Role of Soil Profile Depth in Effective Irrigation Scheduling

The depth of the soil profile is a critical factor in irrigation engineering, often estimated as 1–1.5 meters, usually referred to as root zone depth below ground based on crop and soil types, as well as practitioner experience. This traditional approach can lead to errors in irrigation planning. This study combines Richards' equation with the Soil Conservation Service Curve Number (SCS-CN) method and soil column principles from geotechnical engineering to create a formula for determining the adequate soil profile depth that provides the maximum water storage capacity. This soil profile depth depends on the soil's hydraulic and storage properties. The relationship is then linked with the SCS-CN parameter (curve number) for practical applications like irrigation scheduling. Results of this study show that for sandy soil, the proposed method can save 83% and 75% of irrigation water compared to the traditional fixed depths of 1.5m and 1m, respectively. For clayey soil, water savings can reach 94% and 92%, respectively. This method also helps to estimate field capacity, average moisture content, and maximum water storage capacity for various soil types, improving water management and irrigation efficiency in field applications.