Cultivating Improved Varieties of Maize Does Not Guarantee Sufficient Dietary Provision of Fe and Zn in a Maize–Bean Intercropping System in Eastern Uganda: Evaluating Effects of Climate and Soil Types

Abstract

Since hunger and malnutrition are affecting billions of people, the effect of cropping seasons, soil types and climatic conditions (temperature and precipitation) on yield, iron (Fe), zinc (Zn) and amino acids content in grains of hybrid maize (Zea mays), at smallholder farms in Eastern Uganda, was examined. Thirty-six (36) on-farm experiments under maize–bean intercropping with NPK fertilizer were established across three soil types (Petric Plinthosols, Lixic Ferralsols and Vertisols) and growing conditions (seasons, temperature and rainfall). We found significant differences in the grain yield between seasons, but not between soil types. Fe (mean of 22.48 mg/kg) in maize–grains significantly correlated with Zn (mean of 23.21 mg/kg), soil pH, soil organic matter and total nitrogen. Grain amino acid concentrations differed significantly between the seasons and across soil types. Precipitation and temperature did not significantly influence grain-yield nor grain Fe and Zn contents. For two seasons, the hybrid maize variety did not perform better than other varieties in the regions. Thus, a critical finding is that improved varieties of maize is not enough to facilitate increased Fe and Zn uptake nor amino acids content in their grains to desired levels. Hence, a diet dominated by maize will not supply sufficient micronutrients (Fe and Zn) to meet the human dietary requirements in this region.