Soils of the Closed Forest zone of Ghana

Abstract

This is a study of the edaphic factor in the ecology of the tropical rain forest. Within this environment, the processes of soil formation have been intense in operation and of long duration, and soils with distinct properties have developed. The factors of pedogenesis underlying the formation of the soils of the closed forest zone af Ghana are outlined according to the evidence of profile morphology, and the characteristic features of the great sail groups which occur are described. On the basis of their physical properties and nutrient status in relation to the tropical environment, principles of agricultural land use are indicated.

A geographical approach is maintained throughout. The spatial relations of soils as expanses forming integral parts of the landscape are emphasised and, in conclusion, the special contributions which the geographer can make to pedology are summarised.

The thesis is based on work carried out in Ghana as a member of the Department of Soil and Land -Use Survey from 1953 to 1957. By 1955, Charter had devised methods of soil surveying for tropical forest lands (Charter, 1949a, 1949e), developed the organisation required for such projects (Charter 1950, S. L.U. S. 1957), and established the characteristics of the principal cocoa growing soils (Charter, 1949b). Just over 2,000 square miles of the forest zone had been surveyed. From 1953 to 1957, a further 14,000 square miles approximately of the forest zone were surveyed, of which the Kumasi Region (3,300 square miles) and the Birim Basin (1,500 square miles) were completed by the author.

Field work occupied some 30 months in total. It was during this period that the soil relationships with vegetation, geomorphology and parent material were observed and recorded, and these form the basis of the thesis. Although the forest surveys covered just over 50 per cent of the forest zone, they had been carefully selected so that the pattern of soils over the major geological formations under a representative range of vegetation and climatic conditions could be studied and comprehended. This was done in 1956 and 1957 when the author was responsible for forest zone surveys and for the correlation of data from all surveys throughout the country. During this period, various maps were produced of soils at different levels of classification for the country as a whole (S.L.U.S., 1958), the correlation of field characteristics and analytical data for the major forest soils was demonstrated (Crosbie and de Bndredy, 1956), and the latter soils were also classified in terms of suitability for cocoa production (Crosbie, 1957a).

There has been no previous account of pedogenesis in Ghana. In the second part of the thesis however, the classification scheme of C. F. Charter is adopted as a framework for description because it is soundly based on genetic factors. A chapter entitled 'Lower Slope Soils' has been included iá this section because of the areal extent of these soils in the aggregate and because they do not conform to any of the classification categories of Charter.

The principles of agricultural land -use outlined in the final section are evolved on the donnant environmental factors of climate and soil described in the main text.