Crotalaria (New)

General Information and Agronomic Aspects of Crotalaria 

Introduction

Crotalaria ochroleuca is a plant species belonging to the Crotalaria genus in family Fabaceae. The genus includes around 600 species mostly found in the tropical and subtropical regions, with Africa having the highest number of species at approximately 400. These plants can be found in various habitats, such as damp grasslands, floodplains, and along the edges of rivers and swamps. Crotalaria juncea, commonly known as sun hemp, is the most well-known species of the genus due to its use as a fiber crop and green manure. Apart from the cultivated C. brevidens, C. ochroleuca, and C. natalitia, some wild Crotalaria species, such as C. anthyllopsis Welw. ex Baker and C. Florida Welw. ex Baker, are occasionally collected as potherbs. C. ochroleuca and C. brevidens are two closely related African species used as vegetables. However, it can be difficult to distinguish between them as some information cannot be attributed to a specific species with certainty. C. ochroleuca can be identified by its pale-yellow flowers and fat pods, whereas C. brevidens has bright yellow flowers and a narrow diameter. Additionally, C. ochroleuca has a mild flavor, while C. brevidens is bitter. Despite their similarities, both species are commonly referred to as rattle pod, rattlebox, sun hemp, or slender leaf.

Crotalaria ochroleuca is a versatile plant species that has been used in various ways across Africa. In countries like Tanzania, Kenya and Uganda, the young leaves and shoots of the plant are cooked and consumed as a vegetable, similar to spinach. Apart from its culinary uses, the plant has also been traditionally used in medicine to treat various ailments like diarrhea, wounds, coughs, and rheumatism. This is due to the presence of alkaloids, flavonoids, and saponins that have potent medicinal properties. Furthermore, the plant has the ability to fix nitrogen in the soil, making it a valuable crop as a green manure and cover crop in areas with poor soil fertility. Its aesthetic appeal has also made it a popular ornamental plant in gardens and parks. The plant has recently been used as an agent to promote the germination of Striga, the parasitic plant that is a significant concern for maize and millet growers in Africa, and subsequently dies due to the lack of a suitable host plant. C. ochroleuca is also known to suppress Meloidogyne root-knot nematode populations and is locally used by East African farmers either in crop rotations or as a companion crop with nematode-susceptible vegetables such as tomatoes Additionally, oil extracted from its seed is sometimes used as an insect repellant.

(Abukutsa-Onyango, M.O., 2004, Sheahan, C.M. 2012, Schippers, R.R., 2004

Species account

Crotalaria ochroleuca is a tall, erect herb that can be either an annual or a short-lived perennial plant. It typically grows to a height of 0.5-1.5 m and has leaves divided into three narrow leaflets that are usually smaller than 13 cm long by 3 cm wide. The plant's stems have ascending branches and are ribbed. The flowers are yellow and have a noticeable purple vein. The plant produces fat pods that are shortly stalked and have blunt ends. These pods can grow up to 7 cm long by 2 cm wide and are slightly longitudinally compressed on one side. C. ochroleuca is mainly cultivated for its vegetables in tropical Africa, specifically from West Africa to the Sudan and south to Angola, Mozambique, Zimbabwe, and Botswana. The plant is distinguished from the Crotalaria brevidens species by its pod size and mild taste.

Related species

Crotalaria brevidens is a drought-tolerant species that grows up to 1.2 m tall. It has bluish-green leaves divided into three narrow leaflets, bright yellow flowers with conspicuous reddish-purple veins, and long, thin black pods. Native of tropical Africa from Nigeria to Ethiopia and south to Tanzania, it has been introduced in trials for use as a green manure crop. Its roots nodulate profusely, making it useful as green manure to improve soil structure and add nitrogen through the activity of Rhizobium bacteria. Native of tropical Africa from Nigeria to Ethiopia and south to Tanzania, introduced in trials for use as a green manure crop elsewhere. Its bitter taste is appreciated by older adults and it is usually cooked with Corchorus or milk to mask the bitterness.
(Maundu et al., 1999, Schippers 2002, Abukutsa-Onyango, 2007).

