The intrazonal soils include the soils from less common parent materials and those influenced by high ground water; and the azonal soils are youthful, owing to recent renewal by sedimentation or erosion.

The rendzina and other calcareous (or lime-rich) soils, mostly from limestones, occur both in the subhumid areas (such as near Oamaru, in North Canterbury, and in Hawke's Bay), where they are associated with yellow-grey earths, and in the humid areas (particularly North Auckland), where they are associated with northern or southern and central yellow-brown earths. They are fertile, with deep, dark, granular topsoils. In the drier areas they are used for intensive arable farming and sheep farming and, near Oamaru, for poultry farming; in the humid areas, for dairying and fat lambs. The yellow-brown sands, from coastal sand drifts of various ages, occur on sandhills which dry out excessively in summer and sand plains where ground water approaches the surface in winter. The drier soils are used for grazing; the soils with moister subsoils, after fertilising with phosphate and potash, are used for sheep farming and dairying. Where the subsoils are loose, blowing is a problem.

The yellow-brown pumice soils of central North Island are formed mostly on two volcanic-ash showers that fell 800 and 1,700 years ago. Their topsoils are mostly sands or sandy loams and the subsoils pumice sands and gravels. Because the cattle and sheep on them became bush sick, they were difficult to farm for many years and large areas were planted in exotic forests. The ailment, however, is now overcome by topdressing with cobaltised superphosphate and, except where droughty, the soils can be converted into good farm land. In addition to phosphate, they need consolidation and, after continued use, potash top-dressing. The yellow-brown loams are derived mostly from fine-textured ashes erupted by volcanoes in central North Island and by Mount Egmont and occur around the margin of the pumice soils, which are younger. They are very friable, loamy soils, respond well to superphosphate topdressing, and give slight to good responses to lime; potash responses are expected to increase with continued use. The soils are used mainly for dairying and fat-lamb production.

The red-brown loams and brown granular loams and clays are formed from basalts and andesitic ash or andesites, respectively rocks which are volcanic and are rich in iron and aluminium. They are friable soils with strong structures and a marked power to fix phosphates. The younger, more fertile soils (comprising half the total) respond to superphosphate and lime, those from basalt responding also to potash: they are used for dairying, fat-lamb production, and sheep grazing, and in places for market gardens and orchards. The older soils have lower natural fertility and include the strongly acid granular soils and the moderately acid ironstone soils: they carry fair pastures when top-dressed with lime, phosphate, and potash and, on the acid soils, with molybdenised superphosphate.

The organic soils are peaty and occur mostly in the Auckland district. Where mellow and fertile they can be farmed satisfactorily, but the peats of acid bogs require special treatment. The gley soils are formed under the influence of ground water, which causes the formation of grey subsoils commonly mottled with rust colours. They, too, occur mostly in the Auckland district and, when drained, are used for dairying and fat-lamb production.

The recent soils from alluvium are formed from flood sediments on river flats. For the most part they are fertile, deep loams, but some are gravelly with excessive drainage. They are used mainly for fat lambs and dairying; also, in drier areas, for cereals, pasture and vegetable seed crops, pulse crops for canning, pip and stone fruits, small fruits, and tobacco. The recent soils from volcanic ash occur mostly around the active volcanoes of Ngauruhoe and Ruapehu, and also around Mount Tarawera. Where they cover the pumice soils their cobalt content offsets the deficiency in the pumice.

The steepland soils occupy about half the area of New Zealand, being most extensive on the axial ranges and in north-west Nelson and east Taranaki. Although showing characters related to the zone where they occur, they are, for the most part, shallow and their subsoils vary widely in fertility according to the underlying rock. Being relatively unstable they are periodically renewed by erosion which, when the plant cover is disturbed by man, becomes accelerated, with obvious effects, not only on the hillsides, but also on the rivers and river flats. Besides the steepland brown-grey earths and steepland yellow-grey earths, these soils include the high country steepland yellow-brown earths, the central and southern steep-land yellow-brown earths (2 million acres of which have high natural fertility), other steepland yellow-brown soils, and the podzolised steepland soils, which are largely in forest, have low natural fertility, and occur mainly in western Nelson, Westland, and western Southland.

