by G. TONDEUR
Director, Soil Conservation Mission, Belgian Congo
Extracts from a case study prepared in connection with a general FAO enquiry on shifting cultivation
IN the heart of Africa on both sides of the equator from approximately 5°N. latitude to 13° 30' S., the Belgian Congo covers an area of over 2.5 million square kilometers. Its climate is wholly equatorial and tropical. Approximately half the area is under dense forest while the rest consists of fairly well wooded grassy savanna. The topography may be likened to a bowl in which the central hollow is bordered by higher plateaus. This bowl is called the Equatorial or Central Basin.
In general, the type of agriculture traditional throughout the country before the penetration of European influence can be classed as shifting cultivation. This primitive agriculture was on a bare subsistence level. In fact, there was no such thing as a produce market. Wild fruits, fish and game supplemented cultivated crops.
Under such a primitive agricultural system the individual, family or village never grew crops continuously on the same plot of ground. Cultivation alternated with very long fallow periods, and there were frequent shifts to new land, leaving used land to lie fallow. But the dwellings of the cultivators, grouped into fairly large villages, were of a more stable nature, even though they were always built of perishable material such as straw, leaves, tree branches, rammed clay or earth. The villages tended to remain while the area cultivated shifted. In fact, except for the Pygmies, who did not do farming of any sort, there were no truly nomad peoples in the Congo, although a few tribes were semi-nomadic.
Shifting cultivation is still practiced in both the forest region and in the savanna, and owing to the wide range of physical conditions peculiar to these vast regions, has assumed a variety of forms. They are lumped together for convenience under the name of the "Bantu agricultural system", as the Bantus are the main ethnic group to which belong the peoples of the Belgian Congo, particularly those of the Equatorial Basin.
REASONS FOR SHIFTING CULTIVATION
Shifting cultivation in the Belgian Congo is not today regarded as a necessarily unsuitable type of agriculture, but rather as the inevitable outgrowth of various particular local factors. After an initial period when European settlers thought they could impose a European way of farming, the prevailing opinion has been that it is the only type of farming that conserves the soil, at least so far as present knowledge goes.
Physiographical factors
The zone under consideration here, the Central Congo Basin, has largely resulted from the progressive drying up of an inland sea called Lake Busira (old lake of the Kasai Basin). This geological phenomenon was due to the cutting through of the Crystal Mountains by the Congo River on its way to the sea. The drying up process is still continuing and many lakes such as the Tumba and Leopold II, and vast expanses of marshy forest, are remnants of this great lake.
The land exposed through the disappearance of this lake is for the most part flat. The central part, lying inside the wide sweep of the Congo River, and the western area enclosed by the Congo and Ubangi rivers, consists of low-lying, often marshy, ground raised slightly above the river level. Beyond the sweep of the Congo River and south of the Kasai River, the ground rises gradually. Some of the plateaus in this tableland formation, like the Yangambi, are now considered to be of aeolian origin, as they are apparently derived from the dunes deposited around its edges by Lake Busira during the Pleistocene period.
The outline of these plateaus has been progressively smoothed down by erosion and, in addition, gullied by the crowded watercourse network covering them so that it now appears very slightly undulating, intersected by fairly deep valleys.
In principle and by definition, the confines of the Central Basin may be considered the same as those of the equatorial forest. Thus both the climate and the climatic vegetation of the zone can be described together.
The climate is distinctly equatorial: rainfall is well distributed over the whole area, with two annual minima and maxima points, high constant humidity and temperature. Compared with equatorial regions in other parts of the world, this zone has relatively low rainfall and limited sunshine. The rains are chiefly continental and SO are somewhat variable.
The annual amount of sunshine totals 1,952 hours, only 45 percent of the possible insolation.
Vegetation, naturally, consists of rain forest. It varies in appearance with local variations in soil and climate but still forms a very uniform cover over the entire zone. Apart from a few man-made clearings this cover is unbroken except for some treeless marshy formations, a few grassy tracts of dry land and, towards the perimeter, sometimes very large strips of savanna included in the forest and marking the transition to the tropical savannas.
