Suboptimal Irrigation Strategies for Alfalfa in the Lower Colorado Region, 2009

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2 Suboptimal Irrigation Strategies for Alfalfa in the Lower Colorado Region, 2009 Michael J. Ottman Summary Alfalfa has the highest water requirement of any crop grown in Arizona, and any strategies that conserve water growing this crop could have a large impact on water availability in the state. The purpose of this study is to determine yield and profitability of sub-optimal irrigation strategies in alfalfa. An irrigation study was conducted at the University of Arizona Maricopa Agricultural Center on a sandy clay loam soil. The following irrigation treatments are included in this study: 1) One irrigation per cutting, 2) Two irrigations per cutting, 3) Summer (August) irrigation termination, 4) Winter (December, January, February) irrigation termination, and 5) Summer and Winter irrigation termination. The Winter irrigation termination treatments were initiated in December 2009 and data is not available yet for these treatments. The amount of water applied from January through November 2009 was 69.7 inches (one irrigation per cut), 80.5 inches (two irrigations per cut), and 78.6 (Summer irrigation termination). The annual hay yields were 12.5 tons/acre (one irrigation per cut), 13.7 tons/acre (two irrigations per cut), and 12.9 tons/acre (Summer irrigation termination). Sub-optimal irrigation increased the forage quality by decreasing fiber (ADF and NDF) and increasing protein content. Sub-optimal irrigation did not reduce stand density. The water use efficiency of applied water (plus rainfall) was not affected by irrigation treatment. Introduction More water is applied to alfalfa than any other crop in Arizona due to the acreage planted and the water requirements of the crop. Alfalfa is the major field crop in the state with 250,000 acres in 2006, followed by cotton (188,000 acres), and wheat (79,000 acres) [NASS, 2008]. The annual water requirement or consumptive use of alfalfa is 74 inches, higher than the water requirement of cotton (41 inches) and wheat (23 inches) [Erie et al., 1965]. The water requirement of alfalfa is higher than most crops since it is a perennial and grows most of the year in Arizona in contrast to the 6-7 month growing season of cotton and the 4-5 month growing season of wheat. Alfalfa is in high demand by the dairy and horse industries. There really is no substitute for alfalfa in the diet of these animals since alfalfa is such a highly nutritious feed. Since 1993, alfalfa acreage has increased from 150,000 to 250,000 acres (NASS, 2008). This increase in alfalfa acres has been spurred by the expansion of the dairy industry and an increase in the number of horses in the state. The demand for alfalfa in Arizona will continue in the foreseeable future since dairies are generally located near population centers to lower transportation cost of milk and the number of horses is correlated with human population. Also, alfalfa acreage is declining in the Imperial and Palo Verde Valleys of California near the Arizona border due to limited water supplies and transfer of water to urban areas. Water supplies can be variable due to drought or reduced by demands from municipalities. So, how will this steady or perhaps increased water demand for alfalfa be met? One way is through suboptimal irrigation, or irrigating alfalfa with less water than it needs for optimum growth. Some research has been conducted on strategies to apply less water to alfalfa, but it is difficult to directly apply the results of most of these studies to the Phoenix region. Reduced irrigation has been investigated in the Imperial Valley of California (Robinson et al., 1994), but this study was conducted on a soil with high water holding capacity and a shallow water table. Studies in the Fresno, CA (Frate et al., 1991), Davis, CA (Hanson et al., 2007), New Mexico (Wilson et al., 1983), Nevada (Guitjens and Jensen, 1988), and Cyprus (Metochis and Orphanos, 1981) are not directly applicable since the water demand by alfalfa in those locations is much less than that in Phoenix. Research on reduced irrigation of alfalfa in the summer conducted in regions with little or no summer rainfall, such as in California or Cyprus, is not applicable to the 2010 Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 1

3 Phoenix region which does have a summer rainy season. Summer rain may rescue the crop from imminent failure from irrigation termination. Irrigation studies applicable to the Phoenix region have been conducted in Mesa (Schonhorst et al., 1963) and Tucson (Schneiter, 1973) where it was shown that stands and subsequent yields were not damaged by irrigation termination in the summer, but other irrigation strategies were not investigated. An irrigation termination study conducted at Maricopa (Ottman et al., 1996) demonstrated the adverse effects of withholding irrigation water for several months, but strategies that have a less severe affect on yield were not investigated. The purpose of this and many of the other irrigation termination studies has generally been to demonstrate the effects of withholding irrigation water for a long period of time due to critical water shortages or transfers to municipalities. Many of these studies have shown that prolonged irrigation termination can have a temporary or permanent affect on yield depending on soil and climatic conditions. Most farmers would be reluctant to reduce irrigation to the degree where forage yield and stands are permanently reduced. Less drastic reductions in irrigation water applications may be more palatable to alfalfa producers. Several strategies are: 1) Irrigation termination in August during the summer slump when alfalfa growth is much reduced due to heat. During this time period, the grower is battling weeds and insects, the cost of producing this cutting is high, and the hay produced during this time is of reduced quality and receives a lower price, 2) Irrigation termination during the winter after the last cutting in fall until the first cutting in spring. Similar to the August cutting, the alfalfa producer is battling weeds and insects such as the Egyptian alfalfa weevil during this time period and the cost of production for this cutting can be high. It is difficult to make hay during the winter due to cool weather, rainfall, and generally poor drying conditions. Although prices for quality hay are usually high during the winter, most hay produced during this time is not of high quality due to frost damage, rain damage, or bleaching from prolonged field exposure during the drying process. Up to half of the annual precipitation (~3.5 inches) may be received during this period in the Phoenix region, so some alfalfa production may be possible without irrigation, 3) Irrigating once instead of twice per cutting could maintain alfalfa production throughout the year without significantly reducing yields. Alfalfa is a deep-rooted crop and its effective rooting depth is 6 to 8 feet. It may be possible to meet the water requirements of alfalfa each cutting with a single irrigation using less water than two irrigations. This strategy may be particularly effective with the shorter cutting cycles more common in recent years employed as an effort to improve hay quality. The objective of this study is to determine the yield and profitability of sub-optimal irrigation strategies in alfalfa. Materials and Methods A field study of suboptimal irrigation strategies for alfalfa was established at the University of Arizona Maricopa Agricultural Center. CUF 101 alfalfa was seeded with a Brillion seeder on 29 Oct 2008 at a rate of 25 lbs seed/acre on a sandy clay loam soil. The preplant phosphate level in the soil was 5.0 ppm PO 4 -P, which is considered low, and 200 lbs/acre of ammonium phosphate fertilizer ( ) was applied on 27 Jan The experimental area was flood irrigated as necessary to establish a stand before irrigation treatments are initiated. Once a stand was established, the experimental area was divided into basins 30 ft x 60 ft in size which were surrounded by earthen berms that allowed each basin to be watered individually. Water was delivered to each basin or plot using by tapping into the pressurized water system with 8 inch polypipe fitted with slide gates that could be opened to deliver water as required. The following irrigation treatments were replicated four times in a randomized complete block experimental design: 1) One irrigation per cutting, 2) Two irrigations per cutting, 3) Summer (August) irrigation termination, 4) Winter (December, January, February) irrigation termination, and 5) Summer and Winter irrigation termination. (Table 1). The irrigation termination treatments were irrigated twice per cutting. The amount of irrigation water applied was based on soil water measurements to a depth of 10 ft using a neutron probe (Table 2). The forage was harvested with a Carter forage harvester by taking two 40-inch passes through the crop. A sample of forage was obtained each harvest to adjust yield for moisture content and to perform quality analysis on the forage. Stand was evaluated on 31 July 2009 and 4 Dec 2009 by counting crowns in two 2 ft x 4 ft areas Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 2

