The predominant concern when discussing motorization is the degrading effect on soil and water resources. In general, motorization of tillage entails an intensification of the disturbance of the soil. This results from both an increase in the intensity of movement and crumbling action when high power tractors are used and from an increase in the volume of soil that is disturbed because of greater working depth. Because of this intensification of tillage the use of motorized tillage is likely to increase soil and water losses, increase erosion and degradation of soil resources. Eventually this can result in loss of soil fertility, soil stability and other soil properties favourable to plant growth. FAO estimated in 1984 that if soil erosion continues unchecked between 1975 and the year 2000, about 18% of the rain fed cropland of the developing tropical countries will be lost and that rain fed crop productivity will fall by about 29% (FAO, 1984).

Respondents considered soil-related issues to be the main concern when using motorized tillage. Nearly all respondents mentioned the degradation of soil resources resulting from motorized tillage: erosion, degradation of soil structure, decrease in organic matter content, depletion of soil fertility, wind erosion, etc. Soil compaction and the formation of plough soles, both more serious problems than generally believed, were mentioned only a few times.

The causes most listed for soil degradation were the misuse and bad management of the equipment. Most respondents reported a general misuse, but others gave more detailed insight into the problem: tillage done not on the contour, too deep, maladjustment of implements or ploughing done at incorrect moisture content. Insufficient training of the tractor drivers was often attributed to these problems.

However important the adoption of a non-indigenous technology to match local circumstances is, it appears to be non existent in motorized tillage. It is true that disc ploughs are, in most cases, a better match for West African circumstances than the mouldboard plough because of easier use and sturdiness. And the fact that disc harrows are used for primary instead of secondary tillage also represents a kind of adaptation. But given that most of the implements and tractors seen in West Africa are second hand items designed for and used in other cropping and tillage systems, means that the rate of adaptation is low. Although not mentioned very often, the respondents confirm this to be a problem. In addition, in the cases of large scale government or sponsor driven introduction of tractors and implements, needs assessment studies are rarely done ,and there are numerous examples of failure because of this very reason. For example, one respondent found disc implements such as the disc plough and disc harrow to be inappropriate because they spread weeds with rhizomes.

Several respondents found the low level of mechanization in their country to be a problem in and of itself. Direct consequences are the under-exploitation of arable land and untimeliness of operations. One respondent mentioned that operations such as planting, weeding and harvesting are not mechanized, which results in a higher workload for these activities.

The lack of support to mechanization is seen as the main reason for the limited use of mechanized inputs. Farmers face difficulties in obtaining spare parts and after sales services. The scarcity of well-trained mechanics increases the breakdown rate of machinery. On the field level there is reportedly a general ignorance and mistrust towards mechanization. Institutional support to mechanization from government or other institutions, except for a few cases where large scale tractorization is in place, is generally non-existent.

Mechanization requires a certain farming system that is not often found in West Africa. The first major constraint in this matter is the size of the holdings per farmer and the size of each field, which hampers the effective use of tractors and results in a high percentage of non productive usage. Secondly, field clearing is a problem. Even when disc implements that can more easily overcome stumps and stones are used, fully cleared fields are rare. Steep slopes were mentioned as another constraint. Lastly, poor or non-existent access roads were found to contribute to the high breakdown rates of machinery.

Mechanization represents a high-cost, and often a high foreign exchange technology that low income farmers with limited capital can rarely afford. Together with the issues listed above, this is a paramount constraint for mechanization. Under mechanization programmes, farmers have often been provided with tractors for far less than the actual prize or under a credit scheme which invariably has very low recovery rates. Once confronted with the ‘real’ market prices of spare parts and maintenance, farmers will not be able to sustain their machinery. Prices for fuel and lubricants may also render tractorization unsustainable.

Notwithstanding the low level of motorization in West Africa, the specialists working in the field of tillage all consider the drawbacks of motorized tillage to be very important and serious. Most respondents said that mechanization is indispensable to increase productivity, production and meet the growing demands for food. At the same time they realize that current methods of motorized tillage are damaging the natural resources to the extent that there are irreversible environmental effects that will negatively affect food production, food security and food self-sufficiency. To avoid this, a careful and well considered guidance of the motorization process is needed, with special attention given to soil and water conservation.