P solubility and release kinetics in the leachate of saline–sodic soil: Effect of reclamation strategies and water quality

Abstract

Phosphorus release kinetics of soil undergoing intensive leaching is important for evaluating the mobility of the soil phosphorus in an agroecosystem. The interactive effect of organic and inorganic amendments and irrigation water quality regulate the P release kinetics in the leachate during reclamation. This study attempted to characterize the P release behavior of the saline–sodic soil amended with gypsum alone (G25 and G50: 25 and 50% gypsum requirement:) or with farmyard manure (G25FYM) and city waste compost from Karnal (G25CK) and Delhi (G25CD). Amended soils were leached with canal water (CW), and saline water [60.0 me L–1 with SAR 5 (SAR5), and SAR 15 mmol1/2 L–1/2(SAR15)]. The P release was best described by the Elovich equation followed by parabolic-diffusion and power function. The slope of the Elovich (1/β), power function (b), and parabolic diffusion function (R) were 1.36, 2.62, 3.63, and 1.48, 2.43, 3.98 times greater for SAR5 and SAR15, respectively, compared to CW. The 1/β and R were lowest for G50 irrespective of water quality and increased with a decrease in gypsum applied. The 1/β and R for G25FYM, G25CK, and G25CD were 11–31% higher than the G25. The leachate index of Ca2+, HCO3–, SO42–, pH, Na+: (Cl–+SO42–) ratio explained about 76% variability in the P release rate. The 1/β and R showed a significant correlation with CEC, CaCO3, and pHs of the soil. The saturation index of P minerals was significantly greater for CW compared to SAR5 and SAR15. The higher 1/β value was associated with lower post-leaching PNaHCO3 content in the soil. During leaching, soil solution P concentration was regulated by TCP2, TCPb, and HP. This study infers that desorption and diffusion–dissolution reactions based kinetic equations can successfully explain the P release behavior in saline-sodic soil. Further, high SAR water tended to increase the leaching rate of P during reclamation and it can be managed by manipulating the Ca2+ supply in soil solution.