Summary About 3950 million ha (30%) of the total ice-free land area in the world is under acid soils. Acid soils are characterized by low fertility caused by high levels of Al, Mn, and Fe, and deficiencies of P, Ca, Mg, K, S, and Zn. Of these, Al toxicity and P deficiency seem to be the most important causes for low maize yields (about 400 kg/ha for land race cultivars) in these soils. Maize is a staple for millions of people in developing countries where imports are growing up by 1.5 million tons (7%) per year. There are at least two alternatives to