Rates for maintenance requirements depend on the original fertility of the soil and its ability to retain applied phosphate in a form which is not readily available to plants. The correct rates depend on the amount of growth of the pasture which, together with management factors and type of farming practised, determine the losses of phosphorus through transfer of fertility and through stock and stock produce sold off the farm. Very little experimental work has been done on maintenance requirements, but it appears that these may vary from 1 cwt superphosphate per acre every few years on the more fertile soils of the South Island to 3–4 cwt per acre each year on some of the “high phosphate fixing” volcanic soils of the North Island.

Recommended rates of application of superphosphate needed to obtain vigorous initial growth of pasture sown on cultivated but previously unimproved land are approximately as follows:

1. Rainfall 40 in. – 200 in.

   1. poor initial phosphorus fertility, 6–9 cwt/acre.

   2. medium initial phosphorus fertility, 3–5 cwt/acre.

2. Rainfall 30 in. – 40 in.

   1. poor initial phosphorus fertility, 3–5 cwt/acre.

   2. medium initial phosphorus fertility, 2–3 cwt/acre.

3. Rainfall 15 in. – 30 in.

   1. poor initial phosphorus fertility, 3–5 cwt/acre.

   2. medium initial phosphorus fertility, 1–2 cwt/acre.

Where unimproved phosphate-deficient pasture containing little clover is oversown with clover seeds, initial rates of application of phosphatic fertilisers seldom need to exceed 3–4 cwt/acre because heavier rates cannot be utilised fully straight away. It is usually important, however, to consolidate pasture improvement by regular annual dressings for several years.

The fertilisers most commonly used to supply phosphorus are: (1) Superphosphate containing this element in a water soluble form, (2) “Aerial superphosphate” (90 parts of superphosphate reverted with 10 parts of ground serpentine rock) in which the phosphates are partly water soluble, and (3) Serpentine superphosphate (75 per cent parts of superphosphate reverted with 25 parts of ground serpentine rock) which contains phosphorus mainly in a water insoluble but yet readily available form.

Some lime-reverted superphosphate is also used, particularly in the South Island, where it is desirable to drill in small crop seeds with a phosphatic fertiliser. Superphosphate in contact with turnip, swede, chou moellier, rape, clover, and other small seeds may cause serious loss of germination. Fully reverted and therefore water-insoluble forms do not cause germination injury.

The use of serpentine-reverted superphosphate is peculiar to New Zealand. Serpentine superphosphate has three advantages. It is superior in physical qualities to ordinary superphosphate in that it flows more freely, does not set hard on storage under damp conditions, and does not rot bags. It contains about 5 per cent of magnesium, a considerable proportion of which has been shown to be available to plants. In contrast to superphosphate it stores reasonably well when mixed with soluble potassic fertilisers. Its main disadvantage is a lower phosphorus and sulphur content per unit than that in superphosphate. Both fertilisers are the same price. Aerial superphosphate combines good physical qualities with a higher phosphorus and sulphur content than that in serpentine superphosphate, but it is not satisfactory when mixed with potassium chloride, and it is expected to cause germination damage if sown in contact with small seeds.

The greater part of unimproved land needs phosphatic fertilisers. Exceptions are some of the fertile river flats of both Islands, and some of the soils in the dry parts of Central Otago, and of inland South Canterbury and, possibly, of Marlborough. Therefore it is seldom a question of whether to use or not to use phosphatic fertilisers. The question is rather how much to use initially during the period of pasture improvement, and how much to use to maintain pasture production at a desirable level.

Pastures take up very large amounts of plant nutrients from the soil. The herbage is then consumed by stock and the nutrients contained are in great part returned to the soil in the form of dung and urine. There is in this way a cycle of fertility from soil to pasture herbage to livestock – to urine and dung – and back again to the soil and a return to herbage. This cycle is not a perfect one. The nutrients are continually being depleted in various ways. A proportion of them is retained in animal products, such as milk. P. D. Sears (J. Brit. Grassl. Soc., Vol. 5, 1950, pp. 267–280) estimates that 600 lb gallons of milk contain the equivalents of the following fertilisers:

• 160 lb sulphate of ammonia (nitrogen).

