Characterizing groundwater use by cotton using weighing lysimeters

摘要

Two weighing lysimeters were used to measure crop evapotranspiration of subsurface drip irrigated cotton. A saline water table (14 dS/m) was maintained in one of the lysimeters. Groundwater use as part of crop evapotranspiration was characterized using hourly measurements of the water level in a groundwater supply tank (Mariotte bottle). Irrigation management, changes in crop water requirements, and changes in soil hydraulic conductivity were shown to affect saline groundwater use. Groundwater contribution of up to 30 percent of daily crop water use was measured. On a seasonal basis, only 8 percent of the total crop water use originated from the groundwater. Data were compared to previously developed crop coefficients, and some adjustments were made to these coefficients. The largest groundwater contribution was shown to occur at the end of the growing season, when roots are fully developed and irrigation is terminated. Differences in root development were observed in the presence of shallow groundwater compared with no groundwater table.