Pasture Topdressing in North Island

New Zealand Journal of Agriculture, Volume 93, Issue 1, 16 July 1956, Page 40

Pasture Topdressing in North Island

By

C. DURING,

Research Officer, Department of Agriculture, Wellington

IT is always difficult to say exactly what fertiliser and how much fertiliser and lime should • be applied to a given field. This complexity arises because there are many factors to considereconomics, management, past topdressing history, and soil type. The influence of soil type in fertiliser requirements may be very distinct. In this the first of a series of articles fertiliser, lime, and trace element requirements of pastures are discussed in terms of important soil groups. These soil groups comprise related soils occurring under similar climatic and topographical conditions and follow the genetic classification adopted by the Soil Bureau, Department of Scientific and Industrial Research (I). In the next article of the series the mineral requirements of airborne volcanic ash soils will be discussed.

THE Soil Bureau distinguishes soils by their parent material and the development they have undergone since changing from parent rock to the present soil supporting pasture, scrub, or forest. This article is limited to describing soils of the North Island formed on sedimentary rocks. These are rocks derived from material such as sand, silt, and fine clay deposited by rivers in ancient seas and later raised by earth movements to form the present outline of New Zealand. Limestone is also a sedimentary rock. The soils derived from sedimentary rock and coastal sands vary greatly in

natural mineral fertility. Even the . poorest soils, however, can be brought to a high level of mineral fertility by the application of a few simple chemical compounds. These are phosphatic fertilisers, potassic fertilisers, ground limestone, and perhaps molyb-

denum and copper salts. On very limited areas zinc, magnesium sulphate, and boron may further raise fertility. In the North Island nearly all soils derived from sedimentary rock need phosphatic fertilisers. The rate at which these should be applied depends less on the natural fertility of the soil than on the kind of pasture it will grow and its capacity to fix applied phosphate in a form unavailable to plants. Soils on which subterranean clover or Lotus uliginosus (.major) would be the main legume in the pasture would need less phosphate than soils on which good white clover pastures are desired. Soils receiving a high average rainfall usually need more phosphate to keep pasture from reverting to scrub and weeds than soils in the dry districts of, for instance, central Hawke’s Bay. Little is known about the extent to which phosphate is fixed in an unavailable form on soils derived from sedimentary rocks. Only a few years ago failure of water soluble phosphates to stimulate pastures was attributed to phosphate fixation; today there is some evidence that this may be due to trace element deficiencies,

notably of molybdenum. Long-term trials to obtain an estimate of phosphate fixation have not been done except on a few experimental stations.

Liming improves the fertility of most soils derived from sedimentary rock. Some soils derived from limestone and calcareous mudstones and sandstones in the drier east coast districts of the Wairarapa and Hawke’s Bay are an exception. Particularly, the steep hills formed from these parent materials need no lime. The

rate at which lime should be applied to be effective depends largely on soil type. Quite small amounts of lime, from 2cwt. to 6cwt. per acre, markedly improve pasture production on some soils in the southern half of the North Island. The more clayey soils of the warm and moist northern districts, however, show a need z or heavy liming. In the past 2 tons per acre and over was advised on many clay soils and gumland soils near and north of Auckland. Now it is known

that by the use of molybdenum good pastures can be produced with lighter rates of liming than seemed possible before.

The use of potassic fertilisers on soils derived from sedimentary rocks is often advised in the naturally infertile gumlands north of Auckland and on some of the yellow-grey earths of the Manawatu. On soils derived from wind-blown sands potassic fertilisers may be payable on the moister sand

flats along the Manawatu coast. Potash deficiencies are also expected to occur in all districts where the rainfall exceeds 60in. to 70in. per annum, particularly on fields frequently cut for hay. Pasture responses to small amounts of copper sulphate have been observed only in the last 2 years. Several soil types are involved, namely peats, young coastal sands, very poor pipe clay gumland, sandy gumlands, and some hill soils derived from sandstone. Molybdenum deficiencies are found in many soils. The most spectacular pasture responses to this element have occurred on clay hills derived from sandstones in the Warkworth district, north of Auckland. Zinc, magnesium, and boron deficiencies so far seem to be of very minor and only local significance in pasture production. SOIL GROUPS Yellow-grey Earths Concurrent with overseas practice the names adopted for the main soil groups often describe the dominant colour of their profile. It is a nomenclature somewhat confusing but difficult to change. . The yellow-grey earths are associated with an annual average rainfall of about 20in. to 35in. They occur therefore only in the driest districts of the North Island, in central Hawke’s Bay (see map on page 43). Most soils from this group are formed from limestone, mudstone, and sandstone, but a small proportion of pumice may be present. The quite large areas of flat land in central Hawke’s Bay are mainly derived from old alluvium deposited by rivers from material carried down from the hills. The parent material of the old alluvia is therefore similar to that of the hills. The soils formed on the old alluvia, however, often differ quite markedly from hill soils. Being flat or nearly so, they are more receptive to rainfall;‘there is less run off, hence more leaching; and there is more moisture for chemical and biological activity, hence more advanced soil development. Often there is a well-developed clay pan in the subsoil which is practically absent in hill country. This clay pan formation is typical of yellow-grey earths in both Islands. It makes for pugging in winter and fairly quick drying in summer. Mole drains usually last well on these soils. Owing to the relatively low rainfall the yellow-grey earths are not strongly leached. The word leaching

