A DOMINION PROBLEM

New Zealand Herald, Volume LXXV, Issue 22972, 25 February 1938, Page 18

A DOMINION PROBLEM

DEPLETION OF MINERALS GRASS AND SOIL AFFECTED REPLACEMENT PLAN NEEDED BY H.B.T. Geologically New Zealand is one of the most mixed, and therefore most interesting countries in the world. In their rock and soil formation parts of the South Island show great age, the basic rocks —granites and slates—being prominent in many districts, while the configuration of the country and marine deposits indicate that the land has been subject to more than one tropical period followed by arctic conditions. The soil formed from the erosion of such materials is generally only moderately fertile, but it has the advantage of being much richer in minerals essential to healthy vegetable and animal growth than has the newer volcanic areas of tho north. In comparison the North Island, and particularly the half of this north of a line drawn approximately through l'almerston North, is a mere youth of a country. Only in a few places do the granites and slfites make an appearance, while sea-bed sandstones, mudstones, limestone, and rocks of volcanic origin are jumbled indiscriminately from the highest altitudes to the sea coasts. Mixed Soil Formations The fertility of the soils resulting from the erosion of these mixed rocks and sea-bed deposits varies considerably, according not only to their origin, but to their age. Each district, and often one area separated from another only by a creek or an alteration in the slope of the land, presents an entirely new problem. Erosion, resulting from weather influences, has' not taken place to any great extent, hence only I a lew alluvial Hats and plains bordering on rivers or shallow coastal inlets give an indication of the quality of the composite soil resulting troiu this mixed origin. Most of these alluvial Hats are extremely rich in fertility, but comparatively low in available minerals, and as a result of this, combined with a climate which encourages luxuriant growth, neither the plant growths nor the animals raised on them enjoy robust health. This raises many problems of discovering and supplying mineral deficiencies which may exist. It is unquestionable that the most valuable work which can be done in connection with North Island soils, and indeed only to a lesser extent in the South, is analysis and experimentation to supply the so-called "minor" mineral elements —upon the availability of which healthy growth of vegetable and animals depends. Abundant Minerals Not Available It would be assumed that highly mineralised areas, such as the Coromandel Peninsula, the Great Barrier Island, and the eastern-coast of the North Auckland Peninsula, in which areas almost every mineral can bo found in the volcanically-formed rocks and reefs, would be amply supplied with these in available form for the pastures. Such is not the case, however.

All these particular areas, although there is abundance of iron, copper, and so on, in reefs and rocks, produce .uiilemic stock desperately needing these elements. I have seen sheep and cattle so ravenous for iron—on parts of the Coroinandel Peninsula—where iron ore, among other minerals, was being actually dug from the mines, that they ate linionite (a finely-powdered form of iron oxide, containing cobalt, copper, and other impurities,), as though it were chaff, and with no salt or other admixture to attract them with, its flavour. Soils Too "Young" This anomaly results from the geological newness, or youth, of this highly-mineralised country. There has licit been sufficient time for the disintegrating forces of nature —water, wind, heat and cold —to pulverise arid dissolve the minerals so that they may be taken up by the plants through the water which their roots take in. Another factor, and one which has perhaps the greatest influence on making minerals available to plants, and through them to animals, is bacterial life. Soil bacteria are among the lowliest forms of life which we recognise, and their most valuable work is the conversion of minerals from inorganic to organic form. A large part, perhaps 50 per cent of their food is the inorganic minerals which they dissolve, with acids which they secrete and which, in their excretions and at their death, they pass on in organic and readily-available form to plants. But bacteria cannot live on a diet composed solely of minerals;*they must have, as well, decaying vegetable matter (humus), which keeps them regularly supplied with moisture, some of their food, and a comparatively even temperature in which to live. Much of this highly-mineralised soil to which 1 am particularly referring is very deficient in humus. It is "hard" land with the clay and rock coming practically to the surface, so the bacteria have no medium in which they can live and work in health. Hence we have a deficiency of minerals in a form available to plants, even where there is a superabundance of these elements. Soil Building Arre&ted When the white man first came to these islands the soil was only in the process of being made. Forest trees and deep-rooted plants clothed the land and were bringing up from the deaths the minerals which they needed. 'I hey deposited these, in an organic form, combined with humus, on the soil surface as fallen leaves and other vegetable debris. Before this slow process of Nature's soil building was completed, we denuded the land of its forest and completed tho destruction by repeated burning, until all, or practically all, the humus was dissipated in smoke. The minerals, being non-in-flammable, remained as ash, and for some years this was sufficient to supply tho pasture and stock with their requirements. The time has now come, however, when these reserves are exhausted and both tho fertility , and health of tho country is reaching a low ebb. Means of Checking Decline There are means of checking this decline, and even of reinstating the fertility and reproductivcness of the land; but only if its exhaustion from the past and present faulty methods of farming is discontinued, and scientific methods of soil building are adopted before tho areas have become barnen wastes incapable of profitably supporting livestock. What can, and must be done, if the land is to be saved covers too wide a field to be dealt with in a single article such as this. Indeed, much yet remains to be learned; but unless we in New Zealand are resigned to seeing increasingly large areas go out of production —as grazing land—we must design and follow a logical plan for the reinstatement of fertility. Phosphate, nitrogen, potash and similar commercial fertilisers, besides being uneconomic on much of this land, are not sufficient. We need plants specially adapted to providj abundant humus, and deep-rooted enough to bring up, from depths untapped by ordinary grass, mineral supplies to replace those which we have robbed.