Let us now proceed to discuss its action. Before doing so, however, it is important that we should clearly understand the different chemical forms in which it occurs.

Different Forms of Lime.

Lime occurs chiefly as carbonate of lime in the forms of limestone, marble, or chalk, which are all chemically the same. It occurs also as sulphate of lime or gypsum, as well as in the forms of phosphate and fluoride. In agriculture it is only used—if we except the phosphate, which is applied not on account of its lime, but its phosphoric acid—in the form of the carbonate or mild lime as it is commonly called, burnt, caustic, or quick lime, and as gypsum. As the value of gypsum as a manure is of such importance, and depends not entirely on its being a compound of lime, we shall consider it by itself. Hence we have only to consider here the action of mild and caustic lime.

Caustic Lime.

When limestone or mild lime is submitted to a great heat, such as is practically done on a large scale in lime-kilns, it is converted into caustic lime or lime proper. Limestone is made up, as we have just mentioned, of lime and carbonic acid. The latter ingredient is expelled in the form of a gas, and the lime is left behind. Lime never occurs naturally as caustic lime, for the simple reason that it is impossible for it to remain in this state, owing to the great affinity it has both for water and carbonic acid.

When lime is burnt, and before it is applied to the field, some time is allowed to elapse in order to permit of its absorbing moisture—or becoming slaked, as it is technically called. This it does more or less slowly by absorbing moisture from the air. As, however, the process would take too long, and as, moreover, the absorption of carbonic acid gas would also take place at the same time, lime is generally slaked in another way. This can be done by simply adding water. An objection to this method is, that the lime is not so uniformly slaked as is desirable. It becomes gritty. The usual method is to cover it up with damp earth in heaps, and allow the moisture of the earth to effect the slaking. When lime absorbs water a new chemical compound is formed, known as lime hydrate; and so rapidly does the lime unite with water, that a great deal of heat is evolved in the operation, the temperature produced being considerably above that of boiling-water. The conversion of slaked lime into carbonate of lime or mild lime is a slower process. Sooner or later, however, it takes place, whether the lime is left on the surface of the soil or buried in it.

A knowledge of these elementary chemical facts is necessary in order clearly to understand the nature of the action of lime in agriculture.

The respective action of quicklime and mild lime is, on the whole, similar, although the former is in every case very much more powerful in its effects than the latter.

Lime acts both mechanically and chemically.

Lime may be said to act on the soil both mechanically and chemically. It alters the texture of the soil, and affects its mechanical properties, such as its absorptive, retentive, and capillary powers with regard to water. It acts upon its dormant fertility, and decomposes its mineral substances as well as its organic matter. Lastly, its influence on the micro-organic life of the soil, which plays such an important part in the preparation and elaboration of plant-food, is of the highest importance. We cannot do better, therefore, than discuss its properties under the headings mechanical, chemical, and biological.

I. MECHANICAL FUNCTIONS OF LIME.

Action on Soil's Texture.

The effect of lime upon the texture of a soil is among its most striking properties. Every farmer knows well what a transformation is effected in the texture of a stiff clay soil by the application of a dressing of lime. The adhesive property of the soil—its objectionable tendency to puddle when mixed with water—is greatly lessened, and the soil is rendered very much more friable when it becomes dry. Several reasons exist for this change. In the first place, the tendency to puddle in a clayey soil is due to the fine state of division of the soil-particles. The way in which lime counteracts this adhesive property is by causing a coagulation of the fine soil-particles. This flocculation or aggregation of the fine clay-particles, when mixed with water by lime, is strikingly demonstrated by adding to some muddy water a little lime-water. The result will be that the water will speedily be rendered clear, the fine clay-particles coming together and sinking to the bottom of the vessel. Even a very small quantity of lime will effect this change. This property possessed by lime, we may mention, is utilised in the treatment of sewage. As it is the fine clay-particles that are the chief cause of the puddling of clay soils, their flocculation does much to destroy this objectionable property. Another reason why lime renders a clay soil more friable when dry is, that lime does not undergo any shrinkage in dry weather. As clay soils shrink very much in drying, the mixture with such a substance as lime tends to minimise this tendency to cake in hard lumps. The effect of even a very small addition of lime to a clay soil, in the way of increasing its friable nature, is very striking, and can be easily illustrated by taking two portions of clay, into one of which a small percentage of lime is introduced, and working both into a plastic mass with water, and then allowing them to dry. It will be found that while the one is hard and resists disintegration, that portion to which the lime has been added crumbles away easily to a powder. This effect which lime has in "lightening" heavy soils has been known to last for years. The disintegrating effect of quicklime when applied to heavy soils is also due, it may be added, to the change undergone by the lime itself from the caustic state to the mild state.

Lime renders light Soils more cohesive.

Although it may seem somewhat paradoxical, lime, it would appear, in some cases exercises an effect upon the soil exactly the reverse of what has just been stated. That lime should act as a binding agent is only natural when we reflect on the way in which it acts when used as mortar. It is quite to be understood, therefore, that its action on light friable soils should be to increase their cohesive powers, and at the same time to increase the capillary power of the soil to absorb water from the lower layers. The extent of this action, of course, would depend on the form in which the lime is applied, and the amount. A striking example of the binding power of lime is to be found in certain soils extremely rich in lime, in which what is known as a lime-pan has been formed at some distance from the surface.

II. CHEMICAL ACTION OF LIME.

But more important probably than even its mechanical action is the chemical action of lime. It is a most important agent in unlocking the inert fertility of the soil. This it does by decomposing different minerals and setting free the potash they contain. The disintegrating power of lime in this respect depends, of course, on its chemical condition, the caustic form being much more potent than the other forms. Its action in decomposing vegetable matter and rendering the inert nitrogen it contains available for the plant's use, is also one of its most important properties, and accounts for its beneficial action when applied to soils, such as peaty soils, rich in organic matter. Again, its use as a corrective for sour lands has long been practically recognised. The presence of acidity in a soil is hurtful to vegetable life. Lime, by neutralising this acidity, removes the sourness of the land, and does much to restore it to a condition suitable for the growth of cultivated crops. The generation of sourness in a soil is almost sure to give rise to certain poisonous compounds. Lime, therefore, in sweetening a soil, prevents the formation of these poisonous compounds. Badly drained and sour meadow-lands, as every farmer knows, are immensely benefited by the application of this useful manure; for not merely is their sourness removed and their general condition ameliorated, but many of the coarser and lower forms of plant-life, which alone flourish on such soils, are killed out, and the more nutritive grasses are allowed to flourish instead. The action of lime in promoting the formation of a class of compounds of great importance in the soil—viz., hydrated silicates—is worthy of notice. According to the commonly accepted theory, much of the available mineral fertilising matter of the soil is retained in the form of these hydrated silicates. Hence lime, by increasing these compounds, not merely adds to the amount of the available fertility in the soil, but also increases its absorptive power for food-constituents.

III. BIOLOGICAL ACTION OF LIME.

The last way in which lime acts is what we have termed biological. By this we mean the important role lime plays in promoting or retarding, as the case may be, the various kinds of fermentative action which go on so abundantly in all soils. The presence of carbonate of lime in the soil is a necessary condition for the process of nitrification. Lime is the base with which the nitric acid, when it is formed, combines; and as we have seen, when discussing nitrification, soils of a chalky nature are among those best suited to promote the natural formation of nitrates. This is one of the reasons for the beneficial effects produced by lime when applied to peaty soils. Not merely does it help to decompose the organic matter so abundant in such soils, but it also furnishes the base with which the nitric acid may combine when it is formed. But while the action of lime is to promote fermentation, it must not be forgotten that there may be cases in which its action is rather the reverse of this. Fermentation of organic matter goes on when there is a certain amount of alkalinity present; while, on the other hand, the presence of acidity seems to retard and check it. Too great an amount of alkalinity, however, would, in the first instance, retard fermentation as much as too great acidity. It has been claimed that the addition of caustic lime to fresh urine may act in this way; and if this were so, the addition of lime to farmyard manure might, to a certain extent, be defended. The experiment, however, would be a hazardous one and not to be recommended, as loss of ammonia would most likely ensue.