Soil factors
Generally speaking, the Basin's soils are very poor from an agricultural standpoint. type studied most thoroughly to date is the Yangambi yellow ochre sand. Consisting of wind deposits, it forms very deep (1,000-4,000 centimeters) homogeneous strata.
The physical features make the soil very permeable. This permeability, together with the equatorial climate, abundant rains and high temperature, have caused very pronounced leaching out of plant nutrients.
The upper horizons are a sort of residual sand formed almost entirely of quartz mixed with a kaolin clay. This clay is apparently a recent product resulting from the decomposition of the more unstable minerals, accompanied by the release and leaching out of the plant nutrients.
The soils related to the Yangambi type may all be described as very poor in mineral reserves. They are acid and all the chemical constituents are concentrated in the humus-producing horizon. The latter, in a soil in good condition, has a pH of 4.1 to 4.5, and an organic carbon content of 1 to 2 percent. The total exchangeable-bases rarely exceed 2 milligram equivalents per 100 grams of soil and are 70 to 80 percent calcium. Potash and, in particular, magnesia, occur in trace quantities (0.1 milligram equivalent). The P2O5 content ranges around 1 to 3 milligrams per 100 grams of soil. Part of the phosphates are fixed in the iron compounds and consequently cannot be utilized by plants.
The nutrient content increases with depth in proportion as the effects of leaching diminish. The top layer? however, contains a fair amount of chemicals because of the organic matter present, derived from the litter of forest trees which, through their deep rooting system, penetrate into the lower layers not yet completely sterilized by leaching. It is to be noted also that the top layer is more sandy.
The true significance of the organic carbon content is worth special consideration. Only a small proportion of this organic matter is true humus, namely, that fraction of the organic colloids of the soil which can combine with the minerals in the soil to form the stable organic-mineral aggregates.
The marked acidity of the Basin's soils makes for fungal rather than bacterial decomposition of the organic matter and the predominance of unstable organic mineral complexes.
Lastly, the soil's inability to retain the kaolin clay bases accentuates its poorness for cropping.
Soils similar to the Yangambi type occur over a very considerable part of the Central Basin. Towards the south they are bordered by sandier, acid soils which are similarly infertile. Towards the west and the southwest the soil is more clayey but the ground is usually low-lying marsh. In the north, higher-lying areas of fine sand and more clayey soils are found. Roughly the Yangambi type represents the average fertility of the Basin lands.
The low fertility of the Central Basin contrasts with the luxuriant appearance of the equatorial forest, often wrongly considered as a sign of an inexhaustible soil fertility reserve.1 Even before any soil analyses were made, disappointing experience showed that this rich plant formation could grow permanently on soil of a very poor chemical composition and only temporary fertility.
1Compare The Amazon Valley, Unasylva Vol. VII, No.. 3, September 1953.
Unlike forests in temperate regions, African equatorial forests have practically no ground litter and so there is little accumulation of humus and infiltration. This is due to the rapid destruction of the plant residues through an intense microbial activity consequent on high temperature and constant humidity. Termites also play an important part in the destruction of the dead plant material, so much so that the organic matter content of the forest ground is a bare 1.8 percent.
Clearing the forest to cultivate the land means that a considerable quantity of organic matter is provided to the soil in a short time. Leaves, branches, boughs, fruits, climbers, etc. together with tree trunks and stumps form an inextricable tangle on the ground. Obstruction is so great that it is impossible to start cultivation until this mass of debris has been burned. Otherwise only widely spaced tree crops can be grown.
Burning is necessary for several reasons. First, as pointed out above, it frees the ground of the enormous mass of vegetal trash. In addition, it has the important effect of liberating immediately some of the fertilizer minerals contained in this trash. Also, burning stimulates the action of the soil bacteria which help to produce true humus.
