The commercial potential of sugar beet (Beta vulgaris) for sugar production in the Mareeba-Dimbulah Irrigation Area of North Queensland, Australia

Sugarcane is a tropical plant grown for sugar production under a wide range of mainly warmer climates throughout the world whereas under temperate climates sugar beet is grown for sugar production. In Australia, sugarcane is grown predominantly in the tropical and subtropical regions of the east coast. Since 1996 there has been a rapid expansion of sugarcane production in the Mareeba-Dimbulah Irrigation Area (MDIA), which is part ofthe Atherton Tableland region, about 50 km inland from Cairns in north Queensland. The expansion has been due to declining sugar yields from sugarcane grown on the coast, several years of devastating storms and cyclones, population growth of Cairns taking up cane land for residential use and the availability of land and water in the MDIA. A major effect of this rapid expansion of sugarcane in the MDIA has been on the availability, supply and cost of irrigation water and the efficiency of water use has become an important issue for growers. This study investigates the potentia for sugar beet to be included into the cropping options of both established sugarcane farmers and other producers in the MDIA. As sugar beet has never been grown in the MDIA (and not commercially in Australia since the 1930 's) a number ofexperiments were conducted to provide yield information under local conditions. Variety trials studied the performance ofa number ofvarieties used in the main sugar beet growing areas ofthe UK, Europe and the USA. Results showed little difference in sugar yield between varieties which were in the range found under commercial production overseas (1012 t/ha). Nitrogen, irrigation and population experiments at two sites (Southedge and Walkamin) in1999 studied the effects of these inputs on sugar beet growth and yield. At Southedge the amount ofapplied nitrogen was having the greatest effect on root yield with 180 kg/ha N giving the highest sugar yield (13.9 t/ha) while the amount of irrigation and population level were less influential. At 180 kg/ha of N, water use efficiency (WUE) was 11.8 and 2.3 t/ML for root and sugar yield respectively in comparison to an estimated sugarcane WUE in the MDIA ofabout 8 and 1.5 t/MLfor cane and sugar yield. At Walkamin it was population level that was having the greatest effect with 100,000 plants/ha giving very high root yields (>100 t/ha) however the sucrose concentration was much less compared to Southedge and so sugar yields were not as high as may have been expected but still higher than Southedge (about 16 t/ha). Water use was about 50 % more on the heavier soil at Walkamin compared to Southedge with 100,000 plants/ha giving an average WUE of12.7 and 1.8 t/ML for root and sugar yield respectively. Growth analysis studies at Southedge showed that radiation would not be limiting to dry matter production, with the excess radiation increasing water use. At Walkamin dry matter production was related to plant population and a higher radiation use efficiency at Walkamin compared to Southedge. An economic study using simple gross margin analysis and yield data from the Southedge trial showed that sugar heet could be a profitable crop in the MDIA however at the current low world sugar prices commercial production is unlikely.