THE ART OF MANURING IN NEW ZEALAND.

New Zealand Journal of Agriculture, Volume XXXII, Issue 1, 20 January 1926, Page 1

THE ART OF MANURING IN NEW ZEALAND.

B. C. Aston,

F.N.Z.Inst., Chemist to the Department of Agriculture

One and a quarter million New-Zealanders last year spent over per head on phosphates brought from overseas for manuring the soil. This fact is enough to warrant the devotion of a little thought to a big practice which shows signs of still more vigorous growth.

Phosphate., it is only right, should bulk greatest in the farmer’s manure bill. Three kinds of bodies are recognized by the laws of all countries governing the sale of manures, or the stuff from which socalled artificial fertilizers are made. These are substances containing nitrogen, potash salts, and phosphates. In the markets of the world the price of these is in the order in which they are set down, nitrogen costing about five times and potash twice as much as an equal weight of phosphate. It seems providential that what is most needed for New Zealand soils should be the cheapest of the three. It is further satisfactory to know that although available nitrogenous manures are quickly leached out of the soil and disappear into the rivers and sea, phosphates are only lost to a very limited amount. New Zealand soils are for the most part well supplied with nitrogen in an insoluble or unavailable state, from which nitrogen becomes liberated in an available state from time to time sufficiently for ordinary crops. There does not seem to be any reason to worry about nitrogen or potash supplies, but the increasing demand for phosphate suggests that every precaution should be taken to ensure that the full value is obtained from the use of it.

In spite of the fact that nitrogen and potash are so dear and phosphates so cheap, the elements from which nitrogen and potash manures are made are much more abundant in nature than phosphates, four-fifths of the atmosphere consisting of nitrogen, and the soil containing much nitrogenous organic matter. The crust of the earth is estimated to contain about 2-5 per cent, of potassium, but

only o - 1 per cent, of phosphorus. The more abundant elements are dearer because they are in a state which plants cannot use as food. By natural processes more or less slowly, and by artificial methods more or less costly, these inert manurial elements may be made available.

It is fortunate for New Zealand and Australia that the farming demand in the Northern Hemisphere is predominantly for nitrogen rather than for phosphate, while the reverse is the case in the Southern Hemisphere, and that happily within a few days' steam there should be such high-grade deposits of phosphates as those existing at Nauru and Ocean Islands. The leading idea in our southern systems of manuring should be to import only the element which is absolutely deficient in the soil, as phosphate, and to rely on internal sources when the necessity arises for using those elements (nitrogen and potassium) which are present but not immediately available.

The quantities and approximate retail values of fertilizers imported into New Zealand for the year ended 31st March last were as follows, values being given in round numbers :

Phosphates— Tons. £ Bonedust .. ... .. ... .. 2,452 24,500-Bone-char .. .. .. .. .. 396 500 Basic slag . .. .. .. .. .. 45,682 247,000 Rock phosphate.. .. .. .. .. 108,163 702,000* Egyptian phosphate .. .. .. .. 8,530 50,000 ,026,000 Potash— '..■■■■ Potash salts .. .. .. . . ... ■ 7,416 £65,000 Nitrogenous Manures — ■ . ■ ■ £ Sulphate of ammonia .. .. .. .. 841 15,000 Nitrate of soda .. .. .. .. ' . . 816 15,000 ■. ) £30,000 * After grinding, bagging, &c.

Rock phosphate is the only one of these fertilizers which is imported in the unmanufactured state, and the figure £702,000 is arrived at by assuming that all the rock phosphate is bought by the farmer as ground rock phosphate. A large quantity, however, is made into superphosphate, which much increases the cost ; and it is estimated that the portion of the imported phosphate made into super costs the farmer £350,000 more than if it had been merely used as ground rock. This amount, together with a small amount for phosphate rock locally produced and the retail value of the phosphate produced by meat-works in New Zealand (estimated to be about £50,000), makes the total amount spent for phosphates as follows : — £ Imported phosphates .. ' .. . . .. 1,026,000 Cost of making portion into super . . .. 350,000 Locally produced phosphates . . . . . . 50 ,000 ,426,000

To the importations of potash and nitrogenous fertilizers set out in the first table may be added the organic manures produced at local meat-works, the retail value of which is estimated at approximately £200,000. The combined value of these classes then totals the substantial sum of £295,000. The preponderance of the expenditure on phosphatic fertilizers, nevertheless, is overwhelming.

