THE IDEALS OF A SOIL SURVEY.

New Zealand Journal of Agriculture, Volume XXVII, Issue 3, 20 September 1923, Page 131

THE IDEALS OF A SOIL SURVEY.

B. C. ASTON,

F.I.C., F.N.Z.Inst., Chemist to ths Department

A NATIONAL soil survey is a method of classifying lands into groups and types in a manner which designs to express the relationship of one soil to another, and to indicate the relative

value of each. One of the last stages of such a work is the demarking of boundaries of soil types in the form of a soil map. A soil survey therefore seeks to classify land with regard to its quality and usually takes place in settled country, while a land survey deals chiefly with the position of land and usually takes place in virgin country. A topographical survey is a land survey on a larger scale, giving details of surface contour, and showing the chief improvements effected by settlement, such as roads, bridges, and buildings.

The United States Department of Agriculture has among its several organizations a Bureau of Soils, which is charged with the duty of carrying out a soil survey of the American Union. In a little work issued by the Bureau the purpose of a soil survey is described as "to

map, classify, correlate soils, to determine their field characteristics, to report on the actual use being made of the soils and on their adaptations to various crops so far as can be determined, and upon the relative productiveness of the several soil types.” The Bureau

points out (1914) the value of such knowledge to the following classes of people : (1) Scientific men engaged in the investigation of problems relating to plant-production, to farm-management, to farm demonstration, to stock-raising, to problems of rural organization, to roadbuilding—in short, to many branches of agricultural science; (2) the farmer (3) colonists, colonization agencies, investors, development organizations, and individuals; (4) students of geographic,. social, and economic sciences without reference to agricultural industries.

In the 1922 report of the United States Secretary of Agriculture it is stated (page 392) that the soil-survey work is the basis for the experimentation of the various State agricultural experiment stations. As a result of this classification of the soils varietal and fertilizer tests are being established on .the large and important soil types of the United States. That the soil type possesses individual characteristics is becoming more and more recognized by the agriculturist, county farm adviser, and extension-service director. The peculiarities of the various soils must be considered if we are to make the greatest progress in plant breeding and selection, in fertilizer practice, in cultivationin fact, in all work looking to improvement of cultivated crops.

THE BASIS OF CLASSIFICATION.

Every branch of natural science is dependent on some classification of the elements with which it deals before much progress may be made. In chemistry the discovery of the periodic law provided a scheme of classification into which all the known elements could be placed, and in which any future discoveries could be fitted. In botany and zoology schemes of classification based on the natural relationship of plants and animals have been indispensable to the study of those sciences, and in geology a classification based on the age of the rocks has been necessary. So, with soil science—at present in its infancy—it is equally necessary that some scheme of classification should be adopted.

The character which both the British and American authorities are ■ agreed upon accepting as the key to the classification of soils is the size of the particles, and the proportion of the differently sized particles which make up a soil. Hall and Russell, the Rothamsted agricultural chemists, recommend that for the purpose of a survey a large number. of soils should be submitted to mechanical analysis, including the determination of. the organic matter and of calcium carbonate, and 'that then a carefully chosen representative set should be analysed chemically so as to characterize the type ; these can further serve as standards with which farmers’ samples can be compared by the citric-acid method of determining available plantfood. These English authorities agree with Whitney (Chief of the United States Bureau of Soils) that mechanical analysis should form the basis of the survey, because it alone takes into account those physical functions —the regulation . of the water-supply and therefore of the temperature, of the air-supply, and of ease of cultivation, &c. — that play so large a part in determining the value of a soil. This method of classification is, however, not applicable either to chalk

(limestone) or to organic soils. These exceptions occur so rarely that no difficulty will be encountered in New Zealand in adopting soiltexture as a basis of classification.

