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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]

To promote the environmental sustainability of rural sanitation, a soil moisture controlled wastewater subsurface drip irrigation (SDI) dispersal system was field tested in the Black Belt Prairie of Alabama, USA. The soil moisture control strategy was designed to regulate wastewater disposal timing according to drain field conditions to prevent hydraulic overloading and corresponding environmental hazard. CW2D/HYDRUS simulation modeling was utilized to explore difficult-to-measure aspects of system performance. While the control system successfully adapted hydraulic loading rate to changing drain field conditions, saturated field conditions during the dormant season presented practical application challenges. The paired field experiment and simulation model demonstrate that soil biofilm growth was stimulated in the vicinity of drip emitters. Although biofilm growth is critical in maintaining adequate COD and N H 4 + − N removal efficiencies, the efficient removal of biodegradable COD itself by soil biofilm limits denitrification of formed N O 3 − − N. Furthermore, stimulated soil biofilm growth can create soil clogging around drip emitters, which was discerned in the field experiment along with salt accumulation, both of which were verified by simulation. Comparable modeling of system performance in sand and clay media demonstrate that the placement of soil moisture sensors within the drain field can have pronounced impacts on system hydraulic performance, depending on the soil permeability. Overall, the soil moisture control strategy tested is shown as a viable supplemental technology to promote the environmental sustainability of rural sanitation systems. • The system prevents hydraulic dosing during unfavorable drain field conditions. • Bacterial growth around the drip emitters is crucial for wastewater treatment. • Organic carbon and heterotrophs profiles mismatch the demand of denitrification. • System performance is sensitive to soil permeability and feedback sensor position. [ABSTRACT FROM AUTHOR]