Manures and the principles of manuring

Influence of Manure on Composition.

A most interesting point in connection with the manuring of roots is the effect of manure on their composition. This has been most elaborately investigated at Rothamsted and elsewhere. Thus it has been found that the effect of the application of excessive quantities of nitrogenous manures is to produce too great a development of leaves at the expense of the roots.

Nitrogenous Manures increase Sugar in Roots.

Nitrogenous manures also tend to increase the proportion of sugar and diminish the proportion of nitrogenous matter in roots. This has an important bearing on the treatment of roots which are cultivated for their sugar, such as beets, in the growth of which nitrate of soda is the chief artificial manure applied.[245]

The leaf, it may be pointed out, contains a larger percentage of dry matter, both in swedes and in turnips, than the root.

Amount of Nitrogen recovered in Increase of Crop.

With regard to the amount of nitrogen recovered in the increased crop of mangel and roots when manured with different nitrogenous manures, it was found at Rothamsted, as an average of six years, that the following percentages of nitrogen were recovered: When nitrate of soda was applied, 60 per cent of the nitrogen it contained was recovered in the increased crop; when ammonia salts were applied, 52 per cent; when rape-cake was used, 50 per cent; and when a mixture of rape-cake and ammonia salts was used, 46 per cent.

It may be pointed out that the influence of season and climate on the composition of root crops is very great—greater, indeed, than on any other crop. Like oats, turnips grow better in Scotland than in England, the moister climate of the former country being more suitable for their maximum development, and hence the economy of maximum dressings in Scotland.

Norfolk Experiments.

In conclusion, a few words may be said on the Norfolk experiments, carried out under the direction of Mr Cooke for the purpose of ascertaining the best and most economical manure for mangels and swedes on different Norfolk soils. In most of these experiments it was found that superphosphate had not much effect in producing increase of crop in the case of mangels; that the best nitrogenous manure was nitrate of soda; and that on the whole it was not economical to apply farmyard manure at the rate of more than 10 tons per acre. It was further found that, although either potash or common salt gave a decided increase in weight of roots, it was not necessary to give both these manures at once, either of them being about as effective as the other.

Mr Cooke recommends the following manures as best suited for mangels—viz., 2 cwt. nitrate, 3 cwt. common salt, and 2 cwt. superphosphate. Upon certain soils peculiarly adapted to mangels, and in warm localities where larger crops than 25 to 30 tons per acre are habitually grown, it would probably pay to increase or to double the above quantity of nitrate of soda. Ten tons of farmyard manure may, if preferred, be substituted for all or a part of the nitrate of soda, or may even be used in addition to it, according to the resources of the farmer in respect of it, and the return he desires to get from the dung in the first year of application or in future ones. It is best to apply the nitrate of soda in two instalments—half at the time of seeding, and half as a top-dressing immediately after the first hand-hoeing of the roots. A third dressing may often be given with advantage a month later.

Manure for Swedes.

As a complete and economical dressing for swedes in Norfolk, Mr Cooke recommends 3 to 4 cwt. superphosphate, 1 cwt. sulphate of ammonia, and 1/2 cwt. of muriate of potash. Occasionally it may be found advisable to reduce the quantity of sulphate of ammonia, or to leave it out altogether; and in other cases the potash may be judiciously omitted. The entire mixture should be sown at the time of drilling the turnips. If farmyard manure is used—and if used it should be applied in a well-decomposed state—no other manure than 3 cwt. of superphosphate will be required.

Highland Society's Experiments.

Valuable experiments have been carried out on the subject of manuring of turnips by Dr A. P. Aitken, for the Highland and Agricultural Society of Scotland. The following are some of the results to be gathered from these experiments. The effect of a dissolved phosphate as compared with a ground phosphate is to produce a turnip of less feeding value. Superphosphate had a better effect when applied in April than when applied with the seed in June. It was further found that when the nitrogenous manure was given entirely in the form of nitrate of soda or sulphate of ammonia, the latter produced a denser and sounder turnip. Lastly, with regard to the application of potash, it was found that the best way was to apply it several months before sowing. The effect of potash manures is to increase the amount of turnips, but to retard the ripening of the bulbs. The effect of excessive potash manuring is to greatly injure the crop.