SELECTION OF APPROPRIATE FERTILIZERS.

The selection of an appropriate, fertilizer for any crop is governed by a consideration of the facts relating to (1) the soil, (2) the crop, and (3) the climate. .

It is important in this country that one should, disregard any practice which is followed in the Old World in manuring any particular crop. The conditions of climate and soil here are entirely different from those obtaining in England, or indeed, the Northern Hemisphere, and should one endeavour to be guided by what is usual in our antipodes the New Zealand farmer will be sadly led ■ astray The most striking instance of this is in the manuring of cereals. In England oat and wheat crops are manured with a fertilizer which is essentially nitrogenous, but in New Zealand it is to phosphates the farmer looks to increase his .grain crop, and this is true also in Australia. It is probable that in New Zealand the rate at which nitrogenous matter becomes available is much greater than in the colder northern soils.

The soil,- from the farmer’s point of view, is either heavy or light, the heaviness being due to the presence of unusual amounts of clay and sometimes silt; or it may be obviously sandy or gravelly, or peaty land derived from the drainage of a swamp. In some cases dune sandy land may be converted into quite a ■ different soil by the admixture of peaty matter. The sandy land loses all its characters peculiar to sand, and will then respond well to lime and other treatment appropriate to heavier soils.

With heavier soils, in a district with a well-distributed and good rainfall, alkaline manures such as basic super, slag, and other phosphates applied in conjunction with quicklime (but not necessarily in the same season) are indicated ; with the lighter soils acid dressings and carbonate of lime. The extreme type of sandy soils should not, as. a rule, be limed, but improvement, in the- texture should be effected by turning in green manure or applying other manures rich in organic matter. It is best not to apply alkaline manures to sandy soils, but acid and alkaline phosphates (<?.£■'., basic slag and super) may be mixed to produce a neutral manure, with every prospect of being extremely beneficial on sands. A sandy soil is a droughty soil, and - successful farming on sandy soils is contingent not only on a heavy but on a welldistributed rainfall. Fortunately, some of the greatest areas of sandy lands are so interspersed with swamp lands and loams, where the conditions are exactly reversed, that defects of one type are balanced by those of the others on the same farm. The scientific farmer must apply one treatment to his sandhills and another to his swamps, and it must be remembered that extreme types of soil, whether'they be excessively tenacious like clay soils or excessively friable like sands or

fine gravels, must have an extreme treatment. If artificial manures are applied to such soils without previous treatment to improve their physical state the fertilizers will be largely wasted. •

With heavy clays which puddle when worked wet the application of quicklime is at the outset forced on the farmer ; but sandy soils may give results for a number of years before their lack of response to fertilizers forces the farmer to realize the necessity for greenmanuring. Some kinds of sandy lands containing a large amount of silt tend to pack after working and allow the surface water to lie. . It is to these soils that green-manuring has now grown so necessary that further improvement must be on the lines of an organic manuring before artificials can obtain a full response from the crops.

Peaty or drained swampy soils which contain a large amount of organic matter should be treated with insoluble fertilizers after draining. Such soils are strong solvents of many minerals insoluble in pure water, and applications of such material as sand, clay, pumice, papa, or even gravel may be used to supply the deficiency in mineral plant-food and render the soil easier to drain and work. Basic slag or ground raw phosphate of any insoluble kind will work wonders on such lands. The lime-requirement of such lands is very highmuch higher than any. farmer could hope to satisfyand therefore it is a somewhat superfluous task to determine what the lime-requirement is. The proper quantity of lime to put on such a soil is as much as the farmer can afford. This will be well within the requirement.

