ABSTRACT
The crop available nitrogen (N) budget includes crop N uptake, denitrification, N leaching below the root zone, annual change in available N storage in the soil profile, net mineralization, and fixation. The largest annual component of the N budget for corn-soybean systems is generally crop N uptake; therefore, this component must be estimated correctly for accurate model simulations. Despite the apparent importance of crop N uptake to N in tile drainage, little information is available quantifying this effect. Applying regression to the results of Malone et al. with an application rate of 150 kg N/ha during corn years resulted in an equation that described 96% of variation in the Root Zone Water Quality Model (RZWQM)-estimated N loss in tile drainage using the variables precipitation and RZWQM-estimated soil-derived N uptake. A maximum N-uptake rate of 2.0 compared with 1.0 results in greater corn yield and lower N loss in tile drains over the long-term simulations.
