Site-specific irrigation scheduling using one-layer soil hydraulic properties and inverse modeling

Site-specific soil hydraulic properties (SHPs) are critical for determining irrigation thresholds and adopting the best irrigation practices. In this study, we optimized two single-layer SHPs for two management zones (namely, zone 1 and zone 2) delineated in a crop field using topographic attributes, soil texture, and historical crop yield to demonstrate the need for zone-specific SHPs. The inverse HYDRUS-1D model was used to optimize a single-layer zone-specific SHPs using multilayered observed soil water pressure heads (h) measured in both zones. Statistical indices for goodness of fit showed that a single layer SHPs simulate h during the growing season well. The irrigation thresholds and amounts determined using zone-specific optimized SHPs were used to trigger irriga-tions. Different irrigation scenarios using 15 cm, 30 cm, and 60 cm soil depths were developed using the zone-specific optimized SHPs in the HYDRUS-1D model to meet irrigation water demand and reduce water stress. The ratio of actual root water uptake (ARWU) and potential root water uptake (PRWU) were calculated to compare improvements in satisfying daily water demand and to reduce the water stress under different irrigation sce-narios. Out of the total irrigation water triggered during growing seasons, greater than 61 % and 75 % in zone 1 was triggered in July 2018 and in May-June 2019, respectively. However, greater than 73 % in July 2018 and greater than 72 % in May-June 2019 were triggered in zone 2. Based on the simulations of various irrigation scenarios in HYDRUS-1D, we found that installing sensors at 15 cm or 30 cm can help meet the daily irrigation water demand on time than sensors at 60 cm depth. This study discussed the importance of critical water de-mands due to the distribution of precipitation over the growing season and need of zone-specific optimized SHPs for site-specific irrigation management within the field.