Phosphorus speciation in manure and fertilizer impacted Mid‐Atlantic coastal plain soils

Abstract

AbstractHistorical applications of manures and fertilizers at rates exceeding crop P removal in the Mid‐Atlantic region (United States) have resulted in decades of increased water quality degradation from P losses in agricultural runoff. As such, many growers in this region face restrictions on future P applications. An improved understanding of the fate, transformations, and availability of P is needed to manage P‐enriched soils. We paired chemical extractions (i.e., Mehlich‐3, water extractable P, and chemical fractionation) with nondestructive methods (i.e., x‐ray absorption near edge structure [XANES] spectroscopy and x‐ray fluorescence [XRF]) to investigate P dynamics in eight P‐enriched Mid‐Atlantic soils with various management histories. Chemical fractionation and XRF data were used to support XANES linear combination fits, allowing for identification of various Al, Ca, and Fe phosphates and P sorbed phases in soils amended with fertilizer, poultry litter, or dairy manure. Management history and P speciation were used to make qualitative comparisons between the eight legacy P soils; we also speculate about how P speciation may affect future management of these soils with and without additional P applications. With continued P applications, we expect an increase in semicrystalline Al and Fe‐P, P sorbed to Al (hydro)oxides, and insoluble Ca‐P species in these soils for all P sources. Under drawdown scenarios, we expect plant P uptake first from semicrystalline Al and Fe phosphates followed by P sorbed phases. Our results can help guide management decisions on coastal plain soils with a history of P application.