Action of Lime on Nitrogenous Organic Matter.

The action of lime on nitrogenous organic matter is of a very striking kind, and is by no means very clearly understood. As we have pointed out, it sometimes acts as an antiseptic or preservative; and this antiseptic or preservative action has been explained on the assumption that insoluble albuminates of lime are formed. Its action in such industries as calico-printing, where it has been used along with casein for fixing colouring matter; or in sugar-refining, where it is used for clarifying the sugar by precipitating the albuminous matter in solution in the saccharine liquor; or lastly, in purifying sewage,—has been cited in support of this theory. While, however, there may be circumstances in which lime, especially in its caustic form, acts as an antiseptic, its general tendency is to promote these fermentative changes, such as nitrification, so important to plant-life.

An important use of lime in agriculture is in preventing the action of certain fungoid diseases, such as "rust," "smut," "finger-and-toe," &c., as well as in killing, as every horticulturist and farmer knows, slugs, &c.

Recapitulation.

We may, in conclusion, sum up in a single paragraph the different ways in which lime acts. Its action is mechanical, chemical, and biological. It acts on the texture of the soil, rendering clay soils more friable, and exerting a certain binding effect on loose soils. It decomposes the minerals containing potash and other food-constituents, and renders them available for the plant's needs. It further decomposes organic matter, and promotes the important process of nitrification. It increases the power of a soil to fix such valuable food-constituents as ammonia and potash. It neutralises sourness, and prevents the formation of poisonous compounds in the soil. It increases the capillary condition of the soil, prevents fungoid diseases, and promotes the growth of the more nutritive herbage in pasture-land.



CHAPTER XXI.

INDIRECT MANURES—GYPSUM, SALT, ETC.

GYPSUM.

In the previous chapter mention was made of gypsum as a compound of lime, but no reference to its action as a manure was made. In the past, gypsum was used extensively and highly valued. It was found to be of especial value for clover; and there is a story told of Benjamin Franklin which illustrates the very striking nature of its action on this crop. It is related that he once printed with gypsum the words "This has been plastered" on a field of clover, and that for a long time afterwards the legend was plainly discernible on account of the luxuriance of the clover on the parts of the field which had been thus treated.

Mode in which gypsum acts.

Despite the fact that gypsum is a most ancient manure, it is only of late years that we have come to understand the true nature of its action. For long it was believed that the reason of its striking effect in promoting clover was due to the fact that, as clover was a lime-loving plant, the action of gypsum was owing to the lime it contained. That, however, the action of gypsum is not due to the fact that it supplies lime to the plant, seems evident when it is stated that were this so, any other form of lime would have the same beneficial effect. It is well known, however, that this is not so. Besides, as we have already pointed out, lime is not a constituent which most soils lack, so far as the needs of the crop are concerned. There is a certain amount of truth in the old belief that gypsum enriches the soil in ammonia by fixing it from the air. The power that gypsum has as a fixer of ammonia has already been referred to in the chapter on Farmyard Manure; but in this case the gypsum is brought in contact with the ammonia. The origin of this old belief was due to a misconception as to the amount of ammonia in the atmosphere. No doubt gypsum greatly increases the power of a soil to absorb ammonia from the air; but the quantity of ammonia in the air is so very trifling, that its action in this respect is hardly worth considering. The true explanation of the action of gypsum is to be found in its effect on the double silicates, which it decomposes, the potash being set free. Its action is similar to that of other lime compounds, only more characteristic. As a manure, therefore, its action is indirect, and its true function is to oust the potash from its compounds. Its peculiarly favourable action on clover is due to the fact that clover specially benefits by potash, and that adding gypsum practically amounts to adding potash. Of course it should be borne in mind that the soil must contain potash compounds if gypsum is to have its full effect. Now, however, that potash salts suitable for manuring purposes are abundant, it may well be doubted whether it is not better to apply potash directly. Further, it must be borne in mind that gypsum is applied to the soil whenever it receives a dressing of superphosphate of lime, as gypsum is one of the products formed by treating insoluble phosphate of lime with sulphuric acid.

It is possible that gypsum may act as an oxidising agent in the soil, just as iron in the ferric condition does. It has a large quantity of oxygen in its composition, and under certain conditions may act as a carrier of oxygen to the lower layers of the soil. When it is used, it should be applied some months before the crop is sown.

Gypsum, therefore, although it contains two necessary plant-constituents, lime and sulphuric acid, cannot be regarded as a direct manure; and as its action comes to be more fully understood, its use, which was never very abundant in this country, will probably decrease. We have already, in the chapter on Nitrification, referred to the action of gypsum in promoting nitrification.

SALT.

The action of salt as a manure presents a problem which is at once of the highest interest and surrounded with the greatest difficulties. In view of the large quantities now used for agricultural purposes, a somewhat detailed examination of the nature of its action is not out of place in a work such as the present.

Antiquity of the Use of Salt.

The recognition of the manurial functions of salt dates back to the very earliest times. Its use among the ancients is testified by numerous allusions in the Old Testament; while, according to Pliny, it was a well-known manure in Italy. The Persians and the Chinese seem also to have used it from time immemorial, the former more especially for date-trees.

Nature of its Action.

Despite, however, the great antiquity of its use, much difference of opinion seems always to have existed as to the exact method of its action, and as to its merits as a manure in promoting vegetable growth. It furnishes, in fact, a good example of the difficulty which exists in the case of many manures, whose action is chiefly indirect, of fully understanding their influence on the soil and on the crop. In fact, the action of salt is probably more complicated than that of any other manurial substance.

Salt not a necessary Plant-food.

We have already seen that neither sodium nor chlorine—the two constituent elements of salt—are in all probability absolutely necessary plant-foods. If they are necessary, the plant only requires them in minute quantities. Despite this fact, soda is an ash-constituent of nearly every plant, and in many cases one of the most abundant. In amount it is one of the most variable of all the ash-constituents, being present in some plants only in minute quantities, while in others it occurs in large quantities. Mangel and plants of the cabbage tribe may be cited as examples of plants containing large amounts of soda in their composition. But the plants which contain it in largest quantity are those which thrive on the sea-coast, and it has been thought that for them at least salt is a necessary manure. This, however, does not seem to be the case. In fact, the amount of soda in a plant seems to be largely a matter of accident. It may be added that the succulent portions of a plant are generally richest in soda.

Can Soda replace Potash?

Again, it has been believed that soda is capable of replacing potash in the plant; but this does not seem to be the case to any extent. The view that soda is able to replace potash, it has been thought, is supported by the variation which exists in the proportion of soda and potash in different plants. It must be remembered, however, that it is highly probable that most plants contain a larger quantity of ash-constituents than is absolutely necessary for their healthy growth. Especially is this the case with such a necessary plant-food as potash, of which there is generally present, in all likelihood, an excess. The variation in the quantity of potash and soda present in many plants under different circumstances can scarcely, therefore, be regarded as furnishing a proof of the replacement of potash by soda. Incidentally we may mention, as a fact worthy of notice, that cultivated plants have more potash and less soda in their composition than wild plants. What has been said of soda may be held to apply equally to chlorine, as it seems to be chiefly in the form of common salt that soda enters the plant. The amount of salt, therefore, present in plants must be regarded as largely accidental and dependent on external circumstances, such as the nature of the soil, &c.

Salt of universal Occurrence.

