following years of biosolids application; and the potential increased environment risk of P when applying an agronomic N rate or excessive rate of biosolids. To address questions related to N dynamics, we utilized research results collected between 1993 and 24 from a site in Eastern Colorado that received, 1, 2, 3, 4, and 5 dry tons biosolids A -1. To address questions related to P dynamics, results collected between 1982 and 23 from a second Eastern Colorado site which received, 3, 6, 12, and 18 dry tons biosolids A -1 were used. First-year biosolids N mineralization rates were estimated at 25-32% and 21-27%, respectively; long-term first-year N mineralization rate ranged between 27-33%. Based on wheat-grain N uptake, we found that an application rate of 1 dry ton biosolids A -1 supplied about 2 lbs N A -1. Based on the Colorado P index risk assessment, biosolids applied at agronomic N rates would not force producers to alter application strategies. However, based on this risk assessment, biosolids over-application would force land application rates to be based on crop P requirements. Previous results showed that a minimum of 3 cropping cycles were necessary to reduce soil P concentrations to levels considered less likely to cause environmental degradation. A future reduction in water availability may force some Idaho growers to shift from irrigated to dryland cropping systems. Coupled with the increased production of dairy waste, land applicators will need to find new means to protect natural resources under dryland conditions. Results from our studies have the potential to improve nutrient use efficiency and minimize environmental risk associated with dryland organic waste land application. INTRODUCTION Between 21 and 25, the number of dairies in Idaho decreased by 15%; however, the number of dairy cows increased by nearly 24% (Holley and Church, 26). Results imply that confined animal feeding operations (CAFOs) are becoming larger. Concurrently, the demand for water in the Western US has increased due to a number of factors such as drought, industrial demand, and population growth. Thus, in the future, Idaho producers will most likely be asked to provide high-yielding, high-quality crops to support the dairy industry, while being faced with a reduction in available water. Many reduced-water use or dryland crops will be grown on soils in close proximity to CAFOs. These soils will most likely receive greater quantities of animal waste as compared to soils located at greater distances from the CAFO, forcing producers to follow strict nutrient management plans. Best management practices will be coupled with waste applications based on agronomic requirements of crops to be grown. Organic waste beneficial-use programs have been shown to effectively recycle plant nutrients when applied at agronomic rates. The USEPA (1993) 4 CFR Part 53 regulations for 13

17 beneficial use of biosolids (sewage sludge) promotes recycling of this material on some crop lands since it is an excellent source of several plant nutrients such as N and P. However, mismanagement of N and P can lead to environmental issues such as ground/surface water contamination and waterway eutrophication. Thus, nutrient availability, transport, and fate concerns have arisen when organic wastes such as biosolids have been applied to dryland agroecosystems. For continuous land application programs under dryland conditions, an important environmental quality and protection question is: How much N will be supplied by biosolids? Short and long-term answers to this question are important because most states require biosolids, as with other organic wastes, to be applied at the agronomic rate for N. And, because biosolids organic N concentrations are much greater than inorganic N forms, one may ask the following questions: What is the apparent first-year N mineralization rate in dryland agroecosystems? What is the first-year N mineralization rate during years of increased precipitation as compared to that during years of drought? In some situations, application of biosolids at an agronomic-rate must be based on P rather than N availability. For example, concerns about agricultural-p pollution of surface water prompted the state of Maryland to require P-based agronomic rates (Shober and Sims, 23). Applying agronomic rates of biosolids and many other organic materials based on N equivalency leads to soil P accumulation, since the P amounts applied exceed crop removal (Shober and Sims, 23). Consequently, tracking labile P levels is crucial in any organic waste beneficial-use program. Because organic waste application based on N equivalency tends to oversupply P, one may ask the following questions: Is the excess soil P an environmental concern? If errors were made in agronomic rate calculations and over-application occurred, what would the repercussions be in terms of excess soil P? The objectives of this research were to assess the 12-year or 2-year impact of repeated, increasing biosolids applications on the: 1) biosolids N equivalency; 2) N mineralization rate of biosolids applied to a dryland winter wheat fallow agroecosystem over 6 years of above average precipitation, 6 years of below average precipitation, and over the 12 year study period; 3) total recovery of biosolids applied P; 4) dominant inorganic soil P phases; and 5) potential of increased environment risk of P when applying an agronomic N rate or excessive rate of biosolids. MATERIALS AND METHODS Nitrogen Field Study The N field study began in the summer of 1993 on plots approximately 2 miles east of Brighton, CO. From 1993 to 24, anaerobically digested biosolids were collected prior to land application and analyzed for organic N, ammoniacal nitrogen (NH 4 -N), and nitrate nitrogen (NO 3 -N) (Table 1). Every year, biosolids were hand-applied to 6 ft by 56 ft plots at rates equal to, 1, 2, 3, 4, and 5 dry tons A -1, hand raked to improve uniformity, and incorporated to a depth of ~ 8 inches. Every year, urea fertilizer (46--) was hand applied to non-biosolids plots at rates of, 2, 4, 6, 8, and 1 lbs A -1. These rates bracket those commonly used on dryland wheat in Colorado (typically 2-3 dry tons biosolids A -1 ; 4 lbs N fertilizer A -1 ). Four replications of all treatments were used in a randomized complete block arrangement. Grain samples were collected from all cropping years, and grain N concentration was determined by dividing protein content found with a Dickey John GAC III near infra-red analyzer by 5.7. Grain N uptake (N u ) was determined by N u = N c *Y*1, where N c = grain N concentration and Y = grain yield. Linear regression analyses were then completed for the effects of biosolids and N fertilizer rates 14

18 on N u for each harvest, and for the total grain yield and cumulative N u for the first and second 6-year period, and over the 12 yrs of study. The first 6-year period ( ) were years of above average precipitation; the second 6-year period ( ) experienced drought conditions. We took the average intercept for each material s linear regression model and completed a second set of regression analyses where the intercept for the biosolids and the N fertilizer models were set to the average intercept of both. This approach allowed us to equate the N fertilizer to the biosolids regression equation. Nitrogen fertilizer equivalency (N E ) was then found by calculating the ratio of the slope of the biosolids curve to the slope of the N curve as: N E = B slope /N slope. Plant available N (N p ) from the USEPA (1983) calculation was next determined, assuming an application rate of 1 dry ton biosolids A -1 and a first-yr mineralization rate of 2%: N p = [N NO3 + K v (N NH4 ) +.2(N o )] + residual, where N NO3 = biosolids NO 3 -N content, K v = NH 4 -N volatilization factor (assumed to be a range of for complete loss to 1. for complete recovery of NH 4 -N), N NH4 = biosolids NH 4 -N content, N o = biosolids organic N content, and residual = residual N o from previous two biosolids applications. Using N E, N p, and assuming a 2% first-yr mineralization rate (USEPA, 1983), the effective N mineralization rates (M r ) for the first and second 6-year periods, and over the entire 12-year period was determined using M r = (N E *.2)/N p. Phosphorus Field Study The P field study began in the summer of 1982 on plots approximately 15 miles east of Brighton, CO. Every other year from 1982 to 22, anaerobically digested biosolids were handapplied to 12 ft by 56 ft plots at rates equal to, 3, 6, 12, and 18 dry tons A -1, hand raked to improve uniformity, and incorporated to a depth of 8 inches. Biosolids were not applied in 1998 due to a potential land sale. Biosolids were collected every year prior to land application, and analyzed for total P (Table 1). The 18 dry tons A -1 application rate was discontinued in 1992 because it was deemed excessive in terms of many soil parameters (N, P, micronutrients). In a previous study, we utilized the 18 dry tons A -1 plots to determine the time necessary for P to be reduced to concentrations which would lower environmental risk (Barbarick and Ippolito, 23). Four replications of all treatments were used in a randomized complete block arrangement. Yearly and cumulative masses of biosolids-borne P applied for each application rate were determined (i.e. P inputs). Yearly wheat grain samples were collected, digested with concentrated HNO 3, and analyzed for P. Yearly and cumulative masses of grain-p removed were determined based on P content and yield of grain. Phosphorus contained within wheat straw was assumed to be returned to the soil during conventional tillage practices. The potential soil P accumulation was estimated as the difference between the amount of biosolids P added and the amount of P removed in grain. Soil samples were collected from the -8 and 8-24 inch depths from each plot following the 23 wheat harvest. Soils were air-dried, crushed to pass a.8 inch sieve, and total P determined using a 4 M HNO 3 digest. The actual increase in total soil P (- to 24 inch depth) was calculated from the difference between the 1982 and 23 total soil P concentrations. Dominant inorganic soil P mineral phases (soluble, aluminum (Al)-bound, iron (Fe)-bound, occluded, calcium (Ca)-bound) were determined in the soil surface (-8 inches) and subsurface (8-24 inches). Finally, a P risk index assessment was used, based on, among other factors, soil AB-DTPA test P, to determine P risk associated with agronomic or excessive biosolids application rates. Values for soil AB-DTPA test P are typically half of soil Olsen test P values commonly used for Idaho soils. 15

19 RESULTS AND DISCUSSION Nitrogen Field Study Twelve years of biosolids applications produced N equivalencies, based on winter wheatgrain N uptake, of about 2 lbs N A -1 (Table 1). A dryland winter wheat crop typically requires about 4 lbs N A -1 ; thus, approximately 2 dry tons biosolids A -1 would meet the crop N needs. Estimated biosolids first-year N mineralization rates over 6 years of above average precipitation were 25 to 32%, while over 6 years of below average precipitation were 21-27%. Over the 12 year study period, estimated first year N mineralization rates ranged from 27-33%. In Washington, Cogger et al. (1998) found that dryland winter wheat recovered 11to 44% of biosolids-borne N. Using 12-week laboratory incubations, Lerch et al. (1992) found a 55% mineralization for the L/E biosolids. He et al. (2) reported 48% N mineralization from pelletized biosolids. Results from our research can aid land applicators in determining first-year N release from this organic waste under dryland conditions. Erring on the side of conservatism (i.e. greater first-year N mineralization), organic waste applicators could calculate and supply the crop N needs while protecting the environment against off-site N transport. Table 1. Organic N, NH 4 -N, and NO 3 -N in biosolids applied from 1993 to 24 on the N field study plots. Biosolids-borne P applied from 1982 to 23 on the P field study plots. N Field Study Yr applied Organic N NH 4 -N NO 3 -N P Field Study Yr Applied P lbs ton lbs ton < < < < < < < < < <.2 Phosphorus Field Study Based on the difference between cumulative biosolids P added and cumulative grain P removed, predicted accumulated soil P in the, 3, 6, 12, and 18 tons biosolids A -1 treatments were -1, 18, 36, 76, and 36 lbs P, respectively (Table 2). The 1982 background soil P content (- 24-inch depth) was 6 lbs (Utschig et al. 1983). Increases in soil P within the -24-inch depth were evident for the control and all treatments in 23, and actual and predicted increases for each treatment compared poorly. However, the control ( tons A -1 ) rate showed an increase of 11 lbs P over the site life, while the predicted P accumulation showed a decrease of 1 lb P. The control P increase could have been due to soil tillage redistribution (Yingming and Corey, 1993) since the research site is managed using conventional tillage practices. If actual increases for all biosolids rates were adjusted based on the difference between the control actual increase and the control predicted increase, 11 - (-1) or 12 lbs P, predicted and adjusted actual increases were more comparable (Table 2). Based on the adjustment, percent recovery in this study ranged from 92 to 128%. Essentially, most of the added P can still be accounted for in the plots. We 16

