Modelling the effects of mulching and fallow cropping on water balance in the Chinese Loess Plateau

To improve water use efficiency on drylands it is essential to understand the mechanisms affecting water balance partitioning in arable land ecosystems. A field experiment was conducted, from October 2001 to October 2004, to evaluate the effects of field management regimes on water balance and water use efficiency in a winter wheat (Triticum aestivum L.) system in the Loess Plateau, China. The field management regimes tested were: (i) conventional agricultural management (winter wheat followed by a ploughed summer fallow); (ii) conventional management plus a fallow crop used as green manure; (iii) application of wheat straw mulch (0.8 kg m−2), which was retained throughout the year (no summer ploughing). A process-oriented ecosystem model (CoupModel) was calibrated with field measurements of soil water contents, leaf area indices, plant heights and crop yields, then used to generate comparative simulations of the water balance partitioning under the wheat straw mulch, fallow crop and conventional management regimes. The simulations indicated that during the experimental period mulching increased soil water storage by 5–8%, decreased soil evaporation by 11–13%, and increased wheat transpiration by 2–5% compared with the conventional management regime, thus increasing the wheat yield and water use efficiency. Furthermore, water reached deeper horizons under mulching than under conventional practice, resulting in 15% more deep percolation in a wet year. The simulation results also indicated that growing green manure during the fallow period decreased soil water storage, leading to lower wheat yields. Mulching proved to be an efficient measure for increasing yields, and possibly contributed to groundwater recharge.