The astonishing resources of the physic nut tree

In Cape Verde, an interesting project has been set up on behalf of the Ministry of Rural Development, at Loura, a village of 110 families, 25 km from the capital. The aim of the project is to create an agro-industrial unit to produce and process physic nuts. The physic nut tree, also known as jatropha and the oil tree, is a shrub that had already been cultivated in Benin, Madagascar, and the Cape Verde islands during the Second World War for the manufacture of soap and the extraction of fuel oil from the seeds. But these activities were abandoned in the 1950s with the boom in the oil industry. On an area of about 100 hectares, 100 000 shrubs have been planted, and experts responsible for the initiative hope that by 1990 they will be producing around 175 tons of physic nuts. A semi-industrial process will be used to extract 50 000 litres of oil a year. Artisanal methods obtain only 35 500 litres and cost twice as much. Jatrophas are an important source of energy, and the major objective of the project is, of course, to produce fuel, sufficient to run the semi-industrial plant and to make possible the introduction of experimental stoves into homes and thus save fuelwood. Physic nut oil will also replace lamp oil in the home, and residues from the agro-industrial complex at Loura will be used to run generators. This raw material should also yield 4.5 tons of soap a year at an expected retail cost of FF 90/kg, substantially less than imported soap, which costs FF 115/kg.

The promoters of the project hope to create a new economic activity for Loura with positive social and political effects, but they also expect jatropha plantations to be an important ecological achievement. The project is part of a reforestation programme to prevent erosion. Planted in hedges, the shrubs can function as windbreaks to protect annual crops.

It is hoped that this initiative will be an example for other villages of Africa, Asia, and Central America where the shrub grows.

The jatropha, indigenous to the arid regions of Brazil, is an oleaginous shrub (Jatropha curcas) and a member of the family Euphorbiaceae. It was introduced to the Cape Verde islands in the sixteenth century by Portuguese navigators, but it has also been cultivated in India for several generations. It grows both spontaneously and under cultivation in village plots, both in dry tropical countries and in humid equatorial regions. Although it prefers cool soils, it also grows vigorously - with almost no care - on arid escarpments, and can adapt to long periods without rain.

The jatropha is a vigorous softwood plant, 2-6 metres tall. It flowers twice a year; its fruit, indehiscent on the tree (i.e., it does not open spontaneously when it ripens), is a small dark-brown spherical capsule that contains the seeds. Propagation takes place in the rainy season by cuttings or by seeds. The plant begins to bear fruit at three or four years and remains productive for 30 to 50 years.

The numerous properties of jatropha seem to warrant expanding cultivation. Indeed, the shrub is used in many tropical countries as a windbreak, as a barrier against erosion, to make enclosures, and as fuelwood. The fact that it adapts to ecologically deprived areas means that it can easily be integrated in reforestation programmes. According to Georges Martin, an authority on the species, it could be extremely useful in fighting desert encroachment in the Sahel. Jatropha also has therapeutic properties; it is used in Indian vedic traditional medicine and is renowned as a cathartic. All its various parts find medical uses in western and southern Africa, Burma, Brazil, Japan, Cape Verde, and Thailand.

A decoction of its roots can be used as a remedy for digestion problems. Its leaves are used for skin troubles (particularly scabies and dartres); and, in the past, Senegalese women used them to protect their hands when applying henna to their hair.

Because the sap is a coagulant, it is used to dress wounds. And finally, the curcas oil extracted from the seeds contains a toxic principle which, though it cannot be used for human consumption, is known for its purgative and diuretic effects. In addition to its medical properties, jatropha is apparently also a molluscicide, as proven by an experiment performed in Senegal by the Parasitological Department of the National Stockbreeding and Veterinary Research laboratory of Dakar. According to G. Vassiliades, author of the report on this study, the leaves, stems, seeds and kernels have the properties required to combat aquatic molluscs, such as Lymnaea natalensis or Bulinus guernei, carriers of human and animal disease.

But jatropha has an even more important characteristic. Its oil, which has always been used to make soap, varnish, and dyes, and as lamp oil, is a very efficient fuel.

