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close this book Agro-forestry in the African Humid Tropics (1982)
close this folder Traditional agro-forestry systems: Prospects for development
View the document The role of trees in farming systems in the humid tropics
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View the document Impact of agricultural systems and rural development on Nigerian forests
View the document Crop mixtures in traditional systems
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View the document Summary of discussion: Traditional agro-forestry systems

Agricultural tree crops as a no-tillage system

Agricultural tree crops as a no-tillage system

R.D. Bowers
International Institute of Tropical Agriculture, Ibadan, Nigeria


The crisis in tropical agriculture is demonstrated by falling food production and migration to the towns It is argued that this is an inevitable process resulting from the inability of tropical agriculture to compete with the industrialized agriculture of the temperate zones. Industrial agriculture is a high-input agriculture, and success or failure depends on the input:output ratio. In the humid tropics, the input: output ratio is unfavourable, and industrial agriculture therefore impossible; hence the only viable form of production is subsistence farming. The obvious alternative to subsistence farming is mixed tree cropping, in which the characteristics of the natural forest cover are copied as closely as possible. Only in this way can the productive potential of the environment be realized and the fertility of the soil maintained. Crop mixtures may be selected from oil palm, coconut palm, breadfruit, plantains, coffee, cocoa, cola, citrus, and other trees. A plea is made for a research programme to be devoted to mixed tree cropping as one of the possible ways to improve the agriculture of the region lying between 10°N and 10°S.


The growth of temperate agriculture over many centuries has involved the destruction of forests and the planting of annual crops in their place. Land clearing and progress are seen to be linked. When developers come to tropical Africa, they assume that clearing the forest is progress; likewise, African people, anxious of emulating progress seen in other countries, follow the same course.

As an agricultural engineer, I suppose that I should be in the camp of forest destroyers, and I certainly would be if I thought that this policy could be successful in economic terms and acceptable ecologically. But all the evidence indicates that the widespread clearing of tropical forest and the large-scale planting of annual crops leads to financial and ecological disaster. The worst possible combination of circumstances for Nigeria would be for the fertility of the soil to run out at the same time as the oil runs out-a possibility which could well arise unless great care is exercised. A new type of agriculture, such as that based on mixed tree cropping, must be developed with all urgency, as it offers, perhaps, the only hope for the future.


I propose that there is a crisis in the agriculture of the region Iying between 10°N and 10°S and that there must be a reason for it.

The evidence for this crisis is falling food production and an increase in food imports. Further evidence is the mass migration from the rural areas to the towns. For those who stay in the country, the standard of living remains low, and there is little hope of improvement. The great majority of the people in the countryside are still subsistence farmers, just as they were before and during the period of colonialism, depending for the most part on the unaided strength of their bodies to wrest a living from the soil. They would seem to live in a world with which Western technology is unable to communicate.

Over the past 30 years, there has been no lack of attempts to improve agriculture in the humid tropics. That none of these efforts has significantly changed the methods of production, even in a limited area, cannot reasonably be held to be a result of bad luck or bad management. There must be fundamental economic reasons to explain why these attempts have failed so catastrophically. The competitiveness of tropical agriculture has seriously declined in relation to temperate agriculture; the reasons for this decline include:

  • The development of bigger and more effective machines. Just as it is no longer possible for a person with a headpan to shift earth competitively against one with a Caterpillar D9, so it is no longer possible for a person with a sickle to compete against one with a combine harvester; 30 years ago, however, when machines were smaller and less efficient, it was still possible for hand labour to compete;
  • All major crops have now been mechanized; 30 years ago, machines had not been perfected for the harvesting of cotton, groundnuts, or sugar cane. Production of these crops can now only be competitive (and provide the producer with a reasonable standard of living) if they are mechanized; and
  • Temperate region substitutes have been found for tropical crops. Soybean, sunflower, and oilseed rape have greatly reduced the demand for groundnut oil. Cotton has been displaced to a considerable extent by artificial fibres. Cane sugar has been threatened by sugar beet and, more recently, by high-fructose corn syrup.

Agriculture has gone through three phases: subsistence farming, commercial farming, and industrial farming. This last phase is still in full evolution and is rapidly displacing all forms of small-scale production because it is economically more efficient. Never in the history of human beings have the main food items been produced so cheaply in real terms as they are now in the temperate countries.

Industrial agriculture is, of necessity, a high-input agriculture because it depends on inputs of machinery, fertilizers, herbicides, insecticides, etc. Because labour forms a small part of production costs, the system cannot be made to work by a substitution of labour and land for capital.

Success or failure of industrial agriculture depends on the input:output ratio expressed as the cost of the various inputs that are needed to produce a given value of produce. By using this ratio, one can compare the efficiency of production at different places (table 1).

A profit of $0.05 is made on every dollar of produce in the USA, whereas a loss of $1.20 per dollar of produce occurs in the tropics. The loss has to be covered, for example by subsidizing inputs to subsidize the price, or by introducing import restrictions that keep the price artificially high. Support for the reliability of such input:output ratios is provided by the comparative farm gate prices of maize- approximately $1 50/t in the USA vs. $450/t in Nigeria.

Generally, profitability increases as expenditures on machinery and chemical inputs increase, up to a limit of about $0.55 per dollar. If the inputs cost more than about $0.65, commercial production is no longer possible. Production becomes economically absurd if the foreign exchange cost of the inputs exceeds the foreign exchange cost of the product.