describes the process by which minerals in the soil are carried down by percolating water as soluble salts from the top layers to deeper layers, often outside the reach of feeding roots. Naturally the higher the average rainfall is the more water tends to percolate through the soil and the more severe the leaching, or the removal of minerals from the topsoil, tends to be. Many of these minerals are essential to plant growth, and hence a strongly leached soil is usually a soil with low natural fertility. However, though high and well-distributed rainfall in time tends to produce poor soils, it also is essential to high pasture production. For this reason many of New Zealand’s naturally poor soils have a very high potential productivity, provided the right plant nutrients are added, and the better soils of the drier climates, which were the ones to be farmed first, do not always offer the same scope for improvement. The yellow-grey earths of central Hawke’s Bay are a relatively fertile group of soils; they seem to contain very few areas of molybdenum or other trace element deficiencies and they need little or no lime to grow good pastures. Pasture Responses Generally pasture responses in these soils to lime, fertilisers, and trace elements can be summarised as follows: — Responses to lime are very slight to slight. Responses to superphosphate and serpentine superphosphate are good. Lime reverted superphosphate seems less efficient. Ground Nauru rock and North African rock phosphates have given poor responses* in the very few trials in which they were included. , . Slight responses to potash are not uncommon in pasture trials. . Molybdenum has not been tried very thoroughly in central Hawke’s Bay; a good response has occurred on one soil type only, Waipukurau sandy loam. .

Cobalt deficiencies in stock are not known to occur. As the effect of lime dressings on t?” first call is for superphosphate. The use of potashi is not ad^sede^| pt such b as hay field? deficient areas Rate of Application ot Superphosphate In central Hawke’s Bay the rate , of application of phosphates is closely linked to the potential productivity of the pastures and the intensity with which a farmer wishes to utilise his property. For instance, the soils which hold white clover-ryegrass pastures well;, through - the frequent dry summers may well . receive annual dressings of wt. of .superphosphate per acre. The lighter, shallow soils of the hills and many of the stony fiats which revert \ to subterranean clover pastures • can do with lighter annual dressings, IJcwt. to lcwt. per acre - ■ In central Hawke’s Bay topdressing widens the gap between pasture production in winter and spring and production in summer. Winter and spring production is stimulated, but summer production, particularly in a drought year, may remain low. Regular topdressing, therefore, tends to force farmers to meet the widening gap in seasonal food supplies by changing from * breeding sheep to fattening

sheep, or by growing more lucerne, making hay or silage, and providing more supplementary crops for —■ ' Yellow-grey Earths Transitional to Yellow-brown Earths The transitional yellow-grey earths occupy « large-area in the Manawatu district, occurring in one block from Wanganui to the Manawatu Gorge and continuing south in a narrow strip along the Tararua Range from the Manawatu Gorge to Shannon (see map on page 43). Towns such as Marton, Halcombe, Bulls, Sanson, Feilding, and part of Palmerston North lie on these soils. Marton loam is a typical soil type of this group. Smaller areas of the transitional yellow-grey earths occur in the Wairarapa and in Hawke’s Bay. ■ transitional vellow-erev parths are assoc i a t e d with a higher rainfall (30in tQ 40in year) f han are the proper yellow-grey earths, and for - this reason they are slightly more leached. Leaching, however, has been offset to some extent 'by the heavy native bush which grew on some of these soils. This statement needs to be explained. All plants absorb nutri- ■ ents from the soil, carry them to the leaves and stems, and finally return them to the soil surface, for instance, by way of the fallen leaves. Whether the soil beneath a plant remains fertile

