Sustainable alternatives to shifting cultivation. Shifting cul­tivation was the most widespread form of land use in the tropics and subtropics, but over the past decades, a transi­tion occurred to managed fallows or continuous cropping with crop rotation in densely populated areas. Alternatives to slash-and-burn clearing have been developed, which bet­ter conserve the organic matter accumulated during the fal­low periods. Managed fallows and sound rotations may en­hance soil fertility regeneration and even produce additional benefits. This allows for extending cropping periods and reducing fallow periods without compromising sustainabil­ity. The resulting "offshoots" of shifting cultivation raise a number of issues to be addressed by AKST. Firstly, it will be important to understand the transition process, its drivers and the newly emerging problems in order to assist farm­ers. Secondly, for targeted up-scaling of local experiences, it will be crucial to examine the potentials and limitations of different offshoots of shifting cultivation (Franzel et al., 2004).
     In less favored areas, low external input agriculture is the rule, as in these circumstances the use of mineral fertil­izers and pesticides is risky and only profitable in selected cases (e.g., in high value crops). Most of the successful in­novations developed for these areas built strongly on local knowledge.
     Due to the site specificity of these innovations, transfer to other unfavorable environments has worked only to a very limited extent (Stoop et al., 2002). The challenge for