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 itself insufficient upset to cause salting, but when there is overgrazing in the catchments and insufficient water use, the excess water seeps to lower levels carrying with it the small amount of salt brought in by the rain. In this way slightly saline water, if not used by vegetation in the areas of seepage, enables a concentration of salt by evaporation and a level can be reached which will inhibit plant growth. Stock tend to concentrate on and eat out pastures growing on these seepage areas and this tends to intensify incipient trouble. There is a characteristic succession of vegetation on the seepage areas with the increasing accumulation of salt, the normal species giving way to more halophytic species and ultimately even these will die.

Early recognition of salting enables rapid reclamation merely by improving water use in the catchment and fencing out the incipient salt area to prevent overgrazing by stock. In advanced stages however, reclamation is beset with all the problems normally associated with soils of high salinity.

It is now becoming clearer that adequate water use in catchments at least in some of the wetter areas, cannot be properly achieved by improved annual pastures alone, and to restore a hydrologic balance either perennial pastures or some trees will be needed if not on the catchment, at least as buffer areas just above the seepage areas.

For the correction of both tunnelling and salting the establishment of better pasture cover is essential and until recently this has not been easy. ANDERSON & MOYE (1952) showed that soils in New South Wales similar to these were deficient in molybdenum and that they were too acid for the quick multiplication of Rhizobium spp. to enable proper nodulation of subterranean clover. Later this was confirmed for these soils by NEWMAN (1955) and pastures having subterranean clover as the legume constituent can now be readily established using lime-pelleted seed and molybdated superphosphate as fertilizer.

It is not surprising that these soils should be deficient in molybdenum in view of their mode of formation outlined by DOWNES (1954). For the same reason it is not surprising that the character of the soils should enable tunnelling, and that salting should also occur.

In fact investigations show that the whole environment is potentially unstable and requires careful handling to avoid trouble. Possibly a little less intensive grazing could have avoided all of these problems.

Nevertheless the better understanding of the total environment has brought the solution of the problems and there has been a general increase of productivity in recent years from a level of about ½ sheep to the acre to more than 2 sheep to the acre in some places.

Because such spectacular results have been obtained, there is a tendency to forsake ecological principles in the application of this new knowledge. Thousands of acres of the steeper parts of this country are now being seeded and topdressed from the air and many consider that all the land use problems have been solved. However proper land use is a dynamic thing in which the solution of one set of problems produces others.

On such steep slopes it will be difficult to manage the pastures to prevent clover dominance which after a time leads to a build-up in the nitrogen status and an invasion of nitrogen-loving plants - mostly annual grasses and weeds. The stability and higher productivity could be short lived particularly if there were to be a run of drier than normal seasons. The replacement of native perennial grasses by annual species - pastures at first and weeds later - will not provide an adequate vegetative cover in times of drought. There is a need to find out how to establish a useful perennial grass species along with the clover so that use can be made of the improved nitrogen status to prevent weed invasion and also to provide a reasonable cover in dry seasons. Such problems must be recognized and solutions to them found if there is to be a stable environment at a high level of productivity. Ecological ingenuity will be required to solve them.

Soil and Ecological Surveys as a basis for the determination

of land use

Because soil conservation is fundamentally an ecological problem of adjusting the system of land use to suit the environment, then it is essential to obtain all possible data concerning the various features of each environment. Complete studies of areas reveal that environmental units can be recognized. each of which by virtue of the integration of its particular soils, climate, vegetation and topography provides the basis for determination of suitable forms of land use which will provide for overcoming the problems and hazards which it presents. Such units can be recognized at different levels of generalization according to whether the determination of land use needs to be at the broad scale, that is, whether the unit is suitable for agriculture or forestry; or at the narrow scale, for individual farm planning where the problem is the assessment of suitability of areas for specific crops or pastures.

DOWNES (1949) recognized the existence of such units and their significance and called them units of land husbandry. These units were at an intermediate scale between the two extremes mentioned above and within each such unit a further subdivision of land classes was devised for the purpose of farm planning.

CHRISTIAN et al. (1952) recognized land systems as a broad unit in their study of large areas of land in northern Australia.

DOWNES et al. (1957) have now rationalized soil and ecological surveys on a reasonable basis which enables the recognition and mapping of units at different levels of intensity and at the same time provides a means of correlating the units and their relative significance at these different levels. Four units are recognized, the component, the land unit, the land system, and the geographic zone.

