Section M—Chairman'S Address
The Role of Soil Science in New Zealand Problems
This the 8th New Zealand Science Congress is the first of its kind at which Soil Science has been accorded the status of a separate section. Previously it has been included with Agriculture and Forestry or Ecology, although at a healthy meeting in 1946 Pedology attained the rank of a subsection of the Geological Sciences. This is also the first conference of the newly established but very virile New Zealand Society of Soil Science—a society which we sincerely hope will go from strength to strength as the years go by.
Recognition of soil science in this way augurs well for a country of which some 96 per cent of its exports stem from the soil. It now remains for soil scientists to meet this increasing recognition by accepting greater responsibility in the investigation and solution of New Zealand problems.
Soil Science : Its Nature And Origin.
At this juncture it is pertinent to answer the queries of devotees of “the older and more cultured sciences.” Just what is soil science? What role can it be expected to fulfil and what are the types of problems which it can help to solve?
Soil science is not easy to define and a speaker at the 4th International Congress endeavoured to drive home this point, by suggesting that perhaps “Soil Science was the science practised by soil scientists.” Such a definition, however, would hardly suit our present purpose.
In a broad sense soil science may be said to be the study of soil and its relationship to its environment. It includes not only the study of soil as a natural body but also such environmental relationships as those between soil and plant, the significance of soil properties to land use, and the principles of soil management practices. It stems from two great schools of thought—that of Western Europe which followed the teachings of Leibig (1840)1 that productiveness depends on maintaining the correct balance of mineral elements in the soil—and that of the Russian school of Dokuchaev (1879)2 who studied the soil as a natural body and taught that “soil is very much like a living thing, born of parent rock and slowly developing under the influence of climate, vegetation and relief of the land “and that differences in these factors make for differences in soils.3
[Footnote] 1. Liebig, J., 1840. Chemistry in its application to agriculture and physiology. (Report to British Association).
[Footnote] 2 Dokuchaev, V. V., 1879. Abridged historical account and critical examination of the principal soil classifications existing (Russian). Trans. St. Petersburg Soc of Nat. 10: 64–67.
[Footnote] 3. Hambidge, G., 1938. Soils and Men—A Summary. In “Soils and Men,” pp. 38–9 U. S. Dept. Agric.
Each school had something to contribute to soil science. Leibig's followers concentrated on the needs of the plant and so arose the study of soil fertility, the unit of study being the field or plot and the methods used being largely those of experiment. The followers of the Russian school conceived the idea that soil was worthy of study for itself alone. The units studied were natural ones and the method of study was to observe the soil in the field and endeavour to induce the laws governing its formation. With the rise of Leibig's teaching much was learned about soils that was useful but it was not until the beginning of the present century when the teachings of the Russian school that the soil was “one of the harmoniously organised bodies in nature “1 had been disseminated that the knowledge gained from farming, from forestry, from agricultural chemistry, from biology and from geology, could be co-ordinated into the organised body of knowledge which is to-day recognised as soil science.2 Unfortunately, neither the body of knowledge nor the attitudes of mind of the specialists engaged in soil work are so fully unified as we could desire. The integration of the two schools of thought has been a slow process and even in New Zealand to-day evidences of the cleavage persist. The pasture expert, who claims that extensive soil studies are unnecessary because, given sufficient moisture and suitable temperatures, ryegrass and white clover can be grown on any soil by supplying the right fertilizers, is merely harking back to the old Leibig school and fails to appreciate that soil science has something outside the restricted field of nutrient balance to contribute to pasture problems. We must be careful not to be misled by such anachronisms. Unless we can weld together the various branches of soil science whether they stem from the study of the soil, the plant, or the engineering problem, our science is likely to fall apart—” another Tower of Babel which tumbled because the specialists did not know how to get together.” To illustrate this need for integration, let us take, as an example, a problem which I believe we will have to face on many of our best farms in the not too distant future.
