Farm manures

Preface

Thirty 3^ears ago Orange Judd Company published a little book, written by Joseph Harris, entitled ''Talks on Manures," a book which was the most thoroughly practical discussion of the problems relating to the maintenance of soil fertility which had appeared up to that date. Written in a most entertaining style, and from the standpoint of the practical farmer, it has been of incalculable benefit to the agriculture of our country. The book is still abundantly worth reading, and ought to be in the library of every English-speaking farmer.

At the time when this book was written there was, in all the world, just one institution in which the soil had been studied by the method of systematic field experiment for a sufficient length of time to afford data of any scientific value, and Mr. Harris made extensive use of these data — the Rothamsted experiments — in the preparation of his book. It is true that the experiment station at Moeckern had been established at about the same time as the one at Rothamsted ; but the German investigations had been directed almost altogether along the line of laboratory research.

The materials, therefore, for "Talks on Manures" were necessarily derived from the experience of practical farmers, and while such experience is not to be despised, but, on the contrary, must be weliv' PREFACE

corned as an indispensable check upon the deductions from scientific investigation, yet it lacks the accuracy which can only result from long-continued work under a systematic method in which the scales and measuring rod are in constant use.

Since the publication of Mr. Harris's book, agricultural experiment stations have been established in practically every civilized country in the world, and these institutions are now accumulating a body of knowledge which, while still falling far short of completeness, is yet affording a much clearer conception of the nature of the problems under consideration than was possible to the most advanced students of agriculture a generation ago, and it would seem to be time that some of the results of this work should be arranged in a more convenient form for ready reference than is afforded by the various bulletins and other publications in which they have been published, and this is the reason for the publication of this book.

In the preparation of this volume no attempt has been made to treat the subject exhaustively. A few paragraphs have been introduced on the origin and nature of the soil, which seem to be essential to a clear understanding of the effects produced by manure ; but it is hoped that these will serve to whet the appetite for a more thorough treatment of the subject, as given by King, Hilgard, Hopkins, Hall, Van Slyke and Merrill.

It has been necessary to quote some experiments with commercial fertilizers, in order to arrive at a

PREFACE V

standard of value for manure, but the comprehensive treatment of this phase of the subject has been left to others.

Even in the branch of the general subject of fertility maintenance which is treated in the following pages — the production and management of farm manures — no attempt has been made to include all the data available. It has seemed better to limit the discussion for the present to such points as have been most definitely established by long-continued investigation.

The book is offered with a deep consciousness of its many defects, both in arrangement and treatment, but it is hoped that it may add a little to the definiteness of our knowledge ; that it may encourage a larger production and aid in a wiser treatment and use of farm manures by the practical farmer, and that it may serve as a stimulus to more extended and more exact research by the scientific investigator.

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Contents

Chapter Page

I. The Origin of the Soil i

III. The Feeding of the Plant 35

Chapter I The Soil

The earth a cooling globe — Some astronomers believe that the solid earth of today was at one time a red-hot, molten mass ; that the water which now fills oceans, lakes and rivers existed then only in the elemental gases surrounding this fiery ball ; that the surface of the globe slowly cooled until a thin crust of solid rock was formed; that with further cooling the hydrogen of the enveloping gases combined with oxygen to form the vapor of water; that in time the cooling had progressed sufficiently for this vapor to condense into a shallow, boiling sea, covering the entire surface of the globe; that the steam from this hot sea rested upon it in a pall so dense as to shut out the light of the sun, and "darkness was upon the face of the deep."

As the crust of the earth cooled, the mist became less dense; in time the light of the sun penetrated sufficiently to establish the difference between day and night; then the land began to rise from the sea; the "firmament" appeared "in the midst of the waters, and divided the waters which were under the firmament from the waters which were above the firmament."

With the gradual cooling of the crust of the earth and its consequent contraction, it began to wrinkle, as the skin of an apple does in drying; the waters were gathered together into seas, and the dry land arose between them in low-lying continents, raised but slightly above the surrounding, shallow seas ; these continents later were traversed by great mountain chains as the crust was forced upward by the increasing internal contraction.

The sides of these primeval mountains were almost constantly drenched with torrential rains, falling from the saturated atmosphere, slowly scouring away the surface of the rock and carrying the detritus to lower levels. Lichens began to grow upon the rocks, each plant loosening a few grains of the rocky material. In time frost came to the assistance of rain and plant roots, and thus by forces whose work was almost imperceptible, but which had eons of time for its performance, the surface of the uplifted mountains was slowly ground to powder.