20 regressed cumulative mass of P applied versus cumulative biosolids applied, and showed that at agronomic rates, about.13 lbs P A -1 should be redistributed per year due to conventional tillage. Table 2. The 1982 background total soil P content, harvest total soil P content, actual increase in total soil P content, predicted total soil P content increase (based on background P, biosolids-applied P, and crop removal of P), adjusted actual total soil P content (based on subtraction of control actual increase from predicted increase, or -12 lbs), and adjusted percent P recovery. Biosolids rate 1982 background harvest Actual increase Predicted increase Adjusted actual increase Adjusted percent recovery tons A lbs P in the -24-inch soil depth % The 18 tons biosolids A -1 application rate was discontinued in Increasing biosolids rate did not affect soluble and Ca-bound P fractions in the -8-inch soil depth (data not shown). As compared to other soil fractions, the soluble fraction was relatively low because this fraction forms strong complexes with other soil mineral phases (i.e. Al-, Fe-, Ca-bound phases). No difference in the Ca-bound P phase was due to excess free Ca present in the system, because this soil was derived from calcareous parent material. However, increasing biosolids rate increased P associated with the Al-bound, Fe-bound, and occluded phases. Maguire et al. (2) utilized the same P fractionation technique and found that biosolids additions led to increases in both Al and Fe-bound P fractions when compared to untreated control soils. We observed the Fe-P fraction dominating all biosolids amended soil fractions, likely due to the addition of amorphous Fe-oxide phases, since Fe is routinely added during wastewater treatment. Iron phases appeared to be transported downward, precipitating in the subsoil as occluded species. This P phase should not move deeper under dryland conditions. Based on the Colorado P index risk assessment, the biosolids agronomic rate (2 dry tons A -1 ) placed offsite P movement risk in the medium category. Accordingly, biosolids application could continue to be based on the crop N needs; best management practices should be considered to further lessen the potential offsite P movement. A tripling of the dryland wheat agronomic rate (6 tons A -1 ) increased the offsite risk movement to a level considered very high, based solely on increased soil test P. Biosolids application would have to be based on crop P requirements instead of N. This would limit the biosolids amount land-applied, and a supplemental N source would be needed to supply crop N requirements. Based on previous research (Barbarick and Ippolito, 23), biosolids land application would need to cease for about 6 years (3 cropping cycles) to allow a reduction in soil test P levels comparable to agronomic rates. These results emphasize the need to strictly follow sound environmental practices when land-applying organic wastes. Reductions in future water availability in Idaho will more than likely shift agricultural practices towards the use of reduced or dryland agroecosystems. And, with the increasing Idaho dairy herd population, an understanding of organic waste utilization under reduced water conditions will be needed. Dryland production can be improved, input costs reduced, and environmental quality enhanced with scientifically sound knowledge of crop growth coupled 17

21 with nutrient management and dynamics. Results from our research emphasize the need to strictly follow sound environmental practices when land-applying organic wastes. REFERENCES Barbarick, K.A., and J.A. Ippolito. 23. Termination of sewage biosolids application affects wheat yield and other agronomic characteristics. Agron. J. 95: Cogger, C.G., D.M. Sullivan, A.I. Bary, and J.A. Kropf Matching plant available nitrogen from biosolids with dryland wheat needs. J. Prod. Agric. 11: He, Z.L., A.K. Alva, P. Yan, Y.C. Li, D.V. Calvert, P.J. Stofella, and D.J. Banks. 2. Nitrogen mineralization and transformation from composts and biosolids during field incubation in a sandy soil. Soil Sci. 165: Holley, D., and J. Church. 26. The economic and fiscal impacts of the dairy farming and dairy product manufacturing industries in south central Idaho. Boise State Univ. Boise, ID. Available at: 2Fiscal%2Impacts.pdf (verified 28 January 28). Lerch, R.N., K.A. Barbarick, L.E. Sommers, and D.G. Westfall Evaluation of sewage sludge proteins as labile carbon and nitrogen sources. Soil Sci. Soc. Am. J. 56: Maguire, R.O., J.T. Sims, and F.J. Coale. 2. Phosphorus fractionation in biosolids-amended soils: Relationship to soluble and desorbable phosphorus. Soil Sci. Soc. Am. J. 64: Shober, A.L., and J.T. Sims. 23. Phosphorus restrictions for land application of biosolids: Current status and future trends. J. Environ. Qual. 32: U.S. Environmental Protection Agency Standards for the use or disposal of sewage sludge. Fed. Regist. 58: Utschig, J.M., K.A. Barbarick, R.H. Follett, and D.G. Westfall Application of liquid sewage sludge to dryland wheat: Annual Report for the cities of Littleton and Englewood, CO. Colorado State University. Fort Collins, CO. Yingming, L., and R.B. Corey Redistribution of sludge-borne cadmium, copper, and zinc in a cultivated plot. J. Environ. Qual. 22:

22 POTATO VARIETY RESPONSE TO PHOSPHORUS FERTILIZER Mike Thornton 1, Deron Beck 1, Jeff Stark 2 and Bryan Hopkins 3 1 University of Idaho, Parma Research and Extension Center 2 University of Idaho, Idaho Falls Research and Extension Center 3 Brigham Young University, Provo, UT ABSTRACT The response of four potato varieties (Russet Burbank, Ranger Russet, Shepody, 6LS) to applied fertilizer P was evaluated in a three year study (25-27) at Parma, ID. Soils with relatively low soil test P levels (5 to 15 ppm) were fertilized with (, 1, 2, 3 lbs P 2 O 5 /acre) applied as a spring broadcast prior to bedding. Plant development, measured as ground cover, was significantly reduced at low fertilizer P levels. Petiole P concentration increased with increasing fertilizer rate in all cultivars except Shepody. Total and US No.1 yields were generally optimum at the 2 lb rate. Ranger Russet and 6LS tended to exhibit a stronger yield response to P fertilizer than Shepody or Russet Burbank. Total P uptake by tubers, based on tuber nutrient content and dry matter yield, indicated that potatoes removed 21 to 33 lbs P per acre, with a slight increase in this value with increasing fertilizer rate. These results show that new potato varieties may exhibit differences in plant P status and yield response to applied P fertilizer compared to Russet Burbank. INTRODUCTION Phosphorus is a critical nutrient in potato plant and tuber development, and plant P status has been shown to be closely related to yield. Recommendations on P fertilizer rates and inseason petiole P concentrations for potatoes were primarily developed for Russet Burbank, the most widely grown variety in Idaho. However, the proportion of acreage planted to Russet Burbank has been declining, while newer varieties such as Shepody and Ranger Russet are increasing. There is relatively little information available on the P fertilizer requirements of potato varieties other than Russet Burbank. Work that has been done with respect to N management shows substantial differences among varieties. The objective of this research was to compare the response to fertilizer P rate of four potato varieties in terms of plant growth, petiole P concentration, tuber yield and total P uptake. METHODS Fields for these studies were chosen each year based on soil test P concentrations. The fields had not been cropped to potatoes for at least 4 years prior to these studies, and were usually in small grains the year prior to the trial. Soil P concentrations ranged from 5 to 15 ppm (Table 1), and were considered likely to result in a significant response to P fertilizer. Four rates of P fertilizer (, 1, 2, 3 lbs P 2 O 5 /acre) were broadcast applied as in the spring prior to potato planting. The P fertilizer, along with enough urea to balance the total amount of nitrogen applied, was incorporated into the bed during the hilling operation. Cut certified seed of four potato varieties (Russet Burbank, Ranger Russet, Shepody, 6LS) was planted with a mechanical planter in early April of 25, 26 and 27. Individual plots were 6 rows wide by 3 feet in length. The experimental design was a randomized split plot with 5 replications. Ground cover was determined weekly from emergence through full row closure and after the beginning of vine senescence until vine kill as a measure of plant growth. The data are 19

23 expressed as the relative area under the ground cover curve (RAUGCC). Tissue P concentration was determined on the 4 th petiole at two dates during mid-season each year. Total vine and tuber dry matter and tissue P concentration were determined on 5 plant samples from the border rows of each plot on these same dates. At harvest, tubers from the middle two rows of each plot were collected, graded by size, and weighed. Tuber specific gravity and incidence of hollow heart and brown center were determined on a 2 tuber sample from each plot. Table 1. Soil analysis results for the experimental fields at the Parma Research and Extension Center during 25 to 27. Year ph Free lime (%) P concentration (ppm) RESULTS AND DISCUSSION Plant development was more impacted by fertilizer P rate in Shepody compared to the other varieties (Figure 1). This was due to a slight delay in early season plant growth at low fertilizer rates, followed by more rapid senescence at the end of the season. The variety 6LS was observed to exhibit severe early season plant stunting under low fertilizer P rates. However, the vigorous vine growth habit of this variety resulted in complete row closure in all treatments, and relatively less impact on ground cover over the entire season. Petiole P concentrations in mid-july to early August ranged from.17 to.28%. Ranger Russet generally had the highest petiole P levels at any given fertilizer rate while Russet Burbank was the lowest (Figure 2). There was a significant increase in Petiole P levels with increasing P fertilizer rate in all varieties except Shepody. Petiole P concentrations in Russet Burbank and 6LS were often below the critical concentration of.22% recommended by the University of Idaho (Stark, Westermann and Hopkins, 24). Total and US No.1 tuber yield were generally optimum at the 2 lbs P 2 O 5 /acre rate (Figure 3A,B). Ranger Russet and 6LS exhibited a greater response to P rate compared to Russet Burbank and Shepody. Total P uptake in tuber tissue was also optimum at 2 to 3 lbs P 2 O 5 /acre (Figure 4). P uptake ranged from 21 to 33 lbs/acre, and there was a slight increase in total P removal in tubers as fertilizer P rate increased. 2

