|Saseendran, S - COLO STATE UNIVERSITY|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 11, 2005
Publication Date: June 13, 2005
Citation: Saseendran, S.A., Nielsen, D.C., Ma, L., Ahuja, L.R., Vigil, M.F., Benjamin, J.G., Halvorson, A.D. 2005. Effectiveness of RZWQM for simulating alternative Great Plains cropping systems. Agronomy Journal 97:1183-1193. Interpretive Summary: Dryland cropping systems in the central Great Plains are changing from conventionally tilled wheat-fallow W-F(CT)to no-till wheat-fallow W-F(NT) and wheat-corn-fallow (W-C-F). The Root Zone Water Quality model (RZWQM) allows users to determine the effects of changing cropping system practices on many parameters, including crop water use, yield, and changes to soil organic matter (SOC), and allows for extension of research results obtained at one location to areas with differing soils and climate. This paper discusses the evaluation of RZWQM to simulate three cropping systems using data collected in northeastern Colorado over a 10-yr period. The model underestimated crop water use, but winter wheat and corn yields were generally well estimated. The model appears to need improvement regarding simulation of leaf area development. The model predicted a 17% decline in SOC in the top 10 cm of soil over a 10-yr period for W-F(CT), 1% decline for W-F (NT), and 21% increase for W-C-F. 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).
Technical Abstract: 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 two-yr winter wheat (Triticum aestivum L.) - fallow rotation and a more complex wheat-corn (Zea mays L.)-fallow rotation under tilled and no-till 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 (ET) 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. Higher soil water and crop yield measured for not-tillage (NT) compared with conventional tillage (CT) were simulated reasonably well. Measured and predicted soil organic carbon (SOC) and an active organic matter pool designated fraction organic matter (FOM) were both greater in the surface 0.10 m for NT compared with CT after 11 years. 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).