In 1985, the National Botanical Research Institute of Lucknow in India published the conclusions of its research: curcas oil mainly consists of glycerides, and of stearic, palmitic, myristic, oleic and linoeic acids; its molecular structure is comparable to that of colza oil; it has absolute viscosity, determined at a temperature of 35°C and 100°C, and very weak acidity. With all these properties, it can be used as a lubricant and converted to replacement fuel in diesel engines. The numerous properties of this plant definitely imply that it could be used to give new impetus to economic activity in certain developing countries. But, as stressed by G. Martin and A. Mayeux, engineers at the Institute for Research on Oils and Oilseeds in Paris, in an article on energy oil crops, it is essential to continue to set up and implement research programmes in order to create a real jatropha development policy.

Anne Le Nir

Colombia's Green College for the environment

Colombia is a country endowed with rich natural resources, but each year half a million hectares of its forests are destroyed, and its majestic Magdalena River is now so polluted and blocked by sediment that it has reached an all but irreversible state of degradation. Colombia, however, is the country where 40 Concejos verdes, town councils with the job of defending and managing the environment, were set up by Margarita Marino de Botero. Since July 1987, it has also been the site of a trail-blazing experiment, the continent's first school of ecology, set up by Margarita the Green in the seventeenth-century convent of San Francisco in the pretty colonial town of Villa de Leyva.

For its motto, the Green College in Villa de Leyva has taken Goethe's words: "All theory is grey but the tree of life is green and always in flower." Its aim is to bring people from different fields of study and from different social and political groups under its roof. Together they seek new methods of development and environmental defence in Colombia, Latin America, and the Third World. Studies of everyday life, of social and technical change, and of the problems these have caused will provide the basis for an advanced training course to take place each year in July and August. Run by a team of academics from Colombia and abroad, the course will teach community leaders, workers, farmers, and civil servants about social and environmental problems.

The aim of the college is "to create a permanent service offering information and seminars on handling natural resources, conservation, overall management, planning, carrying out and evaluating projects, regional development, use of appropriate technology, and communication techniques." It also considers itself to be a supportive structure for popular organizations and local associations in poor suburbs and small townships, and an instrument for encouraging communal action for environmental protection.

The college will remain outside the normal education programme, working as an open school, and a high level parallel establishment. It has the backing of the European Community, Colombia's Friedrich Ebert Foundation, Canada's Development Agency, the International Union for Nature Conservation, the Italian Government, Spain's Santillana Foundation, the Independent World Commission on Humanitarian Issues, and, in Colombia itself, the Caja de Credito Agrario (agrarian credit fund), the National Apprenticeship Service SENA, and the Central Mortgage Bank.

Courses offered at the Green College in Villa de Leyva include citizens' rights and the environment, the relationship between technological change, industry, and the environment, social movements and environmental responsibility, and the concept of habitable space. Working with the Centro de Investigaciones pro defensa de los Intereses Pos (PROBUBLICOS, the centres for research on defending public interests), the college has drawn up a plan for putting Colombia's environment legislation into practice, and founded an office offering legal aid to concejos verdes as they fight to protect community interests.

With Colombia's National Apprenticeship Service, the college is looking into a project offering training on local environmental problems and their solutions, and also the founding of an ecological centre to study appropriate technology and experiments in biological agriculture. With the Caja de Crto Agrario, the college is beginning to study an environment training project aimed at the nation's users of agricultural credits, and at public officials in the agricultural sector; the course will fill them in on environmental defence legislation and the extension of credit lines and technical assistance, taking ecological concerns into consideration.

Goethe, the teachers, and Margarita agree that the debates and lessons should not remain on a purely theoretical plane, and that they should not be limited to a high-level minority. They believe, on the contrary, that the college's activities should be closely connected with social practice, participation, and concrete problems, and therefore should play an active role in the cultural and democratic development of the community. Margarita Marino de Botero, creator of the Green campaign and the concejos verdes used by the Government to encourage democratic community organization, is now, with her college in Villa de Leyva, trying to provide a scientific aid which, through close contact between theory and social practice, will allow consciousness of the environment to be introduced into Colombia, by permanently studying economic, technical, and social problems which arise with development and the transformation of the rural environment, and the relationship between man and nature. Comparisons between Colombian ideas and experiments and those of the rest of Latin America and other areas will mean that the unique Villa de Leyva experience may encourage the formation of similar establishments in other countries, giving a boost to development which takes standards of living into account.

