Study On Nutrents Accumulation And Decomposition Charater Of Astragalus Sinicus L. And Effect Of Application In Paddy Field

Astragalus sinicus L. is one of the main green manures in paddy field of southern China. The nutrient accumulation and nutrient decomposition character of Astragalus sinicus L. and effect of its applying in paddy soil was investigated in this study using the simulation experiment and field experiment, for the purpose of providing some theory basis for the restoration and popularization of the Astragalus sinicus L. applying in paddy soil under the current cropping system.The main results were showed as follows:1.A field experiment was conducted to study the dry matter accumulation and nutrient absorption with 6 varieties of Astragalus sinicus L.. The results showed that, the N contents in the aerial part of Astragalus sinicus L. kept on decreasing before seed mature period as the growth period goes on, and showed a rise trend in the seed mature period time. The P contents in the aerial part increased first and decreased afterwards, with the highest in the mature period. But the K content slowly declined in the whole growth period, while the C content changed a little. The dynamics study of dry matter accumulation and nutrient absorption showed that the flowering period (135～170 days after seedling) was the most rapid accumulation period, had the accumulation of 55.8%-83.7% of the total dry material.The amounts of N, P2O5, K2O and C nutrient accumulation were also the most during this period, in which N,P2O5, K2O and C accumulation were 30.6%-54.7%,40.6%-69.6%,53.6%-82.8% and 55.8%-83.9% of the whole respectively. In summary, the best returning time of Astragalus sinicus L. to the field was the blooming period, when the amount of organisms and nutrient absorption were the most.2.The growth periods of six varieties Astragalus sinicus L. were showed as follows.The growth periods of Xinyang Astragalus sinicus L. and Anhui Dayeqing Astragalus sinicus L. were obviously earlier than the rest four varieties, while the later four varieties had no big different. Judging from the dry matter accumulation and nutrient absorption conditions of six varieties, varieties of Yijiang Astragalus sinicus L. and Zhezi No.5 Astragalus sinicus L. were the better varieties applied in paddy soil of Hubei province.3.The objective of the simulation experiment was to determine the decomposition character of Astragalus sinicus L. and its effect on properties of soil surface solution and soil fertility. The results showed that the decomposition of Astragalus sinicus L. in the first 32 days was much faster and then almost stagnated. The rate of nutrient releasing was characterized as K>P>N>C, and the amount of nutrition released was much higher when Astragalus sinicus L. was in the water. The results also showed that applications of different amounts of Astragalus sinicus L. had no obvious effect on the decomposition rate and nutrient release rate of Astragalus sinicus L.. The dynamic change of EC, pH, and concentration of TN, NH4+-N, NO3--N, TP and TK in the surface solution were measured during the 96 d experiment. The result showed pH changed greatly at the first 2 weeks. The application of Astragalus sinicus L. to soil increased EC, concentration of TN, NH4+-N, TP, TK obviously,and reached the maximum in about 32 days after cultivation. The study of the dynamic change of soil fertility during the whole training period showed that the soil pH was rising after the Astragalus sinicus L. was mixed into soil,and the range was from pH 6.08 up to pH 7.00 when the 96 days cultivation was over. The content of soil NH4+-N, soil available K, total N and organic matter was significantly increased, especially in the first 32 days of cultivation. But the application of Astragalus sinicus L. had little influence on soil NO3-N and soil available P content.4.Effect of Astragalus sinicus L. application on the growth, nutrients absorption, yield of rice, economic benefits and soil fertility were studied by field experiments in Xiaochang and Huangpi city of Hubei province. The results showed that on the premise of 40% reduction in conventional fertilizer situation, application of mixed Astragalus sinicus L.(15000～45000 kg/hm2) and mineral fertilizers both in Huangpi and Xiaochang could have a better or the same effects on rice yields.Both field experiments in Huangpi and Xiaochang showed that the best quantity of Astragalus sinicus L. were 30000 kg/hm2, as the yield of early rice increased by 8.5% and 15.4% respectively compared to common fertilizers. Field experiments in Xiaochang and Huangpi which have the same N, P and K application showed that the treatment applied of only Astragalus sinicus L. and the treatment applied of mixed Astragalus sinicus L.(15000～45000 kg/hm2) and mineral fertilizers had not significant differences on the yield of early rice. In conclusion, application of Astragalus sinicus L. could partly replaced the use of mineral fertilizers, thus increasing the rice yields and the economic benefits from rice growings. In general,20% to 60% of mineral fertilizers application amount could be better substituted by application of Astragalus sinicus L.(15000～45000 kg/hm2).