Nutrient leaching from corn residues under simulated rainfall.

Crop residues left on the soil surface after harvest are effective in reduc ing erosion; however, when subjected to rainfall-leaching, the residues are a significant source of soluble nutrients to agricultural runoff. Nutrient teaching from crop residues as a function of rainfall intensity, and resid ue loading rate, was studied in a series of laboratory experiments under co ntrolled conditions. Using a multiple-intensity rainfall simulator corn (Ze a mays L.) stover placed on a nylon screen at an equivalent field loading r ate of 10 t ha(-1): was subjected to simulated rainfall at intensities of 6 , 12, 25, 51, and 99 mm h(-1). In another series of experiments, simulated rainfall was applied at 25 mm h(-1) to four stover loading rates of 5, 7, 1 0, and 15 t ha(-1). In both experiments, leachate was sampled as a function of time and analyzed for PO4-P, NH4-N, NO3-N, and total organic carbon (TO C). Nutrient concentrations and losses were generally greater at the lower rainfall intensities and higher stover loading rates. In each study, nutrie nt concentrations decreased hyperbolically with either time or cumulative l eachate volume. For all loading rates and rainfall intensities, nutrient am ounts (kg ha(-1)) leached from the stover followed the order C >>N = P; how ever, the amounts of N as (NH4-N + NO3-N) or C leached were less than or eq ual to 1.5% of total nutrient in residue compared with 2.8 to 6.0% of fetal nutrient in residue for P. Stover exposed to field conditions over time sh owed leaching kinetics similar to freshly collected residues.