The list of guests and members of the International Committee of the newly formed college includes such contributors to Ceres as Ignacy Sachs, Johan Galtung, and Andras Biro, political and literary personalities such as Italy's Susanna Agnelli, West Germany's Rudolf Bahro, and Mexico's Ivan Illich, Pablo Gonzalez Casanova, and Rodolfo Stavenhagen, communications experts such as Armand Mattelard, famous architects such as Paolo Soleri, economists such as Spain's Ramon Tamames, Chile's Osvaldo Sunkel, and Brazil's Darcy Ribeiro, and ecologists such as Argentina's Jorge Hardoy. This impressive list, which includes figures from 43 countries, plus the many Colombian professors and collaborators involved, show the importance of this first, innovatory Latin American experiment in creating an awareness of the need for preservation of the natural and cultural environment.

Up to now, ecological awareness in Latin America has not been widespread, and in some countries it has been based purely on European political experience, rather than on thorough knowledge of conditions brought to the continent by development. Balance of payments, and to a lesser extent job creation, benefit from both the policy of substituting imports and from out and out development by means of foreign investment, of the type which prompted the military regime in Brazil in the 1970s to take out full-page advertisements in North American and European papers saying "Take your contamination away from us." Similarly, both policies pay no heed to the natural and human costs of growth of any type. The stir caused by Green Margarita's Green College in Villa de Leyva is encouraging therefore. Its policies are deep, cultural, and carefully thought out, and make a re-evaluation of programmes and laws on land use necessary. The venture is of particular significance because it reaches out to all those people, regardless of nationality, who see that not pitting nature against society is essential, because without nature society will become an impossibility.

Guillermo Almeyra

Winds of change for windmills

In every region of the world, people have devised a host of ways to draw groundwater from its source, among them such traditional devices as buckets attached to ropes or levers, the Archimedean screw, and the shaduf. But whatever the means, until the early nineteenth century, they all had to rely on only four available sources of power - human or animal muscle, the force of running water itself, and the wind.

Attempts to harness the wind have a history that goes back at least 5 000 years to when the Egyptians first used sails to propel boats on the Nile. Fixed windmills are known to have existed in parts of the Middle East by 200 B.C.; by A.D. 1000, they were common around the Mediterranean, and by the twelfth century had reached northern Europe, where they became an important source of energy, primarily for milling grain or, as in the Netherlands, for draining flooded lowlands.

In fact, by the eighteenth century, windmills represented one of the most advanced forms of technology. However, with the invention of the steam engine early in the nineteenth century and later of the internal combustion engine, the value of wind-driven machines for pumping water or other purposes diminished, and windmills seemed relegated to being archaic monuments of a picturesque past. It is therefore something of an irony that the potential of windpumps, after several centuries of neglect, has recently been "rediscovered" and that efforts are being made to develop and promote their use, particularly for remote areas in the developing world. According to the authors of the Windpumping Handbook, there are now between three-quarters of a million and one and a half million windpumps operating around the world, and they are being manufactured and sold in at least 28 countries, 14 of them developing nations.

The UNDP Centre on Small Energy Sources, in its February 1987 Newsletter, cites the renewal of interest in windpumps in a number of Third World countries. In Sri Lanka and Morocco, for example, programmes have been launched to replace tens of thousands of diesel/kerosene pumps with windpumps.

Why this recent interest in an ancient technology? One obvious answer is the realization that the world's supply of fossil fuels is limited, non-renewable, and fast being depleted - the energy crisis that is fueling the incentive to develop all possible sources of alternative energy: nuclear, solar, geothermal, biogas, and wind. But there are other reasons as well. Fossil fuels, which now run most water pumps, must be imported by the majority of developing countries - a significant, often crippling drain on their meagre foreign exchange resources. Internal combustion engines, whether they use petrol, diesel, or kerosene, require frequent and relatively skilled maintenance for which many rural users may be inadequately prepared. Even with proper care, these high-speed engines have a fairly short operating life; repairs require trained technicians and parts are often expensive, in short supply, or simply unavailable. And unless a country is geared to their manufacture, both engines and parts must be purchased abroad with precious foreign exchange.

