The chemical trinity: Nitrogen, phosphorus, and potassium in the history of soil fertility

“ PROBABLY the most important single problem which confronts the farmer to-day is that of the conservation of the fertility of the soil. Fertility may be defined as that condition of the soil which yields the maximum of that material which the plant is capable of using for the best development of those qualities which the farmer desires. ”

“ The modern agriculturist realizes that the soil is a laboratory for the production of plant food and he ordinarily takes more pains to provide a balanced ration for it than he does for his family. Of course the necessity of feeding the soil has been known ever since man began to settle down and the ancient methods of maintaining its fertility, though discovered accidentally and followed blindly, were sound and efficacious. ”

“ Millions have been saved to the farmers in the past; millions will be saved in the future; and all through the aid of scientific research.
The first real substantial assistance received by the farming public from science was in the examination and inspection of commercial fertilizers. Liebig demonstrated that plants secured most of their nutrition from soil ingredients. Nitrogen, potash, and phosphoric acid were those most in demand by the plant, and where crops were removed from the soil these articles of plant food were diminished, thereby reducing cropping capacity. ”

“ In the nutrition of plants four substances are of prime importance. First, carbonic acid gas, which yields carbon, the most widely diffused of all the elements (but which we need not dwell upon here) , since plants take it chiefly from the atmosphere, to which it is supplied unceasingly. After carbonic acid come potash, phosphoric acid, and nitrogen, all of which the roots extract from the soil, where it occurs in some compound or other. These are the ingredients that the soil, if it is to remain fertile, must have given back to it as fast as they are exhausted by the crops. ”

“ The word manure is now applied to any substance which by its application contributes to the fertility of a soil. As has been shown in the previous chapter, the substances necessary for plant-growth which are apt to be lacking in a soil, are only generally three in number—viz., nitrogen, phosphoric acid, and potash. A manure, therefore, is understood to be any substance containing these ingredients, either singly or together, and its commercial value is determined by the amount it contains of these substances. ”

“ I mean the amount of available plant-food in the soil. Nearly all our farms are poorer in plant-food to-day than when first cleared of the original forest, or than they were ten, fifteen, or twenty years later. In other words, the plants and animals that have been sold from the farm, have carried off a considerable amount of plant-food. We have taken far more nitrogen, phosphoric acid, potash, etc., out of the soil, than we have returned to it in the shape of manure. Consequently, the soil must contain less and less of plant-food every year. ”

“ Let us grant that most of our farm lands in the South have been in cultivation for fifty or seventy-five years, and in many instances for one hundred years, it is readily seen that practically all of the phosphorus and nitrogen in the plowed soil have been exhausted. Is it any wonder then that we are having such poor crops? The wonder is that our crops have kept up so well. Unless a radical change is made in our mode of farming, we must expect less and less crops each year until we have no crops, or such little that we can hardly pay the rent. ”

“ It is as much to the futile results of the chemical analyses of soils and fertilizers as applied to the growing of crops as to any other single thing that farmers have been so hostile to 'scientific' farming and to scientific agricultural institutions.
The physical conditions of the soil in regard to fertility are as important perhaps to the farmer as all the others put together, because they are more directly under his control. ”

“ Science was to solve at one fell swoop all the age- old problems of agriculture. And the whole thing was all right in every way but one—it didn't work. The unwelcome and obdurate fact remained that a certain number of pounds of nitrogen, phosphoric acid and potash—about thirty-three—in a ton of good manure would grow bigger crops than would the same number of pounds of the same elements in a bag of chemical fertilizer. ”

“ Nitrogen.—Though we are still far from knowing what are the exact functions which nitrogen fulfils in plant life, there is no doubt as to the important part which it plays in the vegetable growth of the plant and in the formation of stem and leaf. Without a sufficiency of nitrogen the plant would be stunted in growth. Its growth, indeed, may be said to be measured by the supply of nitrogen, for while mineral constituents like phosphoric acid and potash are only taken up to the extent that the plant can use them i.e. ”

“ If the clover and straw had been returned to the land either directly or in farm manure the additional nitrogen thus provided would have been sufficient both to maintain the yield of barley and to prevent the moderate decrease which has occurred in the nitrogen content of the soil.
CHAPTER III PHOSPHORUS: THE MASTER KEY TO PERMANENT AGRICULTURE
THE greatest economic loss that America has ever sustained has been the loss of energy and profit in farming with an inadequate supply of phosphorus. Phosphorus is a Greek word which signifies "light-bringer" ”

“ Phosphorus.—This is the most important mineral element which has to be supplied to the soil by the agency of manuring. It occurs in ordinary fertile soils to the extent of only about .15%, reckoned as phosphoric acid, and though its absence in sufficiency is not so marked or so soon shown under prolonged cultivation as is that of nitrogen, yet the fact that it is needed by all classes of crops, and that its application in manurial form is attended with great benefits, makes its supply one of great importance. ”

“ As agriculture is the fundamental support of America and of all her other great industries, so the fertility of the soil is the absolute support of every form of agriculture. Now, if there is any one factor that can be the most important, where so many are positively essential, then the most important factor in the problem of adopting and maintaining permanent systems of profitable agriculture on American soils is the element phosphorus. ”

