Ratoon management

for disease and pest control as they are applied to the sett and not the soil. Micropropagation techniques whereby certified disease free sugarcane plants are multiplied in vitro, hardened off, field planted and then propagated vegetatively are now being developed in various countries

(Snyman et al. 2008). Micropropagation of one apical leaf roll can yield up to 700 plants compared to 10 plants/stalk using the normal seedling route.

Choice of planting system

The choice of planting system is dependent on soil type, slope, region and a number of other factors.

An example of a planting system choice matrix is provided in appendix 3.

(2008) indicated that responses were largely associated with dry conditions in the early part of the growth of the crop. He summarized yield benefits to trash as followings.

Yield responses to trash

Average responses to trash (T) vs. burning (B) with tops removed (Bto) for all spring and summer harvested crops (starting in September) were 13 % : 10 % : 1 % in dry, average and wet seasons respectively, and for T vs. burnt with tops left scattered (Bt) these figures were 6 % : 5 % : -1 %.

For crops harvested in winter the responses to T vs. Bto were 4 % and -15 % for average and wet years, while the responses to T vs. Bt were -1 % and -13 % for average and wet years respectively.

There are clearly situations where a full trash blanket may be a disadvantage; it is often associated with greater than average rainfall during the pre-canopy period of crop growth. Thompson (1965) also reports on negative or no responses to a trash blanket in terms of yield from trials in Puerto Rico and Australia. Trash blankets are expected to create a problem with furrow irrigation but in at least one instance movement of the water along a furrow has been shown to be possible as it lifts the trash pieces and runs below them.

It is also apparent that burning and leaving the tops scattered provides a yield response which is less than that of a full trash blanket in dry conditions but better than a full trash blanket in wet

conditions.

Decision whether to burn or trash at harvest

Under conditions of full irrigation in dry climatic zones, burning can out yield trashing (Gosnell and Lonsdale 1977). In Zimbabwe over a plant crop and six ratoons, at irrigation levels of 1 and 0.84 x Class ‘A’ pan, burningwas superior to trashing in yield of cane and sugar/ha as well as in stalk count, smut count and most other parameters. At low levels of irrigation (0.68, 0.53 and especially 0.37 x pan) retaining the trash produced increased yield of cane and sugar/ha because of moisture

conservation. Trashing resulted in thicker stalks and lower fiber % cane than did burning at all levels of irrigation.

A number of factors need to be taken into account in the decision to burn or trash at harvest and van Antwerpen et al.( 2008) and Purchase et al. (2008) reported the development of a Decision Support System to evaluate the economics of trashing or burning. They included reference to the fact that a value could be placed on trash if removed and sent to the factory boiler station for use as fuel (see Chapter 13). There is also the possible payment for carbon via the clean development mechanism (CDM) which provided added incentives for trashing as opposed to burning.

Public pressure to eliminate burning

In spite of economic evaluations showing no benefit to trash in certain situations, it is likely that public pressure and a need to reduce greenhouse gases will result in moves to force industries to harvest cane green. Indeed, this is already the case in Brazil where burning will not be allowed after 2014 in fields harvested mechanically. The ramifications of this are that industries will have to find ways to mitigate the negative effects of trashing in these circumstances. If the trash blanket is a disadvantage it will need to be managed by parting the trash over the row or removing it partially or entirely from the field. Adjustments will be required to harvesting operations and managing the trash material, and in this way it is likely that the disadvantages can be overcome.

Burning with tops left scattered is clearly superior to burning with all residue removed. If residue was left lined and not re-burnt there is also likely to be a benefit compared to removing all residues.

