Boron

Boron deficiency is very widespread in New Zealand but affects mainly brassica root crops such as turnips and swedes. Amongst farm crops, lucerne is also sensitive to boron deficiency but apparently to a lesser degree than swedes and turnips. Pasture responses to boron applications are rare, and are probably confined to clovers. For established lucerne, boron is applied as fertiliser borate at a rate of 10–30 lb/acre mixed with phosphatic fertilisers. With swedes and turnips a similar rate of application of borate is needed for the control of “mottle heart” or “brown heart”, but great care must be taken not to apply borates in contact with seed. Control of the few rare cases of boron deficiency in pasture appears to be obtained by 5 lb of fertiliser borate per acre.

Copper

Copper deficiency in New Zealand is more evident in animals than in pasture or crops. In animals copper deficiency can be caused by an excessively high concentration of molybdenum in pastures with copper concentrations which are known to be adequate for stock health when molybdenum levels are lower. There is no evidence that very high, naturally occurring levels of available molybdenum can cause toxicity symptoms in pasture. The rather large amount of “copperised fertilisers” used by farmers are therefore mainly designed to improve stock health rather than pasture vigour. Nevertheless, there is evidence that on some soils of northern Hawke's Bay and north of Auckland, as well as on raw, acid peatland of the Waikato, copper deficiency of pastures may occur.

Other Trace Elements

The other trace elements known to be essential for plant growth are manganese, zinc, iron, chlorine, and cobalt for the proper functioning of clover nodules. Cobalt deficiency severe enough to limit the proper functioning of clover nodules, and therefore nitrogen fixation, would most likely be associated with marked cobalt deficiency of sheep and cattle. If it ever existed, it would by now have been corrected. Manganese deficiency in wheat occurs in Canterbury on a few otherwise quite fertile river flats. It occurs also in a few orchards.

Iron deficiency on the other hand is known to occur in young pastures on some of the acid raw peats of the Waikato, and it is suspected on some soils in northern Hawke's Bay. The most suitable materials for supplying iron to these pastures and their rate of application are not yet known.

Nitrogen

Nitrogen for Pasture: On all but the most fertile soils, the supply of nitrogen to pasture is regulated by the presence and thrift of the right type of clovers. But, in spite of vigorous clover growth, nitrogen deficiency may occur in young pastures and at certain times of the year. In young pastures sown on land of low nitrogen fertility, grasses commonly become nitrogen deficient in spite of vigorously growing clovers. Usually this type of nitrogen deficiency is only of one to a few years' duration. As the nitrogen fixed by the clovers is gradually passed on to the companion grasses, the deficiency corrects itself. In the meantime there is a period of clover dominance during which grasses may just survive. Nitrogenous fertilisers are seldom used to correct this temporary imbalance of clovers to grasses. In fact there is not enough experimental evidence to say whether nitrogenous fertilisers under these conditions are of benefit and, if they are, what would be the best technique of using them. Again, nearly all pastures suffer from seasonal deficiencies of nitrogen. The greatest shortage of this element occurs in late winter - early spring. At this time of the year nitrogenous fertilisers are used occasionally to stimulate out-of-season feed. Quick-acting mineral sources of nitrogen, such as sulphate of ammonia and lime-stabilised ammonium nitrate (both fertilisers contain about 20.5 per cent), are most popular, but ammonium sulphate-nitrate (26 per cent N.) is also being sold in small amounts.

On the whole, therefore, the use of nitrogenous fertilisers on grazed pastures is limited to the stimulation of extra growth from late autumn to early spring. Nitrogenous fertilisers are very effective, however, in raising the yield of paddocks shut up for grass seed.

