From Soil Conservation to Conservation Agriculture

2.1 Soil Tillage Concepts within a Conservation Agriculture
2.1.1 When to Till the Soil
2.1.2 How to Behave in the Field
2.2 Implications for the Farmer
2.2.1 Small Farmers
2.2.2 Mechanised Farmers
2.3 The Role of Agricultural Engineering
2.3.1 Reinforcement of the Commercial Sector to Promote New Implements
2.3.2 Operator Training
2.3.3 Organization of Farmers for Contracting Equipment

3. Summary

1.1 Erosion

Agriculture is world-wide causing serious soil losses. If the destruction of agricultural soils continues in the same way, humans might face serious problems to feed a growing population. There are different causes for this inadequate use of the soil. In many developing countries the hunger is forcing poor people to cultivate areas which are not suitable for agricultural use and which only with major and costly efforts, like the construction of terraces, can be sustainably converted in agricultural land.

However, serious damage, because it is on large scale, is also caused by mechanised farming. As an example may serve the dust bowls of the 30s in the USA that destroyed vast areas of fertile land through wind erosion. The same mistakes are at present still causing important soil losses in the agriculture world-wide.

Erosion has become a direct threat to farmers. Systems where developed to control erosion and conserve the soil which means to avoid that the soil moves from one place to another. Evidence of these concepts for the control of water erosion are contour planting, contour bunds and trenches to avoid down-slope water runoff. In other places, great effort was spent in the construction of terraces. It was recommended not to leave the bare soil unprotected but to cover the surface with stubble or other mulch to break the kinetic energy of wind and water. In short, many efforts where undertaken to avoid that wind and water would move the soil.

1.2 Water Conservation

With all these measures it was not reflected that erosion is not the main problem but only a consequence of the way agricultural soils are treated, particularly in mechanised agriculture. As example might serve the western plains of Nicaragua. This area with the most fertile soils of the country has always been intensively cultivated. Over the last 40 years it converted to a cotton growing area. With the cultivation which until present is nearly exclusively done by disc harrows the soil erosion problems increased. As a solution to the problem terraces were constructed following strictly the contour lines. The result were irregularly shaped plots some of which could hardly been cultivated by a tractor. Those terraces were tilled over 20 or 30 years always with disc tools without any change in implements. To make it worse, tractors had on the small plots to carry out frequent turns. At present, all the soil in the western plains of Nicaragua has serious compaction problems. But what is even worse, the compaction does not permit water infiltration (Kayombo and Lal, 1994). To avoid water logging on the terraces the water is led away in drainage canals. As a consequence of this, the area is now characterised by enormous erosion gullies and the ground water table has considerably fallen.

This shows that soil loss through erosion is only part of the problem. The loss of rain water that cannot infiltrate in the soils to replenish the ground water reserves might on the long term be the more serious problem.

Consequently, the way soil is cultivated must be drastically changed. Soil erosion and water loss is not controlled by mechanical means but only by a living and stable soil structure. Only this can avoid that water runs on the surface rather than being absorbed as completely as possible by the soil.

2. The Concept of Integrated Soil Management - The Conservation Agriculture

2.1 Soil Tillage Concepts within a Conservation Agriculture

Unfortunately there exists no mechanical implement that could create a stable soil structure. Mechanised soil tillage can only destroy this structure. Therefore we need a different concept of soil tillage and profound knowledge of the type of intervention each implement is carrying out in the soil.

Certainly it must be differentiated between different soils and their susceptibility to soil structure losses. However, in any case a stable and optimal soil structure for plant growth as well as for water infiltration and erosion control is only achieved by living biological processes in the edaphon like for example the creation of humus.

2.1.1 When to Till the Soil

Under the above concept the best form of mechanised soil tillage is not to do any. However, the concepts of zero-tillage are not applicable in all cases. Agriculture is always an artificial intervention in natural processes and therefore it has to be accepted that, from case to case, corrective interventions have to be done. Even under zero tillage concepts, some sort of tillage is done through traffic for planting, pest control and harvest. Traffic causes compaction and is as such one form of tillage.

Each time a problem occurs that might call for a tillage intervention the problem should be carefully analysed to find out a way to control it with a minimum intervention in the soil.

Within possible interventions 5 different basic operations of soil tillage can be distinguished:

- turning
- mixing
- loosening
- pulverising
- compacting

In addition to those basic operations of soil tillage some other agricultural operations have a direct effect on the soil:

- mechanical weed control
- shaping of surfaces - ridging, levelling
- harvesting crops like potatoes, beets, peanuts

Each tillage implement carries out a specific spectrum of those basic operations. The knowledge of these characteristics and the availability of adequate equipment allow to limit the intervention to the minimum necessary. Some of the operations of the second category cannot be avoided. But the majority of the basic operations of the first group are not essential for agriculture. This accounts particularly for the turning operation which represents the most drastic intervention in the soil.