Adapted from AVRDC & IPGRI, 2006

2. Crotalaria juncea; is generally considered native to Bangladesh, Bhutan, and India, India but is now widely cultivated in the drier areas of the tropics and subtropics and many temperate regions as a green manure crop, often in rotation or as an intercrop with rice, maize, sorghum, tobacco, cotton, sugarcane, pineapple, coffee, and in orchards. The plant is also used to suppress weeds, prevent soil erosion, and reduce nematode numbers. It is a good indicator plant for potassium and calcium deficiencies. The dried stalks and hay are used as forage, while the woody stems remaining after fibre removal are used as fuel. Seeds are used to produce an adhesive for plywood and as a coffee substitute. They are also used medicinally to purify the blood, to cure impetigo and psoriasis and as an emmenagogue. However, it should be noted that the plant has been reported to be poisonous to livestock, and caution should be taken when feeding it to animals (Maroyi, 2011).

Climatic conditions, soil and water management

Ecological information

Crotalaria ochroleuca is a warm-weather plant that does well in temperatures between 20 – 30 °C for germination and 25 – 35 °C for growth. It adapts to a wide range of soil conditions, but it does not tolerate cool temperatures. The plant thrives in areas with high rainfall (above 600 mm/year) and altitudes of 500-2000 meters. It does best when cultivated under organic conditions due to its ability to fix nitrogen in the soil.

Propagation and planting

Planting

Crotalaria seeds are small in size and require thorough land preparation and a well-prepared bed for good growth. It is recommended to prepare 20 cm high beds during the dry season and 30 cm high beds during the wet season. Land should be prepared to a fine tilth for easy germination. Well-decomposed cattle manure is applied at the rate of about 1-2 kg/m if broadcasting or if sowing in rows, about 0.5 kg/m along the row. If using chicken manure, ¼ - ½ the rate of cattle manure is used.

Seeds are usually sown broadcast or in rows 30cm apart at a seed rate of 4-5 kg/ha. The seed germination capacity is usually good and it germinates in 3-4 days. Thinning is done 6-8 weeks after sowing to a spacing of 10-20 cm x 10-20 cm, depending on both soil fertility and moisture level. Under dry conditions, the spacing may be up to 30 cm x 30 cm. The thinned material can be used as the first harvest. When grown for a single harvest, 4-5 crops per year can be grown, but most farmers prefer to rotate rattlepod with other crops.

Currently there is no selection made to obtain the optimum variety and crops observed represent a mixture of landraces. However, there are clear differences in plant size and architecture, the branching capacity, the shape and the size of the leaves and several other characteristics that may well warrant basic breeding efforts. It is mainly self-pollinating so that a good level of varietal purity could be obtained within a few generations.

Companion crops

Crotalaria is a versatile crop that can be grown as a monocrop or intercropped with other crops that benefit from nitrogen fixation and nematode suppression. The roots of Crotalaria host numerous nodules that convert atmospheric nitrogen into ammonia, which boosts soil fertility for subsequent crops. As a mulch crop, it is sown in rows between the main crops such as bananas, sweet potatoes, kenaf, maize, or coffee. It is an ideal plant for crop rotation because its soil fertility effect lasts up to a year. Crotalaria is commonly used for subsistence farming and sometimes for market gardening. It thrives in semi-arid regions due to its deep taproots and lateral roots that tap into lower soil moisture levels. Broadcasting seeds is the preferred method for growing it as a fallow crop or green manure.