Nitrogen for Crops: The occurrence of nitrogen deficiency in crops depends in some degree on farm management. Crops following medium to good pasture seldom respond to nitrogenous fertilisers. Crops grown following poor pasture sometimes respond to nitrogen, but surprisingly often they do not. Crops grown after a succession of other crops usually respond to the application of nitrogenous fertilisers, except on the most fertile soils. Within this general situation, there is evidence that nitrogen deficiency in crops is less common today than 20 or 30 years ago. Better quality pastures, leading to a greater supply of available soil nitrogen following cultivation, are thought to be the reason for this trend. Crops vary greatly in their demand for nitrogen. Maize appears most sensitive to low levels of available nitrogen, followed by potatoes. Greenfeed cereals are also rather sensitive but not as much as Italian ryegrass. Spring-sown chou moellier and other leafy fodder crops appear to be intermediate in their requirements. Wheat and barley demand moderate nitrogen fertility. At high levels of nitrogen supply, however, lodging and increased susceptibility to disease is common. Swedes and turnips sown in spring also demand only moderate nitrogen fertility, but turnips sown as a catch crop in autumn appear to need a high level of nitrogen fertility.

Crop rotations are usually designed to avoid the need for fertiliser nitrogen. Crops demanding a fairly high level of nitrogen are commonly grown following pasture, and crops demanding less nitrogen fertility are grown after other crops. Thus a typical rotation on Canterbury cropping land might be pasture, potatoes, wheat, barley, pasture. Although some nitrogen would be applied to potatoes, usually 1 cwt of sulphate of ammonia per acre, this is done not so much because a nitrogen response is probable but rather as an insurance appropriate for such a valuable crop.

Organic Fertilisers

Organic fertilisers are produced in large quantities as by-products of the meat export industry, slaughter houses, and soap manufacture. Typical products are bone meal or bone dust containing water-insoluble phosphorus and some nitrogen; dried blood, a good organic source of nitrogen; and tankage, a powder obtained from cooking, drying, and grinding animal refuse of heterogeneous origin. Tankage contains water-insoluble nitrogen and phosphorus. These organic fertilisers of animal origin are mainly used in commercial market gardens, orchards, and by private gardeners. They may be incorporated in proprietary mixtures, but commonly are applied as so called “Blood and Bone”, a mixture of bone dust and dried blood or tankage and dried blood. Blood and bone contains about 4–7 per cent nitrogen and 10–13 per cent phosphorus. Market gardeners commonly apply 1½-2 tons of blood and bone per acre to leafy vegetables. This heavy rate of application is commonly followed by side dressings of soluble inorganic nitrogenous fertilisers during the growing season. Tomatoes, pumpkins, and cucumber also receive large quantities of organic fertilisers.

Small amounts of organic fertilisers are incorporated into proprietary mixtures which are sold to farmers for the manuring of crops and, to a lesser extent, for topdressing of pastures. The use of these manures in farming is not recommended. A vigorous export trade with organic manures has developed in recent years.

Lime, Fertilisers, and Trace Elements

The fertiliser, trace elements, and lime needs of New Zealand soils can be summarised in a simplified form by dividing (most, but not all) soils into four classes. The two larger classes are derived from so-called sedimentary rocks – greywacke (cemented hard sandstones and mudstones), schist (typically found in Otago), and softer mudstones and sandstones. The latter form the basis of many hill-country soils of the North Island. The class of soils with higher mineral fertility occurs in the drier districts (12–25 in. mean annual rainfall). But it also includes the young soils of river flats and the best of the steep hill country in rainier districts. The class with lower mineral fertility occurs in the wetter districts. The other two classes of soils are derived from volcanic ash. They are confined to the North Island. One class is derived from rhyolitic (pumice) ash erupted during the last 2,000 years. Soils derived from these more recent pumice showers are rather low in available trace elements. The other class of soils is derived from older pumice showers and from andesitic ash. Its supply of trace elements generally appears adequate, but phosphorus fixation is high.

The fertiliser elements needed on these four classes of soils and the prevalence of these needs are indicated in the table below.

*Widespread or severe deficiency.

†Moderately widespread or widespread, but moderate deficiency.

‡Sporadic deficiency.

by Cornelius During, B.AGR.SC., formerly Farm Advisory Service, Department of Agriculture, Wellington.