NEW MACHINERY DEVELOPMENT
There has not been a lot of success with the development of 3 and 4 row implements suitable for handling the heavy hard clay soils found in the BRIA. I attribute much of the problem to the inability to achieve sufficiently accurate row spacing while planting into the variable soil conditions found on most BRIA farms. In an attempt to overcome this problem I have imported a computer controlled steering system from the U.S. and this year will be trialing it in combination with a 180" rotaiyhoe-bedformer. If successful, this operation will be substituted for the final
discing prior to planting, and will eliminate the extra operation of manually marking out. This
system will almost certainly be an interim method of row guidance until the inevitable
development of a system based on G.P.S. technology (Global Positioning System).
Profitable yet sustainable sugar growing practices
Paper presented by Dr Graham Kingston Principal Research Officer
Bureau of Sugar Experiment Stations, Bundaberg
INTRODUCTION
Many of you may be concerned at the strong emphasis and varied interpretations placed on that over-used word 'sustainable', in relation to agricultural industries. The most generally accepted definition embraces the need for balance between ecological and economic aspects of sustainability. This is consistent with the goal of the sugar industry to be profitable in the short term, while managing and protecting our base resources to ensure profitability for future generations. This industry goal must also be achieved within the larger community and neighbourhood relations. The challenge for good managers is to adopt best available practices, where integration and good timing of inputs adds value to the whole operation by ensuring productivity and maximising profit by minimising loss of soil, water, nutrients or pesticides from the paddock or root zone.
My topics today include tactical issues, which are critical to short term profitability, as well as more strategic issues which under-pin future productivity and profitability, by maintaining quality of key on and off- farm resources.
MANAGING SOIL ACIDITY
Approximately 90% of soils used for growing cane in Australia are acidic, because of climate and soil forming processes. Acidity is enhanced by long term use of nitrogen fertilisers and annual removal from soil of calcium and magnesium (on average 25kg/ha of each) in cane sent to the mill. Sugarcane is much more tolerant of low pH and associated higher levels of aluminium than are legumes, maize and horticultural species. Significant and regular responses of sugarcane to liming products were not obtained in Queensland until after the mid-1970's. These responses appear largely related to deficiency of calcium as a nutrient. Prior to the early 1970's maintenance levels of calcium were supplied from fertiliser mixtures based on superphosphate, these were replaced by mixtures based on di-ammonium phosphate, which contains no calcium.
Canegrowers have been major users of liming products since 1975. However recent surveys in several southern districts show that some 30% of fields surveyed are still in urgent need of liming.
Analysis of commercial soil test results in north Queensland shows 60% of samples need liming;
the latter samples may be biased because growers would presumably have sampled a higher proportion of fields where they had productivity concerns.
Soil analysis is a reliable indicator of need to apply calcium and/or magnesium based liming products for correction of calcium deficiencies in sugarcane. If rotational crops are grown, more emphasis should be placed on pH. Calcium is not very mobile in plants, but is an essential part of plant cell walls; calcium deficient plants have poor root systems and restricted top growth.
Magnesium is required for chlorophyll used in photosynthesis and for movement of phosphorus in plants. Application of more nitrogen is an often used tactical response to stunted yellowing plants. If the problem is a calcium or magnesium deficiency more nitrogen will do nothing until the main problem is corrected.
Application of 5t/ha of lime is recommended to correct deficiency of calcium in the first instance.
Plant cane responses often cover application costs. Responses may last several crop cycles, but lower rates of It/ha are indicated every five to seven years to maintain soil calcium levels and high
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productivity. Necessity to retreat should be judged from a soil test, as should be the need for a product which also contains magnesium. Calcium and magnesium deficiency often occur together, but deficiency of magnesium only is rare. Use of a magnesic product alone when calcium is marginal causes major nutritional imbalance.
Amelioration of these aspects of soil acidity is the first of the integrated issues which benefit profit and sustainability. Production responses of 10 to 20 tonnes cane/ha often occur after liming.
Improved soil and plant calcium levels mean more extensive and stronger root systems, hence improved crop water use efficiency. Availability of other nutrients such as nitrogen and phosphorus is improved, while potential toxicity from manganese is reduced. Soil structure and tilth improvements benefit infiltration of water and ease of cultivation.
