Comparison of Locally Determined Crop Coefficients to FAO 56 (The Case of Ethiopia)

Abstract

Proper irrigation scheduling and effective water management are impossible without the exact estimation of crop coefficient values in agroecology and crop variety. There is a research gap in the relevance of locally determined crop coefficients compared to the previously determined crop coefficients by FAO56. This review paper aims to compare and evaluate the locally determined crop coefficients with the crop coefficients documented by FAO56. Although different crops are grown in Ethiopian agroecology, only some crops have locally determined crop coefficients. These crops are onion, haricot bean, barley, wheat, tomato, teff, sugarcane, sorghum, cabbage, pepper and sesame. Except for the native crop (teff) of Ethiopia, the locally determined crop coefficient values of all others are compared with the values documented by FAO56. Accordingly, the locally determined crop coefficient values are significantly different compared to the values documented by FAO56. Considering pepper crops as a sample, updated Kc values were 1.19, 1.31, and 1.01 at the initial, mid, and late growing stages; whereas 0.6, 1.05, and 0.9 at the initial, mid, and late growing stages were documented in FAO56 document. The difference that happened between the locally determined crop coefficients and values determined by FAO56 is due to differences in crop variety, agroclimate, and the methods followed for water application and estimation of crop evapotranspiration. In line with this, the use of crop coefficient documented in FAO56 impacts water management and crop productivity, particularly in water scarcity. As reviewed different locally determined crop coefficients for different crops from different research papers, the values oscillated on the crop coefficient determined from FAO56. These oscillations indicate that it causes loss of water and aeration problems due to over-application of irrigation water. On the other hand, moisture scarcity in the crop root zones happens due to little irrigation water application to the crop. Therefore, local determination of crop coefficients for different varieties of crops in different agroecological zones is crucial for water resource projects for irrigation. Further research is required for locally determined crop coefficients considering crop variety, agroecology, and other scientific approaches.