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close this bookCERES No. 135 (FAO Ceres, 1992, 50 p.)
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Maximizing muscle power

Getting the most from hand-tool technology is more than a question of implement design
by K.V. Vanek

More than 90 per cent of African and 60 per cent of Latin American farmers have little or no access to any mechanical energy source but their own muscles. Their extremely low incomes make buying even the simplest implement a major investment - and the number of such farmers is increasing.

As a result, governments in developing countries are being forced to focus more and more sharply on the question: "How can farming systems based chiefly on hand-tool technology boost productivity in a sustainable way, and what inputs are needed to help the process along?"

Simply giving lip-service to the need for "appropriate technology", or calling for a vaguely general "improvement" in tool and implement design won't do much to answer this urgent question. Specific technologies and inputs must be developed for specific situations, taking into account a whole web of factors that affect tool use.

Only when the constraints and advantages of each context are understood can the kind of improvements be made - not only in tool design, but in tool choice and employment - that will lead to real production advances.

Human-power limits

The main limiting factor in human-powered technology is the fact that sustainable human energy inputs are very low. The human body can be compared to a heat engine which uses chemical energy from food as its fuel. This energy is converted to mechanical work with a limited efficiency: part of the energy intake must be used for maintenance of the body itself and only the balance is available for conversion into mechanical work. Under optimum
conditions, human energy conversion efficiency is roughly 20 per cent.

Under the typical tropical conditions of many developing countries (high humidity and high temperature), however, efficiency drops to 10 per cent. This basic limitation is unavoidable, and must be considered in planning.

Most studies of human energy expenditure are expressed in terms of chemical energy expenditure, namely, food energy required to perform a given task. The sustainable human-power potential is quoted at 70 to 500 Watts (FAO, 1991). This corresponds to a net mechanical power of seven to 50 W. assuming a 10 per cent conversion efficiency. Female sustainable power is estimated at 75 per cent, and the power of a child at 50 per cent of that of an adult male.

If a job offers the possibility of alternating between hard and light work, such as pounding grain in a mortar and then sifting, or screening the flour, the hard work done in a relatively short time may equal 70 to 100 W. (As martial arts practitioners are aware, for a brief instant - one second or less - a human can produce power surges of one kilowatt or more.)

The power that can be delivered by farmers is further reduced by the energy conversion factor (always less than 100 per cent) of the tool or simple machine being used, and the efficiency of hand-operated tools can be improved only marginally. The mechanical energy input per unit area of traditional Third World hand-tool technology is approximately 1/50 to 1/100 of the energy input in an industrialized country, where each unit of mechanical energy may be supported by two to four units of additional external inputs (fertilizers, agricultural chemicals, irrigation, etc.).

Even the physical improvement of tools, by using higher-quality materials or more efficient machine parts to make them, can backfire. The "better" tool may cost too much, putting it beyond farmers' pocket-books.

Manpower availability is another key strand in the web. For optimum use of human energy resources, an even distribution of the work load throughout the year is preferable. High-intensity, irrigated paddy rice production with two or three harvests per year provides a close-to-ideal example. At the other end of the spectrum, however, are rain-fed farming systems in arid countries. There, distribution is worst because peak demand is concentrated in a short time, with work loads as much as five times higher than average.

Distribution of work between males and females in traditional societies may further reduce availability of labor during peak seasons.

Given such a multiplicity of factors influencing tool use, to look at the development of human-powered technology as a simple question of tool and implement design - as is done in many development programs - is to ignore reality.

Human-powered agricultural technologies are usually classified by the type of operation they perform - implements for land preparation, sowing and planting, cultivation, harvesting, etc. For purposes of development planning, however, they can be divided according to technical complexity, into three basic groups: (1) simple, rigid tools with no moving parts (hoes, spades, sickles); (2) implements and simple machines for field work; (3) other implements and simple machines for stationary applications.

Possible improvement

The scope for possible improvement will vary with each of these groups, according to the social, geographical and other factors that make up the context in which they are used.

