The Culture Of Vegetables And Flowers From Seeds And Roots Part 19

This is a subject worthy the attention of those who aim at the largest possible production and the highest possible quality of every kind of kitchen-garden crop, for it concerns the natural relations of the plant and the soil as to their several chemical const.i.tuents. The principle may be ill.u.s.trated by considering the demands of two of the most common kitchen-garden crops. If we submit a Cabbage to the destructive agency of fire, and a.n.a.lyse the ashes that remain, we shall find in them, in round numbers, eight per cent. of sulphuric acid, sixteen per cent. of phosphoric acid, four per cent. of soda, forty-eight per cent. of potash, and fifteen per cent. of lime. It is evident that we cannot expect to grow a Cabbage on a soil which is dest.i.tute of these ingredients, to say nothing of others. The obnoxious odour of sulphur emitted by decaying Cabbages might indicate, to anyone accustomed to reflect on ordinary occurrences, that sulphur is an important const.i.tuent of Cabbage. If we submit a Potato tuber to a similar process, the result will be to find in the ashes fifty-nine per cent. of potash, two per cent. of soda, six per cent. of sulphuric acid, nineteen per cent. of phosphoric acid, and two per cent. of lime. The lesson for the cultivator is, that to prepare a soil for Cabbage it is of the utmost importance to employ a manure containing sulphates, phosphates, and potash salts in considerable quant.i.ty; as for the lime, that can be supplied separately, but the Cabbage must have it. On the other hand, to prepare a soil for Potatoes it is necessary to employ a manure strongly charged with salts of potash and phosphates, but it need not be highly charged with soda or lime, for we find but a small proportion of these ingredients in the Potato. There are soils so naturally rich in all that crops require, that they may be tilled for years without the aid of manures, and will not cease to yield an abundant return. But such soils are exceptional, and those that need constant manuring are the rule. One point more, ere we proceed to apply to practice these elementary considerations. In almost every soil, whether strong clay, mellow loam, poor sand, or even chalk, there are comminglings of all the minerals required by plants, and, indeed, if there were not, we should see no herbage on the downs, and no Ivies climbing, as they do, to the topmost heights of limestone rocks. But usually a considerable proportion of those mineral const.i.tuents on which plants feed are locked up in the staple, and are only dissolved out slowly as the rain, the dew, the ever-moving air, and the sunshine operate upon them and make them available. As the rock slowly yields up its phosphates, alkalies and silica to the wild vegetation that runs riot upon it, so the cultivated field (which is but rock in a state of decay) yields up its phosphates, alkalies and silica for the service of plants the more quickly because it is the practice of the cultivator to stir the soil and continually expose fresh surfaces to the transforming power of the atmosphere. It has been said that the air we breathe is a powerful manure. So it is, but not in the sense that is applicable to stable manure or guano. The air may and does afford to plants much of their food, but it can only help them to the minerals they require by dissolving these out of pebbles, flints, nodules of chalk, sandstone, and other substances in the soil which contain them in what may be termed a locked-up condition. Every fresh exposure of the soil to the air, and especially to frost and snow, is as the opening of a new mine of fertilisers for the service of those plants on which man depends for his subsistence.

The application to practice of these considerations is an extremely simple matter in the first instance, but it may become very complicated if followed far enough. Here we can only touch the surface of the subject, yet we hope to do so usefully. Suppose, then, that we grow Cabbage, or Cauliflower, or Broccoli, on the same plot of ground, one crop following the other for a long series of years, and never refresh the soil with manure, it must be evident that we shall, some day or other, find the crop fail through the exhaustion of the soil of its available sulphur, phosphates, lime, or potash. But if this soil were allowed to lie fallow for some time, it would again produce a crop of Cabbage, owing to the liberation of mineral matters which, when the crops were failing, were not released fast enough, but which, during the rest allowed to the soil, acc.u.mulated sufficiently to sustain a crop.