Manuring for rich Crops of Turnips.

In Dr Aitken's own words: "In order to grow a large and at the same time a healthy and nutritious crop of turnips, such a system of manuring or treatment of the soil, by feeding or otherwise, should be practised as will result in the general enriching and raising of the condition of the land, so that the crop may grow naturally and gradually to maturity. For that purpose a larger application of slowly acting manures, of which bone-meal may be taken as the type, is much better suited than smaller applications of the more quickly acting kind. A certain amount of quickly acting manure is very beneficial to the crop, especially in its youth; but the great bulk of the nourishment which the crop requires should be of the slowly rotting or dissolving kind, as uniformly distributed through the soil as possible."

Experiments by the Author.

Experiments by the author on turnip-manuring, carried out in different parts of the South and West of Scotland, showed that while farmyard manure is valuable in giving the crop a good start and bringing it well forward during the period of germination and early growth, by supplying a certain amount of easily assimilable plant-food, and in the case of dry weather attracting a quantity of moisture, its application in quantities of 20 or even 10 tons per acre can scarcely be regarded as profitable, giving to farmyard manure a nominal value of a few shillings a ton. In these experiments slag proved itself a most valuable manure, indeed one of the most economical of all the manures experimented with. They further showed that heavy dressings with superphosphate, amounting to as much as 8 cwt. per acre, are, from an economical point of view, as a rule justifiable in Scotland; and that nitrate of soda and sulphate of ammonia possess practically equal value as a manure for turnips. In almost every one of the experiments the benefit of supplementing superphosphate with nitrogenous manure was shown. Potash was also found in many cases to be a thoroughly paying manure for the turnip crop, when it was applied along with nitrogen and phosphates; but when applied alone, far from exercising any appreciable benefit, it seemed to exert an injurious action.

Potatoes.

Potatoes are often classed along with the root crops, and in their manurial requirements they offer many points of similarity. Next to root crops, they may be said to make the most exhaustive demands on the soil, and therefore require a liberal general manuring. A point of importance in the manuring of potatoes is a good tilth in the soil, so as to enable a free expansion of the tubers to take place. They may be said to grow best on deep warm soils; but, like roots, if liberally manured, they may be successfully grown on any kind of soil. Farmyard manure has long been regarded as specially valuable for the potato crop. In many parts of Scotland it is applied in enormous quantities, ranging from 20 to even 40 tons per acre. There can be little doubt that the value of farmyard manure, as well as other bulky manures, for the potato crop, is partly due to their mechanical influence on the soil. Potatoes are surface-feeders, and require their food in a readily available condition. It is found desirable, therefore, to supplement farmyard manure by readily available artificial manures. Potatoes repay the application of a mixed manure containing all the fertilising ingredients—nitrogen, phosphoric acid, and potash—better than most crops.

Highland Society's Experiments on Potatoes.

The nitrogen is, according to the Highland Society's experiments, best applied in the form of nitrate of soda. Sulphate of ammonia does not seem, when farmyard manure is also applied, to have an equally valuable effect, as it influences the size of the tuber, producing an undue proportion of small potatoes. When no farmyard manure is applied, however, sulphate of ammonia seems to have a good effect, especially in wet seasons.

With regard to the nature of the phosphatic manure to be applied, superphosphate is to be preferred. Potatoes make large demands on potash, and consequently require potassic manures. In consequence of the fact that they receive large applications of farmyard manure, the necessity for adding potash in the form of artificial manures does not generally exist. Potash, if applied in too large quantities, has been found to exert a deleterious effect. We have already pointed out that muriate of potash tends to produce a waxy potato.

The Rothamsted Experiments with Potatoes.

