| Animal traction in Rainfed Agriculture in Africa and South America |
|C. General factors influencing the use of draft animals|
3.1 General background
3.2 Selected zones
3.2.1 Humid zones
3.2.2 Semihumid/semiarid zones
3.2.3 Highlands of the humid tropics
3.2.4 Semiarid zones with winter rains
3.1 General background
Since no large ecologically homogeneous space exists in the tropics and subtropics it is very difficult to make generalized statements regarding the conditions under which agriculture in the lower latitudes (it is understood that this refers to the land area between the equator and 40 degrees latitude) is performed. Nevertheless, an attempt will be undertaken to summarize some of the characteristics of agriculture in this zone.
The average daily amount of sunshine in the tropics has an intensity approximately double that of the temperate zones. Calculations have shown that also the potential to convert solar energy into useful plant mass is substantially greater in tropical and subtropical regions. Individual yields of harvest have also confirmed this (Sanchez, 1976). That the yield per average farm however is low in relation lies in some extent in the limitations set by the natural endowment of a particular area of land. No adapted methods are available for the solution to these problems in most cases.
One primary limiting factor for agricultural development in the equatorial regions is the widespread low residual mineral content of the soil and the rapidly diminishing humus content due to the normally-occurring forms of cultivation affecting soil fertility. On the other hand, the limited water supply in the more arid areas of the tropics and subtropics restricts in the first instance the amount of agricultural activity.
Moreover, the share of water available to the plants compared to the total precipitation in the tropics and subtropics is often lower than in the temperate climates. This is because the drainage and evapotranspiration rates are considerably higher due to the extreme temperatures and deficient water absorption and storage capacity. Thus, crop production is tied to the period when the rains fall. Even short dry periods can cause plant stocks to dry out. Generally, one can say that the certainty of rain decreases with a decline in annual rainfall and therefore increases the risk for crop cultivation. Also hot winds blowing out from desert areas cause a rapid drying within a very short time which leads to wind erosion. (MacArther, 1980) . Rainfall often occurs as cloudbursts, bringing about severe surface drainage and thus water erosion if a protective crop cover is absent. This promotes a rapid depletion of an otherwise good soil structure, evident in tropical soils after removal of vegetation. In addition, intensive rainfall produces serious surface sealing; subsequent dry periods cause compaction of the soil which then cannot be worked.
Infestation by disease, pests and weeds is especially high in more humid regions, and epidemics and pest plagues can develop within a very short time period leading to calamities. In the humid and subhumid regions rapid growth of weeds is as a rule the most significant yield-limiting factor. Thus, weed control requires a progressively increasing investment with higher land-use intensity; meaning a reduction of fallow land.
3.2 Selected climatologic zones
Because of the diversity of the tropical and subtropical climatic zones the various conditions of four different climatic regions are presented here in relation to their agricultural use and the mentioned conditions under which draft animals are mobilized in the respective regions.
3.2.1 Humid zone (permanently green rainforest)
These areas are normally sparsely settled. Exceptions to the rule are island-type centres of population, which are usually limited to advantaged areas (volcanic parent rock, flood plains). The high temperatures and rainfall promote rapid plant growth and require a high time and labour investment for clearance in preparation for soil cultivation. Following the removal of natural vegetation a rapid depletion of organic material occurs, allowing merely a short-term cropping (1 -3 years) of annual plants.
Nutrient losses due to leaching also become apparent in this case due to the low cation exchange capacity of the soil, rendering storage in the soil impossible. Fertilizer is only given in small dosages, depending upon uptake capacity of the plants ("dressing by the spoonful"). Fertilizing with organic material increases the water as well as the nutrient storage capacity and improves the soil structure. However, since depletion is rapid larger quantities of nutrients must be applied.
Shifting cultivation systems are ecologically and ergonomically adapted for the reasons mentioned, as long as the necessary fallow periods are maintained to regenerate the soil. In rainfed agriculture, predominantly mixed cropping, tuberous plants are grown such as cassava, yam and taro; also maize, beans, vegetables, bananas and rice can be cultivated here. Cotton, soybean, sweet potato and groundnut is produced with increasing distance from the equator, particularly in the more heavily populated humid savanna.
Cropping with trees (oilpalm, coconut, cocao, rubber), shrubs (coffee, tea) and perennial crops (sugarcane, bananas) as well as irrigation systems (especially for rice) have been the only forms of successful permanent land use of duration to date.
Conditions for animal traction in the humid zones:
In contrast to the work accomplished with the hoe, where tree stumps and larger trees can remain on the field following slash-and-burn clearance, mechanization even on the niveau of draft animals requires a more intensive clearance; and animals can hardly be employed in this process. Soil tillage is generally not required for perennial cropping. Thus, the possibility of mobilizing draft animals is limited to the transportation sector. Also, the important cultivation of tubers in this region, whose cultivation normally occurs on mounds (yams) and ridges, can only be done to a limited extent with the aid of animal traction
The near year-round humidity and the cultivation of crops lead to a relatively balanced workload without greater peaks. The primary argument for mechanization at all, the reduction of labour peaks, possesses no validity in this case.
