Innovative irrigation water management: a strategy to increase yield and reduce salinity hazard of small scale irrigation in Ethiopia

Abstract

To address the problem of water scarcity and to achieve food self-sufficiency, huge efforts and massive irrigation developments have been made in the last twenty-five years by the Ethiopian Government. However, the performance of many small-scale irrigation (SSI) schemes is still very poor. Deficient irrigation water management is one of the major factors challenging the success and the sustainability of the SSI. Farmers are constrained by inappropriate irrigation management strategies, which result in irrigation water scarcity, yield loss and undesirable environmental impacts in most SSI. The issue of sustainability is given hardly attention.

This thesis tries to assess, understand and evaluate the current irrigation water management practices in relation to crop yield and soil salinization and then come-up with simple and innovative irrigation water management strategies that can influence the farmers’ decision and enable them to cope with the problem of water scarcity and soil salinity.

In Chapter 2 farmers’ irrigation water management practices, challenges, perceptions and adaptation were studied. We evaluated farmers survey data, field observations and measurements and found that the farmers’ perception of the major causes for aggravating water scarcity, crop yield decline and soil salinization were in line with field observations. The overall plot level and scheme level adaptation strategies of the farmers were not good enough. The farmers are constrained by lack of technical knowledge, weak enforcement capability of the Water Users Association (WUA) and poor irrigation infrastructures to manage the irrigation water properly at plot as well as at scheme level.

The government involvement on sustainability of irrigation schemes is poor. Also, the top-down approach by local government authorities has been constraining the farmers’ adaptation strategies. The study showed that allowing beneficiaries to make their own decision resulted in innovative drought adaptation strategies. For sustainable utilization of the irrigation scheme, priority should be given to interventions focused on improvement of water efficiency at farm as well as at scheme level.

In Chapter 3 we developed a simple irrigation scheduling method based on an FAO procedure (Brouwer et al., 1989), the Hargreaves ET0 equation and the opinions of local farmers and extension agents. Then, under participation and close observation of farmers the method was compared to CropWat simulated and local (Traditional) scheduling practices, using maize as indicator crop.

We found that the simple irrigation schedule method resulted in higher grain yield, substantial irrigation water saving and subsequently in significant improvement of water productivity as compared to the other approaches. Farmers’ and experts’ opinions were in favour of the Practical scheduling method. The practical irrigation scheduling method is thus recommended for maize in the Gumselassa area. The presented procedure can be adopted for preparation of irrigation calendars of other crops, and in other regions.

In Chapter 4 we presented a sustainable utilization of the scarce irrigation water resources using cyclic (conjunctive) irrigation strategies for the production of onion. The effects of irrigation strategies using fresh water, moderately-saline water and cyclic combinations of both waters on onion yield and soil salinization were evaluated based on two years experimental data. The study was conducted under close observation and involvement of farmers and extension agents. The results indicated that the cyclic irrigation strategies are promising options for the production of onion without undue onion yield reduction and soil salinization as compared to irrigation using fresh water.

In Chapter 5 the long-term (ten years) impact of cyclic irrigation strategies on relative onion yield and soil health were evaluated. Climatic data, and data collected from the irrigation scheme and the field experiment (Chapter 4) were used to calibrate and validate the Soil-Water-Atmosphere-Plant (SWAP) model. Two scenarios, i.e. 60 mm pre-plant irrigation (PPI) for the 1st case and 70 mm PPI plus 20 percent leaching fraction (LF) for the 2nd case, were used for long-term simulations.

Results of the simulation revealed that salinity build-up is critically affected by irrigation water qualities and the application frequencies and the amount of annual rainfall. Irrigating using seepage water resulted in lower onion yield and higher salt accumulation in the root-zone, for both scenarios. Considering soil salinization, results of the long-term simulation indicated that, the cyclic irrigation strategies can be used safely through increasing the PPT to 70 mm and introducing 20% LF.