Use of saline water for irrigation in monsoon climate and deep water table regions: Simulation modeling with SWAP

SWAP (Soil-Water-Atmosphere-Plant) version 2.0 was evaluated for its capability to simulate crop growth and salinity profiles under various combinations of fresh and saline water use for irrigation at Agra (India), located in a semiarid monsoon climatic region having a deep water table. Best available water (BAW, EC 3.6dS/m) was used for pre-sowing irrigation to wheat crop and thereafter, twelve treatment combinations were imposed with four replications to supplement missed BAW water irrigations with saline water (EC 6/8 and 12dS/m). The model was calibrated and validated using measurements made in field trial during 2000–2003. A close agreement was observed between the measured data and simulated values. SWAP simulated and observed values for the relative yield ranged within absolute deviations of 4.2–9.7%. The validated model was later used to illustrate the consequences of long-term use of saline water on crop growth and salinity profiles. Simulated results confirmed that a yield potential exceeding 80% could be maintained by substituting saline waters up to 8dS/m in the absence of fresh water following a pre-sowing irrigation with BAW. This strategy helps to overcome the build-up of salts particularly in years when the monsoon rainfall is below average. It could be shown and concluded that seasonal build-up of salts due to use of saline water in winter season (November–April) crops is leached during the monsoon season (June–September) when rainfall at least during the months of July and August exceeds the potential evapotranspiration. On the whole, short-term field observations could be confirmed with application of SWAP that long-term use of saline water in monsoon climate under deep water table conditions is sustainable.