depends largely on the rate at which the plant absorbs nutrients and returns them to the surface. Plants with a *° r p ! ant c nutn sucn as calcium, S se whe detrimental effects ol leaching quite considerably. Other plants with a low rate of growth and j 0„ plant nutrient demands do little to dimmish the severity of leaching and leave an infertile soil. a hard clay pan 18in. to 24in. below the surface is commonly found in this soil group and is particularly evident a t the beginning of a downward slope, The occurrence of heavy, brown iron concretions in the clay pan has caused many to call them “ironstone” soils, a name which should be reserved for the volcanic “ironstone” soils found north of Auckland, mainly in Bay of Islands County. The Department of Agriculture and Massey Agricultural College have carried out numerous experiments on the transitional yellow-grey earths and their requirements for vigorous pasture growth are therefore well known, Future Responses / Phls knowledge of pasture responses to lime, fertilisers, and trace elements can be summarised as follows: Lime gives good responses up to pH 6.0 to 6.2 but seems of no benefit above pH 6.0 to 6.2. Many unlimed

soils have a soil reaction of pH 5.4 to 5.7; they respond quite well to small dressings of lime, say 3cwt. to scwt. per acre, but an initial dressing of 1 ton per acre is far more effective; maintenance dressings of lOcwt. per acre every 3 years are advocated.

Of the phosphatic fertilisers, superphosphate, serpentine superphosphate, basic slag, double superphosphate, and the fusion products of rock phosphate with magnesium silicate rock are all equally good if applied at equivalent rates of phosphorus. North African phosphate has proved good on unlimed ground.

The rate at which these phosphates have to be used to maintain vigorous pastures under good management is believed to be equivalent to that of 2cwt. to 3cwt. of superphosphate per acre each year.

Superphosphate applied at the low rate of lcwt. per acre each year led to pasture deterioration at Massey Agricultural College under heavy stocking and rotational grazing. At the Marton Experimental Area, on the other hand, on a related soil type, 2cwt. per acre applied 16 times over a period of 9 years has resulted in a considerable build-up of residual available phosphate which could maintain pasture production for another 4 years without further topdressing.

Pasture responses to potash are usually slight, but are sometimes good, particularly on hay paddocks. The quick test for potash on the yellow-grey earths may at times indicate a smaller amount of available potash than is really present. Molybdenum has been tried in a large number of trials. Results from these so far have not established a need for using this element. Though several

distinct responses have been observed, they were fleeting. For this reason liming to pH 6.5 and the use of phosphate are still the standard recommendation for pastures, with potash to be used only after a trial strip has proved its value. Yellow-brown Earths The yellow-brown earths occur in districts receiving an average annual rainfall of over 40in. The parent material on which they have developed is similar to that on which the yellow-grey earths were formed, namely sedimentary marine deposits of sandstones, siltstones, and mudstones raised by successive earth movements above sea level and shaped by them and subsequent erosion into hills an mountains. The higher rainthe most striking effects of more intensive weathering is the darker colour of subsoils, a result of the more complete oxidation of iron-containing minerals,

The rate of weathering usually increases with higher average temperatures, so that the yellow-brown earths north of a line roughly coinciding with the historic distribution of the kauri are mainly clays and clay loams, and south of this line this group of soils contains progressively less clay (2) and consists of silt loams and sandy l° ams - The leaching effect of rainfall on the yellow-brown earths cannot be described simply. The rate off leaching is affected by the type of vegetation, by the amount of rainfall, and by the rate of surface erosion. For instance, where vigorous broadleaf forest was sustained, the loss of plant nutrient from the topsoil may be small , but w here kauri (as in the north) or other podocarp species was dominant vegetation the soil ; is quickly depleted of its fertility and its soil structure severely damaged, particularly as the acid litter of decaying leaves typical of many podo-

carp species assists the leaching effect of rain-water and hence accelerates soil deterioration. Slope, however, is another factor which has strongly influenced the development of the yellow-brown earths. On the sloping hill faces, even on slopes of only moderate steepness, much of the rain, instead of penetrating into and percolating through the soil, runs off the surface, removing small quantities of topsoil. This gradual erosion, combined with reduced percolation, keeps hill soils relatively young and more fertile than related soils of the plains or of slight slopes. This influence of slope on soil development is particularly evident north of Auckland.

