Natural and forced soil aeration during agricultural managed aquifer recharge

One of the suggested approaches to mitigate the chronic groundwater depletion in California is agricultural managed aquifer recharge (Ag‐MAR), in which farmland is flooded using excess surface water in order to recharge the underlying aquifer. Successful implementation of Ag‐MAR projects requires careful estimation of the soil aeration status, as prolonged saturated conditions in the rhizosphere can damage crops due to O2 deficiency. We studied the soil aeration status under almond [Prunus dulcis (Mill.) D.A. Webb] trees and cover crops during Ag‐MAR at three sites differing in drainage properties. Water application included several cycles (2–7) and flooding durations (27–63 h) that varied according to the soil infiltration capacity at each site. We used O2 and redox potential as soil aeration quantifiers to test the impact of forced aeration by air‐injection compared with natural soil aeration. Results suggest an average increase of up to 2% O2 at one site, whereas mixed impact was observed at the two other sites. Additionally, no impact on crop yield was observed for one growing season. Results further suggest that natural aeration can support crop O2 demand during Ag‐MAR if flooding duration is controlled according to O2 depletion rates. In large Ag‐MAR projects, forced aeration might be useful to improve local zones of O2 deficiency, which are expected to occur due to topographic irregularities and spatial variability of drainage properties. Core Ideas Soil aeration is suppressed by saturation during Ag‐MAR, which may lead to yield loss. Ag‐MAR soil aeration is better characterized by measuring both soil O2 and redox potential. Adequate aeration of the root zone can be sustained by limiting flood duration. Forced aeration by air injection with subsurface drip can enhance soil aeration during Ag‐MAR.