Animal husbandry is connected with a severe disease pressure (e.g. trypanosomiasis in Africa). Traditionally, only small ruminants, swine and poultry are extensively kept. Cattle husbandry seldom exists; here a lack of draft animals can initially occur. Those adapted to these regions usually have a small frame and can therefore only develop a small amount of traction power. The lush vegetation provides sufficient fodder for the animals so that they are available year-round; however local pastures in humid regions possess lower fodder quality, and often forest must be cleared for the purpose of keeping larger animals.
3.2.2 Semihumid/semiarid zones (arid forest and savanna)
In relation to the more humid savanna regions this area is relatively heavily populated and the pressure on the land is correspondingly high. Due to the small amount of cloud the optimal prerequisites are given for plant growth in terms of the intensity of sunshine. Moisture is the limiting factor for plant growth. Thereby, the vegetation period and cropping is restricted to the rainy season. The natural soil fertility is better here than in the humid tropics, an advantage for agriculture. The humus content is as a rule low, due to the small accumulation of litter and widespread burning. Therefore, the yields could be increased substantially by means of a well regulated organic or mineral fertilization.
Serious competition often prevails in these regions between animal production and crop production. However, the two areas of production can be complementary if plant residues are used as a fodder resource for keeping animals and the animals provide the dung for the fields. Particular exploitation of this fertilizer is normally only carried out in or near farmyards and in horticulture. Because of the time limitation for crop cultivation there is a higher demand for labour at the beginning of the rainy season. Outside the vegetation period the people are sometimes underemployed. Due to the low amount of precipitation drought-resistant crops are grown that have a short vegetation period (e.g. sorghum, millet, cotton, groundnut).
Conditions for animal traction in the semihumid/semiarid zones:
The investment for clearance requires little mechanization, as the natural vegetation is less abundant. Weed invasion becomes less due to low rainfall. The cultivation of local crops can easily be mechanized.
Low yields are harvested due to the dryness. Therefore, large areas must be cultivated to assure food supplies. Workload peaks occur during the short vegetation period. The increase of power forces due to mechanization has great advantages. On the other hand, under a certain duration of the vegetation period the given work timespan can be so short that the introduction of draft-animal mechanization no longer is worthwhile since the animals and implements are not used to capacity (Pingali et al., 1987).
Animal husbandry is widespread and in many areas a tradition of employing draft animals exists. During periods when there is a great deal of work at the beginning of the rainy season the animals are often in such poor condition, due to the lack of fodder in the dry season, that their performance is severely hampered.
3.2.3 Highlands of the humid tropics (approx. 1000 -3000 m)
The tropical highlands at these elevations are often densely populated (e.g. Ethiopia, Kenya, the Andes). Since the soil fertility is generally good and growth periods are long the transition to permanent rainfed cropping is possible. However, due to the various altitudes different conditions can be observed within a short range.
Often there is intensive cultivation of crops and animal husbandry (e.g. highlands of Kenya). Also, regulated fallow systems upto intensive ley systems or permanent land use are found here. In higher regions the cool moderate temperatures allow cropping of plants from temperate latitudes (wheat, barley, potatoes). In some areas shrub crops (tea, coffee) are cultivated.
Conditions for animal traction in the highlands of the humid tropics
Climate and often the types of crops cultivated offer suitable prerequisites for the use of draft animals. Frequently, they have been traditionally employed in these regions (Ethiopia, Andes highlands). Limitations can often occur in these areas due to the rolling landscape, which can reduce the possibilities of mechanization of soil tillage or transportation.
3.2.4 Semiarid zones with winter rains
These zones can normally be found in the subtropics (e.g. Mediterranean region). Precipitation occurs during the cooler seasons and in contrast to areas having summer rains the rainfall intensity is less marked so that the risk of erosion is lower here (Wieneke and Friedrich, 1983).
As opposed to the tropical soils, which often possess a lower water storage capacity, the soils in these areas of the subtropics are more able to save water for subsequent crops, due to the lower evaporation rate during the cool winters. This has led to a cropping system known as dry farming in the semiarid regions of the subtropics. Dry farming is already found at locations having precipitation levels down to 250 mm per annum. Complete fallow is employed in this case. The soil surface is periodically tilled in order to destroy soil capillaries and to remove all plant growth. The function of this full fallow is in the first instance for water storage, since less water evaporates than with growing crops. The precipitation collected in the soil is beneficial to subsequent crops, especially grains (e.g. wheat, barley and millet). The proportion of fallow is found to increase with a decrease in rainfall quantities (Wieneke and Friedrich, 1983; Ruthenberg and Andreae, 1982).
Conditions for animal traction in semiarid winter rainy zones
Keeping livestock is common here as in the semiarid regions having summer rains. The natural plant growth is minimal and crops are very suited to mechanization. The practice of full fallow requires frequent working of the soil; traditionally draft animals are employed for this purpose. In spite of the low supply of fodder and water as well as the high temperatures in these regions the mobilization of adapted draft animals (camel, donkey) has been proven useful. A transition to motorized mechanization has in many cases already taken place in these areas (e.g. Maghreb).
Animal traction in rainfed agriculture in Africa and South America