A popular treatise on agricultural chemistry : intended for the use of the practical farmer

Preface

The reasons which have induced me to publish the following treatise are, a desire to supply a want extensively present amongst Agriculturists, for such general knowledge connected with chemistry as may assist them in their various operations, and also the belief that no work of the kind at present exists, in which the subject chosen is either so fully explained or so well adapted for general perusal.

Until a very recent period, great doubt has existed amongst all writers on Agricultural Chemistry, as to the manner in which plants assimilate the matter composing their structure, not to mention the source from which these matters are derived. In the following pages I have endeavoured to explain these hitherto mysterious operations of nature, in such a way as to be of easy comprehension to all who will take the trouble to investigate the subject.

I must, however, disclaim all merit to myself for any discoveries on the subject, all the knowledge I possess has been derived from the works of Davy, Liebig, Daubeny and Johnson ; and to all those who may wish to pursue

IV PREFACE.

this science farther the above works are confidently recommended, especially Liebig's profound work " On Organic Chemistry, as applied to Agriculture," which contains all that is at present known on the subject, and in which the important discoveries announced are only equalled by the happy manner in which they are illustrated.

It must be permitted to me again to notice that my object in compiling the following pages, has been a desire to convey such information to the Agriculturist as may be found on trial to assist him in his pursuits, and to explain the rationale of some of the processes nature employs in the Vegetable Kingdom — with what success, it is for the reader to determine. With this intention, and this only, have I thrown together the following matter ; and the little merit, if any, to which I may be entitled, must arise from the circumstance of my having in some measure simplified a subject, which, in its usual form, is too abstruse for the general reader.

Salisbury,

November. 1841.

AGRICULTURAL CHEMISTRY.

Introduction

mm'

The subject of the following treatise, is an endeavour to explain, in a familiar manner, the processes nature carries on in the assimilation of the various substances employed in the growth and nutrition of plants.

Until a very recent period the consideration of this subject has been too generally deemed, if not altogether beyond the range of the agriculturist, at all events, as so distantly connected with him, as to be of little direct importance. And although at various periods men, eminent for their talents, and for the successful application of those talents to agriculture, have called the attention of the public to this subject; their endeavours have too often been of little avail, and the application of science to agriculture has been almost entirely neglected.

Now, however, we date from a new era. A variety of circumstances have of late combined, to compel a greater attention on the part of all 2 b INTRODUCTION.

classes to this important study. And the result is, that agriculture as a science has advanced with rapid strides, from darkness to comparative light; and from being the occupation of the lowest class in society, to one that is regarded, and justly so, as affording a field for the employment of the highest intellect; and happily also one in which the greatest exertions may be the most beneficially employed.

The impetus that this science has received may be safely committed, for its farther improvement, to the energy that now pervades the agricultural classes, in the full assurance that no exertions will be spared to carry it out to the fullest extent. The only thing necessary is to convey such information to the agriculturist, as shall tend to elucidate the operations of nature, and thus direct his energies in the right path.

It has hitherto, unfortunately, been too much the habit to consider a knowledge of chemistry necessary, only to those connected in some way or other with the practice of medicine. That such an opinion is founded in error few, in the present day, will be disposed to deny — but when we reflect that no change of any kind in any substance whatever, organized or unorganized, can take place, without such change being governed by chemical laws, — it will be at once admitted, that the study of chemistry is absolutely essential to enable us to understand either the bodies themselves, or the changes they may undergo.

Chemistry, is indeed the universal science;

it concerns every one, and every one ought to study its principles. To every branch of the manufactures of this country, this knowledge has been of the most essential importance : overcoming difficulties hitherto deemed insurmountable; opening new sources of employment, where none had previously existed; improving others to such an extent, that the different productions would scarcely be recognised as belonging to the same class, and lastly, doing all these things so much better and so much cheaper than by the old processes, that the national wealth has thereby been immensely increased, and comforts and even luxuries have been brought within the means of all classes.

It can hardly be necessary to cite examples in which chemistry has produced these results. We have only to look at the various manufactures of iron, glass, porcelain, the powers of steam, and galvanism — destined to surpass steam in its effects, the discovery of the Davy lamp, &iG. to be convinced of the benefits che-. mistry has conferred on mankind, and of its importance as a general study.