Every pastoralist who stocks heavily is familiar with and annoyed by the puddling of the surface soil in wet weather. It seems such a reasonable phenomenon—the farmer carries more stock per acre hence the surface of his fields are more cut up and muddied—that few have paused to realise its significance. Each winter the top inch or so of the soil is remoulded by the hooves of the stock and the larger pore spaces are eliminated so that it drains poorly and is much less aerated. The surface layer ultimately becomes waterlogged and gleyed—a condition which is reflected in delayed spring growth. This condition is transitory and, with the onset of drier weather, pasture comes away readily and the soil resumes its normal appearance. Its significance, however, lies in the fact that here we have an indication of a soil condition that is likely to place a limit on production from our pasture lands. The problem seems to be essentially one of soil strength and, on analysing it still further, we are forced to an interesting conclusion. If we examine the pasture on a low producing farm we find that the pasture is, in the farmers' words “sod bound.” that is, the grass is underlaid by a tight, strong sod. In the poorest fields the pasture plants may even be mor formers and examples have been noted where pastures of paspalum, of browntop, and of fog, have been underlaid by an A0 horizon
[Footnote] 1 Joffe, J. S., 1949. “Pedology.” 2nd Ed., p. 19. Somerset Press, N. J.662 pp.
[Footnote] 2 US. Soil Survey Staff, 1951. “Soil Survey Manual,” p. 1. U.S. Dept. Agric. 503 pp.
Development of soil profiles under pasture
(a) low production(b) medium production(c) high production
of yellowish greasy peat formed from the slowly decomposing leaf bases of the grasses (Fig. 1a). On the better fields, although the organic matter accumulates within the upper part of the mineral soil to form a well defined dark grey or grey brown topsoil, the sod is still tight fibrous and strong (Fig. 1b). Under pastures on a high producing farm, however, there is a very different profile. The farmer, by ameliorating soil acidity, by adding artificial fertilizer, and by causing large quantities of animal manure to be added to the soils, gives rise to those conditions which make for a speedy biologic breakdown of organic residues within the soil. One noticeable change is the rise of a large population of earthworms which tend to break up the sod and which bury the crowns of the pasture plants with worm casts. Measurements taken near Auckland indicate a build up to about one inch of cast soil in ten years. A pasture of this type may be old but the perennial grasses and clovers of which it is composed have rerooted year by year in the worm casts and hence are young and vigorous. Under this high producing pasture the organic cycle is speeded up, organic matter is readily broken down and the nutrient elements speedily released for plant growth, but for this very reason the sod is no longer tight and strong (Fig. 1c). The very things that the farmer has done to produce more feed, in order that he may carry more stock, have resulted in Ins building a weaker turf on which to support them during the winter months. The many possible ways out of this dilemma are an interesting subject of speculation but it is unlikely that a satisfactory solution will be simple and it is obvious that for a complete understanding of the problem we need the co-ordinated help of many branches of soil science.
Soil Science And New Zealand Problems.
Gove Hambidge in “Soils and Men “* states: “The scientist who spends his life studying this dynamic thing, the soil, comes to have a profound respect
[Footnote] * Op. cit. p. 44.
for it. If he has any philosophic turn of mind at all, he can hardly help seeing the soil as the fundamental thing in all human activity “and it is certainly true that “many human activities not ordinarily associated with the soil can be traced back to its influence.” Some of us here are concerned with basic properties of the soil, others with the understanding of the link between soil properties and certain of the arts—farming, forestry, engineering, planning; but tin influence of the soil is by no means limited to direct relations of this kind for wherever a problem is related to environment, study of the soil may play a part in its solution. While many of us recognize the limitations of soil science few of us appreciate its wide scope.
If we except problems of an academic nature such as the unravelling of the history of the earth's surface—to take but one example of this kind in which soil science has played a part—we find that the problems referred to soil scientists fall into four main categories, namely, those arising from:
(1) The interdependence of land use and society.
(2) The use of soils for engineering purposes.
(3) The use of soils for the growing of plants.
(4) The use of soils to support animal life.
(1) Problems Arising from the Interdependence of Land Use and Society:
These problems arise because, in the national economy, soil in the sense of “land “is one of the three main factors of production—land, labour, and capital. Some of the problems are inherent in our way of life, and some are unnecessary difficulties created by unwise planning or by laissez-faire.
An excellent example of the impact of soil conditions on society is that of the west coast of South Island. This will be dealt with by Mr. D. Kennedy later in the programme.
Another typical problem in this field is that of land use in the Pacific Islands where the rising population must be supported in an area of limited land resources. The soil scientist can help by mapping and describing the soil resources and by indicating what are the problems of the various soils, which are likely to be amenable to investigation, and how they should be approached. The Cook Islands, for example, have an area of 47,000 acres and population of 12,971 (31st March, 1951), and although these islands are not at present regarded as overpopulated, the work of Grange and Fox who recently completed a soil Survey of the Islands* has focused attention on problems that lie ahead.