TABLE 1. Indicative Input:Output Ratio of Maize Production in the USA and Nigeria (cents input to produce $1 output)

  USA Nigeria
Land 20 cents 30 cents
Infrastructure and machinery 15 cents 50 cents
Seed and agric. chemicals 35 cents 110 cents
Management and labour 10 cents 30 cents
Finance and taxes 15 cents -
Total cost of production 95 cents 220 cents

Input:output ratios are generally unfavourable in the humid tropics. Low yields are a result of leached soils, heavy runoff, loss of nutrients, and weed competition. Drying and storage in a hot, humid environment present further problems. Generally, unfavourable input:output ratios are found where yields are low. Approximately the same inputs per hectare will produce about 2.5 tonnes of maize in the humid tropics as against 7 tonnes in the USA. In other words, only 0.15 ha of land in the US, as compared with 0.4 ha in the humid tropics, is required to produce 1 tonne of maize. All land, machinery, herbicide and insecticide costs are directly related to area. Thus, they are all three times more expensive in the humid tropics per tonne of maize produced.

Increasing energy costs make the possibility of high-input agriculture recede even further. When inputs are expensive they can only be used where the return per unit used is high; only when inputs are cheap can they be used extensively. Since the oil price rise of 1973, hopes of using expensive inputs in marginal areas have declined.

Subsistence farming is the inevitable consequence of the unfavourable input:output ratios associated with the production of annual crops in the humid tropics. All other forms of annual crop production are economically impossible until such time as the agricultural scientists develop varieties that give input:output ratios comparable with those of similar crops grown in more favourable climates. This conclusion accords with the observable fact that subsistence agriculture is the universal form of annual crop production in West Africa.

But subsistence farming has been shown to have already failed: it cannot produce sufficient surplus to feed the large towns; it cannot supply cheap basic foodstuffs; and it cannot retain the young people on the land. The impasse appears total-the only system that is economically viable is incapable of supporting the modern economy for which developing countries are striving.

The Tree Crop Alternative

The tree crop alternative offers some hope. It is logical in both economic and ecological terms. The climax vegetation of the humid tropics is high forest, which produces the greatest sustainable rate of biomass formation. It captures all solar radiation year-round by virtue of the different layers of foliage. The layers of leaves, twigs, and branches absorb the incoming energy of tropical rainstorms, thus protecting the soil. Organic matter on the forest floor is protected from the direct sun. Runoff is reduced so that more water is available for plant growth, and extensive root systems explore the whole soil profile for nutrients. If society demands that the high forest be removed, it must be replaced by economic crops that copy as closely as possible the characteristics of the natural forest, and that afford equal protection to the environment. If mixed tree cropping is to be freely chosen in preference to annual crops it must show economic advantages.

There are reasons to think mixed tree cropping will significantly outperform annual crops as the cost of highenergy inputs rises because of its low labour requirements; low fertilizer, herbicide, and insecticide requirements; the prospects for an ideal no-tillage system; and rediced weed competition.


Tree crops appear to be so well-suited to the environment and have so many economic advantages that a research programme of tree crop development is urgently required. The potential for tree crops exists and in many cases is already being realized. The oil palm, for example, is by far the most efficient and cheapest source of vegetable oil. Under good conditions it will produce up to 6 tonnes oil/ha. It will, therefore, always hold a competitive advantage over the annual oilseed crops. It may be expected to constitute an important part in any mixed tree crop system. The coconut palm produces a good yield of both oil and protein. Further, the open canopy makes it very suitable for mixed cropping with plantains or bananas. The breadfruit tree (Artocarpus altilus) appears to produce up to 8 tons carbohydrates/ha. Accurate yields are not available because the tree has not been seriously studied. The best cultivars should be assembled to determine its productive capacity under a range of environmental conditions. The shea butter tree (Butyrospermum parkii) should be studied and improved so that it may replace groundnuts in the drier areas.

For the wet tropics, it is suggested that mixed tree cropping is likely to be most effective, as it copies as closely as possible the natural forest. Oil palm or coconut palm would be interplanted with breadfruit to form the top gallery. Beneath this would be planted plantains, cocoa, and coffee, and, in places, as a bottom layer of vegetation, small plots of maize, sweet potato, and cocoyams. The aim would be not to get the maximum yield of one particular crop per unit area but, rather, to maximize total production.

The objective must be to give the people of the wet tropics crops that will outyield and undersell the main food crops grown in the temperate zones. Oil from palm oil already does this; it is to be hoped that carbohydrate from breadfruit would become cheaper than maize as the cost of high energy inputs increases. If the people of the wet tropics attempt to grow temperate crops competitively, they will always be losers, and, if they cannot produce cheap food, industrialization may well be impeded.

Long-term tree research is a most urgent requirement, It is a field that has been totally neglected except in the plantation context. Trees have all the right characteristics for smallholder farmer production in an energy-hungry world, although in some cases breeding programmes must be undertaken to combine desired properties.

It is essential that one get away from the idea that trees only grow in forests or in plantations. This concept has meant that the people of the wet tropics have been (and still are) denied the help of modern research. Economic trees grow just as well on smallholdings as on plantations, and there is little loss of economic efficiency. On has only to think of the struggle of the Chagga people in Tanzania before they were allowed to grow coffee to realize how obstructive the plantation mentality can be.

One cannot know what the future holds but surely one must plan for several different possibilities. One of these is a world of increasing energy shortage, where energy-related products become more and more expensive. In such a situation low energy-input tree crops have a potential that is unmatched. Prudent people do not put all their money on one horse, and scientific researchers and government policymakers should likewise spread their bets. Mixed tree cropping may be a favourite for some, or an outsider to others, but it looks to be so well-suited for the next 20 years that it would be unwise not to put some money on it.