EDITORIAL

For agriculture in the tropics the pendulum of aid-agencies’ emphasis appears now to be swinging away from the strong earlier stress on the scientific aspects of what is needed to get agriculture moving and towards a strong relative stress on a social science panacea. This swing is perhaps understandable, because results of trying to apply purely technical solutions to problems of inadequate plant production - which have a complex of technical, social and economic causes - have not been as successful as hoped.

In recent years it has become abundantly clear that rural families’ motivations and constraints affect their decisions about how best to manage land to improve their families’ conditions, and that purely-technical recommendations for improved plant production may be unacceptable, inappropriate or even downright damaging in this wider human context.

Growing sensitivity to, and understanding of, farm-families’ conditions and aspirations makes easier the growth of confidence – of farmers in their advisers, and of advisers in the farmers they serve. Information and understanding of every sort can then move more easily and credibly in both directions. While this can greatly improve the rapport in rural areas, we should not see this as an end in itself, an alternative to the technological approach, but rather as a valuable complement to it, for the melding of both sets of ‘disciplines’ and the best use of their different but interlinking sets of specific knowledge and skills.

‘Land husbandry’ links the two. Land, with its living and non-living resources and water, is husbanded with lesser or greater skills by people, so that soils may continue to produce plants and water on a sustainable basis, on which all our livelihoods ultimately depend. What we as humankind have done to land that has limited and diminished its potential for sustained satisfaction of our various demands requires not just altered attitudes but also better understanding of the land’s dynamic processes.

From this we must learn better how to restore and then maintain its capacities for self-renewal through the detailed technical understandings and possibilities which we have developed over the last 100 years or more. When populations were low relative to the abundance of fertile land, its recovery after damage could be successfully maintained by shifting cultivation and the adoption of ‘fallow’ periods which allowed sufficient time for biological transformations to take place. No longer. The temptation is now to abandon ‘fallow’ as a concept, rather than to understand its necessity as a means of sustaining productivity in the face of damaging tillage and trampling, and in many situations the net loss of plant nutrients .

A major challenge now is to understand better not only the minutiae of details and processes as we take organisms and materials apart to look at their components, but also how they fit together and function as living entities. When they lose their internal organisation, they lose their usefulness and die. While we know much about what goes on above the soil, we know comparatively little about what goes on – rather than just what exists - below the soil surface, where plants’ roots live. Experiences with residue-based zero-tillage systems in Latin America show the social, environmental, economic and technical advantages of thinking not only like a farmer but also thinking like a root, thinking like a river, to understand better their requirements and what drives their ongoing dynamics.

This interdependence between social and technical aspects of rural life is illustrated by the comments of a well-respected Indian Professor of Agronomy with whom I used to work on an Operational Research Project among 3 villages near Indore in the 1970s. He had always run the Project on the basis of first listening to and discussing with the farmers their problems, observations and ideas as a basis for action. In this he was a maverick because the formal purpose of the Project was to teach the farmers how to go about catchment management and controlling soil erosion; the ultimate success of the project came through developing excellent two-way exchanges of knowledge and concerns between the project’s staff and the villagers, complemented by the offering of already-verified improved farm technologies and possibilities for the farmers to test and adapt. I returned there ten years later, and together we re-visited the farmers and their fields in the Project area and discussed his views about the key components of what lastingly had been achieved in crop and animal production and soil and water management. My notes at our roundup meeting contained the following comments:

· Win the confidence of the farmers by whatever means, and be prepared to listen first and learn from farmers;

· Identify and analyse constraints they face, including those off-farm as well as those on-farm;

· Be sure of success when demonstrating some quick result, in any sphere;

· Use a problem-solving approach, offering an already-proven technology;

· Enlighten farmers’ misconceptions by demonstrating realities of which they may not be aware;

· Keep close contact and provide day-to-day guidance as they move to improve;

· Ensure there is a good feedback loop between farmers, extensionists and researchers, working together in problem-solving and in the realisation of possibilities;

· Limited-period subsidies to resource-poor farmers may be valuable in reducing the uncertainties involved once they have decided to change towards improved practices.

What enabled the villagers to improve their agricultural livelihoods in ways that persisted long after the formal end of the Project was the interlinkage of social and technical knowledge and skills when helping the farmers to realise that they could indeed take some control of their own destinies.

The Editor.

Introduction

Accelerated soil erosion is a result of the operation of the physical forces of wind and water on soil which has become vulnerable because of man's interference with the natural environment. For this reason soil erosion can be viewed as an ecological catastrophy [sic], an upset in the balance of an environment which can frequently lead to such significant changes that a new succession is required to re-establish an ecological equilibrium.

