The principles of manuring; an application of chemistry to agriculture

Front matter

Class Book.

.XlL

Copyright N".

PART 1. Plant Food hi General. Its Nature and Source. J> ^ iP

FARMING is a business, and the successful farmer must be, first of all, a businessman. He follows his avocation, primarily, for the money he can make, and like other business men Dims to get the greatest possible return for the money and labor involved. It is not enough to produce crops, but they must be so produced as to yield a profit on the capital invested. To succeed he must be thoroughly acquainted with every detail of his occupation and must strive to stop all leaks and prevent needless waste. At the same time, he must bear in mind that it is a good business principle to spend a dollar vhenever he can see that it Mill come back to him with interest.

Agriculture differs fmm mercantile pursuits in being not merely a business, but an art '■i>: v/ell — the art of producing plants and animals that are useful to man. To -jnderstand this art necessitates a knowledge of the principles upon which the art of agriculture is founded (sucti, for example, as geology, chemistry, botany, physics and others which might be mentioned), and an understanding of these principles is essential to an intelligent and rational practice. A few years since "anyone could be a farmer." It was only necessary to sow and reap, for Nature dealt lavishly with man and gave to him freely of the fertility she had been storing up for countless ages. A system of extravagant and unbusincss-like farming, however, has so impoverished the soil, in some parts of our country, that many farms are already abandoned, having ceased to be profitable, and that, too, in localities where the land once commanded high prices. This fact is the more lamentable because the exhaustion of the soil might have been prevented by an intelligent foresight on the part of our earlier farmers.

Chemistry has done much to explain how the fertility of the land may be conserved, and it is the aim of this short treatise to present, as briefly as possible, the latest views of agricultural chemists and farmers on Ihis important subject. The intention is to make the series thoroughly practical, and for this reason the minimum of theory and the maximum of demonstrated facts will be given, and all technically chemical language will be avoided when possible. Before taking up the subject of manures and fertilizers it is deemed desirable to devote a short time to the consideration of plant food in general — v/hat it is and from whence it comes.

Plants of First importance to 'he Farmer. — A.11 agricukure depends on the growth of plants and consequently the profit that accrues to the farmer depends, primarily, upon the value of the crops his farm produces. In some styles of farming the profit comes from the sale of crops that are useful in providing food, fuel or raiment for man, while in others the direct gain ccmes from the sale of animals or animal products. Even in the latter case the feeding crops that can be grown on the farm determine its earning power, for the sale of animal products is simply an indirect method of marketing the crops.

The profit from the farm is dependent not only upon the total crop produced, but also, and to perhaps a still larger degree, on the yield per acre. It stands to reason that if the crops now produced on two hundred acre?

could be grown on one hundred, the returns would be greater, providod the labor and other nost involved were not materially increa.sod, for in the latter case the interest on the money invested in one hundred acres of land would be clear gain. On the other hand it is apparent that nothing is gained by increased production per acre if the larger crop is obtained at a total expenditure in excess of that required for the smaller yield. As a matter of *acc our most succes^.sful farmers have demonstrated that the present average of crops can be doubled and at a cost per acre scarcely more than is now required for the half crop. To accomplish this lecessitates a bioader knowledge of the food requiiements of plants than is posse.s^ed by the majority of our farmers. This knowledge being fundamental, it seeni.s strange that more attention has n"^* been devoted to this subject by those vitally irterested. Strange as it may seem, it is a fact that, while he has reasonably clear ideas on foods for animals, the average agriculturist has only very vague and often unfounded notions on the subject of plant food and plant nut ition. A thorough understardin.'? of these subjects on the part of our forerunners in agriculture would have rendered it unnecessary to feel concerned regarding the matter considered under the next heading.

(2) Exhaustion of the Soil. — It is a matter of common experience that continued cropping results in a loss of fertility. The experience of the East teaches some lessons by which the West may profit. In the beginning the productiveness of the rich virgin soil seemed unlimited. For years large crops were produced with apparently no decrease of fertility. Sooner or later, however, the crops Degan to diminish in size, gradually to be sure, but unceasingly, until at last the yield became so small that it no longer paid for the cost and labor of cultivation. This state of affiairs came about more rapidly if the same crop was grown continuously on the same field, as was often done with wheat. The soil was now said to be exhausted and the farms were abandoned. An exhausted soil in this sense means one that will no longer yield profitable returns, and not necessarily one that will produce no crop. As a matter of fact a soil cajinot become exhausted, if by exhaustion we mean total inability to produce a crop.

