Soil water storage compensation potential of herbaceous energy crops in semi-arid region

Large-scale vegetation construction has generally led to soil desiccation in arid and semi-arid regions. Energy crops with high biomass and water use efficiency are generally beneficial to agriculture and the environment. It is necessary to understand how to maintain the dynamic balance of soil moisture and biomass production on herbaceous energy croplands. In this study, soil moisture data at different depths of soil were obtained from long-term field observations for two energy crops, i.e., Panicum virgatum and Miscanthus sinensis, and a forage crop-Medicago sativa. Relative aridity of the soil and plant biomass were compared among different vegetation types, transects, and cultivation years. Medicago sativa soil was severely, even extremely, desiccative with increasing cultivation years, whereas there was nearly no desiccation in the soil of energy crops. The values of compared soil water storage compensation indexes in deep soil layers were higher than those in shallow soil layers, with the evaluated soil water storage compensation index being the smallest in the 40-80 cm layer. Energy crops had significantly higher aboveground biomass, mostly exhibiting more than 2.6 kg m−2, while the aboveground biomass of M. sativa was only above 0.5 kg m−2. Furthermore, the water use efficiencies of energy crops were obviously higher than that of M. sativa (P < 0.05). Our results indicated that deep soil moisture conditions were mainly determined by field crop types. Energy crops may be suitable candidates for compensating soil water storage and maintaining high biomass production in semi-arid regions.