The expanding information on agroforestry research and development around the globe
shows that agroforestry is being promoted and implemented as a means to improve
agricultural production for smallholder farmers with limited labor, financial, and land
capital (Ajayi et al., 2007). In Africa, and particularly southern Africa, the main constraint to
agricultural productivity is soil nutrient deficiency (Scoones & Toulmin, 1999; Sanchez et al.,
1997). For this reason, agroforestry research in the region has focused on soil fertility
replenishment (SFR) technologies over the years and the adoption and scaling-up of these
practices is the main thrust of the ongoing on farm research (Akinnifesi et al., 2008;
Akinnifesi et al, 2010). SFR encompasses a range of agroforestry practices aimed at
increasing crop productivity through growing trees (usually nitrogen-fixing), popularized
as fertilizer tree systems, directly on agricultural land. Fertiliser tree systems involve soil
fertility replenishment through on-farm management of nitrogen-fixing trees (Akinnifesi et
al 2010; Mafongoya et al., 2006). Fertiliser tree systems capitalise on biological N fixation by
legumes to capture atmospheric N and make it available to crops. Most importantly, is the
growing of trees in intimate association with crops in space or time to benefit from
complementarity of resource use (Akinnifesi et al., 2010; Gathumbi et al., 2002). The
different fertiliser tree systems that have been developed and promoted in southern Africa
(see Akinnifesi et al, 2008; 2010) over the last two decades are briefly discussed below. The
type of soil fertility replenishment (SFR) or fertilizer tree system appropriate for a particular
setting is determined by a battery of ecological and social factors.