4 Results and Discussion The irrigation strategy that resulted in the greatest hay yield was, as expected, two irrigations per cutting with no irrigation termination (Table 3). Irrigating once per cutting decreased hay yields by about 9% on an annual basis compared to irrigating twice per cutting. The decrease in yield by irrigating only once instead of twice per cutting was 14% if the cuttings on 4/2 and 7/1 are excluded from the calculation since more than one irrigation was applied for these cuttings. The alfalfa irrigated only once per cutting was shorter than that irrigated twice per cutting and was water stressed in appearance at harvest. The moisture content of forage from this irrigation strategy was less than forage grown with other strategies (data not presented). The annual forage yield for the summer irrigation termination strategy was about 6% lower than irrigating twice per cut for all cuttings. The yield for the forage irrigated twice during this summer termination time (August) was about half of what was obtained in previous cuttings. Therefore, this is a good time to termination irrigation since productivity is so low. Hay yields were limited after the 8/27 cutting by a severe infestation of potato leaf hopper. Hay yields were only about half a ton per acre on 10/2, and recovered somewhat by the next cutting on 12/4. So, the ability of the summer termination treatment to recover after irrigation water was withheld could not be established with certainty since leafhoppers reduced yield of all treatments. The winter termination strategy was initiated in December, and yields from this treatment will not be harvested until next March, so there is no data available at this time to report on the effectiveness of this strategy. Sub-optimal irrigation increased the nutritional quality of the hay (Tables 4-6). Irrigating once per cutting reduced fiber content as measured by acid detergent fiber (ADF) and neutral detergent fiber (NDF) and increased crude protein content. This may have occurred because the crop was at a less advanced stage. The soil was drier at harvest for the treatment irrigated once per cutting, and re-growth was delayed compared to the crop grown with two irrigations per cutting. The plants grown with one irrigation per cutting were shorter at harvest which also indicates they might have been at an earlier stage of growth. The protein content of the treatment irrigated once per cutting was greater than that of the treatment irrigated twice per cutting perhaps because the plant may have been less mature. However, I suspect that the protein content of this treatment may have been reduced using a commercial swather due to increased leaf loss because of the lower moisture content of this forage. The small plot forage harvester we used recovered most of the leaves. Forage quality for the summer irrigation termination strategy was also high since the crop grew very slowly and was immature at harvest due to lack of water and achieved a yield of only 1/3 ton/acre in contrast to the 1 ton/acre achieved by the fully irrigated treatments at the 8/27 cutting. In the first year of this study, sub-optimal irrigation strategies did not reduce stand as is commonly feared (Table 7). However, these irrigation treatments may be relying on moisture in the subsoil for survival, and over time as this source of water is depleted, stand may be adversely affected. The efficiency that hay is produced per unit of irrigation and rainfall (WUE irr ) was not affected by the irrigation strategies in this study so far (Table 7). We are able to apply small amount of water with the irrigation system we used in this study and the amount of water applied each irrigation is close to the amount of water used by the crop. This is not the case with most surface flood systems in commercial practice where the minimum water application is 4 to 6 inches. In our study, we applied 2 to 4 inches of water on several occasions. So, under commercial conditions, the efficiency of irrigating once per cutting may be greater than irrigating twice per cutting due to less loss of water to drainage compared to more frequent irrigation. Also, in our study we re-irrigated the summer termination treatments at the end of summer with enough water to refill the soil profile, which reduced the WUE irr of this treatment. In summary, we have not shown improvements in the efficiency of water use by sub-optimal irrigation strategies in this study. I am considering changes in the protocol of this study for the following year that either mimicks or gives insight into how sub-optimal irrigation strategies would behave under commercial conditions Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 3

5 Acknowledgments This proposal was funded by the US Department of Interior Bureau of Reclamation Lower Colorado Region Phoenix Area Office Water Conservation Field Services Program. The technical assistance of Richard Simer, Rafael Chavez-Alcorta, Patrick Royer, and Mary Comeau is greatly appreciated. References Erie, L.J., O.F. French, and K. Harris Consumptive use of water by crops in Arizona. Technical Bulletin 169. Agricultural Experiment Station, The University of Arizona, Tucson. Frate, C.A., B.A. Roberts, and V.L. Marble Imposed drought stress has no long term effect on established alfalfa. California Agriculture 45(3): Guitjens, J.C., and E.H. Jensen Irrigation for alfalfa grown for hay: Important considerations in a drought year. Fact Sheet Univ. Nevada Coop. Ext., Reno. Hanson, B., D. Putnam, and R. Snyder Deficit irrigation of alfalfa as a strategy for providing water for water-short areas. Agricultural Water Management 93: Metochis, C., and P.I. Orphanos Alfalfa yield and water use when forced into dormancy by withholding water during the summer. Agonomy Journal 73: NASS USDA National Agricultural Statistics Service Quick Stats. Ottman, M.J., B.R. Tickes, and R.L. Roth Alfalfa yield and stand response to irrigation termination in an arid environment. Agronomy Journal 88: Robinson, F.E., L.R. Teuber, and L.K. Gibbs Alfalfa water stress management during summer in Imperial Valley for water conservation. Desert Research and Extension Center, El Centro, CA. Schneiter, A.A Effect of water management on forage production and on carbohydrate and nitrogen constituents of alfalfa (Medicago sativa L.) roots. Ph.D. Diss. Univ. of Arizona, Tucson. Schonhorst, M.H., R.K. Thompson, and R.E. Dennis Does it pay to irrigate alfalfa in the summer? Prog. Agric. Ariz. 15(6):8-9. Wilson, M., B. Melton, J. Arledge, D. Baltensperger, R.M. Salter, and C. Edminster Performance of alfalfa cultivars under less than optimum moisture conditions. Bull New Mexico State Univ., Agric. Exp. Stn., Las Cruces Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 4

6 Table 1. Alfalfa irrigation schedule based on irrigating 7 days after previous cutting and 9 days before subsequent cutting. An X in the table denotes that an irrigation was applied for a treatment on a particular date. The cuttings were scheduled starting about 5 months after planting and then 5, 4, 4, 4, 4, 5, and 9 weeks thereafter for cuttings 2 through 8. Treatment Code Cutting Irrigation Apr Apr 09 X X X X X 23 Apr 09 X X X X 06 May May 09 X X X X X 26 May 09 X X X X 04 Jun Jun 09 X X X X X 23 Jun 09 X X X X 01 Jul Jul 09 X X X X X 21 Jul 09 X X X X 30 Jul Aug 09 X X X 18 Aug 09 X X 27 Aug Sep 09 X X X X X 17 Sep 09 X X X X 02 Oct Oct 09 X X X X X 30 Oct 09 X X X X 03 Dec Dec 09 X X X??? X X 2010 Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 5

