It is believed that sugarcane was first brought to Australia in 1788 on the First Fleet but cultivation was not immediately successful. The first official record of sugarcane in Australia was in 1821 at Port Maquarie NSW, but an industry did not develop until a cane plantation was established near Brisbane in 1862. The first Australian commercial sugar mill began operation in 1864. Sugarcane cultivation spread along the Queensland-New South Wales coastline and in 1870 a system of large central sugar mills, supplied with cane by independent farmers, was introduced by the Colonial Sugar Refining Company (now CSR Ltd) (Canegrowers, http://www.canegrowers.com.au/overview.htm).
Currently, in Australia sugarcane is commercially cultivated over a 2100 km stretch from northern New South Wales (approximately 30°S) to northern Queensland (approximately 17°S) with the actual planting area distributed unevenly across this range. A small industry also exists in the Ord district in Western Australia. About 98% of Australia’s sugar exports originate in the Queensland coastal region (Canegrowers 2004). Queensland’s 2000-01 crop harvest was 28.8 million tonnes of sugarcane, from 424,350 hectares of cultivated land. Each hectare of cane harvested yielded on average 67.8 tonne of cane and 8.94 tonne of sugar. The gross value of Queensland’s 2000-2001 sugar production was $995.6 million (Canegrowers 2004).
1.4.1 Germination and establishment
Commercial sugarcane is propagated vegetatively and germination refers to the initiation of growth from buds present on the planted setts or on the stems of the stools that remain in the soil after harvest of the previous crop. Either whole stalks or stalks cut up into shorter segments called setts are used as planting material (Willcox et al. 2000). Setts are generally planted within a few days of harvest of the cane, in order to achieve a high frequency of germination. Row spacing is about 150cm. Buds on planted setts, or on the plant bases remaining after harvest, germinate within two weeks of planting (or after harvest of the preceding crop). Setts are prone to fungal attack (due to their high sugar content) and are routinely treated with fungicide to protect them until germination. Sugarcane varieties differ in their degree of temperature sensitivity but in general germination is slow at soil temperatures below 18ºC and will be increasingly rapid up to about 35ºC (Bull 2000). Because sugarcane originated in the wet tropics, yields are much higher when the crop is suppled with adequate water. Thus sugarcane is usually irrigated (Ham et al. 2000).
During the initial stages of germination, root primordia around the nodes of the sett produce a flush of roots. These roots are not connected to the primary shoot but are important in maintaining the moisture in the sett. The primary shoot is made up of a number of closely spaced internodes and nodes below ground. Each node develops new bud and root primordia that are the basis of stool establishment. These root primordia germinate to produce the shoot roots that support further plant growth. The shoot is then independent of the original sett (Bull 2000).
While the shoot roots are developing, some of the new buds below ground also germinate to produce secondary shoots or tillers. These, in turn, develop their own root systems and give rise to tertiary shoots (Bull 2000).
Stem elongation is initially rapid and during this phase the fibre content of the stem is high whereas the CCS levels are still quite low. Breeding for high above ground biomass in modern sugarcane varieties means the plant is very top heavy and consequently sugarcane is prone to lodging. Plants recover from lodging by curving of the stem to again grow upright. Only in wetter areas is lodging associated with yield losses (Bull 2000).
1.4.3 Maturation and ripening
Growth rate slows and sucrose content increases approximately 120 days after planting (Bull 2000). Maturation and ripening are reversible processes and are associated with the lower rainfall and cooler temperatures of the winter months. During stem growth, each internode operates as an independent unit. While it has a green leaf attached, the internode completes cell elongation and cell wall thickening and fills with sucrose. Hence internodes generally complete their cycle by the time the attached leaf dies, and the lower internodes are essentially ripe while the upper part of the stem is still growing. The stored sugar is, however, available for translocation to support further tillering and/or growth when conditions are not favourable for photosynthesis (Bull 2000).
As the stem matures, more internodes reach the same condition and sucrose content rises. During this period, the most recently expanded internodes near the top of the stem stop elongating and photosynthates are channelled into storage as sucrose. Factors that affect the maturation of the sugarcane stem include age, nitrogen status and moisture. Environmental factors can influence sucrose accumulation including water stress, nutrient status and temperature.
Sugarcane is usually harvested by cutting stems close to the ground 12 –18 months after planting (Bull 2000). All sugarcane in Australia is harvested mechanically. Sugarcane is routinely harvested before flowering as the process of flowering leads to reduction in stem sugar content.
1.4.4 Ratoon crops
Sugarcane grows perennially and the root system or ratoon that remains in the ground will re-sprout from each stalk. Consequently ratoon crops grow faster than the original plant crop. Although several ratoon crops are possible, cumulative stool damage from harvesting and weed control operations and the impact of pests and diseases eventually lead to declining yield. Thus a maximum of four ratoon crops are typically grown before ploughing out the crop and replanting (Bull 2000). After ploughing the previous ratoons out either another sugarcane crop is planted immediately or the ground is left fallow or planted to legumes with sugarcane again planted the following winter. Planting a legume crop has been shown to improve soil fertility for subsequent sugarcane crops. Removing ratoons with herbicide (glyphosate) rather than by tillage reduces soil compaction and improves soil structure (Willcox et al. 2000).
Sugarcane killing practices often result in inadequate eradication of the old crop (Leibrandt 1993). The efficacy of glyphosate on killing sugarcane is affected by various factors such as cane varieties, soil type and stage of cane growth (Turner 1980). Sugarcane growing in light soils was more susceptible to herbicide treatment than that growing on heavy soils (Turner 1980). The growth stage of sugarcane has a pronounced effect on the efficacy of herbicide application. Sugarcane was killed more easily when the height of the leaf canopy was between 0.4-0.75m. Sugarcane appears to be more difficult to kill with herbicide once some stalks have been produced (Turner 1980).
Research showed that slashing of cane suppresses apical dominance and generally enhances chemical cane killing action on the regrowth (Leibrandt 1993). In addition, considerable improvement of eradication was also obtained when a mechanical under-cutter was used to shear the roots following herbicide application.