Cultivating Erect Milkvetch (Astragalus adsurgens Pall.) (Leguminosae) Improved Soil Properties in Loess Hilly and Gullies in China

Erect milkvetch (Astragalus adsurgens Pall.), a leguminous grass, is a major source of fuel and forage, and has an important role in the restoration of the degraded ecosystems in central and northeastern China. The objective of this work was to investigate how erect milkvetch planting would affect the physical and chemical properties of soil in degraded arable lands. Soil samples at the depths of 0–20 and 20–40 cm were collected from erect milkvetch planting fileds at ages of 0, 1, 2 and 3 yr. Changes in soil bulk density, soil porosity, total N and P, organic matter content, available P, hydrolysable N and available K were measured. The results showed that root biomass and above-ground plant biomass were both significantly increased with plantation age. The significant increase in root nodule biomass was not observed in the first two years. However, it was significantly increased after three years. Root growth of erect milkvetch improved soil structure, and hence, decreased soil bulk density and increased soil porosity. Furthermore, the nitrogen fixation by erect milkvetch and return of erect milkvetch plant to soil increased the soil total N, hydrolysable N and organic matter content of the soil. Low concentrations of P in the soil with erect milkvetch planting could be ascribed to high plant uptakes and possibly to high sequestrations of P in plant biomass. Concentrations of K significantly increased during the first two years of erect milkvetch planting. The high accumulation of K under erect milkvetch cultivation in the first two years could partly be attributed to low plant uptake, and partly to relatively quick recycling within plant-soil systems. Three years after erect milkvetch plantingr, K accumulation at 0–20 cm soil layer was significantly lower than that from non-vegetated field sites, which could be attributed to high plant uptake. These parameters, except for soil bulk density, were all decreased with increasing soil depth. Soil total N, organic matter, porosity and available K in the 20–40 cm layer all showed linear increase trends, and soil bulk density, total P and available P in the depth 0–20 cm layer soil were decreased with increasing planting age. Erect milkvetch establishment could be an effective and applicable measure to improve soil nutrients, and prevent further soil degradation and erosion.