With these preliminary remarks on the importance of obtaining what is known as good tilth, the study of the use of artificial fertilizers may be commenced.

CLIMATIC INFLUENCES (NORTH ISLAND*)

With regard to the climate as a factor in modifying the manuring of the soil, most of the North Island has a rainfall of under 70 in., according to the rainfall map issued by the Meteorological Office. The exceptions to this are not many. Areas round Napier, Cape Palliser, and Wanganui have a rainfall of under 40 in. Gisborne has slightly more, but under 50 in. There are some very high rainfalls in a few higher levels containing areas of no agricultural importance, so that generally speaking one may say that the country is exceptionally well watered and has an average rainfall of under 70 in. Hawke’s Bay has the only climate which would modify the manuring, and in this would indicate the use of superphosphate, and contra-indicate the use of basic slag where a phosphate is to be used. Or, speaking more generally, more soluble manures should be used in a climate like that of Napier, in which 33 in. of rain falls on 102 days, than in one like Auckland, where 43 in. falls on 183 days.

THE GREAT NEED OF PHOSPHATES.

In 1913, after some fourteen years spent in analysing soils from all parts of the Dominion for their manurial ingredients, for both “ total ”

and available plant-food,'the writer Phosphates/’ this Journal. vol. vii, p. 121) showed that, broadly speaking, soils of the northern part of New Zealand, especially those of Auckland, were much poorer in phosphate than those of the South Island. Phosphate deficiency oi soil is the outstanding defect throughout New Zealand, and it is the means of supplying this deficiency that must be first considered. All kinds of phosphates, soluble and insoluble in water, obtain a wonderful response from every crop grown on New Zealand soils. The water-soluble superphosphate, the citrate-soluble phosphate in basic super and slag, and the water- and citrate-insoluble raw phosphates all give excellent results and confirm the results of soil-analyses, which show that phosphate is universally deficient on virgin lands. Unfortunately, this general recognition of the necessity for phosphate has led to great quantities being applied year after year as a sole means of obtaining growth response. Amounts have been put on which cannot possibly have been recovered in the produce -—- crops and stock which are obtained from the soil.

Since this constant application of phosphate has become a stereotyped practice, it is well to consider what becomes of the phosphate, a comparatively small portion of which is removed. The Rothamsted experiments have shown that phosphate is not lost by leaching to any extent on that soil. There is therefore only one explanation, why more phosphate should be required every year, and that is that it is becoming unavailable in the soil. This is especially liable to occur when a water-soluble phosphate is applied to a soil in which there is no calcium carbonate. The phosphate is precipitated in the soil, and if there is no calcium carbonate with which to combine the phosphate the latter no doubt combines with the bases, iron and aluminium. When in this form it is usually regarded as being unavailable for plant-food.

Some attempt should be made to determine whether lands which have been top-dressed for years with phosphate will yield some of their wasted phosphate fertility when treated with lime in one of its forms. But a more rational way of going to work would be to apply lime to the soil before dressing with super, thereby assuring a base in the soil to fix the super, and which at the same time does not permit the phosphate to be thrown out of action by being converted into highly unavailable compounds. We know that the calcium phosphates are all available when finely distributed in the soil, and it should be the aim of every farmer to keep the phosphates available by liming or mixing them with lime, rather than to continue to supply an acid manure year after year.

FUNCTION OF PHOSPHATE.

Phosphates of’calcium hasten the growth of plants, having a very strong action on the young plant and greatly stimulating the development of roots; phosphates increase the proportion of grain to straw and lessen the time the plant takes to reach maturity. Owing to their great influence on root-development phosphates are especially valuable in use with shallow-rooting crops such as barley and turnips. Phosphate has many other functions, but one of the most noticeable effects is the extraordinary increase in palatableness of pastures top-dressed with phosphates. . Stock will travel for miles to graze off top-dressed pasture,

and if a small area on a farm is dressed with phosphate and not fenced off the stock will remain on that area and graze it as closely as a lawn.

