Phosphorus forms and behaviors in selected heavily fertilized soils

Abstract

The objective of this study was to characterize the heavily fertilized soils of northern Iran for their phosphorus (P) fractions and sorption properties for assessing their P availability status in order to minimize P applications and to reduce the danger of P loss to water sources. Different P fractions, namely, total, organic, inorganic, water extractable, and NH₄-lactate extractable P varied widely among the studied soils, indicating a wide variability of P supplying capacity of these soils. High values of degree of phosphorus saturation were observed in soils with low amounts of organic carbon (C) and may indicate high P susceptibility to surface runoff and leaching. The maximum P buffering capacity (MPBC) and adsorption isotherm of P were highest in the sandy clay soil from Jamaleddinkola, which also contained high amounts of iron (Fe), aluminium (Al) and clay particles, and lowest in sandy soil from Deseleh, which contained very high initial NH₄-lactate extractable P and the lowest content of Fe, Al, silt and clay among all the studied soils. The results suggest the importance of accounting for soil properties (especially soil texture and organic matter) along with soil P adsorption capacity when assessing the efficiency of applied P, P accumulation in soils and subsequently P nutrient management.

Keywords:

• phosphorus sorption
• fractionation
• heavily fertilized soils