DEVELOPING IRRIGATION INTERVAL BASED ON SOIL MOISTURE AND EVALUATING ON-FARM IRRIGATION PERFORMANCE FOR KURAZ II SUGARCANE IRRIGATION SCHEME

Abstract

The Kuraz sugarcane irrigation scheme in Southern Ethiopia has faced considerable challenges, primarily due to inefficient irrigation scheduling and poor on-farm irrigation management practices .These issues cause either water stress or excessive water application, negatively impacts key on-farm performance indicators. This study aimed to establish soil moisture-based irrigation intervals and triggers, while evaluating on-farm irrigation performance indicators such as application efficiency, storage efficiency, and percolation loss. Soil water content before and after irrigation, along with bulk density, was estimated using the gravimetric method, and soil texture was determined using the hydrometer test. Field capacity and permanent wilting point were estimated with a pressure plate apparatus. Irrigation water application was measured using a hydro flume, and the flume discharge was calibrated with a known volume bucket. The irrigation duration was recorded using a stopwatch. Reference evapotranspiration and crop water requirements were calculated using the CropWat model based on the Penman-Monteith equation. The results revealed a mean bulk density of 1.32 g/cm³, a field capacity of 39.8%, and a permanent wilting point of 26.2%. The average actual soil moisture depletion was 37.7%, significantly lower than the FAO recommended value of 65%. Soil water content averaged 34.5% before irrigation, increasing to 38.9% afterward, close to field capacity. The average irrigation trigger point was 30.9%, lower than the soil water content after irrigation. Daily crop evapotranspiration for sugarcane ranged from 2.3 mm/day in January to 5.8 mm/day in April, with an average of 4.32 mm/day. The calculated and existing irrigation intervals for sugarcane were as follows: 8 & 6 days (initial stage), 12 & 8 days (development stage), 17 & 10 days (mid stage), and 21 & 15 days (late stage). Application efficiencies ranged from 20.6% to 87.6%, with an average of 44.6%, which is below the recommended levels for surface irrigation. Storage efficiency varied from 72.9% to 99.9%, averaging 79.5%, slightly under the ideal standard. Percolation losses were significant, averaging 55.4%, indicating considerable water loss compared to other studies. This study suggests that soil moisture based irrigation practices are needed to improve efficiency and minimize water loss. Aligning irrigation schedules more closely with soil moisture levels and enhancing monitoring practices could substantially improve irrigation performance.