Manures and the principles of manuring

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:—

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:

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.