Impact of Drip Irrigation on Groundwater Under Contrasting Soil and Hydrogeological Conditions: A Case Study of Cotton in the Khorezm and Andijan Regions, Uzbekistan

Drip irrigation is promoted in Uzbekistan as the main water-saving technology, yet its effect on the groundwater regime depends on site conditions. This study compared drip and furrow irrigation of cotton (Gossypium hirsutum L.) at two sites with medium loam soils but contrasting hydrogeology: salinization-prone meadow-alluvial soils with shallow groundwater (2.0–2.3 m; 1.5 g L⁻¹) in Khorezm (Yangibazar district, 2021–2023) and non-saline light sierozems with deep groundwater (3.5–5.0 m) in Andijan (Jalakuduk district, 2022–2024). Seasonal irrigation depth, groundwater table and salinity, the water–salt balance of the root zone and seed cotton yield were moni-tored. Drip irrigation reduced seasonal irrigation by 36.0–41.1% in Khorezm and by 43.3–47.2% in Andijan. In Khorezm, the water table rose by 0.55 m during the growing season under furrow irrigation but only by 0.20 m under drip, remaining below the 2.0 m critical depth (2.10 m) at the end of the season. Salt input to the soil de-creased by 27.7% and the estimated drainage load by 70.8%, while capillary rise still supplied 25–30% of the total water input. In Andijan, the groundwater regime was practically independent of the irrigation method (change ≤0.01 m), and the benefits were limited to water saving and a yield gain of 0.41 t ha⁻¹. The best regimes were a pre-irrigation soil moisture threshold of 70–80–60% of field capacity with one lateral per row and 1.8 L h⁻¹ emitters in Khorezm (4.23 t ha⁻¹; 1.49 kg m⁻³), and 70–70–60% of field capacity in Andijan (4.23 t ha⁻¹; 1.35 kg m⁻³). Under shallow groundwater, capillary rise must be included in drip irrigation scheduling, and autumn–winter leaching remains necessary.