Other agencies also assisted in the work of soil formation. The waters of the primeval seas were charged, as they are now, with lime and other mineral substances dissolved from the rocks, and in these waters corals and other lime-using forms of aquatic life began their work of rock building. Great beds of limestone accumulated on the bottom of shallow seas, formed by the growth and death of

Tin-: 0R1(]IN OF THE SOIL 3

countless myriads of shell-bearing organisms. With the continued crumpling of the earth's crust, these limestones were sometimes brought to the surface and even thrown up into mountains, to be subjected to disintegrating agencies by which their surfaces were reduced to powder, which was here left in level beds on table lands or plateaus, and then carried down and rearranged in admixture with the detritus from noncalcareous rocks, giving rise to deposits of all gradations, from those rich in lime to those in which this substance is found in very small proportion.

The solvent action of water containing traces of carbonic acid, as do all waters exposed to the air and soil, has been a potent factor in the dissolution of the rocks, of limestones especially, and the redisposition of their particles in other forms. The growth of the higher plants, whose roots also exert a solvent action, as may be seen by tracing the marks of such roots upon the face of the rocks ; the action of earthworms and other earth-burrowing forms of animal life, in bringing to the surface materials from lower depths, and in actually grinding and pulverizing these materials — these have all contributed to the slow pulverization of the rocky earth crust and its conversion into the basis of arable soil.

Moving ice has also played an important part in this work. We have evidence that at one time a large part of the North Temperate zone was covered with a sheet of ice, hundreds and even thousands of feet in thickness which, under the ever accumulating weight of arctic snows, moved slowly southward to meet the sun, by which its southern extremity was melted away, forming great, southward flowing rivers; or, where it terminated in the open seas, breaking off into icebergs, just as the Alaska glaciers and the sheet of ice which covers Greenland in places to the depth of 2,000 feet, are doing today.

This southward moving ice carried with it masses of rock material, broken from the mountain sides along which it passed, or plowed up before it in its irresistible course. These materials were deposited at its southern extremity, sometimes forming large ridges or "moraines" of sand and gravel where the glacier's foot had remained for some time, these being spread out in sheets of greater or less thickness as the increasing heat of the sun drove it back to the north.

Glacial action has been a most important factor in the formation of the soils of the northern part of the United States. By it mountains have been cut down and valleys have been filled, the glacial drift sometimes reaching a thickness of hundreds of feet, and the soil materials have been worked over and rearranged by the floods springing from the glacier's foot, so that glacial soils are generally among the richest in their supply of the mineral elements of plant nutrition, although the physical condition of these soils is often such as to call for the exercise of the highest skill of the farmer in drainage, cultivation and crop rotation, in order to realize their full capacity in crop production.

The mineral basis of the soil has been formed through such agencies as those suggested above. It consists merely of pulverized rock. And that such agencies are sufficient to produce the effect observed cannot be doubted b}^ one who carefully studies their workings, bearing in mind that they have certainly been at work for tens of thousands, probably hundreds of thousands, or even millions, of years. But this mineral basis, of itself, does not constitute a soil ; that term implies a mixture of such a basis with a larger or smaller proportion of decomposed organic matter.

We may grind together a feldspar containing potash ; a dolomite containing lime and magnesia ; an apatite containing phosphates, and so on until we have a combination including all the mineral elements which are formed in the plant ; we may add to these powdered leather, rich in nitrogen ; we may dilute the mixture with pulverized quartz until we have a proportion of these elements to each other and to the entire mass similar to that which we find in the most fertile soils, and we may add distilled water until we have brought our artificial soil into the most perfect moisture condition for plant growth ; but when we attempt to grow plants in this soil they will lead but a stunted and miserable existence.

We are familiar with the fact that the herbivorous animals are able to thrive upon food materials upon which the carnivorous organism Avould starve, and to convert these materials into the most nourishiiig food for the carnivores; but we are only just now learning that, just as the herbivores stand between the carnivores and the plant, and the plant stands between animal life and the soil, so a fourth class of organisms is employed within the soil in working over the minerals there and preparing them for the use of higher vegetation, and that the mediation of these organisms, between the plants we cultivate and the minerals, is as essential as that of the animal which converts these plants into its tissues is to the flesh eater.