Soil-texture in all but humus soils is governed by the size of the inorganic (mineral) particles composing the soil. The nomenclature of these particles is framed on words in common use, but it must be remembered that in soil science they have a definite meaning, and that each term refers to particles of a size varying within definite limits. The coarsest of these particles is termed gravel, and the other sizes are, in. the descending order, called sand, silt, and clay. The first three are further subdivided into fine and coarse fractions. These terms are sufficiently explanatory to enable one to denote the method of allotting a name to any given soil. That sized fraction which is present in greatest amount gives its name to the soil, and those fractions which are present in still large amounts but less than the largest ' give (where present) their name as a qualifying adjective. Thus a soil may be called a fine sandy clay, gravelly sand, or a sandy silt. When only one fraction predominates it is, of course, necessary to use only a simple term to describe it. The dune-sands of the coast are therefore merely sands.” This may seem so obvious as not to need the telling, but it is necessary to caution readers that although the terminology of soils is commonplace it is not loosely, used. A “ sandy silt ” not only means that the soil is composed of particles of definite size (within certain limits) to which the words “ sand ” and

“ silt ” have been allotted, but that the silt predominates in quantity over the sand, and that both occur in the proportions to which that compound name has been allotted. The determination of the proportion in which the differently-sized particles occur is the somewhat lengthy operation of the chemical laboratory known as mechanical analysis or physical analysis.

In the United States it is the practice to prefix a locality-name to the soil-name, indicating the type thus—for example, “ Orangeburg fine sand ” and “ Susquehanna clay.”

MAPPING OF SOILS.

Having shown how. soils are classified it is necessary to show how their distribution is put on record. This may be done in various ways, but the best is by means of a soil. map indicating by various colours the sites of the different types. The presence of certain types sometimes may be inferred by the system of plant-indicators. This method is based on the fact that in some countries certain plants are characteristic of certain soil types and are not found elsewhere in the same abundance or luxuriance. Hence the. vegetation is in some cases a guide to the soil. Minerals or calcic carbonate, for —occasionally may be used as indicators. Lastly, when the parent rock from which the soil was derived is known the soil may be indicated by that means.

A soil survey may be one of three kinds : — (i.) A flying soil survey, which aims at making a rapid examination of the soils of a district with a view to discover the main types which occur, and to describe them. This method is suited to country in the virgin state and when covered by virgin vegetation. An example is

the writer’s survey of the Auckland Islands (1907), in which it was found possible to correlate the main types of soil with reference to the natural vegetation (see this Journal for January, 1911).

(2.) A reconnaissance soil survey, which is a more careful examination with a view to a detailed survey later.

(3.) A detailed survey, which can only be undertaken with the aid of a good base map on a scale sufficient to show the situation and extent of each type when the area is mapped.

Accurate mapping is not attempted in the first two kinds of survey. In these it is sufficient to give such information, be it of topography, appearance of soil, or plant covering, which will enable the man on the land to recognize the soil types by mere description. In the detailed survey the farmer is not put to the trouble of identifying soil types from description, but only has to identify the position of his soil on the map. . .

In the United States the soil surveyor is provided with a base map of one-mile-to-the-inch scale. Each section or square mile is divided into 40-acre plots, on the map, and the surveyor must inspect every 10 acres and determine the type or types of soil composing the section. The different types are indicated on the map in different colours. The samples are drawn for inspection, and, if necessary, for analysis, by means of an auger which may be lengthened to reach subsoil depths. A method of checking the accuracy of the work in the field is for two men to operate . on adjoining strips of land, and if the work is done correctly . the soil-type boundaries will correspond on the line between the strips.

The largest unit used in classifying the lands of the United States is the soil province, which is subdivided into the soil series, which are again divided into the smallest unit, the soil type.

The soil province is a large area of country, not necessarily massed together as the word “ province ” might- seem to imply, but of odd shape, often straggling over huge areas of territory or existing even in disconnected stretches or patches of country. .. The soil provinces of the United States, are some fourteen in number, and owe their individuality to varying causes, some being defined from geographical position, some on geological, and some on climatic grounds. Thus the flood-plains of the great rivers flowing into the Gulf of Mexico are a soil province, the glacial lake and river terraces are another, the limestone uplands and valleys are a third, the Rocky Mountains and plains are a fourth, the arid South-west a fifth, and so on.

