Soil phosphatase enzyme activity as an indicator of phosphorus availability and cycling in phosphorus-deficient agricultural soils

Abstract

Phosphorus deficiency represents a major constraint limiting crop productivity across extensive agricultural regions worldwide, particularly in highly weathered soils where phosphorus becomes immobilized in unavailable forms. This research examined soil phosphatase enzyme activities as indicators of phosphorus availability and cycling across different land use types in the Pampas region of Argentina. Soil samples were collected from forest, grassland, fertilized agricultural, unfertilized agricultural, and degraded sites during autumn 2022. Both acid and alkaline phosphatase activities were quantified using p-nitrophenyl phosphate as substrate. Forest soils exhibited the highest acid phosphatase activity at 187.4 micrograms p-nitrophenol per gram soil per hour, significantly exceeding values in degraded soils which showed only 67.4 micrograms per gram per hour. Strong negative correlations emerged between available phosphorus concentrations and phosphatase activities, confirming enzyme induction under phosphorus limitation. Microbial biomass carbon showed positive correlation with phosphatase activities, indicating the predominantly microbial origin of these enzymes. The research demonstrates that phosphatase activity serves as a sensitive biological indicator of soil phosphorus status and can guide phosphorus management decisions in agricultural systems.