Simple tools with no moving parts - A hoe, used for land preparation, ridging, weeding, etc. is a typical example of this kind of tool. Its movement is guided only by human senses, which may result in uneven depth of hoeing, some places being left untreated, or other forms of unequal quality of work. On the other hand, virtually any piece of land can be hoed, regardless of previous preparation. The hoe is the principal tool of traditional farmers using fallow systems and multicropping techniques.

The shape of the blade and length of the handle are usually very specific to a region or a farming operation, and hoes are not manufactured in many sizes. Farmers usually keep a hoe until it wears out completely. A new hoe will be used for land opening by the strongest member of the family, while worn (and thus smaller and lighter) hoes are used by women and children.

The main scope for further development in this category lies in improving the quality of materials and manufacturing methods. However, this should be carried out gradually and in accord with local conditions. Imposing overly-strict quality standards on hand-tools, or imposing less strict standards prematurely, could create negative effects for local, small-scale manufacturers - such as blacksmiths - who would be unable to meet the standards. They might be forced out of the market by larger tool makers, leading to unemployment, or the resulting tools might become too expensive for local people to buy.

Implements and simple machines for field work The difference between a simple hand-tool and a simple implement can be seen in the next step up from the hoe - the hand-wheel hoe. The latter is guided by a wheel, and the depth of cultivation is adjustable, ensuring greater uniformity of work, higher productivity and less fatigue. The wheel-hoe is more specialized than the ordinary hoe, however.

It is designed for inter-row weeding, and the soil must be well prepared and free of stones, tree stumps, etc. before using it.

Another simple implement is the hand-seed drill, which allows the depth of seeding and discharge to be adjusted within certain limits. The operator simply pushes the seeder, observing and checking its function and maintaining a constant distance between rows. Like the wheel-hoe, it is designed for operating on already well prepared land in intensive farming systems.

There is greater scope for further development of implements and simple machines for field work than there is for improvement of simple hand-tools, but such development must be viewed as a complex approach, which includes many inputs. For example, replacement of hand seed broadcasting by hand-seed drilling will increase production only if other inputs are provided. If fields are not sufficiently levelled, use of the "improved" drill could even result in lower production.

Most simple machines for field work are derived from larger machines designed for animal traction or tractors. For example, a one-row seed drill can be a single element from a multi-row machine. This tends to facilitate development, testing and tool evaluation. Simple machines for stationary applications Threshing, grain dehulling/grinding and oil extracting are very tedious operations, normally carried out in developing countries by women.

These traditional operations often result in food losses due to incomplete threshing, etc. Consequently, much effort has been devoted to improving post harvest processes. The grinding of grain in West Africa is an example. Normally, very fine flour from dehulled grain is preferred. The traditional process consists in pounding the grain in a wooden mortar to dehull it, separating the hulls from the grain, and finally grinding the grain by pounding it into flour. Very frequently, the grain has a high-moisture content before it is ground.

Hand-operated machines exist for both dehulling and grinding, and many have been tested for West African "wet grinding". Nevertheless, this technology has not been adopted, for the unexpected but perfectly logical reason that the ancient African wooden mortar is more energy efficient than modern hand-mills. A group of women in Mali, given a choice of using the hand-operated mills or paying fees to use a diesel-powered mill, picked the diesel option. Their second choice was the traditional mortar.

This was, of course, an exceptional situation. In contrast, small hand-mills for grinding roasted peanuts are very energy efficient and relatively cheap, and are consequently very popular in West Africa.

As this brief overview of hand-tools and hand-powered implements demonstrates, the development approach to human-powered agricultural technology must be seen in its complexity, incorporating both the most efficient application of human power as well as additional sources of external energy inputs - whether improved seeds, fertilizers or agricultural chemicals. The social context must also be taken into account. Finally, the possibility of employing additional mechanical energy inputs - such as those produced by draft animals or even tractors - should be considered for some of the most demanding field operations.

All of the strands of the web are interlinked, and must work together.