However, the constant humidity, torrential rains, absence of a definite dry season and the intense heat cause the minerals released by burning to be leached out very rapidly, either by runoff or by percolation. Unburned plant residues and the colloidal humus of the soil are, in their turn, very rapidly destroyed by oxidation and especially by microbiological activity. The intense solar radiation on the denuded soil accelerates this oxidation. The peptization of the colloids in the upper soil layers brings about their mobilization and flocculation at a lower level with the formation of a hardpan.
Microbial factors
It has been said that the high acidity of forest land fosters the development of fungi rather than of bacteria. It is chiefly the fungi which, with the termites, destroy the vegetal organic matter as it forms. An acidophilic microfauna, consisting mainly of protozoa, helps to counteract bacterial action. The result is an equilibrium corresponding to the equatorial forest climax, suitable for perennial tree crops, for example, rubber and oil palm plantations, cacao cultivation under forest, etc., but not for annual or, in particular, row crops.
This balance is upset immediately after the clearing and burning of the forest. The effects have not yet been fully studied but it may be taken that the microbial life of the soil increases appreciably as it is stimulated by the release of fertilizer minerals after burning, or by the accumulation of an enormous quantity of plant matter if clearing is not followed by burning. This increase in turn accelerates the decomposition of the raw organic matter and of the humus. The process differs depending on whether or not fire is used. If there is no burning, the acidophilic type microflora increases and, especially if tree crops are grown, the forest-microbial equilibrium of the soil tends gradually to he restored. On the contrary, burning followed by cultivation, especially of row crops, departs from this climax, and the rapid development of the bacteria does not last long. As the organic reserve becomes exhausted, the micro-organisms in the soil very rapidly fall back to a level probably lower than that prevailing in the original forest.
A brief cultivation period has to be followed by a long forest fallow whose purpose is to restore the organic humus reserve and the mineral fertility linked to this reserve by drawing on the deeper layers; to destroy ally hardpan that may exist by root penetration; to re-establish the peptization-flocculation balance of the colloids, and the microbial balance in harmony with the climax forest.
As long as the rapid sterilization of the soil can be counteracted only by forest fallow, shifting cultivation will remain an inescapable necessity for the production of annual food and industrial crops.
Biological factors
The adoption of mixed farming, combining cattle-raising with crop growing, might perhaps have enabled primitive peoples to develop a better form of agriculture including the use of organic manure and of draft or pack animals. The prevalence of animal trypanosomiasis throughout the Congo Basin prevented cattle-raising. The tsetse flies found everywhere transmitted the disease. In fact, at the beginning of European penetration, there was not a single head of cattle in the entire region, and the problem of acclimatizing livestock in this area is as yet still far from being solved.
Among the biological factors should also be included human trypanosomiasis and malaria which, being endemic, lower the vitality of the people and often make them unfit to enter upon a more advanced type of agriculture.
Economic and social conditions
The land had no rental or market value and was never the private or exclusive property of any individual. There was no such thing as land ownership. Each cultivator, provided he respected certain customary rules, might clear the forest wherever he wished and grow his temporary crops. The piece of land he abandoned, after he had harvested his crop, returned to the joint ownership of the clan or tribe. However, the individual or his family, in the narrow sense, retained an exclusive right to harvest the fruits of trees that might grow on tile fallow, either wild or planted by him, for instance, sago palm and oil palm. This right, however, must not be taken as being synonymous with ownership in the European sense.
In short, therefore, cropland was considered as a never-failing, inexhaustible gift of God. The idea of private ownership of a restricted land area by individuals, in the European sense of the term, did not exist, but communal ownership by the clan and tribe was thoroughly understood and respected.
Shifting cultivation was the logical result of this land system and the economic and social conditions prevailing in the country, just as it was the sole form of rural economy compatible with the various technical factors described previously.
