Speciation and microscale distribution of phosphorus compounds accumulated in continuously fertilized greenhouse soils

Abstract

The overuse of phosphate fertilizer results in the accumulation of surplus phosphorus (P) compounds in soil, and this trend is particularly intense in greenhouse farming.We aimed to characterize P compounds in greenhouse soils by comparing their speciation in soil samples collected from greenhouses and an open field. Two soil types with different phosphate sorption abilities, namely, Ultisol and Andisol, were considered. Phosphorus compounds in the soil were characterized by bulk soil analysis via acid extraction; molecular-scale analyses by solid-state 31 P nuclear magnetic resonance and P K-edge X-ray absorption near edge structure and spatially resolved analyses by electron probe microanalyzer and micro-X-ray absorption near edge structure. Spectroscopic results showed that a larger proportion of P compounds associated with inorganic P compounds associated with calcium (Ca-P) was present in the greenhouse soil than in the open-field soil. Some P compounds in the greenhouse Andisol were Ca-P, even though Andisol has a high phosphate sorption ability due to an abundance of aluminum-bearing sorbents. Heterogeneously distributed spots of Calcium phosphate, most likely hydroxyapatite or tricalcium phosphate, were found at the microscale in the greenhouse Ultisol soil grain. In addition to the detection of poorly-soluble Ca-P, a larger proportion of Ca-P was potentially plant available. Spatially resolved analyses showed that organic amendments containing Ca-P were incorporated into the Andisol soil grains. Our study demonstrated that Ca-P with different solubilities can serve as a source of phosphate even in soils of high phosphate sorption ability under greenhouse conditions.

Long‐term dairy manure amendment promotes legacy phosphorus buildup and mobility in calcareous soils

“…To determine the less soluble Ca‐P species in the soils, two acid extractions of the soils were performed: (1) 0.001 M H 2 SO 4 (pH = 3), which dissolves the readily available soil P (Truog‐P) (Truog, 1930), and (2) 0.44 M acetic acid (Ac‐P), which is a proximate total soil Ca‐P determination (Yamaguchi et al., 2023). The difference between the dissolved P from these two acid extractions is an estimate of less soluble soil Ca‐P (Yamaguchi et al., 2023). For the Truog‐P extraction, 0.15 g soil was added to 30 mL 0.001 M H 2 SO 4 (pH = 3 adjusted with ammonium sulfate) and shaken for 30 min.…”

“…Additionally, many sequential extraction tests have been developed to interpret speciation of P in the soils (Zhang & Kovar, 2009); however, their accuracy is often critiqued (Barrow et al, 2020). A recent study combined solid-phase nuclear magnetic resonance spectroscopy with P extractions of Andisol and Ultisol soils (pH 6.54-6.77) to discern P species targeted by 0.44 M acetic acid extraction (pH 2.56) and confirmed that the Ca-associated P peak in the soil disappeared after extraction, indicating the dissolution of the Ca-P minerals in the soils (Yamaguchi et al, 2023). They also showed that a soil extraction that used 0.001 M sulfuric acid solution at pH 3, called Truog-P, dissolved the readily soluble Ca-P but not the less soluble Ca-P that was extracted with the acetic acid extraction.…”

“…The readily soluble Ca‐P is an important indicator of plant‐available P from soils (Nagumo et al., 2013; Susuki et al., 1963; Truog, 1930). Based on these results, it is proposed that the difference between 0.44 M acetic acid extractable soil P (Ac‐P) and Truog‐P is a good estimate of the amount of less soluble Ca‐P in the soil (Yamaguchi et al., 2023).…”