Obviously this mode of procedure is unprofitable and tends of necessity to exhaustion, although it must be confessed that utter exhaustion of any soil is a thing at present almost unknown. But, instead of following a practice which impoverishes, let us enrich the soil with manure, and change the crops on the same plot, so that when one crop has largely taxed it for one cla.s.s of minerals, a different crop is grown which will tax it for another cla.s.s of minerals. Take for a moment's consideration one of the necessary const.i.tuents of a fertile soil, common salt (chloride of sodium). In the ash of a Cabbage there is about six per cent. of this mineral, in the Turnip about ten per cent., in the Potato two to three per cent., in the Beet eighteen to twenty per cent. On the other hand the Beet contains very little sulphur, but both Turnip and Beet agree in being strongly charged with potash and soda. It follows that if we crop a piece of ground with Cabbage, and wish to avoid the failure that may occur if we continue to crop with Cabbage, we may expect to do well by giving the ground a dressing of common salt and potash salts, and then crop it with Beet.

The whole subject is not exhausted by this mode of viewing it, for all the facts are not yet fully understood by the ablest of our chemists and physiologists, and crops differ in their methods of seeking nourishment.

We might find two distinct plants nearly agreeing in chemical const.i.tution, and yet one might fail where the other would succeed.

Suppose, for instance, we have grown Cabbage and other surface-rooting crops until the soil begins to fail, even then we might obtain from it a good crop of Parsnips or Carrots, for the simple reason that these send their roots down to a stratum that the Cabbage never reached; and it is most instructive to bear in mind that although the Parsnip will grow on poor land, and pay on land that has been badly tilled for years, yet the ashes of the Parsnip contain thirty-six per cent. of potash, eleven per cent. of lime, eighteen per cent. of phosphoric acid, six per cent. of sulphuric acid, three per cent. of phosphate of iron, and five per cent.

of common salt. How does the Parsnip obtain its mineral food in a soil which for other crops appears to be exhausted? Simply by pushing down for it into a mine that has. .h.i.therto been but little worked, though Cabbage might fail on the same plot because the superficial stratum has been overtaxed.

Having attempted a general, we now proceed to a particular application.

In the first place, good land, well tilled and abundantly manured, cannot be soon exhausted; but even in this case a rotation of crops is advisable. It is less easy to say why than to insist that in practice we find it to be so. The question then arises--What is a rotation of crops?

It is the ordering of a succession in such a manner that the crops will tax the soil for mineral aliments in a different manner. A good rotation will include both chemical and mechanical differences, and place tap-roots in a course between surface roots, as, for example, Carrot, Parsnip, and Beet, after Cabbage, Cauliflower, and Broccoli; and light, quick surface crops, such as Spinach, to serve as subst.i.tutes for fallows. The cropping of the kitchen garden should be, as far as possible, so ordered that plants of the same natural families never immediately succeed one another; and, above all things, it is important to shift from place to place, year after year, the Cabbages and the Potatoes, because these are the most exhaustive crops we grow. In a ton of Potatoes there are about twelve pounds of potash, four pounds of sulphuric acid, four pounds of phosphoric acid, and one pound of magnesia. We may replace these substances by abundant manuring, and we are bound to say that the best rotation will not obviate the necessity for manuring; but even then it is well to crop the plot with Peas, Spinach, Lettuce, and other plants that occupy it for a comparatively brief s.p.a.ce of time, and necessitate much digging and stirring; for these mechanical agencies combine with the manure in preparing the plot to grow Potatoes again much better than if the land were kept to this crop only from year to year. If we could mark out a plot of ground into four parts, we should devote one plot to permanent crops--such as Asparagus, Sea Kale, and Rhubarb--and on the other three keep the crops revolving in some such order as this: No. 1, Potatoes, Celery, Leek, Carrot, Parsnip, Beet, &c. No. 2, Peas, Beans, Onions, Summer Spinach, &c., followed by Turnips for winter use, Cabbage for spring use, and Winter Spinach. No. 3, Bra.s.sicas, including Broccoli, Brussels Sprouts, Kale, &c. In the following year the original No. 1 would be cropped as No. 2, and No. 2 as No. 3. In the third season corresponding changes would be made, const.i.tuting a three-course system. The cultivator must use discretion in cropping vacant ground. As an example it will be obvious that land cleared of Early Potatoes will be very suitable for planting Strawberries. Another point is worth attention: Peas sown on the lines where Celery has been grown will thrive without any preparation beyond levelling the ground and drawing the necessary drills. This is a West of England custom, and it answers exceedingly well.