24 RAUGCC Burbank 6LS Ranger Shepody Fertilizer P (lbs/acre) Figure 1. Influence of fertilizer P rate on ground cover development as expressed by the relative area under the ground cover curve (RAUGCC). Data for each variety is the mean of 5 replications and two years (26-27) at Parma, ID..3 Total P (%) Burbank 6LS Ranger Shepody Fertilizer P (lbs/acre) Figure 2. Influence of fertilizer P rate on total P concentration in the 4 th petiole for samples taken mid July to early August. Data for each variety is the mean of 5 replications and two years (25-26) at Parma, ID. 21

25 (A) 75 7 Burbank Ranger 6LS Shepody Total (cwt/acre) Fertilizer P (lbs/acre) (B) 65 6 Burbank Ranger 6LS Shepody US No. 1 (cwt/acre) Fertilizer P (lbs/acre) Figure 3. Influence of fertilizer P rate on A) total yield and B) US No 1 yield of 4 potato varieties. Data for each variety is the mean of 5 replications and three years (25-27) at Parma, ID. 22

26 35 P Uptake (lbs/acre) 3 25 Burbank 6LS Ranger Shepody Fertilizer P (lbs/acre) Figure 4. Influence of fertilizer P rate on total P uptake by tubers of 4 potato varieties. Data for each variety is the mean of 5 replications and two years (25-26) at Parma, ID. 23

27 BIOFUEL BYPRODUCTS AS NITROGEN SOURCES FOR POTATOES A. Moore 1 and A. Alva 2 1 University of Idaho, Twin Falls Research and Extension Center 2 USDA ARS, Prosser, Washington ABSTRACT The new development of ethanol and biodiesel plants in the United States is creating a large, and potentially excessive, quantity of byproducts in the forms of distillers grains and oilseed meals. The organic nitrogen (N) compounds in these byproducts rapidly mineralize in soils, showing the potential to be used as a N fertilizer source to plants. The objective of this research is to evaluate the application of biofuel byproducts on yield, size distribution, and nutrient uptake for Russet Umatilla potatoes. Canola meal, mustard seed meal, dried distillers grains, and a urea fertilizer (46 %N) were hand-applied at rates of 1, 15, and 2 lb total N/acre. The lowest tuber yield for mustard meal was at the highest N rate, and may be related to the isothiocyanate concentration in the meal. Potatoes fertilized with canola meal, mustard meal, and dried distillers grains had higher tuber yields and proportionally heavier tubers at all rates, compared to potatoes fertilized with urea. It appears that the urea fertilized potatoes were suffering from a sulfur (S) deficiency, which could cause a tuber yield reduction. INTRODUCTION With concerns in the United States regarding the availability of petroleum-based fuels, interest in plant-based fuel feedstocks is on the rise. For example, as of 28, there are seven ethanol plants proposed for Washington and four for Idaho. There are also two active biodiesel operations in Washington and one in Idaho. The biofuel industry introduces the production of new byproducts to our region, specifically dried distillers grains from ethanol production, and canola and mustard meals from biodiesel production. Approximately 56 lbs. of dried distillers grains are generated in the production of one gallon of ethanol, and 11 and 18 lbs of meal is produced to make one gallon of canola and mustard-biodiesel, respectively. One option for recycling biofuel byproducts is to apply the material to croplands as a fertilizer source. During the fermentation process in corn ethanol production, proteins are degraded and starches are converted to ethanol and carbon dioxide, leaving rapidly available organic N compounds that can be released to plants as a primary N source. The crushing and pressing process of canola and mustard seed for oil production leaves highly degradable N compounds in the pressed meals. In a previous study conducted by Moore and Alva, the proportion of N available from the dried distillers grain and mustard meals was 56 and 61%, respectively, over a 21 day incubation period. In addition, both grains and meals contain significant concentrations of phosphorus (P), potassium (K), and S, which are all essential nutrients for plants. Distillers grains and oilseed meals show the potential to be particularly useful fertilizers for potatoes, which have N requirements ranging from 2 to 35 lb/acre, depending on the variety and the growing conditions. These materials also show promise in the organic markets, where economic and effective N sources are often difficult to find. In addition, isothiocyanate compounds in mustard meals have shown the potential suppress weed, fungal, nematode, and insect populations, which would be immensely beneficial for organic growers. 24

28 The objective of this research is to evaluate biofuel byproducts as a nutrient source for Russet Umatilla potatoes by evaluating tuber yield, tuber size distribution, soil ph, and concentrations of nitrate (NO 3 ), P, K, and S in the plant tissue. METHODS The field research for this experiment was conducted on the USDA ARS Research Farm near Paterson, in south central Washington. This region of Washington receives an average of 7-1 inches of precipitation per year, and is regarded as a high yielding region for process potatoes. Russet Umatilla potatoes were planted in a Quincy sand (Mixed, mesic Xeric Torripsamments), and irrigated through pivot irrigation. The pre-plant N source treatments were canola meal, mustard meal pressed from v. Ida Gold mustard seed, dried distillers grains, urea (46% N), and an untreated control. Nitrogen content of the amendments is listed in Table 1. Amendments were hand-applied at rates of 1, 15, and 2 lb total N/acre for all amendments, and incorporated with a roto-tiller prior to planting. The total amount of each material applied is listed in Table 2, based on dry weight. Nitrogen was also applied in-season at a rate of 12 lb N/acre for all plots through multiple application with pivot fertigation as urea ammonium nitrate (UAN), to maximize tuber bulking rates. Tuber yield and size distribution was determined post-harvest for all plots. Soils were sampled monthly for nitrate nitrogen (NO 3 -N) and ammoniacal nitrogen (NH 4 -N) at -12 and inch depths (data not shown). Petioles were sampled weekly at the 5 th node, and analyzed for NO3, P, K, and S concentration in the tissue. Table 1. Nitrogen content of amendments used in this study. Amendment % total N Canola meal 5.3 Mustard meal 4.7 Dried distillers grain 4.3 Urea

29 Table 2. Quantities of amendment applied to meet nitrogen rates. Treatment N rate (lb/acre) Material applied (ton/acre) Mustard meal Canola meal Dried distillers grains Urea RESULTS AND DISCUSSION Overall tuber yields ranging from 8 to 86 cwt./acre did not vary greatly between canola meal, mustard meal, and distillers grains amended soils (Figure 1). We were not expecting a drastic difference in yield among the biofuel byproduct amended soils, as the byproducts have similar N contents and N mineralization rates. Focusing on specific amendments, the lowest tuber yield for mustard meal was at the highest N rate in the experiment at 2 lb total N/acre (figure 1). We speculate that the decrease in yield is related to the isothiocyanate concentration in the meal. Tuber yields were lower for soils amended with urea, using the same total N rate that was used for the biofuel byproduct amendments. This result was not expected, because N in urea is assumed to be 1% available to plants, and oilseed meals and distillers grains have only up to 6% available N. The decrease in yield for urea-amended soils could be related to lack of additional nutrients, specifically S, in the soil. Urea amended soils had a larger proportion of tubers under 4 oz. than the soils amended with biofuel byproducts. Again, this could be related to low S, which is a key component in tuber growth. 26

30 Figure 1. Tuber yields for Russet Umatilla potatoes grown on a Quincy sand in Paterson, Washington, as affected biofuel byproducts as preplant nitrogen sources. Petiole NO 3 -N concentrations for Urea treatment in central Washington were consistently at or above recommended concentrations from WSU extension. For biofuel byproducts, petiole NO 3 -N concentrations were within recommendations for the initial vegetative stages of growth, but at the lower end of the range for the tuberization and tuber bulking stages. Petiole N in distillers grains were similar to control. Based on these results alone, one would expect to see higher tuber yields with the urea treatment. Figure 2. Fifth node petiole NO3-N concentrations from Russet Umatilla potatoes grown on a Quincy sand in Paterson, Washington, as affected biofuel byproducts as preplant nitrogen sources. Recommended Petiole S range for central Washington is between.15 and.2 % S for the duration of the growing season (two black lines). Soils at lower end of recommended S content, at 2 ppm SO 4 -S seem to have created S limiting conditions for tuber growth. Mustard 27

31 meal treated plants were generally within the recommended range of S concentrations, and had the highest petiole S concentrations of all of the amendments used in this study. The isothiocyanate compounds in the mustard meals contain S. Growers may not need to apply S when using mustard meals, depending on application rates and crop needs. Petiole S was generally greater for distillers grains and canola meal than urea. Although not as great as mustard meal, S compounds in canola mea and distillers grains appear to be available for uptake by potato plants, thus contributing to tuber growth. Figure 3. Fifth node petiole S concentrations from Russet Umatilla potatoes grown on a Quincy sand in Paterson, Washington, as affected biofuel byproducts as preplant nitrogen sources Petiole P and K concentrations were similar for all treatments, including the nonamended control, illustrating that the soils were not P or K limiting. In summary, Russet Umatilla potatoes fertilized with canola meal, mustard meal, and dried distillers grains had higher yields and larger tubers compared to urea, at least under S- limiting soil conditions. Applying mustard meal at a N rate of 2 lb N/acre or higher shows the potential to reduce tuber yields, due to toxic concentrations of isothiocyanates. Higher tuber yields and lower nitrogen uptake with biofuel byproducts in comparison to urea may be attributed to the concentration of S and other nutrients in the soil, as well as biological, physical, and/or chemical unknowns. This study will be continued in Paterson, Washington for 28, with an increase in application rates to determine toxicity levels of biofuel byproducts for potatoes. The soils will be supplemented with S fertilizers to verify whether S limiting conditions were actually reducing yields for urea treated tubers. There are also plans underway to investigate the use of biofuel byproducts as fertilizers in south central Idaho, with the expectation that the increased lime content, cooler temperatures, and decreased day length, in comparison to Washington conditions, 28

32 would have an effect on N availability of the products. Specifically, we are planning to include grains and meals in the nutrient management of potatoes, barley, winter wheat, and bean crops grown in rotation on the organic research field site in Kimberly, Idaho. 29