But even were salt a necessary plant-food, its occurrence in the soil is already of sufficient abundance to obviate any necessity for its application. It may be said to be of almost universal occurrence. Even the air contains it in traces. That this is the case in the neighbourhood of the sea-coast is well known; but even in air far inland, accurate analysis of the air would probably demonstrate its presence in greater quantity than is commonly believed. It is a wise provision that plants absorb salt, for it increases their efficiency as food,—the function of salt as a constituent of animal food being of the very highest importance. It is an indispensable food-ingredient for animal life. With regard to ordinary farm-stock, the amount of salt which naturally occurs in their food is quite sufficient. In the case, however, of pastures in countries far removed from the sea, the custom of specially supplying stock with salt is common. This is done by placing a piece of rock-salt in the fields.

Special Sources of Salt.

The salt of commerce is obtained from various sources. Besides the sea, we have ample sources of salt in the large saline deposits found in many parts of Europe, especially in Austria, and in England in Cheshire.

The Action of Salt indirect.

From what has been said above, it is clear that the action of salt as a manure is indirect and not direct. What the nature of that indirect action is we shall now proceed to discuss.

In considering the evidence of the manurial value of salt, we are at once brought face to face with the fact that the experience of its action in the past has as often been unfavourable as favourable. Salt, it is well known, is both an antiseptic and a germicide. It is, indeed, one of the most commonly used of preservatives. When applied in large quantities to the soil, it has a most deleterious action on vegetation. This hurtful action of salt has long been known; and it is as often mentioned in the writings of antiquity on account of its unfavourable as on account of its favourable action. Thus, for example, among the ancient Jews it was customary, after the conquest of a hostile town, to strew salt on the enemy's fields, for the purpose of rendering them barren and unfertile. And again, among the Romans, for the same purpose, salt was often spread on a spot where some great crime had been committed.

While, therefore, its unfavourable action has long been known, the fact that there are circumstances under which its action is, on the contrary, favourable for promoting vegetable growth has also been long recognised. The difficulty for the agricultural student is to reconcile these two seemingly contradictory experiences. For the English agriculturist the subject possesses especial interest, since in England it has been in the past most generally used and its action most discussed since the time of Lord Bacon, who discusses in his writings the action of solutions of it on different plants.

The true explanation of salt being so different in its action is to be found in the quantity applied, the nature of the soil, the crop to which it is applied, and the conditions under which it is applied—i.e., whether it is applied alone or along with other manures.

Mechanical Action on Soils.

In the first place, it must be noted that salt exerts a mechanical action on the soil of a very similar kind to that exercised by lime. When applied to clay soils it causes a flocculation or coagulation of the fine clay-particles, and thus prevents the soil from puddling to the same extent as would otherwise be the case. In fact, an example of this action of salt when in solution causing the precipitation of fine suspended clayey matter, is afforded by the formation of deltas at the mouths of rivers. The power of clarifying muddy water is common indeed to saline solutions. Schloesing attributes the clarifying power of a soil to the presence of the saline matters it contains; and from this point of view it would appear that manures containing any saline substance may exert an important mechanical influence on the soil.

Solvent Action.

But a much more important property of salt is its solvent action on the plant-food present in the soil. Its action in decomposing the minerals containing lime, magnesia, potash, &c., is similar to the action of gypsum. By acting upon the double silicates it liberates these necessary plant-foods. It is not only on the basic substances upon which it acts, but also on the phosphoric and silicic acids, which it sets free. Its power of dissolving ammonia from the soil is considerable. Experiments with a weak solution of salt on a soil by Peters and Eichhorn to test its solvent power, showed that the salt solution dissolved more than twice as much potash and nearly thirty times as much ammonia as an equal quantity of pure water did. When applied to the soil, it seems chiefly to liberate lime and magnesia. The exact nature of the chemical action taking place is a point of some dubiety. According to some, it is changed into nitrate of soda; according to others, into carbonate of soda. The latter theory seems to be the more probable one. Its action on the lime and magnesia compounds is to convert them into chlorides; and this chemical reaction explains the action that salt has in increasing the water-retaining and water-absorbing power of the soil; for the chlorides of magnesia and lime are salts which have a great power of attracting water from the air.

Again, the very fact that salt acts as an antiseptic may serve to explain its beneficial action in certain cases where it prevents rankness of growth. No doubt this was its function when applied along with Peruvian guano. This it might do by preventing too rapid fermentation (nitrification) of the manure, or by actually weakening the plant. Its action when applied with farmyard manure may also be similar. But while its effect in many cases may be towards retarding fermentation, on the other hand its action, when applied along with lime to compost-heaps, is towards promoting more rapid decomposition. Probably a reaction takes place between the lime and the salt, the result of which is the formation of caustic soda.

Such are some of the ways in which salt may act. It must at once be seen how its action in one case will be favourable and in another case unfavourable. There must be fertilising matter present in the soil if it is to act favourably. Again, it will only be under such circumstances, where rankness of growth is likely to ensue, that its antiseptic properties will act favourably and not unfavourably.

Best used in small Quantities along with Manures.

Probably it is for these reasons that its action has been found to be most favourable when applied along with other manures and not alone. Applied along with nitrate of soda, as is commonly done, it doubtless increases the efficiency of the nitrate. Some plants seem to be undoubtedly benefited by salt: of these flax may be mentioned. The application of salt to plants of the cabbage tribe seems also to be highly beneficial. On mangels, along with other manures, it has also been found to have a very favourable effect. But with many crops its action has been proved to be less favourable.

Affects Quality of Crop.

Although salt has often been found to increase the quantity of a crop, the quality of the crop has been made to suffer. Its action on beetroot has been more especially studied. The effect of its application is to lessen the total quantity of dry matter and sugar in the plant. This has been found to be the case both when the salt was applied alone and along with nitrate of soda and other manures. On potatoes, again, its action has been found to be deleterious, lessening their percentage of starch. The deleterious action of chlorides on the quality of potatoes is also seen when potassium chloride is applied. It is for this reason that potash should never be applied to the potato crop in the form of chloride.

In the late Dr Voelcker's opinion, the conditions under which salt had the most favourable action on the mangel crop was in the case of a light sandy soil, and applied at the rate of 4 to 5 cwt. per acre. Its action when applied to clay soils was not so favourable.

Rate of Application.

Lastly, the rate at which it may be applied will naturally vary. From 1 cwt. and even less, up to 6 cwt. or even more, has been the rate at which it has been commonly applied in the past. From what has been said, it will be seen that it is more likely to exert a favourable influence when applied only in small quantities.



CHAPTER XXII.

THE APPLICATION OF MANURES.

The conditions which regulate the application of manures are many and varied, and the subject, it must be admitted, despite the large amount of investigation already carried out, is most imperfectly understood. For these reasons it is impossible to do little more than lay down certain general principles which may be of service to the agriculturist in guiding him in carrying out the manuring of his crops.

Influence of Manures in increasing Soil-fertility.

In the first place it may be asked, How far can what we may call the permanent fertility of a field be influenced by the application of manures? And to this question the answer must be made, that the influence of manuring in increasing soil-fertility is very slight and only very gradually felt. This is illustrated by the difficulty experienced in attempting to restore to a fertile condition a soil which has long been treated by an exhaustive system of cultivation. In such a case it will be found impossible to restore the fertility of the soil, except very gradually. Farmers who farm in new countries, and in rich virgin soils, little realise sometimes how quickly they may impoverish the fertility of their soils by exhaustive treatment, and how slow the process of restoration is. Nor is this strange when we reflect on the relatively small quantities of fertilising ingredients we are in the habit of adding to the soil by the application of manures, and the nature of their action. The small rate at which they are applied, and the impossibility of distributing them equally in the soil, explain how comparatively limited their action must necessarily be. Some manures, it is true—viz., those which are soluble—are more equally distributed; but then such manures, from their very nature, are little likely to affect the permanent fertility of the soil.

