The challenge of HIV/AIDS: Where does agroforestry fit in? - World ...

46World Agroforestry into the Futurea. 9000ControlCrop residuesb.8000 FertilizerCrop residues + fertilizer7000Total millet dry matter (kg ha —1 )6000500040003000Dry matter/N applied (kg ha —1 )120100806040200020100001982 1984 1986 1988 1990 1992 1994 1996Year0Without cropresiduesWith cropresiduesFigure 2. The effects of crop residues and nitrogen fertilizer on (a) total millet dry matter yield and (b) nitrogen use efficiency at Sadoré,Niger (modified from Bationo et al. 1999).by significant advances in scientificunderstanding and practice. These includehigh-precision fertilizer management (e.g.Baidu-Forson and Bationo 1992) and thedevelopment of knowledge-based organicmatter management practices (e.g. Palmet al. 2001 and 2002; Vanlauwe et al.2003). The target of the these practices is,of course, not only to replenish soil nutrientsand improve crop yields but also to(re)build soil fertility for long-term sustainablesoil management. This has always beena target of soil fertility management but hasgained additional impetus with realizationof the wide range of ecosystem goods andservices that stem from the maintenance ofhigh levels of organic matter in the soil. Inparticular, the sequestration of carbon insoil as a means of alleviating the climaticimpacts of excessive greenhouse gas emissionshas become a global objective (Felleret al. 2001; Albrecht and Kandji 2003).Significant questions remain, however. Itis still unclear how to predict the optimumquantitative mix of fertilizers and the variousqualities of organic inputs. Such modelsmust take into consideration the substantialsite variability commonly found onfarmers’ fields, as well as the characteristicheterogeneity of tropical climatic conditions.Furthermore, while good formulaeexist for the provision of nitrogen andphosphorus, the interaction with other nutrients,particularly micronutrients, remainslargely undefined. A significant opportunityfor development exists in this areaof research now that very high priority isbeing given internationally to plant breedingfor micronutrient provision. Most significantly,all the successes tend to remaindisappointingly local in scale. The majorchallenge remains that of determining thenecessary actions to multiply the local successesto achieve impact at a continentalscale (FARA 2003). This requires betterinsight into the relationship between thetechnology performance and the prevailingconditions of the biophysical, institutionaland socioeconomic environments. Thefirst challenge therefore addresses both theadaptive range of the technological menuand the social and economic circumstancesthat influence farmers’ willingnessto adopt.Challenge 1: What are thedeterminants of the adaptive andadoptive advantages of the availabletechnological options for sustainablesoil fertility management?