And if this knowledge is beneficial to the generality of persons, of what paramount importance must it be to the agriculturist, whose every act entails a chemical operation, and who, unless he is enabled in some measure to understand the cause and effect of these changes, will be pursuing his avocation almost by chance, or at least without the means of availing himself of many advantages that may offer ; and farther, when we consider the important interests that are committed to the cultivator of the soil, — that from him and his exertions all earthly beings derive their support, either directly or indirectly ; that the productions of the earth constitute the vast majority of the luxuries and comforts we possess ; that commerce depends almost wholly on agriculture, in its various branches, for its support; that the happiness and comfort of millions is dependent on the production of the earth, and that human happiness is increased or diminished as the supply of food is abundant or otherwise, we have every stimulus to apply our best energies to the cultivation of the soil, independently of the pleasure and satisfaction with which the study of nature is always accompanied, and the individual benefits we derive therefrom.

It may not, after what has already been stated, be deemed necessary to point out in what particular instances chemistry has benefited agriculture ; but still, as some persons may not see the direct and immediate connexion that exists between these sciences, (at the risk of being considered somewhat tedious,) it is suggested, for their consideration, that the analysis of soils is peculiarly a chemical operation, and that as each individual plant requires for its perfection certain substances, the analysis of the soil in which they grow is the only way to discover if such substances are present, and if not, of indicating, what particular one is wanting, which, when discovered, may be supplied by the knowledge chemistry gives us 01 other substances which may contain it.

This is, perhaps, the most important feature of chemistry as applied to agriculture, but still in its subordinate functions of enabling us to discover the elements and consequent value of refuse matters, it may be regarded as a valuable accessory to the farmer, to say nothing of its importance in pointing out remedies for such minor matters as the prevention of smut in corn, by the use of sulphate of copper — the preservation of plants by the galvanic battery— the preservation of timber by the process of kyanising, &c. all of which are of considerable value in their various applications.

To these facts may be added instances, where a knowledge of chemistry has created a new branch of trade entirely for the agriculturist, when if such knowledge had not existed, serious consequences would have ensued. The manufactures of sugar and saltpetre in France during the revolutionary war are the instances alluded to, and the circumstances which led to tlieir introduction there are briefly these:—-' That vvlien France had lost all her colonies and when her coasts were held in a state of strict blockade by the fleets of England, the supply of sugar necessarily failed. It was then that the chemists to whom the Government applied in their emergency, pointed out that sugar might be obtained from the grape and subsequently from the beet root, and to

2* such an extent was this manufacture carried, that France, until a recent period (1834,) was supplied exclusively by her home manufacture."

Again, the same causes prevented France from receiving a supply of saltpetre for the manufacture of gunpowder, but the same energy which induced the home manufacture of sugar, found a means of making saltpetre from the refuse matter of farm-yards; and so great was the supply from this source that it enabled France to maintain her gigantic struggle for the subjugation of Europe, for a protracted period, with unimpaired vigour, when, had not such means been discovered, she must have submitted to what she would have considered a disgraceful peace.

Again, chemistry enables us at once to test the real value of any given substance, without the uncertainty and loss of time attendant on a trial ; and when it is considered how much time must have been lost, how unsatisfactory the results must repeatedly have been, when no such knowledge existed whereby to certify the progress of discovery ; the value of this science may in some measure be estimated.

Other instances might be adduced, if necessary, but enough has been said to show the intimate connexion which ought to exist between chemistry and agriculture. Indeed, the knowledge of the one is essential to success in the other ; and it is hoped that the spirit of inquiry which now exists universally, will induce the establishment of Agricultural Colleges, where young men, after having completed their education, as far as the routine and practical information necessarily connected with farming is concerned, may spend a few months in the acquisition of such chemical knowledge for the analysis of the various soils and products, as will prove benelicial to themselves as well as the community at large.

In the following pages it is intended to explain, as far as our knowledge already extends, the manner in which plants assimilate their food and the sources of its supply. To do this, some preliminary knowledge is necessary ; it is therefore proposed to consider the subjects in the following order.

First — The structure and functions of the different parts of plants.

Second — The general attributes of the soil.

Third — The simple bodies forming the structure of the plant, the sources from which they are obtained, and the manner in which they are assimilated.

And lastly — The specific action of the various manures now in use.

In considering these subjects, it will be assumed that the reader has no previous knowledge of the question. No apology is therefore offered for the elementary character which each chapter will exhibit. It has been the desire of the writer to explain every circumstance as fully as possible, and although the use of technical terms is necessarily unavoidable in such a work, still a moderate degree of attention will overcome all the difficulties, and it is hoped that the information afforded, is of that kind, that no one will regret the trifling efforts it may have cost him to overcome them.