Turning
The most suitable implement for this operation is the mouldboard plough. However, the necessity to bury surface material into the soil and bring soil of deeper horizons to the surface is very limited. The argument that ploughing controls weeds is not necessarily true if the operation is carried out annually: in this case seeds from the last year are brought back to the surface while fresh seeds are conserved for the next year. The use of the plough originated and was justified in situations of limited traction power and with simple planting equipment that required a clean soil surface for proper seeding.

Mixing
This operation can be done with implements like a chisel plough or heavy tine cultivator. It could be justified to facilitate the decomposition of stubble or surface mulch. The depth of intensive mixing is usually not more than 10 cm.

Loosening
This operation is best carried out with a Paraplow which allows loosening without any other intervention in the soil. Under situations of a compacted soil or a soil with an unstable structure this operation creates sufficient pores in the soil to permit water infiltration. However the residual effect of this treatment varies a lot depending on the soil characteristics and subsequent operations (Kayombo and Lal, 1994).

Pulverising
This operation was formerly required for seedbed preparation. For that purpose only a very shallow superficial horizon was necessary to be pulverised. The pulverisation of deeper horizons, as it can be achieved with disc harrows or rotavators, is in no case justified. At present, the technology for planting the majority of field crops without the need of a seedbed exists. Only in very few cases, mainly in horticulture, the fine seedbed preparation might still be required.

Compacting
This operation becomes necessary after a deep loosening operation has been carried out shortly before planting. Compacting is required to assure the capillary contact to the soil and groundwater. For the same reason the seed is after planting usually pressed into the soil which represents also a small compacting operation.

The necessity of many of the above operations resulted from the deficiencies of planting equipment. Definitively none of the operations as such can create an ideal soil structure.

With the disc harrow all five operations are carried out at the same time: the soil is turned, although not as completely as with the mouldboard, it is mixed, loosened, pulverised over the entire working depth by the friction on the rotating discs and compacted beneath the cutting edges of the disc. The long term result is a degraded soil with a noticeable compaction horizon.

2.1.2 How to Behave in the Field

The previous chapters explained that the soil does not need to be tilled in order to obtain the ideal structure - on the contrary, mechanical interventions in the soil should be reduced to the minimum possible. However, some operations related to the cultivation of crops cannot always be avoided as, for example, planting, weeding, fertilising, pest control and harvest. Those interventions inevitably may lead to soil compactions. Some soils under certain conditions can cure themselves from these compactions, others can't. In any case the operator of agricultural machines should be aware of this problem and organise the traffic in the field in a way that passes are minimised and unnecessary traffic is completely avoided. The selection of appropriate equipment like tractors with rubber tracks (Erbach, 1994), soft tyres with low pressure (Vermeulen and Perdok, 1994) and the selection of the right time to access the field help to minimise the negative effects of traffic on the soil (Larson et al., 1994).

An interesting concept to avoid unnecessary compaction of the soil is the controlled traffic. In the ideal form all equipment used by one farmer has the same working width (or a multiple of that). In this way heavily compacted but very limited traffic zones develop. The rest of the field is never compacted which is reflected on the long term in very reduced requirements for soil tillage (Taylor, 1994). However, this systems requires sometimes a complete change in the equipment of a farm and a high level of operator's discipline.

2.2 Implications for the Farmer

2.2.1 Small Farmers

Due to the fact that the most disastrous effects on the soil result from high speeds and from power-take-off-driven implements, problems of soil degradation are less pronounced in animal traction systems. In addition to that the intervention of animal traction in the soil is of very limited depth.

This, however, does not mean that erosion and soil degradation does not exist in animal traction systems. Only the origin of those problems is not so much due to the wrong use of a technology or the selection of the wrong implement, but more due to the fact that the cultivation practice as such is not appropriate. If a slope is deprived from vegetation cover it does not matter too much, how it is done, because it will inevitably cause erosion.

Even for animal traction planting equipment for zero tillage is existing. However, in many cases this equipment is too expensive or sophisticated to justify the purchase for a small subsistence farmer.

2.2.2 Mechanised Farmers

For a mechanised farmer the concept of a more specific tillage within a concept of a conservation agriculture requires, in general, access to implements with more specific mode of action and that means, in the majority of cases, the farmer needs more implements. Only farmers with a very narrow spectrum of crops grown could ideally limit their equipment to planting, application and harvest equipment. Other farmers might always have the necessity for some sort of tillage. The security aspect should also not be forgotten. In case of adverse weather conditions or any other not foreseen events the farmer might wish to be prepared for the necessary soil tillage intervention (Gogerty, 1995).