7 Table 2. Water applied to the various irrigation treatments. The rainfall amount for 2008 from planting to the end of the year was 1.31 inches and for 2009 was 3.83 inches. Irrigation Strategy Cutting Date Irrigation Date One irrigation per cutting Two irrigations per cutting Summer termination Winter termination Summer and Winter termination inches Oct Nov Dec Jan Feb Apr Mar Apr May Apr May Jun May Jun Jul Jun Jul Jul Jul Aug Aug Aug Sep Oct Sep Oct Dec Oct Dec SUM Jan- Nov, Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 6

8 Table 3. Alfalfa hay yield as affected by irrigation strategy in a trial conducted at Maricopa, AZ in Hay Yield Irrigation Strategy 4/2 5/6 6/4 7/1 7/30 8/27 10/2 12/4 Sum Tons/acre One irrigation per cut Two irrigations per cut Summer irrigation termination Winter irrigation termination Summer and winter termination Average CV (%) LSD.05 ns ns ns Table 4. Acid detergent fiber (ADF) of alfalfa as affected by irrigation strategy in a trial conducted at Maricopa, AZ in Acid Detergent Fiber (ADF) Irrigation Strategy 4/2 5/6 6/4 7/1 7/30 8/27 Average % One irrigation per cut Two irrigations per cut Summer irrigation termination Winter irrigation termination Summer and winter termination Average CV (%) LSD.05 ns ns ns Table 5. Neutral detergent fiber (NDF) of alfalfa as affected by irrigation strategy in a trial conducted at Maricopa, AZ in Neutral Detergent Fiber (ADF) Irrigation Strategy 4/2 5/6 6/4 7/1 7/30 8/27 Average % One irrigation per cut Two irrigations per cut Summer irrigation termination Winter irrigation termination Summer and winter termination Average CV (%) LSD.05 ns ns ns Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 7

9 Table 6. Protein content of alfalfa as affected by irrigation strategy in a trial conducted at Maricopa, AZ in Protein Irrigation Strategy 4/2 5/6 6/4 7/1 7/30 8/27 Average % One irrigation per cut Two irrigations per cut Summer irrigation termination Winter irrigation termination Summer and winter termination Average CV (%) LSD.05 ns 1.8 ns ns ns Table 7. Plant stand density measured on 7/31 and 12/4 and water use efficiency of irrigation plus rainfall (WUE irr ) as affected by irrigation strategy in a trial conducted at Maricopa, AZ in Plant stand density Irrigation plus rainfall Irrigation Strategy 7/31 12/4 Water use efficiency plants/ft Tons hay/acre/ft of water One irrigation per cut Two irrigations per cut Summer irrigation termination Winter irrigation termination Summer and winter termination Average CV (%) LSD.05 ns ns ns 2010 Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 8

10 Response of wheat and barley varieties to phosphorus fertilizer, 2009 M. J. Ottman Summary Phosphorus fertilizer represents a significant portion of the cost of producing small grains. Some evidence exists that there are differences in the ability of small grain varieties to take phosphorus up from the soil and utilize this nutrient in the grain. The objective of this study is to determine if barley and wheat varieties grown in Arizona differ in their response to phosphorus fertilizer. A study was initiated at the Maricopa Agricultural Center testing the response of 7 barley and 13 wheat (12 durum wheat and 1 bread wheat) varieties to 2 phosphorus rates (0 and 100 lbs P 2 O 5 /acre). The grain yield increase due to phosphorus application averaged across varieties was 474 lbs/acre for barley and 613 lbs/acre for wheat. The barley varieties differed in their grain yield increase due to phosphorus fertilizer and the greatest increase for the commercial varieties tested was 906 lbs and the smallest increase was 245 lbs. We have no statistical evidence that wheat varieties differed in their response to phosphorus fertilizer. The lack of response to phosphorus fertilizer for a particular variety may save production costs if the fertilizer is not applied, but a significant response to phosphorus fertilizer may pay for the fertilizer cost and increase profits. In this study, the higher yielding varieties tended to have a greater response to phosphorus fertilizer, particularly for the barley. This test will be repeated in 2010 to see if the results obtained this year can be duplicated. Introduction Phosphorus fertilizer costs have increased dramatically in the past few years. In small grain production, fertilizer represents a significant proportion of the cost of production. The availability of soil P can be influenced by root exudates, which are under genetic control (Rengel, 2002). Small grain varieties may differ in their response to phosphorus fertilizer due to the presence or absence of these exudates or other factors (Davies et al., 2002). Citric acid is one of the root exudates that have been identified and related to phosphorus availability. The objective of this study is to determine if wheat and barley varieties grown in Arizona differ in their response to phosphorus fertilizer. Procedure A study was conducted at the University of Arizona Maricopa Agricultural Center to determine if wheat and barley varieties respond to phosphorus fertilizer differently. The soil type was a Casa Grande sandy loam with a preplant soil phosphate level of 4.3 ppm P. P fertilizer treatments were applied before planting at rates of 0 and 100 lbs P 2 O 5 /acre using triple super phosphate (0-45-0) as a fertilizer source. The P fertilizer was applied by hand to plots 5 ft x 20 ft in size. The seed was planted with a cone planter in seven rows spaced 7 inches apart and 20 ft long. The seeding rate was approximately 100 lbs/acre for durum varieties and 85 lbs/acre for barley varieties. The experimental design of the P x Variety Study was a split plot with varieties (9 barley and 13 wheat [12 durum wheat and 1 bread wheat]) as main plots and P rate (0 and 100 lbs P 2 O 5 /acre) as subplots. A P Rate Study with a wider range of P rates (0, 25, 50, 75, 100, and 150 lbs P 2 O 5 /acre) and a single variety (Gustoe barley and Kronos durum) was also conducted to determine if the P rate of 100 lbs P 2 O 5 /acre is adequate for optimum yield. Cultural practices 2010 Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 9