IMPROVED MANAGEMENT OF NUTRIENTS
The benefits to crop nutrition of improved management of acid soils were outlined above.
Additional benefits could accrue from development of better management strategies for nitrogen and wider adoption of current recommendations for phosphorus nutrition.
Nitrogen: Sugarcane is inefficient at recovering applied nitrogen fertiliser, with only 30% of fertiliser N being used by the crop in the year of application; the remaining 70% comes from mineralisation of reserves in the soil organic pool and previous fertiliser N which has joined the
soil pool. Fortunately sugarcane makes very efficient use of acquired nitrogen by producing more plant material per unit of nitrogen than many other crops. The two major issues for improved management of nitrogen are: (a) ability to recognise soil, climate and previous management situations where there is sufficient mineral nitrogen in the potential root zone to grow the target yield without applying nitrogen fertiliser; this is primarily a plant crop after fallow or in rich-land
situations, and (b) ability to customise nitrogen fertiliser applications to take account of nitrogen which is recycled in the GCTB system.
Research by BSES agronomist Les Chapman completed in 1976 showed that soil tests for nitrogen were not a reliable predictor of sugarcane responses to fertiliser nitrogen. There still are no other tools which allow reliable refinement of nitrogen fertiliser strategies. CSIRO staff are
currently incorporating knowledge of soil nitrogen processes into computer models which will take account of soil types, cropping history, previous nitrogen regimes and climate. This approach will allow assessment of the historic risk of different approaches to fertiliser nitrogen management.
Growers have stated that they are most averse to risks of reducing nitrogen rates because of the potential for impact on yield. Thus any new strategies must have high probability of success, as potential $ savings for individual farmers are quite small in relation to production risks. This is tempered however by the environmentally sensitive nature of nitrogen as a nutrient. Therefore it is important that the sugar industry is seen to adopt efficient nitrogen management practice, which minimise potential for off-site effects.
Our nutrient uptake studies show that 50% of the nitrogen acquired by the crop is contained in tops and trash residues left on the soil after green cane harvests. Is it available to succeeding crops? Studies by Les Chapman and his colleagues showed that the green cane mulch contained
104kg N/ha as ratooning. Approximately 9kg/ha of the nitrogen in residues appeared in the next crop, and a further 49kg N/ha was present in old trash and the surface 92cm of soil. Does this
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value increase with time under the GCTB system? The quantitive answer to this question will be provided by research to be conducted within the new Co-operative Research Centre for
Sustainable Sugar Production. Anecdotal evidence suggests opportunity for reduced nitrogen rates after several years under trash, but recommendations cannot be issued at this stage.
Phosphorus: Most of the soils used for growing sugarcane in Australia have medium to high levels of phosphorus, either from natural fertility, such as the Burdekin delta and other alluvia, or from historic use of phosphorus fertilisers at rates higher than those required to balance crop uptake. The probability of response to phosphorus fertiliser decreases for soil test results between
10 and 20 mg P/kg soil; there is no value in maintaining high soil phosphorus levels (>40 mg P/kg soil). Crop uptake will reduce the soil test by approximately 2.5 mg P/kg soil for each year phosphorus fertiliser is not used. Thus soils with phosphorus values of 60 mg P/kg soil could produce for at 8 to 10 years before a maintenance phosphorus fertiliser regime is instituted.
Savings of around $60 /ha/yr are indicated if application rates of 25 kg P/ha are avoided. An application of 20 kg P/ha is still recommended at planting to ensure ready access for the developing root system to a source of phosphorus, so as not to prejudice establishment of the plant crop.
The approach of with-holding phosphorus for ratoons on non-responsive soils is another component of a profitable yet sustainable production system. Phosphorus is one of the environmentally sensitive nutrients. The sugar industry has made a major contribution to reducing potential for environmental impact and increased profitability by adopting the GCTB system which reduces potential for loss of phosphorus with soil erosion; with-holding un-economic levels
of phosphorus is another major contribution.