At the experiment station at Rothamsted, England, barley grown continuously on the same plot for fortythree years without the use of fertilizers of any kind yielded in the fortythird year ten (10) bushels of dressed grain per acre; the average for the last eight years being eleven and three-fourths (11%) bushels. Wheat grown in the same way for fifty years produced in the fiftieth years nine and three-fourths (9% bushels of grain per acre; the average for the last eight years being eleven and one-half (11%) bushels. In these cases the soil seems capable of keeping up this yield indefinitely, for the average for the last twenty years is practically the same as the average given above for the last eight years.

While these facts indicate that the soil can never be comj^letely exhausted, it is exhausted to all practical purposes, when the crop produced ceases to be profitable. The first question that naturally suggasts itself is — Why does the productive power of the soil diminish?

(3) The Plant Removes Something From the Soil.^It is evident that the virgin soils must have contained large quantities of some substance or substances that were necessary to vigorous plant growth and that these materials were removed from the soil when the crop was harvested. It is not possible to explain the rapid decrease in fertility on any other basis, for it seems to be to a certain extent independent of any changes in climatic conditions. The change in the mechanical conditions of the soil has been suggested as a possible explanation for its decreased productive power, but even this does not fully explain it. It is apparent, also, that plants vary in their power to extract these substances from the soil, for it is well known that a soil may be sterile towards one class of plants and still poduce a luxuriant growth of another. To ascertain what these materials are that the plant removes from the soil, it is necessary to analyze the plant and then to determine the sources of the ingredients found. For the purpose of this study the corn or maize plant is chosen, as it is perhaps the most important of all plants to the American farmer. Before st'^ting the analysis, it is advisable to devote a moment to a few preliminary considerations.

(4) Elements and Compounds. —

Chemistry teaciies that all matter is composed of simple substances called elements. Between seventy and

eighty of them are known. They are called elements because they are the simplest substances known and cannot, by any means yet discovered, be separated into simpler or different substances. Iron, gold, silver and sulphur are examples of elements. Two others, both gases (i. e., oxygen and nitrogen) make up the bulk of the air.

Most materials with which we are familiar are complex bodies and combinations of two or more elements. Such bodies are called compounds. While the number of elements is small, there are many thousands of compounds. This is due to the fact that the same elements can combine in many different ways, each combination forming a different compound. Alcohol, sugar, starch and acetic acid, for example, are substances very unlike in their properties, and yet all consist of the three elements, carbon, hydrogen and oxygen, though these elements are present in different proportions. Plants are composed of a large number of compounds and an ideal analysis would first separate the plant into its compounds and then these compounds into the elements of which they are composed. Approximately such an analysis can be made.

(5) Chemical Composition of the Corn Plant. — If a quantity of green corn is allowed to wilt in the sun it loses a large percentage of its weight, due to the evaporation of the water which it contains. If the remainder is now heated in an oven at 212 degrees F. it again decreases in weight, but finally reaches a point where the weight does not change, because all the water is now driven off. Water is composed of the two elements, hydrogen and oxygen. What remains after expelling the water is called the dry matter of the plant. The dry matter burns on being ignited and a very small ?.mount of mineral matter rem.ains which is called ash. The part that burned and completely disappeared is known as organic matter. The organic matter is composed of four classes of compounds known as proteins, fats (ether extract), crude fiber and carbohydrates (nitrogen free extract), and these compounds in turn are made up of the four elements, carbon, oxygen, hydrogen and nitrogen. The ash contains the elements chlorine, potassium, phosphorus, calcium, magnesium, ii'on, sulphur, sodium and silicon. The following table shows the ingredients found in one thousand pounds of the matured corn plant, i. e., when the plant is in condition to be cut for shocking:

COMPOSITION OF THE CORN PLANT.

Corn Plant leOO lbs.

Water J Hydrogen 88.1 793 / Oxyyeii 704.9

Dry I

Matter {

Organic

Matter f Proteia 18.

) Fat 5.

1 Fil)er SO.

I Carbohydrates 12- r Ni troy en 2.9 ! Carbon 90.5 '1 Oxvi^-^en SS-9 I Hydrogen 12 7 f Chlorine 0.4 I Potash 4.0

Phosphoric Acid 1.2 I Lime 1.6 Ash 12 i Majj-nesia 1.4

Iron Oxide 0.3

Sulphuric Acid 0.3

Soda 4 L Silica 24

(NoTK.— All of the elements nieutioned above as occurring in the ash, with the exception of clilorine, are combined with oxyffen. In the table the names under "ash" represent these combinations, i. e. potash is composed of potassium and oxyyen: phosphoric acid is phosphorus and oxygen; lime is calcium and oxygen, etc )

From what has been said it will be seen that of the elements known, only thirteen (13) are found in plants, for what is true of the corn plant holds true of all other plants. It will be shown that of this number, three are probably not necessary to plant growth, leaving only ten elements that are essential. The table shows that three elements (i. e., hydrogen, oxygen and carbon) make up ninety-eight and one-half (98i/^) per cent of the entire composition of the plant, the remaining elements constituting only one and one-half (1%) per cent.

