Changes in inorganic phosphorus fractions in weathered soils under long-term intensive cultivation and irrigation

Conventional intensive cultivation tends to modify the interactions of phosphorus in soil, favoring inorganic forms transformations. The aim of the study was to evaluate the status of inorganic phosphorus and correlate with the chemical, physical and mineralogical soil properties in areas under natural vegetation and different cultivation periods: 1, 17, 22, 28, 32 and 43 years. Soil P was extracted using Chang and Jackson method (Al-P, Fe-P, Ca-P and Residual-P). The micro-chemical map of P concentrations within the representative aggregates was determined by electron probe. Results showed that biofertilizers application in the area under intensive cultivation for 32 years of use significantly increased all soil P fractions (4.249 mg kg−1 in upper soil layer). There was a slight increase in the P at the edges of the aggregates in the first year (0.23%), but at 43 years, there was an increase in contents within the aggregates (0.32%). The intensive cultivation promoted the increase of P content in soil fractions in the arable layer of the soil over time. However, the decline in inorganic P contents after a few years of cultivation suggests that the soils of the studied areas tend to exceed their maximum adsorption capacities in the future.