33 IRRIGATED SMALL GRAIN RESIDUE MANAGEMENT EFFECTS ON SOIL PROPERTIES D. Tarkalson 1, B. Brown 2, H. Kok 3, and D. Bjorneberg 1 1 USDA-ARS, Kimberly, ID 2 University of Idaho, Parma, ID 3 Washington State University and University of Idaho, Moscow, ID ABSTRACT The effects of straw removal from fields under irrigated wheat and barley on soil properties has become a potential concern in Idaho. The demand of straw for animal bedding and feed, and the potential development of cellulosic ethanol production will likely increase in the future. This paper reviews published research assessing the effects of wheat and barley straw removal on soil organic carbon (SOC), and analyzes changes in nutrient cycling within wheat and barley production systems. Six studies compared SOC changes with time in irrigated systems in which wheat was removed or retained. These studies indicate that reductions in SOC due to removal may not be a concern. Soil OC either increased with time or remained constant when residues were removed. It is possible that belowground biomass is supplying C to soils at a rate sufficient to maintain or in some cases, slowly increase SOC with time. A separate research review calculated the minimum aboveground residue required to maintain SOC levels from nine wheat system studies. Eight of the studies were dryland production systems. The grain yields required to produce sufficient above ground biomass to maintain SOC levels ranged from 9 to 122 bu acre -1 for wheat and 14 to 185 bu acre -1 for barley. Wheat straw contains approximately 15, 3.4, and 33 lbs nitrogen (N), phosphorus (P 2 O 5 ), and potassium (K 2 O) ton -1, respectively. Barley straw contains approximately 12, 3.9, and 38 lbs N, P 2 O 5, and K 2 O ton -1, respectively. The calculated total economic value of the N, P 2 O 5, and K 2 O in one ton of wheat and barley straw is $17.91 and $18.18, respectively, based on average nutrient costs in the Pacific Northwest in 27. Rotations including wheat and barley in the irrigated agriculture of Idaho and many other states in the Pacific Northwest are much different than what was reported in the reported studies. There is very little reported data that can be directly related the irrigated rotations in Idaho that include wheat or barley. To fully understand the impacts of crop residue removal from soils in Idaho, research projects need to be conducted on crop rotations that include wheat and barley under irrigated conditions in Idaho. Otherwise the best data available for dissemination is from research conducted in different environments and systems. INTRODUCTION Several factors have led to concerns regarding changes in residue cycling in some crop production systems. These factors include removal of straw from grain fields for animal bedding and feed, increased costs of fertilizers and fuel, and the potential development of cellulosic-based ethanol production. Crop residue cycling in soils is important because residues are a major supply of nutrients (N, P, and K) and organic carbon (OC) to soils. A plethora of reported research demonstrates the role of SOC in the plant/soil system. Organic C positively impacts soil fertility, soil structure, water infiltration, water holding capacity, reduces compaction, and sustains microbial life in soils (Wilhelm et al., 27; Tisdale et al., 1993). Idaho produces 4.5% (8.33 million tons) and 2.8% (3.8 million tons) of the total wheat and barley straw in the U.S., respectively. The demand for straw in Idaho and neighboring states 3

34 for animal bedding is great and the potential for future cellulosic ethanol production will increase the demand. Understanding the effects of straw removal on SOC and nutrient dynamics in soil systems is important in assessing the sustainability of these systems where residues are removed. The objective of this paper is to review published research assessing the effects of wheat and Table 4. Research sources assessing the effects of small grain residue removal strategies on yield, soil physical properties, and soil chemical properties under irrigated conditions. Treatments Selected crop comparisons and Soil properties Source Site Soil Duration Cropping Systems Irrigation Annual precipitation assessed Yr. mm SOC, BD, Ks, MA 11 Cont. W, S-W double crop furrow 33 CT-RR, CT-RI, RT-RR, RT-RI Bordovsky et al. (1999) Munday, TX fine sandy loam 11 Cont. W, S-W double crop furrow 33 CT-RR, CT-RI, RT-RR, RT-RI Bordovsky et al. (1998) Munday, TX fine sandy loam GY, SY 14 Cont. W furrow 37 RB, RR, RI GY, SY, SOC, IF Undersander and Reiger (1985) Etter, TX silty clay loam Bahrani et al. (22) Kushkak, Iran clay loam 3 Cont. W furrow 4 RB, RR, RI GY, SY, SOC Curtin and Fraser (23) Lincoln, New Zealand silt loam 6 W-W-B-B-O-O sprinkler 68 RB, RR, RI GY, SY, SOC Follett et al. ( 25) Mexico clay 5 W-C, W-Bn border 375 CT-RB, CT-RI, GY, SY, SOC NT-RS W = wheat, S = sorghum, B = barley, O = oat, C = corn, Bn = bean. CT-RR = conventional tillage-residue removed after harvest, CT-RI = conventional tillage-residue incorporated by tillage, RT-RR = reduced tillage-residue removed after harvest, RT-RI = reduced tillage-residue incorporated by tillage, CT-RB = conventional tillage-residue burned, NT-RS = no tillage-residue left on surface, RR = residue removed, RI = residue incorporated, RB = residue burned, NT-RS = no till-residue left on surface. GY = grain yield, SY = straw yield, SOC = soil organic carbon, BD = bulk density, Ks = hydraulic conductivity, MA = microaggregation, IF = irrigation water infiltration. All straw yields were calculated using an average harvest index of.45 for wheat. Harvest index = grain yield/(grain yield + stover yield). barley residue removal strategies on crop productivity and soil properties in irrigated systems. METHODS Results from published literature were reviewed to evaluate changes in SOC associated with management practices where aboveground straw was removed or maintained in fields producing wheat. The N, P 2 O 5, and K 2 O content and value of wheat and barley straw were calculated from the average values reported by the NRCS Plant Nutrient Content Database (28). RESULTS AND DISCUSSION Table 1 lists the details of the studies that assessed the effects of small grain residue removal soil properties under irrigated conditions. Soil Organic Carbon The limited data from research reported in this paper indicate that reductions in SOC due to removal may not be a concern. Bordovsky et al. (1999) reported the SOC content in the top 3 to 4 in of soil for an irrigated continuous wheat system under both reduced tillage (RT) and conventional tillage (CT), and a wheatsorghum double crop, but did not conduct statistical comparisons between residue removed (RR) and residue incorporated (RI) treatments for each system involving wheat. The SOC was determined in 1982, 1985, and Trends indicate that in 1982 the SOC (averaged over the three systems) was similar for the RR and RI treatments (3.6 g kg -1 ), but in 1985 and 1987 the SOC in RI treatments were 25% and 38% higher than the RR treatment, respectively. However, when comparing the SOC over time, SOC in both the RI and RR treatments tended to increase over time. 31

35 In the study conducted by Bahrani et al. (22), there was a trend for higher SOC in the to 12 in soil depth under the RI treatment than the RR treatment three years after initiation of the study. The SOC did not decline over time regardless of residue management treatment. Undersander and Reiger (1985) did not show any difference in SOC between residue management treatments (residue burned [RB], RR, and RI) in 1967, 1973, or 198. The average SOC for all treatments in 1967, 1973, or 198 was 7.5, 11.4, and 12.2 g kg -1 in the to 6 in depth, and 6.6, 7.1, and 6.6 g kg -1 in the 6 to 12 in soil depth, respectively. In the to 6 in soil depth, the averaged SOC across all residue management treatments in 1973 and 198 (11.1 and 12.2 g kg -1, respectively) were significantly higher than the SOC in 1967 (7.5 g kg -1 ). However, in the 6 to 12 in depth there was no increase in SOC over time. Curtin and Fraser (23) showed no difference in total SOC between residue management treatments at the end of their 6-year study. Follett et al. (25) found an increase in SOC in the to 12 in depth over 5 years for all treatments at an optimum N application rate. The SOC in the WC-RI (wheat corn rotation, residue incorporated) and WC-RB (wheat corn rotation, residue burned) treatments were not different. The maintenance and increases in SOC over time when residue was removed in these studies are noteworthy and likely result from belowground plant and microbial biomass contributions. The contribution of belowground plant biomass to SOC was not measured in these studies. Understanding the contribution of belowground biomass to SOC is hard to quantify and this can be seen by the variation of values reported in the literature. However, the literature agrees that underground biomass is a significant source of OC to soils. Molina et al. (21) estimated that 24% of the net C fixed by corn is deposited in the soil from belowground biomass. Kmock et al. (1957) reported that the mass of belowground root biomass from plants is similar to the aboveground residue. Gale and Cambardella (2) found that roots contribute a greater amount of C to the soil C pool than aboveground residues. Minimum Aboveground Crop Residue Inputs to Maintain Soil Organic Carbon Johnson et al (26) determined the minimum aboveground crop residue requirements to maintain SOC levels (MSC) in soils from several literature reports. Most of these studies were conducted under rain-fed systems in environments where water inputs from precipitation are variable. Under irrigation, above and belowground biomass production is stabilized at a high level as long as other management practices (i.e. nutrient and pest management) are adequate. Because of the potential variation in crop biomass production under a rain-fed environment, changes in SOC and other soil properties under rain-fed environments can be different than under irrigation. The MSC values from Johnson et al. (26) for wheat were utilized to determine the amount of residue that could be harvested at various levels of grain yield (Figure 1). 32

36 Harvestable Straw (Mg ha -1 ) Nutrient Content and Economic Value of Wheat and Barley Straw Comparisons of the nutrient content per unit mass of straw between values calculated for Idaho using the USDA-NASS and the NRCS Plant Nutrient Database (28) and an extension article authored by Greg Schwab (Washington State University) are shown in Table 2. The differences in values are due to differences in the average nutrient contents of the straws used in Grain Yield (bu acre -1 ) Wheat I Barley C E G C E G I Grain Yield (Mg ha -1 ) Figure 1. Estimated quantities of wheat and barley residue that could be harvested while maintaining soil organic carbon level as a function of grain yield from various published MSC values [A = Black (1973); B and C = Follett et al. (1997); D = Horner et al. (196), Rasmussen et al. (198); E = Follett et al. (25); F = Paustian et al. (1992); G = Horner et al. (196), Paustin et al. (1997), Hobbs and Brown (1965), Rasmussen et al. (198); H = Horner et al. (196), Rasmussen et al. (198); I = Horner et al. (196), Paustin et al. 1997)]. Lines represent linear regression relationships between grain yield and harvestable straw. Data points were not shown in order to make the graphs less cluttered. (Graph based on method used by Wilhelm et al., 27). A B D F H A B D F H Harvestable Straw (tons acre -1 ) the calculations. The economic values are based on average N, P 2 O 5, and K 2 O fertilizer costs of $.53, $.45, and $.26 per lb, respectively (average costs for these nutrients in 27). This gives a nutrient value of $17.91 and $18.18 per ton of straw for wheat and barley, respectively (Table 3). It is important that people using the values in Tables 2 and 3 understand that the values are based on estimated production and average nutrient contents over a wide range of wheat and barley varieties. Actual nutrient concentrations in wheat and barley may vary from the calculated values presented in this review. However, the table values are a good tool for an initial assessment of potential nutrient removal. Nutrient mass and economic value estimates from Tables 2 and 3 are based on 1% straw removal. When straw is baled and removed, lower amounts of straw and nutrients will be exported from the field. To determine the actual amount and economic value of the nutrients exported, the total estimates from Tables 2 and 3 will need to be multiplied by the fraction of straw being removed. 33

