RARELY does a neglected crop offer such promise as the pigeon pea. Not only is it richly laced with minerals, vitamins, fats and protein, but it can fertilise the soil as it grows, provide material for thatching new homes or be burned as a cooking fuel. And for the small farms of the developing world, pigeon pea is becoming a regular money-spinner; Kenya, the world鈥檚 second largest pigeon pea producer, now exports the vegetable to Britain.
Pigeon pea, or Cajanus cajan, is a woody, perennial legume. It contributes about 5 per cent of world鈥檚 legume production, but has been dubbed an 鈥渙rphan鈥� crop by scientists because, unlike mass-market crops such as wheat and rice, pigeon pea has been neglected by researchers.
Plagued by a caterpillar pest, pigeon pea yields have been stagnating since the early 1970s. But now the plant looks set to flourish 鈥� a host of developing countries could benefit as the pigeon pea鈥檚 potential becomes more widely recognised, improved varieties come on to the market, and the plant鈥檚 most damaging predator is successfully driven back.
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Pigeon pea is found in many parts of Asia, Latin America and Africa, but most is grown in India by small farming families, for their own use and for sale in local markets. After a growing season of six to nine months, the peas are harvested from the pods and used mainly as 鈥渄ahl鈥�, a soup served with rice. In some areas, pigeon pea is harvested four to six weeks earlier, before the pods dry out, and eaten as a green vegetable.
鈥淧igeon pea has great potential,鈥� says James Ryan, director-general of the International Crops Research Institute for the Semi-Arid Tropics, based in Hyderabad, in the southeast Indian state of Andhra Pradesh. For the past ten years, the Consultative Group on International Agricultural Research has contributed $700 000 annually towards ICRISAT鈥檚 pigeon pea research. It is an unusually nutritious food, says Laxman Singh, who breeds pigeon peas at lCRISAT. It contains more minerals and ten times more fat than ordinary peas, as well as five times more vitamin A and three times more vitamin C. It has a protein content of up to 28 per cent, making it an excellent complement to mainly cereal or root crop based diets, which are generally protein-deficient. When harvested as a green vegetable, the peas have an even higher protein and fat content than the dry pods.
But pigeon pea isn鈥檛 just a good source of nutrition. Cultivating pigeon pea can improve the land, replenishing essential nitrates, says Singh. The plant roots host bacteria which absorb nitrogen from the air and convert it into soluble nitrates. Singh estimates that the plants provide about 40 kilograms of nitrates per hectare for the next crop, which could wean farmers off expensive, toxic chemical fertilisers. When the pigeon pea is ready for harvesting, its leaves fall to the ground and can be ploughed in, adding more essential nitrogen compounds to the soil. Singh says that this could dramatically improve the land in many northern Indian states, where heavy application of fertilisers to grow wheat has left much of the land highly acidic and almost infertile. 鈥淚n these states, we could see a tripling of arable land under pigeon pea,鈥� he says.
Pigeon pea鈥檚 roots may also help to recycle phosphate nutrients from deep in the soil. A unique characteristic of pigeon pea is that its roots shed piscidic acid. This chemical can dissolve iron phosphates in the soil, making it possible for the plants to absorb these nutrients through their roots, says Ryan. The plants can also improve the structure of the soil, as its deep roots bore channels deep into the ground, increasing the infiltration of water for subsequent crops.
The thick woody stocks of pigeon pea make excellent fuel, and can be used in thatching and basket-making. Ryan is confident that more widespread pigeon pea cultivation could ease the pressure on forests and woodlots. 鈥淎 hectare of pigeon pea gives a family a significant part of its woodfuel requirements,鈥� he says. This could be vital in many developing countries, especially parts of Africa, where acute shortages of fuel for cooking mean that families may periodically have to go without hot food, especially in urban areas.
Garden plants
Unlike wheat or rice, a useful amount of pigeon pea can be grown in small patches 鈥� gardens, hedgerows and borders. And urban agriculture may have to supply more and more food if half of humanity comes to live in urban areas within the next ten years, as UN estimates suggest.
But despite all these advantages, pigeon pea cultivation has stagnated for decades, due in part to the success of its pod borer enemy, the caterpillar Helicoverpa armigera. In some areas of India, especially the warm southern climates where the caterpillar thrives all year round, farmers lose 30 to 60 per cent of their crops to the pest. And frequent use of chemical insecticides may be exacerbating the problem, say the ICRISAT scientists. Its likely that insecticide-resistant forms are beginning to emerge, he says. Also, insecticides have probably wiped out some of the borer鈥檚 natural enemies.
A new, low-cost biological insecticide devised by ICRISAT entomologist Tom Shanower and colleagues could restore the natural balance. It鈥檚 active ingredient is a virus which causes a disease called nuclear polyhedrosis, a naturally occurring disease specific to the pest which kills it in days. Diseased caterpillars are collected from the fields, their bodies are crushed and the virus extracted. It is then prepared in solution and sprayed on the crops.
Thirty-five farmers in the village of Marepally in Andhra Pradesh have been testing the biological insecticide since 1993. 鈥淲e have been very pleased with the first year鈥檚 trials; farmers reported very good control with three sprayings of the insecticide,鈥� says Shanower. On some farms, the pest was entirely wiped out. But it may be several years before the biological insecticide is ready for mass distribution.
A second reason why pigeon pea production has levelled off is that the plant is very sensitive to environmental changes, particularly day-length and temperature 鈥� it is killed off by frost, and growth declines above 40 掳C. But improved varieties, developed by researchers at ICAR, the Indian Council of Agricultural Research based in New Delhi, have become available since 1985. The plants mature to dry pods in only three to four months so they experience fewer climatic changes.
The new varieties bring several improvements: farmers can harvest three crops of pigeon pea on the same plot each year, if irrigation is available during the dry season. It can be available as a green vegetable all year round. The new crops are less fragile in dry spells, growing well even if rainfall is erratic.
Ryan says that pigeon pea could help to solve some of Africa鈥檚 agricultural and energy problems, especially in the east and south where the crop is already becoming more popular. In Kenya, for instance, the plant has reached new heights of popularity and the vegetable is exported to Britain. In Malawi, the UN wants to increase output of the crop to provide dietary protein for refugees.
ICRISAT and ICAR are working on a hybrid pigeon pea which may improve yields by 30 to 40 per cent. The drawback is that farmers have to buy fresh seed each year, so the scientists are hoping to introduce a scheme that will halve the seed cost. But Singh is confident of success. Pigeon pea could expand from the 3.5 million hectares worldwide, that it now covers, to around 4.5 million hectares within five years, he says. 鈥淚t is a crop we are likely to see more of in the future.鈥