Phosphorus Sorption and Redistribution on Soil Solid Phase in a Brazilian Haplorthox Amended with Biosolids

Land application of biosolids (SS) can cause a buildup of phosphorus (P) in the top soil. The changes in the soil P characteristics may be assessed by the sorption isotherm and the sequential fractionation techniques. Samples of Haplorthox were collected from a field experiment where maize was cultivated for two years, after two applications of SS originated from two cities of São Paulo State, Brazil. SS applications added a total of 125, 250, 500, 1000 and 2000 kg ha−1 of P in the area. To perform the sorption isotherms and obtain P maximum sorption capacity (Qmax) and the binding energy, soil samples were submitted to increasing P concentration solutions until equilibrium was reached. Sequential fractionation was done by a sequential extraction with CaCl2, NaHCO3, NaOH, HCl, and HNO3 + HClO4 (residual). Addition of biosolids from both cities to the soil decreased Qmax and the binding energy obtained by the Langmuir equation. SS additions changed the P fractions distribution in the soil by increasing the labile fractions (P-CaCl2 and P-NaHCO3) and the moderately labile fraction (P-NaOH) by 11.2% and 20.3%, respectively, in detriment of the most resistant P fraction