• 60 lb of superphosphate (phosphorus).

• 15 lb of potassium chloride (potassium).

• 25 lb of agricultural limestone (calcium).

These nutrients are also taken up into the flesh and bone of the grazing animals, and this means that their sale causes further depletion. The largest losses, however, of precious minerals may occur within the farm. Transfer in dung and urine from grazed areas to sheds, races, stock camps, gateways, hedges, and trees, leaching generally and especially under urine spots and fixation by the soil, all remove from circulation a serious proportion of the plant nutrients.

Expressed as equivalents of well-known fertilisers, limestone, and trace elements, the annual turnover of nutrients of first-class pasture is approximately as follows:

Nitrogen may suffer the largest losses, followed by calcium, potassium, sulphur, phosphorus, and magnesium.

Under New Zealand conditions adequate amounts of nitrogen are supplied to pastures by clovers, particularly white clovers. The root nodule bacteria of these legumes have the ability to convert atmospheric nitrogen into organic forms which become available to the associated grasses. For this reason, the main purpose of applying fertilisers, lime, and trace elements to the pastures is to stimulate clover growth so that, in turn, grasses may benefit from the nitrogen supplied by these species. Good clover growth means good grasses will grow well.

Clovers, particularly white clovers, need a continuous good supply of phosphorus, potassium, sulphur, magnesium, and several trace elements. In addition, soils must not be too acid. Where soils cannot release these needed elements right through the year at an adequate rate to maintain vigorous clover growth, or where soils are too acid, the supply of nitrogen to grasses will diminish, pasture production will fall, and low-fertility demanding species of grasses will replace high-fertility demanding grasses. This would be the situation on almost all soils in New Zealand if no fertilisers or lime were used. Fertiliser, lime, and trace elements, therefore, are needed to supplement the natural supply of these nutrients from the soil. They are also used to make good any losses which occur under pasture farming as already discussed.

The supplying power of soils for individual nutrients varies considerably. That for phosphorus is inadequate in nearly all soils of New Zealand, that for sulphur and molybdenum is inadequate in a large proportion of soils. The supplying power of potassium depends not only on soil type but to a great degree on the amount of potassium lost on individual farms and paddocks in past years. It also depends on the level of pasture production. Thus paddocks frequently hayed or cropped in the past are usually more potassium-deficient than others. On farms where pasture production is high, there is a need for a rapid release of potassium from the soil and so potassium deficiency is more likely to occur there than on farms with low-quality pastures. Moreover, losses of potassium by transfer and under urine spots are thought to be higher on highly productive farms than on low-producing farms, and higher on dairy than on sheep farms.

The main products of New Zealand agriculture are milk, meat, and wool. These are obtained from cattle and sheep which derive their feed almost entirely from pasture, that is, from grasses and clovers. Nevertheless, the largest acreage of crops is grown for supplementary livestock fodder and a much smaller acreage for human consumption. Since most of the fertilisers used in New Zealand are applied to pastures, it is this practice that is mainly discussed.

(Dicksonia spp., Cyathea spp.).

The profusion of tree ferns could rightly be said to be the most distinctive feature of New Zealand forest. They occur in all forests and are even more plentiful in cut-over and degraded forests where they obtain more light to regenerate and develop. They also appear in plantations of exotic trees as these grow older and open up.

Some six species go to make up what are commonly known as tree ferns. They are all usually single-stemmed and crowned by a huge rosette of leaves which gradually die from the base of the rosette, leaving the stem scarred and naked. These trunks thicken largely by the growth of a thick mat of aerial roots. The most majestic species is the mamaku, Cyathea medullaris, which grows over 40 ft tall and a foot in diameter. Individual fronds grow up to 15 ft long and 6 ft wide. The main stems of the fronds are stout and black. The species grows in lowland forests throughout New Zealand and in the Chatham and Three Kings Islands, in some Pacific Islands, and in Australia.