Wynne and van Antwerpen (2004) concluded that more information was required in a number of areas including: (i) yield benefits of trashing under different circumstances, (ii) cane composition of different cultivars, (iii) rates of cane deterioration, (iv) influence of density on transport costs, (v) labor productivity under different trashing regimes and (vi) the costs associated with bottlenecks at sugar mills if trashing is widely adopted, (vii) the temperature effect in higher altitude areas, and (viii) the economics of trashed cane under irrigation. Subsequently van Antwerpen et al. (2008) conducted an exercise to test the sensitivity of the model by varying a selection of inputs such as the cane price, cost of fertilizers and herbicides and the number of labor units and their payment. All results could be explained using current knowledge with regard to trashing and cane growth, which leads to the conclusion that the model responds logically.

Use of a trash blanket in ratoons has a range of effects, as shown in Box 3.11.

Box 3.11 Positive and negative aspects of a trash blanket Positive effects

 Trash provides an effective physical barrier to weed growth provided sufficient material is available (weed control cost reduced by 35 % (Nùñez and Spaans 2007; Fillols and Callow 2010).

 Trash conserves soil moisture and increases yields in summer and particularly dry seasons (savings of 90 mm evaporation/an) (Thompson 1965).

 Irrigation costs reduced by 10% (Nùñez and Spaans 2007; van Antwerpen et al. 2008).

 Trash may cause a change in the weed spectrum which may be positive or negative (Fillols and Callow 2010).

 Trash provides an effective soil erosion control mechanism and reduces droplet impact on the soil (Moberly and McIntyre 1983).

 Trash reduces the amount of herbicides required and associated costs of chemicals (Nùñez and Spaans 2007).

 Improves soil organic carbon (Eustace et al. 2009).

 Improves N in the cane residues from 0.55 to 0.85 % (Nùñez and Spaans 2007).

 Improves cane yields particularly under rainfed conditions in certain soils (Thompson 1965; van Antwerpen et al. 2008).

 Improves soil fertility and soil health (Graham et al. 1999).

 Improves soil biodiversity of microorganisms (Graham et al. 1999).

 No air pollution or other effects of burning.

 Stalk thickness increased and fiber % cane reduced by trashing under irrigated conditions (Gosnell and Lonsdale 1977).

Negative effects

 Trash may increase the incidence of certain pests (trash worm) (van Antwerpen et al. 2008).

 Trash may suppress cane emergence under cold conditions (van Antwerpen et al. 2008).

 Under conditions of full irrigation in hot climates trashing can reduce cane and sugar yields, stalk counts and other parameters (Gosnell and Lonsdale 1977).

 Furrow irrigation is difficult (but not impossible) under conditions of full trash (see 13.3.3).

 Trash may suppress cane emergence in wet conditions (van Antwerpen et al. 2008).

 Trash blankets may be a fire hazard.

 Increases harvesting costs for manually harvested cane and mechanical by 68 %) (Nùñez and Spaans 2007).

 General reluctance of cutters to harvest green cane.

 Increased extraneous matter usually results from trashing depending on the quality of trashing (Nùñez and Spaans 2007).

Box 3.12 Burnt cane with tops left scattered Advantages

 Provides 60 % of the yield benefit of a full trash blanket in summer and is superior to a trash blanket in the cold winter months (Moberly and McIntyre 1983).

 Field observations indicate that runoff is substantially reduced by any mulch, even when it is present in small quantities (Moberly and McIntyre 1983).

Disadvantages

 No reduction in weed control costs as would be obtained with a full trash blanket.

 Disadvantages associated with burning.

Box 3.13 Burnt cane with tops raked into windrows Advantages

 Provides some soil erosion control and moisture conservation compared with re-burning of residues.

 Allows for a reduction in area to be treated for weed control.

 No trash worm likely.

Disadvantages

 Less effective than scattered tops for erosion control and water conservation.

 Yield disadvantage in dry climates.

 Some rows adjacent to the windrows may be disadvantaged as for a trash blanket.

