Natural and forced soil aeration during agricultural managed aquifer recharge

Abstract

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 O 2 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 O 2 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% O 2 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 O 2 demand during Ag-MAR if flooding duration is controlled according to O 2 depletion rates.In large Ag-MAR projects, forced aeration might be useful to improve local zones of O 2 deficiency, which are expected to occur due to topographic irregularities and spatial variability of drainage properties.

A model for estimating Ag-MAR flooding duration based on crop tolerance, root depth, and soil texture data

“…Hence, we neglect the presence of impermeable layers or shallow groundwater that may restrict deep percolation. Ponded infiltration is expected during Ag-MAR (Bachand et al, 2014;Dahlke et al, 2018a;Dokoozlian et al, 1987;Ganot and Dahlke, 2021) and the 1D assumption is justified by the relatively large horizontal dimensions of a flooded agricultural field (Philip, 1992) while the justification of the homogenous soil profile is site-specific. Water application duration (t wap ), with minimal crop loss, can be estimated based on crop tolerance to waterlogging (t crop ), time to saturate the soil (t sat ) up to the critical water content (θ c ) that blocks oxygen transport at the effective root-depth, and time to drain the soil (t drain ) back to θ c to allow re-aeration of the effective root zone (Fig.…”

“…Field data of four soils from Ag-MAR and flood irrigation studies (Dahlke et al, 2018a;Ganot and Dahlke, 2021;Kallestad et al, 2008a) were used to test the model. Data included volumetric water content and soil oxygen (or redox potential) that were used to obtain θ c for each soil.…”

“…Data included volumetric water content and soil oxygen (or redox potential) that were used to obtain θ c for each soil. For more details on the adequacy of these measurements to quantify the soil aeration status under flooded conditions see Mukhtar et al (1996), Kallestad et al (2008b) and Ganot and Dahlke (2021). We defined the measured θ c as the soil water content value after which soil oxygen recovery begins (i.e., when soil respiration ≈ oxygen supply; see the minimum point on the O 2 curve in Fig.…”

“…This includes crop tolerance to flooding, soil aeration, biogeochemical transformations, long-term impact on soil texture, leaching of pesticides and fertilizers to groundwater, and potential greenhouse gas emissions. Some of these issues have been addressed in recent studies of Ag-MAR, including soil suitability guidelines (O'Geen et al, 2015), nitrate leaching to groundwater (Bachand et al, 2014;Bastani and Harter, 2019;Waterhouse et al, 2020), crop suitability (Dahlke et al, 2018a) and soil aeration (Bachand et al, 2019;Ganot and Dahlke, 2021). In the current study, we focused solely on the question of "how long can water be applied for Ag-MAR with minimal crop damage?…”

Managed aquifer recharge site assessment with electromagnetic imaging: Identification of recharge flow paths

“…The objective is to have the applied water percolate through the subsurface to the water table, which marks the top of aquifer and intended storage location, thus replenishing the groundwater system and storing groundwater for future use in dry years. However, this method involves certain risks that are related to the conditions and hydrogeologic properties of the selected site: Slow infiltration of the water could lead to ponding at the surface or lingering of water in the root zone, both of which may weaken the roots and bases of trees, leaving them susceptible to damage in strong winds (Dahlke et al., 2018; O'Geen et al., 2015; Ganot & Dahlke, 2021). Slow infiltration and subsequent ponding can lead to increased evaporative loss. If the spatial distribution of the sediment types favors lateral over vertical movement, the water may be unable to reach the intended storage location.…”