OPTIMISING WATERMELON IRRIGATION WATER PRODUCTIVITY ON CLAY SOILS IN BARINGO COUNTY: THE ROLE OF SUPER ABSORBENT POLYMER

Abstract

The design and management of irrigation systems require a detailed understanding of soil water movement and distribution. Effectiveness of drip irrigation depends on optimising parameters like frequency, duration, emitter discharge rate, and tubing placement. Numerical simulation helps in evaluating and refining these practices for efficient irrigation. In the ASALs of Kenya, rainfall variability across and within the seasons has resulted in soil moisture deficits. The study tends to determine the soil wetting pattern that meets crop growth conditions thereby reducing evaporation and ensuring water availability to crops. The objective of this research was to optimise watermelon crop water productivity from the water distribution patterns of surface drip irrigation to assess how different frequencies, durations, and soil super absorbents. The simulation used the Hydrus-2D model to analyze soil wetting patterns in Baringo County, a semi-arid region facing drought and inconsistent rainfall. Experimental plots were set up in Noiwet, Mogotio Sub County, with various irrigation frequencies (daily, every two days, every three days) and durations (full, half, one-third of standard time), incorporating soil super absorbents in some treatments. Each setup was replicated three times, and soil wetting depth and width were measured after irrigation using a ruler. Watermelon crops were planted to evaluate water productivity based on different wetting patterns. The Hydrus-2D simulation assessed variations in soil wetting, and water productivity was calculated from crop yields and water usage. Results indicated that soil wetting patterns increased in diameter and depth with reduced irrigation frequency and longer duration. The highest watermelon yield (36.7 ton/ha) was achieved with no super absorbent polymer, irrigated every two days for 9 hours. After calibration the Hydrus-2D model accurately simulated wetted diameters, with a coefficient of determination (R²) of 0.98. It also effectively simulated wetted depths with an R² of 0.99. The optimal treatment, identified using MINITAB software, was daily irrigation for half the standard duration, achieving the best water productivity (18.24 kg/m³) with a soil wetted volume, diameter, and depth of 10,862.3 cm³, 21 cm and 17 cm respectively. This finding suggests that a larger wetted volume does not always equate to higher productivity, and reducing irrigation time can lead to optimal yields. The findings of this study can be used to minimize water loss by reducing evaporation, hence increasing crop production and consequently leading to food sufficiency