The clovers belong to a family of plants which are greatly stimulated by phosphates. Members of this family, the legumes or pod-bearing plants .(Leguminosae), can obtain .the nitrogen they need from the atmosphere with the aid of certain micro-organisms which grow in attachment to the roots of legumes to their mutual good (symbiosis). Hence a dressing of calcium phosphate, by increasing the amount of clovers in . a pasture, also increases the nitrogenous organic matter and so improves the soil. " The organic matter by its decay creates humus, and humus makes available other plant-food, including potash. Hence application of phosphates establishes a cycle of improvement which is as far-reaching as it is important. The most nutritious pastures in England and the best dairy pastures in France are those richest in phosphates.

One cannot consider the action of phosphates on soils without at the same time taking into consideration other fertilizers, and what are called in America “ amendments ” to the land. An amendment is some bulky and cheap material which is used for improving the soil, but, containing no appreciable amount of nitrogen, potash, or phosphoric acid, it cannot rightly be called an artificial fertilizer. Such amendments are lime in any of its forms, stable manure, or any crude refuse used for improving the tilth but not directly for supplying plant-food. Of . these carbonate of lime is in New Zealand the most important. This is merely limestone which has been dried and ground to a “condition which enables it to be sown by a drill or lime-distributor. There are very few North Island types of soils which contain carbonate of lime in the virgin state. Some of the rivers which flow through papa country deposit a sediment from floods which top-dresses the land with material containing a few per cent, of carbonate of lime. The best example of this is at Gisborne (“Notes on Some Poverty Bay Soils,” this Journal, vol. xvii, p. 196). Another instance is the material erupted at the time of the Tarawera eruption in 1886. This particular material fell as a mud, and it now contains several per cent, of a calcareous compound 'soluble in dilute hydrochloric acid but which is not calcium carbonate. In papa soils the calcium often exists as a carbonate to the extent of a few per cent.

Probably the most important function of carbonate of lime on New Zealand soils lies in the favourable influence which a good supply exertsboth on the phosphates naturally present in the soil and on those which are artificially added. Lime prevents the formation of those phosphates of iron and aluminium which are with difficulty available as plantfood. Hilgard, the American agricultural chemist, held that where carbonate of lime was in excess, phosphates might be present in very small amounts, and yet more satisfactory returns be obtained from the land than when lime was deficient and much phosphate was added.. This has been found to be the case in New Zealand. Some of the most fertile lands are those which have carbonate of lime naturally in the soil.. The lesson to be learnt from this is the need of trying to economize in. the application of phosphates by liming those soils which do not effervesce when a small portion is thrown into a dilute solution of spiritsof salts (hydrochloric acid).

NITROGEN.

The next important plant-food to consider is nitrogen. This manurial ingredient is always found in commerce as ammonium salts, nitrate of soda, dried blood, bonedust, or sundry organic manures made by meat-works. It is most largely used in the insoluble form in proprietary mixtures. Those saline forms, the nitrates and the ammonium salts, are used to a small extent, but mainly by market-gardeners. Nitrogen has a very great influence on the leafy parts of plants, and in those crops which are grown for their leaves nitrogen is a valuable fertilizer. The amount used in this country compared with phosphates is insignificant. One may notice that nitrogen delays the maturing of the plant by encouraging the vegetative phase to retard the reproductive phase. Its action is thus opposed to that of phosphate, which hastens the fruiting stage of the plant, thereby securing early maturity and early harvests point of considerable importance in temperate countries with uncertain seasons.

POTASH.

Potash manures are known to exert a very favourable influence , on the health of the plant, making it more resistant against the attacks of fungoid diseases. Potash is essential to the formation of carbohydrates, such as starch, sugar, and cellulose. When the supply of potash is deficient the manufacture of carbohydrates is greatly reduced. Crops rich in these compounds, such as mangolds and potatoes, are said to be specially benefited by potassic manures. Potash tends to prolong growth in cereals and to hasten maturity in mangolds. Comparatively only a small amount of potash manures is imported into New Zealand.