Influence of Farmyard Manure on the Soil.

Of manures which have the best effect in improving a soil's permanent fertility, farmyard manure is undoubtedly the most important. This is owing partly to the fact that it is applied in such large quantities, and partly on account of its composition. Liberal manuring with farmyard manure, systematically carried out, will in time do much to build up a soil's fertility. But liberal manuring with artificial manures will also effect the same end. This it does in an indirect manner by means of the increased crop residues obtained under such treatment. Indeed one of the speediest methods of bringing a soil into good condition is by heavily manuring certain green crops, and then ploughing them in.

Farmyard Manure v. Artificials.

The question how far farmyard manure may be supplanted by artificials is one often discussed. We have already referred to this question in the chapter on Farmyard Manure. It is possible that, with our increasing knowledge of agricultural science, we may in the future be able to dispense with farmyard manure, and make shift to do with artificials alone. At present, however, all our experience points to the fact that the most satisfactory results are obtained from manures by using artificials in conjunction with farmyard manure. It is better both for farmyard manure and artificial manures to be applied together,[241] so that they may mutually act as supplementary the one to the other. While this is so, there may be circumstances in which it will be best to use artificials alone. Where, for example, fields, owing to their situation, are inaccessible, and where the expense of conveying the bulky farmyard manure would be very considerable, it may be found more economical to apply the more concentrated artificial manures. With few exceptions, however, it will be found most desirable to use artificial manures as supplementary to farmyard manure, and not as substitutes for it.

Farmyard Manure not favourable to certain Crops.

While the above is true, it may be well to point out one or two facts regarding the nature of the influence of farmyard manure on certain crops. For instance, it has long been recognised as inadvisable in strong rich soils to apply it directly to certain grain crops, such as barley and wheat, since such a practice is apt to encourage rankness of growth—an undue development of straw at the expense of the grain. It is consequently customary to apply farmyard manure to the preceding crop. The direct application of farmyard manure to wheat, however, according to Sir J. B. Lawes, is not fraught with unfavourable results where the soil is a light one; it is only when the soil is of a heavy nature that it is best to apply it to the preceding crop. Potatoes are another crop to which it is best not to apply it directly. On the other hand, many are of the opinion that mangels seem to be able to benefit from large applications of farmyard manure.

Conditions determining the Application of Artificial Manures.

In the application of artificial manures a large number of considerations have to be taken into account. Among these may be mentioned the nature of the manure itself, and its mechanical and chemical condition; the nature of the soil and its previous treatment with manures, as well as the nature of the climate, the nature of the crop, and the previous cropping. It may be well, therefore, to examine somewhat in detail some of these considerations.

Nature of the Manure.

Nitrogen, phosphoric acid, and potash exist in the common manures, as has already been pointed out, in different states of availability. Nitrogen, for example, may exist in a soluble or insoluble condition, as nitrates, as ammonia, or in various organic forms. Phosphoric acid, similarly, may exist in a soluble form, as it does in superphosphate of lime, or in an insoluble form, as it does in bones or basic slag. Potash, on the other hand, exists—or should exist—in artificial manures only in a soluble form. Now a correct knowledge of the behaviour of these different forms of the common manurial ingredients when applied to the soil is, in the first place, necessary for their successful and economical use.

Nitrogenous Manures.

Thus our knowledge of the inability of the soil-particles to retain nitrogen in the form of nitric acid, as well as our knowledge of the fact that nitrogen is in this form immediately available for the plant's needs, teaches us that nitrate of soda should never be applied before the plant is ready to utilise it—in short, that it should only be applied as a top-dressing; and further, that the use of such a fertiliser in a damp season is less likely to be economical than in a dry one. Again, with regard to nitrogen in the form of ammonia salts, our knowledge of the fact that ammonia is retained by the soil-particles, and that before it becomes available for the plant's needs it has to undergo the process of nitrification, teaches us the desirability of applying it a short time before it is likely to be used. While, lastly, with regard to the nitrogen in the various organic forms in which it occurs, our knowledge of the rate at which these are converted into an available form in the soil will determine when they are best applied. Some forms of organic nitrogen are in a soluble condition, and are quite as speedy in their action as sulphate of ammonia. This is the case with a considerable proportion of the different organic forms of nitrogen present in guano. Other forms of organic nitrogen are only slightly less so—as, for example, dried blood, which ferments very speedily. With regard, therefore, to nitrates and ammonia salts, as well as the more quickly available organic forms of nitrogen, they should either be applied as a top-dressing after the plant has started growth, or only shortly before seed-time. Bones, shoddy, and the various so-called native guanos, should be applied a considerable period before they are likely to be required—not later than the previous autumn.

Phosphatic Manures.

With regard to phosphatic manures the same considerations hold good. Inasmuch as phosphoric acid, whether applied in the soluble condition, as in superphosphate, or the insoluble form, as in bones, basic slag, &c., is not liable to be washed out of the soil, the risk of loss is very slight, and need not be taken into account. As we have pointed out in considering the action of superphosphate, phosphoric acid in this latter form is more speedily available to the crop, and the necessity of applying it much before it is likely to be used does not exist. Hence superphosphate and manures which contain any appreciable amount of soluble phosphoric acid, such as guano, should only be applied shortly before seed-time. Bones, basic slag, or mineral phosphate ought to be applied, on the other hand, a long time before they are likely to be used. Hence an autumn application is to be recommended in the case of such manures.

Potash Manures.

Lastly, with regard to potash manures, as these are soluble, there is no necessity for applying them much before they are likely to be absorbed by the plant. Some are of the opinion that potash is, except in the case of sandy soils, best applied some little time before it is likely to be used, so as to permit of its being washed down into the soil—a process which takes place only comparatively slowly. As potash manures have often been found to give a better result on pastures during the second year than during the first, they are best applied in the autumn.

The above statement as to the behaviour of the different fertilisers when applied to the soil, has a not unimportant bearing on the quantities in which they may safely be respectively applied. The rate at which manures may be applied depends, as we shall immediately see, on other conditions; but what it is here desirable to point out is, that it is not safe to apply such manures as nitrate of soda, or, for that matter, sulphate of ammonia, in large quantities at a time. In fact these manures, especially the former, will best be applied in very small quantities, and rather in several doses. With regard to other manures, more especially phosphatic manures, the same reasons for small application do not exist.

The truth of the above statements is so obvious that it may be regarded as superfluous to make them. As, however, their clear apprehension is essential to understanding the conditions of successful manuring, no apology need be made for making them.

Nature of Soil.

Another condition which has to be taken into account in considering the application of manures is the nature of the soil, as well as its previous treatment. Soils poor in organic matter are those which are most likely to be benefited by the application of nitrogenous manures. Soils of a dry light character require less phosphoric acid than they do of nitrogen and potash; while on a damp and heavy soil phosphatic manures are more likely to be beneficial than nitrogenous or potassic manures. Lastly, a soil rich in organic matter generally requires phosphates, and possibly potash. A point of considerable importance to notice is, that a soil rich in lime can stand a larger application of phosphoric acid than one poor in lime. As a rule, it will be found that the best results with potash will be obtained when applied to a sandy soil. The nature of the soil is an important consideration in determining how far it is advisable to apply readily soluble manures. To a very light and non-retentive soil the risk of loss in applying an easily soluble manure is considerably increased. The nature of the climate is also of importance. Thus, in a dry climate, manures of a soluble nature will have a better effect than in a wet climate, while the opposite will be the case with the more slowly acting manures.

Nature of previous Manuring.