11 are listed in Table 1. The following data was collected: grain yield, test weight, plant height, lodging, heading, flowering, physiological maturity, grain P, grain protein, HVAC, biomass and light interception on Feb 3 at the 5 leaf stage, and light interception on Apr 4 at the milky kernel stage. Grain was harvested with a small plot combine and yields are expressed on an as is moisture basis. HVAC was determined from 10 g of seed. Grain protein was calculated using the combustion method to obtain total N, which was multiplied by 5.7 to obtain protein content and expressed on a 12% moisture basis. Flowering is defined as when about half of the heads are shedding pollen and physiological maturity is defined as when the glumes turn brown. Biomass was determined from a pair of rows each 18 inches in length. Light interception was determined by dividing the average of six readings from a sunfleck ceptometer at ground level by incident light level. Abbreviations for the sources of varieties are: APB = Arizona Plant Breeders, WPB = Western Plant Breeders, WWW = World Wide Wheat, UC = University of California. Results and Discussion This growing season was characterized by above average temperature and low rainfall (Table 2). Temperatures were especially warm during the months of January and May. Temperatures during April were below average. P rate study (6 P rates and 1 barley and 1 wheat variety): Grain yields of Gustoe barley and Kronos durum were increased by phosphorus rates from 0 to 150 lbs P 2 O 5 /acre (Table 3). Yield of Gustoe were increased even at the 150 lbs/acre rate whereas yield of Kronos reached a plateau at about 75 lbs P 2 O 5 /acre. The seed of Gustoe germinated poorly resulting in poor stand establishment, which may explain the lack of a yield plateau for this variety. A different source of seed for Gustoe with better germination was used in the P x Variety study to be discussed below. P rate also increased plant height; decreased time to heading, anthesis, and maturity; increased grain P content; decreased wheat protein; and increased barley biomass and light interception measured on Feb 3. P x variety study (2 P rates and 9 barley and 13 wheat varieties) We measured a P response to most variables (Tables 4-7). P increased yield, test weight, plant height (barley), grain phosphorus, biomass and light interception; decreased time to heading, anthesis, and maturity; but had no effect on plant height (wheat), grain P, and protein. The varieties responded to an application of 100 lbs P 2 O 5 /acre in a similar manner for most of the variables measured (Tables 4-7). However, the P application response was different for barley varieties for grain yield and light interception on Feb 3 and for wheat varieties for heading, anthesis, and light interception on Feb 3. The barley grain yield response to P application ranged from -272 to 906 lbs/acre. The grain yield response to P application was correlated with absolute yield. The variety that had the greatest response to P also had the highest yield, and the variety that had the negative response to P had the lowest yield. The increase in light interception on Feb 3 due to P application ranged from 15 to 28% for barley and 6 to 28% for wheat. The increase in light interception on Feb 3 for the varieties was not necessarily related to yield. Lack of P application delayed heading and anthesis dates in wheat by as much as 4 to 6 days for certain varieties, but this delay did not affect maturity and was not related to yield. In summary, a small or negligible response to phosphorus fertilizer for a particular variety may save production costs if the fertilizer is not applied, but a significant response to phosphorus fertilizer may pay for the fertilizer cost and increase profits. Acknowledgments Financial support for this project was received from the Arizona Grain Research and Promotion Council and the Arizona Crop Improvement Association. The technical assistance of Mary Comeau and Mike Sheedy is greatly appreciated Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 10

12 References Davies, T.G.E., J. Ying, Q. Xu, Z.S. Li, J. Li, and R. Gordon-Weeks Expression analysis of putative highaffinity phosphate transporters in Chinese winter wheats. Plant, Cell and Environment. 25: Rengel, Z Genetic control of root exudation. Plant and Soil 245: Table 1. Cultural practices for the small grain phosphorus trial at Maricopa. Previous crop Soil texture Corn Sandy loam Planting date 12/12/08 Irrigations Nitrogen (lbs N/a) 7 12/12, 1/28, 2/25, 3/13, 3/27, 4/9, 4/ /12: 46 as /28: 50 as /25: 50 as /13: 50 as /27: 50 as Phosphorus (lbs P 2 O 5 /acre) 0 or 100 Pesticides None Harvest date 6/3 Table 2. Climatic data from AZMET for Maricopa during the growing season compared to the long-term average. Climate Unit Year(s) Dec Jan Feb Mar Apr May Dec-May variable Max ºF Temp. ºF Avg Min ºF Temp. ºF Avg Ppt. inches inches Avg Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 11

13 Table 3. Phosphorus rate effect on grain yield and other plant characteristics for Gustoe barley and Kronos durum. Light interception Light interception (Apr 2) Test Plant Headinesiuritphorus Anth- Mat- Grain Phos- Grain Biomass P rate Yield Weight Height Protein HVAC (Feb 3) (Feb 3) lbs/a lbs/a lbs/bu inches % % % lbs/a % % Barley /29 3/27 5/ /27 3/25 5/ /28 3/26 5/ /28 3/26 5/ /27 3/25 5/ /27 3/26 5/ All /27 3/26 5/ P rate * * NS NS NS NS ** NS NS * * NS Linear ** * NS + NS + ** NS NS ** ** NS Quad NS NS * NS NS NS * NS NS NS NS NS Cubic NS NS NS NS NS NS NS NS NS NS NS + Durum /17 3/21 4/ /16 3/20 4/ /16 3/20 4/ /16 3/20 4/ /16 3/20 4/ /16 3/20 4/ All /16 3/20 4/ P rate ** ** NS ** NS NS ** NS NS NS ** NS Linear ** ** NS ** * NS ** + NS NS + NS Quad * NS NS * NS + ** NS NS NS ** NS Cubic NS NS + * NS * NS NS NS NS + NS 2010 Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 12

14 Table 4. Grain yield, test weight, and plant height of barley and wheat varieties as affected by phosphorus fertilizer rates of 0 and 100 lbs P 2 O 5 /acre. Response refers to the difference between the phosphorus rates. The wheat varieties are durums except for Yecora Rojo, which is a bread wheat. Grain Yield Test Weight Plant Height Phosphorus Entry Source 0 lb/a 100 lb/a Response 0 lb/a 100 lb/a Response 0 lb/a 100 lb/a Response lbs/a lbs/bu inches Barley Chico WPB Cochise WPB Gustoe WPB Nebula WPB Commander WWW Max WWW Baretta APB ARGBA2042 WWW Unknown APB Avg LSD.05 * NS NS Entry ** ** ** P rate ** ** ** Entry x P NS NS NS Wheat Alamo WPB Havasu WPB Orita WPB WPB-881 WPB Crown WWW Duraking WWW Q-Max WWW Kronos APB Sky APB Ocotillo APB Westmore APB Maestrale Allstar Yecora Rojo Public Avg LSD.05 * NS NS NS Entry ** ** ** P rate ** ** NS Entry x P NS NS NS * LSD.05 = least significant difference between means within a column with a 5% or less probability the difference is due to chance Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 13

15 Table 5. Heading, anthesis, and physiological maturity of barley and wheat varieties as affected by phosphorus fertilizer rates of 0 and 100 lbs P 2 O 5 /acre. Response refers to the difference between the phosphorus rates. The wheat varieties are durums except for Yecora Rojo, which is a bread wheat. Heading Anthesis Physiological Maturity Phosphorus Entry Source 0 lb/a 100 lb/a Response 0 lb/a 100 lb/a Response 0 lb/a 100 lb/a Response Barley Chico WPB 3/23 3/20-3 3/21 3/18-3 4/30 4/29-1 Cochise WPB 3/14 3/10-4 3/13 3/09-4 4/21 4/21 0 Gustoe WPB 3/26 3/22-4 3/24 3/21-3 5/01 4/30-1 Nebula WPB 3/21 3/17-4 3/19 3/16-3 4/26 4/26 0 Commander WWW 3/25 3/23-2 3/23 3/21-2 5/01 4/28-3 Max WWW 3/24 3/21-3 3/23 3/19-4 5/05 5/03-2 Baretta APB 3/23 3/20-3 3/21 3/19-2 4/27 4/25-2 ARGBA2042 WWW 3/13 3/10-3 3/12 3/10-2 4/20 4/19-1 Unknown APB 3/19 3/15-4 3/17 3/14-3 4/22 4/20-2 Avg --- 3/21 3/18-3 3/20 3/17-3 4/28 4/26-2 LSD.05 * 2 2 NS 2 2 NS 2 2 NS Entry ** ** ** P rate ** ** ** Entry x P NS NS NS Wheat Alamo WPB 3/18 3/17-1 3/22 3/21-1 4/30 4/30 0 Havasu WPB 3/18 3/17-1 3/22 3/21-1 4/28 4/26-2 Orita WPB 3/24 3/23-1 3/29 3/27-2 5/04 5/03-1 WPB-881 WPB 3/18 3/17-1 3/22 3/21-1 4/29 4/28-1 Crown WWW 3/24 3/20-4 3/29 3/23-6 5/04 5/02-2 Duraking WWW 3/23 3/19-4 3/27 3/23-4 5/02 5/01-1 Q-Max WWW 3/27 3/24-3 3/31 3/29-2 5/05 5/04-1 Kronos APB 3/16 3/15-1 3/21 3/19-2 4/29 4/27-2 Sky APB 3/19 3/17-2 3/23 3/22-1 5/03 5/02-1 Ocotillo APB 3/18 3/17-1 3/22 3/21-1 5/01 4/30-1 Westmore APB 3/18 3/17-1 3/22 3/21-1 4/29 4/29 0 Maestrale Allstar 3/20 3/18-2 3/24 3/22-2 4/28 4/28 0 Yecora Rojo Public 3/17 3/16-1 3/21 3/20-1 4/25 4/26 1 Avg --- 3/20 3/18-2 3/24 3/22-2 4/30 4/30 0 LSD.05 * NS Entry ** ** ** P rate ** ** ** Entry x P ** ** NS * LSD.05 = least significant difference between means within a column with a 5% or less probability the difference is due to chance Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 14