With progressive leaching yellowbrown earths in time become podzols. Podzol is a Russian word meaning similar to ash and refers to the light ash-grey or bleached appearance of this type of soil. True podzol profiles can be seen in Northland on the socalled pipe clay gumlands, where the continuous action of rain-water moving through the acid litter* of the kauri forests has reduced plant nutrients to a very low level indeed in the topsoil and subsoil. In the podzols some minerals such as iron and aluminium salts may become concentrated in the subsoil with fine clay and some humus and form a slow-draining, hard pan. This is seen on the sandy gumlands north of Auckland. The range of yellow-brown earths from young and shallow soils to podzols is grouped as follows for the purpose of this article: — 1. Skeletal soils with shallow topsoils occurring on steep slopes. 2. Moderately weathered soils, including soils of many stages of leaching. 3. Strongly weathered soils, also including soils of many stages of leaching. 4. Mature podzols. 1. The Skeletal Soils The skeletal yellow-brown earths with few exceptions represent, the millions of acres of steep hill country soils of the North Island and the Marlborough Sounds which are not derived from overlying volcanic ash or from other related volcanic material. The map on page 41 shows that they are most extensive in the Wellington and Hawke’s Bay Land Districts and south of Auckland. North of Auckland and on the Coromandel Peninsula much of the hill country is not derived from sedimentary rocks but from volcanic andesites and rhyolites. Until a few years ago the outlook for the steep New Zealand hill country was not bright. Deterioration was apparent everywhere, production had declined to a level where upkeep of fences was not economic, and wool prices had not kept up with rising costs. Many hill farms were not

economic units even where they ineluded a fair proportion of ploughable land. In the last few years, however, this has changed somewhat. Good wool prices and the advent of new techniques of topdressing and track making have already done much for ■ hill country improvement. Increased use of superphosphate, combined with clover oversowing is probably, responsible for most of this improvement. Without the introduction of clover white clover, subterranean clover, and perhaps Lotus ulicjiuosus (major) (with or instead of the clovers)little response to topdressing can be expected. Without topdressing oversown clovers seldom establish satisfactorily. Lotus uliginosus (maior} in the wetter districts mav be (major) in the wetter districts may be an exception. Clover seed inoculation may be an important factor in the establishment of white clover, subterranean clover, and red rlnvor nn nnnn+ntr nrkinb w aid red clovei on country which is devoid of these clovers. Clover seed inoculation is already widely practised in Australia and will no doubt become more popular here.

Pasture Responses In dressing, hill country farmers want to know what kind of phosphatic fertiliser they should apply whether liming is absolutely necessary to get pasture responses, and whether molybdenum should be used Molybdenum is deficient in many soils derived from sands tone . How 7 “S, f these sandstones such as g reyW acke, are not easily recognise s d such ’ by farmers or th reason the local instructor should be consulted. The importance of soil type in connection with topdressing has never before been as evident as with molybdenum and it is therefore very necessary that an expert opinion be sought before large quantities of molybdenum superphosphate are applied Fop instance; on one sandy soil in the Wairarapa> probably Ngaumu fine sandy loam, sodium molybdate at 2 Joz. per acre has clearly depressed Pasture growth. In greywacke hills ln One OT tWO CaSCS in the SOUth CHI Manawatu the addition of small quantities of lime to moy bdenum and phosphate plots has improved growth, in the Wellington district, however, on a similar soil, Makara silt loam,

lime has contributed nothing to the effectiveness of molybdenum. North of Napier a thin coat of pumice ash often overlies the sedimentary rock. This pumice is easily mistaken for sandstone. Pastures on these soils are- not known to respond to molybdenum; on the contrary the molybdenum level of the herbage may be already very high and the addition of even small amounts of molybdenum may make the pasture dangerous to st ° ck , . JiiXtremely molybdenum deficient soils have the following features in common. Very slight or disappointing respond? responses to very heavy ap ° f lime ’ good res onses to , If soils are known to respond well to superphosphate or serpentine superphosphate without lime, or with small dressings of lime, only a moderate degree of molybdenum deficiency is UKCiy. The merit of various types of phosPhatic fertilisers can be summed up as follows: Basic slag and molybdenum superphosphate: Basic slag has been rightly

popular on most soils derived from greywacke between Wellington and Palmerston North and in the Wairarapa along the Tararua Range. Basic slag, apart from its quite considerable effect in reducing soil acidity if used over a number of years, contains small amounts of molybdenum and possibly other trace elements such as vanadium which may be of value on a limited number of soils. As it is difficult to , apply from the air, a few trials comparing basic slag with superphosphate . plus light rates of lime and molybdenum superphosphate have been laid down on hill and undulating soils, on which basic slag has the reputation of being a better fertiliser than superphosphate. In these few trials superphosphate combined with molybdenum and sometimes with very light rates of lime promises to be as effective or more effective than basic slag. Molybdenum superphosphate (and sometimes 2cwt. to 3cwt. of lime per acre) is now recommended on soils on which basic slag has been best but where it cannot be applied conveniently. Apart from the districts mentioned . above, molybdenum superphosphate is already being used extensively on large areas of steep hill country in Raglan and Rodney Coun-

