Shallow Groundwater Use 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 use 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 (2m) increased over the years. The columns with higher salinity (EC > 4dS/m) in the shallow groundwater experienced increasing salinity in the soil profile with time, resulting in reduced crop water use from shallow groundwater. Periodic leaching will be required for in-situ use to be a sustainable practice. Statistical analysis demonstrated that shallow groundwater, even marginally saline, contributed significantly to crop yield with significant differences occurring between treatments. Trend analysis demonstrated a significant reduction in yield with time for higher salinity groundwater treatments (EC> 4dS/m), and was characterized by a simple inverse relationship of the log transformed groundwater salinity. Comparing yield data from the control treatment to the groundwater treatment suggests that alfalfa yield could be enhanced from the presence of groundwater salinity up to 6 dS/m at least for the first few years.