The beginning of life occurred as soon as the temperature of the primeval seas was reduced to such a point as to permit its existence. Before the pall of cloud had lifted, the sands of the seashores, no doubt, became inhabited with single-celled, colorless plants, such as the bacteria which are now revealed to us by the microscope as existing in the soil below where light penetrates, and which feed directly upon the soil minerals and the free nitrogen of the air which circulates in the upper layers of the soil, combining these elements in their tissues and leaving them in this combined form as the first step towards their final destiny as human food.

Millenniums passed before the sun's light began to penetrate the cloud, during which the ever-falling rain washed from the slowly rising- shores much of the material combined by these organisms, carrying it into the sea to become there the nutrient substance for the hosts of living things, from the minutest single cell to the leviathan, with which the sea began to be inhabited; but a part of each minute addition to the stock of elementary combination became fixed in the film of moisture surrounding each particle of sand, so that, while the addition to the stock of potential plant food in the land was but a very minute fraction of that carried into the sea, yet there was a steady increase, especially in those portions which had risen above the washing of the waves.

Green plants made their appearance with the first dawning of light ; probably such plants as the lower forms of algae which we find today growing in moist and shaded places, and which also, then as now, were able to feed directly upon the original minerals of the soil and upon atmospheric nitrogen.

With lowercasing light came the higher forms of plant life, first feeding upon the soil food prepared for them by the bacteria and algae, but after their span of life was ended returning their substance to the soil and by their slow decomposition gradually reducing the proportion carried to the sea.

Year after year, century after century, eon after eon, this work went on, each advancing age leaving a little larger the accumulation of organic remains in the soil.

Worms have also contributed materially to soil formation. The cast of a single earthworm, as thrown up between a pair of paving bricks, seems a very insignificant thing ; but when such casts are multiplied by millions, they are no longer insignificant, but become a potent factor among the agencies concerned in soil building. For these casts are the product of a commingling of mineral particles with vegetable matter; these mineral particles are ground to a much finer condition in the digestive organs of the worms, and- are thoroughly mixed with vegetable matter and digestive fluids.

The countless myriads of insects which have their short existence on or in the soil and in the vegetation above it have also contributed materially to the condition which makes the soil a feeding place for the plants we cultivate, through their decay upon it. And the same is true of other forms of animal life which, after their period of existence is over, return their tissues to the elements from which they came — earth to earth and air to air.*

Humus — A heap of bright, yellow straw is built in the barnyard ; the farm animals are given access to it and consume a part of it, trampling the remainder under foot; gradually the heap disappears, and there is left in its stead a comparatively very small quantity of dark material, brown at the surface and still showing the structure of the straw, but black and formless at the bottom. Had the straw been spread upon the land and plowed under, the same transition into a structureless, black substance would have taken place.

If, now, we separate this black substance, as may be done by chemical processes, and subject it to analysis, we shall find it containing the mineral substances of the original straw, such as may not have

*See Darwin's " The Formation of Vegetable Mould."

been washed out by rain, together with a considerable but variable percentage of nitrogen, which has become fixed in a comparatively stable form.

This black substance is humus. It is the product of the decay of organic matter — vegetable and animal — but it is not correct to apply the term humus to such matter during the process of decay. The humus of the soil is its storehouse of available plant food, both mineral and nitrogenous ; plant food that has been wrested from the rocks and the atmosphere by infinitesimal agencies working through eons of time, and stored for the use of humanity ; plant food which we may so utilize as to return it to the soil undiminished or even increased in quantity, or which we may so waste as to leave to those who follow us a sadly diminished heritage.

The skeleton of the soil consists of grains of sand or minute fragments of the rocks from which the soil has been derived, (The larger fragments, or gravel, are not, properly speaking, parts of the soil.) This mineral skeleton may consist of particles so coarse as to be easily discernible, or of atoms of silt or clay so minute that they can only be separately distinguished by the aid of the microscope ; but in either case it is upon these separate particles that the forces impinge which control the growth of vegetation. Practically all soils contain particles of different degrees of fineness, the space between the larger ones being occupied by smaller ones of silt and clay and by fragments of decaying vegetation. Whether the soil be classed as sandy, loamy

THE ORIGIN OF Tllli: SOIL II

or clayey depends upon the relative proportion and character of the coarser and finer particles.

Whatever the size of the particles, it is upon their surfaces only that the various forces act which prepare the food for the plant — the soil water, in which that food is dissolved; the air which furnishes oxygen for the conversion of the insoluble mineral matter into soluble oxides; and the soil organisms, whose growth transforms the inert soil nitrogen into active nitrates, and the mineral elements into available forms.

