NUTRIENT AVAILABILITY TO CORN FROM DAIRY MANURES AND FERTILIZER IN A CALCAREOUS SOIL A. Leytem 1, R. Dungan 1, A. Moore 2, M. Miller 1 1 USDA ARS, Kimberly, Idaho 2 University of Idaho, Twin Falls R&E Center, Twin Falls, Idaho ABSTRACT The expansion of the dairy industry in southern Idaho has lead to increased application of manures to meet crop nutrient demands which can alter the uptake pattern of both macro- and micro-nutrients. A greenhouse study was conducted to determine the effects of dairy manure, composted dairy manure, and fertilizer (mono-ammonium phosphate, MAP) application on soil test phosphorus (P), microbial activity, and nutrient uptake by silage corn. Two Portneuf soils, having either a low or high soil test P concentration, were amended with the three treatments at four application rates of 25, 50, 100, and 200 mg P kg -1 (ppm) with four replications of each treatment in a randomized complete design. Treatments were incubated for two weeks and then planted with corn grown for approximately three weeks. Soil samples were analyzed prior to planting, whereas plant samples were analyzed at the end of the growing period. Increases in Olsen P from P additions were greatest in the MAP and least in the manure treated soils. Plant dry matter production and P uptake did not differ with treatment. Potassium uptake increased with increasing rates of all treatments. Ca uptake decreased in the High-P soils treated with manure and compost, while Mg uptake decreased with compost application in the High-P soil. Zinc uptake increased with manure applications, while Mn uptake decreased with manure application on the High-P soil. It is important to consider plant nutrient interactions when applying manure and compost to feed-crops as imbalances in K, Ca, and Mg can have a negative impact on animal health. INTRODUCTION Expansion of the dairy industry in southern Idaho has lead to an increase in applications of dairy manures and compost to meet crop nutritional requirements. One of the benefits of fertilizing with compost or manure is the provision of secondary nutrients other than nitrogen (N), phosphorus (P), and potassium (K) commonly supplied by commercial fertilizers. This may result in higher tissue macro- and micronutrient contents in crops amended with manure and compost compared to those fertilized with traditional inorganic fertilizers. Conversely, manure and compost additions have also been shown to decrease the uptake of some nutrients (e.g. Warman and Cooper, 2000; Parsons et al., 2007). The application of manure to meet crop N requirements, which has been the common practice in the region, can apply large amounts of P, Ca, and K, as well as other trace minerals and some heavy metals which can affect crop growth and forage quality. For example, high K application rates with manures on grasses have shown to decrease Ca uptake and increase the tetany potential of those grasses (Cherney et al., 2002). In addition, accumulation of K in forages is a concern from an animal health perspective as high levels of K can lead to milk fever in dairy cattle (Tyler and Ensminger, 2006). The over application of P and P accumulation in soils has the potential to create deficiencies and toxicities of other nutrients as well. Manure additions tend to have a liming affect in most soils (Eghball et al., 2004;
Mokolobate and Hayes, 2002), which can have a significant effect on mineral uptake owing to the increase in ph. Manure application also supplies large amounts of organic material which can affect mineral solubility and plant availability. This increase in organic matter also stimulates microorganism activity which can temporarily decrease the availability of some nutrients while enhancing the solubility of others during the breakdown of organic materials in the soil. The objective of this study was to determine the effect of dairy manure, composted dairy manure, and commercial fertilizer on changes in soil test P, plant uptake of K, Ca, Fe, Mg, Mn, P, and Zn concentrations and the possible role of microbial activity in these relationships. MATERIALS AND METHODS Sample Collection and Characterization The soils used in this study were Portneuf silt from 0- to 8- inch depth located at the Northwest Irrigation and Soils Research Laboratory in Kimberly, ID. The soils were chosen to represent a soil that is deficient in P (for optimum crop production, Low-P) as well as a soil typical of those receiving manure applications having a higher Olsen P (High-P). Prior to use in the greenhouse, the bulk soil samples were air-dried, sieved through a 7-mm screen and analyzed for particle size, calcium carbonate equivalent, sodium bicarbonate extractable P, total C, and ph. Four treatments were used, including fertilizer (MAP, 11-52-0), fresh manure collected from an open-lot dairy, composted manure from the same open-lot dairy and a control which received no amendments. Manure samples were dried, ground, and analyzed for total C, total N, Ca, Fe, K, Mg, Mn, P, and Zn. Greenhouse Studies Greenhouse studies with the individual soils were conducted in two sequential experiments. Two mixtures were prepared for each experiment: soil + amendment in 250 ml cups for sampling after two weeks incubation (for soil analysis post treatment application) and soil + amendment in one gallon closed-bottom pots for plant growth studies. Each of the P sources was incorporated (4 replicates of each source) by mixing with each soil at 4 rates: 25, 50, 100, and 200 mg P kg -1 to represent a range of P additions around a typical application rate (60 mg kg -1 ) when manures are applied to meet crop N requirements. Urea was added to all treatments at a rate of 150 mg N kg -1 to satisfy the N requirements of the plants. After incorporation, amended soils were brought to approximately 80% field capacity and incubated in a completely randomized design in the greenhouse for two weeks. Soil moisture content was maintained by adding water to the cups or to the pots every other day. After two weeks incubation, soils were removed from the cups for subsequent analysis and silage corn was planted into the soil pots. After emergence, plants were thinned to six per pot, and were grown for 25 days on the High-P soil and 21 days on the Low-P soil. Whole plant samples were cut 1 cm above the soil surface, dried, weighed, and ground for analysis. All soil samples were analyzed for dehydrogenase activity (DHA), alkaline phosphomonoesterase activity, and Olsen P. Dried plant samples were analyzed for P, Ca, Fe, K, Mg, Mn, and Zn.
