Gypsum is one of the most commonly used soil amendments for reclaiming sodic soils. Laboratory column study was conducted to evaluate the effect of gypsum applied @ 0, 25, 50 and 100 per cent of the gypsum requirement on the behaviour of native phosphate (P) during reclamation of a highly sodic soil (pH 10.4, ESP 83.5). The soil was leached with good quality water (EC 0.3 dS m−1) under a constant water head for ten weeks and phosphate concentration in the leachate was measured at weekly intervals. Samples of leached soil were also subjected to P fractionation to determine how the various inorganic fractions responded to the added gypsum. Results showed that increasing levels of gypsum drastically reduced the P losses and at the 6th week of the experiment no phosphorus was detected in the leachates. Increasing rate of gypsum decreased the water soluble P (H2O-P) substantially but it had little effect on the more strongly adsorbed P fraction (NaOH-P) or Ca-bound P (HCl-P). The main effect of gypsum was to transform the adsorbed P fraction (NaHCO3-P) more labile.
Gypsum, leaching, phosphorus, reclamation, sodic soil
