Estimating soil hydraulic properties of salt-affected agricultural fields in arid and semi-arid environments under different initial wetting conditions

Effective irrigation water management and soil salinity mitigation are crucial for sustainable development in arid and semi-arid regions. Soil hydraulic properties, such as the field saturated soil hydraulic conductivity (Kfs), play a critical role in infiltration, water retention, and salt leaching. These properties, however, vary dynamically due to soil type, irrigation, and agricultural practices, making their accurate estimation challenging. This study estimates the soil hydraulic properties under different wetting conditions, before and after irrigation during the dry season and no-rainfall period in Kenya's Perkerra and Tana Irrigation Schemes to inform monitoring and understand irrigation effects on soil. Single-ring infiltration measurements were performed and the Green-Ampt model, including a modified version for falling water head conditions (GA-G model), was used with Near Least Squared Optimization (NLSO) for parameters estimation . Different calibration strategies were implemented, either allowing parameters to vary within fixed ranges or setting them a priori based on soil characteristics. Results showed that infiltration rates decreased 1.8 times at Perkerra and 2.4 times at Tana after irrigation, reflecting reduced Kfs due to altered soil structure and moisture. Kfs decreased by 4.2 to 4.4 times in Perkerra and 1.1 to 1.6 times in Tana post-irrigation. These reductions highlight significant changes in soil hydraulic properties due to irrigation and agricultural practices. A modified GA-G model accounting for preferential flows (GA-GPF model) achieved better fitting of experimental data. Finally, results were compared with estimates from Rosetta's pedotransfer model. This study highlights the importance of monitoring soil hydraulic properties to enhance irrigation practices and mitigate salinity globally.