A consideration of equal importance is the previous treatment of the soil with manure. For example, where a soil has been liberally treated with farmyard manure, it has been found that mineral manures have a very inferior effect to that obtained by nitrogenous manure. Lawes and Gilbert have found this to be strikingly the case in their experiments on the growth of wheat. In these experiments it was found that the application of mineral manures was accompanied with little or no benefit to the crop, whereas very striking results followed the application of nitrogen. This they attributed to the fact that the supply of mineral fertilisers in the straw of the farmyard manure is largely in excess of the supply of nitrogen. The nature of the action of the manure previously applied is also to be taken into account in determining how long its influence may probably last. Where, for example, the manure has been nitrate of soda or sulphate of ammonia, it may be safely concluded that its direct influence is no longer felt a year after application. The influence of superphosphate of lime, while scarcely so temporary, may be said to last only for a comparatively short time.[242] On the other hand, when the manure applied is of a slow-acting nature, such as bones or basic slag, its influence will probably be felt for a number of years.

Nature of the Crop.

But more important than any of the above-mentioned conditions is the nature of the crop itself. Our knowledge of the requirements of the different farm crops is still very imperfect. A very wide experience, however, of the effect of different manures on different crops, has conclusively proved that their manurial requirements differ very considerably. The subject is complicated by other considerations, such as the nature of the soil, &c.; but notwithstanding this fact, certain points seem to be pretty well established.

In seeking to understand the respective requirements of the different crops for different fertilisers, two important considerations must be borne in mind. These are—(1) the quantities of the three fertilising ingredients—nitrogen, phosphoric acid, and potash—which different crops remove from the soil; and (2) the different power crops possess of assimilating these ingredients.

Amounts of Fertilising Ingredients removed from the Soil by different Crops.

The most convenient way of instituting a comparison between the requirements of the different crops in this respect is by calculating the amount, in pounds, of nitrogen, phosphoric acid, and potash, which average amounts of the different crops remove per acre. The following table shows this for the common crops:—

FERTILISING INGREDIENTS REMOVED FROM SOIL. + -+ + Nitrogen. Phosphoric Potash. Acid. + -+ + Mangels {Root, 22 tons 87 36.4 222.8 {Leaf 51 16.5 77.9 - Total crop 138 52.9 300.7 -+ + Turnips {Root, 17 tons 63 22.4 108.6 {Leaf 49 10.7 40.2 -+ + Total crop 112 33.1 148.8 -+ + Beans {Grain, 30 bushels 77 22.8 24.3 {Straw 29 6.3 42.8 -+ + Total crop 106 29.1 67.1 -+ + Red clover hay, 2 tons 102 24.9 83.4 -+ + Swedes {Root, 14 tons 70 16.9 63.3 {Leaf 28 4.8 16.4 -+ + Total crop 98 21.7 79.7 -+ + Oats {Grain, 45 bushels 38 13.0 9.1 {Straw 17 6.4 37.0 -+ + Total crop 55 19.4 46.1 -+ + Meadow hay, 1-1/2 ton, 49 12.3 50.9 -+ + Wheat {Grain, 30 bushels 33 16.0 9.8 {Straw 15 4.7 25.9 -+ + Total crop 48 20.7 35.7 -+ + Barley {Grain, 30 bushels 35 16.0 9.8 {Straw 13 4.7 25.9 -+ + Total crop 48 20.7 35.7 -+ + Potatoes, 6 tons 47 21.5 76.5 -+ + Maize {Grain, 30 bushels 28 10.0 6.5 {Stalks, &c. 15 8.0 29.8 -+ + Total crop 43 18.0 36.3 + -+ +

From the table it will be seen that the crops which remove the largest quantities of all three fertilising ingredients are the root crops—mangels and turnips; that beans remove twice as much nitrogen as the cereals—oats, barley, and wheat—which, in this respect, practically differ very little from one another; while potatoes remove about the same quantity of nitrogen as the cereals. It will further be noticed that the amounts of phosphoric acid removed by the different crops differ very much less than those of nitrogen and potash. Mangels remove slightly more, and turnips slightly less, than double the amount removed by cereals. Meadow-hay, it will be seen, of all crops removes the least phosphoric acid.

In looking at the amounts of potash, we are at once struck by their great discrepancy. Such a crop as mangels removes more than six times as much potash from the soil as the cereals. Turnips also make large demands on this ingredient, removing over four times as much as the cereals. Leguminous crops, such as red clover and beans, remove about twice as much.

Capacity of Crops for assimilating Manures.

Instructive though these figures undoubtedly are, they must not be regarded, as often erroneously they are, as furnishing by themselves sufficient data upon which to base the practice of manuring. A consideration which is of much greater importance is the capacity that different crops possess for assimilating the various manurial ingredients from the soil. Considered from the point of view of absolute amount, there is in most soils an abundant supply of plant-food; but of this amount only a small proportion is available. Further, the amount of this available plant-food will vary with different crops—one crop being able to grow where another crop would starve. As illustrative of this, in the Norfolk experiments it was found that the turnip was able to assimilate potash from a soil on which the swede was practically starved. It is on this fact more than any other that the principles of manuring are based. Several explanations of the different capacities crops possess of assimilating their food may be put forward. And we may here point out that crops belonging to the same class exhibit, on the whole, a certain amount of similarity in their manurial requirements. Thus, for example, we may say that gramineous crops so far resemble one another in possessing small capacity for assimilating nitrogen, root crops for assimilating phosphoric acid, and leguminous crops for assimilating potash, and that, consequently, these crops are generally most benefited by the application, respectively, of nitrogen, phosphoric acid, and potash. But while a certain general resemblance exists, crops belonging to the same class differ in many cases very considerably, as we shall immediately see.

Difference in Root Systems of different Crops.

One explanation of the different capacity possessed by different crops for absorbing plant-food from the soil is to be found in the difference of their root systems. Every agriculturist knows that crops in this respect differ very widely. Crops having deep roots will naturally have a larger surface of soil from which to draw their food-supplies than crops having shallower roots. Such crops as red clover, wheat, and mangels are able to draw their food-supplies from the subsoil to an extent not possessed by shallower-rooted crops, such as barley, turnips, and grass. Crops having surface-roots, on the other hand, have often greater capacity for assimilating nitrogen,—this ingredient, as has already been pointed out, being chiefly located in the surface-soil. The tendency of growing shallow-rooted crops will therefore be towards impoverishing the surface-soil; whereas the occasional growth of a deep-rooted crop brings the plant-food in the subsoil into requisition. In this connection it may be well to draw attention to the singular capacity possessed by certain crops for absorbing nitrogen. Of these the case of clover is the most striking, and has long puzzled agriculturists. The discovery, which has been repeatedly referred to in these pages, that the leguminous order of crops, to which clover belongs, have the power of absorbing the free nitrogen of the air through the agency of micro-organic life in the plant and in the soil, has furnished an explanation of this long-debated problem.

Period of Growth.

A further reason is the difference in the period of a crop's growth. A crop which grows quickly, and consequently occupies the ground during a comparatively short period, will naturally require a richer soil, and therefore a more liberal treatment with manure, than one whose growth is more gradual.

Another consideration is the season of the year during which active growth of the crops takes place. For example, in the case of the wheat crop, active growth takes place in spring and ceases early in the summer. Since, however, nitrification goes on right through the summer, and nitrates are most abundant in the soil in late summer and autumn, such a crop as wheat is ill suited to obtain any benefit from this bountiful provision of nature, and is consequently particularly benefited by the application of nitrogenous manures. Root crops, on the other hand, sown in summer, continue their active growth into autumn, and are thus enabled to utilise the nitrates formed in the process of nitrification. The custom of sowing a quickly growing green crop, such as rye, mustard, rape, &c., after a wheat crop, is a practice which aims at conserving the nitrates and preventing their loss by autumn and winter rains. The name "catch crop" has been applied to such a crop. By ploughing under the green crop, the nitrogen removed from the soil in the form of easily soluble nitrates is restored in an insoluble organic form, and the soil is at the same time enriched by the addition of much valuable organic matter.[243]

It is chiefly the above facts that form the scientific basis of the long-pursued practice of the rotation of crops.