ties and in other districts north and south of Auckland where skeletal soils derived from greywacke and certain sandstones occur. Superphosphate and serpentine superphosphate: Weight for weight comparisons of these two fertilisers on steep hill country, if anything, have favoured superphosphate, probably because it has a higher phosphorus content. For ease of storage and general handling, however, serpentine superphosphate is often preferred to straight superphosphate. Double superphosphate: Double superphosphate has been tried in the steep hill country east of Taranaki, where it has been as good as superphosphate. It has not been tested critically in those areas such as the east coast of the Wairarapa where high freight costs favour its use compared with ordinary superphosphate. Its regular use cannot yet be recommended on steep, dry hill country until the sulphur requirements of such country are known. Lime: Steep hills, particularly in the southern half of the North Island, are usually not very acid in soil reaction; pH values of 5.4 to 6.0 are common. The calcium status is not particularly

low except on some very poor sandy soils. Heavy applications of lime should therefore not be necessary to get good results from phosphate or phosphate and molybdenum. Trials with lime at rates from 2cwt. to 6cwt. per acre have been carried out on several hill soils, for instance, on Makara silt loam. Generally these light rates have given pasture responses, though sometimes they seem to depress growth slightly if the lime was applied with 2soz. of sodium molybdate per acre. Only trials can tell when it is advisable to use light dressings of lime, when it is sufficient to use just phosphates, when to use phosphates and molybdenum, and when to use all three. Rate of Application of Phosphate One single aerial topdressing with superphosphate or molybdenum superphosphate often causes a visible improvement in pasture. . Everything looks greener from afar and close inspection may reveal that the annual clovers have been stimulated and more white clover than, before is present. Nevertheless, the effect on carrying capacity from one dressing is usually small. For appreciable increases in production clovers need to be fairly vigorous for more than 1

year. Perhaps they must produce surplus nitrogen in a quantity which will allow the , associated grasses to make use of the applied phosphate. That this is so has been proved in subterranean clover pastures in Australia. Usually, annual topdressings for several years are needed for this. With more vigorous, dense pastures the . danger of weed invasion also recedes, provided pasture improvement is accompanied by good pasture management. Pastures on soils receiving a high average annual rainfall, such as in the back country of Taranaki, have been shown to respond particularly well to heavy dressings of phosphate. They respond better to heavier rates than do drier soils, and it is thought that they need heavier and more regular applications to reduce the threat of reversion and weed invasion. If a single topdressing, repeated perhaps only every few years, does little to increase carrying capacity and if several consecutive dressings are needed to give worthwhile improvement in this respect, it is obvious that initial topdressing should be concentrated on one section of the farm rather than be spread thinly over the whole farm. When topdressing has proved that one section can carry much ' more stock than before, it is time to begin on another block and reduce topdressing on the first block to maintenance. Maintenance probably would be seldom more than 2cwt. of superphosphate per acre every second year except perhaps in the high-rainfall areas receiving 60in. and over of rain a year. 2. Moderately Weathered Yellowbrown Earths The map on page 41 shows the distribution of the moderately weathered yellow-brown earths. They are nearly all hilly and undulating soils which can be cultivated by giant disc or plough. They differ from the steep skeletal soils not because of their parent material but because of their easier slope, deeper profile, better water-holding capacity, and thus their higher production potential; - Only a few of these soils have drainage problems. Their fertility depends mainly on parent material. Those derived from poor parent material such as sandstone or argillite and the more infertile type of shale and mudstone could in the virgin state only grow a low - fertility - demanding vegetation which in turn returned little to the soil, thereby doing little to counteract leaching. The naturally fertile soils on which pastures have least deteriorated are mainly derived from limestone, limerich sandstones, and lime-rich mudstones. The good mudstone soils are usually subject to much slipping, but slips heal readily.

