Relative sensitivity of ESP profile to spatial and temporal variability in cation exchange capacity and pore water velocity under simulated field conditions

To assess the effects of spatial variability in soil properties and temporal variability in irrigation water quality, a number of simulations are carried out using an analytical and numerical model (UNSATCHEM). The scaling theory is used for the variability of hydraulic conductivity, and thus for the variability of flow. Monte Carlo simulations are also carried out to investigate the effect of spatial variability of cation exchange capacity on exchangeable sodium percentage (ESP) profile. Field data, published for the semi arid Hisar region in the Haryana State of India, indicate that the cation exchange capacity (Q) and the pore water velocity (image) are log normally distributed. Randomly generated values of Q, image and joint variable Y (equal to image) are used in spatial analysis. Results reveal that spatial variation of the cation exchange capacity and pore water velocity have little effect on ESP development in topsoil, where the soil solution reaches local equilibrium with irrigation water and thus the maximum value of ESP is observed. The alternate use of alkali groundwater and canal water is the cause for temporal variability of irrigation water quality, which significantly influences the ESP-values that develop in the topsoil. The CO2 concentration in root zone, annual rainfall, amount of fresh water available for irrigation and soil texture also affect the alkalisation. Results obtained will be helpful in finding better conjunctive use plans of alkali and canal water depending upon the irrigation water quality and crop tolerances at different growth stage.