Distribution of Nitrogen Forms in Soil Receiving Cattle Feedlot Waste

Abstract Information is limited on changes in distribution of organic and inorganic soil N forms brought about by large applications of feedlot waste. Such information is needed, however, both from an environmental and soil fertility standpoint. This study involves irrigated, continuous, grain sorghum plots (Sorghum bicolor L. Moench) on Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls) which received a total of 176 to 1,614 metric tons/ha of feedlot waste over an 8‐year period. Differences in N forms and amounts observed among plots were confined mainly to the surface 30‐cm soil layer. Increasing waste applications tended to increase the total N content, organic C content, nitrate content, N mineralization, and general biological activity of the respective plots. However, in most cases Duncan's multiple range test indicates the increases were statistically significant (P = 0.05) only at the higher rates. Moreover, chemical patterns of soil organic N forms and C/N ratios remained fairly constant, indicating the overall N distribution was being maintained. In addition, nitrite, exchangeable ammonium, and fixed ammonium contents changed little. Under proper management, any likelihood of long‐term adverse soil N effects appears small.