INTRODUCTION

The soil is one of the essential elements for plant, animal and human life. It is a complex and constantly changing environment which, under normal conditions, is the result of an equilibrium between the forces of soil formation and erosion. In regions covered with vegetation, the humus removed from the soil is usually reconstituted. The natural development of soil with a covering of vegetation is slow; it is estimated that around 3,000-12,000 years are required for the development of 30 cm of soil.

Man extracts from the soil the main part of his food production but increasing demographic pressure forces him to extend land cultivation, intensify production and use techniques that are not always in line with the maintenace of soil fertility. Under the effect of man’s mishandling, the equilibrium is disturbed, erosion accelerates and, in many countries, whole regions are hard hit by this degradation and the fall in soil yield - with disastrous consequences for the physical and economic environment.

Soil conservation and related afforestation schemes have assumed increasing importance. This is due to the fact that, in the developing countries, soil erosion has assumed alarming proportions. There is need for environmental preservation and maintenance of ecological balance which, in itself, is very necessary for maintaining increased food production and, indeed, the very living conditions of the world.

Being relatively more labour-intensive, such soil conservation schemes hold a potential for high labour absorption during the construction phase as well as contributing to the development of land infrastructure for increased food production. The relevance lies in the high labour-intensity, quick wage employment generation for unskilled idle rural labourers and resultant infrastructure development.

Soil conservation is the outcome of a balance between the satisfaction of current and long-term needs. It is a national problem in view of its social and political implications - the solution of which far exceeds the technical and financial capabilities of the farmer alone. Implementation of a soil conservation programme, if it is to be successful, must be understood and supported by the population as a whole. This also presupposes technical innovation and collective awareness which will come about only after information and education campaigns.

The present document does not claim to replace the very abundant literature on this subject to which the reader should refer should he require a deeper knowledge of the subject. Its more modest aim is to assist engineers and senior technicians responsible for planning and implementing soil conservation projects. It contains: a review of the basic data on different types of erosion and control measures making intensive use of unskilled labour, standard methods for the design and planning of projects and, finally, guidelines for site organisation, operation and supervision.

Appendices contain a series of standard plans which, although they may, in many cases, suffice to define the work in hand, are no substitution for the specific studies that should be carried out for each site. It should be emphasised that the plans given are not necessarily the only possible solution to a given problem and that in all cases they have to be adapted to local conditions, customs and traditions especially with regard to the maximum use of local resources which should always be systematically pursued.