Effectiveness of deficit irrigation scheduling on crop water use efficiency- a case of french beans in Njoro Nakuru County Kenya

Abstract

Producing enough food in Kenya to better feed people and generate adequate income for the farmers is a great challenge. This challenge is likely to intensity, with a population that is projected to increase to 66.3 million in 2030. Scarce water resources and growing competition for water will be reduce its availability for irrigation, which necessitating major changes in irrigation management and scheduling in order to increase the efficiency of use of water that is allocated to agriculture, one of the options that can be used to reduce the demand of irrigation water is deficit irrigation. Agriculture needs to increase its production with a small amount of available fresh water. Deficit irrigation is now widely been investigated as one of solution for this problem. Relatively few farmers are equipped to deal with it effectively In this study deficit irrigation was investigated to determine its effectiveness in meeting crop water requirement and saving water with minimum effect on yield. And relationship between crop yield and water supply was investigated. This research was conducted from June 2016 to March 2017 at the Agricultural Engineering department demonstration farm Egerton University, Nakuru, Kenya. The objective of the study was to investigate the effectiveness of deficit irrigation scheduling and water use efficiency of French bean (Phaseolus Valgaris L). The modified FAO Penman Montieth Method was used to calculate evaporation ETo using ETo calculator. Crop coefficients were used to calculate reference evapotranspiration (ETc), the water application levels were 100% of evapotranspiration (ETc), 80% of ETc, 60% of ETc, and 40% of ETc. Based on these irrigation levels, the experiment was laid out using complete randomize block design(CRBD) with six treatments and three replications. Three plants from the inner rows of each experimental unit were randomly selected and tagged for measurement of plant growth variables, which included; plant height, number of branches, leaf area, canopy cover, yield and above ground biomass. Data from the experiment was subjected to analysis of variance (ANOVA) using the GLM procedure of SAS. Data obtained from field experiment was used to calibrate and validate Aqua Crop model to simulate the crop growth. The deficit irrigation levels which were applied throughout the growing season of French beans had significantly (P < 0.001) affected plant height, number of branch , leaf area index and yield. From the results the highest yield was found in treatment 100 of % ETc (8680 kg/ha) while the lowest yield was found in treatment 40%ETc (3158 kg/ha). The highest and lowest crop water use efficiency (3.05 kg/m3) and (2.44kg/m3) respectively were found in 80% of ETc and 40%of ETc. Therefore in water scars areas irrigation levels for French beans can be reduced by 20% water requirement without much effecting on yield. The performance of Aqua crop model was good in simulation of final biomass, pod yield and canopy cover for non-stress treatments but it performed less in simulation biomass and pod yield of the treatments less than 60% of ETc ( under the severe water stress throughout the season). The findings verify use of deficit irrigation at 80% in water scare areas with French beans such crop to adopting conditions.