Phosphorus release kinetics in a soil amended with biosolids and vermicompost

Abstract

Wastewater biosolids are large potential sources of macronutrients for agriculture, conservation and restoration of soils; there are, however, few studies on phosphorus (P) release in soils amended with biosolids. Biosolids and vermicomposted biosolids were tested in concentrations (5–30 g amendment kg−1 soil) equivalent to 18–100 Mg ha−1. Desorption of P was determined by successive extractions for 65 days. Soil P was low, and biosolid and vermicompost addition released 8 and 6 times more P, respectively, than soil alone. To describe the release of P, zero-, first- and second-order equations, simple Elovich and power functions and the parabolic diffusion law were compared based on their coefficient of determination (r 2) and standard error (SE). In all treatments, the power function and especially the parabolic diffusion law were the best fit, with 0.898–0.996 r 2 and 0.022–0.732 SE. The general behavior of the kinetic parameters mostly depended on the amendment doses. Eutrophication posited to start beyond 16 mg P kg−1 soil was more likely allayed by a maximum vermicompost dose of 50 Mg ha−1, higher than the 36 Mg ha−1 maximum biosolid dose. The higher vermicompost P addition and lower P release could favor gradual and longer-term P absorption by plants and may reduce leaching or runoff P losses.