16 Table 6. Grain phosphorus, grain protein, and percentage of kernels hard and vitreous and of amber color (HVAC) of barley and wheat varieties as affected by phosphorus fertilizer rates of 0 and 100 lbs P 2 O 5 /acre. Response refers to the difference between the phosphorus rates. The wheat varieties are durums except for Yecora Rojo, which is a bread wheat. Grain Phosphorus Grain Protein HVAC Phosphorus Entry Source 0 lb/a 100 lb/a Response 0 lb/a 100 lb/a Response 0 lb/a 100 lb/a Response % % % Barley Chico WPB Cochise WPB Gustoe WPB Nebula WPB Commander WWW Max WWW Baretta APB ARGBA2042 WWW Unknown APB Avg LSD.05 * NS NS Entry NS ** --- P rate ** NS --- Entry x P NS NS --- Wheat Alamo WPB Havasu WPB Orita WPB WPB-881 WPB Crown WWW Duraking WWW Q-Max WWW Kronos APB Sky APB Ocotillo APB Westmore APB Maestrale Allstar Yecora Rojo Public Avg LSD.05 * NS NS NS NS NS Entry NS NS ** P rate ** + NS Entry x P + NS NS * LSD.05 = least significant difference between means within a column with a 5% or less probability the difference is due to chance Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 15

17 Table 7. Biomass on Feb 3 and light interception by the crop on Feb 3 and Apr 2 of barley and wheat varieties as affected by phosphorus fertilizer rates of 0 and 100 lbs P 2 O 5 /acre. Response refers to the difference between the phosphorus rates. The wheat varieties are durums except for Yecora Rojo, which is a bread wheat. The growth stage was about 5 leaf on Feb 3 and milky kernel on Apr 2. Biomass (Feb 3) Light interception (Feb 3) Light interception (Apr 2) Phosphorus Entry Source 0 lb/a 100 lb/a Response 0 lb/a 100 lb/a Response 0 lb/a 100 lb/a Response lbs/a % % Barley Chico WPB Cochise WPB Gustoe WPB Nebula WPB Commander WWW Max WWW Baretta APB ARGBA2042 WWW Unknown APB Avg LSD.05 * NS NS Entry ** * * P rate ** ** ** Entry x P NS * NS Wheat Alamo WPB Havasu WPB Orita WPB WPB-881 WPB Crown WWW Duraking WWW Q-Max WWW Kronos APB Sky APB Ocotillo APB Westmore APB Maestrale Allstar Yecora Rojo Public Avg LSD.05 * NS NS Entry ** ** NS P rate ** ** ** Entry x P NS + NS * LSD.05 = least significant difference between means within a column with a 5% or less probability the difference is due to chance Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 16

18 Small Grains Variety Evaluation at Maricopa and Yuma, 2009 M. J. Ottman Summary Small grain varieties are evaluated each year by University of Arizona personnel. The purpose of these tests is to characterize varieties in terms of yield and other attributes. Variety performance varies greatly from year to year and several site-years are necessary to adequately characterize the yield potential of a variety. A summary of small grain variety trials conducted by the University of Arizona can be found online at Introduction Small grain varieties were tested as part of the on-going effort to assess variety productivity and characteristics. Barley, durum, and wheat commercial cultivars and experimental lines were tested. The purpose of these tests is to characterize varieties in terms of yield potential, relative maturity, quality, and other characteristics. Small plot variety trials do not substitute for localized on-farm testing of new varieties. Varieties are known to differ in their response to specific management regimes and weather conditions. A summary of small grain variety trials conducted by the University of Arizona is available from your local Cooperative Extension office or online at Procedure Barley, durum, and wheat varieties were evaluated at the following locations: Maricopa by the University of Arizona and Yuma (durum) and Casa Grande (barley) by Western Plant Breeders. The trial at Yuma consisted of a normal planting on Jan 8 and a late planting on Feb 1. The trial conducted by World Wide Wheat is not included in this report due to poor growing conditions and low yield. At all locations, the seed was planted with a cone planter in seven rows spaced 7 inches apart and 20 ft long. The seeding rate was approximately 100 lbs/acre for durum and wheat varieties and 85 lbs/acre for barley varieties. The experimental design was a randomized complete block with 4 replications, barley entries, and durum (or wheat at Maricopa) entries. Growing conditions at each site are listed in Table 1. The following data was collected: grain yield, test weight, plant height, lodging, heading, flowering (Maricopa, UA only), physiological maturity (Maricopa, UA only), grain protein, and HVAC. Grain was harvested with small plot combines and yields are expressed on an as is moisture basis. HVAC was determined from 10 g of seed. Grain protein was determined using the NIRS (WPB) or a C/N analyzer (UA) and expressed on a 12% moisture basis. Flowering is defined as when about half of the heads are shedding pollen and physiological maturity is defined as when the glumes turn brown. Abbreviations for the sources of varieties are: APB = Arizona Plant Breeders, UA = University of Arizona, WPB = Western Plant Breeders, WWW = World Wide Wheat, UC = University of California, RSI = Resource Seeds Inc Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 17

