Yield and water use efficiency for two sweet potato cultivars depending on irrigation depths

The increasing global concern with the efficient production of energy and water resources requires the development of strategies that save water without reducing yield. Therefore, this study was carried out to determine the irrigation depth that provides maximum yield and water efficient use for two sweet potato cultivars. Irrigation depths equivalent to 50, 75, 100 and 125% of the crop evapotranspiration (ETc), calculated by the Irriplus software, were evaluated using a drip irrigation system. The tuberous root yield was determined 187 and 208 days after planting date for Amanda and Duda cultivars, respectively. The highest productivity (49.8 t ha(-1)) of the tuberous roots for 'Amanda' was obtained with a cumulative irrigation depth of 325.5 mm (95.2% of ETc), while for 'Duda' the irrigation depth that resulted in highest productivity (67.1 t ha(-1)) was 347.0 mm (100.4% of ETc). The productivity difference between cultivars was 25.8%, presenting increase in water consumption by 'Duda' of 21.5 mm (6.2% higher). This comparison indicates that 'Duda' presents higher water use efficiency. The increasing irrigation depth resulted in the highest water efficient use (EUA), with maximum value of 16.1 kg m(-3), for irrigation depth of 301.8 mm (87.3% ETc) for 'Amanda'. For 'Duda' the EUA was 320.0 kg m(-3), with irrigation depth of 332.4 mm (96.2% ETc). The productivity obtained with the maximum EUA was 48.6 t ha(-1), representing economy of 23.7 mm, or productivity reduction of only 1.2 t ha(-1) for 'Amanda'. 'Duda' showed productivity equivalent to maximum EUA of 66.3 t ha(-1), representing economy of 14.6 mm, or productivity reduction of 0.8 t ha(-1). The irrigation depths recommended for 'Amanda' and 'Duda', in present edaphoclimatic conditions, were 301.8 and 332.4 mm, respectively.