Green cane trash blanket Australia - Trash blanket

Transcription

1 Green cane trash blanket Australia - Trash blanket Elimination of burning as a pre-harvest treatment of sugar cane, and managing the resultant trash as a protective blanket to give multiple on and off-site benefits. Under conventional production systems, sugar cane is burnt before being harvested. This reduces the volume of trash - comprising green leaves, dead leaves and top growth - making harvesting of the cane simpler, and subsequent cultivation of the soil easier. In the humid tropics of North Queensland, harvesting of cane used to be carried out by hand - as it still is in many parts of the developing tropics. Burning was necessary to make harvesting possible in a dense stand (and to reduce the danger of snakes). However, with the advent of mechanical harvesters in the 1960s, burning continued to be practiced through habit. A new system then brought fundamental changes in soil management: The green cane trash blanket (GCTB) technology refers to the practice of harvesting non-burnt cane, and trash blown out behind in rows by the sugar cane harvester. This trash forms a more or less complete blanket over the field. The harvested lines of cane re-grow ( ratoon ) through this surface cover, and the next year the cycle is repeated: the cane is once again harvested and more trash accumulates in the inter-rows. Generally the basic cropping cycle is the same, whether cane is burnt or not. This involves planting of new cane stock (cuttings or billets ) in the first year, harvesting this plant crop in the second year, and then in years three, four, five and six taking successive ratoon harvests. In year six, after harvest, it is still common, even under the GCTB system, to burn the residual trash so that the old cane stools can be more easily ploughed out, and the ground worked up (cultivated) ready for replanting. A minority of planters, however, are doing away with burning altogether, and ploughing in the residual trash before replanting. A further variation is not to plough out and replant after the harvest in year six, but to spray the old cane stock with glysophate (a broad spectrum non-selective systemic herbicide) to kill it, then to plant a legume (typically soy bean) as a green manure crop, and only replant the subsequent year after ploughing-in the legume. Under this latter system, one year of harvest is lost, but there are added benefits to the structure and nutrient content of the soil. Whatever variation of GCTB is used, there are advantages in terms of increased organic matter, improved soil structure, more biodiversity (especially below ground) and a marked reduction in surface erosion - from over 50 t/ha to around 5 t/ha on average. Less erosion is good for the growers - but is also of crucial importance off-site, as sediment lost from the coastal sugar cane strip is washed out to sea, and damages the growing coral of the Great Barrier Reef. left: Harvesting of green sugar cane and simultaneous spreading of the separated residues, leaving a dense mulch cover, the so called green cane trash blanket. (Photo: Hanspeter Liniger) right: A ratoon : a re-growing sugar cane sprouts through the trash blanket after harvest. (Photo: Hanspeter Liniger) Location: North Queensland, Australia Region: Ingham Technology area: 800 km 2 Conservation measure: agronomic Stage of intervention: mitigation / reduction of land degradation Origin: Developed through land user`s initiative, Land use type: Cropland: Perennial (non-woody) cropping Climate: humid, tropics WOCAT database reference: T_AUS003en Related approach: The triple bottom line (AUS03) Compiled by: Anthony J. Webster, CSIRO Date: Classification Land use problems: - Conventional burning of sugar cane before harvest can lead to compaction of top soil and reduced organic matter. There is also, despite the low slopes, a serious problem of sheet/rill erosion that has a negative impact both on the fields, and also off-site on the coral reef. (expert's point of view) soil erosion, weeds, flooding (land user's point of view)

