Modeling for conjunctive use irrigation planning in sodic groundwater areas

Prevalent irrigation water quality guidelines for use of sodic groundwater on sandy loam soils of Haryana for kharif (monsoon) fallow–rabi (winter) wheat crop rotation were investigated through modeling with UNSATCHEM. Three sandy loam soils that vary with respect to soil CEC (Cation Exchange Capacity) and Ks (Saturated Hydraulic Conductivity) were considered in the modeling. A procedure was developed to identify safe SAR value for sodic groundwater at a constant RSC for individual farm/soil considering soil CEC and proportions of sodic and fresh waters used for irrigation as variables. The criterion was that if the SAR of available sodic groundwater exceeded the safe SAR-value for irrigation water, a reduction in crop yield occurs. With this assumption, the procedure was tested with published data and the specific data collected from farmers’ fields. If SAR of groundwater exceeds the safe SAR-value, rice–wheat rotation is assumed to be not sustainable in the long-term. The sustainability of rice–wheat crop rotation in sodic groundwater areas in the Assandh and Nissang blocks of the Karnal district of Haryana was assessed. The described procedure of identifying the safe SAR-values for individual farm/soil is more appropriate and flexible than already existing guidelines and could be easily used for efficient conjunctive water use planning of sodic and fresh water.