The Rothamsted experimenters have very fully investigated the conditions of the manurial requirements of potatoes. In these experiments potatoes were grown year after year in the same field. It was found that the effect of mineral manures alone was greater than the effect of nitrogenous manures alone, and that of mineral manures phosphates, as a rule, had a better effect than potash; that under the action of the growth of potatoes a greater exhaustion of phosphates than of potash takes place in the soil; and lastly, that it is essential to have an abundant supply of the different fertilising ingredients in order to grow successful crops. In the Rothamsted experiments, the slow action of farmyard manure in supplying fertilising ingredients to the potatoes is strikingly demonstrated. Thus, although farmyard manure was applied at such a rate that more than 200 lb. of nitrogen were added to the soil, the result was inferior to that obtained from the application of 86 lb. of nitrogen applied in the form of readily available artificial manure.

Effect of Farmyard Manure on Potatoes.

It may be said, in this respect, that the potato is less able to utilise the fertilising ingredients of farmyard manure than any other of the farm crops. Yet, despite this fact, farmyard manure has been found to be one of the best manures to apply. The reconciliation of these seemingly contradictory statements depends on the influence exerted by the farmyard manure on the mechanical condition of the soil, rendering it more porous and easily permeable to the surface-roots, upon the development of which the success of the crop so much depends. The beneficial effect of farmyard manure is also doubtless due to the increased temperature which large applications of it produce in a soil.

Sir J. Henry Gilbert, in his well-known Cirencester Lecture on the Growth of Potatoes, cites several examples of the manurial treatment of potatoes in different parts of the country. In Forfarshire, farmyard manure or stable manure is largely employed (at the rate of 12 to 14 tons, and in some cases even 20 tons per acre), and it is also largely supplemented by artificial manures. These latter are applied to the extent of about 10 cwt., and consist of superphosphate, dissolved bones, and potash salts. Six tons of potatoes are considered a fair crop. In East Lothian the manuring is similar, with the exception that farmyard manure is applied in even larger quantities—30 to 40 tons being often used. Sometimes potatoes are grown with artificial manures alone. It would seem that the usual crop of potatoes ranges from 4 to 8 tons per acre.

Manuring of Potatoes in Jersey.

The manuring of the potato crop, so largely grown in Jersey in the Channel Islands, is of interest. Potatoes are there grown two or three years, then corn, then grass for a few years, then potatoes again, no special rotation of crops being followed. Either farmyard manure or sea-weed is applied at the rate of 25 to 30 tons per acre, supplemented by 8 to 12 cwt. of artificial manures.

These statements show how prevalent the practice of heavily manuring the potato crop is.

The Influence of Manure on the Composition of the Potato.

The influence of manure on the composition of the potato crop is of much interest. Potatoes grown without manure, just as in the case of roots, are found to have a larger percentage of nitrogen than potatoes grown with manure. The effect of manuring, therefore, is to increase the proportion of starch, which is the most important constituent of the potato. Mineral manures have a greater effect in increasing the percentage of starch than purely nitrogenous manures; but when used together, a still greater increase is obtained than when used singly. The effect of nitrogenous manures on the composition of roots and potatoes is thus seen to be similar. In the case of both crops the effect is to increase the proportion of the characteristic carbohydrate constituent, which in roots is sugar, and in potatoes starch. Potatoes, like roots, are also much influenced by the season. The effect of season and manuring on the potato disease is worthy of notice. Wet seasons are favourable to the development of the disease. It has been found that in a highly nitrogenous manured crop the proportion of diseased tubers is greater than in a non-manured crop.

LEGUMINOUS CROPS.

We have already referred to the manuring of crops of the leguminous class in discussing the manuring of meadows and permanent pasture. It was there pointed out that the tendency of certain manures was to encourage the growth of the leguminous plants of the herbage, while other manures had the effect of encouraging those of the gramineous class. It was pointed out that a manure which had this effect was potash, or any manure which owed its characteristic action to the fact that it supplied potash to the soil or set it free in the soil.

Leguminous Plants benefit by Potash.

This is one of the most important points to notice in manuring leguminous plants. Just as we can say that nitrogenous manures are specially beneficial to cereals, and phosphatic manures to roots, so potash is the special manure for leguminous crops.

Nitrogenous Manures may actually be hurtful.