Variation in Composition of Crops.

A point of considerable interest is the influence exerted by manures on the composition of crops. It has been assumed in the preceding pages that the composition of crops of the same plant is uniform; but this is not strictly the case, as it has been proved that not merely the manure and soil have an appreciable influence on the crop's composition, but so also has the climate.

Absorption of Plant-food.

The laws regulating the absorption of plant-food are most interesting, although, unfortunately, very imperfectly understood as yet. The fertilising ingredients are capable of considerable movement in the plant, and are only absorbed up to a certain period of growth. This in many plants is reached when they flower. After this period they are no longer capable of absorbing any more food. The popular belief that plants in ripening exhaust the soil of its fertilising matters is consequently a fallacy.

Fertilising Ingredients lodge in the Seed.

The tendency of fertilising matters is to move upward in the plant as it matures, and finally to become lodged in the seed. It is for this reason that the cereals prove such an exhaustive crop. That nature, however, can in certain cases be very economical of her food-supplies, is strikingly illustrated by the fact that much of the fertilising matter contained in the mature leaves in autumn passes back into the tree before the leaves fall from it.

Forms in which Nitrogen exists in Plants.

The form in which nitrogen is present in the plant is chiefly as albuminoids. As, however, albuminoids belong to that class of bodies known as colloids, which cannot easily pass through porous membranes like those forming the walls of plant-cells, they are changed during certain periods of the plant's growth into amides, which are crystalloids, and consequently able to move freely about in the plant. Amides are most abundant in young plants during the period of their most active growth, and as the plant ripens the amides seem to be largely converted into albuminoids.

While the subject is not very clearly understood, it would seem to be pretty conclusively proved that there is a direct relation between the amount of the phosphoric acid and of the nitrogen absorbed.

Bearing of above Facts on Agricultural Practice.

The bearing of these facts upon practice is obvious. In the first place, they show how important it is that plants should be well fed when they are young, and that in the practice of green manuring it is best to plough in the crop when it is in flower, as no additional benefit is gained by allowing it to ripen, seeing that no further absorption of fertilising ingredients takes place after the period of flowering.

Influence of excessive Manuring of Crops.

The influence of large quantities of manures is seen in the case of certain root crops. It is found, in such a case, that while the roots are larger, they are more watery in composition and of less nutritive value. Again, it seems to be a fact pretty generally known to practical men, that nitrate of soda seems to have a bad effect on the quality of hay. It would seem, further, that the influence of nitrogenous fertilisers on cereals is to increase the percentage of nitrogen in the grain, but that they have no such influence in the case of leguminous crops. Phosphatic manures, on the other hand, in the case of leguminous crops, seem to have the effect of diminishing the amount of nitrogen in the seed.

FOOTNOTES:

[241] Though not necessarily at the same time or to each succeeding crop. There may be comparatively long intervals between the applications of farmyard manure in many cases.

[242] Of course what is meant here is the direct influence of such manures. Their indirect value may be shown in the soil by the increased crop residues they give rise to.

[243] This is very concisely and clearly put in Mr Warington's admirable 'Chemistry of the Farm.'



CHAPTER XXIII.

MANURING OF THE COMMON FARM CROPS.

In this chapter we shall attempt to summarise briefly the results of experiments on the manuring of some of the commoner crops, and we shall start with the manuring of cereals.

CEREALS.

As we have already pointed out, a certain similarity in the manurial requirements of the different members of this class exists. They are characterised, for one thing, by the comparatively small quantity of nitrogen they remove from the soil—less than either leguminous or root crops. Of this nitrogen the larger proportion—amounting to two-thirds—is contained in the grain, the straw only containing about a quarter of the total amount of nitrogen in the plant. The amount of phosphoric acid they remove from the soil is not much less than that removed by the other two classes of crops; but this, again, is also chiefly in the grain. It is on this account that the cereals may be regarded, in a sense, as exhaustive crops, seeing that the grain is almost invariably sold off the farm. But, on the other hand, owing to the comparatively small demands they make on fertilising ingredients, cereals will continue to grow on poor land for a longer period than most crops,—a fact of very great importance for mankind.

Especially benefited by Nitrogenous Manures.

Despite the fact that cereals remove comparatively little nitrogen from the soil, it is somewhat striking to find that they are chiefly benefited by the application of nitrogenous manures. This fact may be explained by the shortness of the period of their growth, and the fact that they assimilate their nitrogen in spring and early summer, and are thus unable to utilise to the full the nitrates which accumulate in the soil during later summer and autumn. As they seem to absorb their nitrogen almost exclusively in the form of nitrates, they are especially benefited by the application of nitrate of soda.

Power of absorbing Silicates.

A characteristic feature in the composition of cereals is the large amount of silica they contain. In common with the grasses, they seem to possess a power, not possessed by other crops, of feeding upon silicates.

The special manure, therefore, required for cereals is a nitrogenous manure, and that, as a rule, of a speedily available character, such as nitrate of soda or sulphate of ammonia. Furthermore, certain members of the group are also specially benefited by phosphatic manures.

We shall now consider individually a few of the more important cereal crops.

BARLEY.

Of cereal crops barley deserves to be considered first, owing to the fact that it is, of all grain crops, the most widely distributed. In England, in amount, it comes next to wheat among cereals. Its habits have also been studied in a very elaborate and careful manner, and have been made the subject of many experiments, both in this country and abroad.

Period of Growth.

The first point to notice about barley is the fact that its period of growth is a short one. This has a most important bearing on its treatment with manure. It may be said to ripen, on an average, in thirteen or fourteen weeks in this country; although in Norway and Sweden its period of growth is much less—viz., from six to seven weeks. Indeed no fewer than three crops have been obtained in one year in certain districts in these countries, and two crops are common. With regard to the period of its growth, it differs from wheat, which in its general manurial requirements it resembles. Wheat, which is largely sown in autumn, has four or five months' start of barley. From the fact that it is a short-lived crop, and that its roots are shallower than wheat, and draw their nourishment chiefly from the surface-soil, it benefits to a greater extent from liberal manuring than wheat, which is more independent of artificial supplies of fertilisers.

Most suitable Soil.

Again, while wheat does well on a heavy soil, and does not require a fine surface-tilth, barley does best on a light, rich, friable soil. It has, however, been very successfully grown on a heavy soil after wheat. Barley benefits more than wheat does from the application of superphosphate of lime, or some other readily available phosphatic manure. This may be accounted for by its shorter period of growth and shallower root system, which thus prevent it drawing much mineral sustenance from the subsoil. In fact, spring-sown crops, as a rule, benefit more from superphosphate than autumn-sown crops. The exhaustion of a soil under barley is essentially, as in the case of wheat, one of nitrogen, as Sir J. Henry Gilbert has pointed out.[244]

Farmyard Manure not suitable.

It has been urged, with some show of reason, that farmyard manure is not suitable for barley, as its action is too slow to have much influence on so short-lived a plant, and that only quick-acting manures should be used. Where farmyard manure is applied, it should be to the preceding crop; and this is advisable for more reasons than one.

Importance of uniform Manuring of Barley.

The use to which barley is put—viz., for malting purposes—renders the uniformity of its composition a point of great importance. Since its quality is very largely influenced by its treatment with manures, special care has to be exercised in their application. Grown as it generally is after roots, fed off with sheep, its quality, it is alleged, is apt to suffer from the unequal distribution of the manure applied in this way. It has consequently been recommended, in order to avoid this inequality, rather to grow a wheat crop immediately preceding the barley.