The subalpine gley soils and subalpine gley podzols and their steepland counterparts occur in approximately the same districts as the podzolised steepland soils, but at elevations above 3,000 ft in the south and 5,000 ft in the north. Their rainfall is greater than 80 in. per year; they are largely in subalpine scrub and tussock; and they extend up to the alpine soils at high elevations where vegetation is for the most part sparse or absent and much bare rock and ice are present.

The zonal soils are formed on normal sites from ordinary siliceous rocks and show clearly the impress of climate and vegetation. If the soils from unusual parent materials (such as volcanic ash) and those occupying special sites (such as steep slopes and hollows) are set aside, a simple pattern of zonal soils is revealed. It consists of the brown-grey earths of the semi-arid areas where the rainfall is less than about 20 in. a year; the yellow-grey earths of sub-humid areas where the rainfall is approximately 20–40 in. a year; the high country, central and southern, and northern yellow-brown earths of the humid regions where the rainfall is well distributed and is greater than approximately 40 in. a year; and the corresponding podzolised yellow-brown earths and podzols resulting from excessive leaching beneath an acid litter of decomposing vegetation.

The brown-grey earths occupy the dry intermontane basins of Central Otago and the Mackenzie Plains, where rainfall is insufficient for plant requirements for most of the year (diag. 7A). They are generally rich in plant nutrients and are weakly acid to alkaline, with salty patches in places. Many of them are stony. Their chief need is water, but irrigation must be practised with care to avoid waterlogging or the spreading of salts. They produce fine wools and store sheep and, where irrigated, fat lambs; lucerne is grown and, in favoured spots, brassica and other seed crops and stone fruits.

The southern and central yellow-grey earths are the seasonally dry soils of Southern Otago, Canterbury, Wairarapa, Hawke's Bay, and Manawatu, where rainfall is inadequate for plant growth for a third to a half of the year (diag. 7B). They are moderately to weakly acid and the older soils have a thick, hard pan in the subsoil. The drier soils, formed under tussock, are used for mixed arable farming and fat lambs and the moister soils, mostly formed under forest, are used also for dairying. Pastures on these soils respond to phosphate fertilisers. Shallow and stony soils related to the yellow-grey earths cover much of Canterbury Plains: they are used for sheepfarming, including fat lambs; with irrigation they carry over four ewes per acre and grow cereal and pasture-seed crops.

The high country, southern and central, and northern yellow-brown earths are commonly referred to collectively as the “yellow-brown earths”, but, owing to their very different properties, they really comprise three groups, which are given distinctive technical names. With their podzolised counterparts, they occur in humid regions where the rainfall is sufficient on the average for plant growth for the greater part of the year (diag. 7C), and for iron compounds to decompose and stain the soils yellow.

The high country yellow-brown earths on the cold uplands east of the Southern Alps are developed under tussock at high elevations. They have yellow friable subsoils and are moderately acid and strongly leached. Where oversown with clovers they respond to molybdenised superphosphate and sulphur. They are used mostly for wool production and some store sheep. The southern and central yellow-brown earths of the cool and the mild districts, like Southland and Wellington, were formed under forest and have nutty subsoils. When sown to pasture with lime and superphosphate (in places molybdenised superphosphate) they are used for dairying and fat lambs on the rolling land and for wool production, store stock, and some fat lambs on the more hilly slopes. Cattle are also run to help control pasture growth and prevent its reversion to scrub and fern. The related podzolised yellow-brown earths and podzols are best developed in Southland. They are formed under rimu-kamahi forest and are very leached, with acid grey structureless topsoils and with thin iron pans in the subsoils in places. They are being brought under pasture for sheep and cattle grazing. Waterlogged counterparts of these soils, the gley podzols or “pakihi soils”, occur in Westland where the rainfall is 100 in. or so per year (diag. 7D). They are structureless and their chief problem is one of drainage to remove the excess water. They are not readily utilised after the native forest has been removed. The northern yellow-brown earths formed under mixed forest in the warm, moist climate of North Auckland are mostly heavy clays containing kaolin, which tends to absorb alumina and consequently to retain phosphate in a relatively unavailable form. The more fertile soils are moderately acid, but support good pastures when topdressed with lime and phosphate, in places molybdenised: the rolling land is used for dairying and fat lambs, the hills for sheep and cattle grazing. The less fertile soils support fair pastures when topdressed with lime and superphosphate: on the easier land many dairy and fat-lamb farms are situated, but pastures on the hill country are less easy to maintain. The northern podzolised yellow-brown earths and podzols have thin, grey, structureless topsoils overlying a grey, siliceous horizon and are strongly acid and very low in plant nutrients. Where formed under kauri forest they are known as “gum-lands”. In places, especially where the soils are sandy, farming should be approached with caution, because subsoil pans of humus and iron impede drainage; otherwise the soils can be brought to support good dairy pastures.