But we have, further, an even more striking characteristic of leguminous crops to notice. We have seen that, with regard to the crops already discussed, while there are cases in which a fertilising ingredient may be of no value, or may positively exert a hurtful action on the crops, such cases are only exceptional. With regard to leguminous crops, however, we find that almost invariably they derive little or no benefit from the use of artificial nitrogenous manures. And this is all the more striking since they contain large quantities of nitrogen in their composition—twice as much as the cereals. The fact, which has long been noticed with regard to certain members of this class of plants, such as clover, that not only do they contain a large amount of nitrogen, but that by growing them on a soil the soil is largely enriched in this valuable fertilising constituent, has long waited for a satisfactory explanation, which at last has been forthcoming. The discovery that leguminous crops can draw on the boundless store of nitrogen present in the air has done much to clear up the mystery. There are, however, other problems with regard to the growth of leguminous plants which still await solution.

Clover-sickness.

One of these is the fact that land on which a leguminous crop like clover has been growing for a number of years becomes unfit to support its growth any longer. Such a soil is termed "clover-sick"; and many have been the theories put forward to explain the phenomenon, but none of them can be regarded as satisfactory.

The knowledge that leguminous plants have the power of deriving their nitrogen from the air, furnishes us with an economical means of enriching our soils in nitrogen. By growing leguminous crops alternately with cereals, for example, the air should be made to furnish the necessary nitrogenous manure. As a matter of fact, modified forms of such a practice have long been in use—indeed the ordinary rotations of crops are, to a certain extent, adaptations of this practice.

Alternate Wheat and Beans Rotation.

An interesting experiment carried out at Rothamsted may be here cited which illustrates in a striking manner the truth of the above statement. Wheat and the leguminous crop beans were grown alternately. It was found that almost as much wheat (containing nearly as much nitrogen) was yielded in eight crops of wheat so grown as was yielded by sixteen crops of wheat grown consecutively in an adjoining field.

The most commonly cultivated leguminous crops are clover, beans, and peas. Clover having been already discussed, we need only say a word or two on the manuring of beans and peas.

Beans.

Beans do best on strong land, and, unlike some of the crops considered, do not require a particularly fine tilth. They are generally grown after cereals, and as a rule are sown in spring. More rarely, however, they are sown in autumn. Spring-sown beans take about seven months to come to maturity. They are much affected, like other crops, but to a greater extent, by the nature of the season—a wet season inducing an undue development of straw.

Manure for Beans.

In common practice the manure used for the bean crop is farmyard manure, applied to the soil in autumn after the harvest of the wheat, barley, or other cereal crop grown. So common is this practice, that the belief commonly exists that farmyard manure is necessary for a successful bean crop. But experiments conducted at the Highland Society's Experiment Station at Pumpherston show that full crops of beans may be grown with the aid of artificial manures on soils which have received no application of farmyard manure for ten years.

Relative Value of Manurial Ingredients.

In the Appendix[246] will be found a table giving the results of manurial experiments with the nitrogenous, phosphatic, and potash manures on beans, carried out by Dr A. P. Aitken at the Highland Society's Experiment Station. From these experiments it will be seen that the application of phosphates and nitrogenous manures, either alone or together, exerted a comparatively small effect in increasing the yield of beans compared with that obtained with potash, either alone or combined with phosphates. As Dr Aitken says, "Without potash in the manure, the other two ingredients are of very little use, unless, indeed, the land be very rich in potash."

Gypsum.

Gypsum has a good effect on the bean crop, both on account of the lime it contains, and of its indirect action in setting free potash.

Superphosphate is a much better manure than insoluble phosphates, and similarly, in the few cases where nitrogenous manures are beneficial, the speediest acting are best. Hence nitrate of soda is to be preferred to other nitrogenous manures. When it is applied, it should be applied in small quantities. A slow-acting nitrogenous manure is positively injurious; so also, according to Dr Aitken, is nitrate of soda, applied as a top-dressing to the crop.

Of potash manures, the muriate seems to be more effective than the sulphate.

Effect of Manure on Composition of Crop.

Lastly, we may refer to the effect of manures on the composition of the crop. This is, on the whole, very slight, especially when compared with the effect manures exert on the composition of such crops as turnips or potatoes. It is the quantity and not the quality of the crop which the manure affects in the case of beans.

