| The green manure crop has a well-developed root system and it can release organic acids to the soil during growth period or after incorporation.These organic acids can chelate soil metal ions,adjust soil p H,and increase the effectiveness of phosphorus(P),thus the green manure crop has a strong utilization ability of phosphate rock.In this study,field and pot trials were used to determine the effects of different amounts of phosphate rock on the growth and nutrient utilization of green manure and following rice,as well as the use efficiency of phosphate rock by different types of green manure,which provided a scientific basis for the efficient utilization of phosphate rock resources and the optimization of green manure planting and utilization technology.The main results are as follows:(1)There was a trend of yield increase in Chinese milk vetch after the application of different amount of phosphate rock.The application of phosphate rock in Chongyang resulted in an average yield increase of 26.6%,with significant yield increases of 37.7%and 57.4% with the application of 900 and 1500 kg/ha of phosphate rock,respectively.In Suizhou,the same treatments resulted in an average yield increase of 23.3% and a maximum yield increase of 27.8%.The higher efficiency of phosphate rock on Chinese milk vetch in Chongyang was probably related to its more acidic soil.In Wuhan with neutral soil p H,there was a tendency to reduce the yield of Smooth vetch and Hairy vetch after the application of phosphate rock,and the yield increase of Chinese milk vetch was not obvious.(2)Application of phosphate rock could improve the nutrient accumulation in green manure.The application of different amounts of phosphate rock in Chongyang increased the accumulation of nitrogen(N),P and potassium(K)in Chinese milk vetch by 20.8%,36.1% and 71.7%,respectively,on average,among which the accumulation of P and K of Chinese milk vetch with the application of 600,900 and 1500 kg/ha phosphate rock increased significantly by 37.5%,45.0%,74.1% and 68.5%,76.2% and 121.2%,respectively.The increase in the accumulation of different nutrients in Chinese milk vetch at Suizhou was different,and the average increase in N(24.2%)was higher than that at Chongyang,while the average increase in P and K(21.8% and 21.8%)was significantly lower than that at Chongyang.The application of phosphate rock caused an increasing trend in N,P and K concentrations in Smooth vetch and Hairy vetch,but the changes in total nutrient accumulation were not significant.(3)The pot study showed that both planting green manure and applying phosphate rock treatments increased rice grain yield.In the trial with different types of green manure,the increase in rice grain yield was 6.4%-24.6% for planting Chinese milk vetch,Smooth vetch and Hairy vetch,respectively,without phosphate rock,and such increase was24.4%-60.5% when phosphate rock was applied.Comparing with green manure treatment without phosphate rock,planting green manure with phosphate rock increased rice grain yield by 10.2%-21.5%,and the effect on yield increase was Hairy vetch > Smooth vetch >Chinese milk vetch.Among the treatments with different phosphate rock dosages,planting Chinese milk vetch with application of 900,1200,and 1500 kg/ha phosphate rock significantly increased rice grain yield by 17.3%,31.2%,and 22.0%,respectively.Comparing with green manure treatment without phosphate rock,planting Chinese milk vetch with phosphate rock increased rice grain yield by 5.5%-23.2%,with a significant yield increase of 23.2% for 1200 kg/ha phosphate rock.(4)Regardless of the application of phosphate rock,planting green manure increased the accumulation of N and P in rice grains at harvest.In the trial with different types of green manure,the N and P accumulation of rice grain in the treatments with phosphate rock increased by 19.0%-19.9% and 8.5%-42.1%,respectively,comparing with that without phosphate rock application.The effect on the increase of N accumulation was Hairy vetch > Smooth vetch > Chinese milk vetch,and on the increase of P accumulation was Smooth vetch > Hairy vetch > Chinese milk vetch.In the trial with different phosphate rock,the accumulation of N and P in rice grain increased on average by 15.6% and 15.7%,respectively,in the treatments planting Chinese milk vetch with phosphate rock from 0 to 1500 kg/ha.Comparing with Chinese milk vetch treatment without phosphate rock,the accumulation of N and P in rice grain increased on average by 10.9% and 11.0%,respectively,in the treatment applying phosphate rock.(5)Application of different amounts of phosphate rock increased the soil available P content at the full blooming stage of Chinese milk vetch.The increase ranged from26.8% to 68.2% in Chongyang and from 41.4% to 153.7% in Suizhou.In the pot study,the application of different amounts of phosphate rock increased soil available P content at the full blooming stage of Chinese milk vetch by 13.2% on average.At the rice tillering and harvesting stages,the soil total N increased by 2.0%-6.1% and 2.0%-8.0%,respectively,the soil available P increased by 3.5% and 9.0%,respectively,and the soil available K increased by 4.1% and 19.4%,respectively.The soil organic matter content at the rice harvesting stage increased by 10.6% on average.(6)The incorporation of Chinese milk vetch,Hairy vetch,and Smooth vetch had a tendency to improve soil fertility,and soil available K and organic matter content increased more obviously.The effect of green manure with phosphate rock on improving soil fertility was more obvious during the full blooming period of green manure.The contents of soil available P and K and organic matter increased by 2.1%-36.9%,3.2%-48.6%,and 9.3%-20.2%,respectively,comparing with the corresponding green manure treatments without phosphate rock.The soil fertility was not significantly affected during rice growth period. |