RESULTS AND DISCUSSION Soil Test Phosphorus Olsen P increased with increasing P application rate for all treatments on both the Highand Low-P soils (Figure 1). The rate of increase was significantly different among the treatments following the trend: MAP = compost > manure on the Low-P soil and MAP > compost > manure on the High-P soil. Previous studies (Leytem and Westermann, 2005; Leytem et al., 2005; Leytem and Bjorneberg, 2009) reported that the amount of C added with the P source had a large impact on P solubility in the soil, and strong negative trends were found between the C:P ratio of the manures and Olsen P. Similarly, this study observed a strong negative relationship between the C:P ratio of the source materials and Olsen P. Soil microbial activity is thought to relate to this reduction in soluble P with increasing C. Increased C stimulates microbial growth and P is immobilized in microbial tissues. Figure 2 demonstrates that dehydrogenase activity (an estimate of microbial activity) significantly increased with increasing rates of manure application relative to compost and MAP treatments. Similarly, phosphatase activity (an indication of P mineralization) increased significantly with increasing rates of manure application relative to compost and MAP treatments (Fig. 3). These data provide strong evidence that microbial activity in the treated soils is, at least in part, responsible for the differences in P solubility found between manure, compost, and MAP. Additionally, changes in ph with treatment application likely influenced P solubility in the treated soils (Figure 4). For both soils, the MAP treatment significantly decreased the soil ph with increasing P application rate, while there was little to no effect by additions of manure and compost on soil ph. On the Low-P soil, ph decreased from 7.89 to 7.40 with increasing MAP addition, while on the High-P soil, ph decreased from 7.53 to 6.82. Phosphorus solubility is lowest between ph units of 7.6 to 7.8, with increasing solubility at ph values both above and below this range (Mengel and Kirkby, 1987). Therefore, P solubility would be enhanced by the decrease in soil ph and, combined with the low microbial activity in the MAP amended soils, could explain the enhanced solubility of MAP P compared to P from manure and compost treatments. Dry Matter Production and Tissue Nutrient Concentrations There were no visual signs of deficiency or phytotoxicity for any of the treatments on either soil and all tissue nutrient concentrations were within sufficiency ranges, with a few notable differences between treatments. Application rate significantly affected dry matter production on the Low-P soil but not on High-P soil (Tables 1 and 2) and no treatment effect on dry matter production was observed for either soil. Expectedly, the lack of P response in the High-P soil and the significant P response in the Low-P soil strongly suggests that P was limiting in the Low-P soils but not in the High-P soils. The lack of a treatment effect on both Low- and High-P soils suggests that, while P source can significantly alter Olsen P concentrations, P source may not have a significant impact on total corn silage yields in an agricultural field. This suggests that P rate may be a more critical predictor of silage yield than Olsen P concentrations when comparing fertilizer, manure, and compost P sources. This also suggests that relationships between Olsen P and silage yield may differ between fertilizer and manure sources of P. P uptake increased with increasing application rate, with the greatest increase occurring with the MAP application, while the manure and compost treatments did not differ. This increase in P uptake from the MAP treatments is likely a result of the enhanced P solubility and decrease in soil ph in these treatments, both of which would favor enhanced P uptake by plants (Mengel