Peas.

Peas are not grown to anything like the same extent as beans. As a rule, when they are cultivated it is along with beans, when they are necessarily manured in a similar manner. If grown alone, however, it may be well to point out that peas do best, unlike beans, on light, friable, chalky loam. When grown in clay they tend to develop an undue amount of straw. The effect of season on the crop is similar to that exerted on the bean crop. In conclusion, it may be pointed out that it is alleged that the effect of farmyard manure on peas is to force the straw.

In concluding this chapter a word or two may be said on the manuring of two other crops which are cultivated to a considerable extent in this country—viz., hops and cabbages.

Hops.

The requirements of the hop crop in the matter of manures are rather singular. It has been pointed out that in the case of most crops quick-acting manures are to be preferred to slow-acting manures. With hops, however, the case is very different; for they require, and cannot be successfully cultivated without, slow-acting manures. Hops are especially benefited by bulky nitrogenous manures—such as shoddy, horn-meal, hide-scraps, hoofs, rape-dust, &c.; and it is only when quick-acting manures are applied along with such slow-acting manures that they will exercise their full influence. It is best to manure hops twice a-year,—in spring with farmyard manure, supplemented by a slow-acting nitrogenous manure, such as shoddy; and again in summer with a more quickly acting manure. The dressings applied to hops are enormous relatively to those used on other farm crops.

Cabbages.

Cabbages belong to that class of crops known as gross feeders, to which any sort of manure, applied in almost any quantities, does not come amiss. Cabbages grow best on good loams with a well-drained porous subsoil, although they also do well on clay soils. The quantity of fertilising ingredients, especially potash, which a large crop of cabbage removes from the soil is very great. They consequently require large quantities of manure, and are especially benefited by saline manures—such as kainit and common salt—and liberal doses of nitrate of soda, which may be regarded as the most effective of manures for all the cabbage tribe. Farmyard manure may be applied with benefit in larger quantities than it would be applied to any other crop.

FOOTNOTES:

APPENDIX TO CHAPTER XXIII.

NOTE I. (p. 526).

Experiments on the Manuring of Beans.

Experiments with beans carried out at the Highland and Agricultural Society's Experiment Station at Pumpherston, showing the effect of potash:—

CHAPTER XXIV.

ON THE METHOD OF APPLICATION AND
ON THE MIXING OF MANURES.

Having considered the manuring of the different crops, we may now pass on to the consideration of some points in the method of application and on the mixing of manures.

Equal Distribution of Manures.

A most important object in applying manures is to effect equal distribution of the manure in the soil. This is often, however, unusually difficult to do, especially in the case of artificial manures, where the quantity to be spread over a large area of the soil is extremely small. The difficulty in the case of farmyard or other very bulky manure is not so great. In order to overcome this difficulty in the case of artificial manures, it is often advisable to mix them with some such substance as sand, ashes, loam, peat, or salt. The manure is thus diluted in strength, and a very much larger bulk of substance is obtained to work with. Circumstances must decide which of these substances to use. If the soil be a heavy clay, the addition of sand or ashes may have an important mechanical effect in improving its texture; while, on the other hand, if it be a light soil, the addition of peat may improve its mechanical condition. It must also be remembered that peat itself contains a large amount of nitrogen, and thus forms a manure of some value. In using loam or peat to mix with artificial manures, they should be first dried and then riddled; while if ashes be used, they should be previously reduced to a fine state. Wood-ashes, however, must be used with caution, and ought not to be mixed with ammoniacal manures, as they are apt to contain caustic alkali, which would tend to drive off the ammonia in a volatile state.

It has been recommended, in order to save trouble and effect equal distribution, that the manure to be applied should always be made up to the same amount, so that the farmer by experience may ascertain the rate at which to apply it. And here it may be well to say a word or two on the subject of mixing manures—a subject with which the farmer is not always so conversant as it is desirable in the interests of his own pocket he should be.

Mixing Manures.

