|Bakhsh, A - IOWA STATE UNIVERSITY|
|Kanwar, R - IOWA STATE UNIVERSITY|
Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Abstract Only
Publication Acceptance Date: July 21, 1999
Publication Date: N/A
Technical Abstract: The objective of this study was to use the RZWQM (Root Zone Water Quality Model V3.25) to evaluate the effects of N-fertilizer management practices on corn yield and NO3-N losses with subsurface drainage using field experimental data from 1996 and 1998. Fertilizer (actual N) was applied under randomized block design at three rates. During calibration of the tile flow component of the model, the drainable porosity (difference between porosity and field capacity at 1/3 bar) was found as the key parameter in controlling the size and shape of the tile flow hydrograph. After calibrating the tile flow simulations, the NO3-N losses and crop yield simulations were conducted after running the model several times to get the equilibrium conditions for various humus and micro-organism pools. Overall, the model predicted tile flow, NO3-N concentrations, NO3-N losses, and grain yield satisfactorily by showing an average difference of 6.1%, -6.1%, 0.5%, and 3.8%, respectively, between predicted and observed values for all the treatments during 1996 and 1998. Model simulations showed that doubling treatment 1 (67 kg/ha) increased grain yield by 41% and NO3-N losses by 13%, tripling treatment 1 increased grain yield by 68% and NO3-N losses by 24%, and quadrupling treatment 1 increased grain yield by 61% and NO3-N losses by 44%. The model simulations showed that the increase in yield was not linear compared with NO3-N losses as a result of the increase in N-application. The yield was found to increase until 200 kg/ha of N-fertilizer was used. Overall analysis of the study shows that the RZWQM has the potential to help farmers make decisions about various N-fertilizer inputs while protecting the soil and water resources.