37 Table 2. Average nutrient content in straw per unit mass of straw calculated from data from the NRCS Plant Nutrient Content Database and data reported in a Washington State University Extension publication authored by Greg Schwab. Crop Source lb N/ton lb P 2 O 5 /ton lb K 2 O/ton Wheat NRCS Plant Nutrient Content Database Schwab (Washington State University Extension) Barley NRCS Plant Nutrient Content Database Schwab (Washington State University Extension) Table 3. Average value of nutrients in wheat and barley straw. Crop N P 2 O 5 K 2 O Total $ Mg -1 ($ ton -1 ) Wheat 8.66 (7.86) 1.68 (1.53) 9.4 (8.53) (17.91) Barley 7.11 (6.45) 1.93 (1.75) 1.99 (9.97) 2.4 (18.18) Straw production was calculated from grain data using equation (1), grain test weights of 6 and 48 lbs bu -1 and harvest index values of.45 and.5 for wheat and barley, respectively. Approximately one ton of straw per 27.3 and 41.7 bu of grain for wheat and barley, respectively. Based on plant nutrient content values from the NRCS Plant Nutrient Content Database ( Values from Table 9 were used in the calculations. Nutrient values of $.53,.45, and.26 were used per lb of N, P 2 O 5, and K 2 O. Values were based on data from the USDA- NASS and represented average fertilizer prices in the Northwest U.S. in 27. ( CONCLUSIONS The limited data from research evaluated in this paper assessing residue management of wheat and other small grains under irrigated conditions indicate that reductions in SOC due to removal may not be a concern. However, there is very little reported data that directly relates to irrigated rotations in Idaho that include wheat or barley. To fully understand the impacts of crop residues on soils in Idaho, research projects need to be conducted that account for the major crop rotations that include wheat and barley under irrigated conditions. Otherwise, the best data available for dissemination is from research conducted in different environments and systems. Nutrients are removed from the soil/plant system when straw is harvested. Producers will need to determine the cost of nutrients removed from their systems to determine the value of the straw. REFERENCES Bahrani, M.J., M. Kheradnam, Y.Emam, H.Ghadiri, and M.T. Assad. 22. Effects of tillage methods on wheat yield and yield components in continuous wheat cropping. Experimental Agriculture 38: Black, A.L Soil property changes associated with crop residue management in a wheatfallow rotation. Soil Science Society of America Journal. 37: Bordovsky, D.G., M. Choudhary, and C.J. Gerard Effect of tillage, cropping, and residue management on soil properties in the Texas Rolling Plains. Soil Science 164: Bordovsky, D.G., M. Choudhary, and C.J. Gerard Tillage effects on grain sorghum and wheat yields in the Texas Rolling Plains. Agron. J. 9:

38 Curtin, D., and P.M. Fraser. 23. Soil organic matter as influenced by straw management practices and inclusion of grass and clover seed crops in cereal rotations. Aus. J. Soil Res. 41: Follett, R.F., J.Z. Castellanos, and E.D. Buenger. 25. Carbon dynamics and sequestration in an irrigated vertisol in central Mexico. Soil & Tillage Research. 83: Follett, R.F., E.A. Paul, S.W. Leavitt, A.D. Halvorson, D. Lyon, and G.A. Peterson Carbon isotope ratios of Great Plains soils and in wheat-fallow systems. Soil Science Society of America Journal. 61: Gale, W.J., and C.A. Cambardella. 2. Carbon dynamics of surface residue and root-derived organic matter under simulated no-till. Soil Sci. Soc. Am. J. 64: Hobbs, J.A., and P.I. Brown Effects of cropping and management on nitrogen and organic carbon contents of a western Kansas soil. Technical Bulletin 144. Kansas State University Agricultural Experiment Station, Manhattan, KS. Horner, G.M., M.M. Overson, G.O. Baker, and W.W. Pawson Effect of cropping practices on yield, soil organic, matter, and erosion in the Pacific Northwest wheat region. Coop. Bull. 1. Washington Agric. Exp. Stn., Pullman; Idaho Agric. Exp. Stn., Moscow; Oregon Agric. Exp. Stn., Corvallis; USDA-ARS, Washington, DC. Johnson, J.M.F., R.R. Allmaras, and D.C. Reicosky. 26. Estimated source carbon from crop residues, roots and rhizodeposits using the national grain-yield database. Agron. J. 98: Kmoch, H.G., R.E. Ramig, R.L. Fox, and F.E. Kochler Root development of winter wheat as influenced by soil moisture and nitrogen fertilization. Agronomy Journal. 49:2-25. Molina, J.A.E., C.E. Clapp, D.R. Linden, R.R. Allmaras, M.F. Layese, R.H. Dowdy, and H.H. Cheng. 21. Modeling incorporation of corn (Zea mays L.) carbon from roots and rhizodeposition into soil organic matter. Soil Biol. Biochem. 33: NRCS. Plant Nutrient Content Database. 28. [Online]. Available at (Verified January, 28). Paustian, K., H.P. Collins, and E.A. Paul Management controls on soil carbon. p In E.A. Paul et al. (ed.) Soil organic matter in temperate agroecosystems: Long-term experiments in North America. CRC Press, Boca Raton, FL. Paustian, K., W.J. Parton, and J. Persson Modeling soil organic matter in organicamended and nitrogen-fertilized long-term plots. Soil Science Society of America Journal. 56: Rasmussen, P.E., R.R. Allmaras, C.R. Rohde, and N.C. Roager, Jr Crop residue influences on soil carbon and nitrogen in a wheat-fallow system. Soil Science Society of America Journal. 44: Schwab, G. The value of straw. Washington State University Extension Publication. Tisdale, S.L., W.L. Nelson, J.D. Beaton, J.L. Havlin Soil Fertility and fertilizers. 5 th Edition. MacMillan Publishing Company, New York. Undersander, D.J., and C. Reiger Effect of wheat residue management on continuous production of irrigated winter wheat. Agron. J. 77: USDA-NASS 28. Crops and Plants [Online]. Available at (Verified January, 28). Wilhelm, W.W., J.M.F. Johnson, D.L. Karlen, and D.T. Lightle. 27. Corn stover to sustain soil organic matter carbon further constrains biomass supply. Agron. J. 99:

39 EVALUATION OF STRIP-TILLAGE AND FERTILIZER PLACEMENT IN SOUTHERN IDAHO CORN PRODUCTION D.Tarkalson and D. Bjorneberg USDA-ARS, Kimberly, ID ABSTRACT Strip tillage (ST) and associated nutrient placement can potentially help producers reduce fuel and machinery costs, increase yield, and reduce soil erosion compared to chisel tillage (CT). This study was initiated to evaluate corn production (Zea mays L.) under ST and CT, and various nitrogen (N) and phosphorus (P) fertilizer placements. The effects of tillage practice and N and P placement on grain and biomass yield of field corn was assessed on two sites at the USDA- ARS Northwest Irrigation & Soils Research Laboratory at Kimberly, ID with different levels of soil fertility and productivity. Two sites were selected in a furrow irrigated field that had been previously cropped to alfalfa. Site A was located in the top half of the field and Site B was located in the bottom half of the field. Site A had lower levels of soil organic carbon (OC) and soil test P and potassium (K) compared to Site B. The treatments were 1) ST with deep placement of N and broadcast P; 2) ST with 2 by 2 placement of N and broadcast P; 3) ST with deep placement of N and P; 4) CT with 2 by 2 placement of N and broadcast P; and 5) CT with broadcast N and P. The grain yields at Site A were greater for ST compared to CT. The deep band placement of N and P with ST had a yield (175 bu acre -1 ) advantage of 23 and 16 bu acre -1 over both CT treatments, respectively and increased yields to levels similar to the average of Site B (178 bu acre -1 ). No differences in grain yield occurred at Site B for all treatments. There were no differences in biomass yield of corn at the VT (tassel) growth stage and grain harvest time at both sites. The average total dry matter biomass at grain harvest time was 9.1 and 1.4 tons acre -1 averaged over all treatments, respectively. Data from year one of this study indicates that ST and deep band placement of N and P increased corn grain yield over CT and conventional fertilizer placement methods in highly eroded low fertile soils. Irrespective of the potential yield increases, there may be an economic advantage associated with less fuel due to less tillage passages with ST compared to CT. Because the data presented in this paper is from one year, caution should be exercised in extrapolating these results from year to year due to the variability in crop production associated with time-specific factors. This study will be carried out over a least one to two more years before final conclusions and recommendations are issued. INTRODUCTION The use of ST and other conservation tillage practices are used to conserve soil and soil water through residue management and reduce tillage costs in many areas of the Corn Belt. However, in the Pacific Northwest these tillage practices are less common. Research is needed to evaluate these tillage practices in the Pacific Northwest to determine their production and economic feasibility. Strip tillage is a practice that creates a residue free and tilled zone, approximately 6 to 15 inches wide and 6 to 8 inches deep. The remaining portion of the field is not tilled, and the residue from the previous crop remains on the soil surface. Studies have shown that corn production under ST is comparable to or greater than CT (Vetsch and Randall, 22; Mallarino et al., 1999; Griffith et al., 1973). However, Vyn and Raimbault (1992) showed that ST reduced corn yields compared to moldboard plow in southern Ontario. 36

