Soil texture as a regulatory pathway for the enrichment of aggregate-associated phosphorus

Soil phosphorus (P) loss induced by erosion is an imminent threat to global food security, and as the linkage between erosion and P loss, aggregate is the unit for soil P storage. This study investigated the impacts of soil texture on aggregate-associated P and its enrichment rate by using soils with four typical textures (silty clay, clay loam, silty clay loam, and loam) from croplands with the same field management in Danjiangkou (Hubei, China), the water source for the Middle Route of South-to-North Water Diversion. The initial P concentration in the range of 36.5 to 411.2 mg kg(-1) was generated by laboratory incubation, and aggregate-associated P was determined by the combination of wet sieving and molybdenum blue colorimetric method. Aggregate-associated P was shown to be mainly concentrated in <0.05 mm aggregates (23.20-315.52 mg kg(-1)), accounting for 30.71%-35.28% of P concentration for a unit mass of soil. In addition, aggregate-associated P and its enrichment rate generally decreased with the decline of clay content (333.76-63.25 mg kg(-1) in 1-0.5 mm size aggregate) under the same aggregate size fraction, while they all exhibited a unimodal distribution (increasing first and then decreasing) with decreasing aggregate size. Moreover, clay content made the most contribution to the increase of aggregate-associated P (R-2 > 0.56) and its enrichment rate (R-2 = 64.4%, p < 0.01), while CaCO(3 )showed a contrary trend (R-2 > 0.56, and R-2 = 49.1%, p < 0.01). Collectively, variations of aggregate-associated P and ERi were mainly attributed to soil clay fraction-regulated P adsorption.