Abstract:

Rotation of rice and green manure crops is a common practice in red soil rice fields in southern China. This study investigated the effect of green manure on activating phosphate rock powder and its impact on the yield and phosphorus absorption of subsequent rice crops， to test the efficacy of using phosphate rock powder to replace phosphate fertilizer in red paddy soil. Pot experiments comprising two factors： green manure cultivars and rate of phosphate rock powder， were conducted in Nanchang city， Jiangxi Province. The green manure crops tested were Chinese milk vetch （Astragalus sinicus） （MV）， rape （Brassica napus） （RA）， and ryegrass （Lolium multiflorum） （RY） with a winter fallow （WF） as control. The phosphate rock powder application rates were 0 （P₀）， 0.74 （P₁）， and 1.48 g·kg^-1 （P₂）. The dry weight of green manure during flowering， phosphorus absorption， the soil phosphorus pool， and phosphatase activity were measured， as well as the yield and phosphorus absorption of early and late rice. The results showed that the average aboveground dry matter weights of MVP₂， RAP₂， and RYP₂ treatments were 18.31， 18.07， and 25.33 g·pot^-1， respectively. These values were increases of 42.0%， 42.7%， and 38.6%， respectively， compared to the P₀ treatment. The average phosphorus absorption amounts were 49.10， 60.83， and 36.13 mg·pot^-1， respectively， representing increases of 40.5%， 86.7%， and 45.5%， respectively， compared to the P₀ treatment. Compared to the P₀ treatment， applying phosphate rock powder increased soil total phosphorus， microbial phosphorus content， and stable phosphorus pool percentage by 13.4%-34.2%， 23.0%- 93.2%， and 4.0%-10.6% respectively. Compared to WF treatment， the active phosphorus pool ratio in green manure treatments increased by 0.4%-1.0%， while the moderately active phosphorus pool ratio decreased by 0.6%-2.9%. The average grain yields of early and late rice were 26.33-45.87 g·pot^-1 and 39.17-49.04 g·pot^-1 respectively. Compared to the P₀ treatment， the late rice grain yield increased by 8.5% and 11.8% in the MVP₁ and MVP₂ treatments， respectively， and the phosphorus absorption of early rice increased by 34.4% and 23.3% in the MVP₁ and MVP₂ treatments， respectively. The RAP₁ treatment increased the late rice grain yield by 9.1%. The phosphorus absorption of early rice increased by 20.0% in the RYP₁ treatment. Compared with the WF treatment， the utilization rates of phosphate rock powder in the early rice season for MVP₁， RAP₁， and RYP₁ treatments increased by 2.2%， 1.5%， and 2.3%， respectively. For the MVP₂ treatment， there was an increase of 1.9%. Additionally， the utilization rate of phosphate rock powder for MVP₁ treatment in the late rice season increased by 2.6%. In conclusion， applying phosphate rock powder increased the biomass and phosphorus absorption of green manure， with better solubilization effects observed in Chinese milk vetch and rape than ryegrass. Using Chinese milk vetch as the green manure crop resulted in higher yield， phosphorus absorption， and phosphate rock powder utilization efficiency in second-crop rice than rape and ryegrass treatments.

Key words: green manure, phosphate rock powder, rice yield, rice phosphorus absorption