Implications of Soil-Acidity Tolerant Maize Cultivars to Increase Production in Developing Countries

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 increasing maize production in acid soils. The first is to use amendments (lime, gypsum) to correct soil acidity. This is expensive and not available for small farmers. Another disadvantage is that only the upper 30 cm of soil is corrected making maize roots to be concentrated in that layer and not growing beyond. The second approach is to develop tolerant cultivars. This solution is relatively inexpensive, environmentally clean, permanent, and energy conserving. International Center for the Improvement of Wheat and Maize (CIMMYT), in collaboration with several National Agriculture Research NARS all over the world, has been developing soil-acidity tolerant maize cultivars to increase maize production. For this purpose, acid soil tolerant maize populations were formed and recurrent selection was used to improve these populations for grain yield under both acid and normal soils. Cultivars developed from these populations show a consistent increase in grain yield in both acid and non-acidic soils. Under acid soils, the average grain yield of genotypes used to form the base population in 1977, was below 0.4 t/ha. The average grain yield of acid soil tolerant open pollinated varieties (OPVs) developed in 1993 and evaluated across 13 acid soil environments was 3.2 t/ha, while that of non conventional hybrids developed in 1995 and evaluated across six acid soil environments was 3.84 t/ha. In acid soils, high parent heterosis of up to 42.5% has been observed in inter-variety crosses and up to 261% in single crosses. Also, although superiority of hybrids compared to OPVs has been reported, OPVs will continue to be more important than hybrids for the acid soils over the next years, due to the poor economic conditions of farmers cultivating them. From our agronomic research, response to P of Sikuani, an acid soil tolerant cultivar, is higher than that of Tuxpeno (a susceptible cultivar) both in acidic and non-acidic soils. Grain yield of maize was higher using amendments with Ca, Mg, and S than with Ca and Mg only, although there were no differences among methods of application of amendments. Studies of microelements in acid soils showed a highly significant response to Zn. Planting maize in association with pastures in savannas could be a profitable alternative for farmers allowing them to raise more animals/ha with an associated gain of weight/animal. We are also looking for morphological and biochemical traits that may improve grain yield. Molecular and physiological studies are being continued to improve the efficiency of our breeding program. These activities are being developed in collaboration with prominent universities and research institutions worldwide.