Husbandry

To ensure proper growth of Crotalaria Ochroleuca, it is recommended to thin the seedlings to a spacing of 15cm within the rows after one month of sowing. The excess plants can be consumed or sold. Weed control is essential, and hand weeding is the preferred method to maintain nutrient efficiency and good sanitation for healthy crops. Additionally, hand weeding will help control the parasitic weed Cuscuta suaveolens, which feeds on the roots of this crop and can hinder healthy growth if not kept under control. For optimal growth of slender leaf (Crotalaria brevidens), it is more effective to use farmyard manure instead of artificial fertilizers. Applying 20 tons of cattle manure per hectare is recommended. Inadequate rainfall can be supplemented with irrigation, especially in the early stages. Despite its ability to fix nitrogen, Rattlepod (Crotalaria ochroleuca) responds well to manure and biofertilizers.

Harvest, post-harvest practices and markets

1. Harvest

The first harvest of Crotalaria ochroleuca occurs about 4-6 weeks after sowing. At this time, the seedlings are thinned to 15cm within the rows. These thinned plants are used for the first harvest, and farmers can use ratoon systems from there to maintain desired spacing. To induce side shoots, the main stem is picked 15cm above the ground. Side shoots can then be harvested at 2-week intervals, with nitrogen fertilizer applied as topdressing to enhance their growth. This system has the advantage that some shoots can always be harvested, making it the preferred method for subsistence farming. The crop can continue to be harvested for over six months, and some farmers have been known to harvest a crop for a full year. As long as plants are cut for their shoots, no flowers, and therefore no seed, will be formed. Most farmers stop harvesting with the onset of the dry season, allowing the plant to flower and produce seed. Alternatively, farmers can harvest Crotalaria by uprooting it just before flowering when the stems are about 40cm tall and 8 weeks old. This method is commonly used when growing the crop as a catch crop between other crops. For mulching, the plants are uprooted or cut at soil level and placed between the crop rows.

(AVRDC & IPGRI, 2006, Grubben et al., 2004).

2. Post-Harvest

Fresh products are highly perishable, which is why they are so expensive in cities far away from the production areas. The leaves are picked up early or late in the afternoon, depending on when the product is delivered to the market. Once picked, roots should be washed in the case of uprooted plants. The shoots are tied in bundles and regularly sprinkled with water to reduce deterioration. Once tied up into bundles, the product should be put on a wire mesh if having to stay overnight. The product should not be stacked on one another as the leaves would be easily damaged. At 20-30ºC, they will last for 1 day; for longer storage, they should be kept below 20ºC. The leaves are often dried to be sold during the dry season. Drying in the sun takes 3-4 days during the dry season and 6-7 days during the rainy season. The flowers of Sunhemp can be dried under a shade for later use. These dried flowers retain their special flavour and are highly valued for use in soups (AVRDC & IPGRI, 2006).

3. Markets

Despite their nutritional benefits, the market value of crotalaria leafy vegetables in Africa is relatively low compared to other popular vegetable. Crotalaria is primarily grown in rural areas, where they are consumed locally or sold in local markets. Key factors contributing to its low market value include lack of consumer awareness about its nutritional benefits, misconceptions about its toxicity, and competition from other popular vegetables. To improve its status, consumers need to be educated about its nutritional benefits and new recipes and cooking methods need to be developed to make it more appealing. Additionally, more investment is needed in commercial production and distribution to increase availability in African markets

Nutritional value and recipes

Crotalaria leaves are a nutritious food source containing pro-vitamin A, calcium, iron, magnesium, protein, and fibre. They are particularly valuable in rural areas as they provide 100% of the daily requirement for some nutrients. Although bitter due to phytochemicals, they are an appealing dietary option. Furthermore, it is low in fat and calories, making it a healthy option for individuals who desire to maintain a balanced diet. Harvesting during the flowering stage optimizes nutrition value for some nutrients.

Table 1: Nutrient content of Crotalaria brevidens/100 g edible portion

Source: African Leafy vegetable market and Gardening practices by IPGRI & AVRDC 2006 (Unpublished)

a Lewis, J. 2019. Codex nutrient reference values. Rome. FAO and WHO

g Mayo Clinic

(Heuzé et al., 2017, AVRDC & IPGRI, 2006).

