2017 OFR demonstration site monitoring and analyses: Effects on soil hydrology and salinity, and potential implications on soil oxygen

Abstract

On-farm recharge (OFR) is a practice that uses surface water to alleviate demand on and replenish groundwater supplies. It can take on two forms: in lieu recharge and direct recharge. In lieu recharge utilizes surface water supplies instead of groundwater to irrigate crops. Direct recharge applies water beyond the needs of the crop and replenishes the groundwater supply. ...The present study examined OFR with grapes, walnuts, and pistachios at six sites in the San Joaquin Valley, plus one additional site from a previous study, also in the San Joaquin Valley. Each site was comprised of a recharge plot that received direct recharge paired with a control plot with the same crop and soil characteristics, but meant to receive in lieu recharge (via the flood system) or drip application with groundwater. At the end of the 2017 recharge demonstration, however, three control plots had also received direct recharge from water applications that exceeded the crop’s water demand. At another site, both control and test plots had only received in lieu recharge due to limited surface water amounts or the host growers’ more conservative volume of water application. ...The present study only covers one season of recharge. Long-term effects of recharge are not described by the present study and will require further monitoring. Further study is needed of the dynamics of soil oxygen during and after recharge events. Similarly, the fate of the water after it infiltrates past the root zone is not always known and the rate at which recharged water will reach an aquifer is seldom known for deep aquifers. A method to predict the fate of water quickly and broadly would be quite helpful in developing an on-farm recharge strategy. The present study does not look at the effects of recharge on soil biological processes, such as microbial respiration and plant oxygen demand. Further study of the recharge tolerance of specific species and rootstocks, as well as the impact on plant disease, is crucial.