Pasture Responses Lime: Liming is usually desirable on silt loams and sandy loams with pH 5.7 and under, and on the heavier soils with pH 5.4 and under. The only safe guide to liming, however, is given by trial and experience. The rate of liming which can be carried out economically, is often dictated by slope and accessibility. Experiments with light rates of lime have not been put down on these hill soils except in the Wellington and Palmerston North districts, where 3cwt. of lime per acre applied with superphosphate has resulted in marked improvement of pastures compared with results from treatment with superphosphate alone. All the soils on which light rates of lime have given good responses are thought to be slightly : molybdenum deficient. Molybdenum: In southern Hawke’s Bay and the Wairarapa many new trials with molybdenum have been put down very recently and results are not yet known. . In the Taihape, Hunterville, Taumarunui, and Wanganui districts molybdenum-responsive soils derived from sedimentary rock, if they occur at all, will be small in extent. None has been found so far. Molybdenum-responsive soils in this group are mainly confined to the Wellington, Wairarapa, and Manawatu districts. Molybdenum superphosphate or serpentine superphosphate seems the most convenient form in which to apply molybdenum. As in the current commercial product 1 ton of fertiliser contains the equivalent of lib. of sodium molybdate, it is estimated that 3cwt. of molybdenum superphosphate per acre supplies enough molybdenum for at least 3 to 4 years on most soil types. Very likely the effect of one such application of molybdenum will last much longer than 3 years on many soil types in this group. Rate of Application of Phosphate When deteriorated pastures on poor hill soils are being converted into better pastures by cultivation or simply by oversowing of clovers and topdressing experience seems to in- . dicate that for the first 3 years regular topdressing with superphosphate at 3cwt. per acre is necessary. The maintenance dressing on most soils is frequently 3cwt. of superphosphate every second year. Several successive topdressings and clover oversowings can change brown-top-danthonia pastures carrying f sheep per acre to white cloversubterranean clover-browntop-dogstail-ryegrass pastures carrying 2 to 3 ewes per acre. 3. Strongly Weathered Yellow-brown Earths (4) The warmer and more humid the climate is the more intense is the chemical weathering. Partly for this reason greywacke north of Auckland has given rise to a different soil from that formed on greywacke on the

Marlborough Sounds area. This also applies to soils formed on other parent materials which: occur both . north of Auckland and south of the Waikato. The north of Auckland soils of this group contain more clay and less sand. They are therefore much heavier soils, more difficult to cultivate, stickier when wet, and much , harder and prone to crack when dry. Most of the strongly weathered yellow-brown earths of the north are on undulating to hilly country, popularly known as clay hills. Pasture Responses Fertiliser requirements of pastures on these soils can be discussed only if this group is split up . further into steep hill soils, moderately hilly soils, and nearly flat and undulating soils. In general the easier the topography is . the more rain is absorbed and. the less erosion takes place. On the steeper soils much of the rain runs off and takes some of the topsoil with it. The result is that the steeper soils are younger soils, less leached by percolating rain-water, and less strongly weathered than the less steep soils. For this reason the steep hill soils are often quite fertile and have persisted in permanent pasture for many years without. topdressing. The Auckland climate, however, favours the ingress of secondary growth. Pastures on the less steep hills and the lightly undulating clay soils have often been replaced by manuka and other weeds. As it was usual to burn the manuka scrub periodically, the organic matter in the topsoil has been largely destroyed, leaving a soil very hard to cultivate and very poor in plant nutrients. Molybdenum promises to be of much more importance on the strongly weathered clay soils of Auckland than on the moderately weathered silt loams farther south. In the south pasture responses to molybdenum have been slight , and have been confined mainly to the greywacke hills of Wellington and the Tararua foothills. In the north excellent responses are obtained on large areas, for instance, on soils derived from fertile sandstone formations, typified by the picturesque coastal hills of Warkworth (Puhoi clay loams and Whangaripo clay loam) . Good responses are also obtained on the far less fertile soils derived from greywacke, forming nearly all of the coastal hills between Whangarei and the Bay of Islands (Marua clay loam and Rangiora clay). Other molyb-denum-responsive soils derived from sedimentary rock are found scattered right through the North Auckland Peninsula. In fact, there are not many clay hill and undulating soils between Auckland and Wellsford on which pastures do not respond to molybdenum unless they have been heavily limed in the past or already topdressed with molybdenum or repeated applications of basic slag. The use of molybdenum should save lime in the northern half of the North

Island. Limited evidence from topdressing trials indicates that in the presence of molybdenum the liming of clay soils to only pH 5.6 to 5.8 is sufficient for maximum production. In the absence of molybdenum a soil reaction of pH 6.2 to 6.5 seems desirable. As li to 2 tons of lime may be needed to change the soil reaction from the pH level required in the presence of a few ounces of applied molybdenum to that required in the absence of molybdenum, the saving to the farmer is considerable. If soils have already been limed to pH 6.2 to 6.5, topdressing with molybdenum is not expected to affect pasture growth. Pasture responses to molybdenum, however, have occasionally been observed at pH levels <5.9 to 6.2) slightly below ' On the steep hills to which heavy dressings of lime cannot applied molybdenum superphosphate or molybdenum serpentine superphosphate applied every 3 to 4 years may at least partially replace the hitherto popular basic slag.

