Applying Liquid Dairy Waste to Silt Loam Soils Cropped to Corn and Alfalfa-Orchard Grass

Three-year and 2-year field experiments were conducted to study the effects on crop yield and soil and plant composition of applying dairy slurry to Kokomo silt loam cropped to corn (Zea mays L.) and Crosby silt loam fallowed and subsequently planted to alfalfa (Medicago sativa)-orchard grass (Dactylis glomerata), respectively. Anaerobic dairy slurry (6.4 to 9.1% dry matter) was applied at rates 112, 224, and 336 metric tons/ha, providing an average of 304, 609, and 914 kg N/ha; 60, 121, and 181 kg P/ha; 293, 587, and 880 kg K/ha; and 61, 121, and 181 kg Na/ha, respectively, per year. A check treatment was also included. Maximum corn grain and silage production was obtained with the 224-metric ton slurry rate. Plant composition was not affected by waste applications except total N levels in corn leaves increased with increasing waste rates during the second year. Except for NH₄⁺-N, the concentrations of soil constituents measured (NO₃⁻-N, P, K, Na, EC) were increased by waste applications, especially with the 224- and 336-metric ton rates, compared to the check. Similarly, as compared to the check, all soil constituents measured were increased by waste applications on the fallow soil. One year of alfalfa-orchard grass cropping, however, reduced the levels of all measured soil components except P and K to concentrations similar to or lower than the initial values. Alfalfa-orchard grass growth was variable, but the 112-metric ton application rate appeared to support maximum yields. In general, the concentrations of P and K in forage tissue tended to increase with increasing waste application rate. Under the climatic conditions of this study, annual dairy slurry applications of < 224 metric tons/ha to soil cropped with corn and 112 metric tons/ha to fallow soil subsequently planted with alfalfa-orchard grass had no detrimental effects on the chemical composition of two silt loam soils or on plant composition.