Effect of Soil Moisture Distribution of HDPS Cotton under Deficit Subsurface Drip Irrigated Condition

Cotton (Gossypium spp.) is an economically important fibre crop. In India, cotton is cultivated in about 129 lakh hectares with a total production of 336 lakh bales and an average productivity of 443 kg ha⁻¹. In recent years, the High-Density Planting System has emerged as a promising technology for enhancing cotton productivity. Efficient irrigation management is crucial for sustaining yield under limited water availability. A field experiment was conducted during the summer and winter seasons of 2024-25 at the Wetland Farm, Department of Agronomy, Tamil Nadu Agricultural University, and Coimbatore, to study soil moisture dynamics in HDPS cotton under subsurface drip irrigation. The experiment was laid out in a split-split plot design with three irrigation levels in the main plots (1.0, 0.8 and 0.6 ETc), two cotton varieties in the sub-plots (CO 17 and VPT 2) and three nitrogen management strategies in the sub-sub plots (control, 100% RDN through granular urea, and 50% RDN through granular urea + nano urea applied in three splits at 25, 45 and 65 DAS), each replicated thrice. Soil moisture distribution was assessed at 0-10 cm and 10-20 cm depths during the vegetative stage in both seasons. Results revealed that soil moisture content was higher under 1.0 ETc irrigation compared to 0.8 and 0.6 ETc levels. Across irrigation treatments, soil moisture was highest near the drip line at the centre of the bed and gradually decreased towards the periphery of the wetting front. Vertically, the 10-20 cm depth consistently recorded higher soil moisture content than the 0-10 cm depth, irrespective of irrigation regimes. These findings highlight the potential of subsurface drip irrigation for efficient soil moisture management and sustainable cotton production under water-limited conditions.