NORTH ISLAND CENTRAL

New Zealand Herald, Volume LXVIII, Issue 20969, 4 September 1931, Page 14

NORTH ISLAND CENTRAL

VOLCANIC AND PUMICE SOIL. CENTRES OF ACTIVITY. AGRICULTURAL POSSIBILITIES. Largo deposits of volcanic ojectnmenla cover enormous tracts of country in the Rotorua-Taupo zone, but it is only during the last year that a full realisation lias been arrived at of the very widespread naluro of volcanic deposits throughout the whole of tho central North Island territory, said Mr. T. Rigg in a lecture to the Wellington Philosophical Society. From the work that has been done in the course of the soil reconnaissance survey during the last 12 months, it has been ascertained that volcanic deposits cover the whole country from Kawhia Harbour and Mount Egmont on tho west coast, to Tauranga and Whakatano 011 the Bay of Plenty, and Napier on tho east coast. Throe great centres of volcanic activity wcro concerned in this widespread distribution of ash. These centres were located in the R6torua zone, the Taupo zone, and Mount Egmont. In tho case of volcanic activity in tho Rotorua and Taupo zones it is evident that several vents were responsible for the distribution of volcanic material. In tho Taupo zone the more important vents were situated in or iienr Lake Taupo, but Mounts Tonga riro and Ngauruhoc also have contributed.

Of tho volcanic deposits which arc responsible for the spils of the central territories, tho most o.xtensivo deposit is one that has come f*om a vast eruption near Lake Taupo. Material from this eruption, which apparently took place in comparatively recent times, covers the whole country from To Kuiti and Taumarunui, in the west, and extends almost as far as Napier in tho east. Waiouru, in tho south, and Rotorua, in the north, mark the limits of well-defined deposition in the north and south. Eruptions from Mount Egmont aro responsible for tho soil types covering a groat part of Taranaki, extending almost as far as Ohakune, in the east, and probably as far as Ohura and the Mokau Ilivcr, in tho north. Ash From Unknown Source. Between the Mokau River and Te Awamutu the principal soil covering is derived from another source. This ash appears to be much older than that from the eruptions of> Mount Egmont and from Taupo. Tho same ash in tho district between To Awamutu and Futaruru contributes largely to the soils of this district, but there appears to bo a superficial coating of ash an unknown source which materially influences the characteristic properties of these soils. Ash from vents in tho Rotorua centre covers large tracts of country between Rotorua and Tauranga and Whakatane, The eruption of Mount Tarawera in recent times covered, in its turn, earlier deposits from the Rotorua centre lying between Mount, Tarawera and Opotiki. Ash from the Ngauruhoo eruption covers a somewhat restricted area in the vicinity of the mountain and overlies the Taupo ash. Volcanic ash from Mount Tonganro is almost entirely covered by ash from the last Taupo eruption, but a considerable area of soil between Waiouru and Taihape has been identified as from the Tongarlro eruption. « Chemical analyses show that ash from ,Ihe Egmont, Tongariro and Ngauruhoe eruptions is andesitic in origin and is well Supplied with line and other bases. The phosphoric content of ash from these eruptions is notably high. Tho • chemical analyses suggest that the soils derived from the weathering of these ash deposits are of high potential fertility. Changes in Country. The rhyolitio deposits of Taupo and the Rotorua centre, compared/ with soils derived from the recent Egmont end Ngau. ruhoe deposits, are low in lime and phosphorio acid. The ash coating in the To Kuiti district probably is andesitic in origin, _ but great leaching of lime and other bapps has taken place. The great chemical and textual changes which are associated with tho volcanic deposits very clearly point to tho desirability of very detailed laboratory examinations in order to determine more accurately, the distinctive properties of the volcanic soils. This is a matter of great importance to tho development of agriculture in the Volcanic territory, as farming experience already has shown that difficulties are frequently encountered in connection with the {[razing of stock on established pastures. A particular type of stock ailment affecting 1 sheep in the country west of Te Kuiti in recent years has occasioned much concern to farmers in this district. Investigations carried out by Mr, B. C. Aston, under -the auspices of the Department of Scientific and Industrial Research, liavo shown that the pastures contain low amounts of lime and phosphate. ment with mixtures of Jimo and superphosphate, accompanied by close grazing of tlie pastures, lias resulted in great improvement in stock hoalth on certain farms, and also has greatly improved the carrying capacity of the land. < ' The incidence of slock ailment in tha country to the west of Te Kuiti must not be confused with bush-sickness, which has presented such groat difficulties to the extension of agriculture in certain areas covered by Taupo and Rotorua rhyolitic deposits. Stock Ailments Cured.

Bush-sickness in its acuta form has been noticeable in particular localities from the moment when the land was broken in. Generally, bush-sickness diminished in sevority under ordinary farm management. The reverse appears to bo tho caso in connection with the " dopinoss" affecting shocp in tho districts west of To Kuiti.

The long and careful work of Mr. B. 0. Aston, of the Department of Agriculture, has shown that typical bush-sick-ness on volcanic soils is associated with soils of a somewhat coarse texture. As a. result of pasture and soil analyses, a deficiency of iron in tho foed of stock has boon suggested as tho cause of bush-sick-ness.

Inuring (lie conduct, of tho present soil survey, tlie observations that have been .made show that bush-sickness is vory definitely associated with particular volcanic deposits, and is not common to all the soil types dorivod from ash deposits. Tho rhyolitic ash from tho Rolorua centre, covering tho country north of this centre to tho Bay of Plenty, and the Taupo doposit of widespread distribution, tiro very definitely associated with bush-sickness. Tho ailment occurs at such widely separated points as Mamaku, Ngaronia and Kopaki, which are all located on the Taupo deposit, Intensive Agriculture. In connection with tho development of volcanic soils, the whole area of country covered by tho Taupo deposits must be regarded with some suspicion in view of the incidence of bush-sickness at at least three points widely separated. Tho success thai has been obtained by the use of iron "licks" in combating tins ailment, however, gives great hope for tho oventual development of intensive agriculture on large areas of tho Taupo deposit. In selected localities in this section tho carrying capacity of pastures sown to English grasses and clovers and top-dressed with superphosphates has been notably high, arid if the bogey of bush-sickness could bo definitely removed there is little question that very large areas of the Taupo deposit could be successfully farmed.