The windpump, such as the one designed by the Intermediate Technology Development Group, a British charity dedicated to increasing the income-generating capabilities of poor people in rural areas of the developing world, avoids all these problems. It runs on a free energy source. It requires little maintenance and has a life of 20 years or more. It is simple enough in design and materials to be manufactured by small scale industry and thus can be made locally, saving on cost and foreign exchange, as well as providing local employment.

Unfortunately, for all the wind pump's advantages, it has at least one major limitation. It will work only where there is adequate wind - meaning wind with the proper speed, frequency, and timing. Modern wind pumps need a minimum wind speed of about 2.5 metres per second (6 mph or 5 knots) and are designed to furl in winds above 10-12 m/s. The wind must also blow frequently enough to permit the pump to draw sufficient water to meet the needs of humans, animals, or crops, and it must blow during the seasons when rainwater is scarce or absent. Fortunately, these conditions are met in perhaps half the world's land mass.

However, the presence of adequate wind is not in itself a guarantee that windpumps will be feasible. The pumps can be installed only where there is minimal turbulence caused by hills, valleys, trees, and buildings, and, of course, where the water table is near enough to the surface - 200 metres or less. Air density also affects the windpump's efficiency. It is estimated that a well-designed windmill can harness 25-40 per cent of the wind's kinetic energy, but this energy is reduced by factors which lower air density, especially altitude. For example, at 1000 metres, wind at a given speed loses some 11 per cent of its sea-level kinetic energy, although this loss is frequently compensated for by higher wind speeds.

The modern windpump consists of five basic components: wind sails, a tail, a transmission mechanism, a tower, and the pump, together with some type of storage system. A variety of designs have been developed for each of these elements. The most common sail is the multibladed, horizontal axis type. The tail, which projects from the rear of the rotating blades, serves to keep the sail facing into the wind and, in high winds (usually above 10-12 m/s), furls the sails by turning them parallel to the windstream, thus reducing the danger of damage. The transmission converts the rotary motion of the sail's axis into a form suitable for driving the pump. The tower, normally between 10 and 20 metres high, serves two purposes: it raises the sail above ground turbulence and up where wind speeds are higher because not slowed by ground friction. The type of pump will depend on the "pump head", the distance the water must be lifted. For surface or shallow water, a suction pump is normally used, while for deep wells, some form of centrifugal or positive displacement pump is more appropriate. Because the centrifugal type requires high rotation speeds and will work only within a narrow rotation speed range, the positive displacement pump is usually preferred.

While much has changed over the centuries, many things have remained the same. One of these is man's need for fresh water, a need as imperative today as it was thousands of years ago. Another is man's continual search for ways to ease the burden of physical labour by harnessing the forces of nature. Millions of fertile acres in the developing world still yield marginal crops because they are not adequately irrigated; millions of people, most of them women, spend grueling hours a day just hauling water for domestic use. The ancient technology of windmills, updated, is beginnning once again to play a significant role in providing rural folk with the necessary power to obtain this life-giving liquid.

Farhana Haque

Mauritania's reluctant fisherfolk

With a GDP of $420 per caput, the Islamic Republic of Mauritania is classified as a middle-income country. Until 1983, most of its foreign currency resources came from its exports of iron, copper, and gypsum. Since the late 1970s, however, the mining industry has been declining in favour of the fisheries, which now provide the country's most abundant resources. This is only a relative abundance, but the Mauritanian Government plans to further the development of the fishing sector.

On its 500 km of Atlantic coastline from Nouadhibou in the north to the banks of the Senegal river in the south, Mauritania has some of the world's richest fishing grounds. FAO estimates the annual potential catch to be 600 000 metric tons, with no risk of depleting the waters: tunas, molluscs, crustaceans, and octopus proliferate in this cold area of the Atlantic Ocean. In 1984, the catch was around $148 million dollars, roughly half the value of all other exports. In 1985, Mauritania exported a record 373 000 tons of fish, bringing in $224 million - a gigantic leap ahead over the $14 million of 1979. The fishing industry's share of the GDP was 11.1 per cent in 1985, an increase from only 6.5 per cent in 1982. These are the results of a successful new fishing policy launched in 1979, with an annual increase rate of I l per cent.

