Evaluation of Deficit Irrigation on Water Productivity and Yield Response of Beans Using AquaCrop in Eldoret, Kenya.

Abstract

Kenya’s renewable fresh water per capita is below the UN recommended benchmark of 1000 m 3 /capita/year, making it a water scarce country. Over 80 percent of this freshwater is utilized in agricultural production. The increase in human population means that even more water will be channeled towards food production. Kenya predominantly depends on rain- fed agriculture for its food production; this makes the country susceptible to acute food shortages. An increase in food production needs to be coupled with an increase in crop water productivity in order to ensure the sustainability of the water resources. Beans (Phaseolus Vulgaris L.) are the primary source of protein for most households in Kenya. Despite this fact, there is a supply deficit dry spells. An irrigation study was carried out at Moi University. In this study, the effect of deficit irrigation as a mitigation measure to curb the shortage of beans during dry spells while ensuring sustainable use of water resources was investigated. This was carried out through modeling of water productivity (WP) and yield (Y) of beans using the FAO AquaCrop model. Field experiments were set up in a Randomized Complete Block Design (RCBD) arranged in split plots and replicated three times. Two water treatment strategies were employed (deficit irrigation, full irrigation). In the full irrigation supply, the crop was kept at 100% of irrigation requirement (T100) and data collected from these plots was used in AquaCrop model calibration. There were three levels of deficit irrigation at 80%, 60% and 50% of irrigation requirement (T80, T60, T50) these were used in model validation. The model prediction of bean yields showed a good agreement with observed values with an R 2 of 0.83, Willmott’s index of agreement of 0.97 and root mean square error of 0.4014 t/ha. The T100 irrigation treatment had the highest observed Y of 4.238 t/ha with a water productivity of 1.01 kg/m 3 . The T80, T60, and T50 treatments exhibited a drop in Y, 4.138, 2.254 and 1.702 t/ha respectively, and WP of 1.29, 0.92 and 0.77 kg/m 3 respectively. The highest WP, as well as the lowest yield reduction of 2.36%, was observed in the T80 treatment, this signifies water savings of up to 20% which translates to 750 m 3 /ha. The highest yield reduction of 59.84% was obtained in T50 treatment, coupled with a drop in WP. Subsequently, frequency analysis was carried out on historical rainfall data of 22 years (1990-2011). The years 2007, 2002 and 2004 were obtained as the typical climatic conditions of dry, wet, and average years respectively. Deficit irrigation strategies were designed according to the level of sensitivity of the growth stages. The calibrated model was then used for simulation of Y and WP for the dry, wet and dry seasons. The results confirmed that the most water sensitive stages were at the flowering and yield formation. Consequently, irrigation schedules to relay information to stakeholders were produced. Improving water productivity is the most appropriate strategy for increasing food production for a fast growing population due to its consideration of the sustainability of water resources. Deficit irrigation results in yield reduction as observed in this study, but the amount of water saved can be used to irrigate more land or be utilized elsewhere. As a result, the high opportunity cost of water compensates for the economic loss due to reduction in yields.