MANAGING SOIL COMPACTION
Soil compaction during harvest and in-field transport of cane is a basic concern to growers, and is the prime reason for cultivation, other than weed control and seed bed preparation. Questions which arise from this issue for managers are: under what conditions does significant compaction occur, what level of compaction and change in soil properties affects production and what conditions and techniques are required to relieve compaction. These issues are of increasing relevance with wider adoption of green cane trash blanket (GCTB) and other minimum tillage systems. Non-tillage of ratoon fields is the norm in southern Afiica and increasing areas of Queensland and New South Wales. Can we manage these systems to give desired productivity and length of ratoon cycles?
While growers readily recognise compaction events and scientists can measure its effects on soil properties, effects on productivity have been variable in experiments in Australia and elsewhere in the world. Compaction increases soils bulk density which effectively makes the soil stronger and harder for roots to penetrate. Reduced soil porosity makes water less available when it is held in a higher proportion of finer pores. Thus we might expect comapction to affect productivity in
drier years when a smaller root system will severely restrict access of the crop to water and nutrients. A wet harvest followed by a dry growing season would be a classic set of circumstances for ramfed areas and reduced water penetration would increase problems for irrigators. I am
classifying stool damage by harvesters and transporters as a separate but related issue to compaction.
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BSES soil physicist Dr Mike Braunack has measured effects of compaction on soil properties and yield. Yield was reduced by first ratoon at Ingham, where conventional haulouts were used; while at Tully use of high flotation transporters was instrumental in delaying productivity impacts until second ratoon. Mike's experiments are in rows spaced at 1.5m and involves traffic on the stool, near the stool and in the centre of the interspace. Yield effects for conventional haulouts at Ingham were of increasing severity for inter-row, near row and row impact. Row impact was also
most severe for high flotation gear at Tully where differences between near-row and inter-row were small. Yield effects mirror the changes in soil properties under the row from traffic in the different positions.
The take home message is that adverse yield effects will be minimised by keeping traffic as far away from the stool as possible. This means that row spacing should be not less than 1.5m and
should preferably approach 1.8m. Such wide row spacings have adverse production impacts themselves and innovative dual row planting with controlled traffic paths may be required. Shorter term measures will include high flotation transporters, restricting weight of in-field loads and, where possible, delaying harvest until fields are less susceptible to compaction. The longer-term benefits of organic matter and earth worms in the GCTB system on minimising or restoring effects
of compaction are under evaluation.
BETTER PRODUCTION AND HARVESTING SYSTEMS
Better production systems A better production system should improve productivity, profitability
and life-style, while reducing risks associated with production and its off-farm impact. The GCTB system has fulfilled these criteria on most farms north of Townsville, where adoption at district level ranges from 58 to 98%. Lower adoption in the Burdekin (1 to 10%) the central and southern districts (5 to 35%) and in New South Wales (0 to 12%) hinges on real and perceived problems with components of the above performance criteria.
The GCTB system has benefited the industry by:
• Many cases of improved yield; up to 9 to 12 TC/ha in rainfed systems;
• Improved conservation of soil moisture; up to 200 mm prior to canopy closure in the Burdekin region;
• Reduced cultivation and herbicide inputs; but the weed population is changing and vines need special attention;
• Marked improvements in control of soil erosion and cleaner streams;
• Avoiding deterioration of burnt cane after rainfall;
• Improving life-style of farmers and urban people when cane is not burnt;
• Unqualified improvements in soil structure;
• Improved profitability.
In areas of lower adoption the following points are seen as significant issues:
• A high risk of poorer yield and ratoon failures associated with cooler and wet soil conditions, especially for cane harvested before September;
• Adverse effects of trash blankets on efficiency of furrow irrigation systems;
• Impact of, and management required for pests such as army worms and weevil borer;
• Fertiliser placement and fertiliser rates;
• Capability of available older harvesters to successfully cut un-burnt cane;
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• Slower harvest rates, especially for heavy crops and where contracts exceed 50,000 tonnes per season.
Major research projects are in place to address most of the above concerns. Research findings and industry experience has shown the importance of good surface drainage in the success of the GCTB system. Full benefits of the system are not realised until three to four years into the system;
therefore it is important to plan for its adoption by laser grading of fields, and in wetter areas adopting a form of mounded or bedded culture. Formation of mounds at ploughout, prior to the wet season, is preferable to formation just prior to planting. Where this is not possible, such as in ploughout re-plant fields, in-adequate soil moisture in the spring can prejudice crop establishment. In such situations a significant mound can be built after crop establishment.
