Abstract
AbstractAgricultural managed aquifer recharge (Ag‐MAR) is a concept in which farmland is flooded during the winter using excess surface water to recharge the underlying groundwater. In this study, we show how different recharge practices affect NO3− leaching and mineralization–denitrification processes in different soil systems. Two contrasting soil textures (sand and fine sandy loam) from the Central Valley, California, were repeatedly flooded with 15 cm of water at varying time intervals in field and soil column experiments. Nitrogen species (NO3–, NH4+, total N), total C, dissolved O2, and moisture content were measured throughout the experiments. Results show that when flooding occurs at longer intervals (every 1–2 wk), N mineralization increases, leading to an increase of mobile NO3− in the upper root zone and leaching of significant quantities of NO3− from both soil textures (137.3 ± 6.6% [sand] and 145.7 ± 5.8% [fine sandy loam] of initial residual soil NO3−) during subsequent flooding events. Laboratory mineralization incubations show that long flooding intervals promote mineralization and production of excess NO3− at rates of 0.11–3.93 mg N kg–1 wk–1 (sand) and 0.08–3.41 mg N kg–1 wk–1 (fine sandy loam). Decreasing the flooding frequency to 72 h reduces potential mineralization, decreasing the amount of NO3− leached during flooding events (31.7 ± 3.8% [sand] and 64.7 ± 10.4% [fine sandy loam] of initial residual soil NO3–). The results indicate that implementing recharge as repeated events over a long (multiple‐week) time horizon might increase the total amount of NO3− potentially available for leaching to groundwater.
Highlights
Dependence on groundwater for irrigation and consumptive use has resulted in the widespread depletion of groundwater aquifers across the world (Dalin et al, 2019; Wada et al., Abbreviations: Agricultural managed aquifer recharge (Ag-MAR), agricultural managed aquifer recharge; HF, high-frequency flooding; LF, low-frequency flooding; MAR, managed aquifer recharge; total C (TC), total carbon; total N (TN), total nitrogen; VWC, volumetric soil water content; water applications (WAs), water application.2014)
Moisture sensors showed that flooding events on the fine sandy loam took between 48 and 72 h to return from saturation (0.35– 0.4 cm3 cm−3) to pre-flooding soil water content (0.15– 0.2 cm3 cm−3)
Total NO3––N loads in the 400-cm soil cores taken from the flood-irrigated fine sandy loam before Ag-MAR flooding were lower than those from the sand, between 26.0 and 99.1 kg ha−1 in the Ag-MAR treatment and 21.3 and 201.6 kg ha−1 in the control in 2015–2016
Summary
Dependence on groundwater for irrigation and consumptive use has resulted in the widespread depletion of groundwater aquifers across the world (Dalin et al, 2019; Wada et al., Abbreviations: Ag-MAR, agricultural managed aquifer recharge; HF, high-frequency flooding; LF, low-frequency flooding; MAR, managed aquifer recharge; TC, total carbon; TN, total nitrogen; VWC, volumetric soil water content; WA, water application.2014). Managing groundwater in California has increased the interest in and use of managed aquifer recharge (MAR) technologies that purposefully recharge water to aquifers for subsequent recovery or environmental benefit (Dillon et al, 2009). Agricultural managed aquifer recharge (Ag-MAR) is a promising form of managed aquifer recharge, where farmland is flooded during the winter using excess surface water in Vadose Zone J. Over 3.6 million ha of suitable farmland that is connected to water conveyance systems has been identified for Ag-MAR throughout the Central Valley of California (O’Geen et al, 2015). Some of these lands support infiltration rates in excess of 50 cm d−1, raising questions on how Ag-
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