Relationships between abiotic and biotic soil properties during fallow periods in the sudanian zone of Senegal

Abstract

Relationships between soil characteristics, various forms of soil organic matter, microbial biomass and the structure of phytoparasitic nematode populations were investigated in six fallow fields aged from 1 to 26 years in the West African Savanna (WAS) belt in southern Senegal. Soil sampling was performed along two transects in each field. Herbaceous biomass and soil physical, chemical and biological characteristics were studied with principal component analysis (PCA) and the relationships between the parameters were extracted with co-inertia analysis. Soil properties (mainly calcium, magnesium and total carbon content, and cation exchange capacity) slightly improved in the upper soil layer (0-5 cm) during the succession of vegetation. In contrast, in the 0-10 cm soil layer, microbial biomass and total soil organic carbon content showed no clear pattern of change over time, while highest charcoal stocks were found in older fallows where bush fires are frequent. In the 0-40 cm layer, living root biomass increased and herbaceous biomass decreased through the chronosequence. Evidence is presented here for particular relationships between some of the carbon components and the structure of the nematode community. #Pratylenchus and #Ditylenchus species were associated with the grass vegetation of the youngest fallows. In contrast #Helicotylenchus and #Scutellonema were present in old fallows. The multiplication of the latter appeared closely related to the presence of woody fine roots, whereas, that of the former seemed to be favoured by the presence of the coarsest root of trees. #Xiphinema$ had a higher density in soils with higher bulk density. Microbial biomass was not affected by fallow duration and was not correlated with the abundance of non-parasitic nematodes... (D'après résumé d'auteur