RZWQM2 Simulations of Alternative Cropping Systems with and without Summer Crops in the Central Great Plains.

Integration and synthesis of data accruing from complex alternative crop rotation experiments across locations and climates is a challenge to agriculturists.  System simulation models are potential tools to address this challenge.  In this study, we simulated three long-term (1991 to 2008) dryland crop rotation experiments conducted on a Weld silt loam soil in  the semi-arid climate at Akron, Colorado as alternatives to the conventional tilled winter wheat (Triticum aestivum L.)-fallow {WF (CT)} rotation: wheat-fallow under no-tillage {WF (NT)}, and wheat-corn-fallow (WCF) and wheat-corn-proso millet (WCM).  We used the DSSAT v4.0 crop modules for wheat, corn (Zea mays L.), and proso millet (Panicum miliaceum L.) in RZWQM2.  Measured grain yields and biomass of the crops in the rotations were simulated reasonably well with model prediction efficiency (E) ranging between 0.59 and 0.85,  and 0.32 and 0.93; R² ranging between 0.63 and  0.91, and 0.37 and 0.93; and RMSE ranging between 313 and 528 kg ha^-1, and 715 and 2337 kg ha^-1; respectively.   Differential long-term performances of the three crops in different rotations were also simulated well.  The simulation results established the potential of the model for simulations of the various dryland alternative crop rotation experiments for decision support and extrapolation of results to other locations and climates.