Validity Of The Accumulated Phosphorus Of Soil In Protective Farmland

Protective farmland derived from dark brown soils were collected for experiments about the content of different forms of phosphorus and successive spinach planting without phosphorus fertilized, searched about the validity of accumulative phosphorus and the change rule of different forms of phosphorus. In order to clarified the validity of the accumulative phosphorus in protective farmland. The results showed that the content of inorganic phosphorus, organic phosphorus and available phosphorus in protected farmland were greater than the open farmland soils were measured. Composed of the inorganic phosphorus, iron (Fe) P accounts for the main part in the protective farmland soil of 0-20 cm, and Fe-P and O-P account for the main part in the protective farmland soil of 20-40 cm, then were aluminum (Al) P and calcium (Ca) P, at least for the H2O-P. Composed of the organic phosphorus, moderately labile organic phosphorus accounts for the main part in the 0-20cm and 20～40 cm. Then were moderately stable organic phosphorus and highly stable organic phosphorus, at least for the labile organic phosphorus. The content of available phosphorus decreased under the successive spinach planting without phosphorus fertilized. The trend of total inorganic phosphorus smoothly at first and then increased a little, the trend of total organic phosphorus smoothly with cropping. Through the trend of inorganic phosphorus and organic phosphorus with cropping, Al-P, Fe-P and Ca-P could serve as a source of phosphorus. O-P could be used as slow-release source of phosphorus. Each component of organic phosphorus was trended to inorganic phosphorus. Between Bray-P, Al-P, Fe-P O-P and labile organic phosphorus were positive correlation, and H2O-P, Ca-P, moderately labile organic phosphorus, moderately stable organic phosphorus and highly stable organic phosphorus were positive correlation. While H2O-P mainly through other forms of phosphorus worked on the Bray-P. Through data analysis and model fitting obtained, the soil phosphorus deficiency critical value was 200mg·kg-1. The model:y= 4.0030+0.0295 x(R= 0.99) was obtained from data fitted. It could be used for predicted the cropping times that the phosphorus satisfied the growth of spinach when the content of Bray-P was known. Summarily, phosphorus accumulation was the main characteristic of soil in the protective farmland. Accumulative phosphorus had a higher validity. Predicted the cropping times through the model, could fully excavated the potentiality of accumulative phosphorus and reduce the use of phosphorus fertilizer. Help to improve the utilization ratio of phosphorus fertilizer and control the area pollution of phosphorus in agricultural.