Intrazonal and Azonal Soils
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.