THE CHEMISTRY OF GARDEN CROPS

A Consideration of the chemistry of the crops that engage attention in this country will afford an explanation of one great difference between farming and gardening. And this difference should be kept in mind by all cla.s.ses of cultivators as the basis of operations in tillage, cropping, and the order and character of rotations. The first thing to discover in the cropping of a farm is the kind of vegetation for which the land is best adapted to insure, in a run of seasons, fairly profitable results.

If the soil is unfit for cereals, then it is sheer folly to sow any more corn than may be needful for convenience, as, for example, to supply straw for thatching and litter, and oats for horses, to save cost of carriage, &c. On large farms that are far removed from markets it is often necessary to risk a few crops that the land is ill fitted for, in order to satisfy the requirements of the homestead, and to save the outlay of money and the inconvenience of hauling from distant markets.

But everywhere the cropping must be adapted to the soil and the climate as nearly as possible, both to simplify operations and enlarge to the utmost the chances of success. In the cropping of a garden this plain procedure cannot be followed. We are compelled certainly to consider what the soil and climate will especially favour amongst garden crops, but, notwithstanding this, the gardener must grow whatever the household requires. He may have to grow Peas on a hot shallow sand; and Potatoes and Carrots on a cold clay; and Asparagus on a shallow bed of pebbles and potsherds. To the gardener the chemistry of crops is a matter of great importance, because he cannot restrict his operations to such crops as the land is particularly adapted for, but must endeavour to make the land capable of carrying more or less of all the vegetables and fruits that find a place in the catalogue of domestic wants. That he must fail at certain points is inevitable; nevertheless his aim will be, and must be, of a somewhat universal kind, and a clear idea of the relations of plants to the soil in which they grow will be of constant and incalculable value to him.

We are bound to say at the outset that a complete essay on the chemistry of vegetation is not our purpose. We are anxious to convey some useful information, and to kindle sufficient interest to induce those who have hitherto given but slight attention to this question to inquire further, with a view to get far beyond the point at which we shall have to quit the subject.

Plants consist of two cla.s.ses of const.i.tuents--the Inorganic, which may be called the foundation; and the Organic, which may be considered the superstructure. With the former of these we are princ.i.p.ally concerned here. A plant must derive from the soil certain proportions of silica, lime, sulphur, phosphates, alkalies, and other mineral const.i.tuents, or it cannot exist at all; but, given these, the manufacture of fibre, starch, gum, sugar, and other organic products depends on the action of light, heat, atmospheric air, and moisture, for the organic products have to be created by chemical (or vital) action within the structure, or, as we sometimes say, the tissues of the plant itself. To a very great extent the agencies that conduce to the elaboration of organic products are beyond our control (though not entirely so), whereas we can directly, and to a considerable degree, provide the plant with the minerals it more particularly requires; first, by choosing the ground for it, and next by tilling and manuring in a suitable manner. A clay soil, in which, in addition to the predominating alumina, there is a fair proportion of lime, may be regarded as the most fertile for all purposes; but we have few such in Britain, our clays being mostly of an obdurate texture, retentive of moisture, and requiring much cultivation, and containing, moreover, salts of iron in proportions and forms almost poisonous to plants. But there are profound resources in most clays, so that if it is difficult to tame them, it is also difficult to exhaust them. Hence a clay that has been well cultivated through several generations will generally produce a fair return for whatever crop may be put upon it. Limestone soils are usually very porous and deficient of clay, and therefore have no sustaining power. Many of our great tracts of mountain limestone are mere sheep-walks, and would be comparatively worthless except for the lime that may be obtained by burning. On the other hand, chalk, which is a more recent form of carbonate of lime, is often highly productive, more especially where, through long cultivation, it has been much broken up, and has become loamy through acc.u.mulation of humus. Between the oldest limestone and the latest chalk there are many intermediate kinds of calcareous soils, and they are mostly good, owing to their richness in phosphates, the products of the marine organisms of which these rocks in great part, and in some cases wholly, consist. For the growth of cereals these calcareous soils need a certain proportion of silica, and where they have this we see some of the finest crops of Wheat, Trifolium, Peas and Beans in these islands.