Norfolk Experiments on Barley.

Mr Cooke, in summing up the results of the interesting Norfolk experiments on barley, points out that in these experiments barley always was benefited by nitrogenous manures, sometimes by superphosphate of lime, and more rarely by potash; that of nitrogenous manures those of quickest action exerted the best influence. On an average it was found that 1 cwt. nitrate of soda per acre gave an increase of 8 bushels of barley, and 2 cwt. gave 14 bushels; while 3/4 cwt. sulphate of ammonia (i.e., the amount containing the same quantity of nitrogen as 1 cwt. nitrate of soda) gave only 5-1/2 bushels of an increase, and 1-1/2 cwt. (= 2 cwt. nitrate of soda) gave 10 bushels.

Mr Cooke recommends the following manures for the barley crop. From 1/4 to 1 cwt. of nitrate of soda, according to previous treatment of soil; from 1 to 2 cwt. super; and where it is required, from 1/2 to 1 cwt. muriate of potash.

Proportion of Grain to Straw.

Professor Hellriegel, the distinguished German investigator, has carried out most elaborate experiments on a small scale, with a view to investigating the habits of the barley plant. In the most perfectly developed of these plants, grown under the most favourable conditions, he found that the grain and straw were about equal in weight. Such a proportion of grain is, however, never realised in practice, the proportion of 2 of grain to 3 of straw being probably the common one.

WHEAT.

Wheat occupies the first position amongst cereals, in respect of extent of cultivation, in England. As a rule it is sown in autumn, although it is also sown in spring. It is generally taken after rotation grasses or a leguminous crop, such as peas or beans, or after potatoes or roots.

Unlike barley, it does best on a clay soil, or at any rate on a firm soil, and requires a moist seed-bed. From the fact that wheat is often sown after such a crop as potatoes or a root crop to which a liberal application of manure has been given, it is not so necessary to manure it except with a top-dressing of nitrate of soda. In short, it is usually considered highly desirable to get land into "good heart" before wheat, so that the wheat may obtain its nourishment from the residue of the previous crop and the farmyard manure previously applied.

Although, therefore, as a rule, the only manure it will be found necessary to add to wheat is a nitrogenous manure, such as nitrate of soda or sulphate of ammonia, still there are circumstances in which it will be well to supplement these by phosphatic or even potassic manures. On a light soil it may be advisable to add superphosphate of lime, guano, or bone-meal, in quantities of 2 to 3 cwt. per acre, in addition to a nitrogenous manure.

Rothamsted Experiments on Wheat.

Of experiments carried out on the growth of wheat, those which have now been in progress for over half a century at Rothamsted are the most valuable and famous. In these experiments the comparative value of nitrogen and mineral manures on this crop was strikingly exemplified. The former gave a most marked increase in the crop, while with the latter little or no increase was obtained. A combination of nitrogenous and mineral manures, on the other hand, gave the most striking results. An explanation of these results may be afforded by the fact that in ordinary farming an excess of mineral matter, as compared with nitrates, is returned to the soil in the crop residues and in the straw of the farmyard manure.

Of nitrogenous manures, nitrate of soda, on the whole, showed better results than sulphate of ammonia.

Continuous Growth of Wheat.

The possibility of growing fair crops of wheat year after year for fifty years on the same land, and that without any manure whatever, is among the most striking of the results of these famous Rothamsted wheat experiments.

Flitcham Experiments.

In conclusion, we may refer to Mr Cooke's Flitcham experiments. These were carried out for the purpose of ascertaining the most suitable manure for the wheat crop under different conditions.

It will be sufficient here to give the recommendations made by Mr Cooke as the practical outcome of these experiments.

He recommends the application of 10 tons of farmyard manure on light or mixed soils, after rotation seeds, ploughed in in the autumn, with from 1/4 to 1 cwt. of nitrate of soda, sown in the spring. In certain cases farmyard manure will be sufficient without the nitrate of soda. When farmyard manure is not available, the most effective and economical substitute is 4 cwt. per acre of rape-cake, ploughed in in the autumn, or 1 cwt. of sulphate of ammonia, sown in the spring, with, in either case, 1 cwt. of nitrate of soda as a spring top-dressing. In addition to the above, on land in doubtful agricultural condition, or exceptionally deficient in one or other of these ingredients, Mr Cooke recommends the addition of 2 cwt. superphosphate, or 1 cwt. muriate of potash, or both of these manures, ploughed or harrowed in in autumn.

OATS.

Like barley, oats are generally sown in spring, and, like barley, may be described as a shallow-rooted crop. They require, therefore, manures which are readily available, and their demands on the different fertilising ingredients are very similar to barley. The manures which will pay best, consequently, for oats, are nitrate of soda, used as a top-dressing, and superphosphate of lime, applied along with the seed. Probably upon no other crop is nitrate of soda so safe and so effective as upon oats. In some respects, however, oats differ strikingly from barley.

A very hardy Crop.

In the first place, oats are a much hardier crop than barley or wheat. They can grow on a wonderfully wide range of soil, and under comparatively adverse circumstances, both of climate and situation. They are better suited for a damp climate such as our own than a warm climate. They may be described as of all crops the least fastidious, and will flourish on sandy, peaty, or clayey soils. While this is so, they show a preference for soils rich in decayed vegetable matter. It is for this reason that they flourish so well on soils freshly broken up from pasture, and are often the first crop to be grown on such soils.

Require mixed Nitrogenous Manuring.

Stoeckhardt has found, in experiments on the manuring of the oat crop, that they greedily absorb nitrogen during nearly the whole period of their growth, and that, consequently, it is desirable to manure them with a mixed nitrogenous manure which shall contain nitrogen, both in a readily available form to supply the plant during the early stages of its growth, and in a less available form for the later stages of growth. He was of the opinion that in this way a continuous and satisfactory growth of the crop would be promoted.

Arendt's Experiments.

The oat-plant has been made the subject of many elaborate investigations. Of these, those carried out by Arendt are the most elaborate and best known. In these experiments the composition of the oat-plant at different stages of growth was investigated. It was found that the oat-plant increased during the whole period of its life, and that two-thirds of the nitrogen absorbed was absorbed during the later period of growth. It has since been shown, however, that the absorption of nitrogen is very much influenced by circumstances. Indeed its composition is peculiarly susceptible to the influence of manures, and especially the influence of weather. Thus Arendt found that the assimilation of nitrogen is checked by cold wet weather; while, on the other hand, it is promoted by warm dry weather. The grain of oats grown in warm seasons is better developed, and in composition more nutritious (i.e., contains more nitrogen), than that of oats grown in wet seasons, while the reverse is the case with the straw.

"Avenine."

A point of considerable interest in connection with the composition of oats is the fact that it contains a body which exerts a strikingly stimulating effect on the nervous system of the animal, and to which the name "avenine" has been given.

Quantities of Manures.

The quantities of manures which may be applied to the oat crop are similar in amount to those which ought to be applied to barley—from 1/2 to 1 cwt. of nitrate of soda, and from 2 to 3 cwt. superphosphate of lime. Very often, however, the oat crop receives directly little or no manure. In the Highland and Agricultural Society of Scotland's experiments, sulphate of ammonia was found to be of very much less value than nitrate of soda as a manure for oats. Potash manures, especially muriate of potash, had a very beneficial effect. The general conclusions drawn from these experiments were, that the treatment of the land should be such as to accumulate organic matter in it, to prevent too great a loss of moisture, and to provide the young plant with manures that come speedily into operation.

GRASS.

The manuring of grass is a question of very great interest and importance, but is, at the same time, beset with peculiar difficulties. Grass is grown under two conditions—first, that grown on soils exclusively set apart for its continuous growth (permanent pasture); and secondly, that grown for the purpose of being converted into hay and of providing pasture in the ordinary rotation of crops (rotation seeds). The manuring of the former is somewhat different from the manuring of the latter.

