Benchmarking nutritional water productivity of twenty vegetables - A review

Traditional vegetables are piloted as champion species for sub-Saharan Africa, a region experiencing high levels of nutritional food insecurity and water scarcity. The important benefits of traditional vegetables over alien vegetables are; (i) their high nutrient density (iron, zinc, and β-carotene), (ii) their productivity under water stress, and (iii) their availability to rural resource-poor households. However, information on these benefits is anecdotal. The objectives of this study were to benchmark nutritional water productivity [NWP = (aboveground edible biomass and/ or storage organ biomass/actual evapotranspiration) × nutritional content of a product] of ten traditional vegetables and compare them with ten alien vegetables. We selected vegetables that are widely utilized by rural resource-poor households. A comprehensive literature search was conducted using common databases. Data [biomass (aboveground biomass and/ or storage organ), water use, and nutrient concentration] sourced from the literature were used to compute water productivity, nutritional yield (NY), and NWP of selected vegetables. Our results revealed that the water productivity of traditional vegetables was comparable to that of alien vegetables. In addition, traditional vegetables were superior in nutritional yield (Fe-NY and Zn-NY) and NWP (Fe-NWP and Zn-NWP) of micronutrients. Alien vegetables were rich in β-carotene-NY and β-carotene-NWP; this is contrary to the anecdotal information. We acknowledge the weakness of our approach; generating the NWP database using two independent datasets (crop water productivity and the nutrient concentration databases). However, this was the only pragmatic approach to establish first-order estimates of NWP for selected groups of vegetables. We propose that future research should be conducted to validate these results.