Nutritional quality of selected African leafy vegetables cultivated under varying water regimes and different harvests

Abstract

African leafy vegetables (ALVs) are considered rich in micronutrients and adapted to marginal production areas than their exotic counterparts. However, information on ALV nutritional content when grown under limited moisture is scant in the literature. In this study, we evaluated the nutritional composition of three ALVs (Amaranthus cruentus L., Corchorus olitorius L, and Vigna unguiculata (L.) Walp) – to varying water regimes using Beta vulgaris L. as a reference crop. The experimental trial was carried out at the Agricultural Research Council (ARC) in Roodeplaat, Pretoria over two summer seasons, 2015–2016 and 2016–2017. The irrigation levels were: 30%, 60% and 100% of crop water requirement (ETc) and nutrients were analysed at each harvest. From the nutritional analysis, under severe drought conditions (30% ETc) Ca and Mg were high in A. cruentus and C. olitorius while only Ca was high in B. vulgaris. The following were also observed: Na, K and Zn in A. cruentus, Zn in C. olitorius, P and K in V. unguiculata, Na and Zn in Beta vulgaris increased with increase in water application from 30 to 60% ETc. Further increase in water application did not improve the nutrient content. Leaf Fe, Zn, Mn, Mg, Ca increased as time of harvesting increased from 6 to 8 weeks, with no further increase at 10 weeks in A. cruentus, V. unguiculata and B. vulgaris. In C. olitorius, Fe, Zn, Mn, Mg and Na were high when harvested early at 6 weeks than during late harvesting at 8 and 10 weeks. Early and medium harvesting has potential to retain nutrient in leafy vegetables. Application of 60% ETc led to improved nutritional yield in all crops while concentration of nutrient under water stress indicates the potential of production in marginal areas.