FACTORS THAT JUSTIFY THE CONTINUANCE OF SHIFTING CULTIVATION
The first reaction of European agricultural experts was to condemn the traditional system of agriculture and advocate the application of technical principles suited to European agriculture. The results of this policy were disastrous, as may be amply demonstrated by the very careful research work undertaken at the Yangambi Experiment Station.2
2Headquarters of a chain of research centers III Africa directed by the Belgian Institut national pour l'etude agronomique du Congo beige (INEAC).
The farming method adopted by the Food Crop Division at Yangambi since 1932 was to prepare the site by clearcutting of the forest, eradication of the stumps, complete burning, deep plowing, seeding with a mixture of Calopogonium and Pueraria, maintenance of the ground cover for a year, deep plowing under of the cover, second plowing, hoeing and raking.
On the ground thus prepared the following crop rotation was practiced: paddy the first season, groundnuts the second, and cassava the third. After the cassava was harvested, the Calopogonium-Pueraria cover was restored and maintained for a year, and the crop rotation then repeated.
With this system the rice yield on a single area might drop from 2,311 to 565 kilograms per hectare in three years, and the groundnut crop from 1,362 to 191 kilograms per hectare in five crop seasons. As for cassava, the first crop yield per hectare was about 45 tons but the next one only 30 tons.
Such a drastic falling-off in yield is obviously due to the decline in soil fertility but it has not been determined whether the chief cause is the loss in chemical fertility, the lowering of the humus level, deterioration in soil structure or in microbial balance.
Such a decline in yields definitely condemns the intensive forms of agriculture proposed to replace the shifting cultivation system, so long as it is not possible, by means other than forest fallow, to:
1. replenish the reserve chemical fertilizer elements in the soil;
2. maintain the organic matter level;
3. ensure the protection of the soil structure and the microbiological balance.
The rhizosphere of cultivated plants could be replenished with mineral nutrients by the application of chemical fertilizers, although there are many difficulties in the way, chiefly technical but also economic and social. The technical difficulty is that all the fertilizer experiments conducted so far in the forest zone have proved inconclusive, generally uneconomic and sometimes negative. This is due to the rapid leaching out of the soluble elements or the fixing of the phosphates in insoluble form by iron compounds.
The effects of the rapid leaching out of the fertilizer elements could be counteracted in the case of annuals by side dressings during the growing period. This method allows plants which have a sufficiently developed root system to absorb the soluble fertilizers rapidly before they are leached out by the rains. For perennials, the application of top dressings within the reach of the absorbing roots ought to be satisfactory.
To prevent the fixing of the phosphate fertilizers in insoluble form, methods that reduce the surface of contact between the soil particles and the minerals applied have been suggested. One method particularly highly recommended is the application of fertilizer in the form of briquettes buried in the soil at the level of the absorbing roots. This method, however, has not yet been applied on a large scale. Lastly, the absorbing complex of the soil could be saturated by heavy applications, as is done in other equatorial regions, and for this natural phosphate fertilizer (rock phosphate) would be more satisfactory than soluble fertilizer (superphosphate).
But even if the adaptation of such methods to local conditions made the application of chemical fertilizers feasible, their widespread use would still be prohibitively expensive. The local cultivator chiefly grows food crops of little market value and too bulky for long distance haulage. The industrial crops that he cultivates like cotton and Urena, also have a low money value because of the high cost of delivery to the international market. Added to this, there is no domestic production of fertilizers which therefore would have to be imported. The development of nitrogen fertilizer production in the country would be possible under the present electrification plan but no large deposits of potash and phosphate fertilizers have as yet been discovered. Only magnesium could be produced in large quantities from the magnesian waters of certain lakes and rivers.,
Lastly, there is the simple-minded and primitive nature of the people, their fatalism and their attachment to ancestral customs. Agricultural knowledge is still extremely elementary. Considerable extension and demonstration work would be needed to make the practice of fertilizer application general. Apparently it would be useless to appeal to the individual native grower, and the only possible way this could be done would be through agricultural co-operatives. Recently a campaign to group cultivators into co-operatives was launched, which may perhaps be a means of promoting the introduction of fertilizers if their use is technically advisable.
