Long-term effect of cover crop on rainwater balance components and use efficiency in the no-tilled and rainfed corn and soybean rotation system

Incorporating cover crops into row crop production systems can affect soil water dynamics and crop production. However, the effect of this practice has not been well investigated in the northeast Mississippi USA. We calibrated and validated the cropping system model (Root Zone Water Quality Model, RZWQM2) using 4-yr (2014–2017) field data in the humid Mississippi Blackland Prairie, and also used this model to simulate the long-term (1938–2017) effects of a winter wheat (Triticum aestivum L.) cover crop on hydrological variables, crop yield, and water use efficiency (WUE, grain yield per unit of evapotranspiration) in a rainfed and no-tilled corn (Zea mays L.) and soybean (Glycine max L.) cropping system. Compared to no cover crop scenarios, long-term simulation demonstrates that average annual percolation under the cover crop system was decreased by 36 mm. Average annual actual evapotranspiration were 36 mm higher under cover crop system than no cover crop system. Simulated annual runoff for cover crop scenario was not different from values simulated for no cover crop scenario. Predicted actual evaporation during cash crop growth periods under cover crop plots was 25% less than under no cover crop plots due to mulch cover when averaged over the whole modeling period. Compared with no cover crop scenarios, the estimated crop evapotranspiration under cover crop scenario was reduced by 6.6% (31 mm) during corn growth period and by 3.7% (19 mm) during soybean growth period. Yearly predicted crop yields for corn and soybean did not improve, respectively, in the cover crop-based cropping system. Compared to the plots with no cover crop, the simulation of WUE for corn and soybean were respectively improved by 6.4% (1.49 kg m−3 versus 1.40 kg m−3) and by 5.0% (0.63 kg m−3 versus 0.60 kg m−3) for the plots with cover crop, largely due to the decrease in surface evaporation without sacrificing crop growth. These results suggest that long-term use of wheat cover crop to summer crops rotation is a promising practice to decrease deep percolation and restrict surface evaporation, and also improved crops WUE in the corn and soybean rotation in subtropical agro-system.