Before the advent of civilized man, ecological catastrophes probably occurred only at infrequent intervals, but for the past 3,000 years man has had a devastating influence in changing the face of the earth. It is mainly because of his activities in certain kinds of environments that soil erosion has occurred.

The most recent devastating changes in natural environments have occurred in countries settled by white men, where a new human culture has replaced an older one, and where forms of land use which may have

been suitable for one kind of environment have been applied in others in which there are significantly different conditions.

Australia is one of the most recently settled countries, and the effects of such treatment are now reaching their peak of severity.

New people in a new environment

The natural environments of Australia were first subjected to the changes imposed by civilized man when the British people established a penal colony in 1788 on the site where Sydney now stands. For about twenty years the new settlement had a precarious existence. There was a constant struggle to produce the necessities of life on a relatively small area of useful land between the mountains, which presented a seemingly impenetrable barrier to the inland, and the sea. The colony was frequently on the point of starvation which was only averted by the timely arrival of supply ships.

There were three reasons for these agricultural difficulties. The soils were poor; the strains of crop plants were not suited to the different conditions of moisture, light and temperature; and there was a shortage of skilled agriculturalists.

Since this inauspicious beginning, exploration and settlement along with the breeding and adaptation of crops and animals suitable for the new environments have advanced in stages.

At first there was broad-scale use of the land. The holdings were large and open range grazing was practised. Small holdings close to towns provided the major food requirements. About a hundred years later, the large holdings in more favoured environments were subdivided into farms on which a broad-scale agriculture developed. By improvements in agricultural technology and machinery this type of farming has reached a peak of efficiency with respect to production per man.

During both of these stages of development there was an attitude of exploitation which still persists in some environments today. However, in others the soil erosion resulting from the systems of land use and management made men realize that their problems were not at an end, and that they had not yet fitted onto their environment.

In the meantime, the closer settlement in the better rainfall areas had virtually forced the broad-scale grazing into the more arid environments and again there was trouble with soil erosion.

These events have drawn attention to the need to move toward the final stage of the settlement and development of the continent, that of soil conservation. It is now becoming more generally accepted that by the use of all possible technological information, permanent systems of land use can and must be devised and introduced for each of the many types of environments. Only when this stage has been reached can civilized man be said to have reached a balance with his environment.

However, the achievement of this ambition is not without its problems which are plainly ecological in character. Their solution will only come from a more intimate knowledge of the different environments, and the reasons why the land use systems which have already been imposed have upset the balance, and what changes need to be made to re-establish an equilibrium. It will need too, a more general appreciation that proper land use is in fact applied ecology.

In spite of the problems which still remain to be solved, the effect of settlement and development has been dramatic. From a small isolated penal settlement unable to produce sufficient food for its needs there has developed a country which now depends on its exports of primary produce for most of its overseas income. This achievement has been gained at a price, the price of soil erosion in many kinds of environment and even complete destruction in some.

Such a result is not surprising when the habits of the white settlers and their domesticated animals are compared ecologically with those of the native people and fauna.

The effect of settlement

Continental Australia has been isolated from other land masses of the world since the early Tertiary period. In such isolation a characteristic flora and fauna have evolved and survived without competition from species which have subsequently been evolved in other parts of the world. In relation to area, the aboriginal and fauna populations were small. These species were able to survive because of their nomadic habit in seeking their food requirements over vast areas in accordance with seasonal conditions. The vegetation evolved under these conditions of light pressure.

With the influx of white man and his domesticated animals, the whole system was changed. Larger numbers of people and of hard footed, closer-grazing animals were confined on specific areas in a settled existence. The resulting constant pressure on the environment irrespective of the variable climatic conditions has had significant effects. Clearing of vegetation, seasonal burning, cultivating and constant hard grazing were all radical changes which have upset the ecological equilibrium in various kinds of environments.

The various manifestations of wrong land use and the upsetting of the ecological equilibrium are merely reflections of how different environments have been able to react to the imposed conditions. In some places, there has been little actual loss of soil but merely a declining productivity due to deterioration of the physical condition, chemical fertility, or moisture status of the soil. In other places, there has been complete loss of vegetative cover and a hardening of the soil to an arid and inhospitable environment for any form of vegetation. In others, there have been tremendous losses of soil from the surface and from scoured gullies. In some wetter environments landslips have become frequent occurrences; while in drier environments, sand dune systems have become unstable and are being redistributed around the countryside.

