Effets des principales essences de la grande muraille verte sénégalaise sur les taux d'azote minéral du sol et la biomasse microbienne | Effects of major woody species of the Senegalese Great Green Wall on N mineralization and microbial biomass in soils

An experiment was conducted over nine months in a field system in northern Senegal in order to determine the effects on soil nitrogen (N) cycling and the microbial biomass-C properties of five plant species proposed for the Senegalese Great Green Wall (GGW): Acacia senegal (L.) Willd., Acacia tortilis var. raddiana (Savi) Brenan, Balanites aegyptiaca (L.) Del., Boscia senegalensis (Pers.) Lam. ex Poir., and Sclerocarya birrea (A. Rich.) Hochst. Soil samples were collected to a depth of 0-10 cm, outside (control) and beneath tree canopies. Microbial biomass, inorganic N content and net mineralization of organic N were determined for the soil samples collected under trees, and compared to soils collected outside tree canopies. The results showed that concentrations of inorganic N and soil microbial biomass-C were generally higher under canopy cover and differed according to species. In May 2014 (end of the dry season), microbial biomass-C was higher under A. senegal (31.8 mg C/kg soil) and lower under B. senegalensis and in the control sample from outside the canopy (17 mg C/kg soil). A higher microbial biomass-C content was found under A. senegal (49 mg C/kg soil) and B. aegyptiaca (53.7 mg C/kg soil) in October 2014 (end of the rainy season) and in January 2015 (middle of the dry season). In May 2014, the concentration of ammonium was significantly higher under B. senegalensis (11.17 mu g/g soil), while the control sample (outside the canopy) had the lowest concentration (4.93 mu g/g soil). For nitrates, there was no significant difference between canopy species (P <= 0.05). These results can provide guidance for selecting tree species for the GGW according to their functioning and their effects on soil quality.