Simulated effects of cover crops with no-tillage on soil and crop productivity in rainfed semi-arid cotton production systems

Cover cropping and no-tillage (NT) practices are promoted for soil health and environmental benefits. However, producing enough quantity of biomass to meet expected benefits can be a challenge in semi-arid cropping sys-tems where water resources are limited, and producers have lingering questions regarding cover crop selection, termination timings, water use, and their subsequent effect on cash crop. The objective of this study was to assess the impacts of cover crops with NT on soil and crop productivity in a rainfed, continuous cotton (Gossypium hirsutum L.) system using the Denitrification Decomposition (DNDC) model. Treatments included: (a) conven-tional till (CT); (b) NT, and NT with the following cover crops: (c) Austrian winter pea (Pisum sativum L.) (Pea); (d) crimson clover (Trifolium incarnatum L.) (Clover); (e) hairy vetch (Vicia villosa L.) (Vetch); (f) a multi-species mixture (Mixture); and (g) winter wheat (Triticum aestivum L.) (Wheat). The DNDC model adequately simulated the seed cotton yield and cover crop biomass during calibration (root mean square error (RMSE) = 200 and 398 kg ha-1, respectively) and validation (RMSE = 277 and 270 kg ha-1, respectively). Stocks of soil organic carbon (SOC) and total nitrogen (TN) were simulated with Nash-Sutcliffe efficiency (NSE) of 0.91 and 0.78 during calibration, and with NSE of 0.88 and 0.75, respectively during validation. Long-term simulations revealed: (1) Vetch and Pea produced greater biomass and hence highest SOC and TN contents, which was followed by Mixture, Wheat, and Clover; (2) cotton yield in cover crop treatments was no different to that in non-cover crop treatments when cover crop was terminated about six weeks prior to cotton planting; (3) later termination of cover crops can result in greater cotton yield loss due to soil water depletion by cover crops. Overall, this study highlights the potential of conservation practices, such as cover crops and NT to improve soil health without significant loss in cotton yields.