Study On The Optimal Allocation Of Green Manure And The Substitution Effect Of Nitrogen Fertilizer In Anhui Paddy Field

It is of great theoretical and practical significance to study the effects of different green manures on plant nutrient content and soil fertility under different sowing methods,so as to screen suitable planting methods for different kinds of green manures,and to improve the efficient utilization of nutrient resources of green manures in Anhui rice area.In this study,a field experiment was conducted in Shucheng County,Lu’an City,Anhui Province from2021 to 2022 to study the effects of different configurations of leguminous green manure（Chinese milk vetch/hairy vetch）and gramineous green manure（ryegrass）on green manure,rice and soil fertility.The main results are as follows:（1）By analyzing the effects of different planting methods of leguminous green manure and gramineous green manure on fresh grass yield and nutrient accumulation,the results showed that the fresh grass yield of mixed sowing of hairy vetch and ryegrass was the highest in all treatments,reaching 31 582 kg·ha,and the fresh grass yield of mixed sowing of Chinese milk vetch and ryegrass was also higher than that of single sowing of Chinese milk vetch and ryegrass.Except for Chinese milk vetch treatment,there was no significant difference in nutrient accumulation of phosphorus and potassium,but there was a significant effect on nitrogen accumulation.The nitrogen accumulation of mixed sowing of hairy vetch and ryegrass was significantly higher than that of mixed sowing of Chinese milk vetch and ryegrass,and significantly higher than that of single sowing of Chinese milk vetch and ryegrass.The comprehensive results showed that the mixed planting of hairy vetch and ryegrass not only had the highest fresh grass yield,but also had higher nutrient accumulation,which was the best planting mode in this experimental area.（2）Different configurations of leguminous green manure and gramineous green manure had significant effects on rice yield and nutrient absorption.Different green manure returning to the field increased rice yield,especially the treatment of hairy vetch and Chinese milk vetch+ryegrass returning to the field,the rice yield was significantly increased by 6.54%and 6.25%compared with the winter fallow treatment.The absorption of nitrogen,phosphorus and potassium nutrients in rice plants was promoted by returning green manure to the field,and the effect of nitrogen and phosphorus absorption in rice plants was the best.The potassium absorption effect of hairy vetch+ryegrass treatment was the best,which was 15.67%higher than that of winter fallow treatment.At the same time,a comprehensive comparison of the nutrient absorption of rice plants by green manure mixed sowing and single green manure returning to the field showed that the nitrogen uptake of rice grains treated with Chinese milk vetch+ryegrass was significantly higher than that of ryegrass single treatment.The potassium uptake of rice straw and shoots treated with Chinese milk vetch+ryegrass and hairy vetch+ryegrass was also significantly higher than that of ryegrass single treatment.Therefore,mixed sowing increased the nutrient absorption of rice plants compared with ryegrass single sowing treatment.（3）Planting green manure in paddy fields in Anhui has a significant effect on soil fertility.Before the green manure was turned over,planting ryegrass had the greatest increase in soil organic matter content,which was 11.25%higher than that of winter fallow treatment.Planting milk vetch and hairy vetch had the best effect on soil total nitrogen,available phosphorus and available potassium content.During the rice harvest period,the ryegrass returning treatment still had the best effect on soil organic matter improvement;the soil total nitrogen content of Chinese milk vetch and hairy vetch returning to the field was significantly higher than that of single ryegrass returning to the field,and there was no significant difference among the green manure treatments except for the ryegrass treatment.The content of available phosphorus in soil treated with hairy vetch was the highest,reaching 16.11 mg·kg^-1.The content of soil available potassium was 134.96 mg·kg^-1,which was significantly higher than that of other treatments.（4）Green manure can replace 30%nitrogen fertilizer input in rice season in Anhui paddy field.The reduction of 30%chemical nitrogen fertilizer in each green manure treatment can ensure stable yield and yield increase of rice.The total nitrogen uptake of Chinese milk vetch and hairy vetch single sowing treatment was still 4.58%and 4.49%higher than that of conventional fertilization treatment（winter fallow 100%N）under the condition of 30%nitrogen reduction.At the same time,on the basis of reducing 30%chemical nitrogen fertilizer,turning over Chinese milk vetch,hairy vetch,Chinese milk vetch+ryegrass,hairy vetch+ryegrass is beneficial to improve the partial productivity of nitrogen fertilizer and agronomic efficiency of nitrogen fertilizer in rice season.Compared with conventional fertilization（winter fallow 100%N）,green manure combined with 30%nitrogen fertilizer reduction can ensure the stability and improvement of paddy soil fertility to a certain extent.The content of soil available phosphorus increased by 12.12%-36.78%,and the content of soil available potassium increased by 1.86%-26.26%.Soil organic matter increased by 4.23%-26.34%,and soil total nitrogen content increased by 3.01%-12.03%except for ryegrass.The comprehensive results showed that the nitrogen fertilizer substitution potential of Chinese milk vetch and hairy vetch was higher.