Effects of longterm plant Medicago sativa Linn. on soil nitrogen nutrient

The results of 13 years long-term fertilization and rotation test show that the application of nitrogenous fertilizer, phosphorate fertilizer and organic fertilizer in combination(NPM) can enhance the content of nitrate-N more effectively than that of application of only phosphorate fertilizer. There is a deficiency of nitrate-N in deeper soil layer after a longer time of planting Medicago sativa Linn. and a higher utilization ratio of nitrate-N of planting Medicago sativa Linn. than that of winter wheat. Among all treatments, the ammonium-N of planted Medigao sativa Linn. is the highest than that of other crops, and also the ammounum of CK and NPM are higher than that of P and the bareness disposal. Compared to other rotation systems, Medicago sative Linn. has better effect than others on improving the level of organic-N mineral potential.