2 Land use Climate Degradation Conservation measure Perennial (non-woody) cropping rainfed humid Soil erosion by water: loss of topsoil / surface erosion, offsite degradation effects, Chemical soil deterioration: fertility decline and reduced organic matter content Agronomic Stage of intervention Origin Level of technical knowledge Prevention Mitigation / Reduction Rehabilitation Main causes of land degradation: Land users initiative Experiments / Research Externally introduced Agricultural advisor Land user Main technical functions: - control of raindrop splash - improvement of ground cover - improvement of soil structure - control of dispersed runoff Secondary technical functions: - increase in organic matter - increase of infiltration - increase in soil fertility - increase in surface roughness Environment Natural Environment Average annual rainfall (mm) Altitude (m a.s.l.) Landform Slope (%) > 4000 mm mm mm mm mm mm mm mm < 250 mm > <100 plateau / plains ridges mountain slopes hill slopes footslopes valley floors flat gentle moderate rolling hilly steep very steep Soil depth (cm) >120 Growing season(s): 300 days(aug - May) Soil texture: medium (loam) Soil fertility: high, medium Topsoil organic matter: low (<1%) Soil drainage/infiltration: good Human Environment Cropland per household (ha) < ,000 1,000-10,000 >10,000 Land ownership: individual, titled Land use rights: individual Relative level of wealth: average Importance of off-farm income: 10-50% of all income: various off-farm enterprises undertaken to supplement income during years of poor sugar prices Access to service and infrastructure: Market orientation: commercial / market Mechanization: Livestock grazing on cropland:

3 Technical drawing Harvester harvesting cane and depositing trash on surface (Anthony J.Webster) Implementation activities, inputs and costs Establishment activities Maintenance/recurrent activities - mulching of inter-rows with trash [previously: burn cane with associated trash and then harvest] - fertilize cane - spray with Amicide (very efficient herbicide, systemic and non-selective) - spray with Amicide Maintenance/recurrent inputs and costs per ha per year Inputs Agricultural Costs (US$) % met by land user - fertilizer % - herbicides % Other - Contract harvesting % TOTAL % Remarks: The year budgeted above is a non-planting year, the costs therefore refer to an established crop which grows throughout the year and is harvested in August. The assumption is a cane yield of 80 t/ha. Each of the three categories of costing groups machinery, labour (at US$12 per hour) and inputs together. The comparative costs for a burnt cane crop system with the same yield are (a) contract harvesting = US$ 378 (b) fertilizer = US$ 120 (c) herbicide = US$ 56, plus (d) cultivation = US$ 30. Note that under the burnt cane system, soil cultivation/tillage is required, but the cost of harvesting is a little cheaper. The total for the burnt crop system is US$ 584 compared with US$ 543 for the GCTB crop, representing a saving of approx. US$ 40 (around 7%) per hectare per year. Assessment

4 Impacts of the Technology Production and socio-economic benefits Production and socio-economic disadvantages increased farm income Socio-cultural benefits Socio-cultural disadvantages improved conservation / erosion knowledge enhanced reputation of sugar cane growers as 'environmentally friendly' Ecological benefits reduced surface runoff improved soil cover reduced soil loss increased soil organic matter / below ground C loss of nutrients reduced, inproved soil structure biodiversity enhancement (above and below ground) increased soil moisture improved excess water drainage increase in soil fertility Off-site benefits Ecological disadvantages Off-site disadvantages reduced downstream siltation reduced wind transported sediments reduced downstream flooding reduced groundwater river pollution Contribution to human well-being / livelihoods Benefits /costs according to land user Benefits compared with costs short-term: long-term: Establishment not specified not specified Maintenance / recurrent slightly positive positive Acceptance / adoption: 95% of land user families have implemented the technology voluntary. There is little trend towards (growing) spontaneous adoption of the technology. It is possible that the few growers who persist in burning will eventually adopt the GCTB system through social and environmental pressure. Concluding statements Strengths and how to sustain/improve Weaknesses and how to overcome GCTB systems offer multiple on-farm environmental benefits Continue to refine the system, by encouraging (a) non burning of trash in the Increases overall farm income by maintaining yields of sugar cane while Continue to refine the system. Some burning still continues through (a) the few farmers who have not yet adopted GCTB and (b) the common practice of burning trash before replanting Continue to encourage non-burning for multiple reasons. GCTB systems provide protection to the coral reef, through substantially reducing the sediment yield that reaches the lagoon and thence the Great Barrier Reef Give recognition to the growers for their overall environmental contribution.

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