| Phosphorus is one of the essential nutrients for crop growth and plays a key role in the formation of crop yields.The application of phosphate fertilizer in the process of alfalfa cultivation and management is also one of the important management methods,how to scientifically and rationally apply phosphorus fertilizer to improve the yield of alfalfa forage is the key content of its cultivation management research.Based on this,in this paper,a pot experiment was used to treat alfalfa with different phosphorus application amounts and depths of phosphorus application,the test set up 0,5.2,10.4,15.6,20.8 g/m2,a total of 5 phosphorus application levels（Na H2PO4analytical pure）,respectively expressed as P0,P5,P10,P15,P20;set 5,10,15,20 cm total the four phosphorus application depths are represented by D5,D10,D15and D20respectively;By measuring the above-ground and underground biomass,plant height,stem diameter,underground root structure,C,N,P and nutritional quality of leaves and stems and other related indicators,the effect of phosphorus addition on the biomass,quality and root characteristics of alfalfa was discussed.The rules can provide reference for the cultivation and management of alfalfa.the result shows:1 The depth of phosphorus application has a significant effect on the above-ground biomass,below-ground biomass and total biomass;the level of phosphorus application has a very significant effect on the biomass and total biomass of the first and second crops;except for the above-ground biomass of the first crop,the interaction effect the effects on the biomass of alfalfa were extremely significant.The above-ground biomass and total biomass of the second crop gradually increased with the increase of the phosphorus application level,and the maximum above-ground biomass,underground biomass and total biomass of the second crop all appeared at the phosphorus application depth of 15 cm,and the phosphorus application level of 15.6 g/m2,the values were 797.45 g/m2,689.79 g/m2,and1891.83 g/m2,respectively.2 Phosphorus application depth had a significant effect on the root shoot ratio of the first crop and stem contribution rate,and had a very significant effect on the root shoot ratio of the second crop,leaf and root contribution rate;Phosphorus application level had a very significant effect on the root shoot ratio of the first and second crops,stem contribution rate and root contribution rate;Interaction had a significant effect on root contribution rate,and had a very significant effect on root shoot ratio of the first and second crops and leaf contribution rate;The maximum values of root shoot ratio of the second crops and root contribution rate appeared under the condition of phosphorus application depth of 10 cm and phosphorus application level of 0 g/basin,which were2.67and 74.19%respectively.The effects of phosphorus application depth,phosphorus application level and their interaction on plant height and stem diameter of Alfalfa in the first and second stubble reached a significant level.Except for the stem diameter of the first crop,with the increase of phosphorus application level,the plant height and stem diameter of the first and second crops increased first and then decreased,the maximum plant height of the first and second crops appeared under the condition of phosphorus application depth of 15 cm and phosphorus application level of 15.6 g/m2,and the values were 58.79 cm and64.19 cm respectively.3 Phosphorus application depth had a very significant effect on the surface are a,volume,number of root tips,,number of connections,number of nodes,number of bif urcations,number of intersections of the first crop,length,surface area,volume,number of root tips,number of connections,number of nodes,number of bifurcations and num ber of intersections of the second crop;Except for the average diameter of the seco nd crop,Phosphorus application level and interaction had significant effects on root l ength,surface area,volume,average diameter,number of root tips,number of connection s,number of nodes,number of bifurcations and number of intersections.The maximum values of root length,surface area,connection number,number of nodes,bifurcation nu mber and crossing number of the first crop all appear at the phosphorus application depth of 15 cm,the phosphorus application level of 15.6 g/m2,and the values are7288.48 cm/plant,3527.54 cm2/plant,20380.25 number/plant,15084 number/plant,10238number/plant,2872 number/plant.4 Except for the P content of the second crop root,the depth of phosphorus application had a significant effect on root C,N and P in the first and second crops;The effects of phosphorus application level on the contents of C,N and P in alfalfa were very significant;Its interaction had a significant effect on the N content of the first crop and the P content of the second crop.The contents of N and P in the first and second crops reached the minimum under the condition of phosphorus application depth of 5 cm and phosphorus application level of 5.2 g/m2.The maximum values of C and P contents in the first crop appeared at the phosphorus application depth of 15 cm,the phosphorus application level of15.6 g/m2,the phosphorus application depth of 10 cm,the phosphorus application level of15.6 g/m2,and the values were 47.14%and 0.34%.5 The depth of phosphorus application had a significant effect on the CP of the first and second crop leaves,ADF,CP of the first crop stem and EE of the second crop stem,and NDF of the first crop stem;The effect of phosphorus application level on CP of the first and second crop leaves and the nutritional quality of the first and second crop stems was very significant,but not on other nutritional quality of leaves;The interaction had a significant effect on ADF of the second crop leaves,but had no significant effect on other nutritional qualities of leaves and stems;The maximum values of ADF and NDF of the first cutting stem appeared under the condition of phosphorus application depth of 10 cm and phosphorus application level of 20.8 g/m2,and the values were 46.61%and 65.59%respectively. |
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