C. dealbata or ponga has distinctive whitish under surfaces to the leaves. It grows to 30 ft tall and the fronds to 10 ft long. Distribution is in lowland and montane forests throughout the North and South Islands and the Chatham and Lord Howe Islands. A very beautiful species with pale, brownish-green fronds, and as widely spread as the above two, is C. smithii.

Wheki or Dicksonia squarrosa is probably the commonest tree fern and the most persistent after the removal of forest. It often forms groves by means of spreading underground rhizomes which give rise to several stems. D. fibrosa, kuripaka, is one of the smaller-growing tree ferns and reaches a height of about 15 ft. The stem is very densely covered with a mat of rootlets.

by Alec Lindsay Poole, M.SC., B.FOR.SC., F.R.S.N.Z., Director-General of Forests, Wellington.

Climbing ferns are a feature of our forest, and there are also many perching ferns. Some of these have been mentioned already as mange mange, Lygodium articulatum, which climbs by its midribs, the perching Asplenium flaccidum, and others. The Polypodiaceae is a large family of ferns, mainly of climbing or creeping habit. The fronds are usually simple, firm or leathery in texture, with prominent sori and covered on the under surface by light-coloured hairs. Five genera are represented in New Zealand, the names of which have undergone various changes, as shown in brackets. The genus Pyrossia is represented by P. serpens (Cyclophorus serpens), with a large rhizome thickly covered with brown scales it climbs up trunks of trees or over rocks. This small fern is found everywhere, the very thick leathery entire leaves vary in shape, and have a thick felting of star-shaped hairs. There are three species of the genus Microsorum (Phymatodes or Polypodium), M. scandens, with long, much branched rhizomes, covered with dark-brown scales, and M. diversifolia, with irregularly lobed, bright-green fronds. Both are very abundant on trees and rocks. M. novae zealandiae is a larger fern with stout rhizomes and large leaves, deeply cut; it is confined to forests in the North Island. There are four species of the genus Grammatis (Polypodium) which are small perching ferns. Anarthropteris lanceolata (Polypodium) represents another genus; it has simple, bright green, rather fleshy leaves, and is common on tree trunks, especially in the north. Ctenopteris heterophylla (syn. Polypodium grammatidis and Grammatis heterophylla) is abundant throughout the country as an epiphyte.

Our ferns provide much of interest. A number hybridise vigorously; some have variant forms not fully understood, and probably with further research the number of our species will be increased. In the meantime many problems await the keen investigator. A rich field is open also to the horticulturist, since many of our species are easy to grow. From various points of view, then, New Zealand can count itself fortunate in its rich bounty of ferns.

Note: The names used in this article differ in some cases from those in Allan's Flora. As regards the Hymenophyllaceae, Mecodium, Sphaerocionium, Craspedophyllum, and Apteropteris are listed in Allan as subgenera of Hymenophyllum and Macroglena; and Selenodesmium and Cardiomanes as sub-genera of Trichomanes. Allan's names are listed in brackets in the following list of generic names: Leptopteris (Todea), Dicranopteris (Gleichenia), Cyclosorus (Thelypteris), Microsorium (Phymatodes), Lastreopsis hispida (Rumohra hispida).

by Marguerite Winifred Crookes, M.A., Botanist, Auckland.

• New Zealand Ferns, Crookes, M. W., and Dobbie, H. B. (1963)
• Flora of New Zealand, Vol. 1, Allan, H. H. (1961)
• The Vegetation of New Zealand, Cockayne, L. (1928)
• Manual of New Zealand Flora, Cheeseman, T. F. (1925).

There are but two species in New Zealand which grow only in water. One is the common Azolla, and the other the rarely found Pilularia. Neither of these is very fern-like. Azolla filiculoides, var. rubra, is found as a thick covering over large areas of ponds and slowly moving streams. Each plant is very small with overlapping leaves which enclose air and this enables the plant to keep above water. Pilularia novaezealandiae has tiny grass-like leaves; the spores are in small rounded structures resembling “pills”.

