Dual crop coefficients and performance of evapotranspiration methods in irrigated wheat

Abstract

Water availability, fertilizer management and crop rotation are fundamental to the sustainability of agriculture and food security. Thus, the objective of this study was the determination of crops coefficients, verification and comparison of methods of estimation and determination of the evapotranspiration of irrigated wheat. The experiment was carried out during two consecutive years, in which BRS 254 varieties were cultivated in 2016 and BRS 394 in the year 2017. The evapotranspiration was estimated and determined using the dual kc methodology, FAO-56, with plants grown in 12 lysimeters filled with soil monoliths, and the loss of water by evaporation measured by weighing small-lysimeters. Evapotranspiration was also determined by the water balance method. The results measured in the lysimeters (standard method) were compared with the data simulated by the dual kc method and determined by method of soil water balance, in order to determine the accuracy and efficiency of the methods used. The coefficients used to determine the efficiency of the methods were the RMSE, the RSR and the confidence index "c". The total evapotranspiration of the crop in both years of cultivation was 360 mm, with mean values of 3.87 mm d-1 for cultivar BRS 254 and 4.10 mm d-1 for cultivar BRS 394. The basal crops coefficients in the emergence, tillering, flowering, maturation and harvest stages were 0.42, 0.78, 0.94, 0.74 and 0.47 for cultivar BRS 254 and 0.28, 0.27, 0.65, 0.98 and 0.66 for cultivar BRS 394. The soil water evaporation coefficients at the respective stages are 0.72, 0.52, 0.39, 0.58 and 0.13 for cultivar BRS 254 and 1.04, 0.96, 0.65, 0.34 and 0.51 for cultivar BRS 394. Ke represents on average about 47% of the evapotranspiration of the irrigated wheat crop. Between methods tested, lysimeter is the best to wheat transpiration followed by FAO method and soil water balance. The use of any methods should consider the objectives and resources availability.