Phosphorus Accumulation, Translocation In Soils Of Sunlight Greenhouse

Phosphorus (P) as an essential element of plant has been considered as the main factor leading to eutrophication problem. The excessive accumulation of soil P could decrease P adsorption ability, and it is easier for P to lose from soil and contaminate water body. The greenhouse area has increased quickly in recent years in north China, and great use of manure and P fertilizer causing P accumulated a lot in greenhouse soil. Recent studies most concentrated on the accumulation form and content of soil P in the surface layer, but researches about accumulation characteristics of soil P in the subsurface layer are rare. There is a close relationship between P leaching and adsorption characteristic, while few studies are conducted on it in greenhouse.In that case, this study was carried out to study the form and content of accumulated P, adsorption characteristics of soil P, and leaching characteristics of accumulated P in different years of greenhouse, evaluate the accumulation and leaching characteristics of P in greenhouse, and provide the science knowledge on guiding the reasonable fertilization and protecting environment. The conclusions were as follows:(1) The content of organic matter increased with the years of greenhouse, and pH of soil in greenhouse was lower than that of field soil. The contents of total P, Olsen-P and H2O-P of greenhouse soil significantly increased in comparison with the crop land. The averages of Olsen-P and H2O-P in 0～20cm layer of greenhouse soil were 227 mg kg^-1 and 8.45 mg kg^-1, respectively. The contents of total P, Olsen-P and H2O-P in 0～20cm layer of greenhouse soil were 1.78, 8.00 and 3.70 times that of crop land soil, respectively; for the 20～40cm soil layer, the contents of total P, Olsen-P and H2O-P was 0.62, 3.24 and 2.53 times that of crop land soil, respectively. The contents of different forms of P increased as the greenhouse planting lengthening. There were significant positive correlation between soil TP, Olsen-P, and H2O-P, as well as the relationship between Olsen-P and H2O-P.(2) Langmuir equation of soil P in different years of greenhouse showed that, the Langmuir equation fitted the phosphorus isothermal adsorption curve of soils very well. In comparison with cropland soil, the maximum phosphorus adsorption of greenhouse soil was decreased; and the maximum phosphorus adsorption of greenhouse soil was also decreased as the increasing years of soil under sunlight greenhouse. Among different soil types, the maximum phosphorus adsorption of Lou soil was higher than alluvial soil. Among different soil layers, the maximum phosphorus adsorption of the 20⁴0cm layer was higher than the 0²0cm layer. The constant K value in the greenhouse was also lower than the cropland soil, and it decreased with the greenhouse plant years increased. Correlation analysis showed that soil organic matter content, phosphorus content, pH value were the main factors affecting soil phosphorus sorption in greenhouse.(3) Undisturbed soil column is used to study the characteristics of the movement of P in greenhouse, the results showed that the concentration of P in leached solution in 10 years greenhouse was significantly higher than that in one year greenhouse, and the corresponding value in greenhouse was higher than that in cropland. The total leaching amount of P in10 years greenhouse (28.93mg /soil column) was significantly higher than that in one year greenhouse(10.94 mg /soil column), and the corresponding value in one year greenhouse was also significantly higher than that of cropland soil(1.22 mg /soil column). These results demonstrated that the amount of P loss through leaching increased with the lengthening of greenhouse cultivating. Soluble P was the main form in the leaching solution. Molybdate reactive phosphorus (MRP) was the main form in soluble P in leaching solution in greenhouse cultivation, while Particulate phosphorus (PP) was the main form in cropland soil.(4) It was generally acknowledged that, when the content of Olsen-P surpassed 60 mg kg^-1, or DPS was higher than 25%, leaching loss of P would happen. According to these two indices, the content of soil Olsen-P and DPS were both greater than the critical values in the older greenhouses in this study, which indicated that the P leaching risk caused by the excessive accumulation of soil P in greenhouse should be paid more attention.