40 Although ST allows for the deep banding of fertilizers, differences in fertilizer placement must be compared to CT practices in order to assess overall differences between the systems. Many studies have observed mixed results when evaluating fertilizer placement in corn production. Most studies, though, have shown that starter fertilizer placed in a band near the seed can benefit early corn growth (Vetsch and Randall, 22). However, increases in corn grain yields are less common. Low initial soil test P concentrations are the most common conditions in which corn grain yields increased as a result of starter fertilizer applications. Wolkowski (2) found that corn yield with 2 by 2 (2 inches to the side and 2 inched below the seed) placement of starter fertilizer at planting was better than deep placement of fertilizer in the fall under zone tillage. The objective of this research was to evaluate the production of corn under ST and CT, and various N and P fertilizer placements. METHODS The field study was initiated in 27 at the USDA-ARS Northwest Irrigation & Soils Research Lab in Kimberly, ID, on a Portneuf silt loam soil (coarse-silty mixed mesic Durixerollic Calciorthid). The site was cropped to alfalfa (Medicago sativa L.) from 24 to 26 under furrow irrigation. In October 26 and April 27 the alfalfa at the field site was sprayed with LV4 at a rate of 1.5 qt acre -1 and roundup at a rate of 1 qt acre -1, respectively. The field sloped from east to west and was divided into two study sites. Site A was located on the east side of the field and had an average slope of 2%. Site B was located on the west side of the field and had a slope of 1%. Each site had the same treatments and replication strategy. In 27, prior to field operations, twenty soil sub-samples were collected at depths of to 12 and 12 to 24 inches across all replications for both Site A and Site B. The subsamples from each site and depth were composited. The composited samples were air dried, ground to pass through a 2 mm sieve, and analyze for organic C (OC) by combusting 5 mg of sample in FlashEA1112 CNH analyzer (CE Elantech, Lakewood, NJ), soil test P and K (bicarbonate extractable, Olsen et al., 1954), and nitrate nitrogen (NO 3 -N) and ammoniacal nitrogen (NH 4 -N) (Keeney and Nelsen, 1982). Treatments consisted of: 1) ST with deep placement of N and broadcast P; 2) ST with 2 by 2 placement of N and broadcast P; 3) ST with deep placement of N and P; 4) CT with 2 by 2 placement of N and broadcast P; and 5) CT with broadcast N and P (Table 1). Total N and P rates of 15 lbs N acre -1 and 58 lbs P 2 O 5 acre -1 were applied to the treatments as urea (46--) and mono-ammonium phosphate (11-52-). Nitrogen fertilizer application rate was based on University of Idaho recommendations for corn grain (Brown and Westermann, 1988) at a yield goal of 175 bu acre -1, and NO 3 -N and NH 4 -N concentrations in the -12 and inch depth at Site A. A 6 lbs N acre -1 alfalfa credit was applied. All treatments were replicated 4 times in a randomized complete block design. Fertilizers were either broadcast prior to tillage (Broadcast), placed 2 inches to the side and 2 inches below the seed at planting (2*2), or placed 7 inches below the soil surface directly below the seed during ST (Deep). Fertilizer application rates and timing information are presented in Table 1. 37

41 Table 1. Rates and timing of N and P applications for all treatments. Treatment Tillage ST ST ST CT CT N Placement Deep 2*2 Deep 2*2 Broadcast lbs N acre May May May May Total P Placement Broadcast Broadcast Deep Broadcast Broadcast lbs P 2 O 5 acre May May Total Chisel tillage treatments consisted of chisel plow and tandem disk (May 11) and roller harrow (May 16). The broadcast application of urea on May 16 to Treatment 5 was immediately incorporated with the roller harrow. Strip tillage occurred on May 23. Corn (Pioneer 3523, GDD 5F = 253) was planted to the entire study area on May 24 at a rate of 31, seeds acre -1. All plots were irrigated at rates to meet the crop water requirement. On June 21, all ST plots were sprayed with Clarity herbicide at a rate of.75 pints acre -1 to kill volunteer alfalfa. A 12-plant sample was taken from each plot at Sites A and B at the V12 growth stage (July 2) to determine plant biomass (dry matter [DM] basis). The entire plant sample from each plot was weighted as-is directly after removal from the plots, chopped with a commercial wood chipper, and a subsample collected and weighted. The subsample was dried in an oven at 14 degrees F and re-weighted to determine the percent dry matter of the sample. On October 9, corn grain and plant samples were collected from each plot at Sites A and B. A 6-plant sample was collected to determine final plant biomass (DM basis). All ears from 4 ft of row, was collected to determine grain yield (reported at 15.5% moisture). RESULTS AND DISCUSSION Soil Analysis Soil OC, soil test P, and soil test K in the to 12 and 12 to 24 inch depth were lower at Site A than Site B (Table 2). At Site A, soil test P in the surface 12 inches was considered low to marginal according to the University of Idaho fertilizer recommendations for field corn (Brown and Westermann, 1988). The recommendations suggested application of 2 to 14 lbs P 2 O 5 acre - 1 depending on the soil lime content (from 5 to 15 calcium carbonate (CaCO3) equivalents). The soil test K at Site A suggested no additional K fertilizer inputs (the critical level is 15 ppm). At Site B, soil test P and K were high in the surface 12 inches and fertilizer inputs for these nutrients would not be recommended. The difference in OC, soil test P and K levels between the two sites was likely due to furrow irrigated induced soil erosion from Site A (2% slope) to Site B (1% slope). Due to fertility differences, Site B would likely be more productive than Site A. 38

42 Table 2. Selected soil chemical properties from Site A and Site B at depths of -12 and inches. Soil Sample Analyte Site A Site B Depth (in) OC (%) P (mg/kg) K (mg/kg) NO 3 -N (mg/kg) NH 4 -N (mg/kg) OC (%).5.12 P (mg/kg) K (mg/kg) NO 3 -N (mg/kg) NH 4 -N (mg/kg) Grain Yield There were significant differences in grain yields between treatments at Site A (Figure 1). Treatment 3 (ST-deep N-deep P) at Site A had greater grain yields than both the CT treatments. Treatment 3 grain yields were 23 and 16 bu acre -1 greater than Treatment 4 (CT-2*2-broadcast P) and Treatment 5 (CT-broadcast N-broadcast P), respectively. A direct comparison of tillage effects on grain yield could be made between Treatments 2 (ST 2*2 N and broadcast P) and 4 (CT 2*2 N and broadcast P) due to the two treatments having the same fertilizer placements. Strip tillage had a greater grain yield compared to CT (+14 bu acre -1 ). There was no significant difference in grain yield between the ST treatments (Treatments 1, 2, and 3), but a trend for increased yield with the deep N and P placement was evident (Treatment 3). Averaged over all treatments, the grain yield at Sites A and B were 164 bu acre -1 and 178 bu acre -1, respectively. Unlike site A, there were no grain yield differences between treatments at Site B. The response of grain yield to tillage and nutrient placement at Site A was likely a result of the overall lower fertility status associated with furrow irrigated induced soil, OC, and nutrient transport. The impact of tillage and nutrient placement was negligible at Site B due to an overall greater level of fertility, a result of soil, OC, and nutrient deposition from Site A. These results indicate that corn grown in areas of fields with shallower soil depths, low in OC, and nutrients due to erosion and other factors may have a greater yield response to ST and deep placement of N and P compared to CT and conventional fertilizer placements. Biomass Yield There were no significant differences in the biomass yield between treatments at the V12 growth stage (data not shown) or a final harvest at both sites (Figure 2). Site A biomass yield trends were similar to Site A grain yield trends. 39

43 185 a 18 Site A 1. a Site A ab ab 9.5 a a a Corn Grain Yield (bu acre -1 ) a a a c a bc a Site B Total Dry Matter (tons acre -1 ) a a a a a a Site B ST - Deep N - Broadcast P ST - 2*2 N - Broadcast P ST - Deep N - Deep P CT - 2*2 N - Broadcast P CT - Broadcast N - Broadcast P Figure 1. Corn grain yield for tillage and fertilizer placement treatments at Site A and Site B locations in 27. Error bars are the standard errors of the treatment means. Treatments with the same letter are not significantly different at the.5 level. ST - Deep N - Broadcast P ST - 2*2 N - Broadcast P ST - Deep N - Deep P CT - 2*2 N - Broadcast P CT - Broadcast N - Broadcast P Figure 2. Corn biomass yield at grain harvest time for tillage and fertilizer placement treatments at Site A and Site B locations in 27. Error bars are the standard errors of the treatment means. Treatments with the same letter are not significantly different at the.5 level. 4

44 CONCLUSIONS Results from one year of research indicated that ST provided a corn grain production advantage over CT associated with tillage as well as fertilizer placement on highly eroded, low fertile soils. On the more fertile site, there were no differences in corn grain yield between ST and CT or fertilizer placement strategies. Although no economic analysis has been conducted to date, there may be an economic advantage for ST over CT due to potential fuel savings associated with less tillage passes at both research sites. Remember, due to the variability in crop production associated with time-specific factors, caution should be exercised in extrapolating these results from year to year. This study will be carried out over a least one to two more years before final conclusions and recommendations are issued. These data should be viewed as only preliminary. REFERENCES Brown, B.D., and D.T. Westermann Idaho Fertilizer Guide: Irrigated field corn for silage or grain. Current Information Series No University of Idaho Extension, Moscow, ID. Griffith, D.R., J.V. Mannering, H.M. Galloway, S.D. Parsons, and C.B. Richey Effects of eight-planting systems on soil temperature, percent stand, plant growth, and yield of corn on five Indiana soils. Agron. J. 65: Keeney, D.R., and D.W. Nelson Nitrogen: Inorganic forms. In Methods of soil analysis, Part 2, Chemical and microbiological properties, nd ed. A.L. Page (ed). American Society of Agronomy and Soil Science Society of America. Madison, WI. Mallarino, A.P., J.M. Bordoli, and R. Borges Phosphorus and potassium placement effects on early growth and nutrient uptake of no-till corn and relationships with grain yield. Agron. J. 91: Olsen, S.R., C.V. Cole, F.S. Watanabe, and L.A. Dean Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA. Circ 939. U.S. Government Printing Office, Washington, DC. Vetsch, J.A., and G.W. Randall. 22. Corn production as affected by tillage system and starter fertilizer. Agron. J. 94: Vyn, T.J., and B.A. Raimbault Evaluation of strip tillage systems for corn production in Ontario. Agron. J. 93: Wolkowski, R.P. 2. Row-placed fertilizer for maize grown with an in-row crop residue management system in southern Wisconsin. Soil Tillage Res. 54:

45 NITROGEN PLACEMENT, ROW SPACING, AND WATER MANAGEMENT FOR FURROW-IRRIGATED FIELD CORN G. Lehrsch, R. Sojka, and D. Westermann USDA-ARS, Kimberly, ID ABSTRACT Banding and sidedressing nitrogen (N) fertilizer on a never-irrigated side of a row of corn (Zea mays L.) were hypothesized to maintain yield and decrease nitrate leaching. In a two-year field study on a Portneuf silt loam (Durinodic Xeric Haplocalcid) in southern Idaho, we evaluated effects on yield and N uptake of 1) urea placement (broadcast pre-plant vs. band at planting), 2) row spacings (3-in vs. an offset 22-in spacing in which every pair of 22-in rows was positioned close to a furrow rather than each row on a bed center), and 3) water management. Our water management, termed irrigated furrow positioning, consisted of everysecond furrow irrigation in which we applied water to either a) the same or b) the opposite side of the row with successive irrigations, the latter called alternating furrow irrigation. At season s end, we harvested 2 ft of row at three locations in each plot for silage and at three other locations for grain. Grain yield was not affected by the positioning of the irrigated furrow. However, averaged across years, grain yield from 22-in rows was 113 bu acre -1 from banded plots, 5% greater (P<.5) than broadcast plots. Two-year average grain yield from 3-in rows was 17 bu acre -1, with no difference between banding and broadcasting. In the second year, N uptake in grain averaged across row spacings was 72.3 lb acre -1 from banded plots and 65.5 lb acre -1 from broadcast plots (P<.1). Silage yield increased up to 26% and N uptake in silage increased up to 21% from banding, compared to broadcasting, where we irrigated the same furrow in the study s second year. In both years, grain and silage yield and N uptake in grain and silage were similar or greater where urea was banded on one side of a row rather than broadcast. INTRODUCTION Minimizing fertilizer N contact with water moving downward from irrigation furrows should keep nitrate in the surface horizons of the soil profile, allowing the fertilizer N to be more available for crop uptake and less susceptible to leaching from the root zone. This goal may be achieved by banding and sidedressing N fertilizer on one side of a corn row and irrigating the other. However, fertilizer N may be positionally unavailable if the soil in contact with the fertilizer granules is too dry for root growth or extension, thereby reducing crop N uptake and yield. If one periodically wets this dry soil by irrigating the furrow near the N fertilizer, nitrate may be leached from the root zone or transported horizontally and upward to or near the surface into drier soil where uptake is less. The research objective was to evaluate effects of N placement, row spacing, and irrigated furrow positioning on the yield of field corn grain and silage and on N uptake in grain and silage. 42

46 METHODS The experiment was a split-split plot design with four replications. The main plot effect was irrigated-furrow positioning. In one treatment, we irrigated the same furrow all season (Furrow A in Fig. 1). In the other treatment, we irrigated alternating furrows (Furrow A, then B, then A, etc.) with successive irrigations. The subplot treatments were the row spacings shown in Fig. 2. The sub-subplot treatments (N fertilizer placements) were: 1) half of the N requirement broadcast pre-plant then half sidedressed 6 wks after planting, 2) half of the N banded at planting then half sidedressed, or 3) no N fertilizer applied. Placement of N (always as urea, 46% N) is shown in Fig. 1. Each plot was four rows wide and 335 ft long. Figure 1. Positioning of seed (S), banded N (Nba), sidedressed N (Nsd), and broadcast N (Nbr) for 3in rows where we irrigated the same furrow (A). Where we irrigated alternating furrows, we irrigated Furrow A first, then B, then A, etc. Equipotential and flow lines are conceptually shown. Each spring prior to planting, we incorporated P and, into selected plots, broadcastapplied N according to University of Idaho soil test recommendations. In mid-may, Pioneer 391 corn was planted at the 2-in depth at a population of 26,9 plants acre-1. At planting, N was banded 2 inches to the side and 1 inch below the seed, thus placing the N about 2 inches above the water surface when irrigating. Six weeks after planting, the sidedressed N was knifed into bed shoulders as a band 3 in beneath the soil surface and 5 in to the dry furrow side of the emerged corn (Fig. 1). Each year, we applied equal volumes of water to every other furrow of all plots with irrigations that were 12 hours long for the 3-in rows and 8.8 h for the 22-in rows. In 1988, we used an inflow of 4 gal min-1 to irrigate 9 times, each time applying 2.8 in of water (in gross). In 1989, we used an inflow of 5 gal min-1 to irrigate 7 times, applying 3.5 in of water each time. From each plot, we harvested 2 ft of row at each of three locations for silage yield and, later, at three other locations for grain yield. 43

47 3-in. Row Spacing 22-in. Row Spacing N ba N ba 3 in. 44 in. (Avg. = 22 in.) 7 in. 15 in. Figure 2. Row spacings were standard 3 in and an offset 22 in. Offset rows were positioned close to the irrigated furrow to increase water availability and decrease furrow erosion. RESULTS AND DISCUSSION Grain yield Averaged across years, grain yield was not affected by irrigated-furrow positioning (data not shown). Repeatedly irrigating the same furrow yielded 99 bu acre -1 versus 98 bu acre -1 (not significant, NS) when irrigating alternating furrows. Two-year average yield revealed an interaction between row spacing and N placement (Table 1). When averaged across years, grain yield from 22-in rows was 5% greater (P=.51) from banded than broadcast N. Grain yield from banded N was similar to or greater than was seen from broadcast N, regardless of row spacing. Two-year average grain yield from 3-in rows was similar, whether urea was banded or broadcast. When averaged across years and irrigated furrow positionings, grain yields did not differ from one row spacing to the other at any N placement (Table 1). Table 1. Row spacing and N placement effects on corn grain yield, averaged across years and irrigated furrow positioning. Corn grain yield N placement Row spacing Banded & sidedressed Broadcast & sidedressed Unfertilized in bu acre Yields adjusted to 15.5% moisture. LSD.5 = 5.9 bu acre 1 to separate placement means at either row spacing. Row spacing effects were not significant at 5%. 44

48 When grain yield was averaged across irrigated furrow positioning and N placement, however, row spacing was important. In 1988, corn in 22-in rows yielded 128 bu acre -1, 6% more (P<.29) than the 12 bu acre -1 from 3-in rows. In 1989, the trend reversed with 77 bu acre -1 from 3-in rows vs. 7 bu acre -1 from 22-in rows, significantly different at P<.33. In 1988, residual soil N concentrations were relatively high, not likely growth- or yield-limiting. In 1989, with much less residual N in the soil, N was likely scavenged more efficiently by roots that were more evenly distributed under 3-in than 22-in rows. Also, irrigation water was closer to the banded and sidedressed N fertilizer with 22-in than 3-in rows (Fig. 2), likely leaching more fertilizer N and soil N from the corn s root zone under narrower than wider rows, particularly in 1989 (Lehrsch et al., 21). Nitrogen placement effects on grain yield depended upon the year (Table 2). In 1988, grain yield was statistically equal where N was banded and later sidedressed and where N was broadcast, then sidedressed. In 1989, yield was 11% greater (P<.2) from banded N than broadcast N. Again, banding maintained or increased yield, especially in 1989 with much less residual N in the spring soil profile (soil N data not shown). Also in 1989, soil nitrate nitrogen (NO 3 -N) was likely leached from corn root zones by two relatively large, early-season irrigations (Lehrsch et al., 2 and 21). Table 2. Nitrogen placement effects on grain yield in 1988 and Grain yield N placement bu acre 1 Banded & sidedressed Broadcast & sidedressed Unfertilized Yields adjusted to 15.5% moisture. LSD.5 = 5.9 bu acre 1 to separate placement means in either year. Nitrogen uptake in grain Nitrogen uptake in grain averaged 9.9 lb acre -1 in 1988, but only 55. lb acre -1 in 1989, due in part to low uptake and yield in unfertilized plots in 1989 (Table 2). Irrigated-furrow positioning did not affect N uptake either year (data not shown). Row spacing effects were only significant in 1989 when N uptake was 14% greater (P<.5) from 3-in than 22-in rows (Table 3). Equal spacing between 3-in rows compared to unequal spacing between 22-in rows (Fig. 2) likely led to more uniform root distribution in and more efficient N removal from the N-depleted profile. 45

49 Table 3. Row spacing effects on N uptake in corn grain in 1988 and N uptake in corn grain Row spacing in lb acre LSD.5 NS 4.1 Nitrogen placement effects on N uptake in grain depended upon the year (Fig. 3). Nitrogen uptake in grain was similar for banded and broadcast N placement in In 1989, in contrast, banding compared to broadcasting increased N uptake more than 1% (P<.1). 1 8 LSD.5 N uptake in grain (lb/a) Banded Broadcast Unfertilized LSD.5 Figure 3. N placement effects on N uptake in corn grain, averaged across row spacings, in 1988 and Silage yield Silage yield averaged 9. ton acre 1 in 1988 and 9.1 ton acre 1 from N-fertilized plots in Yields were marginal because the corn cultivar was better adapted to produce grain than silage and plant populations were less than optimum for silage production. Research findings (Lehrsch et al., 2) suggested two recommendations for silage producers. First, when growing silage in 22-in rows and irrigating the same furrow, a producer should apply N in a band rather than broadcast pre-plant to increase yield, potentially by 26%. Second, in soil profiles with little Banded Broadcast Unfertilized 46

50 residual N, producers who grow silage in 22-in rows should irrigate the same rather than alternating furrows to avoid silage yield losses that may approach 18%. When averaged across furrow positioning, 1988 silage yields were similar among row spacings. From fertilized plots in 1989, however, silage yields were 4.5% greater from 3-in than 22-in rows, 9.2 versus 8.8 ton acre 1, respectively, not significant at P=.5. Nitrogen uptake in silage When averaged across years and irrigated furrow positioning, N uptake in silage was consistently greater with 3-in than 22-in rows at every placement, although the differences were seldom significant at the 5% level (data not shown). Irrigated furrow positioning did not affect silage N at any placement in 1988 or 1989 (Table 4). However, where water was applied all season to the same furrow, N uptake from banding was similar to that from broadcasting in the first year but was 21% greater (P<.1) in the second year. From an N deficient soil profile, fertilizer N was used more efficiently from banding than broadcasting when the same furrow was irrigated throughout the season. Table 4. Irrigated furrow positioning and N placement effects on N uptake in corn silage in 1988 and Data have been averaged across row spacings. N uptake in silage N placement Irrigated furrow positioning Banded & sidedressed Broadcast & sidedressed Unfert. lb acre Alternating furrow 144 a 135 ab 121 b Same furrow 133 a 137 a 13 a 1989 Alternating furrow 117 a 114 a 54 b Same furrow 125 a 14 b 54 c Irrigated furrow positioning did not affect N uptake at any placement in either year. Within a row for each year, means followed by the same letter are not significantly different at P=.5. CONCLUSIONS Corn grain yield and N uptake in grain were similar or greater where urea was banded on one side of a row, rather than broadcast pre-plant. In Portneuf silt loam relatively deficient in N at planting, wider row spacings increased both grain yield and N uptake in grain. Silage yield and N uptake in silage were either maintained or increased where we banded N on one side of a row and repeatedly irrigated the other side. Where we irrigated the same furrow, silage yield increased up to 26% and N uptake in silage increased up to 21% from banding, compared to 47