It is to be feared that not unfrequently indiscriminate mixing may cause very serious loss in the most valuable constituent of a manure. It may be well, therefore, to point out one or two of the causes of the loss that is apt to ensue on the mixing of different kinds of manures together.

As the subject depends for its clear comprehension on certain chemical elementary principles, it may be well for the benefit of non-chemical readers to state these pretty fully.

Risks of Loss in Mixtures.

The risks of loss which may occur from the mixing of artificial manures together may be of different kinds. One is the risk of actual loss of a valuable ingredient through volatilisation; another is the risk of the deterioration of the value of a mixture through change of the chemical state of a valuable ingredient. Undoubtedly the most common and most serious source of loss is the former. Of the three valuable manurial ingredients—nitrogen, phosphoric acid, and potash—only the first is liable to loss by volatilisation, and this generally only when the nitrogen is either in the form of ammonia or nitric acid.

Loss of Ammonia.

Ammonia, when uncombined, is a very volatile gas with a pungent smell, a property which enables its escape from a manure mixture to be very easily detected. It belongs to a class of substances which are known chemically as bases, and which have the power of combining with acids and forming salts. Sulphate of ammonia is a salt formed—as its name indicates—by the union of the base, ammonia, with the acid, sulphuric acid. Now when ammonia unites with sulphuric acid and forms sulphate of ammonia, it is no longer volatile and liable to escape as a gas, but becomes "fixed," as it is called.

Although most salts are more or less stable bodies—not liable to change—if left alone, and not submitted to a high temperature or chemical action, they can be easily decomposed if they are heated or brought into contact with some other substance which will give rise to chemical action. Sulphate of ammonia is a salt that is very easily decomposed. This is due to the fact that its base, ammonia, is very volatile, and not capable of being held very firmly by an acid, even by sulphuric, which is among the least volatile of all the common acids. If, therefore, sulphate of ammonia be heated above the boiling-point of water, or brought in contact with any other substance which will give rise to chemical action, it is easily decomposed. Now a salt may be acted upon by a base or an acid or another salt. When it is brought in contact with a base, if the base with which it is brought in contact be a stronger base than the base of the salt, the salt is decomposed, and a new salt is formed. The acid, in short, exchanges its old base for the new one.

Effect of Lime on Ammonia Salt.

This is exactly what takes place when the base lime comes in contact with an ammonium salt, such as sulphate of ammonia. The sulphuric acid exchanges its old base, ammonia, for the stronger base, lime, and sulphate of lime is formed, and ammonia is set free as a gas, and escapes and is lost. Sulphate of ammonia, or any substance in which there is an ammonia salt, must never be brought in contact with free lime, otherwise the ammonia will be lost, and should be harrowed in on chalky soils for this reason.

It is different entirely with gypsum—which is sulphate of lime—or phosphate of lime, both of which may be safely mixed with sulphate of ammonia without any danger of escape of ammonia. It follows from the above that a mixture which must on no account be tried is slag phosphate and sulphate of ammonia. This is because the slag phosphate contains a large percentage of free lime, which would at once, on being brought in contact with the sulphate of ammonia, decompose it, and cause the ammonia to be lost. For this same reason guano must not be mixed with slag. It is perhaps unnecessary, however, to warn one against so doing, as it is not likely such a mixture would be made, as the ratio of phosphoric acid to nitrogen in guanos is generally greater than is required. If it be desired to mix the slag with a quickly available form of nitrogen, nitrate of soda is not liable to loss; although for other reasons it is not desirable to apply nitrate of soda along with the slag, as the former manure should be applied almost always as a top-dressing.

Loss of Nitric Acid.

The risks of the loss of nitrogen in the form of nitric acid, although not so great as they are in the case of ammonia, are still considerable. As nitric acid is not a base but an acid, what is to be avoided in mixing nitrates is bringing them in contact with any other manure which contains another free and stronger acid—as, for example, superphosphate. The free acid present in superphosphate has the tendency to drive out the nitric acid from the nitrate and usurp its place. The risk of loss of expulsion in the above cases is always augmented by the rise of temperature which invariably accompanies chemical action of any kind; and although the loss of nitrogen, in the form of nitric acid, caused by mixing superphosphate and nitrate of soda, might, under ordinary circumstances, amount to very little, yet, if the mixture were to be allowed to stand any time, and the temperature of the mass to be heightened, the loss which would undoubtedly then ensue would be considerable.