A farmer who actually would have only a disc harrow and eventually a disc plough might need a subsoiler or paraplow, a chisel plough, a mouldboard plough and other implements depending on the soil type and climate (Reynolds, 1995). Many of these implements might not even be used every year. In this case the farmer would have to bear a much higher investment in machinery than with the traditional system.

In addition to this, the farmer might have to change other pieces of his machine park. Regardless, whether the new system is reduced or zero tillage there will be always more crop residue on the surface. This means that the planting equipment must be adapted or even replaced. For row crops that would allow mechanical weed control special high residue cultivators are required.

These changes are usually very significant for a farmer and make the transition expensive and risky. Without special technical assistance and, in some cases, other incentives it is difficult to convince farmers to change their tillage practice.

2.3 The Role of Agricultural Engineering 2.3.1 Reinforcement of the Commercial Sector to Promote New Implements

Whenever extension services carry out validation trials of new tillage methods including changes of equipment the private sector of dealers and manufacturers should always be involved. This would guarantee that implements required for the new technologies are commercially available.

Normally the impulse for these technological changes should come from the commercial sector. Unfortunately in many countries this sector is not sufficiently professional to take the technological lead. The economic reality of many countries inhibits also this sort of commercial initiative. Therefore dealers usually offer with a minimum investment equipment generally known which the farmers buy without special promotion. This leads to a vicious circle where the farmer only buys what he knows and the commercial sector also only offers what the farmer knows.

Mechanisms must be identified to break this technological stagnation.

2.3.2 Operator Training

Tractor operators usually do not receive special training and very rarely know how to correctly adjust tillage implements. Lack of professionality, wrong equipment settings, among other problems, make the negative effects of traditional tillage implements even worse. One example is the frequent desire of tractor operators to work at high speeds sacrificing in this way work quality and causing unnecessary pulverisation. Many countries have no capacities, what so ever, to train agricultural machinery operators. Therefore it results difficult to introduce new equipment that might require special operator training.

Field traffic and measures to reduce traffic induced compactions as far as possible also depend very much on the training of the operators.

These measures start with the tyres and the pressures used and end with the organization of the work in the field to reduce as far as possible unnecessary turns and trips. In this context the awareness about the susceptibility of a freshly loosened soil to recompaction is also very important. With respect to this frequently mistakes result in serious compactions for example of headlands and consequently to a significant reduction in the water infiltration capacity.

Solutions for adequate and sustainable operator training are essential for improvements in that sector.

2.3.3 Organization of Farmers for Contracting Equipment

Possible solutions to the mentioned problems of a high investment charge for farmers would be systems of shared equipment use which could be organized between farmers or using contractor services. This would not only reduce the financial burden of each farmer but would also facilitate the updating of the equipment to the latest technological developments and the training of specialised machine operators.

This sector also requires appropriate specific solutions for each country or region which should be developed and evaluated.

3. Summary

Soil and water conservation leads to problems, not only of technical origin. To achieve real changes in the field farmers must be offered appropriate technologies in an integrated way reflecting all aspects of their farming system. The only way, this offer can be sustainably presented, is through the commercial sector. Incentives and, above all, training for dealers and manufacturers of agricultural equipment, for farmers and machinery operators are necessary to achieve this. Innovative concepts for the use of the equipment are necessary to reduce the financial burden of the farmers. These aspects which are essential to achieve changes in the soil tillage practice require inputs from agricultural engineering in an integrated way.

Bibliography

Erbach, D.C. (1994): Benefits of Tracked Vehicles in Crop Production; in: B.D. Soane and C. van Ouwerkerk (Eds.): Soil Compaction in Crop Production, Amsterdam 1994

Gogerty, R. (1995): When One Tillage System Isn't Enough; The Furrow 100(4): 37-38

Kayombo, B. and R. Lal (1994): Responses of Tropical Crops to Soil Compaction; in: B.D. Soane and C. van Ouwerkerk (Eds.): Soil Compaction in Crop Production, Amsterdam 1994

Larson, W.E., A. Eynard, A. Hadas and J. Lipiec (1994): Control and Avoidance of Soil Compaction in Practice; in: B.D. Soane and C. van Ouwerkerk (Eds.): Soil Compaction in Crop Production, Amsterdam 1994

Reynolds, R. (1995): New Ways to Break Old Ground; Deere & Company, Moline/Illinois, USA

Taylor, J.H. (1994): Development and Benefits of Vehicle Gantries and Controlled Traffic Systems; in: B.D. Soane and C. van Ouwerkerk (Eds.): Soil Compaction in Crop Production, Amsterdam 1994

Vermeulen, G.D. and U.D. Perdok (1994): Benefits of Low Ground Pressure Tyre Equipment; in: B.D. Soane and C. van Ouwerkerk (Eds.): Soil Compaction in Crop Production, Amsterdam 1994