| There is experiment field in Korla, the south of Xinjiang. By doing field fertilizer experiment with three factors three levels orthogonal experiment design of alfalfa, the objective of this study showed that the effects of applied nitrogen, phosphorus, potassium ratio fertilizer on alfalfa hay yields, nutrient absorption and soil fertility in the first year and the following year. Meanwhile in northern Xinjiang studying change of soil fertility of alfalfa in the fourth year, the main conclusions were as follows:Yields: Based on hay yield of the first year for ternary quadratic function simulation model to be fertilizer. Using frequency analysis method seeked optimum, we obtained that fertilizer inputs were N: 42.4～55.0 kg/hm2, P2O5: 118.5～173.5 kg/hm2, K2O: 71.5～90.7 kg/hm2 respectively in the similar soil conditions planting alfalfa. In this interval of fertilization, alfalfa hay yield could be predicted 9 500~10 500 kg/hm2.The aftereffect of fertilization on the yield: N fertilizer had little effect on yield of alfalfa in the second year. Phosphate fertilizer plays an important role for alfalfa production, But P fertilizer is not the more the better, and K had a certain role to the second year of alfalfa, it had stated aftereffect.Nutrient absorption : In this experiment, alfalfa absorption of the first year per hectare of N, P2O5, K2O were 263.32 kg, 52.60 kg and 307.0 kg, a ratio of N, P2O5, K2O was 1:0.20:1.17; alfalfa absorption of the second year per hectare of N, P2O5 and K2O were 585.44 kg, 93.60 kg and 839.28 kg, the ratio of its was 1:0.16:1.43.Nitrogen, phosphorus and potassium absorption of the first year of alfalfa per 100 kg hay production respectively is3.27 kg, 0.30 kg and 3.10 kg; the second year per 100 kg hay production about nitrogen, phosphorus and potassium absorption respectively is 2.86 kg, 0.23 kg and 3.44 kg.Soil Fertility: To the south of Xinjiang, alfalfa was planted in the first year, soil organic matter content had declined; Soil available nitrogen content had downward trend with soil depth; Soil available phosphorus content of fertilization treatments was significantly higher than lack of fertilization; Soil available potassium had upward trend with the soil depth, and after the first year the soil available potassium content declined fast; soil soluble salts of the first year down faster.Alfalfa was planted in the second year, the fertilization of soil nutrients are not low or raise simply, soil organic matter accumulation obviously in the second year, more than the former level; Available soil nitrogen had larger changes in the second year, and tends to be stable; In the second year of soil phosphorus content had a great relationship with fertilizer of the first year, but in the latter part of the second year have a declined range; Soil available potassium had an upward trend in the second year than the first year, and it had steady change in the second year; Taking off salt rate of 0～20 cm NPK fertilizer treatment reached 82.3%, taking off salt rate of ck reached 75.6%, while soil soluble salts of fertilization had little change; pH had little changes in early of second, and the later of year compared with the preliminary drop of 0.4～0.8.In northern Xinjiang, the fourth year results showed that fertilization had a certain role on soil organic matter. Soil available nitrogen in the topsoil had a slight increase, soil available phosphorus content was the highest in the surface, soil phosphorus content mainly by the input of the balance of phosphorus, and the total phosphorus content had little change with growth crop. soil available potassium content change was not relation to years of cultivation and increase growth, after a certain number of years, growing alfalfa absorb much available potassium and soil available potassium content had declined faster, but alfalfa fertilization had contributed to the maintenance of total potassium content.
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