Chapter II, Dn The Structure And Functions Of The Different Parts Of Plants

The first step, necessary to the proper comprehension of the processes nature employs in the assimilation and growth of plants is a perfect knowledge of the organs each plant possesses, and the functions these organs perform in the development of the different parts of the vegetable structure.

Without such knowledge it will be impossible to understand how plants derive their nutriment from the air and the soil, and indeed it is and must be the basis of all information on the subject.

It is proposed, therefore, to give such a general description of the functions of each organ of plants, as connected with the assimilation of their various component parts, before proceeding to the consideration of the matter so assimilated.

It is first necessary to note, that certain conditions are as necessary in the vegetable as in the animal kingdom for the development of a perfect plant.

In the latter case a due supply of fresh air.

14 STRUCTURE AND FUNCTIONS

food and liquid of some kind are the essentials necessary for the sustenance of animal life, and should but one of these be wanting, although the other two may be supplied in excess, death will ensue. So it is with plants; certain conditions are necessary to bring them to maturity, and those of each genus require a peculiar treatment to bring them to perfection; and it is the study of these peculiar conditions and the successful application of various manures to forward the development of the different organs, or the application of other substances to neutralize any quality in a peculiar soil, which would be prejudicial to the growth of a certain crop, which constitutes agricultural chemistry in its widest and most extended sense.

As a general rule, all plants consist of a root, stem, and leaves, and these organs again have a direct and distinct reference to the production of a fruit, the which being accomplished, the plant either dies entirely or lies torpid for a season, until a succession of the same circumstances which gave it life in the first instance, shall again call its productive organs into action.

The root of a plant performs the two important offices of retaining it in a fixed position and of supplying it with a great part of its nourishment, and it may therefore be considered as analogous in some measure to the mouth and limbs of an animal.

It is not at all necessary in this place to consider the different forms the root assumes in different plants, it is sufficient for our purpose

OF PLANTS. 15

to know that the roots of all plants perform the same function, that of absorbing nutriment from the surrounding substances for the nutrition of the plant.

It may be and is matter of wonderment, that such a vast variety of shapes, should be given to an organ, provided in all cases for the same purposes; but here our inquiry must cease, an all- wise Providence has so endowed and created them, and man even with his finite understanding is capable of appreciating the benefit he derives from such an arrangement.

A root usually consists of several parts, the body, the crown or collar, the branches and the fibres, which latter seem indispensable in all plants.

The most essential part of every root is the crown, which is the portion of the plant between the stem or leaves, and the body of the root. In many plants of a hardy nature nearly the whole of the body of the root ma}^ be cut away, and yet, if the crown be uninjured, still the plant will flourish, but in the generality of plants, if the crown be injured, no matter how perfect soever the body may be, the plant is usually destroyed.

This remark applies to almost all kinds of grasses, but there are some so tenacious of life (such as the common couch-grass and plantain) that they can only be extirpated by removing every portion of the body of the root.

When the crown of a root is slender it dries up as the seeds ripen, and the plant soon dies; such plants are termed annuals, as wheat, bar-

VB( STRUCTURE AND FUNCTIONS

ley, oats, &c., but when the crown, from any cause, such as the soil, climate, or culture, is rendered strong, such annuals are brought to grow two years and then are called biennials, or for a succession of years and then are called perennials.

The fibres, though an essential part of each root, may be removed in most cases without injury to the plant, provided the crown is sufficiently healthy and vigorous to push out new ones. It is at the tips of these fibres that the spongelets are placed, which absorb the pabulum from the soil, and in the event of the spongelet being removed by any cause from the point of the fibre, two lateral shoots immediately are thrown out, (provided the plant is sufficiently vigorous to bear the temporary loss it thus sustains,) each provided with its spongelet, and thus the destruction of the one becomes a source of strength to the plant. It was on this principle that TuU's famous horse-hoeing husbandry was founded: "that by ploughing between the rows of wheat, and thereby cutting off the tips of the fibres, that for every spongelet thus destroyed two were reproduced by the plant, thus giving the plant two spongelets where one had previously existed." There were other collateral benefits to be derived from this method, but the one in question was one of the principal.

That plants have the power of accommodating themselves to circumstances is proved in a most beautiful manner from the fact, that when planted in a dry and arid soil an infi-

OF PLANTS. 17

nitely greater number of fibres and spongelets are produced, than when the same plant is grown in a moist and fertile soil.

