Agroecological Impacts from Salinization and Waterlogging in an Irrigated River Valley

Extensive field data and calibrated flow and salt-transport models characterize the spatial and temporal patterns of salinity and waterlogging in an irrigated western river valley. Over three irrigation seasons, average seasonal aquifer recharge from irrigated fields in a 50,600  ha study area ranges from 0.59  to  0.99  m, including contribution from precipitation. The salinity of irrigation water varies from 618  to  1,090  mg/L. The water table is shallow, with 16 to 33% of irrigated land underlaid by an average water table less than 2  m deep. Average water table salinity ranges from 2,680  to  3,015  mg/L, and average soil salinity from 2,490  to  3,860  mg/L. Crop yield reductions from salinity and waterlogging range from 0 to 89% on fields, with regional averages ranging from 11 to 19%. Annual salt loading to the river from subsurface return flows, generated in large part by dissolution from irrigation recharge, averages about 533  kg/irrigated  ha  per  km. Upflux from shallow water tables under fallow ground contributes to about 65  million  m3 (52,600  acre-ft) per year of nonbeneficial consumption. Beyond problem identification, the developed database and models provide a basis for effectively addressing these problems through a systematic and comparative assessment of alternative solutions.