The environmental conditions that control soil formation tend also to govern the kinds of land use. Thus a close relationship between soils and land use arises, not only from the characteristics inherent in the soils themselves, but also from the joint environmental factors, such as climate or topography.

The diverse soil-forming conditions in New Zealand have led to a great variety of soil-forming processes, which have proved a useful aid in understanding the soil pattern and in sorting the soils into classes. Two main kinds of soil classification are used in New Zealand. The first is a genetic classification according to soil-forming processes and is used for scientific and general purposes. The second is a classification according to soil types and series and is used for mapping and land-use purposes.

For scientific purposes the genetic classification provides the various soil classes with precise technical names, such as “fulvic soils”. Over the years, however, the main soil groups have become better known to the layman by common names, such as “central yellow-brown earths”. It has been found practical, therefore, to retain the common names for popular use. They are set out with their technical and overseas equivalents in table 1.

For mapping purposes the basic unit of classification is the soil type which is relatively uniform in properties from the standpoint of land use. It is given a geographic name and a textural name, such as “Judgeford silt loam”, and these are supplemented where necessary by other descriptive terms, as in “Okaihau gravelly friable clay”. Where required, the soil type is subdivided into phases according to characteristics of lesser significance in soil classification but potentially significant to land use; or it may be classed with similar soils to form a series, the members of which have the same geographic name and are developed from the same kind of parent materials.

Alpine soils, bare rock, etc. (3 ¾ million acres) and coastal sands (¼ million acres).

*Including brown granualr loams from volcanic ash.

The soil complex is a compound mapping unit consisting of a mixture of two or more soil types which are too intimately associated in the soil pattern to be indicated separately on ordinary detailed soil maps. Hill soils and steepland soils are the particular soil complexes due to slope on hilly and steep terrain respectively; they are distinguished as special mapping units in New Zealand, where they are extensive and are widely used for farming and forestry. The soil association, like the complex, consists of a mixture of two or more soil types, but the soil pattern is sufficiently coarse to be resolved on ordinary detailed maps. The soil set, which is a convenient mapping unit used on general surveys in New Zealand, contains similar soils or similar assemblages of soils.

Soil maps showing these units are published in three main series: 4 miles to an inch (1: 253440) for general surveys, 1 and 2 miles to an inch (1:63360 and 1:126720) for district surveys, and 20 and 40 chains to an inch (1:15840 and 1:31680) for detailed surveys. General surveys show the main sets of soils and their general relation to land forms and are used to assist investigations and planning on the regional or national scale. District surveys show soil types or (in places) combinations of types, assist the study of local soil problems, provide a basis for assembling and distributing information related to soils, and are used directly for advising on pastoral land use. Detailed surveys delineate soil types and land-use phases, show the soil pattern in relation to farm boundaries and subdivisional fences, and are used directly for advising on intensive forms of land use, such as fruitgrowing and cash cropping.

