N fate and transport under variable cropping history and fertilizer rate on loamy sand and clay loam soils: I. Calibration of the LEACHMN model

Abstract

The need for efficient use of agricultural chemicals and their potential adverse impact on critical water resources have increased the use of simulation models of the soil and plant system. Nevertheless, there is currently little or no agreement concerning model validity and applicability in varied soils and environments. The research version of LEACHMN (the N subroutine of LEACHM) was calibrated using field data including soil physical, hydraulic, and chemical properties, and maize (Zea maysL.) N uptake collected from a 3-yr nitrate leaching experiment. The field site consisted of plot-size lysimeters on clay loam and loamy sand soils with N fertilizer rates of 22, 100 and 134 kg Nh a 1 . The calibration involved adjusting nitrification, denitrification, and volatilization rate constants to optimize the fit between predicted and measured data. When calibrated for each treatment-year combination and soil type, the model simulations of soil profile NO 3‐N distribution were generally successful. The N transformation rate constants yielded by the calibration efforts were similar or close to those used in other model simulation studies. At both sites, the calibrated rate constants for the first year (following sod plowdown) were different from those for the subsequent two years. Denitrification rate constants were consistently higher for the clay site than for the sand site, while the nitrification rate constants were lower. N rate of application appeared not to affect the rate constants within each year-site combination, suggesting that cropping history and soil type had the greatest effect on N transformation rates.