Effect of Manure on Herbage of Pastures.

The nature of the herbage growing on pasture is very much influenced by the manure applied. This, indeed, is one of the most noteworthy features connected with the manuring of grass, and has been especially observed in the Rothamsted experiments, where the influence of the different manures on the various kinds of herbage has been investigated with great care. The herbage constituting pasture is, as every farmer knows, of a varied description. We have in pastures a mixture of plants belonging both to the gramineous and leguminous classes, as well as a variety of weeds. Now the result of the application of different manures tends respectively to foster the different kinds of grasses. Thus when one kind of manure is applied, grasses of one kind tend to predominate and crowd out grasses of another. It has been found that the more highly pasture-land is manured the simpler is the nature of its herbage (that is, the fewer are the different kinds of herbage growing on it). Unmanured pasture, on the other hand, is more complex in its herbage. The result is, that the application of manure to pasture-land is attended with certain dangers. To maintain good pasture it is desirable to effect a proper balance between the different kinds of grasses. For this reason permanent pasture may be said to be, of all crops, the least commonly manured. As a rule it is only manured by the droppings of the cattle and sheep feeding upon it.

Influence of Farmyard Manure.

It is found that the influence of farmyard manure upon the composition of the pasture does not tend, to the same extent, to the undue development of one type of herbage over another; and in this respect it is probably to be preferred to artificial manures.

The same reasons, however, do not hold with regard to rotation seeds, where an abundant growth is desired, and complexity of herbage is not so important. A further reason which exists for the manuring of meadow-land is the greater impoverishment of the soil taking place under such conditions. As illustrating the influence of different manures on different kinds of herbage, it may be mentioned that in New England wood-ashes, a manure commonly used there, have been observed, when applied to pasture, to bring in white clover, and that the application of gypsum had the same effect. An explanation of this fact may be found in the influence of potash on leguminous crops. The chief value of wood-ashes as a manure is due to the large percentage of potash they contain, while the value of gypsum is probably to be accounted for by the fact that it has an indirect action, and sets free potash from its inert compounds in the soil. In the Rothamsted experiments this point has been verified, and potash has been shown to increase the proportion of leguminous plants on a grass-field. Nitrogenous manures, on the other hand, more especially sulphate of ammonia, have been found to increase the proportion of grasses proper, and to diminish the proportion of leguminous plants. The effect of farmyard manure, while less marked in inducing simplicity of herbage, has a similar effect to sulphate of ammonia; while phosphates and other mineral manures exercise an influence similar to that of potash. Mixtures of mineral and nitrogenous manures gave the largest returns obtained, but their influence was to increase the proportion of grasses proper. Sewage irrigation also tends chiefly to develop grasses.

Influence of Soil and Season on Pastures.

Manures are not the only factors influencing the quality of pastures. The nature of the soil, as well as the age of the pasture and the character of the season, exert a very considerable influence. Grass growing on damp or badly drained soil is invariably of poor quality, the coarser grasses predominating. Old pastures, again, are generally of better quality than new ones.

MANURING OF MEADOW-LAND.

Nitrate of soda is a common manure for grass grown for hay. It is often applied at the rate of 2 or 3 cwt. per acre. It is best, however, to apply it in smaller doses. On soils where lime is abundant, superphosphate may be applied, if necessary, at the rate of 2 or 3 cwt. per acre, or bones at a similar rate. Basic slag has been found to meet with good results as a manure for grass-land, especially where the soil is rich in organic matter.

Bangor Experiments.

Mr Gilchrist of University College, Bangor, as a result of numerous experiments carried out in different parts of Wales, recommends for rye-grass and clover hay on land in good condition 1 cwt. of nitrate of soda or sulphate of ammonia per acre, the former being applied about the middle of April, the latter during March. For land in poor condition, the addition of 2 cwt. of superphosphate is recommended—this to be applied some time between December and March. Farmyard manure may be usefully applied to young grass and clover seeds in the autumn, more especially on light soils. For meadow-land which is growing hay every year, Mr Gilchrist further recommends the following 4-course rotation of manuring:—

First year, 15 tons farmyard manure, applied in the autumn.

Second year, 1 cwt. nitrate of soda.

Third year, 4 cwt. basic slag or 3 cwt. superphosphate and 1 cwt. nitrate of soda.

Fourth year, 1 cwt. nitrate of soda.

Norfolk Experiments.

Mr Cooke, from his Norfolk experiments, recommends the following manures for rotation seeds:—

One to 1-1/2 cwt. nitrate of soda as a top-dressing in early spring. Where the clover plant is a good one, and it is particularly desired to cultivate it, he recommends as a dressing 1 cwt. of muriate of potash per acre, to be applied immediately after the clover is sown. The practice of dressing growing seeds in their first winter has, so far as the experiments in Norfolk go, less to recommend it than the earlier dressing.

MANURING OF PERMANENT PASTURES.

In this case the manure should be applied so as not to impair the quality of the herbage. Slow-acting manures are consequently best, such as basic slag or bones, which have been found to be of special value. On wet or marshy land after draining, lime is perhaps one of the best manures to apply in the first instance. As we have already said, farmyard manure will do more to maintain the quality of pasture than any kind of artificial manure. Mr Cooke is of opinion that no system of manuring yet discovered will both thicken and improve the herbage at all equally in success to the careful and regular feeding upon the grass of cattle or sheep, the animals having a good allowance of decorticated cotton-cake, or even of linseed-cake.

ROOTS.

Of all crops roots may be said to require the most liberal application of manure, and to respond most freely to it. They contain large quantities of the fertilising ingredients—nitrogen, phosphates, and potash—and may be regarded as exceedingly exhaustive crops. This is especially the case with regard to mangels, which make particularly large demands on a soil's fertilising ingredients.

Turnips are characterised by the large amount of sulphur they contain; and, according to some, this explains the beneficial effect which gypsum has when applied to them as a manure. This, however, is more probably to be explained by the indirect action of gypsum in setting free the potash of the soil. The fact that the successful cultivation of root crops depends on the application of large quantities of manure, is recognised in practice, as they receive the most manure of any crop of the rotation. Roots flourish best on a light soil which is neither too wet nor too dry; but with liberal manuring and careful tillage, they may be said to do well on any soil. Mangels are generally more benefited by the application of nitrogenous manures than are turnips or swedes, which, it would seem, have a greater power of absorbing nitrogen from the soil than the first-named crop; but it is a mistake to suppose that any of the root crops are not dependent on a ready supply of nitrogen; and the fact that large crops of turnips can often be grown by the application of superphosphate alone, may be taken as a proof that the soil contains plenty of nitrogen. Mangels are, from their deeper roots, more capable of drawing their supply of phosphoric acid from the soil than turnips. They respond, therefore, as a rule, less freely than turnips or swedes to an application of superphosphate. Generally speaking, we may say that the characteristic manure for turnips is superphosphate, and that for mangels is a nitrogenous manure such as nitrate of soda or sulphate of ammonia.

A special reason for manuring root crops is the fact that they are more liable to disease than other crops; and this is especially the case in the early stages of their growth. One of the great benefits conferred on the turnip crop by an application of superphosphate, is the help it gives the crop to pass safely the critical period of its growth. The superphosphate is best drilled in with the seed, in quantities varying from 3 to 5 cwt. In Scotland, it may be well to point out, the manure applied to this crop is very much in excess of the amount customarily applied in England; for in the former country larger applications of manure may be profitably employed. Roots generally receive a large dressing of farmyard manure. Salt has been found in some districts to have a very good effect on the mangel crop, and potash is often found to amply repay application.

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.