The size of the soil particles is an important factor in determining the rate at which the plant food is made available. F. H. King has shown that the surface area is in inverse proportion to the size of the particles. For example, a marble, i inch in diameter, would have a superficial area of 3.1416 inches, and a cubic foot of such marbles would have a total area of 37.7 square feet, while a cubic foot of soil grains .001 inch in diameter, would have an area of 37,700 square feet, or nearly an acre. Hence, a fine-grained soil exposes a very much larger surface to solvent action than a coarse-grained one, so long as the size and condition of the particles are such that they move freely upon each other and allow water to penetrate their interstices, as sands and silts. In clays, however, the soil particles are so fine that the water cannot circulate freely ; hence a clay may be rich in the mineral elements of fertility. and yet its physical condition may be such that its plant food will be yielded up "to the growing crop with extreme slowness; while a sandy soil, though showing under analysis smaller quantities of the elements essential to crop production, may yet give larger yields.

When, however, the texture of the clay is altered, by manuring or by the turning under of vegetation, it often becomes more productive than the naturally looser soils.

On the other hand, in a coarse, sandy soil the particles are separated by such large interstices as to permit too easy a passage for the rain water, and it passes below the reach of the plant roots before it becomes sufficiently saturated with the mineral elements required for plant nutrition.

For both classes of soils the remedy is the same, the incorporation of vegetable matter. Such matter loosens the clays by separating their particles, and makes the sands more compact by filling their interstices with finer material, while its decay not only furnishes plant food directly, but also serves indirectly to bring the soil and atmospheric elements into combinations available for plant sustenance.

The cycle of life — A dead animal, lying exposed in summer weather, is soon attacked by flies, whose maggots devour the carcass, converting the carbon, oxygen and nitrogen of its dead tissues into their own living substance. A dead plant, covered with a few inches of soil, is attacked by millions of microscopic plants (bacteria), which consume its tissues, recombining the carbon, oxygen and nitrogen of those tissues into the protoplasm which fills their cells.

The maggots are transformed into flies and these, if not devoured by other animals, live out their cycle of existence and then are consumed by molds and these in turn by bacteria. Bacteria also may be consumed by other organisms (amoebae), as has quite recently been shown at the Rothamsted experiment station, or they may reach their natural life limit — a matter of a few hours, probably — when their cells will be decomposed with the formation of oxides of nitrogen and carbon (nitric and carbonic acids), the nitric acid to be absorbed by the soil water and carried to the roots of growing vegetation, if there be such vegetation in the vicinity, otherwise to be carried into the drainage or separated into its elements; the carbon dioxide to escape into the free air, there to be captured again by the foliage of green-leaved plants.

In some such way as this the never-ending cycle of life moves on ; the aztobacter seizing upon the surfaces of the soil particles and combining their phosphorus, potassium and calcium with atmospheric nitrogen ; this combination to be passed on to the higher plants, which add to it the carbon dioxide of the air; these plants to be consumed by the herbivores and their tissues to be converted into bone and nerve and milk and muscle ; the herbivores to serve as the food of the carnivores, and these in turn to feed the worm, and the worm the bacteria, the cycle thus returning to the plane from which it started.

Geological Classification of Soils

The geologist classifies soils in four principal groups, according to their origin, namely : Sedentary or residual soils, or those which have been formed where they now lie by the decomposition of the underlying rock ; alluvial soils, or those which have been transported by rivers and deposited upon their flood plains — soils to which the farmer applies the name "bottom lands" ; glacial or drift soils, or those which owe their origin to the action of moving ice, by which agency a part or all of their material has been transported for long distances and deposited at the foot of continental glaciers ; and seolian or loess soils, which have been formed from dust blown by the wind.

Residual soils vary greatly in quality, owing to the character of the rocks from which they have been derived. Thus the soil of the famous *'Blue Grass" region of Kentucky is due to the weathering of the underlying limestone, while in other places sandstones, shales and granites have given origin to soils of very different character. In fact, it is a matter of general observation that soils formed wholly or in part from limestone are, as a rule, much more productive and more durable than those derived from noncalcareous rocks, although it sometimes happens that a limestone soil has been so improvidently managed that its natural superiority has vanished.

Alluvial soils — The superior fertility of alluvial

Tin-: ORIGIN OF THE SOIL 1 5

or bottom lands has been recognized since man began to till the soil, and the cause of this superiority is easily understood by one who observes the turbid streams which course down every hillside in times of freshet, carrying down the wealth of the highlands and spreading it over the flood plains of the rivers. It is no unusual thing to see such deposits reach a thickness varying from a quarter to half an inch, after an ordinary spring flood of today, and our floods are evidently much smaller than those of former days, as shown by the greater width of the earlier flood plains, which include the second and third bottoms, so called, or the river terraces. Only a tenth of an inch annually would mean ten inches in a century or a hundred inches in a thousand years, but in geologic time "A thousand years are but as yesterday when it is past, and as a watch in the night."

