A recent study in Zambia and Malawi has found that growing Gliricidia trees on maize farms boosts yield by 50%. This happens because the Gliricidia trees fix nitrogen from the air and, as I understand it, some of it comes out from their roots, benefiting the maize; this is a substitute for fertilizer. This could be a boon to Malawi especially, since the country’s program of fertilizer subsidies is increasingly hard for the government to afford.
Peter Aagard’s comments are thoughtful but I think maybe incorrect – he points out that you can’t just look at the agronomic benefits of planting the trees; this is an economic problem, and it must be both profitable and affordable within household’s credit constraints: “Researchers tend to focus on the agronomic benefits of technologies, while ignoring whether they are actually doable by labour-constrained households.” Labor constraints are a legitimate concern, but in general Malawian farmers are anything but labor-constrained. For a large part of the year (including most of the 5-odd months I’ve been here this time) they have nearly nothing to do. They are labor-constrained around planting and harvest time (and maybe in between, too, I’ve never been around during that period). The key question is whether those short periods when labor is at a premium overlap with the two or three times per year you need to prune the trees. If not, this innovation seems eminently affordable.