The component is the unit recognized in the most detailed investigation and is consequently the basic unit for considering land use. A component is uniform with respect to its potential, problems and hazards. Agronomic investigations need to be based on components because they cannot be truly related to a wider range of conditions. The component is an area of land in which the climate, parent material, soil, vegetation and topography are uniform within the limits significant for a particular form of land use. In practice when studying land for potential development this is interpreted as being the most likely form of land use. Thus in areas where irrigation is likely, the component would accommodate soil variations of not greater than the tvpe-phase level whereas for country where grazing of the native vegetation is likely to be the land use, the range of variation within the component might be at a sub-formation level for structure and sub-association level for floristics (sensu BEADLE & COSTIN, 1952).

The land unit is an area in which there are a limited number of components occurring in a consistent sequence to form a characteristic pattern or landscape. It is the unit most commonly used for mapping.

The land system is comparable with that defined by CHRISTIAN et al. (1952) and consists of a combination of land units, land form constituting the major factor of grouping.

The geographic zone is a unit used for the initial subdivision of large area of country and is an area in which similar land systems are included, the chief land forms of the systems being common.

To indicate the relative levels of generalization the scales of the final map are: for components 40 chn = 1 inch; for land units 2 miles = 1 inch; for land systems 8 miles = 1 inch; and geographic zones 32 miles = 1 inch.

Surveys in which land units are mapped provide a compromise by which sufficient knowledge of the country is obtained for the determination of land use with a reasonable speed of survey. Information is obtained about all the components which occur within the land units and their relative proportions and location in relation to each other. Such a survey provides the preliminary information required for a detailed component survey if this is required at a later date for the purposes of subdivision and farm planning.

In conjunction with soil-ecological surveys at all levels every effort is made to understand the origin and development of the land forms, soils, and the vegetation types; in fact a knowledge of the dynamics of the environment is an important aspect of the investigations if the problems and hazards under likely forms of land use are to be foreseen.

Agricultural ecology and farm planning for conservation

Agriculture abounds in ecological problems, weed control, and pasture establishment and management being excellent examples. But in addition to such facets of agriculture in which the ecological implications are obvious it is important to understand that the agricultural use of land is an ecological problem.

Farm planning is the co-ordination of technological knowledge into a system of land husbandry in which each part of the farm is put to its best and proper use. Ideally, good farming represents a situation in which man and his animals have established a dynamically balanced ecological unit.

It is useless to consider individual technological advances in isolation because any change imposed on the environment results in other changes which can be either beneficial or detrimental from either the physical or economic aspects. Farm planning consists in a basic assessment of the natural resources of the farms and their potentiality. For this purpose the farm needs to be classified on the basis of components or the somewhat comparable units known to conservationists as land classes. The components can be readily characterised in terms of land classes.

From this basic information the alternative farming systems which can be safely and profitably used may be determined and when the choice is made the detailed planning can begin.

DICKINSON & DOWNES (1953) have indicated the step-by-step procedure in farm planning for an area within the type of problem country discussed earlier in this paper. The major subdivision is based on a separation of land classes, since these areas will need different treatment and management because of the different problems and hazards they present. Subsequent subdivision aims to provide paddocks of the most efficient and economical size to carry out the proposed system of farm management, to provide water supply and access to paddocks which are aimed to give convenience, but at the same time do not create hazards and subsequent erosion

To indicate the complexity of such a total approach the factors influencing the final paddock size on a sheep grazing property can be elaborated. Initially the soil, slope, climate, and aspect, will determine the type of pasture and potential productivity. The type of pasture will determine the type of grazing management with respect to the grazing pressure to be applied in accordance with the season of the year, and the frequency with which it shall be left for a hay crop. To obtain the proper grazing pressure on the right occasions requires careful flock management procedure, and, according to flock management methods and breeding programme, so does the paddock size need to be designed. In addition to these criteria the water supply facilities need to be designed to enable the combined pasture and flock management programme to be carried out as planned.

So farm planning for conservation and proper use of an environment is a process of integration of knowledge of the behaviour of plants and animals in relation to each other and their environment, truly a problem of applied ecology.

The whole basis of soil conservation, erosion control and reclamation is ecological. For soil conservation there is a need to assess the nature and dynamics of environments so that systems of land use can be devised to give the desired production on a permanent basis.

Erosion control is basically an understanding of the reasons for the upset equilibrium and the mechanics of erosion processes to devise methods for re-establishing a balance. Reclamation is a matter of assessing the nature of the modified environment so that suitable primary and secondary [plant] colonizers can be found to occupy the available niches and so begin a succession to a new equilibrium.

R.G.Downes