The practice of clearing and burning the soil has been used in Brazil since colonial times. Also in sugarcane production, burning has been commonly used as it increases the throughput in both manual and mechanical harvesting. Producers utilizing green cane harvest practices report 30 to 40 per cent lower daily tonnage for unburned cane when compared to burned cane (Ripoli et al., 1990). The sugarcane burning practice is now undergoing severe restriction due to increasing urbanization, particularly in southern parts of the country. Still, in the State of Sao Paulo, green cane harvesting is only practised in a 1 km radius around the cities as a result of law enforcement (Governo do Estado de Sao Paulo, 1988).

The reason for preventing the burning of sugarcane fields is to avoid emissions to the environment (i. e. pollutants such as CO and particulates), which have impact on human health (i. e. respiratory illnesses) and human amenity. Furthermore, valuable cane residues that could otherwise be utilized for energy purposes are lost in the burning process. Long-term trash mulching can reduce nitrate fertilizer applications by 40 kg N/ha, mainly as a result of reduced nitrate leaching (Vallis et al., 1996).

Field burning also results in sucrose losses by exudation on the surface of cane stalks. Ripoli et al. (1996) have found ethanol losses in the range of 59 to 135 liters/ha due to such practices. Work done by Fernandes and Irvine (1986) on commercial sugarcane fields of several companies indicated that the actual sugar yield was below the potential existing in the field, both through manual cut (-17 per cent) and through chopper harvester (—21 per cent). These losses occurred in burning, harvesting, loading, transportation, and reduction in cane quality.

The interest in mechanical harvesting grew strong in the 1970s due to studies that forecasted labor shortage (Stupiello and Fernandes, 1984). Mechanization efforts did not succeed at that time and the interest eventually faded in the 1980s, partly due to the deterioration of the Brazilian economy. By the middle of the 1990s, the question had regained interest (Furnari Neto et al., 1996). The main difference in studies done today is the emphasis on reduction of production costs, mechanical harvesting being one step in this direction. Today’s cost for manual harvesting and loading of burned cane may exceed US$ 4.00/ton (Coletti, 1997) while mechanical harvesting hardly reaches US$ 2.00/ton (Lima, 1998)[8]. In the case of green cane harvesting, data is still unreliable but there are indications that manual cutting exceeds US$ 6.00/ton while mechanical harvesting is around US$ 3.00/ton.

Both the ergonometric and economic arguments indicate that green cane har­vesting is likely to foster mechanization of harvesting practices in Brazil. A signifi­cant expansion of mechanized practices, however, will depend on improvements to the available mechanical harvesting technology. This includes the considerations listed below.

• The machine throughput and harvesting costs should not be but marginally affected by the amount of trash.

• It should be possible to remove the trash from the field for other purposes, such as energy conversion. So far, there are no adequate cane varieties and agro­nomic experiences to manage trash blanketed cane fields (Sizuo and Arizono, 1987).

• A percentage of the straw should be left in the fields for weed control and moisture conservation in cases where agronomic management techniques are well established.

• The present system of whole cane harvesting should be maintained to avoid unnecessary investments associated with the change to chopped cane as well as to avoid raw material (sucrose) loss associated with the chopping and cleaning processes, which represents an unacceptable technological step back in the Brazilian context.

The present field experience with whole cane harvesters together with recent develo­pments on whole cane mechanical cleaning (Tanaka, 1996) as well as on machine right angle turning and pilling (Braunbeck and Magalhaes, 1996) added to the known potential of computerized engineering resources applied to machine design, anticipate the feasibility to develop a whole cane harvesting equipment taking into account the aforementioned features. Meanwhile, the mechanical harvesting expansion faces financial and technical constraints such as: shortage of skilled labor; bad field lay­outs and poorly performing harvester technology for the existing fields; lack of capital; existing whole cane transportation and reception at the factory different from the emerging chopped cane system; and design for maximum 12 per cent soil slopes for present harvesters which limits its use to about 45 per cent of the sugarcane areas.

