Effect of date and final irrigation on yield and yield components of sunflowers in a semi-arid environment

In the semi-arid irrigation areas of south-western New South Wales, many sunflower crops receive no irrigation after flowering. In these dry climates, such premature termination of irrigation could be leading to substantial yield losses. The effect of date of final irrigation on yield and yield components of sunflowers (cv. VNIIMK 6540) was thus examined in two experiments. In the first experiment, seed yield was increased by 19 per cent when final irrigation was applied 22 days after mid-flowering, rather than at mid-flowering. The higher yield resulted principally from an increase in the number of harvestable seeds. Higher frequency of irrigation further increased seed yield by 9 per cent via increase in seed weight. Estimated total consumptive water use by treatments ranged from 546 to 677 mm and the regression of yield (kg ha-1) on water use (mm) was y = 3.9x - 47.4 (r = 0.77, P < 0.001). In the second experiment, in which all treatments were irrigated at a high frequency, seed yield was increased by 30 per cent and total oil yield by 48 per cent when final irrigation was applied 16 days after mid-flowering, rather than at mid-flowering. Both seed weight and seed number were increased by the later irrigation. No further yield improvement was achieved by extending the irrigation season to encompass physiological maturity (a mean 31 days after mid-flowering).