EXAMPLES OF AMERICAN AND EUROPEAN PRACTICE

When the soils of a province have a common origin, differing only in texture, and are alike in colour and physical properties other than those affected by texture, this collection of soils is termed a soil series, and these are arranged, according to texture, into soil types. Thus in the glacial and loessal* soil province, which includes the State

of New York, we have the Miami series, which comprises fourteen types of soil, ranging from Miami stony sand (the coarsest texture, of which there are 100,000 acres) down to the Miami clay loam (the finest texture, of which there are nearly 2,000,000 acres).

We learn that the Miami series is one of the most widely distributed and complete soil series that has been established. The series is characterized by the light colour of the surface soils, by derivation from glacial material, or by being timbered, either now or originally. The heavier members of the series arc better adapted to wheat than the corresponding members of - the Marshall series, but they do' not produce as large yields of maize. The clay loam is the most important for general farming, and forms the principal type of soil in western Ohio and central and eastern Indiana. It is especially well adapted to small grain and grass crops. The silt loam is more rolling and hilly than the clay loam, and is not so well suited to general farming. Wheat does better upon it than upon the Marshall silt loam, with which it is closely associated, but the yields of maize are considerably less. It is also well adapted to fruit, especially apples. The sandy loam' and fine sandy loam are used for general agriculture, but are especially adapted to medium and late market-garden crops and fruit. The loam is suited to maize and potatoes, while small grain and grass are grown, but with less success than upon the clay loam. Strawberries and raspberries, as well as other small-fruits, do well on this type. The stony sand, gravelly sand, and gravel are not of much agricultural value under present conditions. The stony loam is a good general-farming soil, is also well adapted to apples, and furnishes excellent pasture, while in New York lucerne, is grown upon it very successfully. The stony sandy loam and gravelly sandy loam are not strong soils, but are fairly well suited to light farming, fruit, and market-garden crops. The sand and fine sand are not adapted to general farming, but are the best early market-garden soils of this section. Such is a brief example of an American soil survey and its application in a most closely settled rural area.

Sir A. D. Hall considers that only by comparison with the type soil can the analysis of any particular soil be interpreted. The fact that a soil from a given arable field contains 0-15 per cent, of phosphoric acid takes a very different aspect when it is known that the soils of the same type contain as a rule 0-18 to 0-20 per cent., particularly if also the response of that kind of land is known by field trials ■ or from the accumulated experience of farmers.

The importance of a soil survey in an old and closely settled country like England is different from that in a comparatively new country like the United States or New Zealand. The importance in the older country is largely in its application to the saving of the manure bills of farmers by their adoption of more efficient fertilizers. “ By having the requirements of their land made known to them, enormous economies might/'’ says the last-quoted authority, “ be effected in the bills of almost every farmer using artificial manures, if the latter were properly adapted to his soils and crops.” He concludes that it is not too much to say that the information as to manuring which is being accumulated at

many experimental centres throughout the country can only be rendered properly available by the execution , of a soil survey in the district under consideration.

The United, States stands foremost in the extent of its soil-survey activities, but in. some other countries, notably Prussia, Belgium,, and France, soil survey, is by no means neglected. A beautiful example of the latter country’s work is copied into the Journal of the Ministry of Agriculture (England) for April, 1920, page 57. The map is roughly on a sixth-of-a-mile-to-the-inch scale. The different geological formations are shown in different colours, and on each is inserted a particoloured disk-shaped portion, the colours of which correspond to the legends “ organic matter,” “ chalk,” “ clay,” and “ sand,” while the size of each colour corresponds to the proportions of those ingredients present in the soil. Another figure of rectangular shape gives at a glance the proportion, expressed as parts per thousand in the soil, of nitrogen, phosphoric acid, potash, and lime. In this . map, indicating about four square miles, there are depicted four geological formations, and on them are indicated the results of eight mechanical analyses and thirty chemical analyses.

A NEW ZEALAND ILLUSTRATION, AND THE MATTER OF COST.