and Kirkby, 1987). Both the manure and compost contained significant concentrations of Ca, which may have precipitated with ortho-p to form insoluble Ca-P precipitates. In addition, both the manure and compost contained Fe which could form Fe phosphates thereby reducing P solubility. Other macronutrients of interest included calcium, magnesium, and potassium. On the Low-P soils, K uptake increased for all treatments with compost showing the greatest increase in K uptake. On the High-P soil, K uptake increased with increasing application rates similarly for all treatments. Calcium uptake increased with all treatments on the low-p soil with the greatest increase occurring in the MAP treatment. Calcium uptake decreased significantly on the high-p soil for increasing rates of manure and compost, while little significant effect was observed in the MAP treatments. This decrease could be related to cation competition with K and by the formation of Ca-P precipitates in manure and compost treated soils. On the Low-P soils, Mg uptake increased with increasing application rate for all treatments with the greatest increase occurring in the MAP treatment. On the High-P soils, Mg uptake increased with increasing application rate of MAP and manure up to 100 mg P kg -1, above which uptake leveled off for MAP and decreased for manure. Mg uptake decreased with increasing application rates of compost. High levels of K may inhibit Mg uptake due to cation competition. The balance between K, Ca, and Mg uptake is a concern from an animal health perspective as forages with K:(Ca+Mg) ratios greater than 2.2:1 can cause grass tetany in ruminants (Grunes et al., 1970). This ratio exceeds 2.2:1 for all rates and treatments in this study, but it is important to keep in mind that plant samples were collected after only approximately 3 weeks and therefore this may not represent the ratio in the corn at maturity. Additions of manure and compost can have a significant impact on micronutrient uptake as well. For example, on the Low-P soil, Mn uptake increased with increasing application rate for MAP and compost treatments, while manure showed little rate response. No statistically significant effects of rate or treatment on Mn uptake were observed on the High P soil. The solubility and plant availability of Mn in soil is the lowest at ph values of 7.2 to 7.7. Although the application of MAP on the High-P soil decreased ph from 7.4 to 6.8, there was a slight decrease in Mn uptake above the 100 mg P kg -1 rate, suggesting that other factors are affecting Mn availability in these soils. On both the Low- and High-P soils, Zn uptake increased with increasing manure applications but leveled off above 100 mg P kg -1 on the High P soil. Zn uptake also increased for the MAP and compost treatments on the Low-P soil and showed no significant rate response for the High-P soil. The enhanced uptake of Zn in the manure treatments may have been due to the higher concentrations of Zn in the manure relative to the other treatments, which could have had a positive effect on plant uptake. Additionally Zn uptake could be affected by complexation with organic acids in manure treated soils.
Table 1: Dry matter production and corn nutrient uptake for the Low-P soil. Treatment Application Rate (mg P kg -1 ) 0* 25 50 100 200 Dry Weight (g) MAP 2.08 3.26 4.48 4.32 5.98 Manure 2.99 4.01 4.44 4.74 Compost 3.52 3.73 4.43 4.82 P uptake, mg MAP 5.54 10.72 14.66 19.83 32.03 Manure 8.99 12.03 15.00 19.46 Compost 11.59 8.20 13.82 19.13 Ca uptake, mg MAP 18.84 22.85 24.43 26.44 38.16 Manure 15.87 16.92 18.03 23.35 Compost 21.58 14.72 21.34 25.67 K uptake, mg MAP 128.6 170.5 203.9 203.7 259.7 Manure 150.7 182.9 212.6 267.0 Compost 212.2 144.1 229.0 312.0 Mg uptake, mg MAP 9.74 12.66 15.26 16.61 25.96 Manure 10.39 12.72 14.96 16.72 Compost 13.11 8.83 12.51 14.90 Mn uptake, mg MAP 0.33 0.45 0.52 0.58 0.77 Manure 0.34 0.41 0.41 0.39 Compost 0.47 0.32 0.46 0.58 Zn uptake, mg MAP 0.11 0.13 0.17 0.16 0.23 Manure 0.13 0.17 0.22 0.28 Compost 0.16 0.10 0.15 0.21
Table 2: Dry matter production and corn nutrient uptake for the High-P soil. Treatment Application Rate (mg P kg -1 ) 0* 25 50 100 200 Dry Weight (g) MAP 12.12 12.78 13.22 13.12 12.97 Manure 13.04 13.14 13.44 12.94 Compost 12.74 12.66 12.76 12.4 P uptake, mg MAP 34.29 46.14 54.50 73.44 92.02 Manure 42.47 46.07 57.57 55.57 Compost 43.90 45.49 50.86 55.45 Ca uptake, mg MAP 95.36 90.45 93.37 94.58 98.08 Manure 95.92 89.79 86.70 67.78 Compost 81.78 84.95 78.71 71.94 K uptake, mg MAP 613.09 694.75 717.19 746.52 745.07 Manure 715.74 741.99 818.42 791.73 Compost 679.77 704.15 742.67 752.97 Mg uptake, mg MAP 35.62 38.28 41.12 44.60 46.24 Manure 39.81 39.90 43.23 35.51 Compost 33.14 33.71 32.45 30.43 Mn uptake, mg MAP 1.86 2.11 2.21 2.11 2.00 Manure 1.99 1.96 2.09 1.66 Compost 1.79 1.84 1.90 1.79 Zn Uptake, mg MAP 0.43 0.44 0.45 0.43 0.47 Manure 0.50 0.55 0.72 0.68 Compost 0.42 0.47 0.47 0.47
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