These different effects of upsetting the ecological equilibrium are indicators of the inherent weaknesses of the different environments. In some places highly specialized vegetation could not stand up to the imposed conditions; in others, poorly structured soils collapsed completely under cultivation and the pounding action of rain, and in others, naturally unstable topographic conditions have become even more unstable.

Although soil erosion due to wind is an important problem in large areas of the dry inland parts of Australia, it is erosion by water which has caused the greatest amount of damage and economic loss. Water erosion is more common in the better rainfall areas where it affects the more productive and more valuable land. These are also the more populated and more highly developed areas and so erosion by water is more likely to cause damage to public utilities such as roads and railways. Furthermore, some of the most spectacular erosion, even in the dry lands of the interior, is the result of water action.

It would be wrong to imagine that soil erosion in Australia is as bad or so widespread as in the Middle East, or that it is comparable even with the erosion which has occurred in the United States of America. There are large areas of most hazardous country in Australia which have not yet been affected by erosion to any appreciable extent. In fact there is more erosion in some of the less hazardous environments in both the Middle East and the United States and even the moors of Scotland than can be found in areas of comparable hazard in Australia. Maps of soil erosion do not provide a satisfactory comparison of the conservation needs of different countries. They merely provide a qualitative assessment of the damage without giving any indication of the nature of the environment or its inherent hazard.

The erosion which has taken place in Australia has occurred on areas with a high degree of erosion hazard which formerly was not readily recognized. This has created numerous problems of soil conservation, but fortunately it is not too late to make their solution worthwhile over most of the continent.

The problem of soil conservation

Soil conservation in any environment is fundamentally a problem of determining the correct form of land use and management. The correct form of land use and management is one which provides a higher level, or different form, of productivity than that available in the natural state, but this new productivity must be capable of being maintained indefinitely. This means that the balance of the natural environment must be replaced by another balanced system under the changed form of land use. The determination of correct land use is therefore a problem of applied ecology.

Natural environments have evolved to a condition where, from the available constellation of plant and animal species, communities have developed in which there is a relative abundance of the various species best able to survive in association and competition with each other under the existing soil, climate, and topographic conditions.

A natural environment represents a maximum productivity of plants and animals at that stage of its succession, of the species available during the developmental and evolutionary processes. It represents a permanent natural productivity which will be maintained indefinitely or even increased by successional changes unless there is some catastrophic force imposed on it. These naturally infrequent catastrophies may result from geological upheaval, vulcanism, climatic change, or the occurrence of mutant species having overwhelming advantage in competition with others.

However, except for seasonal changes temporarily favouring one species against another, natural environments are in a state of equilibrium over long periods. Even a run of seasons favouring certain groups of species does not significantly upset the balance to any marked extent, because these same conditions inevitably favour predators or parasites which will tend to reduce the numbers of the favoured species. If not for these reasons, competition for food or water supply tends to restore the environment to its normal condition once more.

Man's objective in land use is to either raise the productivity of the environment or to produce in it other plants and animals which are of more value to him. This requires a change in the environment and the balance must be upset, but unless a new equilibrium is established under the changed land use, the interference will set off a chain of reactions comparable to those which could be expected only rarely under natural conditions.

The ecological problem of land use and soil conservation is the provision of more desirable species to occupy artificially created niches from which a new equilibrium of maximum productivity will result.

Since Australia has been isolated from other land masses for a long period of geological time, there is every reason to believe that many plant and animal species, which were unavailable during the evolution of its natural environments, might find suitable niches. In fact the history of some introduced species, their rapid colonization and adaptation to the environmental conditions confirms this. Some introduced species have become pests but this merely indicates the need for balance. The European rabbit and prickly pear (Opuntia sp.) are two such examples of introductions which were too successful and for which suitable opposition has now been introduced. Of the more useful species, Monterey Pine (P. radiata), subterranean clover (T. subterraneurn) and domestic sheep are good examples. These have not yet been incorporated into properly balanced environments, although sheep and subterranean clover together are getting close to a desirable balance in some localities.

There is a wide range [of] environments and although there may be superficial similarity between some of them, each presents its own particular problems of land use and development to achieve a high level of permanent productivity and soil conservation.

Some environments and their problems

To outline the ecology of erosion and conservation in many of the Australian environments would be a formidable task. Only brief mention of a few will be made here and one environment will be treated in more detail later.