The soils have been grouped into three classes:
Class 1—Suitable for both annual and tree crops (9,523 acres).
Class 2—Suitable for tree crops (16,453 acres).
Class 3—Problem soils at present not utilized (21,005 acres).
There is thus approximately but three-quarters of an acre of first class land to each person on the Islands and it is clear that any marked increase in population will require not only improved production on the soils of Class 1 but also the better utilization of the soils of Classes 2 and 3.
The Class 2 land has easy slopes, and of the soils 7,822 acres are derived wholly or in part from basaltic parent materials and are rocky, while 8,631 acres
[Footnote] * Grange, L. I., Fox, J. P., 1953 Soils of the Lower Cook Group Soil Bul. Bull. (n.s) 8.
are derived from coral sands. Of the Class 3 land about half is steep and the remainder, 10,000 to 11,000 acres, consists of infertile soils derived from basalt and covering easy and hilly slopes. These latter soils are representative of the fernlands of the Pacific, which occur from Mangarewa in the east to New Guinea and the Philippines in the west. In order to utilize these soils efficiently the two main problems to be solved are the unbalance in the nutrients in the soils from coral sand and the low nutrient content of the more mature of the soils from basalt. The purchase of large quantities of bulky fertilizers such as would be used on infertile soils in New Zealand are not suited to the economy of the Islands nor could they be readily transported. Burning of the basalt soils to release unavailable phosphate and the better use of legumes have been suggested as worthy of experiment. Some success has been gained with citrus by spraying with zinc salts and it would also be worth while finding out how far nutrient sprays can be used to correct unbalance in vegetation on the coral sands.
As an example of a problem* arising from unwise planning the siting of the Borough of Hastings may be taken (Fig 2). This town has grown up around the railway station and now extends over approximately 2,600 acres of Hastings and Twyford soils, two of the most productive soils in New Zealand. Farms on these carry up to 10 ewes or produce up to 1,000 bushels of fruit per acre and they are also capable of growing well a wide variety of crops. From the residential point of view a much better site for the town would be three miles away on the drier Matapiro soils of the downlands of Havelock North where the setting is healthier and more aesthetic Had the railway followed the route originally proposed this is where the borough would have been sited. The Matapiro soils carry about 2 ewes per acre and the kinds of crops that can be economically grown on them are few. A rough computation, taking the conservative figures of 6 ewes per acre as the potential of the Hastings and Twyford soils and 2 ewes per acre as that of the Matapiro soils, indicates that the equivalent of at least 10,000 ewes has been lost to production. More important than this, however, is the covering with buildings of all-purpose cropping land— land of which New Zealand has far too little.
For his home the average New Zealander demands a house with a section of land where he can grow a garden, but this desirable state of which we are so proud has undoubtedly led to the laisser-faire spread of cities and towns over valuable agricultural land. The City of Auckland with its attendant boroughs is a prune example of this and it is interesting to note in passing that one of the best arguments for the speedy erection of the Harbour Bridge is that it will tend to divert the spread of the city to the north and away from the more fertile lands to the south. If the population of New Zealand is to expand at the present rate, then sooner or later we must learn to come to terms with our environment if we are not to jeopardize the volume of our agricultural produce upon which our standard of living so largely depends. For the well-being of our nation the expansion of built up areas should not be lightly embarked upon. We need to know the soil type, some estimate of its agricultural potential, the probable average production of home gardens, and a host of other questions before a sound decision can be made as to the siting of a proposed built up
[Footnote] * P. IIV Comm I. J. Pohlen.
area. The necessary information can be provided by the soil scientist, the agriculturalist, and the engineer, but the main question must be answered by society itself.
(2) Problems Arising Out of the Use of Soils for Engineering Purposes.
The soil is a material which the engineer must suffer. It is placed on the site by nature—but nature has not seen fit to make it to the engineer's specifications. Whether he uses it as a material from which to make structures such as houses or earth dams, whether he uses it as a foundation on which to erect structures such as buildings, or whether he uses it as a receptacle to contain drainage or irrigation channels, pipes, piles, and the like, its complex nature and unusual properties pose problems at every turn. This is not always appreciated for, as Lowe-Brown says, “Not even the most experienced engineer would attempt to assess the strength of concrete without some knowledge of its composition, yet quite inexperienced engineers have in the past ventured to assess the bearing power of soil with a degree of accuracy quite out of proportion to their knowledge of its nature.”* New Zealand contains many examples of buildings whose construction has been costly largely because the site has been badly selected, and there have been examples of structures which became unusable because the soils were too weak to support them. By supplying pre-knowledge of this kind it is the function of soil science to show how such economic waste can be avoided.