With such encouraging figures, it would be logical to conclude that Mauritania is exploiting its coastal waters and its EEZ with no problems, and that its population, anxious to consume the ocean's plentiful resources, is provided with the noble proteins by sailor-fishermen bound to the sea by an ancient tradition. But this is not so. Mauritanians regard the ocean with mistrust and fishermen with contempt: they shy away from balistes and octopus and are reluctant to set foot on a boat. According to a 1980 survey, the inhabitants of Nouakchott consume 16 kg of fish per caput a year (less than half the 35.4 kg/person/year for the total population of sub-Saharan Africa), against 0.3 kg per caput countrywide. These results indicate that fish consumption is increasing partly because prolonged drought has affected the economy of the nomads, forcing them to settle, and introducing them to new foods through food aid (rations distributed to nomads who flocked to the outskirts of the towns contained dried fish). But today, it is still only the poorest inhabitants of Nouakchott who give a slight preference to fish in their diet. In fact 51.8 per cent of the families with an income of less than FF 1 000 eat more fish than meat. However, since the price of fish is approaching that of mutton, the economic advantage tends to disappear. The Government hopes that its extension campaigns and the expansion of the marketing network toward the hinterland will encourage consumers to eat much more fish.

About 20 years ago, faced with the aversion of the majority of the population to anything concerning the sea, the lack of a maritime tradition, and the failure to form a national fishing fleet in the 1960s, the Government turned to foreign countries and, up to 1979, small foreign (mainly Soviet and Japanese) fleets fished on an industrial scale under licence. Almost the entire catch was, and still is, exported, and the host country thus loses control over a key sector of its economy. For instance, the Mauritanian Government made enormous investments in refrigeration and storage units on the mainland (90 000 and 240 000 metric tons capacity respectively), but overall, they operated to only 15 per cent of their capacity, since nearly all the foreign fishing boats were equipped to refrigerate or freeze the fish on board. The rapid increase of foreign participation in industrial fishing has therefore not led to a comparable increase in the volume of fish processed at Nouadhibou, the heart of the fishing industry.

Under its new fishing policy, in 1979 the Government implemented several measures to "Mauritanianize" the sector in order better to control the exploitation rate of fishery resources and to make them more financially profitable. It decided against granting fishing rights to foreign companies or countries. Since 1980, any foreign firm or national fishing in the Mauritanian EEZ is required to form a semi-public company in which the Mauritanian public or private sector is the major shareholder.

Agreements have been negotiated with more than ten countries, but the largest semi-public companies have been formed with Algeria, Libya, Romania, USSR, and the Republic of Korea.

Any company thus formed must also undertake to construct landbased facilities and train local workers. The law of November 1982 stipulates that all catches from Mauritanian waters must be unloaded for processing and export. Since May 1984, sales and exports theoretically take place through the SMCP (Mauritanian fish marketing company). Today, Mauritania has a fleet of 250 boats, including 66 freezer trawlers and 35 wet fish trawlers.

Crews are a problem. In compliance with the law, half the crew must be Mauritanian, but owner-fishermen respect the law in their own way. They pay a phantom crew that remains on land, and they take Koreans on board. As a result, industrial fisheries that account for 98 per cent of the catch employ only 350 Mauritanians.

Despite the progress made in recent years in fishing catches and financial efficiency, most of the foreign currency revenues go back abroad (about 80 per cent in 1983) where they are used to purchase equipment and for maintenance and labour. All things considered, the contribution of the fishing sector to the budget and to Mauritania's trade balance is still lower than it could be.

