Effects Of Water-phosphorus Coupling On Yield And Quality Of Alfalfa

Irrigation and phosphorous application rates are two key factors affecting the yiel d of alfalfa(Medicago sativa)pastures.In order to explore the optimal water and phosphorus coupling ratio suitable for alfalfa with high quality and high yield,the intrinsic mechanism of water and phosphorus coupling to promote plant water conservation and yield assurance was further elucidated,which provided a scientific basis for the collaborative management of water and fertilizer in alfalfa cultivation grasslands in arid and semi-arid areas of China.In this study,the effects of different irrigation amounts(40 %～45 %,60 %～65 %,80 %～85 % soil saturated water content)and phosphorus application(0,64,127,191 mg/kg)on alfalfa production performance,physiological and biochemical characteristics and forage quality were analyzed by greenhouse potting experiments,and the results showed that:(1)The irrigation amount,phosphorus application rate and the coupling of the two significantly affected the production performance index of alfalfa(P<0.05).With the increase of irrigation amount,the plant height,number of branches,first and second alfalfa plant height,number of branches,first and second alfalfa hay yields and taproot length all showed an increasing trend,and reached a peak under the treatment of80 %～85 % of the saturated water content of the soil.The main stem thickness,leaf-tostem ratio,hay yield and root neck diameter of the third and fourth stubble showed a trend of first increasing and then decreasing,and the peak was reached under the treatment of irrigation amount of 60 %～65 % of soil saturated water content.With the increase of phosphorus application,the plant height,root biomass and root volume of alfalfa below 10 cm showed a gradual increase trend,and reached a peak when the phosphorus application rate was 191 mg/kg.The number of branches,the thickness of the main stem and the yield of hay showed a trend of first increasing and then decreasing,reaching a peak when the phosphorus application rate was 127 mg/kg.The results of fminsearch function optimization showed that the plant height of alfalfa four crops had the optimal value under the irrigation amount of 80%～85% and the phosphorus application rate of 191mg/kg.Under the irrigation amount of 60%～65% and the phosphorus application rate of 127 mg/kg,the main stem thickness of the four stubbles alfalfa,the yield of the third stubble hay and the yield of the fourth stubble hay had the optimal values.(2)The amount of irrigation,phosphorus application and the coupling of the two significantly affected the physiological and biochemical indexes of alfalfa(P<0.05).With the increase of irrigation amount,alfalfa Pn,Tr,chlorophyll b,chlorophyll(a+b),POD,CAT,soluble sugar and soluble protein all showed a trend of first increasing and then decreasing,and peaked under the treatment of 60 %～65 % of the saturated water content of the soil.With the increase of phosphorus application,the contents of alfalfa Pn,Ci,Tr,chlorophyll a,SOD,POD,CAT,Pro,soluble sugar and soluble protein also showed a trend of first increasing and then decreasing,and peaked at 127 mg/kg under the treatment of 127 mg/kg.The results of fminsearch function optimization showed that alfalfa Pn,Tr,chlorophyll a,chlorophyll b,chlorophyll(a+b),leaf SOD,POD,CAT activity,soluble sugar and soluble protein content were optimal under the treatment of60%～65 % and phosphorus application rate of 127 mg/kg.(3)The amount of irrigation,phosphorus application and the coupling of the two significantly affected the nutritional quality and relative feeding value of alfalfa(P<0.05).With the increase of irrigation amount and phosphorus application,alfalfa CP,EE,CA,DMI,DDM and RFV showed a trend of first increasing and then decreasing,and reached a peak when the irrigation amount was 60 %～65 % of the soil saturated water content and the phosphorus application rate was 127 mg/kg.The contents of alfalfa CF,NDF and ADF decreased first and then increased with the increase of irrigation amount and phosphorus application,and there was a minimum value under the treatment of 60 %～65 % of soil saturated water content and 127 mg/kg under the treatment of 127 mg/kg under the treatment of 60 %～65 % of soil saturated water content and phosphorus application.The results of fminsearch function optimization showed that alfalfa had maximum values and minimum values for CCF,EE,CA,DMI,DDM and RFV under the irrigation rate of 60 %～65 % and phosphorus application rate of 127 mg/kg.