Lablab purpureus (Dolichos lablab, hyacinth bean, njahi)
Lablab is a widely adapted, drought-resistant legume with tremendous potential to improve soil health, while also contributing to human and animal health. It has never reached its potential, possibly because it is always introduced to farmers as a crop with a primary purpose of soil improvement. Better to introduce it as a food crop with benefits.
A valuable multipurpose crop: Lablab has many benefits, explained below, that need to be communicated to farmers. But especially show farmers that the grain and tender leaves are delicious when properly prepared. Since lablab is a new crop for many farmers, providing additional training on utilization, cooking and nutrition is essential to motivate farmers’ interest.
Food for people
Edible grain: Grain comes in three colors: black, white and brown/tan. The black is the most common in the market but the white and tan seeded types may have a broader consumer appeal.
Nutritional value: The grain is highly nutritious. It is generally high in protein, iron, magnesium, copper and B1 vitamins. It is especially known for its high iron content and is used in some cultures as medicinal food for women who have just given birth.
Grain quality: The plant pods do not all mature at once. The first grain harvested is always of the highest quantity and quality. It is wise to avoid mixing this with subsequent grain harvests as the amount of unusable grain increases with each harvest. This increases the labor requirements for preparing seed or food, as one needs to remove off-color and shriveled grains.
Need for simple processing of the grain prior to cooking: The grain also contains anti-nutritional factors that can be mostly eliminated by simple but thorough washing and overnight soaking and discarding of the soak water.
It is critical to emphasize specific pre-cooking processing steps when introducing the crop. The majority of consumers will find it unpalatable if it goes straight from the harvest sack to the cooking pot. However, people like it when the proper processing steps are followed.
Tender leaves as vegetables: The tender leaves of lablab make a delicious vegetable. The cooked greens are soft, non-fibrous and not bitter.
Food for the soil (fertilizer value)
Medium- and late-maturing lablab varieties are good nitrogen fixers. A vigorous crop can fix up to 150 kg N/ha (Ojiem, PhD research) and greatly boost productivity of a subsequently sown, heavy- feeding crop.
Lablab also produces lots of residue in the form of litter, stems and roots. This increases particulate organic matter (POM), which cycles through the soil food web and helps create healthy soils. In soils with low levels of available P, high residue production is good for getting P to cycle organically.
Grain legumes that are high yielding but produce little residue do not offer the same benefits. Plant breeders have redesigned their “improved” varieties to push their nutrients into the grain. This comes at the expense of sustainable soil management, since they take more from the soil than they give back.
Weed control value
A vigorously growing lablab crop forms a good ground cover that suppress all types of weeds in a subsequent crop. This reduces the amount of labor that farmers need to use weeding a subsequent crop.
However, its most important role for affected farmers may be reclaiming striga-infested land. Striga is an indicator plant for poor soil health. When striga infestation is severe, a field becomes effectively useless for cereal production. We are encouraging the research farmers to put their trial plots on striga-infested lands so that farmers can appreciate the differences between management practices that suppress rather than promote striga.
Research results from western Kenya have shown that, compared to other commonly grown grain legumes, such as common bean, groundnuts and soya, lablab is the most effective at reducing striga germination and increasing cereal yields in striga-infested fields.
Fodder value
The plants are high in nitrogen and, when fed to dairy cows, will increase milk production. Dairy farmers in places with long dry seasons can use this as a dry season forage. In places like Brazil and Australia, the animals are allowed to graze the crop in the field, with supervision. The animals are removed before they kill the plants, which will regenerate when it rains.
Still, as with any new feed, it’s best to introduce it gradually.
Production information
Niche within farm: Best grown in the middle fields where the main cereal production takes place. Though broadly adapted to many soil types, it is sensitive to Aluminum toxicity and generally will not perform well on soils with pH of 5 or less.
Planting time: Best sown in the second, shorter season in bi-modal rainfall sites. Time the planting so that the pods mature during the dry season. The flowers, pods and seeds are favorites of insect pests but this timing of planting enables the crop to escape insect pressure., though build up of black bean aphids can still occur.
Establishment: Extremely susceptible to pre- and post-emergence damping off. Do not plant during times of heavy rainfall. Planting under such conditions virtually guarantees a poor stand with many gaps. Seedlings remain susceptible for the first 30 days after emergence.
Spacing: Plant rows 60 cm apart and 30 cm within the row, planting two seeds per hole. In many environments, the plant is capable of surviving the dry season. But it must form a complete groundcover before the dry season sets in if it is to survive. If you are late to plant, decrease the between row spacing to 45 cm between rows to give the canopy a better chance to close.
Growth habit: It has an indeterminate growth habit which means it can continue to grow vegetatively even after it has enters a reproductive phase. This has both advantages and disadvantages. The advantages are that it can often recover from stresses, such as damage from hailstones or drought, which would kill plants with a determinate habit . A major disadvantage is that the crop needs incremental harvesting. If the crop is not harvested as the pods ripen, bruchids and molds will essentially destroy the grain before it leaves the field.
Post harvest protection of the grain: The grain is highly attractive to bruchids, which lay their eggs on the pods in the field. Failure to take measures against bruchids will ruin stored grain in a very short time.
Residue management: The appropriate time interval between residue incorporation and planting will depend on residue quality. If the plant has dropped all of its leaves and the residue consists of just dry stem and leaf litter, it will require about 2 weeks between incorporation and planting. If the plants still have green leaves, they will decompose more rapidly and you can plant 7-10 days after incorporation. You don’t want to wait too long since nutrients released from the residues can easily be leached if there are no plant roots to take them up.
In Kitale, we allow dried plants to regrow with the very first rainfall coming out of the dry season to increase the N contribution of the residues and reduce nutrient immobilization. Then we incorporate the residues with a tractor (disc plough) and plant within 10 days
Varieties used in the trial
Not all farmers were given the same varieties. Characteristics of all the varieties distributed for the research are given below.
DL1002 and Eldoret black (Early): Two early maturing black-seeded varieties that reach 50% flowering within 51-60 DAP, depending on elevation/temperature.
Rongai, Eldoret cream and Echo cream: Three light-color-grained varieties that reach 50% flowering in 61-80 DAP, depending on elevation/temperature. If these can fit into the cropping system, they are more valuable than the early maturing varieties as they produce a lot more biomass, which is believed to improve striga suppression and accelerate progress in improving soil health. (See top of page photo of Lablab Rongai growing during the dry season in Kitale, Kenya.)
The Manor House hub has more than 15 varieties of lablab, which are available to partners to trial in their areas. We recommend the medium- and late-maturing varieties to reap the most overall benefits.
All varieties with black grain have purple flowers. Varieties with white, tan or brown grain have white flowers.