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 sitespecific 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 ( qfc) 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 qfc. The results showed that the optimized FC at qfc 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 (ETc) 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.

Automated summary

This study focused on determining zone-specific field capacity (FC) and irrigation thresholds using a negligible drainage flux (qfc) criterion in Alabama, USA. The results showed that the optimized FC values were more accurate than the raw values, and the proposed method can help improve irrigation management.