Root zone nitrogen simulation model for land application of sewage sludges

Abstract

A root zone nitrogen simulation model was developed for the evaluation of the long term effects upon soil root zone nitrogen of various sewage sludge application rates, methods of sludge application, ammonia nitrogen fertilizer application and no fertilization. Effects examined include crop yield, root zone nitrogen build up, nitrate nitrogen leaching and crop nitrogen uptake as a percentage of nitrogen applied. Simulation results indicated that nitrate nitrogen leaching had a direct linear relationship to sludge application at the simulated application rates. The leaching rate increased 21 kg per ha per year for each metric ton (t) of sludge incorporated into farm soils and 22 kg per ha per year for each metric ton incorporated into stripmine soils. Surface application of sludge resulted in leaching rates 50% lower than incorporation. Crop uptake of nitrogen was simulated using Michaelis—Menten/Monod kinetics. The maximum uptake of nitrogen was 135 kg per ha per year for an incorporated loading rate of 25 t per ha per year. Depending upon the site, 25 t per ha per year of sludge built up organic nitrogen in the root zone by 8400 to 10,000 kg/ha over a 50-year period. Rigorous validation was not attempted but most model outputs compared favorably to literature values. Simulated application of 300 kg per ha per year of ammonia nitrogen yielded a 98-kg per ha per year crop nitrogen yield which is approximately average for the U.S. corn belt.