Abstract:

A number of studies have tested the effect of woody and herbaceous legumes on soil fertility and
maize yields in sub-Saharan Africa. Results have been mixed, however, generating debate about their
effects on maize productivity. A meta-analysis was conducted with the aim of evaluating the evidence
of yield benefits, or otherwise, from woody legumes and herbaceous green manure legume (HGML)
treatments (Ts). Ninety-four peer-reviewed publications from West, East and Southern Africa had data
complete enough to qualify for inclusion in the analysis. With unfertilized maize as the control (C)
in all studies, 54 publications compared maize yield using HGMLs, 28 using non-coppicing woody
legumes, 10 using coppicing woody legumes, 29 using natural fallows and 52 using fully fertilized
maize monoculture. Mixed linear modelling of yield difference (D = T-C) and response ratio (RR =
T/C) indicated that the yield response to legumes is positive. The mean yield increase over unfertilized
maize was highest at 2.3 tonnes per hectare (t ha-1) for fully fertilized maize and lowest at 0.3 t ha-1
following natural fallows. The increase in yield over unfertilized maize was 1.6 t ha-1 using coppicing
woody legumes, 1.3 t ha-1 using non-coppicing woody legumes and 0.8 t ha-1 using HGMLs. The
coefficient of variation in D was highest using natural fallows at 229%, followed by HGMLs at 136%,
non-coppicing legumes at 113% and coppicing legumes at 92%.