Potential for managed aquifer recharge on alfalfa crop land in California.
University of California, Davis
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Agricultural groundwater banking (ag-GB) seeks to opportunistically use winter storm flows from surface water sources for the artificial recharge of groundwater by spreading water onto crop land. Among the over 400 crops grown in California alfalfa represents an attractive cropping system to implement ag-GB practices on. Alfalfa is attractive for ag-GB for several reasons: 1) it comprises greater than one million acres in CA (high probability of finding suitable soil types and infrastructure); 2) it requires relatively low N fertilizer and agrochemical inputs compared to other crops (limited environmental impact of flooding); and 3) it is often flood irrigated using surface water (high capacity conveyance system). In addition, utilizing mature alfalfa fields at or near the end of a rotation (e.g. after 4 years) poses little risk for economically significant crop loss or negative environmental impacts. Preliminary studies of the tolerance of alfalfa to large winter irrigation events conducted during the 2014/2015 recharge season suggest alfalfa is capable of withstanding cumulative applications of water in the order of 4 to 6 feet during the months of January, February and March. Where water was delivered to fields as several pulsed applications, no complications due to excess water were observed. In a treatment where water was continuously applied to dormant alfalfa over a 6 week period, with a cumulative application of 29 feet of water, a statistically significant decline of biomass was observed in the second cutting. Since site specific characteristics influence the subsurface storage capacity, travel times and the recoverability of “banked” water at these preliminary experimental sites more research is necessary to identify the bounds on crop tolerance for different site conditions.