Two large genera worthy of note are Blechnum and Asplenium. There are about 15 species of the genus Blechnum in New Zealand, mostly ferns with simple leaflets (pinnae). The Cape Blechnum, B. capense, is a feature of the landscape almost everywhere, on roadside cuttings and banks of streams. The young fronds are of reddish colour, and mature fronds may grow to nearly 10 ft. B. discolor has stiff, green fronds, whitish below, and it spreads freely by stolons. The same habit of vegetative reproduction is seen in the “miniature tree fern”, B. fraseri, with a small crown of leaves several feet above the ground. B. filiforme has a juvenile form with small, rounded leaves, but the mature form is a climber with long, pointed, sterile fronds, up to 30 in. long, and very narrow fertile fronds. B. membranaceum, B. lanceolatum, and the large B. norfolkianum are closely related forms. Two seaside species, B. durum and B. banksii, are common, especially in the south. Throughout the genus the fertile fronds are very narrow, purely spore bearing, and differ greatly from the sterile fronds which provide the food for the plant.

Closely related to Blechnum is Doodia, two species of which are common. In the north D. media covers whole hillsides with its autumn coloured fronds. D. candata is smaller, not so common, and found only in the North Island.

There are about 15 species of spleenworts, genus Asplenium. Some of these have simple leaflets, as A. lucidum, the beautiful widespread shining spleenwort, and the shore spleenwort, A. obtusatum. Among species with more divided fronds is the hen and chickens, A. bulbiferum, which bears tiny young plants on the surface of the frond. The somewhat similar A. lamprophyllum contains oil of wintergreen. A. flaccidum is found in several forms; it may grow erect from the ground, but is best known as it hangs from the branches of trees with long, narrow, drooping fronds of a leathery texture.

There are in New Zealand five species of the shield fern, genus Polystichum, one of which has been reported only from Kapiti Island. The scaly shield fern, P. vestitum, forms a prominent feature of forest, especially in the south, where its dark-green leaves form a spreading crown up to 6 ft across. P. sylvaticum is smaller, while P. cystostegia, with rather pale-green fronds, is found in alpine regions. P. richardii is very dark green, harsh to the touch, and the large, rounded sori are covered by an indusium with a central black spot. This species is fairly common, and often found near the sea.

The genus Lastreopsis is represented by the widespread hairy fern of the forests and the velvet form, L. velutina, of dry places. L. glabella and L. microsona have similar finely cut fronds.

Six species of maidenhair ferns are found in New Zealand, the most common of which are Adiantum cunninghamii and the closely related A. fulvum. Growing in the sun is A. aethiopicum and A. hispidulum, with bristly hairs and autumn coloured young fronds. The large A. formosum is found in only a few places in the North Island, while A. diaphanum is a modest little form common in shady places.

In open country, by roadsides and streams, and covering hillsides, a great variety of ferns is found. The ubiquitous bracken, Pteridium esculentum, the farmer's misery, grows to 6 ft in height and spreads rapidly by means of rhizomes. These are starchy and were used by the Maoris both as food and as medicine. The lace fern, Paesia scaberula, is less troublesome but may over-run considerable areas; it is light green, sticky, with finely cut fronds. Histiopteris incisa is a large wayside fern. Particularly in the south it grows with the tall Hypolepsis tenuifolia and the smaller H. rugosula. On roadsides, as well as in forests, is found the large tufted Cyclosurus penniger. In swamps in the North Island are Thelypteris palustris and three species of Cyclosurus. C. gongylodes is common near thermal springs. These latter are commonly known as species of Dryopteris. Cystopteris is a genus of small ferns with pale membranous fronds found throughout the country in dry open places, in clefts of rock, and in mountain districts. Three species of Lindsaea of the family Pteridaceae are L. viridis, a beautiful little fern with narrow, pale green fronds, found on the banks of streams; more widespread, especially in the North Island, is L. trichomanoides, with golden brown stems, found in dry places; and L. linearis, with small, narrow fronds, found amongst the manuka and light scrub in many localities. There are two species of Pellaea, of which P. rotundifolia is usually regarded as a drought-resisting fern and is very common, but P. falcata, of similar dry habitats, is comparatively rare.