If we could mix some of our obdurate clays with our barren limestones, the two comparatively worthless staples would probably prove remarkably fertile. Although this is impossible, a consideration of the chemistry of the imaginary mixture may be useful, more especially to the gardener, who can in a small way accomplish many things that are impracticable on a great scale. Sandy soils are characterised by excess of silica, and deficiency of alumina, phosphates and potash. Here the mechanical texture is as serious a matter as it is in the case of clay. The sand is too loose as the clay is too pasty, and it may be that we have to prevent the estate from being blown away. It is especially worthy of observation, however, that sandy soils are the most readily amenable of any to the operation of tillage. If we cannot take much out of them, we can put any amount into them, and it is always necessary to calculate where the process of enrichment is to stop. It is not less worthy of observation that sandy soils can be rendered capable of producing almost every kind of crop, save cereals and pulse, and even these can be secured where there is some basis of peat or loam or clay with the sand.

The parks and gardens of Paris, Versailles, and Haarlem are on deep sands that drift before the wind when left exposed for any length of time with no crop upon them; and not only do we see the finest of Potatoes and the most nutritious of herbage produced on these soils, but good Cauliflowers, Peas, Beans, Onions, fruits, and big trees of sound timber.

Garden soils usually consist of loam of some kind, the consequence of long cultivation. Natural loams are the result of the decay and admixture of various earths, and they are mostly of a mellow texture, easily worked and highly productive. They are, as a rule, the best of all soils, and their goodness is in part due to the fact that they contain a little of everything, with no great predominance of any one particular earth. Cultivation also produces loam. On a clay land we find a top crust of clayey loam, and on a lime or chalk land a top crust of calcareous loam. Where cultivation has been long pursued the staple is broken and manures are put on, and the roots of plants a.s.sist in disintegration and decomposition. Thus there is acc.u.mulation of humus and a decomposition of the rock proceeding together, and a loam of some sort is the result. Hence the necessity of caution in respect of deep trenching, for if we bury the top soil and put in its place a crude material that has not before seen daylight, we may lose ten years in profitable cropping, because we must now begin to tame a savage soil that we have been at great pains to bring up, to cover a stratum of a good material prepared for us by the combined operations of Nature and Art during, perhaps, several centuries. But deep and good garden soils may be safely trenched and freely knocked about, because not only does the process favour the deep rooting of the plants, but it favours also that disintegration which is one of the causes of fertility. Every pebble is capable of imparting to the soil a solution--infinitesimal, perhaps, but not the less real--of silica, or lime, or potash, or phosphates, or perhaps of all these; but it must be exposed to light and air and moisture to enable it to part with a portion of its substance, and thus it is that mechanical tillage is of the first importance in all agricultural and horticultural operations.

The princ.i.p.al inorganic or mineral const.i.tuents of plants are potash, soda, lime, iron, phosphorus, sulphur, chlorine, and silica. Clays and loams are generally rich in potash, sulphur, and phosphates, but deficient in soluble silica and lime. Limestone and chalk are usually rich in lime and phosphates, but deficient in humus, silica, sulphur, and alkalies. Sandy soils are rich in silica, but are generally poor in respect of phosphates and alkalies. Therefore, on a clay or loam, farmyard manure is invaluable, because it contains ingredients that all crops appreciate, and also because it is helpful in breaking up the texture of the soil. The occasional application of lime also is important for its almost magical effect on garden soil that has been liberally manured and heavily cropped for a long term of years.

Calcareous soils are greatly benefited by a free application to them of manure from the stable and cow-byre; but as a rule it would be like carrying coals to Newcastle to dress these soils with lime. Clay may be put on with advantage; and nothing benefits a hot chalky soil more than a good dose of mud from ponds and ditches, which supplies at once humus, alumina, and silicates, and gives 'staple' to the soil, while preventing it also from 'burning.' In the manuring of sandy soils great care is requisite, because of their absorbing power. In the bulb-growing districts of Holland, manure from cowsheds is worth an enormous price for digging into loose sand for a crop of Potatoes, to be followed by bulbs. Sandy soils are generally deficient in phosphates and alkalies; hence it will on such soils be frequently found that kainit (a crude form of potash) and superphosphate of lime will conjointly produce the best results, more especially in raising Potatoes, Onions, and Carrots, which are particularly well adapted for sandy soils. Probably one of the best fertilisers is genuine farmyard manure from stall-fed cattle, for it contains phosphates, alkalies, and silicates in available forms. For similar reasons Peruvian Guano is often useful on such soils. Artificial manure should be selected with a view to correct the deficiencies of the soil, and to satisfy the requirements of the crops to be grown on it.

