In situ use of groundwater by alfalfa

Disposal of saline drainage water is a significant problem for irrigated agriculture. One proposal is to recycle drainage water to irrigate salt tolerant crops until the volume has been reduced sufficiently to enable final disposal by evaporation. Part of this concept requires in situ crop water reuse from shallow groundwater; and data is needed to quantify the potential use of groundwater by alternative crops. A column lysimeter study was initiated to determine the potential crop water use from shallow groundwater by alfalfa as a function of groundwater quality and depth to groundwater. The results demonstrated that up to 50% of the crop water use could be met from shallow groundwater (<1.2 m) with an electrical conductivity less than 4 dS/m, and that the potential crop water use from deeper groundwater (2 m) increased over the years. The columns with high salinity (>4 dS/m) in the shallow groundwater experienced increased salinity in the soil profile with time, which resulted in reduced crop water use from shallow groundwater. Yields decreased with time as the groundwater salinity increased and periodic leaching will be required for in situ use to be a sustainable practice. Statistical analysis of crop yield demonstrated that there was significant use of groundwater with an EC of 6 dS/m for a few years.