Potash deficiencies are unfortunately becoming fairly common on the more leached clay soils of easier contour, particularly on soils derived from some of the sandstone formations, for instance Warkworth clay. These are the same soils on which pastures respond so excellently to molybdenum, Though farmers therefore may hope that they will save a little money on lime, they will perhaps have to spend a good deal more on potassic fertilisers in the future. How much potash is required on different soil types to maintain good pastures is a question which is now being studied by cooperative trials. q f th n t nn which po °f h X become FpXblem is Se Waik clay the d j ant u t on the so-called gumlands just north of Auckland. It is a soil which could very ™“ ght d?e°stajs d ot P SmT e <un to 4 tons per acre in the initial stage of development) and phosphate. Today ft i s known that with the use of molybdenum the initial dressings of lime can be reduced to about 2 tons

per acre. Potash deficiency, however, is becoming more common, particularly on fields frequently cut for hay, and there is some evidence that once the potash ■ reserves of this soil have been exhausted rather large quantities of potash may be needed , to restore them. 4. Mature Podzols Mature podzol soils are popularly known as the pipe clay gumlands and P J P e clay gumland flats. A good example is the Wharekohe silt loam, “-S already indicated water passing through the acid litter shed by the . aurl tree , has great powers of speed”gtLP S'dS Auckland “e m^str£s ceeds 50in The north of Auckland po d zo i s are unique in that they may have up to several tcct ol almost pure s “ lC a silt and sand containing most plant nutrients in only very small amounts (5). However, the depth of this impoverished and very acid layer of silica varies considerably from place

to place, according to slope and the trees which have formerly grown there. The topsoil of these podzols is pale grey to white and the vegetation consists mostly of stunted manuka. Drainage is often poor. In spite of the unattractive appearance and original poverty of these soils, they can be made to support quite good dairy pasture. Perhaps as knowledge of their trace element requirements increases some of the better-drained soils may be induced to grow excellent dairy pasture. The great advantage of pipe clay gumlands is that their pastures stand up better to dry weather than do those on the more fertile volcanic soils found in the same localities. A disadvantage of these podzols is poor water supply for stock and excessive pugging in winter. Farms containing both pipe clay gumlands and volcanic soils are ideal for these reasons. The deeply leached gumlands somewhat resemble a sand culture to which everything must be added or may have to be added in the near future to obtain optimum growth. Lime, phosphate, potash, molybdenum, copper, manganese, and boron may all need to be added in future to obtain firstclass pasture. Lime requirements are not high when the extreme acidity of the virgin soils (pH 4.1 to 4.8) is considered. It is necessary to raise the pH values by about one unit or a little less. This is done by the ploughing in of lj to 2 tons of lime per acre in the gumland pipe clays and probably with a little less on the sandy gumlands (Wharekohe sandy loam). Maintenance dressings are estimated to be 1 ton per acre every 4 years. Superphosphate or serpentine superphosphate is commonly applied at 3cwt. per acre three times in the first 12 to 14 months after virgin pipe clay gumlands have been converted into pasture. The phosphate maintenance requirements of pastures on these soils have not been studied sufficiently in critical trials. Very likely they are not large, say, 2cwt. to 3cwt. of superphosphate per acre, and diminish as the residual phosphate level is built up by years of regular topdressing. Provided the recommended quantities of lime are applied, basic slag and North African phosphate are not superior to superphosphate; in fact they may be slightly inferior. Potash deficiency is general on the deeply podzolised pipe clay gumlands. Good pastures cannot be maintained for long without potash. The recommended rate of application is about lcwt. of muriate of potash per acre each year. Trials with molybdenum on pastures on Wharekohe silt loam illustrate the variability of the pipe clay gumlands. With a similar soil reaction a molybdenum response has been obtained near Kaikohe but not near Whangarei.