A GCTB experiment at Rocky Point has shown small responses to trash over the last two growing seasons, which were drier than usual. An experiment has been planted at Bundaberg to
determine whether trash has a negative impact on ratoon yields under cool and wet conditions, if best management practice is employed.
Nutrient management should not be a constraint to adoption of GCTB. Many growers still prefer to broadcast urea onto trash blankets. Recent research from the Cairns area by David Calcino and Drew Burgess has shown that best yields are consistently obtained when urea is placed sub-
surface beside the trash. This placement was also better than delaying the broadcasting of urea until cane was 50cm high.
While GCTB experiments under scheduled flood irrigation in the Burdekin area show responses to trash retention, most of the results for irrigated trash blankets in overseas studies are either negative or neutral for yields in relation to burnt cane. A yield neutral result would be acceptable if irrigation requirements are reduced. However water conservation benefits of trash blankest will not be realised unless irrigation frequency is adjusted. It is also possible that failure to reduce water applications during the pre-canopy closure phase of ratoon crops could lead to overwatering and attendant risks of loss of nitrogen through denitrification.
Problems associated with rate harvest of large un-burnt crops of cane are issues for the Burdekin and two year crops in New South Wales, These issues and ameliorative opportunities will be addressed this year by Gavin McMahon in a project supported by the Sugar Research and Development Corporation.
Better harvesting systems The profitability and sustainability of more efficient and productive management systems is jeopardised if there is significant loss of cane during harvest. Extensive field surveys confirmed that harvesting losses were widespread, and supported earlier findings by Ross Ridge and colleagues of around 6% loss in burnt cane and 8 to 10% in un-burnt cane. These figures represented loss of $76m per year in 1993. It was also estimated that losses from dirt in cane added another $15m to industry losses. A major extension program was commenced in 1992 to address these as high priority issues.
Cane harvesting losses can be summarised into four main categories:
• Pick-up loss - includes loss from knock-down assemblies, brittle varieties and poor or high base cutter operation. Field conditions have a major impact for pick-up losses and dirt
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entering harvesters. Narrow rows (<1.5m), poor filling in of furrows, incorrect hilling up and inter-row furrow contribute to adverse results.
Chop and extractor loss-includes cane lost by incorrectly adjusted chop mechanisms and cane thrown out during cleaning. Correct chopper adjustment avoids small wedges being chipped from each billet cut, while modifications to deflector plates and fan speed of primary extractors have had major impact on cane losses, as shown in Table 1. There was little change in extraneous matter in most cases. The electronic cane loss monitor facilities adjustment of fan speed.
Boot and elevator loss - is caused by billets falling from the machine. Loss is minimised by awareness, response and co-ordination between harvester and handout drivers.
Spillage loss - occurs during transfer of cane from harvester to haulout and transfers at sidings or to road transport.
Table 1 Case studies illustrating major reductions to harvesting losses in 1993 (from Tony Linedale).
Harvester modification
Fan speed reduction in primary extractor: 13 cases (mainly green cane)
Deflector plate
modification: 9 cases
Cane loss (t/ha) Before
11.1
12.8
After 3.6
3.8
% reduction in loss Average
68
70
Range 19-90
41-90
Many of the modifications can be effected for low to medium cost. Because of the magnitude of expected reductions to losses, most modification are very cost effective and provide improved yields to benefit all sectors of the industry. Reducing dirt in the cane supply will be the focus of
activity for the 1995 season.
CONTROLLING PESTS AND DISEASE
Productivity and profitability are adversely affected by the impact of pests and disease on sugarcane, while heavy reliance on a narrow range of chemicals for control of certain pests has major implications for sustainability of current farming techniques in some areas.
Controlling pests The nineteen species of canegrubs which attack sugarcane represent the most
significant insect pest problem for the sugar industry. In 1993 yield losses of approximately $3m were recorded in addition to the $5m spent on canegrub insecticides. We currently rely heavily on suSConBlue and to a lesser extent on Mocap and Rugby for control of canegrubs. Need for alternative control methods and products is highlighted by the recent apparent failures of suSCon and Mocap to control Childers canegrub and of suSCon against greyback grub in the Burdekin.
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