Performance assessment of a bamboo-drip irrigation system

Abstract

Despite its high efficiency and productivity potential in regions subject to scarce water supply, conventional drip irrigation is still expensive and therefore only being adopted slowly in West Africa where 80% of vegetable gardens and small farms are still watered by hand. Much effort has been made so far, and some less costly drip kits were implemented in the region, but are rare due to the still high investment cost. As an alternative and further-going option, a novel bamboo-drip system was created and assessed in terms of performance with regard to hydraulics and uniformity in the laboratory, and yields, water productivity and soil-water management in situ under field conditions. Then the layout of the system was optimized in order to identify a spacing with the best compromise between deep percolation and fresh yields on a sandy loam soil.<br /> In the laboratory, the bamboo system was tested at four pressure heads. For hydraulic performance assessment, coefficients of variation of emitter flow were determined with regard to bamboo material, emitter precision and emitter plugging, and compared to the ASAE EP405.1 standards. The analyses reveal that plugging is the most important factor causing emitter flow to vary in the system. For uniformity performance assessment, the Christiansen uniformity coefficient was determined and compared to ASABE EP458 standards. Results show that the bamboo-drip system has good performance, and hydraulic characteristics similar to conventional drip systems under suitable pressure conditions.<br /> An in-situ test was conducted in a farmer's field (south-west Benin) in 2015 and repeated in 2016. Tomato was selected as the test crop due to its relevance for smallholder farmers and its suitability for drip systems. The experimental design was a three-plot randomized block with three repetitions, and each block in the bamboo-drip system was compared to plastic-drip and watering-can systems. The bamboo system was compared to the two systems with regard to yield, irrigation water productivity, soil-water potential and soil-water content, which were also compared to the main characteristics of soil-water storage behavior in each plot. Comparisons were performed with STATA 13.0 at 5% significance level. <br /> For assessment of yield and water productivity performance, one-way analysis of variance (ANOVA) was used, and results show that the bamboo system led to yields in the range of the two other systems in both cropping seasons. Its water productivity was found to be similar to that of the plastic-drip system in both seasons, but 99% (2015) and 85% (2016) higher than that of the can system.<br /> For soil-water management performance assessment, soil-water content and matric potential were determined at five positions in and around the plants' rooting area, and one-way ANOVA used for comparisons between irrigation treatments. T-test was also employed to compare soil-water content to major characteristics of soil-water storage behavior in each plot. Results show that soil-water management under the bamboo system is good. Soil-water content and potential in the bamboo system were in acceptable ranges for crop growth during both cropping seasons. Soil-water content under this system was slightly above field capacity in the vicinity of the rooting front during mid and late seasons, where over-irrigation was more pronounced. Soil-water matric potential fluctuation intervals and ranges under the bamboo system were higher in areas closer to where the plant sits laterally and vertically, and lower close to the rooting front. They were also higher in this system compared to the watering-can system. <br /> For layout optimization, HYDRUS 2D and AquaCrop software packages were used to simulate hydrologic and agronomic behavior of the bamboo system with spacing decreasing by increments of 1 cm from 30 to 60 cm. Then, under the GAMS model, CONOPT Solver was used to integrate hydrologic and agronomic behavior of the system, and identified 34 cm as best spacing where the best deep percolation - fresh yield compromise on sandy loam soil was observed.<br /> Useful life, economic analysis and performance improvement possibilities of the bamboo system need to be investigated in long-term time-series studies. However, this system promises a more productive use of water on a small scale, improved food security, and increased income at the household level, culminating in a better rural and peri-urban economy.