86PRATACULTURALSCIENCE(V01．26．No．12)12／2009————————————————————————————————————————————————————————————————————————————一一Effect of different planting years on the yield of alfalfa and content ofN，P，K in soilTAIJi—cheng，ZHANGLi～yan，YANGHeng—shan(College ofAgronomy，InnerMongoliaUniversity forNationalities，Tongliao0，China)Abstract：The alfalfa growing for1，2，3，4 arid6 years on experimenta】farm ofInnerMongoliaUni— versity forNationalities were u、sed to study the yield variation and the content ofN，P andK in soil．The results showed that the yield decreased along wi t h l he growth year and the yield in second vear was the highest．7Fhe content of totalN，availableN andP increased along with the growth year．7Fhe totalP increased at the beginning and then decreased，availableK and totalK decreased．Nulrienl contents within0 tO40 cm soil layer decreased as the depth increasing．The nutriellt’contents within40 tO50cm soil layer were higher than those in30 t。40 cm1aver．Key words：alfalfa；planting years；yield；nutrient

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