Tuesday, November 14, 2006 - 3:15 PM
148-8

Crop Productivity and Nutrient Cycling in Coppiced Indigenous Shrub Intercrop Systems of the Sahel.

Ekwe Dossa1, Ibrahima Diedhiou2, Mamadou Khouma2, Modou Sene2, Aminata Badiane2, and Richard Dick3. (1) Oregon State Univ, 3017 ALS, Soil Science, Corvallis OR, OR 97331, (2) ISRA, Route des Hydrocarbures, Dakar, Senegal, (3) Ohio State Univ, 2021 Coffey Road, SENR Kottman 210, Columbus, OH 43210

Native shrubs (Guiera senegalensis and Piliostigma reticulatum) that coexist to varying degrees in cropped fields of the Sahel have largely been ignored in terms of research. These regrow over the dry winter followed by farmer coppicing and burning of shrub residue in the spring prior to planting. We hypothesized that the presence of shrubs in farmers' fields and an annual non-thermal return of shrub residues to soils would alter the N/P cycling and nutrient efficiency for crops.  The objective was to determine the N and P budgets and temporal dynamics in shrub-crop (peanut and pearl millet) systems. Field plots were established in Senegal, West Africa, at two sites in 2003; 1) P. reticulatum in the higher rainfall south (700-900 mm)  and G. senegalensis in the lower rainfall (200-400 mm) northern region. These have a split-plot design with shrub (absence or presence) as a main plot and fertilizer (0, 0.5, 1 and 1.5 dose of recommended NPK) at subplot level. In 2004 and 2005 the presence shrubs increased peanut and millet yields by about 50% over non-shrub plots. The presence of shrubs increased fertilizer efficiency and yields at all fertilizer rates – even when no fertilizer was applied. A second study on shrub biomass in the absence of plants (factorial of 1500 or 3000 kg ha-1 by 0, 0.5 or 1.0 X the recommended NPK fertilizer dose) investigated N and P cycling, C fractions and crop yield. In 2004 and 2005 there were no negative effects of shrub biomass on crop establishment or yields, which provides evidence that shrub residue need not be burned.  Non-thermal biomass management is increasing particulate organic matter of soils and improving soil quality in these sandy soils.