Conservation Agriculture (2003, Vol. 23 No. 1) - SIA

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by Kenrick Chandon & L. Oliva Agra
It is well known that ‘virgin land” produces much higher crop yields than soils repeatedly cultivated. While it may never be possible to fully maintain virgin land productivity, it would be worthwhile trying to reduce the decline that comes from continuous cropping. This is being attempted under a concept known as ‘conservation agriculture.’

After viewing the results of modern farming methods, scientists have come to conclude that old-fashioned methods were indeed best for preserving soil productivity. Modern methods tend to result in more rapid soil degradation and therefore less sustainable agriculture. For instance, when the sugar industry turned to pre-harvest burning of trash, in the early sixties, to facilitate mechanical cane loading, this was the modern thing to do. That came at a cost however, as organic matter, which used to be returned to the soil when the trash decayed in green cane harvesting, was now lost. Soil became more exposed to erosion during rains and tended to dry out more quickly during droughts. Gradually, such soils became less productive.

Heavy machinery simplified land preparation, making possible the ploughing of large areas more thoroughly and in much shorter time than before. At the same time we were loosening and exposing vast tracts of land to forces of erosion in a manner unheard of when we were restricted to the use of the fork and hoe.
We sometimes make matters worse by furrowing down-slope rather than along contours, speeding up soil loss from erosion. Meanwhile the weight of machinery and equipment used in cane cultivation and harvesting compressed the soil making it less suitable for the passage of roots.

In summary, our forefathers were practicing a form of agriculture that preserved the land far better than we do now. Their careful management meant that we inherited soil with inherent high yielding capability. That is a legacy we have largely squandered.
Nonetheless, it would be impractical to go back to the old fashioned methods. What conservation agriculture seeks to do is to use modern methods to achieve the same end results our forefathers did.

The objectives of Conservation Agriculture are:
1. to reduce soil degradation
2. to conserve, improve and make more efficient use of natural resources

Conservation agriculture is now rapidly gaining popularity across the world. The Sugar Industry Research Institute has been approaching it by focussing on the areas of reduced tillage, trash blanketing, crop rotation and the application of manures. In this issue, reduced tillage technology will be discussed.

In conservation agri-culture, crops are grown with minimal tillage of the soil. Typical land preparation involves several passes of tractors and equipment to do ripping, ploughing, harrowing and furrowing, often with some operations repeated. The objective is to produce a seedbed of uniform tilth to a depth of at least 18 inches.
With reduced tillage, the same depth and quality of soil tilth is achieved with far fewer number of operations - often no more than one pass of equipment as against the typical five or six passes in conventional land preparation. Cultivation is restricted to only the strips of land in which the crop will be planted. However, these strips are cultivated no less thoroughly. Reduced tillage therefore uses less energy, disturbs less soil surface, retains the mulching effect of the crop residue and, most importantly, is less costly.
Over the last five years, SIRI has designed and developed special machines for reduced tillage. The first was a single row machine, given the name RTM 1.5, Figure 1, and the second a double row (RTM 3.0), Figure 2.


Old foliage killed by Roundup spray. Planting furrow opened by one pass of the Reduced Tillage machine

Land preparation completed

Sprouts emerged, old banks still present

Cane growth after 4 months - old banks destroyed by inter-row cultivation

Cane field at 6 months
The sequence of events in replanting a field using the reduced tillage approach is as follows:
1. Destroy the old cane stools with a chemical (glyphosate) spray when the sprouts are about four weeks old
2. Prepare the seedbed with one pass of the Reduced Tillage Machine (RTM), which opens a furrow in the inter-row space (Figure 2)
3. Drop seed cane
4. Apply fertiliser
5. Cover with conventional tractor drawn covering tool
6. Inter-row cultivate when cane is sufficiently grown to destroy old banks and build up bank along new cane row (Figure 4)

SIRI used the single row machine (RTM1.5) to prepare a field at its experiment farm at Springfield in 1999. Without use of chemicals to kill the old stubble, the bank was split and the new cane inserted. This field was furrow irrigated. Establishment was quite good, as there was no need for supplying, but not all of the old stubble was killed and there were volunteers (approximately 5%) of the old variety mixed with the new. However, growth and yield were quite acceptable being at or above farm average for plant cane and three ratoon cycles so far.
In August 2002, the newly developed double row machine (RTM3.0) was used to prepare another field at Springfield. This field was treated in the manner outlined where glyphosate was used to kill old stubble and the seed planted in the inter-row spaces. Drip irrigation tubes were laid along with the canes before covering. Figure 5 shows that at 6 months this field looks as good as any planted in conventional manner.

Reduced tillage is therefore important in conservation agriculture as it results in minimal disturbance of the soil, thus reducing risk of soil erosion while producing an adequate growth environment for the crop. At the same time, there are other obvious benefits such as:
1. reduced fuel consumption during land preparation
2. reduced establishment cost of up to 50%
3. increase in land prepared in an hour
All this is achieved with no appreciable difference in growth and yield between the reduced and conventional tillage.
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