Complimentary recipes

The preparation of Crotalaria ochroleuca vegetable varies greatly across different African regions. There are various processing techniques for this vegetable, including boiling, mashing with maize, and cooking with cereals or dried tubers flour. In boiling, the leaves are softened and may be salted or mixed with butter before being fried to add flavor. The vegetable is often eaten with starchy foods such as stiff porridge. To enhance its mildly bitter taste, it is often cooked with other vegetables such as amaranth, cowpea, or pumpkin leaves, or with milk. 

In mashing with maize, the vegetable is cooked with maize, a mixture of maize, a pulse, pumpkins, or a starchy tuber like potato. These are mashed together, and butter may be added or the food fried. In cooking with cereals or dried tuber flour, the vegetable is boiled together with flour, and the mixture may be solid or semi-solid. In times of famine, the vegetable may be boiled and eaten with nothing else. In some communities, young pods and flowers are used in soups, but excessive consumption of the latter can cause drowsiness. 

a) Mitoo (Crotalaria sp.) and Mlenda (Corchorus sp.) with groundnut 

Ingredients

100 g Crotalaria leaves 
40 g jute mallow leaves 
2 tablespoonful traditional salt
1 tablespoonful or 20 g ghee or cow fat
1 tablespoonful groundnut 
½ cup water
Salt to taste
Preparation

Remove stalks off the leaves
Wash the vegetables and allow draining
Chop the vegetables roughly and mix them 
Add the traditional salt to the water and place on fire to boil
Add the vegetables, and boil them for 5 minutes. Keep stirring them as they cook 
Add the groundnut paste and ghee/cow fat then cook for 3 minutes
Serve hot with ugali
Variation

The same recipe is used when cooking Crotalaria and amaranth. However, two ingredients are eliminated i.e. traditional salt and groundnuts. Traditional salt is not used when cooking Amaranthus as it is a soft vegetable. Sour milk could however be used in place of ghee

Source: Cookbook for traditional vegetables (IPGRI, 2006). 

b) Mitoo 
Ingredients

2 bunches Crotalaria leaves (Crotalaria ochroleuca)
2 bunches of jute mallow leaves
1 bunch cowpea leaves
5 tablespoonful plant traditional salt 
2 cups water
Salt to taste
Preparation:

Remove the stalks off the vegetables, mix them all together and wash 
Add plant ash filtrate to water and let it boil for 5 minutes
Add vegetables to the boiling water and boil for 10 minutes under moderate heat
Add salt to taste
Serve with ugali
Remarks:

Frequent and continuous stirring causes mitoo to become more bitter. However, some people appreciate the taste. 

Crotalaria brevidens has been found to be more bitter than Crotalaria ochroleuca.

Many farmers do not recommend the use of the ordinary bicarbonate of soda, (Magadi soda) as they say it can be bad for the bones in the long run. This vegetable is common among the Luhya and Luo communities of Kenya. The dish is slimy and slightly bitter due to the 2 vegetables crotalaria.

Source: Cookbook for traditional vegetables (IPGRI, 2006). 

c) Fried mitoo

Ingredients

100 g Crotalaria
20 g onions 
30g (1 tablespoonful) butter/margarine
1 Cup  water
¼ cup fresh cream
Seasoning (optional)
Preparation

Remove the leaves off the stems and wash them
Bring the water to boil and add salt
Blanch the vegetables for 3 minutes
Drain the hot water, run cold water through the vegetable and drain
Heat the butter and fry the chopped onions slightly, without letting them brown
Add the vegetables, stir and allow cooking for 2 minutes
Add cream and seasoning of choice, stir
Serve with preferred starch and stew
Source: Cookbook for traditional vegetables (IPGRI, 2006).