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.