β-Carotene yield and productivity of orange-fleshed sweet potato (Ipomoea batatas L. Lam.) as influenced by irrigation and fertilizer application treatments

β-Carotene rich orange-fleshed sweet potatoes are increasingly used in community-based interventions aimed at addressing vitamin A deficiency, but are often cultivated in marginal soils and with sub-optimal agricultural inputs. The aim of the study was to determine (i) β-carotene content, β-carotene yield and water productivity at increments of water application, and, (ii) β-carotene content and β-carotene yield at increments of chemical fertilizer application for orange-fleshed sweet potato in separate field trials. β-Carotene content at the low irrigation treatment was between 15 and 34% higher than at optimal irrigation treatment. Increased water application brought about a two-fold increase in β-carotene yield per unit area. The best combination of β-carotene yield and water productivity (g β-carotene ha−1 mm−1 water applied) was achieved at the intermediate (60%) irrigation treatment. Calculations showed that 1 ha of orange-fleshed sweet potato produced at the intermediate water application at yield level of 24.6–28.4 t ha−1, can potentially provide 452–730 households (of six persons) with an adequate amount of vitamin A over a period of 180 days. β-Carotene content was 14% higher for both intermediate (50%) and high (100%) fertilizer treatments, compared to the 0% fertilizer treatment. β-Carotene yield increased two-fold at the intermediate and four-fold at the high fertilization treatment. This paper provides novel information on the effect of irrigation on β-carotene yield, as well as β-carotene water productivity in orange-fleshed sweet potato. Follow-up research on a range of varieties is suggested toward obtaining recommendations for broad application in vitamin A crop-based interventions to optimize the β-carotene yield in orange-fleshed sweet potato.

► An increase in irrigation increased root yield, but reduced β-carotene content.
► β-Carotene yield over the different water regimes ranged from 2.07 to 9.73 kg ha−1.
► Water productivity for β-carotene ranged from 11.7 to 19.8 g ha−1 mm−1.
► Fertilization increased root yield, β-carotene content and β-carotene yield.