The use of HYDRUS-2D to simulate intermittent Agricultural Managed Aquifer Recharge (Ag-MAR) in alfalfa in the San Joaquin Valley

Authors: BALI, KHALED - Kearney Agricultural Center; MOHAMED, ABDELMONEIM - Kearney Agricultural Center; Begna, Sultan; Wang, Dong; PUTNAM, DANIEL - University Of California, Davis; DAHLKE, HELEN - University Of California, Davis; ELTARABILY, MOHAMED - University Of California, Davis

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2023
Publication Date: 3/30/2023
Citation: Bali, K.M., Mohamed, A.Z., Begna, S.H., Wang, D., Putnam, D., Dahlke, H., Eltarabily, M.G. 2023. The use of HYDRUS-2D to simulate intermittent Agricultural Managed Aquifer Recharge (Ag-MAR) in Alfalfa in the San Joaquin Valley. Agricultural Water Management. 282. Article 108296. https://doi.org/10.1016/j.agwat.2023.108296.
DOI: https://doi.org/10.1016/j.agwat.2023.108296

Interpretive Summary: Agricultural Managed Aquifer Recharge (Ag-MAR) is a potential and sustainable practice where agricultural lands can be used to recharge depleted aquifers using excess rainfall surface water during winter. This practice has been implemented in California to address some of the recurring droughts and groundwater depletion and potentially to comply with Sustainable Ground Water Management Act (SGMA). A two-dimensional model, HYDRUS-2D, was used to estimate the net recharge amount (below the 1.20 m alfalfa rootzone) of Ag-MAR on sandy loam alfalfa field experiment at University of California, Kearney Agricultural Research and Extension Center in the San Joaquin Valley, California in 2020-2022. The alfalfa field had two irrigation treatments: full irrigation (FI) during the entire growing season (March thru November) and mid-summer deficit irrigation (MSDI) treatments. Ground water recharge flux, evapotranspiration, soil moisture dynamics, and root water uptake were simulated for the recharge period in mid- to late- winter in alfalfa. Previously FI treatments led to cumulative groundwater recharge (calculated from soil water balance) of 1458.6, 1687.4, and 1415.1 mm for 2020, 2021, and 2022, respectively amounting 85, 89, and 84% of the applied irrigation water in these years, respectively. MSDI treatment had net groundwater recharge of 1336.5, 1497.8, and 1272.3 mm for 2020, 2021, and 2022, respectively. Simulation results showed that the potential recharge under FI scenario were much greater than in the MSDI treatment. A very good agreement was obtained between the HYDRUS-2D simulations and soil water balance measurements with R2= 0.91, and 0.89 for the previous FI and MSDI treatments, respectively. Results from this study provided us with a better understanding of the potential implementation of different Ag-MAR strategies on agricultural fields of alfalfa with various irrigation practices such as FI and MSDI. Results from this work could help in providing stakeholders in California with tools for sustainably managing groundwater recharge using alfalfa fields in the San Joaquin Valley and utilizing Ag-MAR as part of meeting the SGMA goals as an integral part of California's water portfolio to sustain groundwater resources.

Technical Abstract: Agricultural Managed Aquifer Recharge (Ag-MAR) is a potential and sustainable practice where agricultural lands can be used to recharge depleted aquifers using excess rainfall surface water during winter. This practice has been implemented in California to address some of the recurring droughts and groundwater depletion and potentially to comply with Sustainable Ground Water Management Act (SGMA). However, there is little information on the amount of Ag-MAR that can be applied on crops such as alfalfa, a crop suitable for such practice. A two-dimensional model, HYDRUS-2D, was used to estimate the net recharge amount (below the 1.20 m alfalfa rootzone) of Ag-MAR on sandy loam alfalfa field experiment, at University of California, Kearney Agricultural Research and Extension Center in the San Joaquin Valley, California in 2020-2022. The alfalfa field had two irrigation treatments: full irrigation (FI) during the entire growing season (March through November) and mid-summer deficit irrigation (MSDI) treatments (complete irrigation cutoff after the August cutting). Recharge flux, evapotranspiration (ET), soil moisture dynamics, and root water uptake were simulated for the recharge period in mid- to late- winter. Actual alfalfa evapotranspiration (ETa) values during the the flooding periods were 134.8, 150.3, and 186.2 mm, for 2020, 2021, and 2022 respectively. Rainfall values during the flooding periods were 51.9, 27.9, and 40.4 mm for 2020, 2021, and 2022, respectively. Previously FI treatments led to cumulative groundwater recharge (calculated from soil water balance) of 1458.6, 1687.4, and 1415.1 mm for 2020, 2021, and 2022, respectively. These amounts corresponded to net recharge of 85.07, 89.07, and 84.12% of the applied irrigation water in 2020, 2021, and 2022, respectively. While MSDI treatment had net groundwater recharge of 1336.5, 1497.8, and 1272.3 mm for 2020, 2021, and 2022, respectively amounting 77.94, 79.06, and 75.63% of the applied irrigation water. Simulation results showed that the potential recharge under FI scenario were 1536.0, 1707.1, and 14666.9 mm with 89.58, 90.09, and 87.20% of the applied water for 2020, 2021, and 2022, respectively. The MSDI treatment resulted in reduction in cumulative recharge flux as compared to FI treatments due to the initial low soil water storage. The simulated recharge amounts of the MSDI treatment were 1365.2, 1576.8, and 1390.7 mm amounting 79.62, 83.22, and 82.67% of the applied water for 2020, 2021, and 2022, respectively. A very good agreement was obtained between the HYDRUS-2D simulations and soil water balance measurements with R2= 0.91, and 0.89 for the previous FI and MSDI treatments, respectively. Results from this study provided us with a better understanding of the potential implementation of different Ag-MAR strategies on agricultural fields of alfalfa with various irrigation practices such as FI and MSDI. Results from this work could help in providing stakeholders in California with tools for sustainably managing groundwater recharge using alfalfa fields in the San Joaquin Valley and utilizing Ag-MAR as part of meeting the SGMA goals as an integral part of California's water portfolio to sustain groundwater resources.