Assessment of nutritional water productivity and improvement strategies for traditional vegetables in South Africa

In sub-Saharan Africa, micronutrient (iron, zinc, and vitamin A) deficiencies are a major problem, affecting rural resource-poor households. Thirty-four percent of rural resource-poor households in sub-Saharan rely on agriculture; therefore, agriculture remains the main vehicle that can address food and nutritional insecurity. Over the past decades, some progress has been made in addressing issues around food insecurity. However, most attention has been given to promoting mainstream crops [Zea mays (maize), Oryza sativa (rice), and Triticum aestivum (wheat)], neglecting traditional vegetables which are presumed to be nutrient (iron, zinc, and β-carotene) dense, show a short crop cycle and low use of agronomic inputs in terms of water and fertiliser, and are abundant in the ‘’wild’’ or next to cereal crops as weeds. However, information on these benefits was anecdotal; assumptions were that traditional vegetables grow naturally without being supplied with fertiliser and water.

To the best of our knowledge, yield response of traditional vegetables to water and fertility stresses has not been assessed in a systematic method. This thesis aims to evaluate nutritional water productivity [NWP (above ground edible biomass and/ or storage organ biomass/ actual evapotranspiration) x nutrient content of a product] of traditional vegetables under a range of water levels, from rainfed to fully irrigated conditions.

We conclude that traditional vegetables could contribute to the daily-recommended nutrient intake for rural resource poor households. For example, under moderate water stress, amaranth and spider flower required less water (amaranth = 3544 litres day-1; spider flower = 5057 litres day-1) to meet total human nutritional requirements for a family of six, compared to Swiss chard (5992 litres day-1).