Abstract:A field experiment was conducted to study the effects of different rice stubble heights (15 cm, 30 cm and 40 cm, marked as low, middle and high stubble respectively) on the growth, nutrient accumulation of astragalus sinicus L. (Chinese milk vetch) and soil nutrients, chemical properties and microbes after milk vetch returned to the field. The results showed that rice stubble height significantly affected the growth, nutrient accumulation and soil fertilizing effects of milk vetch. The number of milk vetch per unit area decreased significantly with the decrease of stubble height. Plant height, stem diameter, fresh and dry weight of milk vetch per plant were in the order of high stubble > middle stubble > low stubble, except the number of branches per plant, and the difference was significant or extremely significant between high and low stubble. Grass yield of milk vetch was significantly affected by stubble height, and the fresh and hay yields of milk vetch per unit area decreased significantly with the decrease of stubble height. The fresh and hay yields of milk vetch under high stubble were the highest, reaching 19.22 t/hm2and 3.27 t/hm2, and increased by 15.21 t/hm2 and 2.53 t/hm2 compared with low stubble. There was no significant difference in the contents of carbon, nitrogen, phosphorus and potassium of milk vetch between different stubble heights, but the plant nutrient accumulation increased significantly with the increase of rice stubble height, and the accumulation trend was consistent for all nutrients. There was no significant difference in soil pH after milk vetch returned to field under different stubble heights, but it was slightly higher than that before the test. Soil conductivity was higher in high stubble than in middle and low stubble, and the differences between different stubble heights were all extremely significant. There were great differences in soil nutrients after milk vetch returned to field, and showed decreasing trend with the decrease of stubble height. The contents of organic matter, total nitrogen, alkali-hydrolyzable nitrogen, available phosphorus and potassium under high stubble increased by 41.51%, 27.35%, 34.96%, 68.78% and 82.12% respectively compared with those in low stubble. There were differences in culturable microbe population after milk vetch returned to field under different stubble heights. The numbers of bacteria, fungi and actinomycetes were the highest under high stubble, and the differences were significant except actinomycetes. Among them, the number of bacteria was most affected. The number of bacteria under high stubble was significantly larger than middle and low stubble, and the difference was significant between middle and low stubble. To sum up, rice high stubble (40 cm) could promote more the biomass, nutrient accumulation and soil fertilizing effect of milk vetch than those of medium and low stubble (≤ 30cm).