Although studies in soil mechanics were carried out by Coulomb as far back as 1776, and a French engineer. Collin, in 1846, actually constructed a machine to measure the shear strength of clays, little use was made of such work until Terzaghi published his textbook on soil mechanics in Vienna in 1925, and it is in this work that modern soil mechanics had its origin. He first propounded the theory of consolidation of clays based on experiments with small discs of soil compressed between porous stones. He showed that when a load was placed on saturated soil it was in the first instance carried by the soil water and that as this gradually migrated away the soil consolidated until the load was eventually borne by more closely knitted solid particles. He related the rate of consolidation of the soil to such properties as compressibility, permeability, and porosity, and showed that from a study of small samples taken through the various horizons the total amount and the approximate rate of settlement under a given surface load could be predicted with reasonable accuracy. From this apparently small beginning soil mechanics has expanded, an expansion that became exceedingly rapid following the outbreak of World War II. Dealing as it does with soil strength it clearly has an essential place in the consideration of building foundations, and one has only to instance the damage to roads in Auckland following the change-over from trams to trolley-buses to realize its importance in the consideration of road foundations. Since in 1951–52 the maintenance of roads alone amounted to more than £8 ½ million and the total expenditure on roads was almost £17 million it is clear that New Zealand cannot afford to neglect the pursuance of soil mechanics studies and the applications of its findings.
[Footnote] * Lowe-Brown, W. L., 1945. An Introduction to Soil Mechanics, p. 2 Sn Isaac Pitman & Sons, Ltd., London.
Another line of study which is yielding data of importance to the engineer is that of soil corrosion. From a consideration of such soil properties as acidity, oxidation reduction, resistivity, waterholding capacity, and differential aeration, and from the study of bacteria able to live in poorly aerated conditions, it is becoming more and more practicable to predict the rate with which various materials will be corroded in different soils. Recent results from steel plates buried in modal soils covering a wide range of New Zealand's important soil groups have shown that the most dangerous soils from the corrosive point of view are those of heavy textures where high conductivity is associated with low pH. Consideration of a large steel pipeline at present being laid indicates the significance and relatively small cost of initial scientific work of this kind. The pipeline has an expected life of approximately 60 years and may cost in the vicinity of £3 million. Soil corrosion investigations along the route, designed to guide the engineer in taking precautions to counter corrosion and so reduce maintenance and extend the life of the pipeline, have cost less than £1,000 an amount equivalent to less than a week in its estimated life.
(3) Problems Arising from the Use of the Soil for the Growing of Plants.
The bulk of the problems in this category arise from the fact that conditions required for the optimum growth of the desired plant are not those existing in the soil, and the questions asked are “How far can soil conditions be modified to meet the needs of the plant? “and “How far are such modifications practicable ?” A far-sighted soil scientist however will also remember that the soil is a dynamic body, and will be on the look-out for changes that may be induced by these modifications, for some changes, difficult to detect in their early stages, may eventually lead to undesirable results. For example, soil scientists making irrigation surveys at Maniototo and Pisa Flats not only delineated those areas needing irrigation but also, and rightly, drew attention to the fact that precautions would have to be taken to prevent the waterlogging and the spread of salts over certain areas, and the development of undesirable properties in saline spots that were to be de-salted.
An excellent example of the investigation of problems of this kind is the work of Dr. E. B. Davies and his colleagues in demonstrating that increased pasture growth could be attained on some of our soils by the use of minute amounts of molybdenum salts, as little as 1/16th oz. per acre giving responses in some trials. This work is well known to you all. Its effect on the development of and production from large areas of difficult hill land may well be of profound importance in New Zealand's economy. Excluding the “high country “we have some 10 million acres of this kind of land and the importance of any work leading to increased carrying capacity upon it can readily be visualized for an increase of 1 stock unit per acre would lead to an increase of 20 per cent, in the stock population of New Zealand. Follow-up work by the Extension Division of the Department of Agriculture is already under way linking responses to soil types in order to find on which areas pastures respond to molybdenum, but hand in hand with this should go more work on the molybdenum already held in the soil and on the reaction of our soils themselves to molybdenum dressings. A better understanding of these aspects will help us not only to elucidate apparent anomalies in pasture response but also place as in a better position to meet induced problems such as the one referred to in
the warning voiced by Dr. I. J. Cunningham—that an increase in the molybdenum/copper ratio in pastures can be dangerous to stock health.
