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close this bookBiotechnology and the Future of World Agriculture (GRAIN, 1991)
close this folderThe original biotechnologist
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View the documentDiversity for production
View the documentMultiple cropping, multiple benefits
View the documentBiotechnology for the people
View the documentPromoting people's participation

Multiple cropping, multiple benefits

The high level of sophistication of indigenous farming systems becomes really apparent when farmers start planting different crops together on the same plot. In what looks to many agronomists like a total mess, many farmers get the maximum out of their tiny fields by combining different crops that complement each other efficiently. To a large extent ignored by 'modem science', farmers, for centuries, have been practicing what became known as mixed cropping, intercropping, or multiple cropping. Systems can be as simple as a typical maize-bean association and as complex as a tropical forest where up to 20 crops are grown in the same plot. In Africa, for example, 98% of all cowpeas - the continent's most important legume - are grown in combination with other crops. In Nigeria alone, over 80% of all cropland is given over to mixed cropping. Farmers in India use more than 80 crops in multiple cropping combinations." When Nairobi-based ICIPE, an international centre that studies insect pests, did a survey amongst farmers in Western Kenya, it found over 200 crop combinations in that region alone. (12) The advantages are tremendous, especially for small farmers. ICIPE drew its conclusions: 'If people are doing this despite official instructions to the opposite, there must be something very important to it. (13)

One important element in such systems can be the use of green manure. Without using any chemical fertilizer, farmers on the north coast of Honduras obtain double the average national yield by sowing velvet bean in their maize crop. The bean is sown a month or two after planting the maize. When the maize is harvested, the beans take over and form a massive green canopy of up to 20 centimetres thick that covers the soil. The next maize crop is planted directly through the mulch which is formed from the bean crop layer. Apart from obtaining the benefits of the nitrogen fixed by the bean, soil erosion is prevented and the soil structure is improved. Also the bean mulch suppresses weed growth, thus eliminating the need for herbicides or manual weeding. (14)

Intercropping can also provide for a highly effective means of pest control at virtually no cost. A study on plant-feeding insects showed that 60% of all species tested were less abundant in mixtures than in monocultures. (15) In Colombia, it was found that beans grown with maize had 25% fewer leaf-hoppers and 45% fewer leaf-beetles than monocultured beans; the maize had 23% fewer army worms as well. (16) Problems with fungal and virus diseases also diminished considerably. Cassava interplanted with bean reduced fungal infections on both crops, while virus infections of cowpea diminish when this crop is grown with cassava or plantain. (17) Before pesticides even existed, farmers took notice and developed their strategies. But then, intercropping is only one of the elements in farmers' strategies to minimize crop losses due to pests and diseases. Use of local resistant crop varieties, proper seed and land preparation, rotation techniques and plant extracts, are just some of the others. Farmers attending training courses on crop protection in Cameroon, for example, told their instructors that they were having excellent results in combating several insect pests by using extracts of Jimson Weed, castor oil, 'God's tobacco' and papaya, to mention just a few. (18)

But perhaps the most challenging feature of many of the mixed cropping systems is that they optimize the use of natural resources without destroying them. Interplanted crops tend to cover the soil better, thus avoiding erosion, while at the same time repressing undesirable weeds. Different crops need different nutrients and have different ways of finding them. Some send their roots deep down, while others stay in the top layer of the soil. Together they form excellent partners while obtaining up to twice the level of nutrients from the soil compared to their monocultured counterparts. At the same time, multiple cropping systems often bring far more fertility and structure back to the soil via plant residues. This is especially the case when legumes are part of the system as they increase the nitrogen fixing capacity of the crop system. The closer a farming system comes to a natural ecosystem, the more likely it is to be sustainable. While scientists still try to grasp the meaning and function of typical two-crop interplantings, farmers in, for example, Nigeria, have developed systems of tree and crop production that reflect the natural multi-storeyed structure of a rain forest. SPORE, the newsletter from the Technical Centre for Agriculture and Rural Dissemination (CTA), explains what they consist of:

Breadfruit, Raffia and pear trees are planted below taller coconut and oil palms. A mixture of shorter trees such as mango, lime and kolanut come next, followed by a lower layer of bananas, plantains and papaya. Cassava, cocoyam and pepper bushes grow to about two metres. Maize, groundouts and other vegetables are grown in small clearings . . . This farming system is virtually self-sustaining. A relatively large population is being supported on fairly poor soil, by combining livestock, use of organic fertilizers, high crop diversity and control of soil erosion. (19)

Annual yield of a single plot 416 square meters, Philippines

Table 9.1 Ten reasons for multiple cropping

Perhaps the most important misconception about these complex farming systems is the claim that they tend to produce less than monocultures. They might produce quantitatively less of one and the same crop, but generally the combinations yield far more. Researchers in Mexico established that 1.73 hectares of land would be needed to obtain the same amount of food as one hectare of a mixture of maize, bean and squash. (20) Bolivian farmers intercrop beans, potatoes and lupine and in virtually all cases obtain higher yields compared to monocropping. Additionally, viral and fungal diseases are significantly lower in the mixed cultures and the intercropped potatoes store better. (21) Graph 9.1 shows the extent of one year's production on a small poly-cultured plot of about 400 square metres in the Philippines in which 12 different crops produce over two tonnes of fruits, vegetables, spices and cash crops - a yield of about 50,000 kilograms per hectare! No hybrid seeds, irrigation or mechanical farm implements, and only a small amount of chicken manure, were used. (22)

Often ignored in official production statistics are the multiple uses that crops can have. While a typical local vegetable can be grown mainly for its leaves, its roots might have medicinal properties. Shrubs and trees, apart from producing food, can provide foodstuff for animals and timber for building and fuel. Perhaps the prime example of a multiple use crop is the coconut, 'the tree of a hundred uses'. While production statistics mainly focus on the industrial products such as oil, local farmers use the crop for a whole range of purposes. Coconut flesh and milk are consumed fresh, the copra is used to produce oil for local use, the trunk is used as construction material, the palm as thatch or to make brooms and baskets, the shell as fuel and the sap of the tree is the basis for local wine production.

Diversity is the key element in all these different farming practices. There is a tremendous degree of biological diversity in the number of crops and the amount of different varieties of the same species used. There is also a broad diversity in the different strategies applied to maintain and improve soil structure and fertility, to minimize crop losses, or to combine plant and animal production. Up to now we have especially focused on crop production, but often the very core of many indigenous farming systems is the combination of animal and crop production. In most industrialized countries the tendency has been neatly to separate these. But combined plant and animal production provides numerous benefits, as animal dung is brought back to the field while additional output is obtained. Many rice farmers raise fish in their paddies, harvesting up to 500 kilograms per hectare of additional protein-rich food at virtually no cost. Apart from providing meat and milk, buffaloes provide traction power, natural fertilizer and a whole series of other benefits. (23) Invisible in most production statistics, this mixed food production at all levels forms the backbone of most indigenous farming practices.