Deep ripping in ratoons

Tejada (2010) showed benefits from subsoiling in terms of reducing compaction and increasing available moisture in an Alfisol in Colombia. Moberly (1969) reported on the effects of subsoiling in ratoon cane growing on 11 different soils in the South African sugar industry. The study was

conducted because of the perception that subsoiling is beneficial because it shatters compacted soil layers, prunes the old root system, encourages the speedy development of new roots, results in improved rates of water infiltration, improves soil aeration, increases the effective rooting depth of the crop, and facilitates root penetration. Moberly reported that of the 11 soils tested three showed statistically significant reductions in yield, seven showed no difference and one showed a significant benefit. Deep tillage was compared with standard interrow cultivation. He concluded that, “Any benefits which may accrue from this practice such as soil aeration, the increase in effective rooting depth and the prevention of runoff, are seemingly nullified by the effects of root damage caused by the subsoiler tines.”

Deep ripping in ratoons was tested by Leibbrandt (1985) under irrigated conditions in Swaziland, and no benefits were recorded. A reason put forward for the lack of response was that the soils were generally of montmorillonitic clay and any compaction was alleviated by irrigation. Swinford and Boevey (1984) recorded yield responses from ripping in a Longlands form soil which had been intentionally severely compacted. van Antwerpen et al. (2000) observed that yields could be reduced by 50 % from stool damage caused by cane haulage; machinery use infield was likely to increase;

that harvesting in wet weather would sometimes be unavoidable and that an option was to use controlled traffic. Attempt should be made to use equipment that allows fewer passes, and that organic material, e.g. filter cake (especially with a low bulk density and in reasonable amounts, e.g.

15 t/ha) should be applied. Tire design and pressure were also mentioned.

Box 3.14 Recommendations and conclusions on deep ripping (from van Antwerpen et al.

2000)

1. Damage to sugarcane stools and soil compaction are two separate issues, but they can occur simultaneously, especially with wet soil.

2. Stool damage caused by cane haulage equipment can reduce yields by as much as 50 % and reduce the number of ratoons before plough out.

In order to make provision for this growers should consider:

 Increasing the row spacing to suit the track width of infield equipment.

 Using pre-planned permanent zones for infield traffic. The principles of controlled zones for traffic and the use of infield tracks should be combined to restrict the area affected

by compaction and to keep compacted zones in selected interrows.

 Not allowing transport into fields when soils are wet. Using transport with long tire and track footprints in the direction of travel rather than those with the same contact area but that are wider and shorter. Transport travelling in the interrow but next to the row is bound to cause surface root damage and compaction close to the stool, which will almost certainly have a negative effect on yield. A distance of 0.75 m between edge of the row and the wheel, as reported in the literature, will certainly be effective in avoiding stool damage and will reduce the effect of soil compaction on yield, but is unlikely to be accepted by growers as a practical measure.

 A more acceptable distance between the edge of the row and the side of the wheel would be 0.40 m, assuming that the width of the tire is 0.6 m.

 When labor is plentiful, cane can be carried out to the nearest hard surfaced road.

 This means that total interrow spacing from the centre of one row to the centre of the next row should be 1.8 m (or wider). However, this will not suit all farming systems and growers should decide on a row spacing that will best suit their infield transport. Alleviation of soil compaction with a subsoiler is a popular technique with growers although the results from trials conducted in South Africa and Swaziland have shown no yield benefit from this practice.

 Only soils with an E-horizon in the grey soil group have shown a positive yield response to subsoiling, although limited.

 It appears that the likelihood of a positive response to subsoiling is low in soils with a high clay content. An alternative to subsoiling is to harvest cane on soils most susceptible to compaction during the dry months. The observation that subsoiling with a vertical mulcher is more efficient in alleviating compaction compared with a single tine ripper has been confirmed.

 Where soil compaction is a major problem and there is a choice of organic materials available, the principle to be applied is the use of organic materials of lowest density, as these will be more effective in reducing soil density.

 Where there is little choice of material, any type of organic material in reasonable

quantities will be better than none because of the general decline of soil organic matter in cultivated soils.

3.2.6 Summary of factors for consideration in achieving good management practices for ratoon