While we have thus dealt princ.i.p.ally with the Inorganic or mineral const.i.tuents of plants, and the way in which the deficiencies of the soil in respect of any of them may be supplied by artificial applications, we must not ignore the other cla.s.s of const.i.tuents, the Organic. These are supplied almost entirely from the atmosphere itself, though, to a limited extent, the presence in the soil of humus or vegetable matter contributes also. Yet this latter, as seen in the case of land heavily dressed with farmyard or stable manure, vegetable refuse, &c, exercises important functions in other directions. Not only are mineral const.i.tuents, in forms available for a.s.similation, supplied, but soils so treated derive peculiar advantages as regards their mechanical state and improved physical conditions, chiefly in respect of retention of moisture, warmth, &c. Thus, sandy soils, which are very apt, through poverty in humus, to lose their moisture readily and to 'burn,' are rendered more retentive of moisture and fertilising const.i.tuents by the use of farmyard manure, &c., and have more 'staple'

or substance given to them, while heavy, tenacious clays are opened out, lightened, and rendered more amenable to the influences of drainage, aeration, &c., and so become less cold and inactive.

For the present purpose the princ.i.p.al garden crops may be grouped in two cla.s.ses, in accordance with their main characteristics and the predominance of certain of their mineral elements. The figures given on the following page show the average percentage proportions of the several minerals in the ashes of the different plants.

In Cla.s.s I. Phosphates and Potash predominate. This cla.s.s consists of the less succulent plants, and includes the following: The Pea: containing, in 100 parts of the ashes, phosphates, thirty-six; potash, forty. Bean: phosphates, thirty; potash, forty-four. Potato (tubers only): phosphates, nineteen; potash, fifty-nine; soda, two; lime, two; sulphuric acid, six. Parsnip: phosphates, eighteen; potash, thirty-six; lime, eleven; salt, five. Carrot: phosphates, twelve; potash, thirty-six; soda, thirteen; sulphuric acid, six. Jerusalem Artichoke: phosphates, sixteen; potash, sixty-five.

In Cla.s.s II. Sulphur, Lime and Soda Salts are predominant. This cla.s.s consists of the more succulent plants, and includes the following: Cabbage: containing, in 100 parts of the ashes, phosphates, sixteen; potash, forty-eight; soda, four; lime, fifteen; sulphuric acid, eight.

Turnip: phosphates, thirteen; potash, thirty-nine; soda, five; lime, ten; sulphuric acid, fourteen. Beet: phosphates, fourteen; potash, forty-nine; soda, nineteen; lime, six; sulphuric acid, five.

As a matter of course, Lentils and other kinds of pulse agree more or less with Peas and Beans in the predominance of phosphates and potash.

So, again, all the Bra.s.sicas, whether Kales, Cauliflower, or whatever else, agree nearly with the Cabbage in the prominent presence of lime and sulphur; ingredients which fully account for the offensive odour of these vegetables when in a state of decay. Fruits as a rule are highly charged with alkalies, and are rarely deficient in phosphates; moreover, stone-fruits require lime, for they have to make bone as well as flesh when they produce a crop. As regards the alkalies, plants appear capable of subst.i.tuting soda for potash under some circ.u.mstances, but it would not be prudent for the cultivator to a.s.sume that the cheaper alkali might take the place of the more costly one as a mineral agent, for Nature is stern and constant in her ways, and it can hardly be supposed that a plant in which potash normally predominates can attain to perfection in a soil deficient in potash, however well supplied it may be with soda. The cheaper alkali in combination as salt (chloride of sodium) may, however, be usually employed in aid of quick-growing green crops; and more or less with tap-roots and Bra.s.sicas. Salt, too, is very useful in a dry season by reason of its power of attracting and retaining moisture. As regards Potatoes, it is worthy of observation that they contain but a trace of silica, and yet they generally thrive on sand, and in many instances crops grown on sand are free from disease and of high quality, although the weight may not be great. The mechanical texture of the soil has much to do with this; and when that is aided by a supply of potash and phosphates, whether from farmyard manure or artificials, sandy soils become highly productive of Potatoes of the very finest quality. On the other hand, Potatoes also grow well on limestone and chalk, and yet there is but little lime in them. Here, again, mechanical texture explains the case in part, and it is further explained by the sufficiency of potash and phosphates, as also of magnesia, which enters in a special manner into the mineral const.i.tution of this root.

