Enhancing Water Security Through Automated Drip Irrigation: Impacts on Soil Moisture Dynamics and Brinjal Yield in Semi-arid Systems

Improving irrigation efficiency is essential for sustaining vegetable production in water-limited environments, yet field-scale evaluations of practical time-based automated drip irrigation systems remain limited. This study compared an Automated Drip Irrigation Treatment (ADIT) employing scheduled time-based irrigation with a Manually Operated Drip Irrigation Treatment (MDIT) under polythene mulch for brinjal ( Solanum melongena L. ) cultivation in sandy loam soil during the 2025 Yala season in Sri Lanka. Soil moisture dynamics, irrigation uniformity, root distribution, wetting patterns, crop water requirement, yield, and irrigation water-use efficiency (IWUE) were evaluated using field measurements together with CropWat and HYDRUS-1D simulations. ADIT achieved consistently higher irrigation performance, with Christiansen’s coefficient of uniformity (CU) of 91–93%, emission uniformity (EU) of 90–92%, and distribution uniformity (DU) of 88%, compared with 75–80%, 78–82%, and 72%, respectively, under MDIT. Improved water distribution resulted in more stable root-zone soil moisture conditions, while HYDRUS-1D simulations predicted substantially lower deep percolation losses under ADIT than MDIT during crop development. Field observations also showed greater lateral root spread (40.7 cm vs 33.0 cm), higher irrigation water-use efficiency (4.91 vs 3.37 kg m -3 ), and greater marketable yield (22.3 vs 16.7 t ha -1 ; 2.35 vs 1.62 kg plant -1 ) under ADIT. Because the evaluated irrigation configurations differed in hydraulic characteristics as well as irrigation control strategy, and the study was conducted as a single-season field-scale pilot without replicated treatment plots, the findings should be interpreted as comparative evidence of system-level performance rather than effects attributable solely to automation. Nevertheless, the evaluated ADIT configuration demonstrated considerable potential for improving irrigation performance and water productivity under sandy loam, semi-arid conditions, warranting validation through replicated experiments using hydraulically identical irrigation systems.