Sugarcane yield responses from furrow irrigation at Mackay

Six varieties, only two of which are still commercials, were grown for seven ratoons in irrigated and rainfed experiments at the Sugar Experiment Station, Mackay. For these two varieties, 0124 and 0138, yield responses from furrow irrigation averaged 27.3 tonneslha per annum from the application of 4.0 ML of water, to give an irrigation water use efficiency of 6.8 tonnes/ML. Total water use efficiencies for rainfed and irrigated experiments were not different at 12.0 ± 0.5 and 11.5 ± 0.5 tonnes cane/ML of total plant available water, i.e., effective rainfall plus irrigation water. Only 49% of the rainfall of 1717 mm per year was effectively used for cane growth. Irrigation resulted in additional runoff and deep drainage, amounting to 29% of the irrigation water applied. Number of stalks increased from 7.8 to 12.4 per m2 from first to seventh ratoons, with irrigation having no effect, despite an increase in gappiness of 11.9% to 28.4%. The increase in cane yield from irrigation was mainly due to an increase in stalk weight, from a high of 1.59 kg and 1.44 kg in first ratoons to 1.13 kg and 0.87 kg in seventh ratoons for irrigated and rainfed cane, respectively. There was a pattern for total water use efficiency for individual varieties to be highest in rainfed compared with irrigated when there was an irrigation demand in excess of 4 MLlha, and vice versa. Responses from irrigation and profitability were certainly higher in the 1990s than in the 1970s.