19 Discussion This growing season was characterized by above average temperature and low rainfall (Table 2). Temperatures were especially warm during the months of January and May. Temperatures during April were below average. Yield and plant characteristics of the varieties are presented for the various locations in Tables 3-6 and a summary of the grain yields at all locations is presented in Table 7. The WPB barley trial at Casa Grande had low yields (5105 lbs/acre) but not below the threshold level of 5000 lbs/acre where I do not report the data. The trial at Maricopa sustained bird damage in some plots, and plots with bird damage were excluded from the yield analysis. The birds did not damage the barley, but they damaged some of the durum plots and damaged enough of the wheat plots that yields could not be reported. Several locations and years are needed to accurately assess variety performance. The results of this trial are most useful when combined with data from previous years. A summary of small grain variety trials conducted by the University of Arizona can be found online at Acknowledgments Financial support for this project was received from the Arizona Grain Research and Promotion Council and the Arizona Crop Improvement Association. I wish to thank Kim Shantz of Westbred for conducting the trials in Yuma and Casa Grande. The technical assistance of Mary Comeau and Mike Sheedy is greatly appreciated. Dr. Rufus Chaney, USDA, Beltville, MD analyzed the durum and wheat grain from Maricopa for copper, zinc, and cadmium. The additional quality analysis of durum grown at Maricopa was provided by Greg Viers, Wheat Procurement Officer for Barilla. Richard Cooley of Agrotera facilitated the analyses of copper, zinc, and cadmium and the additional quality analysis. Table 1. Cultural practices for the small grains variety trials at the various locations. The durum at Yuma was planted at two dates, 2 reps normal and 2 reps late, but the data is presented as on average of these two dates. Durum Durum Barley Cultural Maricopa Yuma Yuma Late Planting Casa Grande information (U of A) (WPB) (WPB) (WPB) Previous crop Corn Lettuce Lettuce Sorghum Soil texture Sandy clay loam Clay loam Clay loam Sandy clay loam Planting date 12/12/08 1/8/09 2/1/09 1/20/09 Irrigations 7 12/12, 1/28, 2/25, 3/13, 3/27, 4/9, 4/22 6 1/8, 3/1, 3/26, 4/12, 4/26, 5/8 7 2/1, 3/1/ 3/26, 4/12, 4/26, 5/8, 5/19 Unknown Nitrogen (lbs N/a) /12: 46 as /28: 46 as /25: 46 as /13: 46 as /27: 46 as /1: 100 as /26: 100 as /12: 25 as /1: 100 as /26: 100 as /12: 25 as Unknown Phosphorus (lbs P 2 O 5 /acre) Unknown Pesticides None None None Unknown Harvest date 6/3 6/2 6/10 6/ Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 18

20 Table 2. Climatic data from AZMET for Maricopa and Yuma Valley during the 2009 growing season compared to the long-term average. Climate Unit Year(s) Dec Jan Feb Mar Apr May Dec-May variable Maricopa Max ºF Temp. ºF Avg Min ºF Temp. ºF Avg Ppt. inches inches Avg Yuma Max ºF Temp. ºF Avg Min ºF Temp. ºF Avg Ppt. inches inches Avg Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 19

21 Table 3. Barley variety yield results from Maricopa (UA), Entry Source Grain Yield a Test Weight Plant Height Lodging Heading Flowering Maturity lbs/acre lbs/bu inches % Chico WPB /22 3/20 4/29 Cochise WPB /10 3/09 4/22 Gustoe WPB /21 3/19 4/26 Nebula WPB /16 3/15 4/26 Commander WWW /24 3/22 4/30 Max WWW /21 3/19 5/03 Baretta APB /20 3/19 4/26 ARGBA2042 WWW /10 3/10 4/19 BA4513 WWW /22 3/20 4/29 BA8017 WWW /23 3/21 5/04 B APB /13 3/12 4/23 Unkown 2- row APB /15 3/14 4/20 Avg /18 3/16 4/27 a Grain yield: LSD (5%) = 575 lbs/acre and cv = 4.6%. Table 4. Barley variety yield results from Casa Grande (WPB), Entry Source Grain Yield a lbs/acre Chico WPB 4236 Cochise WPB 4590 Gustoe WPB 5431 Nebula WPB 4991 Commander WWW 5021 Max WWW 5912 Baretta APB 5027 ARGBA2042 WWW 5587 BA4513 WWW 6061 BA8017 WWW 4906 B APB 5136 Unkown 2- row APB 4483 ISHI UC 5491 Avg a Grain yield: LSD (5%) = 806 lbs/acre and cv = 11.1% Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 20

22 Table 5. Durum and wheat variety yield results from Maricopa (UA), Grain yield is not reported for the wheat entries due to bird damage. Entry Source Grain Yield a Test Weight Plant Height Lodging Heading Flowering Maturity Grain Protein HVAC lbs/acre lbs/bu inches % % % % Durum Alamo WPB /17 3/21 4/ Havasu WPB /17 3/21 4/ Orita WPB /22 3/27 5/ WPB-881 WPB /17 3/21 4/ Crown WWW /20 3/23 5/ Duraking WWW /20 3/24 5/ Q-Max WWW /25 3/29 5/ Kronos APB /16 3/19 4/ Sky APB /18 3/22 5/ Ocotillo APB /17 3/21 4/ Westmore APB /16 3/21 4/ ARGD7050 WWW /18 3/22 5/ D65750 WWW /25 3/30 5/ Dking206white WWW /17 3/21 5/ UT12074 WWW /16 3/21 5/ D05AZ-335 APB /17 3/21 5/ D1-2 APB /17 3/21 5/ D1-1-5P APB /20 3/24 5/ D2-97 APB /15 3/19 4/ Fortissimo RSI /22 3/28 5/ RSI 59 RSI /24 3/29 5/ Volante RSI /19 3/24 5/ Maestrale Allstar /17 3/21 4/ Saragolla Allstar /18 3/22 5/ Levante Allstar /28 4/01 5/ Avg /18 3/23 4/ Wheat Blanca Fuerte RSI /18 3/22 5/ Blanca Grande RSI /14 3/18 4/ Blanca Royal RSI /16 3/20 4/ Sagittario Allstar /24 3/29 5/ Vaiolet Allstar /29 4/01 5/ Yecora Rojo UC /16 3/20 4/ Avg /19 3/23 4/ a Grain yield: LSD (5%) = 658 lbs/acre and cv = 5.8% Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 21

23 Table 6. Durum variety yield results from Yuma (WPB), Entry Source Grain Yield a Test Weight Plant Height Lodging Heading Grain Protein HVAC Leaf Rust Stripe Rust lbs/acre lbs/bu inches % % % Durum Alamo WPB / Havasu WPB / Orita WPB / WPB-881 WPB / Crown WWW / Duraking WWW / Q-Max WWW / Kronos APB / Sky APB / Ocotillo APB / Westmore APB / ARGD7050 WWW / D65750 WWW / Dking206white WWW / UT12074 WWW / D05AZ-335 APB / D1-2 APB / D1-1-5P APB / D2-97 APB / ATIL-2001 CIMMYT / Avg / a Grain yield: LSD (5%) = 798 lbs/acre and cv = 7.5% Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 22

24 Table 7. Summary of small grain variety yield results for 2009 from Maricopa (U of A), Yuma (WPB durum) and Casa Grande (WPB barley). Grain yield (% of location average for these entries) Maricopa (U of A) Yuma (durum) or Casa Grande (barley) (WPB) Standard Deviation Entry Source Mean Barley Chico WPB Cochise WPB Gustoe WPB Nebula WPB Commander WWW Max WWW Baretta APB ARGBA2042 WWW BA4513 WWW BA8017 WWW B APB Unkown 2- row APB Durum Alamo WPB Havasu WPB Orita WPB WPB-881 WPB Crown WWW Duraking WWW Q-Max WWW Kronos APB Sky APB Ocotillo APB Westmore APB YU WPB ARGD7050 WWW D65750 WWW Dking206white WWW UT12074 WWW D05AZ-335 APB D1-2 APB D1-1-5P APB D2-97 APB Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 23

