| The investigation of the yield, soil quality and species diversity of alfalfa grassland was carried out from 2005 to 2006 in gully region of the Loess Plateau. It was mainly studied that the change of productivity, soil quality and species diversity with growth years and the effect of fertilizer on the productivity and soil fertility in alfalfa grassland, based on the Long-term experiments of wheat-alfalfa rotation and alfalfa continuous cropping. The main results were shown as follows:1.Alfalfa could grow for more than 10 years in this region, and achieve the growth peak in the 6th or 7th year. The highest yield was about 18142.6 kg/hm2; the multiple regression equation between alfalfa yield and growth stages was y = -0.3582x4 + 26.392x3 - 651.72x2 + 5489.5x - 324.09, R2=0.99**.2.The succession process of the grassland could be divided into three stages , including artificial alfalfa grassland stage (1～11 years) , transitional stage from artificial to natural grassland (11～26 years) , and natural grassland stage dominated by Stipa bungeana ( > 26 years). Alfalfa grassland had been changed to natural grassland for 26 years. It could postpone the natural vegetation succession process with applying fertilizer.3.The soil water wasted seriously with alfalfa growth years, and the dried soil layer became thicker and thicker. The depth of dry layer below 2m changed from 1.2m(the second year of planting) to 8.6m(the 18th year), the water content of which was only 8.7%; the soil water above 3m soil layer could recovered naturally, but that was difficult for below 3m layers.4.With the years of alfalfa growth, the content of soil organic matter, total nitrogen, and total phosphorus increased 1.8~40.9%, 6.7%～47.2%, and 3.3%~16.4%, respectively. But the content of available phosphorus decreased from 13.23mg/kg (the 1st year of planting) to 2.65 mg/kg (the 26th year), and the decrease rate was 80.0%. The balance between N and P nutrient was broken. Soil urease and alkaline phosphatase activities were increased significantly after alfalfa planted.5.The yield of alfalfa increased 14.9% per year with applying NPM fertilizer for 23 years. The soil bulk density decreased 14.2% and total soil porosity increased 7.6%. Meanwhile, the content of total organic matter, total nitrogen, alkali-hydrolyzable nitrogen and available phosphorus were increased 54.7%, 55.7%, 36.8 and 467.6%, respectively. For Long-term applying phosphorus, the yield of alfalfa increased 8.7% per year; soil bulk density increased 6.0%; total soil porosity decreased 2.4%. The total organic matter, total nitrogen, alkali-hydrolyzable nitrogen and available phosphorus content were increased 4.1%, 12.4%, 7.3% and 288.2%, respectively. With long-term NPM supply and P supply, the water content in 3m layer was decreased 63.0mm and 60.6mm, respectively. Compared with applying P, continuously applying NPM could increased the water content in 0-60cm layer.6.In the wheat-alfalfa rotation systerm, the yield of alfalfa growing for 4 years increased 82.3%, compared with that planted 1 year. Meanwhile, The content of total organic matter, total nitrogen, alkali-hydrolyzable nitrogen increased 32.3%, 18.8% ,and 15.7%, respectively. However, the available phosphorus content decreased. Soil catalase activity was reduced significantly after aldalfa planted, but urease, alkaline phosphatase, and invertase activities were increased significantly.
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