Thus far we have not even mentioned nitrogen, or its common form of salts of ammonia; nor have we mentioned carbon, or its very familiar form of carbonic acid. These are important elements of plant growth; and they account for the efficacy of manures derived directly from the animal kingdom, as, for example, the droppings of animals, including guano, which consisted originally of the droppings of sea-birds. Some of the nitrogen in these substances, however, is of an evanescent character, and rapidly flies away in the form of carbonate of ammonia; hence, a heap of farmyard manure, left for several years, loses much of its value as manure, and guano should be kept in bulk as long as possible, and protected from the atmosphere, or its ammonia will largely disappear. One difficulty experienced by chemists and others in preparing artificial manures is that of 'fixing' the needful ammonia, so that it may be kept from being dissipated in the atmosphere, and at the same time be always in a state in which it can be appropriated by the plant. In all good manures, however, there is a certain proportion of it in combination, and in many instances the percentage of nitrogen is made the test of the value of a manure.

The importance of humus--the black earthy substance resulting from the decay of vegetation--in a soil is that it contains in an a.s.similable form many of the ingredients essential to plant life. Humus when it decomposes gives off carbonic acid, which breaks up the mineral substances in the soil and renders them available as plant food. When vegetable refuse is burned, the nitrogen--one of the costliest const.i.tuents--is dissipated and lost. But by burying the refuse the soil gets back a proportion of the organic nitrogen it surrendered and something over in the way of soluble phosphatic and pota.s.sic salts; and as this organic nitrogen a.s.sumes ultimately the form of nitric acid, it can be a.s.similated by the growing plant, to the great benefit of whatever crop may occupy the ground.

The practical conclusion is, that in the treatment of the soil a skilful gardener will endeavour to promote its fertility by affording the natural influences of rain, frost and sun full opportunity of liberating the const.i.tuents that are locked up in the staple; by restoring in the form of refuse as much as possible of what the soil has parted with in vegetation; and by the addition of such fertilising agents as are adapted to rectify the natural deficiencies of the soil. Thus, instead of following a process of exhaustion, the resources of the garden may be annually augmented.

ARTIFICIAL MANURES AND THEIR APPLICATION TO GARDEN CROPS

Plants, like animals, require food for their sustenance and development, and when this is administered in insufficient quant.i.ties, or unsuitable foods are supplied, they remain small, starved, and unhealthy.

The chemical elements composing the natural food of ordinary crops are ten in number, viz.--carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, pota.s.sium, calcium, magnesium, and iron. These are obtained from the soil and air, and unless all of them are available plants will not grow. The absence of even one of them is as disastrous as the want of all, and a deficiency of one cannot be made up by an excess of another; for example, if the soil is deficient in pota.s.sium the crop suffers and cannot be improved by adding iron or magnesium. All the food-elements are found in adequate quant.i.ties in practically all soils and the surrounding air, except three--nitrogen, pota.s.sium, and phosphorus. These are often present in reduced amount, or in a state unsuited to plants; in such cases the deficiency must be made up before remunerative healthy crops can be grown, and it is with this express object that manures are added to the soil.

One of the best known substances employed in this way is farmyard manure, which is indirectly derived from plants and contains all the elements needed for the growth of crops. It is, however, of very variable composition and rarely, or never, contains these elements in the most suitable proportions, and its value can always be greatly improved by supplementing its action with one or other of the so-called artificial manures or fertilisers. Although it is strongly advisable to add farmyard manure or vegetable composts to the soil of all gardens now and again, in order to keep the texture of the soil in a satisfactory condition, excellent crops can be grown by the use of artificial fertilisers alone. To obtain the best results from these some experience is of course necessary, but the following details regarding the nature and application of the commoner and more useful kinds should prove a serviceable guide in the majority of cases.

Artificial manures may be divided into three cla.s.ses:--

1. The Nitrogenous cla.s.s, of which nitrate of soda and sulphate of ammonia are examples.

2. The Phosphatic cla.s.s, such as superphosphate, basic slag, and steamed bone flour.

3. The Potash cla.s.s, including kainit and sulphate of potash. The several examples of each cla.s.s contain only one of the three important plant food-elements, and as a single element can only be of use when the others are present in the soil, it is generally advisable to apply one from each cla.s.s, either separately or mixed, in order to insure that the crop is supplied with nitrogen, phosphates, and potash.

