Interactions Between Heavy Manure Applications and Nutrient Uptake in Silage Corn.

Corn silage is the predominant crop in Idaho used for recovering phosphorus (P) that has accumulated in soils from dairy manure applications. However, little is known about how much phosphorus and other nutrients are being recovered under Idaho conditions. The objective of the study is to estimate phosphorus removal by irrigated corn silage crops cultivated throughout Southern Idaho with variable soil test P concentrations, and to identify effects of increasing soil test P on potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), and manganese (Mn). Forty-two different corn silage fields in 2008 and 2009 were selected throughout Southern Idaho for soil and whole plant sampling at harvest. Soils were analyzed for Olsen P, plant tissue was measure for total P content, and dry and wet yields were calculated based on field weights and drying of plant tissue. Average phosphorus concentration in the whole plant tissue at harvest was 0.2078 % (table 2), with 39 of the 42 fields sampled between 0.15 and 0.25 % (figure 1). Increasing Olsen P in the soil from 3 to 200 ppm had no significant effect on tissue P over 20 ppm, Increasing Olsen P in the soil also did not appear to affect K or Zn concentrations in the tissue. However, it appears that Mg, Ca, and Mn plant tissue concentrations may be decreasing with increased Olsen P, especially on silt-textured soils for Ca and Mn. Controlled studies are needed to verify these relationships. Other factors such as manure source and irrigation method will be incorporated in future analyses of this dataset.