Effects Of Incorporation Of Milk Vetch (Astragalus Sinicus) On Fertility Characters Of Paddy Soil In South China

There is a large area of winter fallow paddy field in South China, resulting in underutilizing water and heat resources as well as possible loss of nutrient elements by rainfall. Milk vetch (Astragalus sinsicus) is an important kind of green manure crops in China. Winter fallow paddy fields could be utilized to cultivate milk vetch in South China as green manure, forming green manure– rice intercropping patterns, which are more beneficial to both environment and economy.In order to reveal the effects of cultivating and incorporating milk vetch on paddy soil, soil nutrient status, soil enzyme activities and soil microbe numbers were investigated at different stages of milk vetch and rice in Jiangxi, Hunan and Zhejiang since 2009 to 2010. The main results were as follows:1. Green manure increased acid-base buffer capacity and electrical conductivity in soil. In Jiangxi, the soil pH of acidic paddy raised after incorporating milk vetch, while fluctuated in the treatments without milk vetch at the same period. In Hunan, a high soil pH site, the soil pH of the treatment of milk vetch only (GM) decreased compared with that of the control treatment (CK), and the treatment of combination of chemical fertilizer and milk vetch (GMF) could keep the soil pH at a changeless level compared with the treatment of chemical fertilizer only (F). In Jiangxi and Hunan, the electrical conductivity of GM increased by 15.5% and 5.7% respectively at the late rice harvest stages compared with that of CK. The soil electrical conductivities maintained high and stable levels after cultivating and incorporating milk vetch.2. Green manure increased organic carbon content in soil, and improved soil nutrient status as well. In Jiangxi and Hunan, the organic carbon contents of GM increased by 1.73 g/kg and 8.95 g/kg compared with that of CK, and the organic carbon contents of GMF increased by 2.00 g/kg and 4.66 g/kg compared with that of F, respectively. In Zhejiang, organic carbon content in soil also increased after incorporating green manure. In Jiangxi, the total nitrogen content of GM was 0.24 mg/kg higher than that of CK, and the total nitrogen content of GMF was 0.13 mg/kg higher than that of F. In Hunan, the similar results were observed. The rapidly available phosphorus content was also improved in different sites after incorporating green manure. In Jiangxi, compared with F, GMF treatment increased the content by 1.35 mg/kg at the harvest stage of late rice. In Zhejiang, 2 green manure treatments increased the rapidly available phosphorus content by 6.18 mg/kg and 6.92 mg/kg, respectively, at the harvest stage of rice.3. Green manure affected soil enzyme activities. In Hunan, the soil acid phosphate enzyme activity of GM and GMF treatments increased by 18.5% and 18.4% compared with that of CK and F treatments respectively at the full flowering stage of milk vetch. In Jiangxi, it reached a high level at the stage of early rice harvest in the GM treatment, but no obvious regulations were found at other stages. The soil phosphate enzyme activity increased after cultivating green manures in Zhejiang, and the treatment of mix-sowing of milk vetch and ryegrass showed better effect than the treatment of milk vetch. In Hunan, incorporating milk vetch increased the neutral phosphate enzyme activity at the full-bloom stage of milk vetch and the late rice harvest stage, and stronger activities were found at the early rice harvest stage in CK and F treatments. In Jiangxi, the neutral phosphate enzyme activity was increased in GM treatment at both early and late rice harvest stages, and no clear variations in different treatments were found in Zhejiang.4. Green manure promoted growth of microorganisms. In Jiangxi, GMF treatment increased the numbers of bacteria, epiphyte and cellulose decomposition bacteria. The numbers of bacteria and ammonifying bacteria of GM treatment increased at the 2 growth stages of milk vetch, while the numbers of actinomyces and epiphyte increased after incorporation of milk vetch. In Hunan, the numbers of epiphyte, actinomyces, ammonifying bacteria and cellulose decomposition bacteria of GMF treatment increased in comparison with that of F treatment. When without fertilizer, cultivating and incorporating milk vetch promoted the growth of actinomyces and epiphyte in the soil, and the numbers of bacteria, ammonifying bacteria and cellulose decomposition bacteria increased after incorporation of milk vetch. In Zhejiang, the mix-sowing treatment showed better effects on the growths of bacteria and epiphyte, the treatment of milk vetch had nice effect on the growth of actinomyces and promoted the number of epiphyte to a certain degree as well. No significant effects were found on ammonifying bacteria and cellulose decomposition bacteria by green manures in Zhejiang.