Restoring soil water content after alfalfa and Korshinsk peashrub conversion to cropland and grassland

Abstract

AbstractThe introduction of Korshinsk peashrub (Caragana korshinskii) and alfalfa (Medicago sativa) as restorative vegetation in the Loess Plateau, China has resulted in the widespread occurrence of a dried soil layer (DSL). Soil water recovery with respect to the soil water content (SWC) following the occurrence of a DSL (i.e., DSL‐SWC recovery time) and the effect of the number of planting years of restorative vegetation on soil water recovery have received little attention. The aim of this study was to investigate soil water dynamics after vegetation conversion (include three fields of converting cropland with soybean or millet into alfalfa land, three fields of converting alfalfa land into soybean land or four fields of converting peashrub land into natural grassland) in the Liudaogou watershed in a water‐wind erosion crisscross region in the Loess Plateau, China. With this aim in mind, we conducted in‐situ field experiments for 3 or 5 years and continuously monitored the SWC in a 0–5 m or 0–8 m profile. The results showed that the SWC increased drastically after alfalfa was converted to soybean, especially after consecutive wet year when the SWC of 0–800 cm profile was recharged up to 0.16 cm3 cm−3, which means the DSL‐SWC in the 0–800 cm profile recovered within 5 years. The DSL‐SWC of the profile improved obviously within 3 years after peashrub was converted to natural grass. The SWC of the two fields was 0.16 cm3 cm−3 and 0.15 cm3 cm−3, respectively. The SWC depletion time was 6.1, 7.5, and 8.4 years in the three fields converted from cropland to alfalfa. Based on our findings, the number of alfalfa planting years should not exceed 8 years. However, planting years of peashrub needs further study because it has excellent drought resistance and a long root system. Taking the advantages and disadvantages of two restoration management methods into account, alfalfa‐crop rotations and natural grasslands are the two best choices for ecological restoration in the Loess Plateau, China.