COSTIN (1954, 1957) has shown how man's activity has led to instability and damage in the alpine and subalpine environments in S.E. Australia. Grazing and burning of these natural alpine tussock grasslands (Poa caespitosa) has caused a deterioration and vegetative change which has enabled both wind and water erosion to occur. In some places the damage has been severe. In addition moss beds and bogs which normally occur in the lower situations on the peneplain have been dried out and destroyed as a result of stock trampling. The reclamation and re-establishment of a balanced environment in these areas having an elevation of more than 4,500 feet above sea level is difficult because of the harsh climatic conditions, and the depletion of the plant species specialized for life in such an environment.

In the wet sclerophyll forests successive forest fires have obliterated certain valuable timber species in some areas, and in others the more fire sensitive and more valuable species have been replaced by more fire resistant forms. Clearing in the wet forest areas for use either for crops or pasture has not been entirely successful. In the tropical areas high intensity rains, even on the naturally well structured soils, have caused considerable erosion. In the south, although good pastures have been established in some places, the hydrological balance has not been maintained. The replacement of deep rooting trees by perennial grasses apparently enables the soils to become excessively wet at depth and landslips become common.

In the drier areas BEADLE (1948) has outlined the consequences of use of many kinds of environments in western New South Wales. Here the problem is one of excessive grazing of vegetative types not evolved to cope with such treatment. In some areas the result has been large areas of "scalded" plains on which there is not a vestige of vegetation and the bare soil is in such a condition that it will not readily permit the entry of water.

In even drier environments of the arid interior, RATCLIFFE (1936) has described the ecological imbalance of certain kinds of environments as a result of man's occupation and use. His discussion of ecological differences between the natural and present use of the Saltbush (Atriplex vesicarium) environment is particularly revealing. His conclusion concerning the proper use of the dry country virtually means that it should be treated in the way it was accustomed to being treated under natural conditions – “Inconstant stocking, the figures varying between wide limits so as to take full advantage of the flush [of] feed in good seasons and to avoid damage to the perennial vegetation in bad." This is precisely the way in which this country was used by the native fauna.

A difficult but interesting environment

The ecological implications of erosion control and soil conservation are exemplified by one particular type of environment which occurs widely in Victoria, the south-eastern State of the continent. In this environment there has been considerable instability and consequent erosion of various kinds as a result of what had appeared to be a reasonable and relatively mild form of land use.

The environment has a rolling to hilly topography on which the original vegetation was a dry sclerophyll forest of Eucalyptus spp. with a sparse under-storey of shrubs and perennial grasses. The rainfall ranges from 20" - 30" per annum most of which falls during the winter months which is the growing season. Rainfall during the summer consists mainly of isolated thunderstorms which are of little value for plant growth because of the hot conditions and high evaporation. The hydrology of the environment is such that rainfail and evapotranspiration approximately balance and consequently there are no permanent streams. Flood flows can occur when rainfall intensity exceeds the infiltration capacity of the soils or late in the winter when steady rain falls on already saturated soils. Under natural conditions there was a delicate hydrological balance. The soils are formed on fine sandstones and shales and they are relatively shallow having an average depth of from 3 to 4 feet.

The environment is subject to accession of oceanic or ‘cyclic’ salts. ANDERSON (1941, 1945) and later LESLIE & HUTTON (1958) have shown that over these areas about 10 to 30 lbs. of salt per acre can be brought in by rain each year. These amounts of salt are in themselves relatively insignificant except in those areas where the relation between rainfall and evaporation precludes their complete leaching out of the soil season by season, thus enabling their accumulation. DOWNES (1954) has put forward the thesis that the soils in this environment are solodic, and have been formed as a result of the salinization and subsequent leaching of the pre-existing soils. In recent geological time there have been significant changes of climate which would have enabled considerable accumulation of salt during dry periods and its subsequent leaching during wet periods within certain zones which can be correlated with present day climatic limits. The zone in which this environment occurs is one in which the most intensive solodization would have been possible.

It is because of such a genesis that the soils have certain properties which make them susceptible to the curious forms of erosion which have subsequently occurred. The soils have a relatively shallow, poorly structured, compact loam surface horizon over a bleached structureless subsurface horizon beneath which there is a sharp transition to a heavy clay. The heavy clay subsoil has a moderate medium subangular blocky structure when dry, but when it is wet it disperses so readily that local farmers talk of the subsoils as being “sugary" because they "melt" so easily. In common with other solodic soils they are acid throughout, have a low content of soluble salts and low amounts of exchangeable calcium. In fact the subsoils are hydrogen-magnesium clays.