25 Appendix Table A1. Copper, zinc, and cadmium concentration in the grain of durum and wheat varieties grown at Maricopa (UA), Soils in the Maricopa area have a relatively low cadmium content, and the cadmium content of grain grown in other areas can be higher. This data was provided by Dr. Rufus Chaney, USDA, Beltville, MD. Entry Source Copper Zinc Cadmium ppm ppm ppm Durum Alamo WPB Havasu WPB Orita WPB WPB-881 WPB Kronos APB Sky APB Ocotillo APB Westmore APB D05AZ-335 APB D1-2 APB D1-1-5P APB D2-97 APB Fortissimo RSI RSI 59 RSI Volante RSI Maestrale Allstar Saragolla Allstar Levante Allstar AVG Wheat Blanca Fuerte RSI Blanca Grande RSI Blanca Royal RSI Sagittario Allstar Vaiolet Allstar Yecora Rojo Public AVG Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 24

26 Table A2. Quality analysis for durum grown at Maricopa (UA), Ash and protein are expressed on a dry matter (DM) basis. This data was provided by Greg Viers, Wheat Procurement Officer for Barilla. Entry Source Gluten Quality Ash Color, b Protein Moisture % of DM % of DM % Durum Alamo WPB Havasu WPB Orita WPB Crown WWW Duraking WWW Kronos APB Sky APB Ocotillo APB Westmore APB Fortissimo RSI Volante RSI Maestrale Allstar Saragolla Allstar AVG Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 25

27 Water Use Efficiency of Forage Sorghum Grown with Sub-optimal Irrigation, 2009 Michael J. Ottman Summary A forage sorghum irrigation study was conducted at Maricopa, AZ to determine water use and if sub-optimal irrigation increases water use efficiency and profitability. Sorghum was planted on July 10 with a row spacing of 40 inches and irrigated three times with a total of 8.7 inches of water to establish the crop. Variable amounts of irrigation water were applied commencing on Aug 12 based on 25, 50, 75, and 100% of estimated crop water use (evapotranspiration, ET). The plots were 53.3 ft wide (16 rows) and 40 ft long. ET was estimated from soil water measurements using a neutron probe. The total amount of water applied was 15.5, 19.8, 23.7, and 27.8 inches for the 25, 50, 75, and 100% ET treatments, respectively. The forage was harvested on Oct 28 near the soft dough stage. Forage yields adjusted to 70% moisture were 11.3, 16.4, 21.5, and 23.1 tons/acre for the 25, 50, 75, and 100% ET treatments, respectively. Yield produced per inch of water used by the crop (WUE ET, water use efficiency of water used in ET) increased with water application. Yield produced per inch of water applied to the crop (WUE irr, water use efficiency of irrigation water applied plus rainfall) also increased with water application, but then decreased from the 75 to 100% ET treatments. Nevertheless, sub-optimal irrigation strategies are not economical using the results from this study assuming a water cost of $45 per acre-foot and a sorghum silage value of $20 per ton. For sub-optimal irrigation strategies to be economical, water costs would have to increase, sorghum silage value would have to decrease, or the differences in the irrigation efficiencies of the strategies being compared would have to be greater than measured in the present study. Introduction Water use of forage sorghum in Arizona and similar production areas has been published (Erie et al., 1965). However, this work has come under criticism since deep drainage of soil water apparently was not accounted for and the water use estimates may therefore be too high. Light, frequent irrigations have been shown to increase WUE of forage sorghum (Saeed and Nadi, 1998), but light irrigations are not possible with flood irrigation. In a simulation study with grain sorghum, it was found that WUE was increased by irrigating fewer acres with more water with complementary dryland areas rather than more acres with less water (Baumhardt et al., 2007). The effect of irrigation timing on sweet sorghum was studied by us recently (Miller and Ottman, 2010), and this study revealed that irrigating less frequently resulted in higher water use efficiency. However, the stress imposed by our irrigation treatments were not severe enough to decrease forage yield, so in the proposed study, we intend to introduce more severe stress than the previous study. The objectives of this study are to determine: 1) forage sorghum water use, and 2) if sub-optimal irrigation of forage sorghum increases water use efficiency and potential profitability. Materials and Methods A forage sorghum irrigation experiment was established at the Maricopa Agricultural Center in Maricopa, AZ on a Casa Grande sandy clay loam soil. The previous crop was hesperaloe, a succulent crop grown for fiber. Atrazine was applied preplant for weed control. The forage sorghum hybrid Richardson Seeds Silo 700D was planted on flat ground 7 July 2009 at a seeding rate of 96,000 seeds per acre in 40 inch row spacing. Urea was applied at planting and on 7 Aug 09 at a rate of 100 lbs N/acre each application Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 26

28 A germination irrigation was applied on 7 July 2009 and two more irrigations were applied to establish the crop before differential irrigations were initiated (Table 1). Plots were established by creating basins surrounded by earthen berms so each plot could be irrigated individually with polypipe fitted with gates. Each plot was 53.3 ft wide (16 rows) and 40 ft long. Irrigation treatments were based on target ET levels of 25, 50, 75, and 100% after establishment. ET was calculated from soil water depletion measured before and after each irrigation with a neutron probe in 0.2 m increments to a depth of 3.0 m. The center 5 feet of 2 rows in the plots were hand harvested on 28 Oct 2009 to obtain forage yield. The plants were sampled for moisture determination and the yield was adjusted to 70% moisture content. The experimental design was a randomized complete block with 4 blocks. The data was statistically analyzed using the MIXED procedure in SAS. Results and Discussion Irrigation water application increased most measures of crop growth and development (Table 2). Water application increased sorghum forage yield in a linear fashion with some diminishing returns at the highest rate. Forage yield adjusted to 70% moisture content increased from about 11 to 23 tons/acre with an increase in water application from 15.5 to 27.9 inches. Forage moisture content at harvest increased with water application. Forage protein content at harvest decreased substantially with an increase in water application from 8.58 to 4.75%. Water application increased plant height substantially. The density of stems at harvest was not affected by water application. The plants did not produce productive tillers to any extent, and the number of stems at harvest was roughly 8% less than 3 weeks after planting (data not presented). At harvest, the leaf area index (LAI) was less than 3, for 25 and 50% ET treatments, and greater than 5, for 75 and 100% ET treatments. The difference in LAI among the irrigation treatments can be attributed to less area of brown and green leaves in the lower irrigation treatments but also to premature senescence of the lower leaves in these treatments. The final leaf number increased with water application, and the 25% ET treatment had 3-4 fewer leaves than the other treatments. This can be partially explained by the fact that the 25% treatment had not bloomed by harvest on 10/28, and since cold weather had set in by that time, the chances of ever reaching bloom for this treatment were remote. An increase in water application hastened maturity and the date of 50% bloom. Water use, or evapotranspiration (ET), increased with water application from 14.7 to 23.7 inches. Irrigation efficiency decreased as more water was applied either due to movement of water past the active rooting zone or more water unused and remaining in the soil profile at harvest. Water use efficiency is defined as the tons for crop yield produced per unit of water used by or applied to the crop. The water use efficiency of water used in ET (WUE ET ) increased with the amount of water used by the crop. The water use efficiency of water applied (WUE irr ) also increased with the amount of water applied to the crop, but then decreased at the highest water application amount. The loss in WUE irr with the 100% ET treatment could be explained by losses of water from the root zone or a larger amount of water remaining in the root zone at harvest compared to the other treatments. Whether or not irrigating at 100% ET is the most economical strategy depends on the relative prices of water and sorghum silage. If we assume water costs $45/acre-foot and sorghum silage is worth $20/ton, then the yield increase in our study of 1.6 T/acre is worth $32/acre (1.6 T/acre x $20/T = $32/acre) and pays for the $15 cost of the additional 4.1 inches of water (4.1 inches/12 inches/ft x $45/acre-ft = $15). So, water costs would have to double or sorghum silage prices reduce by half in order for reducing irrigation to 75% ET to be economical. This cost analysis is based on the results of the present study where the difference in irrigation efficiency between the two treatments being compared is relatively small (4%). The likelihood of reduced irrigation strategies being more economical than full irrigation depends not only on the relative costs of water, value of the forage, and expected yield, but also on the differences in water application amounts that might be expected Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 27