Drift soils are variable in character, consisting sometimes of the weathered surfaces of beds of gravel containing a great deal of limestone, forming soils naturally underdrained and rivaling the best limestone soils in productiveness, while sometimes they are found lying on heavy sheets of bowlder clay, rich in the mineral elements which enter into the food of the plant, but requiring drainage and aeration to bring this potential food into an available condition. Sometimes the drift is so modified by the rock upon which it lies as to possess the chief characteristics of a residual soil.

Loess soils have been formed under climatic conditions approaching aridity. It may seem a mystery to the farmer in humid climates that soils even a hundred feet in thickness should have been formed from fine particles of dust, blown by the wind, but the mystery will disappear after he has spent a dry summer on the treeless plains of the semi-arid regions, and watched the clouds of black dust which follow the plowman, filling eyes, nose, ears and mouth, and covering face and hands with such a coating as only coal heavers carry in the humid climates.

A considerable part of the deep, black soils of the rolling prairie region between the Mississippi and the mountains is of this character. Loess is not always black, but is sometimes of much lighter colors, containing a larger proportion of clay; as, for example, the blufifs of the lower Mississippi. The loess soils are very fine grained, and are usually well stored with the elements of fertility.

Sand dunes are another example of seolian soils, but they are much coarser grained, and contain comparatively little matter of vegetable origin. They are as conspicuous for their poverty as the loess soils are for fertility.

Agricultural Classification of Soils

From the earliest ages farmers have based their classification of soils upon the fineness of the particles into which the mineral constituents may be divided, the relative proportion between the mineral

THE ORIGIN OF THE SOIL I7

and organic constituents, and the degree of decomposition which these latter have undergone. Thus we have sandy soils, in which the mineral particles are relatively large, and clays, in which they are impalpably -small, with an intermediate class called silts. When a considerable proportion of organic matter is found in the soil, we call it a loam, and we use the terms "sandy loam," "silty loam" and ''clay loam" to indicate the condition of the predominant mineral constituents. The organic matter may constitute so large a proportion of the soil as to change its color to black, giving us black sands, silts and sometimes clays ; a still greater proportion of organic matter produces muck soils, and these pass into peats, which are composed so largely of partly decayed vegetation that they burn readily when dried, and may be used for fuel.

The Inhabitants of the Soil

The modern science of bacteriology has demonstrated that the soil is inhabited by numerous species of micro-organisms, which play a very important part in the conversion of its stores of plant food into available form, and in the fixation of atmospheric nitrogen. These organisms are single-celled plants, extremely minute in size, colorless when they live below the surface, or green in the case of some low forms of algae found at the surface of the soil.

The first forms of life — Such organisms, growing l8 FARM MANURES

in the sandy beaches of the primeval seas, were probably the first forms of life upon the earth. In these sands they would find the mineral elements essential to their growth, and they would necessarily have the power, possessed by similar organisms today, of fixing the free nitrogen of the air circulating between the particles of sand. In the slow grinding of the rocks into sand and silt they are constantly washed by waves or rain, so that their soluble portions are extracted and removed. A beach sand or freshly ground rock makes but a barren soil, and the washing of the rock powder increases its barrenness ; hence the play of other than physical and chemical forces is required before the barren rock is converted into productive soil. The first of these forces is undoubtedly bacterial growth, which serves as the forerunner to the growth of higher organisms. Not only is it probable that certain bacteria are able to assimilate mineral as well as nitrogenous matters which the higher plants cannot appropriate, but their minute size enables them to penetrate interstices between soil particles which are closed to the roots of higher plants. For example, it has been shown that the particles of clay are not larger than one five-thousandth of an inch in diameter; but some of the soil bacteria are not more than one-sixth as large as these clay particles, and hence are indefinitely smaller than the smallest plant roots.

Nitrification — Another function performed by soil bacteria is the breaking down of dead vegetable

THE ORIGIN OF THE SOIL I9

matter in the soil and the conversion of its nitrogen into nitric acid. This work has been shown to be due to the action of organisms which grow upon such matter, appropriating its carbon and causing the combination of its nitrogen with oxygen, forming nitric acid.