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University of Hohenheim (2008)

Economic analysis and policy implications of wastewater use in agriculture in the central region of Ethiopia

Alebel Bayrau Weldesilassie

Titre : Economic analysis and policy implications of wastewater use in agriculture in the central region of Ethiopia

Auteur : Alebel Bayrau Weldesilassie

Université de soutenance : University of Hohenheim

Grade : /Ph.D. in agricultural Sciences) 2008

Résumé partiel
The general objective of this study was to analyze the impact of wastewater use in agriculture. It mainly focused on three aspects of wastewater use for irrigation and their policy implications : impact on crop production and productivity ; its impact on the health of farmers ; and the value attached to its safe use for irrigation. The main objectives of the study were, therefore, 1) to define the farming system of wastewater farmers and to analyze the impact of wastewater on crop productivity ; 2) to analyze the prevalence of the actual health risks to farmers and estimate the health costs associated with the use of wastewater in irrigation ; and 3) to estimate the farmer’s willingness to pay for improved or safe use of wastewater for crop production. This study used mainly primary data collected from a household survey conducted on 415 wastewater and freshwater farm households operating irrigated agricultural activities within and around Addis Ababa, a central region of Ethiopia. A Cobb Douglas production function is specified to analyze the impact of wastewater on crop productivity. The production function was estimated using a Censored Least Absolute Deviation (CLAD) econometric model. To analyze the health impact of wastewater, the probability of illness was estimated based on the theory of the utility maximizing behavior of households subject to the conventional farm household production model modified by adding a health production function. The economic value of safe use of wastewater is estimated from data obtained from a contingent valuation survey administered by in-person interviews. A dichotomous choice model is used to elicit the farmers’ willingness to pay. Bivariate probit and interval regression models are used to analyze the factors determining the farmers’ willingness to pay for safe use of wastewater for crop production. The study shows that the livelihoods of wastewater farm households depend on the wastewater farm. Income from a wastewater farm accounts for 62% of total annual household income, ranging from 27% to 97%. About 61% of the vegetable market of Addis Ababa, the capital city of Ethiopia with more than five million people, is produced from the wastewater farms. Leafy vegetables, which are eaten raw, are mainly produced in less polluted wastewater farms and root vegetables are produced in more polluted wastewater farms. The study revealed that wastewater farm households use significantly less doses of chemical fertilizer compared to the freshwater irrigators. However, they spend three times more on seed and five times more on farm labor. Net farm return per hectare of plots irrigated with wastewater is significantly higher than for plots irrigated with freshwater. The results also indicate that the predicted median output value per hectare is significantly higher in wastewater irrigated plots compared to plots irrigated with freshwater. The CLAD estimation result shows that higher productivity of wastewater plots is explained by investments in inputs (organic fertilizer, improved seed and agricultural extension services), ownership of plots and levels of pollution of the irrigation water. The overall effect of wastewater on crop productivity is negative and insignificant (compared to freshwater). Plots irrigated with less polluted wastewater are more productive than plots irrigated with more polluted wastewater. The implication of the result is that even if wastewater is a reliable source of irrigation water and contains essential plant nutrients such as NPK, the nutrient content exceeds the recommended level of the plant requirement (e.g. nitrogen) or it contains toxic elements (e.g. nickel, zinc) above the recommended limit, and thereby reduce yield.


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