Statut de la matière organique des sols dans la zone sud-soudanienne au Burkina Faso

Organic matter status in some soils of Burkina Faso south sudanian zone. The study deals with organic matter (OM) of two soils units under natural formations located in the western part of the south sudanian zone of Burkina Faso. The objectives were firstly to increase the knowledges on this main component of soil fertility, secondly to point out the relationships between biological, chemical, physical soils properties and OM. To achieve it, total carbon (C) and nitrogen (N) of twenty-six soil samples issued from the topsoil were determined. Each soil sample was separated in three particles size fractions: (0–50 µm), (50–200 µm), (200–2,000).The amounts of C and N associated with each one were measured. In addition, soil samples were incubated during 31 days for C mineralization measurement, while the microbial biomass C was obtained by the chloroform fumigation – incubation technique. The results showed that total C and N of the whole soil were low and comparable to those of soils from the Burkinabé sahelian region. The distribution of C and N in particles size fractions indicated that (0–50 µm) fraction holded the highest quantities of C and N. The amount of C associated with each fraction was positively correlated with soil nutrients retention capacity. Such a correlation was established between C/N ratios of sandy fractions [(50–200 µm), (200–2,000 µm)] and the cumulative C mineralization. Thus, the study confirmed that pools of organic matter with different function and dynamics depending on their size and degree of decomposition were present in the concerned soils. The influence of texture on biological and organic status of soils was also pointed out. In order to increase soil fertility and to reduce soil degradation hazard, organic inputs were recommended.