Although the problems of this type of country are largely due to the character of the soils, the factors operating to produce such soils are themselves of importance in enabling the operation of processes which produce the problems. Man's activity in this environment has merely been a reduction of tree cover in favour of grass and subsequent overgrazing of that grassland but the results of such treatment have been spectacularly bad.

The first significant disturbance of the environment occurred about eighty years ago when the land was more closely settled. Trees were thinned out and in some places completely cleared to encourage a better growth of the existing perennial grasses of the Danthonia spp. and Stipa spp. This grassland was grazed by sheep. However the grasses themselves had evolved under a condition of occasional browsing by relatively few marsupials and were unable to maintain density and vigour under the constant grazing pressure of sheep, irrespective of the seasonal conditions. In addition, the European rabbit had increased considerably in numbers and this added to the grazing pressure on the vegetation.

Under such treatment the pastures deteriorated in density and vigour and the exposed soil became hard and compacted, the surface became impermeable, productivity declined, and soil erosion became evident. The increased runoff scoured watercourses and they became eroding gullies. But these were only preliminary warnings.

About forty years ago it became evident that as well as the more obvious effects of instability, more insidious troubles had been developing. At that time the first signs of subsoil or tunnel erosion appeared and it has subsequently developed into a widespread and difficult problem.

Yet another problem emerged - the development of salinity in the soils along some of the creek lines and watercourses and on the lower parts of some slopes. At first it appeared to be a minor or transitory problem, but like tunnel erosion, it too increased in incidence and extent, more particularly during the past ten years.

Associated with both of these problems there was the difficulty of establishing improved pastures. Many attempts by landholders had met with outright failure, or at the best only poor germination and lack of persistence. These failures were for many years attributed to climatic conditions, although the climatic data offered no support for such contentions.

Within a space of eighty years, a logical and reasonable system of land use had resulted in a degree of degradation in many places which could never have been imagined by the early settlers and appeared to offer nothing to the present generation but further deterioration at an ever increasing rate.

With the information now available about this environment, it is easier to understand how these results were inevitable, and a closer examination of the problems will reveal this.

Tunnel erosion is a most insidious form of erosion because of the amount of deterioration which occurs before there is any visible sign of damage. The earliest stages are marked by small patches of yellow clay which have oozed through a small crack or ant hole to the surface. At a later stage there may be conspicuous "fans" of yellow clay material which has been washed down slope from small holes. At an even later stage there may be a line of holes upslope from the point where the clay is being washed out. These holes occur where parts of the surface soil have collapsed into the tunnel which has been eroded out of the subsoil below.

The mechanism of tunnel erosion and the reasons for its occurrence were put forward by DOWNES (1946). Basically it is due to deterioration of pasture cover which enables the naturally poorly structured surface soil to develop an impermeable surface condition. This enables increased runoff from a large part of the area and less moisture for plant growth. But in certain places there is an increase of infiltration by the concentration of runoff water. Small natural hollows and old stump holes have better growth of grass and an infiltration capacity of more than 50 times that of the surrounding bare areas. In these places, particularly after a dry summer, the water soaks in rapidly and as it passes into the cracked subsoil it disperses some of the clay and carries it downslope until wetting and swelling of the clay prevents any further such movement.

After many wet and dry seasons much clay from beneath the hollow has been removed, the hollow enlarges and downslope from it there is a partly formed tunnel in the subsoil but nothing visible above ground. At some critical time, possibly the first autumn rain after a drought or prolonged dry summer, the quick movement into the subsoil develops sufficient hydrostatic pressure downslope for some of the liquid clay to be forced through a crack or ant hole to the surface. After the next dry season, when the clay has dried and cracked, there is a complete channel into and out of the subsoil and rapid scouring takes place from this stage to produce characteristic clay "fans". Once tunnels have been formed, they provide a harbour for rabbits in country which previously had not been a desirable habitat for them because the soils were too hard and compact for easy burrowing. The invasion of rabbits adds to the grazing pressure and tends to accentuate the trouble.

Tunnels deepen and widen until the roof of the tunnel can no longer support its own weight and it collapses to form a gully.

Salting in this kind of country was first observed by HOLMES & LEEPER (1939) and later by DOWNES (1949) but it was so limited in extent that it was thought to be of academic interest only. However, recent investigations by COPE (1957) have indicated that it is widespread and increasing; his work also confirms a hypothesis for salting which was accepted but not investigated in detail by the previous observers.

Salting results from an upset of the hydrologic balance of the environment. The removal of trees to grow pastures is probably in its

R.G.Downes