What Is Pumice Soil?

Rotorua Morning Post, Volume 2, Issue 535, 19 May 1933, Page 11

What Is Pumice Soil?

Our Own Correspondent.)

• — 1 a the expert. analyses 3: UNDOUBTED FERTILITY disparagement .disproyed .

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While in another article in this issue Mr. C. Dalgliesli, of the' Agricultural Bepartinent, discusses the approyed methods of farming pumice land, Mr. C. R. Taylor, of the ehemistry division ! of the same department, tells us here just what it meant by the rather vague term "Pumice Soils." "It certainly conveys the idea that the soil' is chiefly arid obyipusly composed of pumice," he says, "but just as certain the terin gives no indication of its fertility. IJnfortunately, however, this was the usual way ,of employing the Word "pumice*."

Not so many years ago, (and even now by nxany) it was the nsual practice to ref er disparagingly to the vast area of whieh Rotorua and Taupo are roughly the centres as the "pumice lands." Now, happily, it is becoming more general to think also of the fertile soils of the Waikato, Mata- : mata, Poverty Bay, King Country and part of the Hawkes Bay districts as being eitber directly f ormed or largely influenced by the same volcanic showers. that at the present day actually underlie most of the area in the Rotorua and Taupo districts. Subsequent local eruptions5 jon a smaller scale have, however, completely covered these old, well-weath-ered, fine-textured, fertile soils in these districts with several layers of a much coarser material that has required a good deal of intensive study to enable it to be farmed profitably. Many Successes From the foregoing it is obvious that to make general stateblents disparaging. to pumice soils is simply to court disproof by hundreds of successful farmers on what may justly be termed pumice land, while on the other hand to boom pumice lands indiscrimiriately as fields for settlement is extremely dangerous, as instances may readily be given of large areas totally unsuitable at present, not so much on aceount of the soil being undesirable, but beeause climatic conditions would render the chance of success remote. This is particularly noticeable in the case of very coarse soils situated at high altitudes and with a heavy rainfall, the deficiency disease known as bush sickness on such areas usually being very acute. In short, there is pumice and pumice. Texture, Altitude, Rain Probably the three main factors aff ecting the development of the coarse pumice types more than any others are texture, altitude and rainfall, and perhaps the most important of these . three is texture, as it is the only one capable of being adequately dealt with by the f armer. Possibly the most practicahle wiay in which pumice soil texture can be amended is by adding to its organic matter and in this respect, of all avenues open to f armer, green manuring appears to be, and has actually been proved, the best method. What is aceomplished in 20 years of ordinary grass-land farming is gained by the ploughing in of one crop of blue lupin or red clover (lupin for oref ereneel .

Humus and Consolidation The incorporation of organic matter is the fundamental treatment ne- ^ cessary to convert coarse pumice soils into profitable farm lands and no better example can be eited than the practice of the- State Forest Service at Whakarewarewa in annually ploughing in blue lupins. Organic matter or hnmus, materially assists in decomposing and breaking down the coarse pumice particles and ihe cultiyation supplies the necessary compaction of the soil which is so essential if the soil is to hold sufficient moisture during periods of drought and also to prevent the excessive leaching of soluble plant \foods when the rainfall is heavy. Undoubtedly the success that has attended the development of the Waikato, Te Awamutu and Matamata districts has been largely due to the much older (geologically) loamy texture, and high organic eontent of these soils, and the writer sees no good reason why the much younger, coarser textured types of the Rotorua and adjoining districts should not with the proper application of knowledge already gained, be, in comparatively few years, in just as enviable a position. Essential Elements Pumice soils generally, provided they are reasonably supplied with humus and moisture, respond in a remarkable degree to suitable top-dress-ing and management. A large number of chemical analy'ses made of the soils of the Rotorua -County hy the Department of Agriculture recently in the course of a reconnaissance survey of the district distinctly shows that of the three main elements necessary to the

growth of plant life, i.e., nitrogen, phosphate and potash, only the l'atter is present in sufficient! quantity. Phosphate, in common with the soils of the rest' of New Zealand, is -extremely low, while the position of nitrogen, ds only to be lexpected in view of "the low humus eontent of most of the area, bush country being perhaps, exeepted. Calcium earbonate (the ordinary lime of commerce) although not overahundant in quantity, was found to he sufficient lat any one timie for plant requirements as -evidenced by- the healthy clover growth. This is due to the comparative rapddity with which the particles of soft pumice, unlike the extremely hard fractions of a more normal soil, decompose and yield up their .plant food. Care in Manuring Possibly when farming has gone on for thirty or more years on the place a small dressing of lime mighf be heneficial, but it certadhly is* not necessary on younger farms and iii this connection a nOte of warnihg will not be out of place. The deficiency dis'-" ease known as bush sickness and *familiar to all who havej attempted to earn a livelihood from the coarser types of pumice* soil, is due to a. shbrtage of lavailable iron in the: soil .and therefore in the pasturje. Lime has a most deleterious effeet on this small amount of available iron) and renders it still inore difficult for the plant to absorb enough for the requirements of the animal, hence stock

become more sick than before the lime was applied. The unfortunate part of over-en-thusiasm an this direction is the fact that it usually takes many years b'ef oxe conditions once mere return to normal. To meet the phosphate deficiency, ' both chemical analysis and actuial live-stock trxals have demonstrated that there is nothing better or more suitable to the peculiar requirements of the pumice soils than a mixture of basic slag and superphosphate, balf and half, thoroughly mixed togethier and applied immediately after mixing at the rate of ahout 3cwt. per acre, preferiably in the autumn. A Useful Mixture , This mixture supplies three important and essential elements at a cost within the reach of all. Slag contains quite a fair amount of readily available iron as well as phosphorus land lime, whilst super, as its name suggests, supplies further phosphorus and gypsum or sulphate of lime. This lime is in an acid form, unlike the earbonate, and its benefits are twofold. The acid in it tends to attack the unavailable iron and so render is more soluble and the soil is enriched in lime to the extent of roughly 60 per cent. of the amount of fertiliser used, without any detrimental effeets on the available iron, as would be the case if a more alkaline form of lime were used. The, fact that lime in generous quantity is being used when the mixture recommended above is applied to the land is rarely appreciated hy the average farmer, hence the desire to use earbonate of lime, resulting, in many cases, in added difficulties only. These remarks are meant only t'o apply to that area which is commonly known as the "pumice lands" and would probably require considerahle modification in the case of more normal soil types, including those areas obviously pumice hut of older origin.