Carbon, Nitrogen and Phosphorus Mineralization in Soils Amended with Native Shrub Residues in Semi-Arid Senegal.
E. Dossa, Oregon State Univ, Dept of Crop and Soil Science, ALS Building 3017, Corvallis, OR 97331, Richard Dick, Ohio State Univ, School of Natural Resources, 2021 Coffey Road, Columbus, OH 43210-1085, Mamadou Khouma, ISRA, BP Route de Hydrocarbons, Dakar, Senegal, and Aminata Badiane, USAID, B.P. 49, Dakar, Senegal.
Two native shrubs Piliostigma reticulatum and Guiera senegalensis are commonly found in farmers' field in parkland systems in the Sahel of Africa but their role in nutrient cycling is not well understood. We investigated C, N and P mineralization of soils collected beneath and outside the canopy of either P. reticulatum or G. senegalensis and amended with shrub leaf, shrub leaf + twig and straw manure. Amended soils were incubated at 30 C for 120 days in two parallel incubations for soils from each shrub species. The CO2 evolved was determined on one incubation, and mineral N and P leached out of soils with a 0.01M CaCl2 solution were monitored on the other incubation, periodically. Cumulative C evolved and N mineralized at 120 days was higher under the canopy of shrubs than outside the canopy. Cumulative P mineralized showed a similar trend with soils from P. reticulatum, but a reverse trend with soils from G. senegalensis, where cumulative P higher outside canopy than beneath the canopy. All amended soils immobilized N during the first 50 days of incubation with P. reticulatumand during the first 77 days of incubation for G. senegalensis. The mixture of Piliostigma leaf + twig slightly improved P mineralization in soil beneath the canopy while twigs of Guiera reduced P availability. These lab results suggest that these shrub residues initially tend to immobolize nutrients after they are incorporated into soils but this effect is moderated by the particular species canopy soil but these outcomes need to be verified under field conditions.