==Nitrogenous manures== specially stimulate the growth of the foliage, stems, and roots of plants, and are therefore of the greatest benefit to Carrots, Parsnips, Turnips, Beet, Celery, Asparagus, Rhubarb, all the Cabbage tribe, and leafy crops generally.

=Nitrate of soda= supplies the single plant food-element, nitrogen, and the soda for all practical purposes may be disregarded. It dissolves very easily in water and is taken up immediately by growing plants, its effect being plainly seen a few days after application. As this artificial readily drains away from uncropped land it should only be administered to growing plants. It is best applied in spring and summer and in small quant.i.ties; for example, at the rate of one pound per square rod, repeated at intervals of two or three weeks, rather than in a single large dose. Nitrate of soda must not be mixed with superphosphate, but it may be added to basic slag and the potash manures.

=Sulphate of ammonia= is another nitrogenous fertiliser, similar in its effects to nitrate of soda, but slower in action since its nitrogen must undergo a change into nitrate before it is available for plants. It is held by the soil, and can therefore be applied earlier in spring than nitrate of soda without fear of loss. The continued use of this manure, however, is liable to make the soil sour, and consequently it should only be employed on ground containing lime, or to which lime has been added. Never mix sulphate of ammonia with basic slag or with lime, but it may be mixed with superphosphate and the potash manures.

==Phosphatic manures== have the opposite effect to the nitrogenous fertilisers, checking rampant growth and encouraging the early formation of flowers, fruit, and seeds. They are comparatively inexpensive and should be liberally applied to all soils for all crops.

=Superphosphate= is an acid manure and best suited for use on soils containing lime. =Basic slag= is a better material for ground deficient in lime, or where 'club-root' is prevalent. It is less soluble and therefore slower in action than superphosphate. Both these fertilisers should be dug into the soil some time before the crop is planted or seed sown--superphosphate at the rate of two to three pounds per square rod; basic slag in larger amount, five to six pounds per square rod.

Superphosphate may also be employed as a top-dressing and worked into the surface around growing plants with the hoe. =Steamed bone meal= or =flour= is another useful phosphatic fertiliser, valuable on the lighter cla.s.ses of soil.

==Potash manures== are of benefit to plants in all stages of growth. They are particularly valuable to Potatoes, leguminous crops, Carrots, Parsnips, Turnips, and Beet. Like the phosphatic manures they should be worked into the soil before seeds are sown or plants are put out.

=Kainit= is best applied in autumn, for it contains a considerable amount of common salt and magnesium compounds which are sometimes deleterious and best washed away in the drainage water during winter. It should be dug in at the rate of about three pounds per square rod.

=Sulphate of potash= is three or four times as rich in potash as kainit, and is correspondingly more expensive; apply in spring and summer, a little in advance of sowing or planting, at the rate of about one pound per square rod.

==Lime==.--- A word or two must be said about lime, which is a natural const.i.tuent of all soils. In many instances there is sufficient for the needs of most plants, but where lime is deficient in quant.i.ty it must be added before healthy crops can be raised. Old gardens to which dung has been freely applied annually require a liberal dressing of lime every few years, or the ground becomes sour and incapable of growing good crops of any kind. To insure the proper action of whatever manures are used and to secure healthy crops, an application of slaked quicklime, at the rate of fourteen to twenty pounds per square rod, is strongly recommended. As a remedy against 'clubbing' or 'finger-and-toe' disease of the Cabbage tribe of plants it is indispensable; it also neutralises the baneful acidity of the land, and opens up stiff soils, making them more easily tilled, more readily penetrated by the air, and warmer by the better drainage of water through them.

The following suggestions for the manuring of the different crops mentioned will be found effective. It is, however, not intended that they should be slavishly followed, for useful subst.i.tutions may be made in the formulae given, if the nature of the various fertilisers is understood and an intelligent grasp is obtained of the principles of manuring enunciated in this and the preceding chapter.

In place of nitrate of soda, a similar quant.i.ty of sulphate of ammonia may be used.

Instead of superphosphate, the following may be advantageously employed: phosphatic guano, or mixtures of basic slag and superphosphate, or bone meal and superphosphate; or basic slag may be applied alone on land deficient in lime.

Four pounds of kainit may also take the place of one pound of sulphate of potash in the suggested mixtures mentioned below.