Phosphorus cycle in agricultural soils. Phosphorus forms and P-sorption properties after long-term mineral and manure applications

Food production requires the application of phosphorus (P) containing-fertilizers but phosphate is a finite reserve that has been estimated to last about 90 yr. In agricultural lands, where the excessive use of fertilizers occurs, significant diffuse P losses to surface and groundwater have been found. Thus, the high P concentration in waters is a major cause of eutrophication with detrimental impacts on the water quality for both of the ecosystem and human health. The knowledge of the different forms of P in the soil and the reactions that happens between P and the soil components is important to better understand the phosphorus behaviour in soils. The effects of a long-term mineral and organic fertilization in three different alkaline soils was considered and the occurrence of different forms of P were investigated. The high fertilisation strictly increased the P saturation of soils, especially in the superficial layers, thus evidencing the resulting movement of P throughout the soil profiles. The movement of the soluble and available P forms from the upper to lower layers has been confirmed in a study on soil profiles and down to 100 cm depth. Relationship between soil test P (STP) and the water soluble P evidenced the necessity of estimating the losses of P via subsurface when P exceed both agronomic and environmental thresholds. Keeping agronomic STP below the environmental threshold is important in developing sustainable agricultural systems, as well as many other areas where human activity impacts on the environment.