Comparisons of water use efficiency under different conversion models of cropland to grassland in the Loess Plateau of China
黄土高原地区不同草地退耕模式水分利用效率的比较

This study was conducted to explore the ecological restoration effects of the different conversion models of cropland to grassland in the semiarid Loess Plateau of China. One natural vegetation recovery model, the fallow (Fa), and three human short-term grass-seeding perturbation models are investigated. The three perturbation models include perennial legume grass of alfalfa Medicago sativa (Ms), two-year life history legume grass of sweetclover Melilotus officinalis (Mo) and perennial legume grass of erect milkvetch Astragalus adsurgens (Aa). All the plots were to recover naturally and were enclosed to avoid grazing and harvesting. The experiments were continued for 3 years. The Mo significantly decreased soil bulk density and facilitated the following wild weed vegetation growth and species recovery after Mo finished its life history. The wild weed biomass and water use efficiency (WUE) of Mo in the first year after its life history finished were twice as much as that of Fa. The Mo also has the highest water recharge efficiency during rainfall events, especially in storms at growing stage. The remained Mo root system facilitated the soil moisture recovery in deep soil. WUE in the Mo was higher than that in Fa and Ms, but it is lower than that in Aa. The Ms has the worst soil moisture condition in deep soil. Wild weed biomass decreased yearly and species has no change in Ms and Aa. It was found that Fa has the best soil water condition but the worst WUE and the lowest aboveground biomass. Therefore, appropriate short-term human perturbation of Mo has positive effects on the vegetation recovery efficiency and was easy to be applied to a large area in the semiarid region of Loess Plateau.