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Study on the possibilities of agricultural valorisation of sugarcane scums and bagasse of SOSUHO (Gabon). As a first step towards the general use of organic fertilizers in improving poor agricultural yields of soils in the province of Haut-Ogooue, in Gabon, we studied germination and growth of seven different types of plants (maize, Zea mays L. var. 60 ; rice Oryza sativa Var. 1345 ; cacao-tree, Theobroma cacao Var. Forastero ; gombo, Hibiscus esculantus Clenson Spineless var ; culin, Cucurbita pepo Basma var ; aubergine, Solanum melongena, Asgrow var ; soya-bean, Glycine max tropical var.) on two six months old sugar cane residues. These residues, froth and bagasse were used by hemselves or mixed with earth or sand. By comparison with commercial compost, we found that froth and bagasse do not inhibit the germination of the seeds studied. However, we found that the growth of all species studied was better in froth than in bagasse. The results of chemical analysis carried out on these residues can explain partially the good growth observed in froth themselves or mixed with earth.

Variations between seasonal samplings of a forest soil were studied during a one year cycle. The total number of microorganisms was maximal in march, while qualitative variations of the bacterial and fungal flora were unimportant. Electron microscope studies showed physiological differences and enabled to evaluate the seasonal variations of the type of associations of soil microbes.

Scanning electron microscopy was used to evidence the aggregated structure of a forest soil as well as the presence of fungal hyphae external to soil aggregates. The supernatant of soil suspension in water mainly contained isolated bacteria, while ultrathin sections of aggregates frequently revealed groups of bacteria surrounded by a sheath of mucilage with adhering clay minerals on the outside. These results confirm the existence of two particular biotopes in the soil studied: one is located inside aggregates, and the other, in the inter-aggregate spaces.

The changes in the soil microflora as a result of introducing various organic substances (gelatin, chitin, cellulose and beech sawdust) into the soil were studied. The work was supplemented by electron-microscopic observations. Substantial shifts in the quantitative composition of the microorganisms take place only in the case of compounds easily accessible to them. Certain substances induce changes in the ratio of the groups comprising the soil micropopulation.