Soil fertility and crop yields under improved-fallow systems in southern Mali † B. Kaya & P. K. R. Nair* School of Forest Resources and Conservation, P.O. Box 110410, University of Florida, Gainesville, FL 32611-0410, USA (*Author for correspondence: E-mail: pknair@ufl.edu) Received 20 March 2000; accepted in revised form 7 August 2000 Key words: biomass transfer, decomposition rate, multipurpose tree, on-farm trial, N uptake Abstract Improved fallows involving short-rotation woody and/or other perennial species are increasingly being tried as a means of sustaining crop production in impoverished farming systems of sub-Saharan Africa. The soil-improving potential of two tree species [Gliricidia sepium (gliricidia) and Pteocarpus erinaceus (pterocarpus)] and a shrubby legume Stylosanthes hamata (stylosanthes) was investigated in a four-year study on farmer’s field and in a research station in the Koutiala region in southern Mali (12.25° N, 5.42° W; 650 to 850 mm annual, unimodal rainfall; on a Typic Plinthustalf). Two strategies for soil improvement were tested: improved fallow sensu stricto and biomass transfer, the former ‘on-farm’ and the latter ‘on-station.’ In the on-farm experiment, maize (Zea mays) yielded best when it followed a two- year fallow of gliricidia alone or in association with stylosanthes. On the research station, maize dry matter production and grain yields during two seasons following the application of ex-situ grown biomass were similar and highest in the stylosanthes- and manure-applied treatments. The biomass decomposi- tion rates of the three species were in the order: gliricidia > stylosanthes > pterocarpus. The treatments did not have any significant effects on the soil fertility parameters that were monitored, possibly because of the short-term nature of the study. The treatments effects on crop yields were, however, significant. Gliricidia + stylosanthes in combination appeared to be particularly promising as short-rotation-fallow species in the region. Agroforestry Systems 52: 1–11, 2001.  2001 Kluwer Academic Publishers. Printed in the Netherlands. Introduction The farming systems in the Koutiala region of Mali are focused on crop and animal husbandry. Major crops include cereals (maize – Zea mays, sorghum – Sorghum bicolor, millet – Pennisetum typhoides) and cash crops (cotton – Gossypium hirsutum, and peanut – Arachis hypogaea). They have evolved in a parkland system that includes long periods of bush fallows, a traditional practice that is recognized to have beneficial effects on maintenance of soil fertility (Kater et al., 1992; Kessler, 1992; Kwesiga and Coe, 1994). Cotton, and to a lesser extent, maize, receive nutrient inputs in organic (manure, household waste, compost) and/or chemical (fertilizers and pesti- cides) forms. Other cereal crops seldom receive any fertilizer. The rapid population growth during the 1980s and 1990s has resulted in intense land use pressure, which, together with the unsustain- † Florida Agricultural Experiment station Journal Series Number R-07718.