Orange-fleshed
sweet potato (OFSP) leaves can be utilised as a fresh green leafy vegetable, in
addition to the traditional use of storage root; therefore, OFSP can be seen as
a “dual-purpose’’ crop. We hypothesized that no vine harvesting combined with
fertiliser application and irrigation will improve the storage root yield and
selected plant parameters (water productivity, leaf and storage root nutrient
concentrations, nutritional yield, and nutritional water productivity). The
objectives of the study were to (i) evaluate the effect of vine harvesting on
the selected plant parameters, and, (ii) assess the effect of irrigation
regimes and soil fertilisation on these selected parameters. Field experiments
were conducted at ARC-VOP, Pretoria, South Africa, during the 2013/14 and
2014/15 seasons. Treatments included irrigation regimes [well-watered (W1) and
supplemental irrigation (W2)], soil fertilisation [well-fertilised (F1) and no
fertiliser application (F2)], and vine harvesting [no vine harvesting (H1) and
vine harvesting (H2)]. For the 2014/15 season, the well-watered regime improved
total storage root yield (W1 = 13.0 t DM ha−1; W2 = 7.5 t DM ha−1).
Under the practice of vine harvesting, soil fertility treatments did not affect
(total dry storage root yield and dry marketable storage root yield) storage
root production. Our results further revealed that vine harvesting reduced
storage root nutrient concentrations (23% for iron; 14% for zinc; 12% for
β-carotene). Nevertheless, total nutritional yields increased; the highest
total nutritional yields for iron, zinc, and β-carotene were found under the
water and nutrient input regime (W1F1). Assessments showed that boiled
orange-fleshed sweet potato aboveground edible biomass could potentially contribute
to the daily-recommended nutritional requirement of iron and vitamin A for a
family of six people. More water was needed to meet the daily-recommended
nutrient intake (iron, zinc, and vitamin A) with OFSP grown as a storage root
crop only than when grown as a dual-purpose crop. Our results indicated that
there is an opportunity to utilise OFSP as a dual-purpose crop for rural
resource-poor households because total nutritional yields (iron, zinc, and
β-carotene) and total nutritional water productivities (iron, zinc, and
β-carotene) were improved. More research is needed to assess the effect of vine
harvesting on a range of OFSP varieties and should be conducted on the farm.
Rural resource-poor households are encouraged to produce OFSP for their own consumption
and the surplus could be sold at the local market.
Keywords
Micronutrient
deficiency
Nutritional
water productivity
Vitamin A
Green leafy
vegetable
Water stress
By Thesis Doctor
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