Introduction
To mechanize means to use machines to accomplish tasks or operations. A machine may be as simple as a wedge or an inclined plane, or as complex as an airplane. Agricul- tural mechanization, therefore, is the use of any machine to accomplish a task or operation involved in agricultural production. It is clear from this definition that agriculture any- where has always been mechanized, employing a combination of three main sources of power: human, animal and mechanical/engine, giving rise to three broad levels of agricul- tural mechanization technology classified as hand-tool technology (HTT), draft-animal technology (DAT) and mechanical-power or engine-power technology (EPT).
Hand-tool technology is the most basic level of agricultural mechanization, where a human being is the power source, using simple tools and implements such as hoes, machetes, sickles, wooden diggers, etc. A farmer using hand-tool technology can cul- tivate only about one hectare of land. He cannot do more than that because of certain scientifically established facts.
Power Production and Consumption by Humans
As a source of power, the human being operates essentially like a heat engine, with built-in overload controls or regulators. Chemical energy input in the form of food is converted into energy output, some of which is useful for doing work. On the average, a healthy person in temperate climates consumes energy at a sustainable rate of only about 300 W, while in tropical climates, as a result of heat stress the rate is reduced to only about 250 W. Many tasks for agricultural production can be performed only at higher rates of energy consumption, however, as shown in Table 1.1. Some actual manual work rates for certain field operations are presented in Table 1.2.
The fact that many primary agricultural production operations demand higher rates of energy than the maximum sustainable rate of energy consumption by humans necessitates
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Table 1.1. Human Power Consumption for Various Farming Activities
Gross power
Activity consumed (Watts)
Clearing bush and scrub 400–600
Felling trees 600
Hoeing 300–500
Ridging, deep digging 400–1000
Planting 200–300
Plowing with animal draft 350–550 Driving single axle tractors 350–650 Driving 4-wheel tractor 150–350
Driving car on farm 150
Source: mainly from Dumin and Passmore, 1967, Energy, work and leisure. Heineman as given by Inns (1992).
Table 1.2. Some Field Operation Rates by Farmers Using Hand-Tools
Average manual work rate
Operation (man days/ha)∗
Land clearing 32.6 (20.1–47.8)
Ridging for cassava 43.8 (29.7–64.5) Mound making for yams 57.8 (35–93) Cassava planting 28.3
Yam planting 17.3
Weeding root crops 36.7 (22.3–77.6) Weeding general 40.0
Cassava harvesting 28.5
Yam harvesting 32.0
∗ Range values in parenthesis [1].
rest periods in manual work. The rest period required can be estimated using the for- mula [2],
Tr =60(1−250/P) where,
Tr=required rest period in min/h of work, and P=actual rate of energy consumption in watts.
Using the formula, it follows that the manual ridging operation which demands 400–
1000 W (Table 1.1) requires rest periods of between 22.5 and 45 minutes per hour of work. Note that at the 1000 W rate of energy consumption, the farmer can work only for 15 minutes, and must rest for 45 minutes, per hour of work. It must be noted here also that an appropriate rest period, as estimated using the above formula, is a physiological necessity inherent in manual work.
Figure 1.1. Sustainable Physical or Power Output by Humans (Inns, p. 2).
Human Work Output
Only about 25 percent of the energy consumed when handling relatively easy tasks such as pedaling, pushing or pulling is converted to actual human work output. Under more difficult work conditions, the efficiency of converting consumed energy to physical work may be as low as 5 percent or less. This means that, at the maximum continuous energy consumption rate of 0.30 kW and conversion efficiency of 25 percent, the phys- ical power output is approximately 0.075 kW sustained for an 8–10 hour work day.
Naturally, higher rates can be maintained for shorter periods only, as shown in Fig.1.1 [2].
Some Compensating Attributes of Human Labor
The discussion thus far and the facts given in Tables 1.1 and 1.2 make it abun- dantly clear that power is the major limitation to increasing the area cultivated by the hand-tool farmer. It should be noted that the problem is not necessarily with the tools used, especially for primary production operations, since efforts made to redesign them have yielded no significant improvements [3, 4]. The toil, drudgery, and severe power constraint on timely field operations, which limit production and earning capacity, are the inherent characteristics of peasant farmers using hand-tool technology; change the technology and you change the farmer’s status [5].
Still, the peasant farmer and his hoe and machete are efficient companions in crop production at the subsistence level where he operates. This is so because of certain human
attributes that compensate significantly for the limited physical power that the farmer can generate. The relevant human attributes are exhibited when the farmer:
• Adopts a working mode that incorporates appropriate rest periods.
• Makes instantaneous decisions as to how much force to exert to accomplish a task, thereby conserving energy.
• Chooses the most appropriate tools for a given production unit operation.
• Changes from one task to another readily and rationally, exhibiting a versatility that no other power source is capable of.
In spite of the inherent compensating characteristics, however, the power needed to operate any human powered tool or machine should not be more than the farmer can potentially supply; the farmer should employ the preferred modes of human power application such as pedaling or simulated walking.
Importance of Human-Powered Agricultural Tools/Machines in the LDC’s
All three levels of technology, HTT, DAT and EPT, are used in the mechanization of agriculture in most countries of Africa and the other less developed countries (LDC’s) of the tropical world. But HTT predominates, especially for production field operations such as land preparation, as shown in Table 1.3.
Table 1.4 also shows that for overall agricultural production, human power accounts for the lion’s share of work in most African and Latin American countries. It has been suggested that a power-use intensity of 0.4 kW/ha is required for effective levels of agricultural mechanization. While that figure may well be controversial, the facts and figures presented in Tables 1.3 and 1.4, and especially those in Table 1.5, show that the power-use intensity in Africa is so low that it should be of serious concern to all. Consid- ering the natural limitations of human powered tools and machines, their predominance in the agriculture of developing countries is an important factor to address when dealing with overall economic development of those countries.
Table 1.3. Sources of Power for Various Primary Land Preparation Operations in Various Countries
% of Total Land Cultivated Draught Engine
Country Human animal (Mech.)
Nigeria 86 4 10
Botswana 20 40 40
Zimbabwe 15 30 55
Tanzania 80 14 6
Kenya 84 12 4
Ethiopia 10 80 10
Zambia 55 15 30
Swaziland 15 35 50
Uganda 70 20 10
China 22 26 52
India 18 21 61
Source: [6].
Table 1.4. Sources of Power for Overall Agricultural Production in Latin America and
Africa (% Share) Latin
Source of Power America Africa Nigeria
Human power 59 89 90
Animal power 19 10 8
Engine power 22 1 2
Source: [7, 8].
Table 1.5. Engine Power Available for Agriculture in Different Countries and Continents Country/Continent W/ha (Hp/acre)
USA 783 (0.430)
Europe 694 (0.340)
Latin America 201 (0.110)
China 142 (0.080)
Africa 37 (0.020)
Nigeria 18 (0.008)
Source: Adapted from [9].