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Simulating Atrazine Transport Using Root Zone Water Quality Model for Iowa Soil Profiles

Dep. of Agricultural and Biosystems Engineering, Iowa State Univ., Ames, IA 50011

L. Ahuja, research leader and soil scientist

USDA-ARS, GPSR, Fort Collins, CO

L. S. Pereira, professor

Dep. de Engenharia Rural, Instituto Superior de Agronomia, UTL, 1399 Lisboa Codex, Portugal

^* Corresponding author (rskanwar{at}iastate.edu).

ABSTRACT

The pesticide component of the Root Zone Water Quality Model (RZWQM) was calibrated and evaluated for two tillage systems: no-till (NT) and moldboard plow (MB). The RZWQM is a process-based model that simulates the water and chemical transport processes in the soil-crop-atmosphere system. Observed data on atrazine concentrations in the soil profile, for model calibration and testing, were obtained from a field study in Iowa.

Two statistical parameters, maximum error (ME) and coefficient of determination (CD), were used to evaluate the ability of the RZWQM to predict atrazine concentrations in the soil profile. The ME, CD, and other statistical tests indicated that there was a significant difference between predicted and observed atrazine concentrations. Comparison of simulated vs. observed atrazine concentrations with 1:1 line showed that atrazine concentrations were overpredicted, especially in the later part of the growing season. However, the model correctly predicted depth of atrazine penetration in the soil profile. Also, the range of predicted atrazine concentrations was within the same order of magnitude as observed concentrations. Although observed atrazine concentrations were usually higher in surface layers under MB than in NT treatment, the model did not show any consistent tillage effects on atrazine distribution in the soil profile. The results from this simulation study indicated that the following factors may be critical and should be considered when simulating pesticide transport in the subsurface environment: (i) macropore flow, (ii) variation in K_oc and pesticide half-life with depth, and (iii) interception of pesticide by surface residue during application.

Paper no. 16332 of the Iowa Home Economics and Agricultural Exp. Stn. Project no. 3003.

Funding for this project was provided by PRAXIS XXI program, Portugal and the USDA-CSRS as a part of the MSEA project.

Received for publication November 27, 1995.