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Download (4Mb) - USQ ePrints - University of Southern Queensland

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milling region is spread across several varying geographic and climate zones. Across these regions<br />

and within regional districts varietal differences in cane yield and CCS vary throughout a harvest<br />

season. Typically, across the Industry, the harvest window tends to start in mid-June and finish by<br />

mid-November, with a season length <strong>of</strong> approximately 20-24 weeks. However, in NSW the season<br />

runs to mid-December <strong>of</strong>ten due to prolonged periods <strong>of</strong> wet-weather.<br />

The increasing risk <strong>of</strong> rainfall-related harvest interruptions is a primary reason why industry is<br />

reluctant to have crushing seasons closer to the end <strong>of</strong> the calendar year. The extent to which rain<br />

stops harvesting depends not only on the amount <strong>of</strong> rain in any given period, but also on soil type,<br />

aspect, slope, temperature and the moisture content <strong>of</strong> the soil before the rain event. Rainfall is not<br />

uniform over a mill region and, therefore, harvesting interruptions to individual farms are also<br />

unpredictable.<br />

The time <strong>of</strong> year when a crop is harvested affects yield by imposing both crop age and seasonal<br />

factors on the crop. The yield <strong>of</strong> the following ratoon crop is affected by the seasonal conditions into<br />

which the new crop grows.<br />

McDonald, Wood and Muchow (1999) showed the importance <strong>of</strong> time <strong>of</strong> harvest and crop age on<br />

crop productivity and pr<strong>of</strong>itability. To fully understand the physiological effects <strong>of</strong> crop age and time<br />

<strong>of</strong> rationing on productivity, the effects <strong>of</strong> climate (temperature and radiation) on a well-managed<br />

crop (where no other factors limit growth) must be separated from other factors which limit growth.<br />

Lawes et al. (2004) analyses suggested that exploitation <strong>of</strong> regional spatial variation would improve<br />

productivity. Sugarcane growers have a lot <strong>of</strong> issues to consider simultaneously when planning<br />

harvest times for individual blocks on farms including variety, crop class, crop age, CCS, cane yield,<br />

soil type and micro-climates. Each blocks location within the farm also comes into the time <strong>of</strong> harvest<br />

decision due to factors such as flood risk and attractiveness to pests.<br />

Regional management differences such as varieties, irrigation, group rotations and mill throughput<br />

means that harvest planning processes also vary across regions, therefore an industry-wide method is<br />

not appropriate.<br />

Therefore, the sugar industry has developed harvest planning tools to better manage: variety<br />

selection, crop age and crop class management, harvester migration and trafficability in wet weather,<br />

risk management <strong>of</strong> harvest, and to plan for better accommodation <strong>of</strong> climate forecasting indicators.<br />

However, these systems have not been adopted by the industry as the most pr<strong>of</strong>itable option for the<br />

industry is also the one with the least equity at the farm and harvester group level.<br />

Mallee System<br />

Mallees are grown as permanent crops. It is expected that mallees will be harvested repeatedly on<br />

about three to seven year rotations, with the length <strong>of</strong> rotation determined by the harvest yield. The<br />

season <strong>of</strong> harvest combined with the soil pr<strong>of</strong>ile (availability <strong>of</strong> soil moisture) will need to be<br />

managed so that mallees liable to be under severe moisture stress on shallow soils are only harvested<br />

in optimal conditions <strong>of</strong> spring and early summer. This is discussed in greater detail in section 1.4.3<br />

and 1.4.4.<br />

2.5.2 Harvest monitoring<br />

Sugar System<br />

Knowing how much cane remains to be harvested during a crushing season has always been an<br />

important task undertaken by mill field staff. The pre-season crop estimates form the basis <strong>of</strong> many<br />

facets <strong>of</strong> raw sugar manufacturing from marketing and logistics, planning mill start dates, cane<br />

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