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Modeling

Effectiveness of RZWQM for Simulating Alternative Great Plains Cropping Systems

^a USDA-ARS, Great Plains Syst. Res., 2150 Centre Ave., Bldg. D, Suite 200, Fort Collins, CO 80526
^b USDA-ARS, Central Great Plains Res. Stn., 40335 County Rd. GG, Akron, CO 80720
^c USDA-ARS, Soil Plant Nutrient Res., 2150 Centre Ave., Bldg. D, Suite 100, Fort Collins, CO 80526

^* Corresponding author (David.Nielsen{at}ars.usda.gov)

Received for publication January 13, 2005. The Root Zone Water Quality Model (RZWQM) is a comprehensive agricultural system model with the capacity to predict crop–environmental response to varying soil and crop management systems. Our objective was to evaluate RZWQM for its ability to simulate a 2-yr winter wheat (Triticum aestivum L.)–fallow (WF) rotation and a more complex wheat–corn (Zea mays L.)–fallow (WCF) rotation under tilled and no-till (NT) conditions on a Weld silt loam soil in semi-arid northeastern Colorado. Measured data from all phases of both rotations were compared with simulated values using root mean square error (RMSE) values to quantify the agreement. Soil water in different layers, total soil profile (180 cm) water contents, and grain yield were accurately predicted with RMSEs ranging between 0.055 and 0.061 m³ m^–3, 4.6 and 7.1 cm, and 244 and 867 kg ha^–1, respectively. Leaf area index (LAI), evapotranspiration, and biomass predictions were less accurate with RMSEs between 0.7 and 1.6 cm², 5.5 and 9.7 cm, and 1027 and 2714 kg ha^–1, respectively. Greater soil water and crop yield measured for NT compared with conventional tillage (CT) were simulated reasonably well. Predicted soil organic C was greater in the surface 0.10 m for NT compared with CT after 11 yr. Although the crop growth component of RZWQM needs improvement, especially with regard to LAI, we conclude the model has potential for simulating alternative crop rotations in the central Great Plains. One potential application for RZWQM in this region may be to predict viable cropping opportunities for evolving conservation programs such as the Conservation Security Program (CSP).

Abbreviations: C, corn • CT, conventional tillage • ET, evapotranspiration • F, fallow • LAI, leaf area index • NT, no-tillage • PSE, precipitation storage efficiency • RMSE, root mean square error • RZWQM, Root Zone Water Quality Model • SOC, total soil organic carbon • SOM, soil organic matter • W, winter wheat • WCF, wheat–corn–fallow (rotation) • WF, winter wheat–fallow (rotation)

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