Study On Phosphorus Adsorption And Desorption Characteristics Of Soil Aggregates In Upland Red Soil Under Long-Term Different Fertilizations

In the red soil areas of our country, due to the special soil formation process, the nutrient phosphorus in plant is very insufficient and it has became one of the main obstacle factors for agricultural production in this region. Soil aggregates is an important component of the soil which is both the basic unit of soil structure and the carrier of plant nutrients. Fertilization can improve the soil nutrient status effectively, which can also indirectly affect the trend of change in soil aggregates and soil phosphorus supply capacity. Therefore, study the composition of soil aggregates under different fertilization as well as soil phosphorus adsorption and desorption characteristics and explore their mechanism is really important for improving the soil phosphorus supply capability. This study use the18a long-term fertilization to do the following research:1) The study of phosphorus fixation ability of soil aggregates aroused from different fertilizations;2) The main impact factors of soil phosphorus adsorption and desorption;3) The analysis of soil phosphorus loss risk of soil aggregates in upland red soil.Use Langmuir equation to get relative parameters of adsorption-desorption procedure to study the adsorption-desorption behaviors of phosphorus on diverse sized soil aggregates originated from different fertilization. The results showed that, phosphorus fertilization, on the one hand, could increase the contents of soil macro-aggregates, total phosphorus and available phosphorus; on the other hand, it significantly reduced the maximum adsorption amount of P and maximum buffer capacity of P and obviously increased soil phosphorus desorption rate. The absorption quantities of phosphate on different aggregate in red upland soil increased with the particle size decreasing. The situation was different in desorption phase, the minimum desorption amount of phosphorus appeared in1～0.25mm aggregates. The long-term inorganic fertilizer joined with stable manure fertilization improved the aggregate composition and the content of macro-aggregates in red soil, At the same time, it decreased the phosphorus fixation in soil aggregates to enhance the efficiency of soil phosphorus in upland red soil.Use Langmuir equation and then get the relative parameters of adsorption-desorption procedure to study the main impacting factors of phosphorus adsorption-desorption behavior in red soil aggregates. The results showed that, after the removal of the organic matter, aggregates with different sizes of every treatment had higher adsorption isothermal curves and larger adsorption quantities than them without treatment. But aggregates with different sizes of every treatment after the removal of ferric and aluminum oxides had lower adsorption isothermal curves and less adsorption quantities than original ones. The differences between different treatments were not significant and the adsorption isothermal curves of different treatments were very similar. This study also showed that the1～0.25mm aggregates had the biggest phosphorus adsorption capacity in these four kinds of aggregates and calcium could cut down the phosphorus adsorption affinity. The result indicated that the ferric and aluminum oxides were important for soil phosphorus adsorption. Increase of soil organic matter, application of lime and decrease of the soil1-0.25mm aggregates contents could reduce the phosphorus fixation in soils.Useing Langmuir equation, the soil easy desorption phosphorus, the obtain balance concentration of phosphorus, the Saturation ratio of soil phosphorus were calculated. Using the relationship of easy desorption and available phosphorus to analyze the risk of the soil phosphorus loss in upland red trailed soil. The result showed that:except for the aggregate with2～1mm and0.25～0.053mm diameter of NK and green manure treatments, the available phosphorus content of different aggregates in other treatments exceed20mg kg-1, It means that the aggregates in upland red soil under long term phosphorus fertilization has already been phosphorus abundant. Specially, the aggregates of stable manure were in the high phosphorus content level and the content increase in the bigger ones. Under this situation, further fertilization is not necessary for common crops’ growth. Available phosphorus content of manure treatment even in0.25～0.053mm aggregates which has the lowest content compare to other aggregates has already got9times exceeding content of phosphorus for crop growth and it is higher than the mutation site of the loss risk220.52mg kg-1. At the same time, the soil DPS values has exceeded environmentally sensitive critical value for15percent which indicate that the risk of soil phosphorus loss has already exit and reducing the phosphorus fertilization is considerable.