Long-term changes in organic matter and microbial properties resulting from manuring practices in an arid cultivated soil in Burkina Faso

Fallows and livestock manure are the main means for improving the fertility of agro-pastoral systems in West African Sahel. As the general shortage of cropland has led to shorter fallow periods, manure appears to be the only means of maintaining soil productivity. Several studies have focused on the general pattern of nutrient release from manure but, so far as we are aware, few studies have investigated the long-term changes of manure input to tropical soils. This research project was carried out on ferralic arenosol in north Burkina Faso to assess the long-term residual effect of organic matter (sheep and goat manure) on land where livestock had been corralled. Microbial activities, soil organic matter and vegetal production were evaluated and a soil organic matter model was then drawn up and fitted to the data. The residual effect decreased rapidly during the first 5 years after corralling but remained significant for up to 11 years. The duration and magnitude of the residual effect depended mainly on the amount of manure applied. The differences in soil organic matter recorded between plots that had not been corralled for many years might result from the different amounts of manure applied in the past. Vegetal production and denitrification potentials were negligible below a minimum soil organic matter threshold. The initial soil organic matter level, the soil organic matter threshold and the residual effect of corralling should be taken in account when advising on the management of ecosystem services such as vegetal production and control of greenhouse gas emissions. For these purposes, it could be useful to produce a more advanced model.