Comparative evaluation of drip irrigation system for optimizing water use and yield of Arabica coffee in Kaliro District.

Abstract

Coffee production in Uganda, particularly Arabica coffee, is increasingly threatened by erratic rainfall patterns and prolonged dry spells linked to climate variability (Impact et al., 2022). In Kaliro District, where farming remains largely rain-fed, this variability exposes coffee plants to moisture stress, resulting in reduced growth and lower yields. Drip irrigation has been widely promoted as an efficient method of supplementing rainfall, yet limited locally generated information exists on which type of drip irrigation system, in-line (integrated emitter) or online (button emitter), performs better under local field conditions. This study therefore sought to comparatively evaluate the in-line and on-line drip irrigation systems for optimising water use and yield of Arabica coffee at Buyode Farm in Kaliro District. A quasi-experimental comparative study design was adopted. Both the on-line and in-line drip irrigation systems were designed considering identical or similar agronomic and climatic conditions. The crop water requirement was estimated using the Food and Agricultural Organization (FAO) Penman-Monteith approach, with reference evapotranspiration (ETo) of 3.95 mm/day obtained from CLIMWAT and CROPWAT using Jinja weather station data, and a crop coefficient (Kc) of 1.05 for mid-season, weedy field conditions. This gave a crop evapotranspiration of 4.1475 mm/day and a peak daily water demand of 16.59 litres per plant at a spacing of 2 by 2 meters. Hydraulic design, using the Hazen-Williams equation, established a 16 mm dripline diameter, a 32 mm submain diameter, and a 40 mm mainline diameter as the most suitable pipe sizes, keeping all friction losses within the allowable 1.0 m limit (10% of the 10 m emitter operating head). The resulting Total Dynamic Head of 19.82 m was comfortably met by a 1.2 m³/h solarpowered submersible pump. Each of the five field blocks was designed with an independent submain and control valve, allowing the blocks to be irrigated separately. An economic and financial feasibility analysis compared installation costs, annual operating costs, net benefit, cost per cubic metre of water delivered, and benefit-cost ratio (BCR) for both systems for a single season. The in-line system had a lower installation cost (UGX 11,465,000 versus UGX 14,185,000), a higher net benefit (UGX 7,747,800 versus UGX 5,027,800), a lower cost per cubic metre of water delivered (UGX 30,924 versus UGX 40,922), and a higher BCR (1.68 versus 1.35) compared to the on-line system. The results of the study show that both systems (in-line and online) are technically feasible for Arabica coffee production in Kaliro district. But the in-line drip systems offer better economic xii performance and lower long term maintenance demands compared to the on-line drip systems. Therefore, the study recommends the adoption of the in-line drip irrigation systems in the remaining coffee blocks at Buyode farm in Kaliro district (Eastern Uganda).