Effects Of Chinese Milk Vetch And Rice Straw Incorporation On Rice Growth And Residual Nitrogen Fate

Chinese milk vetch-rice rotation is an important planting mode of"storing grain in land and in technology".Various organic materials returned to the field supplemented the soil nitrogen pool,meanwhile,the nitrogen added into the field would have different effects on soil nitrogen cycling.In order to reduce the input and loss of nitrogen fertilizer,more attention has been paid to returning organic materials to the field.However,there is still a lack of quantitative study on the utilization of residual nitrogen from fertilizer and green manure under Chinese milk vetch-rice rotation.In the present study,¹⁵N isotope labeling technique was used to quantify crop uptake and residual rate of residual N and straw N from the last crop rotation（2021）with the incorporation of Chinese milk vetch,rice straw and their combination.The residual N from fertilizer and green manure and the N from rice straw were concentrated in order to provide scientific support for fertilizer reduction and efficient use of N under the Chinese milk vetch-rice rotation.The main results are as follows:（1）Chinese milk vetch,rice straw and their combination could ensure rice biomass,promote the absorption and utilization of nutrients by rice,improve soil total N,organic matter,and inorganic N content with 40%N fertilizer reduction.The effects of co-incorporation were better than Chinese milk vetch or rice straw incorporation alone.Compared with single application of 100%N fertilizer,the content of soil total N,organic matter and inorganic N were increased by 13.6%,19.4%and 48.7%,respectively,in the treatment of Chinese milk vetch and rice straw combined incorporation.（2）Under the condition of reducing 40%N fertilizer and co-incorporation of Chinese milk vetch and rice straw,the residual N content of rice in different organs showed the order of straw>panicle>root,and the residual N were taken up with the order of straw N>residual N from green manure>residual N from fertilizer.It can be seen that compared with the residual nitrogen from last season,the N in the rice straw returned to the field is more easily absorbed and utilized by the crop.（3）The content of residual N from green manure of last season in the soil was 756.11mg/pot after the current season with 40%N reduction and Chinese milk vetch was incorporated alone,accounting for 73.4%of the total residual N.The content of straw N left in the soil was 866.18 mg/pot,which accounted for 78.4%of the total input,with40%nitrogen N reduction and rice straw was incorporated alone.It can be seen that residual N from green manure and straw N can still be absorbed and utilized by plants in subsequent rotation.From the long-term effect,full utilization of residual N is an effective way to replace part of nitrogen fertilizer.（4）Under the conditions of reducing 40%N fertilizer application and combined incorporation of Chinese milk vetch and rice straw,the proportion of N loss from chemical fertilizer residual N and straw N was the smallest,which was 20.0%and 5.1%,respectively.When Chinese milk vetch was incorporated alone,the proportion of N loss from green manure residual N was the smallest,which was 20.7%.Therefore,the combined incorporation of Chinese milk vetch and rice straw could improve the utilization of residual N from fertilizer and straw N,and the single incorporation of Chinese milk vetch could improve the utilization of residual N from green manure in the crop-soil system.In summary,the combined incorporation of Chinese milk vetch and rice straw could improve the contents of soil total N,organic matter and inorganic N,and could improve the utilization of residual N from fertilizer and straw N in crop-soil system.Incorporating Chinese milk vetch to the field could ensure the biomass of rice panicle,improve the utilization of residual N from green manure and reduce its loss.Although residual N from green manure and straw N had little contribution to rice N utilization,in the long run,the incorporation of Chinese milk vetch and rice straw could replenish soil N pool,which was an effective way to improve soil fertility,replace part of N fertilizer and reduce N loss.