Effect Of Long-term Phosphor Fertilization On Soil Phosphorus Cycling In Dry Land On Loess Plateau

In recent years, yield and application rate of phosphorus in China have occupied the first place in the world. Accumulated P₂O₅ in the soil has reached up to 8.5×107 t from 1980 to 2007 in China, and has formed the great and potential soil phosphorus pools. Phosphorus used by crop mainly comes from soil, and phosphorus supply has important effect on yield and quality of crop. However, unreasonable and exceed using phosphorus would cause great waste and also lead to water eutrophication and bring environment risk. Therefore, comprehensive management of phosphorus is the key problem for coordination of high crop yield and environment-friendly.The research based on long-time experiment studied influence of different fertilization with wheat yield, soil nutrient and moisture change and using efficiency; studied accumulation and spatial distribution of soil inorganic phosphorus and organic phosphorus in long-term fertilization; studied leaching threshold of phosphorus in different fertilization. It is in hope of effective utilization of phosphorus and supplying basis for agricultural production.On the basis of nitrogen fertilizer increased the phosphate fertilizer could increase the wheat yield, the higher amount phosphorus rate (to 180 kg/hm² )and the higher and stable yield, between N₉₀P₁₃₅ and N₉₀P₁₈₀ the yield are same reached 4272.75 kg/hm². Meanwhile on the basis of nitrogen fertilizer increased the phosphate, the tend of nitrogen partial factor productivity and agronomic efficiency are release, and the phosphorus rate are 0,45,90,135,180 kg/hm² have the significant differences. The soil nutrient contents change results show that the higher the amount of phosphorus fertilizer can supplement the more soil phosphorus, soil total phosphorus and available phosphorus are also increasing. But with the increased amount of phosphorus fertilizer, Soil organic carbon and total nitrogen content is the highest as 7.985 g/kg and 0.951 g/kg in phosphorus rate (135 kg/hm²). and the phosphorus fertilizer can significantly increase the content of soil available K. In different fertilization systems, the water consumption of the N₉₀P₁₈₀ fertilizer can up to 634.1mm, water use efficiency up to 17.4 kg/(ha·mm),and with the increase of water consumption at the same time, the soil appears dry trend. Accumulative phosphorus in the soil has existed mainly in the form of Ca₈-P, Al-P, O-P and Ca₁₀-P in long-term different fertilization. Phosphorus applied to soil changed to Ca₂-P and Ca₈-P firstly, and could not change to O-P easily, but long-term using phosphorus could cause accumulation of Ca₈-P and change to Ca₂-P, so content of O-P increase gradually, and Ca₁₀-P decrease gradually. The results of matrix analysis and path analysis of the components of total phosphorus and organic phosphorus to available phosphorus are that available phosphorus mainly from total phosphorus; soil available phosphorus directly from Ca₂-P; main changing from Ca₈-P to Ca₂-P has indirect effect on available phosphorus content; Al-P and Fe-P could be called active slowly available phosphorus; Ca₁₀-P is the stable component of soil inorganic phosphorus, and O-P and Ca₁₀-P are called potential phosphorus.CaCl₂-P content in arable layer and spatial distribution in profile is generally lower in calcareous soil of north China, and it is considered that soil has strong retention and fixing effect to phosphorus. Arable layer (0-40cm) shows surface aggregation, CaCl₂-P content increases quickly with phosphorus rate, and CaCl₂-P content in max phosphorus rate (180 kg/hm²) is the 10.94 times more than CaCl₂-P content without applied phosphorus. CaCl₂-P shows"S"curve in spatial distribution in soil profile which below 40cm and its content is concentrated between 0.01 and 0.1 mg/kg, which has small amplitude. Soil available phosphorus and water solvable phosphorus have significant correlation with different phosphorus rate. Used Heckrath split-line model, it could get leashing threshold in calcareous soil of northwest China, Olsen-P content is 75.8 mg/kg, and phosphorus existed in the soil maybe output soil through run off and leashing furthermore cause pollution risk to water.Organic phosphorus among different phosphorus rate in arable soil has not significant difference in long-term applied phosphorus. The correlation coefficient between soil organic phosphorus content and total phosphorus content, inorganic phosphorus content, available phosphorus content are 0.7358**, 0.74**, 0.9406**, which reach very significant level.