The fibres, like the leaves of trees, are produced annually, in some cases falling off like leaves, as in the Dahlia; in others increasing in size, and becoming harder like the parent body of the root, and subsequently throwing out new fibres themselves, as is the case with almost all large trees.

Besides this property of absorbing nutriment from the soil, these fibres have the power of throwing off that matter absorbed by the spongelets which is either unnecessary or noxious to the plant, and this may be one of the causes Vvhich prevents plants of any kind from being successfully cultivated on the same soil during a succession of years.

It may here appropriately be mentioned that darkness, or at all events the absence of light, is essential to the development of the fibres of the roots.

The stem is the next part to be considered, but the functions it perforins in the vegetable creation are so subordinate to those performed by the root and leaves, that it will occupy but little time to become acquainted with its offices.

The stem of all plants rises immediately from the crown of the root, and is consequently always above the ground. The same variety prevails in this part of the plant as in the root, for instance : the stems of wheat, barley, and the grasses rise to some height and are termed 3

18 STRUCTURE AND FUNCTIONS

the straw ; the stems of mushrooms, fungi, &c. are termed the stalk, and the stem of the strawberry is termed a runner, all of them being appropriately described from the appearance each presents.

The functions performed by the stem are little more than that of conveying to the different parts of the plant the liquids absorbed by the spongelets of the root. It is somewhat porous, and evaporation of the useless moisture of the plant takes place to some extent on its surface, but compared in this respect with the leaves, its office is unimportant. It consists in all cases of cellular tissue, containing albumen, with a large portion of the earthy and alkaline matter absorbed by the roots, and it partakes largely also of the character of the plant itself in its ultimate analysis, but frequently contains a deposite of resinous or oleaginous matter, differing widely from the products of the other parts of the plant. It possesses the property of throwing out fibres and spongelets under favourable circumstances, and this mode is one of the most common means employed for the propagation of particular shrubs.

The leaves of plants are the next subject for consideration, and the important offices they perform in the nutrition of all plants will merit a careful investigation.

Nature, in all her operations, as far as human knowledge extends, is perfect. Sufficient means are always employed to obtain a given result; and hence we may justly infer that leaves from their immense number and from

OF PLANTS. 19

the great extent of surface that they offer to the action of the air, perforin a most important part in the vegetable kingdom; and it will be seen from the functions now about to be described, that their importance is not overrated.

Leaves perform, in the vegetable kingdom, the same offices as the lungs in the animal kingdom. Through them, from the pores covering their surface, the respiration of the plant is carried on, and more than this, for at the same time that the respiration is going on through their pores, a constant assimilation of one of the gases of the atmosphere (hereafter to be described) is also taking place — and from this source the plant derives a considerable portion of its nourishment; to this also we must add that a constant chemical action is always in operation in the leaves, in the formation of the resinous, and oleaginous, and acid matters they contain. These processes of the leaves are constantly in operation, from the first formation of the leaf until the seed is perfected, and they only cease when, from the ripening of the fruit, their assistance is no longer required.

It is important to remark that light is indispensably necessary to this function of plants ; in its presence, both the mechanical action of evaporation of the watery parts and the secretion of the various gases is carried on vigorously ; but in its absence the plant loses this power, and becomes subject in its turn to the action of the oxygen of the atmosphere.

In speaking of the root of plants it has been

20 STRUCTURE AND FUNCTIONS

noticed, that one condition essential to that part of their structure is darkness; and now it is found that light is equally necessary for the stem and leaves and other green parts of the plant. If proof were wanting to convince us of the almighty mind of the Being who has so wisely constituted this world, it might be found in the simple yet perfect arrangement now under consideration. It is a proof of the most perfect adaptation of the plant, to the conditions and circumstances necessary for its growth.

We now come to speak of the seed or fruit of plants. The object to which all the other functions of the plant are subordinate, or to which at least all parts have reference, and one which in its importance to mankind cannot be too highly appreciated.