(6) Importance of Water to the Plant. — One of the most striking points brought out by the chemical analysis is the large proportion of water that enters into the composition of the plant. A reference to the table shows that nearly eight hundred (800) of the one thousand (1,000) pounds of the matured corn plant consist of water in a form that can be driven off at a heat not above the boiling point. In the organic matter is found 12.7 pounds of hydrogen and 88.9 pounds of oxygen, which practically all came originally from water, making a total of nearly 900 pounds derived from this source. These figures represent but a small part of the water actually required by the crop. Experiments have shown that approximately 300 pounds of water passes through the plant for each pound of dry matter produced, so that 1,000 pounds of corn uses at least 30 tons of water during its growing period. As this quantity of corn can be raised on one-thirtieth of an acre, it follows that to mature an acre of corn the crop must be sup- Ipied with 900 tons of water, or a quantity that would make a layer over the acre eight inches deep.

This, again, takes no account of the amount of water lost from the soil by percolation or drainage. It has been estimated that this quantity is at least equal to that used by vegetation, so that one acre of corn probably requires a precipitation of at least 1,800 tons of water. These statements show clearly the necessity of carefully conserving the moisture of the soil, a point that cannot be too strongly emphasized.

The water all enters the plant at its roots, being absorbed from the soil, and all but a small part of it is given off from the leaves by evaporation or transpiration. Water is important to the plant in several different ways. It is, first of all, the most important food of the plant — in the sense that it supplies the matter composing almost nine-tenths of the weight of the plant. It is also necessary to enable the other food in the soil to enter the plant as these materials can be absorbed by the plant only when they are in solution.

Water is needed to give stiffness or rigidity to the more succulent parts of the plant, as is shown by the drooping of plants when the supply of water is insufficient. It is probable that water performs an important function in controlling the temperature of the plant. The chemical processes in the plant cells produce heat and the excess of heat is removed by transpiration of water through the leaves, just as it is removed from our bodies by the transpiration (perspiration so called) through the skin.

So important to vegetation is the water supply that some investigators claim that the question of fertility is wholly one of having present in the ground the proper amount of moisture and is independent of the chemical composition of the soil, except as this composition affects its power to furnish the plant with water. This view is undoubtedly extreme and is not generally accepted. There is no doubt, however, that the proper condition of moisture is the most important factor in determining the fertility of the land, and that more soils fail to produce good crops for lack of it than for any other cause. In few cases is the water supply sufiicient to produce the maximum crop of which the soil is capable.

(7) Part of the Oxygen From the Air. — A small quantity of the oxygen in the plant probably comes from the air. One-fifth the volume of the air is oxygen and the plant uses this to some extent. Plants breathe in much the same manner that animals do, for all cells must have a supply of oxygen in order to live. The oxygen of the air combines with the materials in the cells, one of the results being the production of heat, just as the oxidation taking place in the animal body produces heat. That heat is evolved by the living vegetable cell can easily be proven experimentally by confining the plant in such a way as to prevent radiation. The rapid heating of silage during the filling of the silo is doubtless due to the breathing process of the cell, the heat in this case being unable to escape.

(8) Carbon in Plants Derived From the Air. — Nearly one-half of the dry matter in the plant consists of the element carbon, all of which is derived from the carbonic acid gas that constitutes about four-hundredths of one por cent of the volume of the atmospl'.ere, or about ons part in ten thousand. Carbonic acid gas is a compound of the elements carbon and oxygen. Green plants have the power to decompose this gas, retaining the carbon, and setting free the oxygen. This process is known as the "fixation (sometimes assimilation) of carbon," and takes place principally in the leaves. The power to fix carbon is dependent in some way on the presence of the green coloring matter (chlorophyll), so that it is only those plants having green leaves that can use the carbonic acid. Such plants as mushrooms and other fungi, for instance, cannot obtain their carbon in this manner, but must procure it through the decomposition of organic matter, or. in other words, must have their food previously prepared for them. Green plants, on the other hand, can manufacture their own food from the inorganic materials of the soil and the atmosphere.