Despite the country’s large production of sugarcane, mechanical harvesting is still hardly employed in Brazil (see also Table 6.3). Although there is no precise figure on the number of harvesting machines in operation today, this number should not be greater than 600 machines harvesting approximately 50000 tons/machine-season making a total of 30 x 106 tons. This represents 10 per cent of the total 300 x 106 tons harvested in the 1997/98 season. Frequent reference is made to the existence of quite high mechanization, but that relates to isolated cases such as Usina Sao Martinho, where 89 per cent of the cane was mechanically harvested already in the 1993/94 season.

Nevertheless, mechanical harvesting is growing fast in the State of Sao Paulo. This is not only due to the good topography of the state but also due to the well — developed road network and availability of skilled labor to operate a mechanized system. When cane producers of other states such as Goias and Mato Grosso implemented mechanical harvesting, they faced serious difficulties in hiring adequate labor to operate and maintain the machinery. It takes several years until the har­vester’s fleet can reach a production of 400 t/machine-day as the season average in 24h/day operations. Usina Sao Martinho, State of Sao Paulo, has exceeded productions of 600 t/machine-day, greatly due to skilled labor and adequate infrastructure, while Usina Sta. Helena, State of Goias, achieved the average harvester throughput of 400 t/machine-day first after 6 years operation.

Chopped cane has higher dirt and trash content. Unloading of chopped cane frequently has lower priority at the mill as a function of its lower quality. It creates a transportation shortage to the harvesting fleet and increases the cost of the operation. Lower cane quality comes mainly from inadequate technology at the machine base cutter which consists of two flat disks with approximately 900-mm diameter each. This defines a 1800 mm wide plane and requires a perfectly levelled soil for the disks to operate very close to the surface without cutting the soil. Recommendations for efficient operation of base cutters require flat and levelled land, but this turns out to be insufficient since the problem remained in Australia even after many years (Ridge and Dick, 1988).

Brazilian undulated cane areas inject large quantities of soil into the harvester. Though it is removed inside the machine, about 0.5 per cent of the soil still remains in the cane and this has an impact in the cane processing at the factory. The soil

Table 6.3. Comparative features of sugarcane harvesting technologies used in Brazil

Type of Harvesting

Parameter Semimechanized Mechanized — chopped cane

Stalk and tops cutting with cane bundling

<1%

600 t/machine-day; loading may achieve 700 t/machine-day

US$ 1.5/t

Requires trained labor; losses of raw material originated from base cutting and elevating rolls; traffic between lines; two passes by the harvesters; damaged stalks by the base cutter and transporting rolls

Minimum incidence of labor (only in operation and maintenance); independence of cutting and transporting operations which eases the operation management; increases

content of hand cut cane will not exceed 0.15 per cent when loaded with properly operated rotary push-pilers. Summarizing, the chopper harvesters present several critical points of cane losses such as the double disk base cutters, the feed rollers, the chopper and the cleaning extractors. These components are responsible for losses ranging from 7 to 15 per cent (Ridge et al., 1984; Fernandes and Irvine, 1986). The solution to this problem will arise from existing and future developments on alternative cutting and feeding mechanisms more than from insisting on extension work to further level cane fields, which creates adverse agronomic conditions for cane longevity and moisture conservation.

The technological innovation and investment capacity of the Brazilian agricul­tural machinery industry is rather small. It essentially limits itself to promoting the chopped cane technology developed abroad. There is also a technical barrier related to the potential use of machinery in areas with an unfavorable topography. Techniques, such as four-wheel steering and traction as well as steel or rubber tracks would allow to extend mechanization up to about 90 per cent of the areas which are currently occupied by sugarcane. Today’s harvesters are mainly one-row machines with high center of gravity using two-wheel traction in the rear and two-wheel steering in the front. This driving and traction configuration is acceptable for agricultural tractors in which alignment with the line of motion is not so important. In the case of harvesters, the lack of machine alignment with the crop lines leads to cane losses and frequent stops due to clogging. It would be technically possible to develop harvesters capable of operating in most of the hilly areas if present harvesting principles were simplified to allow investment on four-wheel traction and steering, still keeping the equipment economically feasible.

A successful implementation of mechanical harvesting in Brazil needs to address a series of technical issues based on topographic, agronomic and sugarcane processing conditions, typical to Brazil. Therefore, a development and economic effort is still required to improve the harvesting efficiency. Table 6.3 compares the features of sugarcane harvesting technologies being used in Brazil, which further illustrates the technological improvements needed.