The economic and financial adjustment programme for 1985-88 clearly puts the emphasis on small-scale fishing, and it is probable that this policy will continue. The situation is not quite what it seems to be, because Mauritania does have a true smallscale fishery tradition thanks to the Imraguens - thought to be an autochthonous race - who have always fished for mullet eggs (which they press, dry, salt, and sell in a wax coating) and numerous coastal species. They live in villages scattered along the coast from Nouadhibou to Nouakchott. The produce is marketed at Nouadhibou by Thimris, the country's only fishing cooperative (three-quarters of its members are Imraguen), and in Nouakchott by SPPAM (Company for the promotion of small-scale fishing in Mauritania). Some 2 000 fishermen fish from pirogues and lanchas whose engines have been boosted thanks to Japanese and Italian contributions as well as to several UNDP projects. In 1985, the small-scale fishing fleet numbered 325 boats.

Imraguens are not alone in practising small-scale fishing: an equivalent number of Senegalese fish in the same manner in the southern part of the country. Potential small-scale catches in Mauritania are estimated at 90 000 metric tons a year, against the present 15 000 tons. Half this production is consumed locally, and the remainder is exported. It is believed that with adequate equipment, the present catch could be tripled. One of the UNDP projects executed by FAO is of special interest. Its aim is to build and repair fishing boats or canoes and launches and introduce mass production of polyester pirogues and launches. The shipyard has been set up on Nouakchott beach. The project started in 1985 for 22 months and has been extended to the end of 1988.

In 1986, the UNDP/FAO project had already achieved a number of objectives, for instance: the creation of a mobile repair shop; construction and maintenance of some 30 heat-insulated crates to preserve fish on board and for Imraguen communities located far from Nouakchott; training fishermen and ship carpenters. Finally, two improved prototype boats were built: one is a 10-metre semi-decked lancha, a variation of the traditional Canary lancha used by Imraguen fishermen. The ACRN (Naval Construction and Repair Yard) used these timber models to make moulds for mass-produced polyester hulls. However, considerable delay in the allocation of funds caused mass production to be postponed. These difficulties were overcome with an extraordinary UNDP-OSRO contribution (made by Indonesian rice growers to FAO in 1986) and with the unfreezing of financing by the Saudi Development Fund, whose delay threatened to compromise this fundamental phase of the ACRN operation. In late 1987, ten boats were built (including three complete boats fitted with Italian engines). The final ACRN output (38 motor boats with a polyester hull) should be ready by the end of 1988.

The retail price of a lancha made by ACRN in $30 000, that of a pirogue $25 000. It is therefore obvious that only rich businessmen, traders and the like, can afford them. But such wealth is not rare in Mauritania, and the boats built under this project are selling like hotcakes. Private shipowners take on Imraguen crews and have an equal share in the sale of the catch.

This motorized fishing industry is considered a small-scale enterprise because it takes place on a day-today basis, close to the coast, using small boats. However, the production is intended for export, which is more profitable than the local market. Today, for instance, there is a boom in octopus sales: 3 500 metric tons purchased by Japanese clients after the product has been frozen at Nouadhibou.

It is encouraging to see that small scale fishing does not rely on international projects and that local initiative is important. A UNDP/FAO mission observed that the fishermen have mastered the use of octopus pots to compete with industrial fishing. They have the same success with lobster fishing. Local initiative is not restricted to fishing alone; it also extends to training and recruiting new fishermen. For instance, the UNDP/FAO mission reports that Imraguen fishermen and Ndiagos recruit and provide on-the-job training for many youngsters from Nouakchott and from the vicinity of the Senegal River.

It is not clear what will happen to the ARCN operation when the project closes at the end of 1988. For the time being revenues from boat sales go into a revolving fund managed by UNDP, used to purchase equipment and to pay the 30 workers employed in the shipyard. After UNDP pulls out, the yard will be privatized: several potential buyers have already expressed their interest in the deal, a sure sign that they consider it a profitable business.

Armelle Braun

Soil erosion data to convince the bank

"Africa's soils are no less problematic than her climate," writes Paul Harrison in The Greening of Africa. "Only 19 per cent of the soils of the continent have no inherent fertility limitations.... The heavy rainfall leaches out the soluble nutrients. High temperatures break down organic matter more rapidly and inhibit the work of bacteria that fix nitrogen from the air. As a result, Africa's soils are among the least fertile in the world. They are often low on nitrogen, which builds leaves, and on phosphorus, essential for root growth. The predominance of coarse particles and the lack of organic matter make for soils that are poor at holding water or nutrients."

