Intensive agricultural practices have significantly degraded physical soil structure and biological function, and altered global N, P, and C cycles in ways that increase dependence on non-renewable nutrient inputs and the potential for nutrient loading in connected ecosystems. Soil health frameworks present a robust and promising approach for shifting soil management paradigms away from simple chemical fertility and toward a focus on soil building and biological nutrient cycling. Existing soil health frameworks include robust assessments of active organic matter fractions and potential organic N, but treatment of P fertility remains relatively simplistic, relying on the same extractable P tests used in standard agronomic soil testing. This study assesses acid phosphatase, the soil enzyme exuded by microbes and some plant roots to hydrolyze important labile organic phosphorus fractions, was assessed on 19 vegetable farms in the Northeastern U.S. across a range of soil and management types. Additionally, soils were assessed for existing soil health metrics that are used to indicate soil C accretion and microbial nutrient cycling (active carbon, short-term mineralizable carbon, soil organic matter). A linear regression model was then fit to consider the potential for current soil health frameworks to capture potential organic P supply and the utility of incorporating the phosphatase assay.
Results/Conclusions
Phosphatase levels increase significantly with management practices that incorporate biomass-based fertilizers such as composted manure, which also correlates with higher levels of soil organic matter. Modeling significantly explains variation in phosphatase levels (R2 = 0.65), with short-term mineralizable carbon proving the most significant (p = 0.000). Yet, while soil test P levels were significantly lower in soils with higher phosphatase levels, soil test P was not significant in the model. Furthermore, the majority of soils assessed had soil test P levels well into the excessive range, suggesting that phosphatase levels in this study may not be a response to P deficiency as past research indicates. These findings suggest that while phosphatase and organic carbon fractions may be sensitive to management, they may not effectively capture biological phosphorus provision in agricultural soils.