Assessment of nutritional water productivity and improvement strategies for traditional vegetables in South Africa
Nyathi, Melvin Kudu - \ 2019
Wageningen University. Promotor(en): P.C. Struik, co-promotor(en): G.E. van Halsema; J.G. Annandale. - Wageningen : Wageningen University - ISBN 9789463950039 - 156
Benchmarking nutritional water productivity of twenty vegetables - A review
Nyathi, M.K. ; Mabhaudhi, T. ; Halsema, G.E. van; Annandale, J.G. ; Struik, P.C. - \ 2019
Agricultural Water Management 221 (2019). - ISSN 0378-3774 - p. 248 - 259.
Hidden hunger - Micronutrients - Nutritional food security - Traditional vegetables - Vitamin A - Water footprint - Water productivity
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.
The dual-purpose use of orange-fleshed sweet potato (Ipomoea batatas var. Bophelo) for improved nutritional food security
Nyathi, M.K. ; Plooy, C.P. Du; Halsema, G.E. Van; Stomph, T.J. ; Annandale, J.G. ; Struik, P.C. - \ 2019
Agricultural Water Management 217 (2019). - ISSN 0378-3774 - p. 23 - 37.
Green leafy vegetable - Micronutrient deficiency - Nutritional water productivity - Vitamin A - Water stress
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.
Nutritional water productivity of selected leafy vegetables
Nyathi, M.K. ; Halsema, G.E. Van; Beletse, Y.G. ; Annandale, J.G. ; Struik, P.C. - \ 2018
Agricultural Water Management 209 (2018). - ISSN 0378-3774 - p. 111 - 122.
African leafy vegetables - Deficit irrigation - Hidden hunger - Indigenous leafy vegetables - Irrigation regimes - Micronutrient deficiency
The major challenge affecting rural resource-poor households (RRPHs) in South Africa is deficiencies in micronutrients (iron and zinc) and vitamin A. Traditional leafy vegetables (TLVs) are dense in iron, zinc, and β-carotene concentrations. Therefore, they are deemed suitable to improve the dietary diversity of RRPHs. The main objective of this study was to assess the effect of irrigation regimes on nutritional water productivity (NWP) of selected leafy vegetables [Amaranthus cruentus (Amaranth) and Cleome gynandra (Spider flower), both TLVs, and Beta vulgaris (Swiss chard)]. Experiments were conducted under a rain shelter at the ARC-VOP, Pretoria, South Africa, during two consecutive seasons (2013/14 and 2014/15). Leafy vegetables were subjected to three irrigation regimes [well-watered (I30), moderate water stress (I50), and severe water stress (I80)]. Data collected [(aboveground biomass (AGB), aboveground edible biomass (AGEB), actual evapotranspiration, and nutrient concentrations (iron, zinc and β-carotene)] were used to calculate NWP of leafy vegetables. Swiss chard exhibited a higher portion of AGEB compared to TLVs due to its larger harvest index (0.57-0.92). Selected TLVs displayed superiority in terms of nutrient richness compared to Swiss chard, under I50. Results indicated that TLVs could provide more than the daily-recommended nutrient intake (DRNI) for vitamin A to all age groups. For iron, Spider flower could supply more than the DRNI to infants between 1 and 3 years of age, whereas for zinc, it could supply approximately 11% to this age group. However, higher micronutrient and β-carotene concentrations did not translate to superior nutritional yield (NY). Swiss chard showed higher Fe-NY and Zn-NY, whereas TLVs were rich in β-carotene-NY. Similarly, Swiss chard demonstrated the highest Fe-NWP (1090 mg m−3) and Zn-NWP (125 mg m−3), whereas Amaranth was larger in β-carotene-NWP (1799 mg m−3), under moderate water stress. These results show that there may be an opportunity to improve NWP under drought conditions. There is a need for future studies that will assess NWP for a wider range of leafy vegetables. These studies should be conducted in different locations and explore the effect of management factors (fertiliser, water stress, planting density and planting date), and soil type on NWP of micronutrients and β-carotene.
Calibration and validation of the AquaCrop model for repeatedly harvested leafy vegetables grown under different irrigation regimes
Nyathi, M.K. ; Halsema, G.E. van; Annandale, J.G. ; Struik, P.C. - \ 2018
Agricultural Water Management 208 (2018). - ISSN 0378-3774 - p. 107 - 119.
Biomass - Crop modelling - Evapotranspiration, indigenous leafy vegetables - Water productivity
Traditional leafy vegetables (TLVs’) are vegetables that were introduced in an area a long time ago, where they adapted to local conditions and became part of the local culture. In Sub-Saharan Africa, the use of TLVs’ as a nutrient dense alternative food source to combat micronutrient deficiency of rural resource-poor households (RRPHs), has gained attention in debates on food and nutrition security. However, TLVs’ are underutilised because of lack of information on their yield response to water and fertiliser. To better assess TLVs’ yield response to water stress, the AquaCrop model was calibrated (using 2013/14 data) and validated (using 2014/15 data) for three repeatedly harvested leafy vegetables [Amaranthus cruentus (Amaranth), Cleome gynandra (Spider flower), and Beta vulgaris (Swiss chard)] in Pretoria, South Africa. Experiments were conducted during two consecutive seasons, in which the selected leafy vegetables were subjected to two irrigation regimes; well-watered (I30) and severe water stress (I80). Measured parameters were canopy cover (CC), soil water content (SWC), aboveground biomass (AGB), actual evapotranspiration (ETa), and water productivity (WP). Statistical indicators [root mean square error (RMSE), RMSE-standard deviation ratio (RSR), R2, and relative deviation] showed good fit between measured and simulated (0.60 < R2 < 0.99, 0.94 < RMSE < 5.44, and 0.04 < RSR < 0.79) values for the well-watered treatment. However, the fit was not as good for the water-stressed treatment for CC, SWC, ETa and WP. Nevertheless, the model simulated the selected parameters satisfactorily. These results revealed that there was a clear difference between transpiration water productivity (WPTr) for C4 crops (Amaranth and Spider flower) and a C3 crop (Swiss chard); WPTr for the C4 crops ranged from 4.61 to 6.86 kg m−3, whereas for the C3 crop, WPTr ranged from 3.11 to 4.43 kg m−3. It is a challenge to simulate yield response of repeatedly harvested leafy vegetables because the model cannot run sequential harvests at one time; therefore, each harvest needs to be simulated separately, making it cumbersome. To design sustainable food production systems that are health-driven and inclusive of RRPHs, we recommend that more vegetables (including traditional vegetables) should be included in the model database, and that sequential harvesting be facilitated.