EVALUATING THE PERFORMANCE OF AQUACROP MODEL IN SIMULATING THE PRODUCTIVITY OF POTATO (Solanum tuberosum L.) CROP UNDER VARIOUS WATER LEVELS AT DEBRE BIRHAN, AMHARA REGIONAL STATE, ETHIOPIA

Abstract

Agricultural sector face the challenge to produce more yield with less water. In this regard, simulation models are basic tools in evaluating the effect of water on crop production. To address this need, FAO has developed yield responses to water model named AquaCrop, which simulates attainable yields of the major field and vegetable crops from their physiological and agronomic background perspective at farm level. The aim of this study was to evaluate the AquaCrop model performance on potato crop growth parameters under various water levels at Debre Birhan, Ethiopia. The AquaCrop is a user-friendly, easy to apply, accurate and robust model, and it addresses conditions where water is a key limiting factor for crop production. The experiment was arranged with Randomized Complete Block Design, with four replications under different water levels 100%, 85%, 70% and 55 % of crop water requirement of potato, which were simulated by the AquaCrop model. The results indicated that the simulated amount of irrigation water for 100% water level was 377.2 mm of water depth in growing season. The growth parameter and tuber yield were significant differences among the water levels at p < 0.05. The fresh potato tuber yield ranges from 35.25 ton/ha to 44.37 ton/ha was obtained in 55% and 100% water levels respectively. The water productivity ranges from 11.59 kg/m3 to 12.67 kg/m 3 was obtained in 100%and 55% water level respectively. Concerning its performance, the AquaCrop model simulated very well in the canopy cover, dry aboveground and tuber biomass and soil water content of the potato crop. The statistical indicators; Nash-Sutcliffe efficiency (NSE), Normalized Root mean square error (NRMSE) index of agreement (d) and Coefficient of determination (R 2 ) showed very well to excellent efficiency observed on dry aboveground and tuber biomass, there values were found to be in the ranges of 0.78 to 0.94, 35.50 to 16.30, 0.96 to 0.99 and 0.98 to 0.96 respectively. However, for soil water content before irrigation, which was found to be poor ranges 0.00 to -0.63, 10.2 to 10.8, 0.78 to 0.51, 0.45 to 0.03 were observed respectively.in the above order. From the results of the study can conclude in two scenarios: first, in case of water scarce area, it may be more profitable for a farmer to maximize crop water productivity instead of maximizing the harvest per unit of land. The saved water can be used to irrigate extra units of land. Second, in case of no water scarce area, it may be more profitable to maximize the yield harvest than crop water productivity. Under the first scenario farmers should adopt 70% of crop water requirement with a 10-days interval, which 16.65% saved water with 10.1% yield penalty over 100%. On the other hand, they should adopt 100% of crop water requirement within 10-days interval In the case of no water scarce area. The future studies shall consider various other stresses such as soil fertility and mulching