The high accumulation of phosphorus in high-yield paddy soils: A new insight from cutans

Phosphorus (P) is a key limiting nutrient for crops. Oscillation of redox conditions usually induces formation of Fe-enriched cutans in the plow layer of paddy soils. This study investigated P biogeochemistry in the cutans, which were collected from high-yield paddy soils in Taihu Lake region, China. Mo & BULL;ssbauer spectroscopy showed that the content of Fe3+ was eight times higher than Fe2+ in the cutans. Based on the evidences from XRD and wet chemical analysis, the enriched Fe in the cutans mostly existed as amorphous oxides, which owned high surface areas for P sorption. In addition, the cutans were composed of spherical particles with diameters of 20-130 & mu;m under microscopy. Moreover , the particles showed evident "trench" structures on their top surface under SEM imaging. These features caused the cutans to retain three times higher P than that in the matrix soils. Furthermore, the cutans demonstrated both high microbial richness and community diversity, in contrast to the matrix soils. In particular, the abundance of phosphate-solubilizing fungi (with relatively highly competitive saprophytic ability) was also significantly promoted. Therefore, the cutans could be considered as hotspots of P accumulation in paddy soils. The subsequent enhancement of the available P would promote rice production.