Environmental conditions responsible for soil formation in New Zealand are varied. The main islands extend south over a distance of a thousand miles, from latitude 34° 24' S to 47° 17' S. Their climate ranges from oceanic to subcontinental, and, from subtropic to cool temperate on the lowlands to alpine on the mountains (maximum elevation of 12,389 ft). They are mostly humid (rainfall, 40–80 in. per annum); however, since the rain comes mostly from the west, the western side of the South Island is superhumid (80–300 in.). Parts of the east and west coasts of the North Island and the east coast of the South Island in the shadow of the mountains are subhumid (20–40 in.), and interior basins of the South Island are semi-arid (12–20 in.). Most of the humid areas were originally in forest or scrub and the drier areas were in tussock grassland, but high on the mountains subalpine scrub, herbfield, or fellfield prevailed.

The topography and geology of New Zealand are similarly varied. Half the country is steep, 20 per cent is moderately steep, and only 30 per cent is rolling or flat land . The largest area of flat land is the Canterbury Plains on the east coast of the South Island. Geologically, New Zealand has a continental structure and is formed predominantly from rocks of sedimentary origin, but in the northern half of the North Island both basaltic and andesitic rocks are important soil formers, and in the middle part of the North Island various ash showers of rhyolitic or andesitic composition blanket the terrain . South of the ash-shower region the impress of the Ice Age is reflected by glacial erosion and deposits of loess and boulders in the South Island, and by corresponding loess-like and stony sedimentary beds and possibly periglacial solifluction in the southern part of the North Island. The Ice Age is also reflected on the coasts and in the valleys by terraces associated with the changes of sea level that accompanied the accumulation of ice in polar regions.

The soil is a natural body embracing not only the topsoil, but also the subsoil and other layers above its parent rock. It is a product of its environment – of the rock waste which is its parent material, of the climate under which it weathers, of the kind of topography upon which it is situated, of the vegetation and other organisms with which it develops, and of the length of time during which it has been developing.

From the standpoint of land use the soil is regarded as a medium of plant growth, but it is not a passive medium. It is an active body comprising not only mineral and organic constituents, but also the soil processes that are continually going on, as well as soil temperature and moisture regimes that keep these processes operating. The dynamic or active soil, as defined in this way, correlates well with the kinds and distribution of soil organisms, with plant growth, with land capability, and with land use.

The activities of these local authorities, which have been constituted to implement the Act, now cover approximately 80 per cent of the country, with an engineering and conservation staff to handle specific and local problems.

by Douglas Archibald Campbell, M.AGR.SC., B.SC., Chief Soil Conservator, Ministry of Works.

Owing to the far-reaching effects of erosion and flooding, the value to New Zealand of soil conservation and river control cannot be overemphasised. Equally important is the availability of technical information and service to farmers prepared to take action. Press publicity is therefore coupled with the publication of bulletins (16 to date) for general use, together with the production and screening of cine-films (10 have been produced to date for theatre circuits and 20 for use in schools and at farmers' meetings).

At Glenmark, near Waipara, North Canterbury, the combined effect of conservation farm plans, operating over an entire problem catchment, has demonstrated that soil erosion and flooding can be effectively controlled. The progression from single conservation practices to combined conservation and good farming has demonstrated the necessity for, and the advantages of, such group action by all farmers in problem catchments. Catchment boards are successfully promoting several such schemes on catchments up to 120,000 acres.

In addition to the board's administrative rate, any special rate for the community works required in the catchment control scheme must be agreed to by the farmer group, while the conservation works done on each farm are subsidised by the Council through the catchment board.

The extensive subsidised river control and drainage works undertaken by fourteen catchment boards and financed largely by the Soil Conservation and Rivers Control Council had to be supported by conservation works in the upper catchments. This has led to a scheme in which farmers are subsidised for conservation works – gully, slip, sheet, and scree erosion control, and dams for flood control – which also benefit lands lower in the catchment.

Single practices such as gully control, terracing, dams, tree planting for stability and windbreaks, fencing to control grazing, initial seeding and fertilising of eroded land, and sand dune stabilisation are subsidised. Experience on cooperative demonstration farms, run in conjunction with farmers, has proved that special soil conservation practices, supported by good farming practices, not only control soil erosion and flooding but also considerably increase production. Hence the rapidly growing trend is now towards integrated erosion control and conservation management schemes, embracing the entire farm unit (conservation farm plans). Some 300 of these are now in operation.