Study On Adsorption And Desorption Of Soil Phosphorus In Loess Plateau Ang The Influencing Factors

Phosphorus (P) is an essential nutrient in crop production. On the one hand, low availability of phosphorus hardly meet the need of crops. P was absorbed, fixed, and deposited by soil. Therefore, there an important attention to how improve soil P and its availability. On the other hand, phosphorus is an important element for water eutrophication, and water pollution by phosphorus loss caused worldwide attention. Calcium carbonate content was high in Loess Plateau soils, which is one of the main matrix for fixed P. Among different soils or on the same soil different layers from top to bottom, the contents of calcium carbonate were obviously different, resulting in a great difference on P adsorption and desorption. Phosphorus adsorption by calcium carbonate was often found previously, however, phosphorus desorption by calcium carbonate was less studied previously, As the environment temperature and bicarbonate ion concentration increased and pollutants such as organic acids in the water and the application of organic fertilizer increased, these will result in changes of P in adsorption and desorption. This is not only related to adjust soil phosphorus nutrient, but is also related to release of phosphorus to the water and environment. So, the study on phosphorus adsorption and desorption is significant.Adsorption and desorption of phosphorus of loess plateau soil such as Lou soil , HeiLu soil and HuangMian soil was studied, which was treated with or without carbonate (1%, 3%, 5%). Based on these study, effects of temperature, bicarbonate, organic acids and manure on the release of phosphorus were investigated, The following was main conclusion of the study and progress:1. At the low P concentration mixed with soil, phosphorus adsorption order of three soils was Lou soil>HeiLu soil>HuangMian soil. While, at the high P concentration mixed with soil, HeiLu soil> Lou soil>HuangMian soil. The order of three contrasted soils about the maximum phosphorus adsorption capacity, phosphorus equilibrium constant, and the maximum buffering capacity of phosphorus was HeiLu soil> Lou soil> Huang Mian soil. As calcium carbonate mixed with the soil, phosphorus adsorption capacity and strength of adsorption (K) have showed an increase trend. Compared with the control, with the relative content of calcium carbonate increasing, phosphorus adsorption by soil gradually increased. When adding phosphorus concentration of 40μg /ml, and the calcium carbonate contents of three soils (Lou soil, HeiLu soil, HuangMian soil) increased by 1%, phosphorus adsorption of three soils averagely increased by 3.69%, 2.84%, and 2.11%, respectively. So, phosphorus adsorption of Lou soil increased more greatly than other soils.2. Phosphorus desorption order of three soils was HuangMian soil>HeiLu soil>Lou soil. Compared with the contrasted soils, when adding phosphorus concentration of 40μg/ml, and the calcium carbonate contents of three soils (Lou soil, HeiLu soil, HuangMian soil) increased by 1%, phosphorus desorption rate of three soils averagely decreased by 1.43%, 0.42%, and 1.50%, respectively. So, phosphorus desorption of Lou soil and HuangMian soil decreased more greatly. The increase of calcium carbonate content reduced the phosphorus release of soil. Order of phosphorus desorption rate in three treatments was 5%CaCO3<3%CaCO3<1%CaCO3<0%CaCO3. In the same phosphorus concentration (40μg/ml) conditions, the order of three soils on phosphorus desorption rate was Lou soil (30.68%)< HeiLu soil (33.92%) Lou soil> HuangMian soil.6. At the phosphorus concentration of 50μg/ml, and compared with the control, the phosphorus release contents of the soils (Lou soil, HeiLu soil and HuangMian soil) with organic manure treatments averaged 36.20mg/kg, 15.77mg/kg, and 6.55mg/kg higher than the contrast, respectively. Phosphorus release rate of soils averagely increased of 12.53%, 7.36%, and 4.26%, respectively. Effect of application of organic manure on phosphorus release in three soils was with the order of Lou soil> HeiLu soil> HuangMian soil. Effect of Organic manure on the phosphorus release of soils decreased with the added calcium carbonate increasing.7. At the added phosphorus concentration of 50μg/ml, the phosphorus release contents of the soils (Lou soil, HeiLu soil and HuangMian soil) with oxalic acid treatments averaged 57.02 mg/kg, 58.54mg/kg, and 55.30mg/kg higher than the control respectively, and release rate of soils averagely increased 16.21%, 13.98%, and 13.93%, respecticvely. The phosphorus release contents of the soils (Lou soil, HeiLu soil and HuangMian soil) with citric acid treatments on average exhibited 34.64mg/kg, 38.32mg/kg, and 21.60mg/kg higher than the control respectively, and release rate of soils averagely increased of 9.37%, 9.08%, and 5.49%,respecticvely. The phosphorus release rate of soils with oxalic acid treatment was higher than that of citric acid treatment, and the phosphorus release effect of organic acids on Lou soil was more obvious. With the increase of calcium carbonate, the effect of oxalic acid and citric acid on phosphorus release was increased in Lou soil and HeiLu soil and the effect on phosphorus release in HuangMian soil decreased when calcium carbonate was added at 5% level.