Other examples of problems in this category will be presented during the programme of this Section. They deal with the relation between soil type and growth of pines in North Auckland and Coromandel Peninsula. Here the problem is not to alter soil conditions to suit the needs of the plant but rather to select from a group of desirable plants the one best adapted to local soil conditions. So far the work has been mainly centred on tracing the effect of existing soil conditions on the growth of the tree, but other experiments necessarily long-term in nature, are designed to measure the effect of the tree-
upon the soil, in order to gauge the consequent effect of such soil changes upon future generations of trees.
(4) Problems Arising from the Influence of the Soil on Animal Life:
As is well known soil conditions are capable of exerting important direct and indirect influences on the animal life which it supports. The most obvious examples of this are apparent in domestic animals where ailments due to deficiencies in phosphorus, cobalt, and copper and the effects of excess of molybdenum are familiar to us all.
Although they clearly exist in some parts of the world, correlations between human health and soil conditions are more difficult to trace in countries such as New Zealand where the food supply is drawn from such a wide variety of sources. A noteworthy example of such a relationship is that obtained by Hercus and others1 when a link was established between soil iodine and endemic goitre. In this work the difficulties to be overcome were enormous for, in addition to gaps in medical knowledge, the knowledge of our soils was so scanty that recourse had to be made to geologic groupings.
Recent investigations by Dr. R. E. T. Hewat.2 Dental Research Officer of Health Department, working in co-operation with officers of Soil Bureau, have brought to light what appear to be positive correlations between the incidence of dental caries and the kinds of soil upon which people live. Hewat has studied the teeth of many thousands of school children each of whom has lived in one locality only and. after correction for age, sex, race, dental hygiene, and class of incidence, a strong correlation with soils appears to persist. These correlations are broadly indicated in Fig. 3.
A possible link is through milk and vegetables, both of which are important items of infant diet and both of which are locally produced. Samples of milk analysed in 1938 by S. T. Wilson for Dr. D. Cook of the Health Department and N. H. Taylor of Soil Bureau clearly indicated that the minor element content of cows' milk could reflect soil conditions and with vegetables the possibility of such a link is. of course, much closer. Work on this important investigation is proceeding:
In dealing with the problems which face him in New Zealand, the soil scientist soon finds that they are rarely those restricted in scope to the soil itself— for tire most part they are related to the use of the soil and hence their investigation calls for co-operative effort by a team of workers, the soil scientists being members of the team. As a group, however, the soil scientists of New Zealand must beware of becoming over involved in practical problems, of living too much on intellectual capital—on basal knowledge gained by the workers of the past without making like contributions themselves. The man who works out some obscure point in our science is just as important to us as a group as is the man who makes a brilliant application of knowledge to farming although society may not recognise it nor give commensurate reward. The soils of New Zealand can be studied nowhere else but in New Zealand and if we are to
[Footnote] 1 Hercus, C. E., Benson, W. N., Carter, C. L., 1925. Endemic Goitre in New Zealand and its Relation to the Soil-Iodine. Journ. Hygiene XXIV, 2. pp. 322–400.
[Footnote] 2 Hewat, R. E. T. Eastcott, D. F., 1954. Dental Caries in New Zealand. (In the press.)
continue to play a worthy part in helping to solve our country's problems it is our clear duty to pursue these studies each according to his bent and capabilities. To know and understand our soils and their relations with their environment, their distribution and their properties, the processes operating within them, the changes that are occurring or can be induced and the significance of all these to human activity, these are the goals of soil science.
We, in this country, are singularly fortunate in that each one of us rubs shoulders with workers in other related fields. We take discussions with farmers, foresters, and engineers for granted. We must not forget, however, that every advantage contains the germ of a disadvantage. So many of us can ask effectively “What must I know in order to do? “but how many of us are so able at asking “What must I do in order to know?” When we find within our ranks men capable of answering this latter question well, let us back them to the full. They are the men who will lay the foundation for dealing with the problems of tomorrow.