29 Acknowledgments This project was funded by the United Sorghum Checkoff Program. Dr. Douglas Hunsaker, USDA-ARS irrigation engineer, provided assistance in the soil water measurements and water use calculations. The technical assistance of Richard Simer, Rafael Chavez-Alcorta, Patrick Royer, and Mary Comeau is greatly appreciated. The seed used in this project (Richardson Seeds Silo 700D ) was donated by Desert Sun Marketing Company, Inc. References Baumhardt, R. L., J. A. Tolk, T. A. Howell, and W. D. Rosenthal Sorghum management practices suited to varying irrigation stategies: A simulation Analysis. Agronomy Journal 99: Erie, L. J., O. F. French, and K. Harris Consumptive use of water by crops in Arizona. Technical Bulletin 169. Univ. Ariz. Ag. Exp. Stn., Tucson. Saeed, I. A. M., and A. H. El-Nadi Forage sorghum yield and water efficiency under variable irrigation. Irrig. Sci. 18: Miller, A. N., and M. J. Ottman Irrigation Frequency Effects on Growth and Yield in Sweet Sorghum. Agronomy Journal 102: Table 1. Irrigation Schedule for a forage sorghum irrigation study conducted in 2009 at Maricopa, AZ on a sandy clay loam soil. Irrigation water was applied at a constant amount until the crop was established before initiating differential irrigation treatments on 8/12. The irrigation treatments after establishment were based on the amount of water required to meet evapotranspiration (ET) requirements of the crop watered at 100% ET. Irrigation amount (after establishment) Irrigation Date Growth Stage 25% ET 50% ET 75% ET 100% ET inches Establishment irrigations 07/07 Planting /15 2-leaf /30 6-leaf Sum Variable irrigations 08/12 10-leaf / leaf / leaf /17 21-leaf /01 Boot Sum Rainfall TOTAL Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 28

30 Table 2. Water application effect on forage sorghum growth and development including on forage yield adjusted to 70% moisture, moisture, protein, height, stem density and green leaf area index (LAI) at harvest, final leaf number, and 50% bloom date. Water applied after establishment Forage Forage Forage Plant Stem Yield Moisture Protein Height Density % ET T/A % % in stems/a Green LAI Leaf Number , % Bloom , / , / , /07 Average , /10 CV (%) Linear ** + ** ** ns ** + -- Quadratic * ns ns ns ns ns ns -- Table 3. Water application effect on water used by the crop in evapotranspiration (ET) and various calculated efficiencies including irrigation efficiency (water used/water applied), and water use efficiency of water applied in irrigation and rainfall (WUE irr, forage yield/water applied), and water use efficiency of water used in ET (WUE ET, forage yield/water used in ET). Water applied Total Water Water Use Irrigation Water applied Water used after establishment Applied (ET) Efficiency WUE irr WUE ET % ET in in % T/A/in T/A/in Average CV (%) Linear ** ** ** * * Quadratic ns ns ns * ns 2010 Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 29

31 Development of Forage Sorghum Tissue Testing for Efficient Fertilization, 2009 Michael Ottman and James Walworth Summary A nitrogen fertilizer study was conducted in order to develop tissue testing guidelines for fertilizer application to forage sorghum. The study was conducted at the University of Arizona Maricopa Agricultural center on a sandy clay loam soil irrigated using surface flood methods. Forage sorghum was planted on 8 July 09 and fertilized with eight N rates varying from 0 to 350 lbs N/acre in 50 lb N/acre increments. The plants were sampled six times during the growing season and the lower stem, most recently developed leaf, and whole plant were analyzed for nitrogen content. Maximum yield at final harvest was obtained at 150 lbs N/acre and plant growth was highly affected by N rate. Before the initiation of rapid growth, the relationship between plant growth and N content in the various tissues was weak (R 2 < 0.20), but was very strong (R 2 >0.50) from the initiation of rapid growth through the pre-boot stage at the time when post-plant nitrogen fertilizer application may be considered. Stem nitrate was most strongly related to yield for the tissues tested, but the relationships between plant growth and total N in the newest leaf and whole plant were also very strong. Preliminary tissue testing guidelines are suggested for nitrate in the stem tissue. The lower stem, newest leaf, and whole plant are all potential candidates for development of tissue testing guidelines for forage sorghum. Introduction The cost of nitrogen fertilizer is important to forage sorghum growers in irrigated areas. Sorghum silage may require about half the nitrogen fertilizer as corn silage. So, when nitrogen fertilizer costs are high, sorghum has a definite advantage over corn. Unfortunately, plant tissue testing guidelines for nitrogen fertilization have not been developed for forage sorghum production in the desert southwest. Soil and plant tissue guidelines for fertilizer application have been published for many crops grown in Arizona (Doerge et al., 1991), but not for forage sorghum. The guidelines involve using a pre-plant soil test in combination with post-plant tissue testing for nitrate. The pre-plant soil testing guidelines will not be addressed in this study but the potential use of post-plant tissue testing will be investigated. The advantage of tissue testing guidelines is that the plant can be an accurate indicator of its own nitrogen fertility status, and take into account growth rate and sources of nitrogen in the soil and water. Tissue testing guidelines have been developed for wheat (Knowles et al., 1991) and other crops where deficient, optimum, and excessive levels are determined and nitrogen fertilizer rates developed for various growth stages. The objective of this study is to develop post-plant nitrogen fertilization guidelines for forage sorghum for silage based on nitrogen content in the plant. Materials and Methods A forage sorghum nitrogen fertilizer experiment was established at the Maricopa Agricultural Center in Maricopa, AZ on a Casa Grande sandy clay loam soil. The previous crop was hesperaloe, a succulent crop grown for fiber. The nitrogen content in the top 6 inches of the soil before planting was 8.3 ppm NO 3 -N and 7.8 ppm NH 4 -N. The nitrate content in the control plots 3 weeks after planting averaged 4.9 ppm NO 3 -N in the top 5 ft of soil. The nitrate content of the irrigation water averaged 1.25 ppm NO 3 -N. Atrazine was applied preplant for weed control. The forage sorghum hybrid Richardson Seeds Silo 700D was planted on flat ground 8 July 2009 at a seeding rate of 96,000 seeds per acre in 40 inch row spacing. A germination irrigation was applied on 8 July 2009 and irrigation water was applied using the border flood method as needed during the season (Table 1) Forage & Grain Report, College of Agriculture and Life Sciences, University of Arizona 30

32