51 broadcasting, in the study s second year. Irrigating the same furrow throughout the season neither reduced the yield of corn grain or silage nor the N uptake in grain or silage. In addition, as reported in Lehrsch et al. (21), positioning irrigation water away from banded and sidedressed N fertilizer also minimized profile NO 3 -N without sacrificing yield. REFERENCES Lehrsch, G. A., R. E. Sojka, and D. T. Westermann. 2. Nitrogen placement, row spacing, and furrow irrigation water positioning effects on corn yield. Agronomy Journal 92: Lehrsch, G. A., R. E. Sojka, and D. T. Westermann. 21. Furrow irrigation and N management strategies to protect water quality. Commun. Soil Sci. Plant Anal. 32:

52 NITROGEN AND WATER USE EFFICIENCY IN ONION PRODUCTION UNDER DRIP AND FURROW IRRIGATION S. J. Reddy 1, J. Neufeld 2, and J. Klauzer 3 1 University of Idaho Extension, Washington County 2 University of Idaho Extension, Canyon County 3 Clearwater Supply Company, Ontario, OR ABSTRACT Groundwater sampling in Washington County indicates that nitrate nitrogen (NO 3 -N) concentrations are frequently above health standards and increasing. The objective of this project was to demonstrate research based onion production practices that can increase water and fertilizer use efficiency, and reduce ground water contamination potential from NO 3 -N while maintaining production. Non-replicated demonstration plots were installed from in onion fields, and used either furrow or drip irrigation. Following standard practices, furrow (control) plots received an average of 275 lb nitrogen (N)/acre/year. Drip irrigation plots received an average of 162 lbs N/acre/year following N fertilizer recommendation rates from University of Idaho and Pacific Northwest onion fertilizer guides, with irrigation scheduling based on soil moisture sensor data. A furrow treatment plot was added in 25, using a reduced average N rate of 161 lb N/acre, again using recommendations from university fertilizer guides. Production inputs were measured and soil nitrate, onion tissue nitrate, water use, fertilizer application, soil N mineralization, crop yield, and bulb sizes were determined. Water use efficiency (WUE) and N use efficiency (NUE) were calculated and compared for all plots. The furrow treatment plots used approximately 4% less N fertilizer than the furrow control, and still produced yields that were only 4.1% to 5.2% less than the control. The drip plot produced the best WUE and NUE when compared to the furrow control. Furrow treatment yield for 27 fit close to the high range of the Preplant Yield Response Curve from the Pacific Northwest onion fertilizer guide, indicating sufficient N availability. The project showed that high onion yields can be produced with reduced N fertilizer application. Demonstration of efficiency through these plot comparisons can help growers keep production costs down, maintain high yields, and minimize N leaching into water supply. INTRODUCTION Groundwater sampling in Canyon County indicates that NO 3 -N concentrations are currently within health standards, but are on the rise. Groundwater sampling in Washington County indicates that NO 3 -N concentrations are frequently above health standards and increasing. Deep percolation of irrigation water containing nitrogen from cropland is recognized as a contributor to groundwater contamination. Onion production has been determined to have one of the highest NO 3 -N leaching potentials. Approximately 9, acres of onions are grown in the Treasure Valley of Idaho. Beginning in 23, applied research and demonstration plots were installed within commercial onion fields that used either furrow or drip irrigation. Plots from these furrow and drip irrigated fields were sampled and compared each year until project completion in 27. The objective of this project was to demonstrate research-based onion production practices that can increase water and fertilizer use efficiency, and reduce ground water contamination potential from NO 3 -N while maintaining production. 49

53 METHODS Soil moisture monitoring equipment was installed in furrow and drip irrigated commercial onion fields in both Canyon and Washington Counties at the start of each production season. Moisture monitoring equipment was used to help schedule irrigations and to help keep onion soil moisture within recommended levels. Data recorded by the monitors was used to compare irrigation efficiency of furrow and drip systems. Throughout the growing season additional data were collected including soil nitrate (NO 3 ), onion tissue NO 3, water use, fertilizer application, soil N mineralization, crop yield and bulb sizes. The data were used to calculate N use efficiency (NUE) and water use efficiency (WUE) between the furrow and drip irrigated treatments. In addition to data collection for comparisons, specific treatments were introduced within the plots during the last three years. These treatments included: 1. Furrow irrigation (Furrow Control) using the grower s customary fertility and irrigation practices; 2. Furrow irrigation (Furrow Treatment) using research based fertility recommendations (PNW 546 and CIS 181); and 3. Drip irrigation (Drip) using research based fertility recommendations (PNW 546 and CIS 181), and irrigation scheduling based on soil moisture sensor data RESULTS AND DISCUSSION Water Management Applied irrigation water and soil moisture status of the plots differed greatly by irrigation system. Furrow irrigated onions averaged more water application than drip irrigated plots (Figure 1), and soil moisture oscillated to a greater extent. Washington County soil moisture graph examples shown in Figures 2 & 3. Figure 1. Seasonal water applications to onion plots by irrigation system vs. ET 5

54 Figure 2. Soil graph (Cbars) of furrow irrigated onions showing great moisture variation. Figure 3. Soil graph (Cbars) of drip irrigated onions showing small moisture variation. Water use efficiency (WUE) of the plots under differing irrigation systems and treatments were compared (Figure 4). WUE is defined as the hundred-weight (Cwt) of onions produced per inch of water applied, including rainfall. The Drip plots consistently showed the highest WUE while the Furrow Control WUE and Furrow Treatment WUE were very similar, but much less. Figure 4. WUE of onion plots by irrigation system. (Surface = Furrow) 51

55 Nitrogen Management Nitrogen fertilizer recommendations for the Furrow Control and Drip plots were calculated using early season soil samples along with estimated yield, estimated N mineralization, and estimated N uptake efficiencies. For example, in the 26 study, yield goals of 95 Cwt/ac were established, and N uptake efficiencies of 4% and 6% were assumed for furrow and drip irrigated onions respectively (PNW 546). A recommendation of 325 lbs N/ac was calculated for the furrow plots and 171 lbs N/ac for the Drip plot (Table 1). The Furrow Control actually received a fall application plus two side-dressings for a total of 283 lbs N/ac. The Furrow Treatment received a fall application plus one side-dressing for a total of 158 lbs/ac, as was recommended. This reduction in N was due to monthly soil testing that indicated sufficient N was present. Soil mineralization tests revealed approximately 12 lbs N became available from May through August. The 26 Drip plot received a total of only 155 lbs N/ac, of which 115 lbs was applied through multiple drip irrigations. Although the 26 Drip plot received comparatively less N per acre, it produced a yield very close to the furrow plots. This is consistent with research showing N can be applied in small amounts frequently and produce high yields. Table 1. Fertilizer recommendations and actual applications for onion plots. Lbs N Lbs N Lbs N Lbs N Lbs N Year Recommended Applied Applied Recommended Applied Furrow Furrow Furrow Drip Drip Control Control Treatment Average High N fertilizer recommendations were anticipated in 26 due to wet weather and expected N leaching. However, actual N fertilizer applications were similar to 25. In both 25 and 26, soil testing indicated adequate N in the Furrow Treatment (>2 ppm), and a second fertilizer application was not needed. Similar recommendations were calculated in 27. The 27 Furrow Treatment received two side-dressings of only 62.5 lbs N each. The Drip plot received 62 lbs N fertilizer above the recommendation due to extreme inconsistencies in soil sample results. Yield These demonstration plots were replicated only by year, so statistical analysis of yields could not be measured. Yields were consistently high, and were reasonable considering the irrigation systems used and inputs applied (Figure 5). The 26 furrow irrigated yields were down 2 percent from 25 due to hot summer weather. However, yields from 25 to 26 drip irrigated plots were down only 1 percent. The yield reduction was smaller in the drip irrigated plots, possibly due to soil moisture management closer to the optimum range (-2 to -25 Cbars) through the growing season (Figure 3). 52

56 Figure 5. Yield (Cwt) of onions by Control and Treatment over 5 year study In both 25 and 26, the Furrow Treatment yields were 4.1 % less than the Furrow Control yields. This slightly lower yield resulted despite 41% less N fertilizer applied to the Treatment than the Control. In 27, the Furrow Treatment yield was 5.2 % less than the Furrow Control. This yield resulted despite 44% less N fertilizer applied to the Treatment than the Control. Root tissue analysis from 25 through 27 showed both Furrow Treatment and Furrow Control N levels within, or close to, adequate levels. In addition, the yield from the 27 Furrow Treatment fit very closely to the high range of the Preplant Yield Response Curve (PNW 546) (6). Figure Furrow Treatment yield compared to research based Preplant Yield Response Curve. Intersection of red lines indicates location of Furrow Treatment within the curve. 53

57 Nitrogen Use Efficiency (NUE) Nitrogen Use Efficiency (NUE) is defined here as the lbs of N used per Cwt of onions produced. Research estimates that a Cwt of onion bulbs requires.19 Lbs N (with 1% uptake efficiency). However, N uptake efficiency for furrow irrigated onions is only about 4%. Consequently, it takes.475 lbs N/Cwt for furrow irrigated onions to get the required.19 lbs N/Cwt. With drip irrigation and an estimated 6% uptake efficiency,.317 lbs N/ac is needed to get.19 lbs N/ac to the onions. In 26, the NUE of the Furrow Control was.65 lbs N/Cwt indicating inefficient use of N (Fig 7). This was the poorest NUE recorded during the project, and was the result of high N fertilizer application in combination with a comparatively low yield. The Furrow Treatment NUE was.47 lbs N/Cwt, and the Drip was.39 lbs N/Cwt of onion bulbs. Both the Furrow Treatment and Drip plots had NUE measurements that came very close to research predictions. The Drip plot NUE was slightly higher than values mentioned in the literature, so opportunities may remain for growers to further reduce their N inputs. In 27, the NUE of the Drip plot was much higher than the Furrow Treatment. This aberration reflects unusual soil sample results that led to more N fertilizer applied than was recommended. The best NUE was produced by the 25 Furrow Treatment plot. This could partly be explained by a combination of reduced N fertilizer, well timed N application, and high yield. Figure 7. NUE (Lbs N/cwt onions) for all plots. (Surface = Furrow) Onion production under different irrigation systems was compared over a five year period. Production inputs were measured while soil, water, and root tissues were sampled for N content. Application of N fertilizer on a Furrow Treatment and Drip plot were determined from initial and monthly soil samples. Finally, onion yields and bulb sizes from different irrigation systems were compared. It was shown that N fertilizer applications can be reduced while maintaining high yields. This information is important to growers who want to improve efficiency of furrow irrigated onions, and especially to growers who may want to transition from furrow to drip irrigation. With more efficient use of irrigation water and N fertilizer, production costs can be held down, yields can be maintained, and leaching of N into water resources can be minimized. With about 9, acres of onions grown in the Treasure Valley of Idaho this could have implications for future groundwater quality. 54