One would like to see authoritative experiments undertaken locally to determine the value of this class of artificials. The action of potash in stimulating the growth of clovers is stated by European authorities to be very marked. The growth of clovers is most marked in all New Zealand soils even without potash applications. Soil-analysis does not indicate any deficiency of potash in New Zealand virgin soil, and the active growth of clovers without help from any added potash would seem to bear this out. For special crops such as potatoes, mangolds, and rape it is, however, always advisable to add potash on all soils, and on black peaty soils it will probably be found beneficial for all crops. It is' said that potash shows good effects on sandy or gravelly soils, but it must be remembered that New Zealand sandy soils, whether dune-sands or pumice-sands, are well supplied with potash minerals. Both magnesium and sodium salts attack the insoluble potash minerals in the soil, and liberate potash from them in a state suitable for absorption by plantroots. Coastal lands may therefore have potash supplied naturally through the action of the sodium chloride brought ashore in the sea-spray.

THE MIXING OF FERTILIZERS.

In the mixing of fertilizers it is important for the farmer to remember one or two cardinal points. Alkaline and acid manures may be mixed only under certain conditions. Thus basic slag and superphosphate if mixed and allowed to stand will set to a hard mass, which

will, if allowed to remain long enough, have to be broken down by a sledge-hammer before it can be distributed. Hence such a mixture must only be made in small quantities at a time and distributed at once. After each day’s work the drill or distributor should be thoroughly cleaned out. The alternative to this procedure is to mix in some diluent which will keep the mixture from setting. An equal bulk of dry pumice or other sand will be very useful in this work, or bonedust or ground rock phosphate may be used if available.

Another point is that alkaline manures must not be mixed with nitrogenous organic manures or ammonium salts. The quicklime or any substance which contains it, such as basic slag, must on no account be mixed with meat manure, blood and bone, or ammonium sulphate. If such a mixture is made, the valuable and volatile ammonia gas is formed, driven off into the atmosphere, and so lost to the farmer. Of course, if basic slag is first mixed with superphosphate until an acid or neutral mixture is formed, and then mixed with blood and bone, no loss will result.

Carbonate of lime may be mixed with superphosphate and mixtures containing superphosphate. Such a mixture drilled in with the seed gives an excellent result with cruciferous crops such as turnips, swedes, and rape, which greatly benefit by an alkaline manure, even on pumice or sandy soils. This is the one exception to the use of lime on pumice lands. The slag-super mixture is, however, likely to give even better results with turnips.

Kainit is a favourite potassic dressing, but it must not be mixed directly with superphosphate and allowed to stand, otherwise it will become a sticky, unmanageable mass. By using a diluent and sowing it quickly in small quantities such a mixture may be safely made. It is perfectly safe to mix superphosphate with sulphate of ammonia, but if mixed with nitrate of soda such a compound must be sown at once.

Generally speaking, any mixture may be made if enough diluent is added and the mixture is not allowed to become alkaline in the presence of ammonium salts or nitrogenous organic matter.

(To be continued.)

Cream-grading.— In his last annual report the Director of the Dairy Division makes the following remarks on this subject : “ The general consensus of opinion amongst the large majority of suppliers and those in control of dairy factories is that the grading should be made compulsory. Voluntary grading would be nearer the ideal, could it be effectively carried out generally. I am of opinion that it will not be so carried out, and that the earlier a compulsory system is approved by the Department the better will it be for all interested in the dairy industry and who have the real interests, of the industry at heart. Legislation is, I believe, necessary for providing for a differential payment for second-grade cream, and without this compulsory grading would be useless. Compulsory grading with differential payment would add greatly to the effectiveness of the farm-aairv instruction work.”

Bee-diseases. —-During 1924-25 further materia] was collected by the Biological Laboratory in the study of Nosema apis, but the organism thus far could not be associated with any specific disease. Another disease of bees- —paralysis-— dealt with from a bacteriological standpoint, but from many examinations the presence of bacteria which would account for the disease could not be demonstrated.

* South Island references under climatic and other headings will be made in a later article of this series.