Soil Division's Work Benefits N.Z. Production

Auckland Star, Volume LXXIII, Issue 177, 29 July 1942, Page 4

Soil Division's Work Benefits N.Z. Production

TVURING recent years New Zealand agricultural difficulties have been lessened by the cumulative knowledge brought to bear on problems of soil deficiency. This knowledge has accrued through the comprehensive, painstaking work of the staff of the New Zealand Soil Division of the Department of Scientific and Industrial Research.

By A. W. B. Powell

This survey reveals that New Zealand soils fall into five of the soil groups' of the world; all the more important groups except one being represented. The five groups represented in New Zealand are termed, respectively, podsols, laterites, chestnut earths, rendzinas and skeletal soils. These groups and stages within them are determined by such factors as parent material, vegetation, topography and age, all of which go to ccpntrol the amount of leaching-out or dissolving away of fertility elements and physical characteristics. Podsol Most Widespread

By far the most widespread soil group in New Zealand is the podsol, an acid leached soil. This group is general in the districts of considerable rainfall, and is characterised by great leaching of both lime and phosphate. The gum lands of North .Auckland and the pakihi lands of the Nelson Province provide typical illustrations of such podsols where the leaching process has exhausted almost the entire reserve of lime and phosphate. Cawthron Institute experiments on the pakihi lands of Nelson have shown that as much as one ton of ground limestone and scwt of superphosphate or other phosphatic fertiliser per acre are essential in the initial establishment of pastures. One hundred years ago Liebig laid the foundations of modern agricultural chemistry in regard to the nutrition of plants and animals. By the analysis of plants he was able to demonstrate that at least 10 elements were invariably present and he concluded that they were indispensable for the proper functioning of plants. Among the inorganic elements he stressed the importance of calcium, phosphorus and potassium for the production of high crop yield. As strongly polsolised soils are particularly low in all the chief plant nutriments, they are among the poorest of our soils.

Reddish Coloured Clays

Laterites are the reddish coloured clays found in many tropical and sub-tropical lands. They are formed by the subaerial decomposition of rocks in situ, especially in low-lying forest lands where the drainage is feeble. The decomposition of the laterites involves a loss of silica and a concentration and oxidation of iron, frequently forming hard surface layers or clay pans. The soils of the Hawke's Bay in general are laterites, being youthful in the stage of losing silica. A later development of the laterites is the leaching from the topsoil of both iron and aluminium, good examples being the ironstone soils of Kerikeri and Okaihau.

Youthful laterite soils-in the process of losing silica are characteristic of the dairying land of western Taranaki and North Auckland. Pastures on these soils respond well to phosphatic topdressings, and the Department of Agriculture has recently advocated the use of potash manures over the greater part of western Taranaki.

The volcanic soils of the Auckland Isthmus are a further example of a laterite, for they represent the first stage in the breaking down of basaltic lava-flows.

Most Healthy for Stock

Rendzina soils formed from limestone have a limited distribution in Hawke's Bay and the Oamaru district. They are characterised by a black loamy topsoil resting on a chocolate-brown clay and are regarded as the most healthy soils for stock.

Skeletal soils are of alluvial origin and lie in practically all the valley bottoms. They are extremely fertile, the heavy soils of the Hastings flats being considered probably the most fertile in this country. Our Soil Division has done great work in its initial classification of New Zealand soils and their efforts provide invaluable data that, correctly interpreted, will doubtless result in a vast improvement in our agricultural production.