Physical and physico-chemical changes in the profile of sodic soil treated with gypsum

Detailed examination of the profile of a brown sodic soil, 40 months after gypsum application, revealed that the effects of gypsum have extended down to a depth of 30 cm compared to 15-20 cm observed about seven months after the treatment. Comparisons also suggested that processes such as leaching and reaction with CO2 created by plant roots have been in operation as evidenced by reduced electrical conductivity (EC) down to 45 cm depth and pH in the 15-30 cm layer of the treated plots. Although the pH was significantly reduced in the surface layer (0-7.5 cm) of the control plots, the EC was increased. Probable reasons for this are discussed. Soil physical improvements in the profile were measured in terms of water penetration and storage, water desorption, aggregate stability, and relative hydraulic conductivity. Field measurements suggested that gypsum did not affect the bulk density in the profile, but increased water penetration and storage. In the laboratory, increased hydraulic conductivity (K), aggregate stability (ASI), and air-filled porosity were obtained for the samples collected from gypsum treated plots down to 30 cm depth. Highly significant negative correlations between the physical parameters (K, ASI) and the corresponding exchangeable sodium percentage (ESP) values supported the conclusion that physical improvements were consequences of gypsum treatment.