Effects of shallow groundwater management on the spatial and temporal variability of boron and salinity in an irrigated field

In some irrigated regions, the disposal of agricultural drainage waters poses significant environmental challenges. Efforts are underway to develop irrigation water management practices that reduce the volume of drainage generated. One such management strategy involves restricting flow in subsurface drains in an effort to raise the water table and induce the consumption of groundwater by crops. A potential complication with this management approach is that upward groundwater flow may salinize the soil and increase concentrations of phytotoxic elements such as B. In this study, salinity and B concentrations were monitored for 3 yr in a 60-ha agricultural field located in San Joaquin Valley, California. The irrigated field was managed according to a restricted drainage, shallow groundwater management technique. Salinity and B measurements were made biannually at approximately 75 sites within the field. Soil salinity and B concentrations were found to be highly correlated in the field. The observed spatial and temporal variability in B and salinity was largely a product of soil textural variations within the field and the associated variations in salt leaching. During the 3-yr study, the field changed very little from one year to the next, although within a given year there were fluctuations related to cropping and irrigation practices and to environmental conditions. However, any changes arising during the growing season were erased in the fallow season by winter rainfall and preplant irrigations that uniformly leached salts from approximately the top 1 m of the field. Overall, it appears that the shallow groundwater management program used in this study could be continued and sustained in this field without increasing soil salinity or B concentrations, and without decreases in yield.