The nitrogen salt which it is safe to mix with superphosphate is sulphate of ammonia.

Reversion of Phosphates.

But, as has already been mentioned, there is another loss which may result from the mixing of manures. This is the deterioration of the value of an ingredient by reason of change of chemical condition. This is a source of loss that was little suspected a number of years ago, but it is now well known that superphosphate of lime, under certain conditions, is changed from its soluble to an insoluble form. We have already referred to the reversion of phosphate in the chapter on the Manufacture of Superphosphates.[247] It was there pointed out that reversion is often caused by the presence of iron and alumina or undissolved phosphate, and that the risk of reversion is therefore very much less in a well-made article, made from pure raw material, than in one made from a raw phosphate containing much iron and alumina. Superphosphates containing a large percentage of insoluble phosphates ought not to be kept too long before being used as a manure, otherwise much of the labour and expense involved in their manufacture will be lost by the reversion of their soluble phosphate. Further, it is highly inadvisable to mix superphosphates with basic slag, which contains a large percentage of both iron and free lime. Lastly, if it is desired to mix superphosphate with insoluble phosphate, the mixture ought to be made just previous to application.

Manurial Ingredients should be applied separately.

The question of applying manure in mixtures is one on which considerable difference of opinion may exist. For many reasons manures are often better applied in the unmixed condition. For example, a mixture of a quickly acting nitrogenous manure with a slowly acting phosphatic manure is not suitable. In such a case either the nitrogenous manure will be applied too long before it is required by the plant, and thus suffer from risk of loss, or the phosphatic manure will not be applied long enough before it is likely to be used. By applying manures in an unmixed condition the chances are that a more economical use of them is made than would otherwise be the case. On the other hand, while the application of the separate constituents may be desirable from the scientific point of view, it involves a considerable amount of extra trouble. Of course a further consideration is the desirability in many cases of having a complete manure. The above hints, therefore, on the risks of loss which exist in mixing manures, may be of service to the agricultural student.

FOOTNOTES:

CHAPTER XXV.

ON THE VALUATION AND ANALYSIS OF MANURES.

Value of Chemical Analysis.

The value of a manure to the farmer depends on the proportion of nitrogen, phosphoric acid, and potash it contains, as well as—and this is hardly less important—the condition in which the ingredients are present. Since these facts can alone be determined by a chemical analysis, it is obvious that manures should always be purchased with a chemical analysis. It is unfortunate, however, that very often a chemical analysis, even when procured, is unintelligible. It may be of advantage, therefore, to say a word or two on the correct interpretation of the significance of the data furnished in the ordinary chemical analysis of manures.

Interpretation of Chemical Analysis.

The first thing that the farmer ought to look for in the analysis of a manure is the amount of nitrogen, phosphoric acid, and potash which the manure contains.

Nitrogen.

The percentage of nitrogen in a manure is generally stated as equal to its equivalent percentage of ammonia. Very often, indeed, in the older analyses, its equivalent of ammonia was alone stated. Now this statement does not necessarily imply that the nitrogen in a manure is actually present in the form of ammonia. Thus, for example, when it is stated in an analysis of bone-meal that it contains 3.5 per cent of nitrogen, equal to 4.20 per cent of ammonia, it is not to be inferred that bone-meal actually contains nitrogen in the form of ammonia. In point of fact the nitrogen is present in an insoluble, slowly available, organic form, which possesses a manurial value very inferior to that possessed by ammonia. This custom is a most unfortunate one, and is much to be regretted, as it is often liable to give rise to serious misunderstanding. It must be remembered, therefore, that an ordinary chemical analysis does not always specify the exact form in which nitrogen is actually present. It is nevertheless of importance for the farmer to know this, of which the nature of the manure analysed is generally a good indication. Unfortunately this is not shown in the case of mixed manures; and this constitutes one of the reasons why mixed manures are sometimes to be regarded with suspicion.