Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/16/2005
Publication Date: 3/15/2006
Citation: Powell, J.M., Wattiaux, M.A., Broderick, G.A., Moreira, V.R., Casler, M.D. 2006. Dairy diet impacts on fecal chemical properties and nitrogen cycling in soils. Soil Science Society of America Journal. 70:786-794. Interpretive Summary: What dairy cows consume not only affects milk production but also the amount and type of nitrogen (N) excreted in manure. These diet impacts on manure N may also influence how much manure N becomes available to crops after manure has been land-applied. Feces from dairy cows fed fourteen typical diets were incubated in a sandy loam and two silt loam soils, and plant available N (PAN, or ammonium- plus nitrate-N) and uptake of N by oats and sorghum were determined over a 5 to 12 month period. Feces from cows fed alfalfa silage (AS)-based diets generally produced higher levels of PAN than soils that received feces from corn silage (CS)-based diets. Application of feces from AS-based diets resulted in higher plant yield and N uptake than feces from CS-based diets. After application to a silt loam soil, feces from high protein (HP) diets produced more PAN than feces from low protein (LP) diets. Feces from LP diets did not affect PAN, but resulted in lower plant yield and N uptake than feces from HP diets. There appears to be a range of diets that satisfy nutritional requirements of high-producing dairy cows and produce feces having different effects on PAN, plant yield and N uptake.
Technical Abstract: Availability of manure nitrogen (N) to crops is mitigated by many factors including manure type and composition. Whereas relationships between dairy diets, milk production, manure N excretion, and urine N losses as ammonia have been documented, very little information exists on how diets impact fecal carbon (C), N content and partitioning, and how these factors impact fecal N mineralization and plant N uptake after application to soil. Feces from 24 to 63 dairy cows (Bos taurus) fed fourteen typical diets were incubated aerobically in a sandy loam and two silt loam soils, and soil inorganic N (IN) was determined periodically during a 365 d period. Feces from twelve of the fourteen diets were applied to the same soils and oat (Avena sativa L.), sorghum (Sorghum bicolor L. Moench) and sorghum ratoon dry matter (DM) and N uptake were determined over a 155 d period. Feces from cows fed alfalfa (Medicago sativa L.) silage (AS)-based diets generally lead to higher soil IN levels than soils amended with feces from corn (Zea mays L.) silage (CS)-based diets, especially in soils amended with feces from CS-low protein (LP) diets; feces from AS-based diets increased plant DM and N uptake; after application to a silt loam, feces from high protein (HP) diets resulted in greater soil IN levels than feces from LP diets; and feces from LP diets did not impact soil IN but decreased plant DM and N uptake. C:N ratios of applied feces were found to be significant predictors of plant DM and N uptake. There appears to be a range of dietary options that satisfy nutritional requirements of high-producing dairy cows and produce feces having differential effects on soil N mineralization and plant N uptake after application to soil.