Objectives
To determine the potential of locally available organic nutrient resources and zinc (Zn) on i) productivity and ii) grain nutritional quality of cowpea grown on a smallholder farm in Zimbabwe.
Methods
Cowpea is an integral grain legume in smallholder cropping systems and diets and is often regarded to as a women crop. An on-farm experiment was established in Hwedza smallholder area, Zimbabwe over 2 seasons on a Zn-deficient sandy soil to determine the influence of different fertilizers on cowpea nutrition. A factorial experimental design was used, comprising two nutrient treatments (cattle manure and N+P fertilizer), with and without ZnSO4 fertilizer. A low N+P treatment was also included. An early maturing cowpea variety, CBC2, was planted. Cowpea biomass and nodulation was quantified at flowering. Grain yield, quantified at physiological maturity, was analysed for nutritional content.
Results
Zinc fertilizer enhanced nodulation and biological nitrogen fixation by between 20% and 40% compared to non-Zn treatments. Cowpea biomass and grain yield ranged from 3.1 to 4.7 t ha-1 and 0.4 – 1.9 t ha-1, respectively with highest yields attained in cattle manure and Zn treatments with grain Zn and crude protein concentrations of 30.2 mg kg-1 and 29.4%, respectively measured in the same treatment compared to 17.2 mg Zn kg-1 and 19.6% protein measured in grains without Zn.
Conclusions
Cowpea performance could be limited by micronutrient deficiencies on granitic sandy soils. Agronomic bio-fortification with Zn fertilizers proved to be an option for enhancing cowpea grain Zn nutritional content thereby contributing to ameliorating dietary micronutrient malnutrition in these communities.
