A methodology to optimize site-specific field capacity and irrigation thresholds.

The determination of field capacity (FC), irrigation thresholds, and irrigation amounts is characterized by site-specific soil hydraulic properties (SHPs). This study, conducted in two zones (zone 1 and zone 2) delineated based on soil, topography, and historical crop yield in Alabama (USA), focused on determining zone-specific FC using negligible drainage flux q fc criterion. The HYDRUS-1D model was used to optimize zone-specific SHPs using measured soil matric potential (h). The zone-specific FCs were determined using optimized and raw SHPs at 0.01 cm/day as q fc. The results showed that the optimized FC at q fc was at −39 kPa in zone 1 and raw FC was at −15 kPa. However, in zone 2, optimized FC was at −25 kPa and raw FC was at −59 kPa. To validate that optimized values are more accurate than raw values, a relationship between accumulated crop evapotranspiration (ET c) and required irrigation amount was determined using optimized parameters (SHPs and FC) and showed a stronger correlation in both zones than using raw parameters (SHPs and FC). At flux-based FC, the optimized irrigation thresholds and amounts in zone 1 were −88 kPa and 20 mm, and raw irrigation threshold and amount were −58 kPa and 33 mm, respectively. In zone 2, the optimized irrigation thresholds and amounts were −45 kPa and 18 mm, and raw irrigation threshold and amount were −116 kPa and 14 mm, respectively. Therefore, using raw and benchmark FC can result in inefficient irrigation strategies. The proposed novel method of optimizing zone-specific FC and irrigation thresholds can help with adopting timely best irrigation management schemes in respective zones. • Soil hydraulic properties (SHPs) were optimized using in-situ soil matric potentials (h) with inverse numerical modeling. • Field capacities (FC) were optimized at a negligible drainage flux criterion of 0.01 cm/day using raw and optimized SHPs. • h at optimized FC yielded the best irrigation recommendation relationships with accumulated crop evapotranspiration. • h at FCs were optimized to −39 kPa and −25 kPa, respectively, in zone 1 and zone 2. • Irrigation thresholds were optimized to −88 kPa and −45 kPa, respectively, in zone 1 and zone 2. [ABSTRACT FROM AUTHOR]