| The quality of Chinese alfalfa is 2-3 grades lower than that of foreign alfalfa.It is difficult to meet the demand of high quality of forage for animal husbandry.Nitrogen nutrition is the key to improve alfalfa yield and quality.Nitrogen sources include biological nitrogen fixation and nitrogen fertilizer.Among them,biological nitrogen fixation has potential application value to reduce pollution of chemical fertilizers and improve yield and quality of alfalfa.Its efficiency varies with the compatibility between host plant,rhizobium and AMF.Therefore,this study explored the quality potential of alfalfa in China and the best biological nitrogen fixation method.Pass indoor hydroponic experiments,the effects of nitrate nitrogen,ammonium nitrogen,biologic one(adding nitrification and urease inhibitors)and biologic two(not adding nitrification and urease inhibitors)on the quality of alfalfa were compared and the best quality level of alfalfa was explored under ideal conditions.Then,pass the sand culture of indoor experiments,the effects of 9 kinds of rhizobium on alfalfa quality were compared,and the effective rhizobium with growth promotion and quality improvement were sorted out.Finally,pass the soil culture of indoor experiments,two strains of efficient rhizobium and two strains of AMF as inoculants,the effects of single inoculation of rhizobium and double inoculation of rhizobium and AMF on alfalfa quality were compared,the combination of alfalfa and strain with best quality was sorted.The main research results are as follows:(1)The potential of alfalfa quality improvement: the results of hydroponic experiment show that nitrate nitrogen was beneficial to the aboveground growth of alfalfa,while ammonium nitrogen was beneficial to the underground growth of alfalfa.With the increase of growing days,nitrate nitrogen had the greatest effect on the growth and quality of alfalfa.The growth days of alfalfa with nitrate nitrogen treatment reached bud stage were 56 days,2 days more than that of ammonium nitrogen,but the total biomass increased by68.61%.After 27 days of growth,compared with biologic one(adding nitrification and urease inhibitors)and biologic two(not adding nitrification and urease inhibitors),the aboveground biomass of alfalfa with ammonium nitrogen and nitrate nitrogen treatment were increased by 144.44%-215.63%.After 39 days of growth,compared with ammonium nitrogen treatment,the biomass of alfalfa with other nitrogen forms decreased by 46.67%-73.33%.After 54 days of growth,the aboveground biomass of alfalfa with nitrate nitrogen treatment was increased by 115.41%-344.04% compared with other nitrogen treatments.Nitrate nitrogen treatment can promote the growth of alfalfa at bud stage and increase the crude protein content of aboveground of alfalfa.The aboveground biomass of alfalfa at bud stage increased by 28.33%-115.41% with nitrate nitrogen treatment compared with other nitrogen forms.The highest crude protein of aboveground of alfalfa was 20.64%,followed by 16.21% with biological two treatment.(2)The sort of efficient rhizobium: the results of sand culture experiment show that efficient rhizobium can significantly promote the growth of alfalfa,the formation of root nodules,and improve the nitrogen fixation ability of alfalfa.Five excellent strains contain RG,01280,01302,01310 and 01314 were sorted out by growth and nodulation indexes.Compared with the control,the aboveground biomass of alfalfa inoculated with 5 superior strains were increased by 238.24%-611.76%.Comprehensive analysis of growth,nitrogen fixation ability and quality indexes,found that the best inoculation effect on alfalfa is strain RG,01302 and 01314,which had higher growth promoting effect and quality improvement effect on ‘Zhongmu No.1’ alfalfa than other strains.The crude protein of aboveground of alfalfa were 20.19% to 20.38%,which reached the level of first grade.(3)The potential of the best combination of biological nitrogen fixation to improve alfalfa quality: double inoculation had synergistic effect on the growth of alfalfa in sterilized soil,while single inoculation could inhibit the growth.The effects of inoculation on alfalfa growth and quality were not significant in unsterilized soils due to the influence of indigenous AMF.The growth and quality of alfalfa had different effects by inoculating different strains.Under the condition of industrialized soil,the aboveground biomass of alfalfa inoculated with G.i+01314 was the highest.The crude protein content of aboveground of alfalfa inoculated with G.m+RG reached 17.91%.In the condition of sterilized soil,the aboveground biomass of alfalfa inoculated with G.i+01314 compared with the control increased by 12.66 times.Comprehensive analysis of growth and quality indexes,it was found that G.i+RG treatment had the best effect on the growth and quality of alfalfa,and was the best combination of rhizobium and AMF.Main conclusions: under the condition of sufficient nutrients in hydroponic culture,nitrate nitrogen is the best nitrogen form for the growth and quality of "Zhongmu No.1" alfalfa,and its crude protein content can reach the level of first grade.By regulating the biological nitrogen fixation process and combining with the characteristics of alfalfa biological nitrogen fixation,the effective rhizobium strains RG,01302 and 01314 were sorted under the condition of sand culture,which could make the crude protein content of alfalfa reach the level of first grade.Under the condition of sterilized and unsterilized soil culture,the double-inoculation of effective rhizobium and AMF showed the best growth promoting effect on alfalfa,but the crude protein content failed to reach the level of first grade.In addition,AMF is the key to the synergistic effect of double inoculation. |
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