Indigenous / Traditional African Leafy Vegetables

 

• Amaranthus species (Amaranths, Pigweed)
• Cleome gynandra (Spider Plant)
• Corchorus spp (Gushe)
• Brasica carinata (Kale)
• Solanum retroflexum (Nightshade)
• Cucurbuta spp (traditional pumpkin)
• Citrallus lanatus (Bitter melon)
• Vigna unguicalata (cowpea)
• Colocasia esculenta (Amadumbe)

Indigenous vegetables are important in improving food security in South Africa and world wide. Most indigenous vegetables are reportedly adapted to diverse conditions including dry land production. Since most of these crops grow naturally in the wild, there is not much information on cultivation practices. Various factors affect the growth of plants and water is amongst the most important, hence lack or excess may result in poor growth and subsequent yield loss. In South Africa, water is a scarce resource due to erratic rainfall as well as the competition for the resource between agriculture and other users. Most small scale farmers do no have enough resources to ensure constant supply of water which is necessary to ensure yields; therefore indigenous crops could offer an opportunity for increased water savings and improved yields. This calls for the need to conduct irrigation studies to determine the water requirements and water use efficiency of these crops.

Traditional leafy vegetable crops such as amaranthus, corchorus and cleome are important sources of food and nutrients. They have high nutritional value and contain significant levels of calcium, iron and vitamins A and C. Amaranthus and chorchorus are also rich in protein and fiber.

Although these crops can be considered as low management crops and can grow in poor soils, preliminary research results show that yield can be increased with fertilizer application. Corchorus productivity can be improved by fertilizer application, especially nitrogen. Nitrogen is also reported to influence the nutritional value (N, Ca and P content). Calcium and magnesium are reported to improve the development of fiber as well as yield and quality of corchorus. Cleome also responds positively to increased soil fertility. For good yields application of nitrogenous fertilizer is recommended. However, very high nitrogen applications will course succulent stems which reduce regeneration and this will be a disadvantage when plants are periodically harvested. Field trials are established to determine the effect of fertilizer (nitrogen, phosphorus and potassium) application on the indigenous vegetables’ growth performance, yield, quality and nutritional value. Pot trials are utilized to identify nutrient deficiency symptoms on a variety of traditional leafy vegetable food crops.

The main objective of this research is to determine the optimum planting date for selected indigenous vegetables in South Africa. Six different planting dates are evaluated for summer vegetables, being monthly planting dates from August to April and five different planting dates for winter vegetables, being monthly planting dates from March to July. The second objective of the study is to determine the best planting method by comparing direct seeding with seedlings.

The following indigenous vegetables are included in this study: Brassica rapa subsp. chinensis (Chinese cabbage), Solanum retroflexum (nightshade), Brassica carinata (Kale), Amaranthus cruentus(pigweed), Cleome gynandra (spider flower) Cucurbita maxima (Pumpkin leaves) and Corchorus olitorius (jews mallow), only Amaranthus will be used for the comparison between direct seeding and seedlings.

Allelopathic effect of Amaranthus

Vegetable amaranthus is mainly grown as a subsistence crop and only surplus are sold to the informal markets. This vegetable is mostly valued by different communities in South Africa and it is preferred for its flavor and palatability by rural communities. It plays an important role in nutrition among the leafy vegetables grown world wide. Several species are collected from the wild for subsistence but only a few are cultivated.
It was reported that several efforts have been made to unravel the taxonomic complex of amaranthus, but this has often led to further confusion due to many varieties, especially within a cultivated group of species.
Among the few common cultivated species are, A. graecizans (L), A. cruentus (L) and A. tricolor (L) and all of them are found in South Africa.

Allelopathy has been known to exist for centuries as way of survival mechanisms by plants. Previous research by the ARC showed that A. cruentus might be allelopathic to several other follow up crops including tomatoes, kale and bambara.
The current research investigates the allelopathic effect of Amaranthus on other crops in order to determine the crops’ feasibility for intercropping and in a rotation system. Seedlings for A. cruentus and A. tricolour are utilized for field as well as pot trials in this investigation.

​Spacing and harvesting methods
Amaranthus are ready for harvest in 20-45 days after sowing, depending on the variety and plant type. The optimum stage for harvest in most types of amaranthus could be fixed between 25-30 days after planting to get the highest yield as well as nutritious and palatable greens. Previous research conducted suggests that a plant density of 100-200 plants/m² can be practiced for the increased yield if uprooting method of harvesting is to be used. The yield can be between 1.0-2.25 kg/m², while 20-25 plant/m² is highly recommended for repeated cuttings. The first cutting can yield 1.0-1.5 kg/m². Continuous cropping of amaranthus may yield up to 30 kg/m² marketable product per year. Both yield and quality of leaves are higher with more frequent cuttings. Amaranthus’ yield can be increased significantly through improved sowing practices and proper choice of variety. The aim of the project is therefore to perfect the production practices of Amaranthus in optimizing spacing and harvesting methods. Seedlings of A. cruentus are utilized for this trial with six spacings and two harvesting methods as treatments on the institute’sI experimental field.

Agronomic traits in Amadumbi
Edible aroids (family Araceae) comprise of many underground food crops grown in several tropical and sub-tropical countries. Amadumbe or Amadumbi (Colocasia esculenta) and tannia (Xanthosoma sagittifolium) are the most important species. Amadumbe has been cultivated in southern Africa since its introduction by the Portuguese traders. Amadumbe is a herbaceous, perennial, tropical root crop that is grown in South African wetlands. Its tubers are processed into various types of food, including pounded’, boiled, roasted or grilled, fried slices, balls, mashed,, chips and Amadumbe flakes. The leaves, and sometimes the stems, are eaten as spinach and provide a supplement to maize. Traditionally Amadumbe is grown as a staple food, but during the past few years it has been used for other food products. These include Amadumbe base (an indigenous tuber and spinach pizza base), crisps, curry, and fresh Amadumbe, known as madumbi.. The inclusion of Amadumbe by a wellknown retail food chain among its products, significantly increased the status of this traditional vegetable and staple food. 

Results from the multidisciplinary research programme include the following:

1. In vitro generation was done successfully with several landraces and the methodology is implemented already as part of the multiplication of experimental material

2. Both tissue culture material and corms might be suitable as propagation material as there are no significant differences in yield of the progeny

3. Results with field trials indicate that corm size of planting material might have a significant effect on the final yield

4. An in-row spacing of 60cm with a between row spacing of 1m seems to be the optimum spacing under the trial conditions.

It is clear from preliminary results that the climatic area (Roodeplaat) is probably not ideal for the production of Amadumbe. The trials will be repeated this season with some attempts to lengthen the growth season by establishing the plants in environmentally controlled glasshouses before transplanting. Field evaluation of landraces and cultivars will also be expanded to other climatic conditions. Several trials were established in order to develop alternative methodology to obtain suitable planting material from corms.

Promotion of African leafy vegetables

The project on commercial production of African leafy vegetables is funded by the National Lottery Distribution Thrust Fund. The project was introduced to the Mukondeni village, in the Limpopo Province with all the conditions clarified in order to align their expectations with the project plan. Interested community members joined to the project in 2006. A working relationship was established between ARC-Roodeplaat and the Mukondeni tribal authority, the community as well as other stakeholders. A key contact person was identified in the community who will liaise with ARC-RoodeplaatI project leaders. A feasibility study on the possibility to commercialize a number of traditional crops is completed and several of these crops seem to be feasible for commercial production by the beneficiaries. Project visits and meetings are done at least once every two months in order to facilitate the establishment of infrastructure before production can commence.