A Study On The Characteristics Of Phosphate Adsorption-Desorption And The Control Of Phosphorus Loss Under Typical Soils In Hunan

With the increasing of application rate year by year, the cumulant of P in farmlands also increased gradually, yet the phosphorus loss (runoff and leaching) became the main source of eutrophication and aroused people's attention. The methods of field monitoring and constant-temperature incubation experiment were adopted to study the forms and contents of P, the characteristics and influencing factors of phosphate adsorption and desorption, the characteristics of phosphorus leaching and the influence of different ecological intercept methods on phosphorus runoff in typical soils(red soil, alluvial soil and purple soil) under different use patterns. The results are as follows:(1) Parent material type and soil utilization both have obvious effect on the distribution of phosphorus.The levels and forms of phosphorus in different soil showed a marked difference: the sequence of phosphorus content from high to low was alluvial soil, red soil and purple soil. Al-P and Fe-P had a high percentage in acidic soil, while Ca-P in alluvial soil and purple soil. Phosphorus's level was the highest in surface soil, and then its content decreased firstly and then tended to be relatively stable. Al-P, Fe-P and O-P mainly enriched in0-20cm soil layer and their distribution trend in the profile was similar to the total P, yet Ca-P had a little change in the profile. Because of different land use pattern, the content of the total P also showed a difference:paddy>dry land. Different types and utilization of soils had a significant effect on content and morphological characteristics of phosphorus, so the control of the risk of phosphorus'loss should be based on different soil types and utilization.(2) The characteristics of phosphate adsorption and desorption in soils under different soil utilizations showed a large difference.The process of soil phosphorus adsorption and desorption is carried out in stages, Langmuir equation has a higher fitting degree than Freundlich equation and the correlation coefficients of Langmuir equation are all above0.9. It is found by comprehensively taking Qm (maximum quantity of adsorption), K (adsorption constant) and MBC (maximum buffing capacity) into account, upland soils are larger than paddy soils in both intensity and capacity of P adsorption. The desorption rate increases with the level of adsorbed P, its size order is dry land<paddy soil. Qm is positively correlated with the content of <0.02mm clay and amorphous iron, the correlation coefficient is0.953and0.938respectively. The characteristics of phosphate adsorption and desorption varies greatly, different phosphorus management measures should be adopted in view of the different soil to achieve crop production and protect environment benefits.(3)A big difference of critical values appeared among different soils, the critical values of phosphorus leaching in6soils fluctuated between9.854-65.372mg·kg-1. The process of phosphorus leaching is carried out in stages and there is a critical point on every curve. The phosphorus concentration in the leaching liquid increased as phosphorus concentration in the eluent increased. The phosphorus leaching risk of six different soils arrays in turn as follows: soil21> soil40> soil1>soil29> soil54> soil47.There was a significantly negative correlation between the critical value of phosphorus leaching and Olsen-P, Fe-P, Al-P, the correlation coefficients were-0.950,-0.834and-0.897respectively.(4) Particulate phosphorus (PP) was the major form of phosphorus loss with the run off, parent material types of soil, rainfall and fertilization are the factors influencing phosphorus loss. The forms, content of phosphorus and the slit loss presented large differences, ecological intercept techonolgy can reduce the phosphorus loss.Compared with conventional fertilization (Ⅰ), treatment(Ⅲ),(Ⅴ) and (Ⅵ) reduce the loss of phosphorus effectively and their loss amount reduced by29.7%,35.9%and26.6%respectively. Treatment(Ⅱ)(mulching straw) shows the best effect, but it increased the loss of water-soluble phosphorus significantly. Thus, more field test should be carried to evaluate the effect of ecological intercept technology on phosphorus comprehensively.(5) Phosphorus source and the ways of phosphorus loss are indispensable elements for phosphorus which desorbed out of soil migrating into water, so we should put more attention on them. On the one hand, the proper application of phosphorus should be carried according to the SPR under different soils and land use patterns and the organic fertilizer should be applied with inorganic fertilizer reasonably; at the same time, we can change the farming conditions to improve availability of phosphorus and reduce the application of phosphorus fertilizer. On the other hand, ecological interception measurements such as buffer zone, wetland, and pond and so on should be used to control the migration of phosphorus from farmlands to water. Ecological intercept treatments can effectively reduce the silt loss, which will greatly decrease the concentration and content of phosphorus in the runoff.