The maintaining of the organic matter level in the soil with the corollary retention of the true humus also presents major difficulties. The chief one lies in the rapid destruction of the organic matter and in the short duration of the humus produced by its decomposition.
In this respect, the types of plant organic matter contributed to the soil must be differentiated, since on this depends the rate at which organic matter will be destroyed. Thus it is recognized that, under equatorial conditions, carbohydrates are decomposed in soil within less than three months, celluloses and hemicelluloses in less than six months, while lignin may last for as long as 17 months.
This corroborates the particular value of forest fallow, as it contributes most of the organic matter in the form of lignin. Still, it is difficult to conceive of a system of intensive agriculture suitable for replacing shifting cultivation that provides lignin, although a system could be envisaged in which a long forest fallow would be applied only at very great intervals, alternating with cropping periods comprising several crop rotations like those mentioned above, but with short intervening artificial fallows and possibly application of mineral fertilizers.
All intensive agriculture systems are in fact based either on the use of green manure crops, compost, farm manure or grass leys. Assuming that a satisfactory method of green manuring could be devised, its application to native agriculture would come up against the same difficulties as the use of fertilizers. The native grower has no draft animals or machines to facilitate the planting and plowing under of green manure crops. In addition, with his mentality it would be most difficult to get him to accept a farming method that requires so much labor without any visible benefit. Lastly, because of the low return on his labor, he is already obliged to devote nearly all of his time to his crops. So it would be impossible to add a technique calling for such a heavy labor expenditure as does green manuring without reducing his crop area, and consequently his already small resources.
The only likely way to obtain a fallow that acts as a soil improver would be to find a plant which, while assuring the regeneration of the soil, could also furnish a commercial crop. In this connection, the cultivation of Abroma augusta has been recommended and experiments have been made.
Theoretically, compost would provide the perfect solution to the difficulties of maintaining soil fertility. Experiments conducted in the Congo forest zone prove, in fact, that the same piece of land can be cultivated continually without resorting to fallow, provided that large quantities of compost are applied every year. But here again this solution cannot be used on a large scale. In fact, it raises a twofold problem, first, the production of enormous quantities of material for composting, transport to the compost pits and the making of compost involve much manual labor and, second, its haulage and spreading on to the field is also an extremely onerous job. This system is particularly inapplicable because the native grower has no carting facilities, and all his labor is already expended directly in productive work.
The same problem arises with mulching, often recommended for tree plantations. Conserving the fertility of a piece of land by mulching entails disposing of a plot of ground at least equivalent in size to produce the straw. That area in turn threatens to deteriorate rapidly if methods for preserving soil fertility cannot be applied. The result is a vicious circle.
In this respect, it must not be forgotten that the rapid destruction of the organic matter and humus in the equatorial zone make it necessary to have much larger quantities of compost than in the subtropical or temperate zones. The composting of crop residues alone would provide only trifling quantities compared with the needs. A supply of plant material of other origin would be indispensable.
As there are no cattle in the Equatorial Basin, having recourse to farm manure is, for the moment, merely an idea. The native grower owns only a few goats and sheep and their excrete could, at the most, suffice to enrich a garbage compost heap. This would barely be enough to manure a home vegetable plot to raise vegetables for everyday consumption. Farm manure cannot possibly be considered for the much larger areas required to produce food and industrial crops. Therefore, it will only be in a subsequent stage of the development of agriculture, when cattle have been acclimatized in the equatorial zone, that it will be possible to contemplate the use of farm manure, though again at that stage, the problems of haulage and conservation of the humus in the soil will arise.
Lastly, ley farming or temporary pasture can only be envisaged when the presence of cattle will allow of recourse to the temporary pasture as a means of ameliorating the soil. In the meantime, its technical suitability would still have to be proved. Leys have the advantage over forest fallow of a better action on soil structure. On the other hand, the shorter grass roots provide less minerals to the arable land and its organic matter is destroyed sooner. It may be difficult to return the land to cultivation after a fey. Naturally, from the economic standpoint, it has the great advantage of allowing a profitable utilization of the fallow and it has the advantage over composting and manuring of eliminating haulage and handling of the organic matter.
