Effect of long‐term fertilization on the transformations of water‐extractable phosphorus in a fluvo‐aquic soil

Abstract

AbstractImproved information on water‐extractable soil P (Pw) and its distribution in various forms is needed to assess its bioavailability and environmental impact. This study investigated Pw in a fluvo‐aquic soil solution in relation to the continuous application of inorganic fertilizer (NPK) and wheat straw–soybean‐based compost for 15 y. Phosphatase‐hydrolysis techniques were used to fractionate organic P (Po) in water extracts of soil into phosphomonoester (Pom) and phosphodiester (Pod). In comparison with the noncomposted treatments, compost application significantly increased the levels of inorganic P (Pi) and Po. Pom was the main form in water‐extractable soil Po (71%–88%), in which sugar phosphate (Pos) occupied 48%–75%, inositol hexakisphosphate (Pop) comprised 13%–23%, and Pod only accounted for a small percentage (11%–26%). Long‐term compost application significantly increased the content of Pom, Pos, and Pod, but decreased the Pop content; the ratio of Pom to Po increased significantly in compost‐treated soil, but the ratio of Pop to Po and Pod to Po significantly decreased. Thus, the equilibrium of phosphatase involved P transformations shifted to Pi in compost‐treated soil. The phosphomonoesterase and phosphodiesterase activities were significantly higher in compost‐treated soil, which favored the transformations of Pod into Pom and Pom into Pi. The ratio of Po to Pw in water extracts of compost‐treated soil was similar to that of control soils with no fertilizer input (CK), but was significantly lower than in NPK treatment, which demonstrated that a larger increase occurred for soil Pi in water extracts of compost‐treated soil. Long‐term compost application in the fluvo‐aquic soil changed the composition of Pw, promoted the rate of P transformations in soil solution, and significantly increased soil P bioavailability.