Research On The Effects Of Phosphorus Application And Soil Moisture Management On The Growth And Development Of Chinese Milk Vetch

Chinese milk vetch（CMV,Astragalus sinicus L.）is mainly used as a green manure to return to the field in southern china.Study the effect of phosphorus and soil moisture have practical significance for reducing the amount of fertilizer input and protecting ecological environment of farmland.Aiming to explore the effect of phosphorus and soil moisture on the growth,nutrient absorption and nitrogen fixation characteristics of CMV in main growth periods,the pot experiment which set four soil moisture levels（25%,50%,75%and 100%of the field water content,W1,W2,W3 and W4,respectively）and four phosphorus application rates(0,30,60,90 kg P₂O₅·hm^-2,P0,P1,P2 and P3,respectively)were conducted.In addition,the effect of phosphorus and soil moisture on the growth and development of CMV was quantitatively analyzed in this experiment,and determined the optimum application amount of phosphorus and soil moisture.The main findings were as follows:1.Soil available phosphorus content and plant growth and aboveground nutrient content absorption were significantly increased in phosphorus application（P<0.05）.In addition,phosphorus increased the root activity and nodule number and weight and nitrogenase activity,but significantly reduced root-shoot ratio and phosphorus utilization efficiency.A comparatived analysis of the biomass and nitrogenase activity indicators that were critical to the effect of turning green manure back into field.The biomass and nitrogenase activity indexes of CMV under the treatment of medium phosphorus（P2）were better than other treatments at the seedling,branching and full flowering stage.The biomass and nitrogenase activity of CMV reached the maximum at the full flowering stage.In addition,the biomass of CMV under P3 treatment was significantly lower than that under P2 treatment at the full flowering stage（P<0.05）.Economic and ecological benefits should be taken into account at the same time.In the actual production,low or medium phosphate fertilizer can be supplemented according to the soil conditions to promote the growth and nodule nitrogen fixation of CMV.Then gave full played to the effect of"increasing nitrogen with phosphorus".2.Suitable soil moisture promoted the growth and development of CMV,while W1treatment significantly reduced the biomass and nutrient absorption and nitrogen fixation of root nodules（P<0.05）.The water requirements of CMV were different in the growth stages.When the field water content was 75%,the plant height,root length and biomass of CMV at the seedling stage showed the best.The CMV growed well when the field water content was at 50%to 75%at the branching stage,and the difference between W2 and W3 treatments was no significant difference（P>0.05）.The CMV growed well when the field water content was 75%at the full flowering stage,and the biomass and root nodule nitrogenase activity were significantly higher than other water treatments（P<0.05）;3.Phosphorus was closely related to water during the growth and development periods of CMV.The promotion effect of phosphorus on the growth and development of CMV depended to a large extenton soil moisture,and the utilization of water was affected by phosphorus.The effect of phosphorus increased with the increased of soil moisture in a certain range.Suitable phosphorus application had a compensation effect on water stress in CMV,especially drought stress to CMV.The phosphorus and soil moisture significantly affected the plant height,root length,biomass,nitrogen and phosphorus accumulation,nitrogenase activity（P<0.05）.However,the interaction of phosphorus and water had no significant effect on the root-shoot ratio,total phosphorus content,nodule number and nodule fresh weight at the seedling stage（P>0.05）.Soil moisture was the key factor to control the growth indicators of CMV in the growth process,while phosphorus was more important for the regulation of the aboveground total phosphorus content and soil AP content.Considering comprehensively the indexes such as the biomass,nitrogen and phosphorus accumulation,root activity and nitrogenase activity of CMV at seedling,branching and full-floweing stages,the best combination of phosphorus and water suitable for the growth and development of CMV was W3P2 treatment,which was suitable the phosphate-water combination model of the growth and development of CMV.