(9.) Sunlight Necessary to Carbon Fixation. — The decomposition of carbonic acid by the plant, and the assimilation of the carbon, takes place only during the daytime. A certain amount of energy is necessary to break apart the carbon and oxygen of carbonic acid and this energy is furnished by the sunlight. The stronger the light the faster the fixation of carbon, which explains the commonly observed fact that most plants grow more vigorously in full sunlight than in shade or diffused light. The plant has not power to use carbonic acid in the absence of light, so that this process ceases during the night.

It is well known that seeds will germinate in the dark and produce a feeble, spindling growth of pale foliage, but that the plants so produced soon cease to develop. Such plants grow until they exhaust the food stored in the seed, but have no power to use the food in the air and soil, and analysis shows that the plant contains less dry matter than was present in the seed.

In the presence of light, however, the plant absorbs the carbonic acid of the air and causes the carbon to combine with the water and other substances taken in through its roots, to form carbohydrates, proteids and other complex compounds of which the plant is composed. It is now generally believed that the green plants derive their carbon solely from the carbonic acid of the atmosphere and are not dependent in any way upon the carbonaceous matter in the soil; in fact, that they are incapable of using carbon except in the form of carbonic acid gas.

Numerous experiments have proven that the supply of carbon in the air is ample for the largest crops. To be sure, in certain pot experiments a larger yield was obtained by increasing the carbonic acid in the air, but under field conditions the yield is limited by other factors and never by the supply of carbon.

All processes of fermentation or decay, all burning and the breathing of animals, combine to return carbonic acid to the air as fast as it is removed by growing plants, consequently the amount of this gas in the atmosphere remains constant. In all probability that now present in the air has been many times built up into organic matter only to be again set free by its decomposition.

(10) Carbon Costs the Farmer Nothing. — The point of practical importance brought out by this study of the fixation of carbon is that the carbon is furnished free of cost. In other words the carbonaceous matter produced in the crop results in no impoverishment of the soil. There is no need then, of supplying strictly carbonaceous manure to the field, as the crop does not use the carbon in the soil. It will be shown later that such manures may indirectly be beneficial to the plant.

(11) The Nitrogen Problem. — A reference to the table given in section 5 shows that only about one and one-half (1%) per cent of the dry matter of the corn plant consists of nitrogen. Some plants contain more nitrogen than this, but the amount rarely equals three per cent of the dry matter or six-tenths of one per cent of the green plant. In spite of the small quantity of nitrogen in the crop it is the most important of all plant foods from the practical point of view. In fact, the solution of the problem of the maintenace of fertility depends upon an economical method of conserving and renewing the nitrogen supply of the soil. This does not imply that it is more necessary to vegetation than are the other constituents, but that it is the most expensive element to furnish by means of fertilizers and is also, unfortunately, the element most easily lost and wasted.

(12) The Nitrogen of Plants Comes From the Soil. — Most of the crops raised by the farmer are entirely dependent on the soil for their supply of nitrogen. Most of the nitrogen present in the soil is locked up in the insoluble organic matter and in this form is not available to plants.

Some of the nitrogen exists in simple compounds called nitrates, which consist of nitric acid combined with one of the mineral elements of the soil. The majority of farm crops can use only that part of the nitrogen in the soil that is present as nitrates, so that so far as the nitrogen is concerned the fertility of the soil depends on its nitrate content. The nitrate present in the soil at any one time is exceedingly small, but, under proper conditions, the supply may be renewed with sufficient rapidity to meet the needs of the plant.

(13) Source of the Nitrogen of the Soil. — A small part of the nitrogen in the soil is derived directly from the atmosphere. Minute traces of ammonia (a compound of nitrogen and hydrogen) are always found in air and during electrical storms small quantities of the nitrogen and oxygen in the atmosphere are combined to form nitric acid. These substances are dissolved in the rain water during showers and are carried into the soil. The quantity received by the soil from this source is very small, amounting only to from six to eight pounds per acre per year, the maximum amount being less than one-tenth that required by a crop of corn. Nearly all of the nitrogen in the soil is present in the more or less decayed organic matter left behind by the plants that it has previously produced. Plants build up the nitrogen into complex protein compounds and, under natural conditions, when they die these substances, in connection with the other constituents of the plant, become a part of the soil. As long as the nitrogen remains in this form it is of no value to the new generation of plants, for the organic matter must first be decomposed and the nitrogen changed into the form of nitrates.

(14) Nitrification. — The soil must not be regarded as an inert mass of mineral matter and refuse of former plant growth. It is, in fact, an immense laboratory in which millions of tiny workmen are bringing about marvelous chemical changes. The principal factors concerned in these transformations are bacteria, of which, it is estimated, there are present in the neighborhood of one hundred fifty millions in each ounce of surface soil. Some of these bacteria cause the fermentations and decay that return the carbonic acid to the air. Others, and these are of particular interest here, bring about the decomposition of the nitrogenous organic matter with the ultimate production of nitrates.

