EXPLORING THE EFFECTIVENESS OF DIFFERENT FERTILIZER FORMULATIONS IN ALLEVIATING ZINC DEFICIENCY IN SMALLHOLDER MAIZE PRODUCTION SYSTEMS IN ZIMBABWE

Fertilization of staple cereal crops in smallholder farming systems of sub-Saharan Africa has mostly focused on supply of nitrogen (N), phosphorus (P) and potassium (K), despite the widespread deficiencies of micronutrients that include zinc (Zn). Cereal crops grown on granitic sandy soils occurring widely in Southern Africa have poor Zn nutrition. This study focused on evaluating the potential of different soil fertility management regimes in enhancing maize (Zea mays L.) productivity, grain nutritional quality and nutrient uptake on nutrient-depleted soils on smallholder farms of Zimbabwe. A preliminary soil fertility survey and on-farm experiments were conducted in different agro-ecological regions (NR) in smallholder farming areas of Wedza (NR II: 750 - 800 mm yr-1) and Makoni (NR III: 650-750 mm yr-1) districts in eastern Zimbabwe. The survey was conducted during the 2008/09 season to evaluate the effect of farmers’ soil fertility management practices on soil Zn status and maize grain nutrient concentrations. Ethylenediaminetetraacetic acid (EDTA) extractable soil Zn from the different farmers’ fields ranged from 0.5 – 2.43 mg kg-1 with the highest concentration associated with application of woodland leaf litter to maize. In both study areas, combined use of organic nutrient resources and inorganic fertilizers produced maize grain yields >2.1 t ha-1, sharply contrasting the non-fertilized treatment which yielded 0.80). An assessment of maize grain yield and quality benefits of Zn following application of organic nutrient resources and mineral fertilizers at different levels indicated that co-application of organic and inorganic fertilizers increased maize yields by 5.5-fold compared to the unfertilized treatment. Maize produced under leaf litter in combination with mineral NPK and Zn had the highest grain Zn concentration of up to 33.0 mg kg-1. Overall results indicated that mineral fertilizers as currently applied by farmers promote Zn mining and are likely to result in long-term severe deficiencies in soils. Integrated soil fertility management practices as currently presented to smallholder farmers are limited by lack of micronutrients which are required to improve available soil Zn, yields and nutritional quality of staple maize grains. While application of Zn- based fertilizers can be an entry point for enhancing grain quality of staple maize, farmers who apply sole mineral fertilizers have a higher demand for Zn than those who use combinations of organic nutrient resources and inorganic fertilizers.,The Harvest Plus Zinc Project Soil Fertility Consortium for Southern Africa (SOFECSA) CIMMY