JWSS - Journal of Water and Soil Science

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Limitation of suitable water resources is the most important problem of agriculture in Iran. Considering the condition of shallow and saline groundwater in many parts of Iran, and relative resistance of safflower to salinity, it is necessary to study the contribution of groundwater to water consumption of safflower. In this research, the effects of different water table depths and salinity of groundwater on contribution of groundwater to evapotranspiration of safflower were studied. The treatments were four levels of water table depth (50, 70, 90, and 120 cm), two levels of groundwater salinity (EC of 0.6, and 10 dSm^-1 ), and two irrigation regimes (irrigation with a depth of water equal to 75 percent of evaporation from water surface and frequency of 5 days, and no irrigation). The experiment was performed in a randomized complete block design with treatment combinations arranged in factorial manner and three replications. For fixing the water table in the pots (PVC pipe 200 mm in diameter and 120 cm high), a special equipment was built on the principle of Marriot bottle that was able to measure the contribution of groundwater to evapotranspiration of the plants. Results showed that salinity of groundwater, irrigation regime, and their interactions have significant effects on evapotranspiration of safflower. In addition, effects of water table depth, salinity of groundwater, irrigation regime, interaction of salinity and water table depth, interaction of water table depth and irrigation regime, and interaction of water table depth, salinity, and irrigation regime on evaporation from soil surface were significant. The ratio of contribution of groundwater to plant water consumption and evapotranspiration was in the range of 52.5 and 54.9% for saline groundwater and 81.7 to 82.7% for fresh groundwater. The ratio of evaporation from soil surface and evapotranspiration was in the range of 4.5 to 53.6% for different treatments. In all treatments of groundwater depths, irrigation treatment significantly decreased evapotranspiration, but no significant change in evapotranspiration was observed in irrigated and no irrigated treatments. Maximum amount of evapotranspiration (251 cm) occurred in the 50 cm depth of groundwater with salinity of 0.6 dS/m under irrigated condition, and minimum amount (43.9 cm) occurred in the 90 cm depth to groundwater with salinity of 10 dS/m under no irrigation condition. Generally, salinity of groundwater caused significant decrease in evapotranspiration, evaporation from soil surface, transpiration, and contribution of groundwater to evapotranspiration.