Conclusion
These conclusions are hardly encouraging. The renewal of the stock of organic matter in equatorial soils, already difficult in itself because of the economic and technical standing of the native grower, and the lack of livestock, is made even more so by the rapidity with which this organic matter is destroyed. Therefore the soil would have to be replenished with humus at a much quicker rate than crop lands in the temperate zones, and very substantial amounts would have to be applied.
In all the fields touched on above, there is huge scope for scientific agricultural research, if it is desired to find farming methods to replace shifting cultivation. Such studies would seek to:
1. work out the agricultural techniques that would save the maximum organic matter in the soil, chiefly by preventing erosion, protecting the soil against excessive aeration, light and heat from the sun: it would be advisable in this respect to adopt a system of unbroken crop rotations and mixed crops, patterned on the native method, together with perennials;2. work out the simplest, most efficient and cheapest methods to supply the soil with organic matter, other than by the forest fallow;
3. devise farming methods compatible with a low level of humus in the soil without endangering the conservation of the agricultural value of the latter.
It seems that the prerequisite for substantial progress along these lines is the introduction and widespread use of cattle in the rural economy.
With the introduction of cattle, the cultivator would at once attain a higher level of agriculture. He would increase the profit-earning capacity of his land by converting, through the cattle, the poor primary products of his crops into valuable secondary products (meat, skins, dairy products). The cattle would also ensure the economic utilization of the fallows, thus raising the return on the land. In this manner, the terrible weakness of the present rural economy could be remedied, and so pave the way for more intensive farming. These prospects, however, lie very far in the future.
The improvement of the shifting cultivation system and the replacing of primitive forms by intensive forms has for the moment to be examined in the light of economic laws. The desired transformation of agriculture is above all a problem of investment. The shifting cultivator starts with nothing, and changing his methods would mean an enormous investment, per unit area, for land improvements such as clearing the ground of stumps, razing of termite hills, irrigation, drainage, laying of roadways, etc.; for buildings such as sheds for produce and silos; for implements, machines and tools, and vehicles for haulage; for cattle and draft or pack animals.
An investment in agriculture can be envisaged only if it will bring about an increased return on the land at least equal to the interest on the capital invested. This is the more true as the cultivator, having no capital, could only invest in agricultural improvements - either individually or co-operatively - through a credit system.
The position is the same in regard to annual production costs. An improvement in agriculture entailing the additional provision of manpower; repayment of buildings and implements; supply of machinery; outlay on chemical fertilizers, insecticides, fungicides, etc., would bring total production cost to an extremely high figure in comparison with the present one. It would only be advisable if the crop return showed a margin of profit higher than that at present. Here, again, it seems that native agriculture cannot bear even a slight increase in production costs
Yet it should be noted that the weakness of shifting cultivation is, to a certain extent, a guarantee of economic stability. In fact, a system in which production costs are limited to family labor and which provides the family's food, also protects the villager from economic troubles caused by serious fluctuations on the produce and labor market. A more elaborate system of agriculture would be much more vulnerable.
However that may be, intensifying agriculture, which means investing capital and increasing production costs, will only be possible if the agricultural economy has an adequate capacity for absorption of investment. If not, economic measures likely to increase such capacity will have to precede the technical measures and create conditions favorable to their application.
It is always wise to avoid upsetting an agricultural system by the precipitate introduction of concepts too strange to the traditional mode of thinking. This is particularly so in the case of the native land tenure system, especially suited to shifting cultivation. It is difficult to integrate an intensive system of agriculture into this framework straight away. In other words, account has to be taken of the human factor, which can only be modified slowly and gradually.
It is not possible therefore, for the present, to abandon the Bantu shifting cultivation system and to replace it by more intensive farming methods.
Translated, from an original French text.