Applying the American method of soil survey to the lands of our Manawatu coastal area, as a hypothetical illustration, we might have —(1) The Tararua series, consisting of the soil-typesgravels, . riversands, loams, and clays—derived from the greywacke rock of the Tararua Range, and combinations of these ; (2) the littoral series, consisting of the dune-sands of the coastal plain, and combinations with various amounts of organic matter ; (3) the Manawatu series, consisting of the clays and silts of the Manawatu River flood-plain, and combinations of these with organic matter ; (4) the Otaki series, consisting of the terrace lands overlying the old Otaki sandstone ; (5) the organic series, consisting of those swamp soils the peaty nature of which has dominated all other constituents.

All the rivers between Paekakariki and the Manawatu River, having their sources in the Tararua Range, would therefore deposit mainly, the Tararua series of sediments, . but the Manawatu River, drawing -its suspended material from many other sources, and the material differing largely in nature, warrants the allotment of a different soil-series name to its flood-plain.

The foregoing is a very rough sketch of a basis for classifying the Manawatu lands. The writer has endeavoured to place the series in the order of their relative importance. In mapping the country the difficulty will be to define the boundaries where one type by admixture imperceptibly shades off into another type. The mechanical analysis has always been used by this Department in classifying soils, and was so used in the Manawatu soil investigations (see Journal, Vols. xx and xxi).

In 1905'more than 20,000 square miles had been surveyed by the United States Bureau of Soils, with the aid of forty-five assistants,

at an average cost of 2| dollars per square mile, not including travellingexpenses. Later costs have been quoted by the same organization at 4 dollars per square mile. Still later no mention is made of the cost. ■ Apparently the value of the work has established itself in the minds of the farmers, and the expense is no longer of interest to them. It is not likely that a detailed soil survey of New Zealand- lands could be made at anything like the cost per unit of area to the United States, whatever it may be at present. In that immense country very large areas occur having a uniform soil origin and structure. The average cost of surveying such a country per square mile must always be small compared with' that for comparatively small islands like New Zealand, where change of soil type is frequent, large-scale maps non-existent, and the surface extremely variable. - - ■ • • , •

CONCLUSION.

The writer’s opinion is that for New Zealand a complete soil survey will come in time, but that much good can be done in the meantime by means of a reconnaissance survey by which one may gain a knowledge of all the types existing, and may describe without being able to map them. By such means a soil survey may be begun, and the descriptions of types should be intelligible to the local scientific officers of the’Department. Although it might not be'possible for them to delimit the boundaries of types, and say just where one soil ends and another begins, it should be possible in typical cases to recognize types. At present, except in pressing cases, the detailed soil survey of New Zealand will be made to coincide with the topographical survey which the Lands Department is executing. Approval has been given to the resumption of the North Island reconnaissance soil survey interrupted by the war and since delayed ' for financial reasons.

No systematic soil survey has been undertaken of the soils of Great Britain, but several most readable treatises have been published on the soils of certain districts. Chief among these is Sir A. D. Hall and Sir John Russell’s delightful “ Agriculture of Soils of Kent, Surrey, and Sussex” (1911). Others are G. W. Robinson’s “Survey of the Soils and Agriculture of Shropshire ” (1912) ; Dr. Luxmore’s “ Soils of Dorset ” ; Goodwin’s “ Soils of Nottinghamshire ” ; L. F. Newman’s Soils and Agriculture of Norfolk” ; and lastly the memoir of Mr. T. H. Rigg (formerly of this Laboratory and now of the Cawthron Institute, Nelson) on “ The Soils and Crops of the Market-garden District of Biggleswade ” (1916). The first two named of these surveyors take a most comprehensive view of their duties, and produce works of value to the historian and rural economist. In the American publications we miss those milestones on the road which a race creeps by to greatness. To quote a few lines from Robinson : “ In Shropshire, at the time of Domesday, . land had a mean annual value of . about 2d. per acre. A horse was worth something of the order of 10s., an ox god., a cow 2od.,.and a slave £1. There were about 25,000 slaves in Shropshire who had .no legal rights whatever.”

It is to be hoped that when New Zealand soil surveys come to be written they may be as true a record of . rural history and - craft as those to which the British .authors have set their names. • ; •

* Loessal material means material deposited by wind