The transformation of organic nitrogen into nitrates undoubtedly results from the action of more than one species of bacteria and takes place in three or more different steps. The organisms necessary to produce these changes are ordinarily present in all soils. Nitrification takes place only when the temperature is more than five degrees above freezing and becomes more rapid with rise of temperature. Hence, it ceases during the winter months and is most vigorous during the hot months of midsummer. The nitrifying bacteria cannot live without a sufficient supply of oxygen, for this reason stirring the soil increases the rate of nitrification. The nitrifying bacteria cannot thrive in a soil that is acid, so that the presence of carbonate of lime or some other substance that will neutralize any acid produced in the soil is essential to nitrification. All of these points will be discussed in greater detail later, for the present it is sufficient to emphasize the importance of the process of nitrification to the growing crop. So vital, indeed, is the subject, that successful agriculture may be said to depend largely on providing proper conditions for rapid nitrification.

(15) Denitrification. — While the nitrifying bacteria may be said to be the farmer's friends, there are, unfortunately, in the soil other organisms that produce evil results. One class of these, known as denitrifying bacteria, decompose the nitrates, and perhaps some other nitrogenous compounds, with the final result that the nitrogen is set free and returned to the air in its elemental condition. This process, of course, robs the soil of a part of its nitrogen and is especially unfortunate in that it removes the part that was most available to the crop. The conditions that are prejudicial to nitrification (i. e., lack of oxygen and presence of acidity) are those that favor denitrification, so that the farmer in producing proper conditions for the former desirable process is at the same time preventing the injurious denitrification.

(16) Can Plants Use Free Nitrogen of the Air? — About four-fifths of the volume of the air consists of the element nitrogen, so that if this was generally available to plants, there could be no such thing as "nitrogen starvation." Perhaps no question in the realm of agricultural chemistry or plant physiology has received so much attention as the relation of the plant to the nitrogen of the atmosphere and many points still remain to be investigated. The question heading this section can best be answered by a very brief historical review of the subject. At one time it was generally believed that the air was the sole source of the nitrogen supply for the plant. The first important experiments that indicated the contrary were those of Boussingault, in which he grew plants in sterile soil free from nitrogen, the plants being so protected that they came in contact with no nitrogen save that of the air. The plants grew for a short time only, and on analysis showed that they contained no more nitrogen than was present in the seed. Similar experiments conducted by Ville gave contrary results. To decide the matter a great number of painstaking experiments were carried out at Rothamsted, England, all of which confirmed the results obtained by Boussingault and the question was considered settled by most experimenters. It occurred to an American investigator (Atwater) that plants grown under natural conditions might use free nitrogen, even though they did not under the conditions of these experiments. He, therefore, grew plants in pots in the open, analyzing the soil before, and the soil plus the plant at the end of the experiment, correcting for the nitrogen carried down in the rain water. He found that while in most cases there was no gain of nitrogen, in some cases there was and that the plants showing a gain of nitrogen invariably belonged to the legumes. It remained for Hellrlegel to explain this phenomenon. He repeated the experiments of Boussingault with this variation, that he added to the soil a small quantity of water leached from a natural soil, so as to introduce any bacteria that might exist naturally in the earth. He found that the legumes grew vigorously while the cereals produced only feeble and short-lived plants. An examination of these legumes showed that they all had little nodules on their roots and these nodules were found to contain innumerable bacteria.

Further experiments have demonstrated that when leguminous plants are grown in soils containing the proper bacteria they can indirectly make use of free nitrogen and are practically independent of the nitrogen in the soil. This property is not a function of the legume itself, but of the bacteria that produce the nodules, and in the absence of these organisms the legumes are quite as dependent upon the supply of nitrates as are the other orders of plants. For all practical purposes then, it may be considered that clover, peas, beans, alfalfa and other legumes derive the bulk of their nitrogen from the air and that in growing them the farmer is not decreasing the nitrogen content of the soil.

(17) Inoculation of the Soil.— Experience has shown that all soils do not contain the bacteria necessary to the fixation of free nitrogen by legumes. They may be introduced into a field by sowing with the seed a small quantity of soil from a field in which the legume has been successfully grown. This has been done so often as to leave no doubt of its practicability. Late investigations have shown that the same species of bacteria will not do for all legumes, so that a soil, for instance, may grow clover to perfection when soy beans or alfalfa will not thrive on it at all. This fact explains many of the disappointments experienced by farmers in the trials of some of the more recently introduced leguminous crops.