It is now being discovered that copper may be essential for vigorous pasture growth on some types of gumland, particularly where past lime has reduced soil acidity to a moderate level—about pH 6.0 and over. Boron and manganese may also become short on very heavily limed pastures and perhaps deficiencies of other trace elements may be brought to light in the next few years. Soils Derived Mainly from Windblown Sands * Extensive areas of soils derived from wind-blown sand occur mainly along the west coast of the North Island. The composition of the wind-blown sand is by no means uniform. Along the Manawatu coast it has only a little pumice ash mixed , in, and in places is quite high in shell lime. Where the water-table is near the surface good pasture can be grown in summer with superphosphate; potash often gives further marked improvement, and lime has also been shown to be of benefit occasionally in spite of quite high original soil pH values (6.5 to 7.0). On the higher and drier parts of these sandy soils very light dressings. of superphosphate may sometimes be payable to encourage subterranean clover. Low copper herbage levels have been found in some places and copper deficiency in cattle is suspected in certain areas. Pastures on some of the damp coastal sand fiats of the Manawatu (Pukepuke black sand) may respond to applications of copper. In Raglan County, west of the Waikato, and northward along the Auckland and Northland coastlines the wind-blown sands often contain a high but variable proportion of pumice and other volcanic' ash. The presence of this ash and the warmer temperatures and higher rainfall . have led to more rapid weathering of the sand or rather of the volcanic ash-sand mixture. Deep sandy loams and even sticky sandy clays occur. The youngest sands around the coast are still little weathered, little consolidated, and droughty, except,where the water-table is high. One trial on such a soil, Pinaki sand, is showing pasture responses to copper, magnesium, and possibly zinc. The older soils farther inland form sandy loams and clays, well drained, not particularly droughty, and capable of carrying good white clover-ryegrass-paspalum pasture. Typical of this group are the Red Hill sandy loams and clay loams. Pastures on the Red Hill sand often respond to applications of lime in spite of apparently satisfactory soil reaction (pH 6.0). This is now thought to be due at least partly to a slight molybdenum deficiency. The parent material of the Red Hill soils, however, is too variable to postulate that this molybdenum deficiency is at all general.

The only, other pasture response to molybdenum on coastal sand soil has been obtained near Wellington. Superphosphate or serpentine superphosphate seems the best phosphatic fertiliser to use on Red Hill soils. Potash deficiencies are uncommon, but are quite likely to develop on fields regularly used for hay and silage crops. Finally there are large areas (about 160,000 acres) of sandy gumlands (6) north of Auckland—between Muriwai and Hokianga and north of Mangonui and Kaitaia. Te Kopuru sand is the main soil type in this group. Kauri forests have destroyed their structure and depleted their plant nutrient reserves. The sandy gumlands soils are true podzols; they are as poor in plant nutrients as the pipe clay gumlands. This in itself would not hamper their development. Unfortunately, however, Te Kopuru sand has often an impermeable, hard pan near the surface which makes the soil wet in winter and dry in summer. Where this hard pan is not strongly developed, however, quite good pastures suitable for fat lamb farming and even dairying can be maintained. As undeveloped Te Kopuru sand is very acid, lime requirements are usually about 1 to tons per acre initially. Of the major elements phosphorus as well as potash is needed to obtain reasonable pasture establishment. Pastures on Te Kopuru sand have responded. to applications of a few trace elements, particularly of copper sulphate at 51b. to 101 b. per acre. Molybdenum also has slightly increased pasture vigour and vanadium has been promising enough to merit further investigation. Copper sulphate should be applied regularly to Te Kopuru sand. Its use is not only desirable because of its beneficial effect on pasture growth, but above all because it will prevent the copperdeficiency symptoms in stock so commonly found on this soil type. For reasons of stock health molybdenum should never be used on pastures on Te Kopuru sand and other sandy gumlands unless copper is also applied (3). References 1. Soil Bureau, Department of Scientific and Industrial Research, “General Survey of the Soils of North Island, New Zealand", Bulletin No. 5 (new series), 1954. 2. N. H. Taylor, unpublished data, 1951. 3. I. J. Cunningham, “New Zealand Journal of Agriculture”, Vol. 90, No. 2, p. 196, 1955. 4. N. H. Taylor, "Pedology as an Aid in Animal Research”, “Australian Veterinary Journal", Vol. 28, No. 7, p. 183, July 1952. 5. N. H. Taylor, J. K. Dixon, and F. T. Seelye, “The Soils of North Auckland Peninsula, New Zealand”, Transactions of the International Congress of Soil Science, Vol; 4, p. 389, Amsterdam, 1950. 6. N. H. Taylor and C. F. Sutherland, “Soils of North Auckland”, Proceedings of the 15th Conference of the New Zealand Grassland Association, p. 25, November 1953.

NEEDS OF NORTH ISLAND SOILS