Seeds vary in size, colour, shape, &c. to such an infinite extent as to be scarcely within the scope of human understanding; but all of them possess one uniform arrangement for the protection of the germ from injury, and it will be important to consider what this general arrangement is, and also the changes that the seed undergoes in the process of germinating. ' All seeds consist of a farinaceous pulpy matter, covered on all sides by two or three membranes which serve to protect the seed from any casual injury. The pulpy matter contains at one end, the heart, or as it is more correctly termed the germ or embryo plant, and in all cases it must be remarked that the pulpy farinaceous matter is the proper food of the nas-

OF PLANTS. Vl

cci.t germ. Some seeds are farther protected by a hard outer covering; but this remark applies only to the seeds of trees. Although the gradations from the hard external shell of the apricot stone, to the membranous covering of the wheat are so gradual, that the line where the one begins and the other encjs, is difficult to be decided on, and indeed whether inclosed in the shell or membrane, the changes ail seeds undergo in the process of germinating, seems to be precisely the same, and it may be worthy of notice here, that so effectual is the membranous covering in protecting the germ from injury, that seeds found in the mummies taken from the pyramids of Egypt, which must be at least 3000 years old, have vegetated, when planted in favourable circumstances; and farther, seeds brought up from the interior of the earth in sinking wells, mines, and other excavations have also germinated, although the period when such seeds could have been deposited in such positions is altogether beyond human conception.

The circumstances necessary for the germination of the seed depend externally on heat, moisture, air, soil and situation ; although these two latter conditions are not in all cases indispensable.

Moisture is absolutely necessary for the seed when planted, its first action is to swell by absorbing the pulpy matter of the pod, which then bursts open and allows the air to act in concert with the water thus absorbed, in creating new compounds, such as starch, sugar,

3*

22 STRUCTURE AND FUNCTIONS

resin, &c. which form the pabulum or nourishment necessary for the young plant in its first stage of existence, and before its organs are sufficiently developed to obtain a supply of food elsewhere.

Heat follows next, and is equally indispensable to the germination of the seed. A temperature below 32° or much above 120° are the extremes, beyond which vegetation does not take place ; in the one case from the freezing or extreme cold, closing the pores of the seed to the moisture, and in the latter from the extreme heat, causing the fluids of the seeds to be too much expanded, when decomposition of the parts takes, place.

Air is also an essential ingredient in the germination of seeds, from the presence of its oxygen. And it is probable, to the absence of this cause, that seeds found buried in the earth, under what would otherwise be considered favourable circumstances for their growth, have lain so long dormant.

Light, so necessary to the favourable growth of the plant itself, is prejudicial to the development of the germ, from its power of disengaging the oxygen necessary to the vitality of the embryo of the plant.

Soil and situation need not here be discussed, as these attributes will be considered more at large in the ensuing chapters.

Electricity is also presumed to have an important effect in causing the germ to vegetate and assume the functions of an organized plant, but as yet this is only a surmise. The know-

OF PLANTS. 23

ledge of this omnipresent agent is yet too limited to say if such is the case, and if so, to say how it operates, but that it does extend and exert its influence on such objects is almost beyond a doubt.

Chapter III. On Soils

To enter fully into this branch of the subject, and with all the detail which its importance deserves, would require a volume of itself, and would far exceed either the limits or the intention of this elementary work.

It must suffice here that a general outline of the characteristics of the soil is given ; that the source from which its fertilizing properties are derived, is pointed out; and that attention is called to the benefit to be always derived from a judicious admixture of the various kinds of soils. This, with a few remarks on the necessity that exists for a rotation of crops, and the benefit that arises from allowing the land either to lie fallow or at least to be cropped only with such crops as do not exhaust the soil, and which from this circumstance are termed fallow crops, will comprise all the information it is proposed to bestow on this subject.

Soils are distinguished by a variety of names, according as a particular substance predomi- Uratesin them. Thus calcareous soils are those containing lime in greater quantity than any other ingredient.

Argillaceous soils are recognised from the clay and the oxides of iron, which predominate in them.

Peaty soils are those where decayed vegetable matter exists to the exclusion of almost all other matter, and all other soils are equally recognised and distinguished from the character of the predominant ingredient.

Sir Humphrey Davy, in his profound work on Agricultural Chemistry, when speaking of soils, says **That for all useful purposes, the various soils are sufficiently recognised, and that any attempt to class them with scientific accuracy, would be a vain labour, the only thing necessary being a clear comprehension of the terms made use of

But in quoting this passage it must be distinctly stated, that this opinion does not militate against that previously expressed, in which a correct analysis of the component parts of the soil is considered to be of the first importance, and one on which the value of agricultural chemistry mainly depends. It is merely intended to state that to attempt a description with scientific accuracy of the various soils would be a hopeless task, without at all detracting from the value of a correct analysis in every position where it is possible.

It is therefore assumed that the recognised distinctions already existing are sufficient for the purposes of agriculture, and the consideration of the functions performed by the soil and the fertilizing properties it contains is at once proceeded with.