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Title: SIMULATING THE IMPACT OF N-FERTILIZER APPLICATION RATES ON NO3-N LOSSES WITH SUBSURFACE DRAINAGE WATER AND CROP YIELD USING RZWQM

Author
item BAKHSH, A - IOWA STATE UNIVERSITY
item KANWAR, R - IOWA STATE UNIVERSITY
item Jaynes, Dan
item Colvin, Thomas
item Ahuja, Lajpat

Submitted to: ASAE Annual International Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/12/2000
Publication Date: 7/12/2000
Citation: BAKHSH, A., KANWAR, R.S., JAYNES, D.B., COLVIN, T.S., AHUJA, L.R. SIMULATING THE IMPACT OF N-FERTILIZER APPLICATION RATES ON NO3-N LOSSES WITH SUBSURFACE DRAINAGE WATER AND CROP YIELD USING RZWQM. ASAE ANNUAL INTERNATIONAL MEETING. 2000. PAPER NO. 00-2071.

Interpretive Summary:

Technical Abstract: Using a model as a management tool requires testing of the model against field measured data prior to its application for solving natural resource problems. Therefore, Root Zone Water Quality Model (RZWQM98) was tested using four years (1996 to 1999)field-measured data to predict the effects of different N-application rates on corn yields and NO3-N losses with subsurface drainage 'tile' water. Three N-application rates (low, medium, and high), each replicated three times, were applied to corn in 1996 and 1998 under randomized complete block design at a tile-trained corn-soybean rotation field in Central Iowa. Model calibration and evaluation was based on field measurements of tile flows, NO3-N losses with tile water and corn-soybean yields. On the average, model predicted tile flow, NO3-N losses with tile water, and yields adequately by showing percent difference of -7%, 21% and -2% respectively, between measured and predicted values. The model successfully incorporated the climatic effects and predicted corn yields were similar to the measured values in 1998 (validation year) despite lower N-fertilizer rates applied in 1998 than 1996. Predicted corn yields remained constant when N-application rate exceeded 170 kg-N/ha in 1998. Model predictions of NO3-N losses with tile water as a function of N-application rates were better in 1998 than 1996 probably due to better estimation of initial conditions in response to continuous model simulations from January 1, 1996 through December 31, 1999. However, model overestimated NO3-N losses with subsurface drainage water during soybean growth period, which may require further refinements in the N-cycling algorithm in relation to N2-fixation and N-uptake processes.