So much for what erosion leaves behind. But what exactly does it wash, or blow, away? How much nitrogen, phosphorus, and organic matter is contained in the soil lost to erosion and what are they worth in dollars and cents?

In 1985 the Soil Conservation Programme of FAO's Land and Water Development Division commissioned a pilot study to put a price tag on soil loss from erosion. The study concentrated on Zimbabwe because that country possessed a large and unique body of data on soil erosion. The data had been collected in the late 1950s and early 1960s at the Henderson Research Station 20 kilometres outside Harare, then Salisbury, during a series of experiments on soil loss, runoff, and nutrient losses. Researchers Michael Stocking and Henry Elwell undertook the "long and painstaking task" of classifying, documenting, and analyzing these records. But 30 files from a separate subprogramme, damaged by rain and eaten by insects, escaped notice until 1984, when, finally, they "were seen to contain a storm-by-storm record of nitrogen, phosphorus and organic carbon concentrates in the sediment samples collected from the Henderson research plots".

The project of analyzing data from more than 2 000 storm soil loss events on four soil types and numerous crops, treatments, and slopes began at the Institute of Agricultural Engineering's Soil Conservation Research Section at Hatcliffe, outside Harare, and the University of East Anglia, Norwich, UK.

There are two trends discernible in soil erosion research today, says Stocking. The first is concern with the on-site effects of erosion rather than with the soil loss itself; the second is the growing need to measure the problem of its seriousness accurately and objectively. Techniques for quantification, he says, offer "an almost bewildering variety of types of measurement and techniques" of which expressing the cost of erosion in monetary terms is "the most useful and relevant" as the information can be used directly in decision-making about land use, forms of soil conservation, and investments in agricultural development.

Stocking concludes that "the appropriate quantification of the impact of erosion should be the highest priority on the agenda of erosion research in the next decade". Among the study's findings: - Enrichment ratios (how much more concentrated a nutrient is in eroded soil than it is in the soil that remains) average about 2.5. That is, soil lost to erosion is 2.5 times richer in nutrients than the soil from which it came. Thus even a very small loss of soil can have dramatic effects on yields.

- The more soil is lost, the more nitrogen, phosphorus, and organic carbon are lost - from all types of soils, slopes, and crops. If erosion rates can be estimated, nutrient losses can be predicted. - Typical rates of erosion range from 3 to 75 metric tons per hectare, depending on type of land use and farming. - The yields of severely eroded soils are often reduced by half. - Investments in fertilizers and chemicals are literally washed away by erosion. - Every year Zimbabwe loses 1.6 million metric tons of nitrogen, 0.24 metric tons of phosphorus, and 15.6 metric tons of organic carbon, which is the equivalent of US$1.5 billion of N and P in fertilizer. - Commercial farmers lose much of the fertilizer they apply. The natural fertility of soil where little or no fertilizer is used is declining. - The soil profile will grow shallower and shallower to the point that within 35-50 years, if present rates of erosion continue, no viable production will be possible from soils now under subsistence farming. - Technology (chemicals, improved seeds, agricultural engineering) has concealed much erosion-induced decline in productivity.

"Soil erosion and soil productivity are inextricably linked.... There is abundant evidence of the erosion productivity relationship: in yields; in nutrient level in eroded soils; in the way the fertility-enhancing crops and good cover crops allow less erosion; in trends in world farming productivity," Stocking writes. "Because erosion selectively removes the finer and more fertile particles in a soil, overall soil fertility is reduced. Indeed, eroded soil contains up to twelve times the concentration of nutrients as the original soil." With a view to better assessment of the effects of erosion and the incorporation of that knowledge into conservation planning and agricultural development, he makes the following recommendations: - greater monitoring of nutrient and organic carbon losses - calculation and reporting of enrichment ratios in relation to soil type, erosion rate, runoff, crop, and management - monitoring of plant-available water and other effects of erosion - improvement of the data base for quantifying the impact of erosion - economic modeling of the costs of erosion.

Maureen B. Fant