“ Without phosphates there can be neither growth nor life. This is why phosphates are so essential to worn-out land, especially where wheat has been grown continuously.
The third is also a mineral element, which completes the trine in fertility. Such crops as the cereals draw mostly on the phosphates within the soil; but a crop of potatoes draws mostly on the potash contained in the soil. You cannot go on indefinitely raising potatoes on the same land without furnishing potash. ”

“ Surely their food problem must be a simple one if the substances necessary to the formation of stem and leaves and blossom can all be got from so little earth. Wherein lies all the difficulty about poor soil which besets the farmer, and why must he buy tons of plant food and drill it carefully into the ground in order to get a remunerative crop of grain? The whole trouble for the farmer arises from the scarcity in the soil of two or three food elements which, although highly important, form I tut a small part of the total weight of growing plants. ”

“ In the supply of nitrogen we have a distinct advantage, because our soil contains nearly three times as much as your most common cultivated land, and even twice as much as your level upland soil, which you consider too poor for farming, but in which phosphorus and not nitrogen must be the first limiting element, the same as with ours. ”

“ One takes it for granted that some fertilizer will be used, for the plants must be normal to seed well. The three essential elements of soil fertility are nitrogen, potassium and phosphorus, and to get the best results compounds of these elements must be present in proper proportions. First, available potash must be present in normal quantity although a certain excess will not be harmful. If nitrates are present in excess, however, vegetative growth will be over stimulated and seed production will be small. ”

“ It would be well for them to know what constitutes fertility, generally speaking. There are three constituent elements of fertility, namely: nitrogen, phosphate and potash. The first element, nitrogen, is what may be termed the motive power in the growing of the crops. There are inexhaustible supplies of this element in the atmosphere, and it only needs to be brought down. It costs you nothing. Help yourself. But it is a very costly element if you have to purchase it as a commercial commodity. Nitrogen, like the air we breathe, we can only use as we need it. ”

“ The truth is that by soil enrichment alone the average crop yields of the United States could be doubled, with the same seed and seasons and with but little more work than is now devoted to the fields; and we should cease trying to deceive ourselves in the hope or belief that the fertility of our soil will be maintained if we continue year after year to take crops from the land and fail to make adequate return.
Nitrogen is both the most abundant agriculturally and the most expensive commercially of all the elements of plant food ”

“ Now let us take a test tube and put into it lime, potash, soda, iron, silicon, or sand, and phosphorus, add to it a grain of corn, and watch results. Under suitable conditions of warmth and moisture the grain will sprout, but when the store of food laid up in it is exhausted our little plant will die. It is obvious that something else is needed for a soil, and analysis shows that it is nitrogen, the gas that forms nearly four fifths of our atmosphere—a gas useless, as such, to animals, but essential to plants. Nitrogen is abundant in Nature. ”

“ It is as nitrates that most plants absorb the nitrogen they require to build up their tissue. In nature the nitrogen, present in the soil as ammonia and different organic forms, is constantly being converted into nitric acid. This conversion of nitrogen into nitrates, known as nitrification, is a process of very great importance, and, as has been already pointed out in the Introductory Chapter, is effected through the agency of micro-organisms (ferments) . ”

“ Untiring research by many men and in many places has taught us that it is the mysterious force in living protoplasm that in its aggressive way reaches out and appropriates the restless molecules of atmospheric nitrogen; that though it destroys it also builds up. Practical experience had taught the ancients that crops of the legume family, crops like clover, beans, lupines, etc., do not exhaust the soil to such an extent as do crops not belonging to the same family. ”

“ The plant gets its phosphorus from phosphoric acid, its potassium from potash, and its calcium from lime.
There is a class of plants which have the power of taking free nitrogen from the air. These are the leguminous plants; such as clover, beans, cowpeas, alfalfa, soy bean, etc. They do it through the acid of microscopic organisms called bacteria which live in nodules or tubercles on the roots of these plants (Figs. 34-35) . Collect roots of these plants and find the nodules on them. The bacteria take nitrogen from the air which penetrates the soil and give it over to the plants. ”

“ The other elements are phosphorus, potassium, magnesium, calcium, iron and sulphur, all of which are secured from the soil. The soil nitrogen is contained in the organic matter or humus, and to maintain the supply of nitrogen we should keep the soil well stored with organic matter, making liberal use of clover or other legumes which have power to secure nitrogen from the inexhaustible supply in the air. ”

“ In Lawes and Gilbert’s experiments, there is a great loss of nitric acid from drainage. In no case has as much nitrogen been obtained in the increased crop as was applied in the manure. There is always a loss and probably always will be. But we should do all we can to make this loss as small as possible, consistent with the production of profitable crops.
There are many ways of lessening this loss of nitric acid. Our farmers sow superphosphate with their wheat in the autumn, and this stimulates, we think, the growth of roots, which ramify in all directions through the soil. ”

“ The phosphate minerals and the fertilizers manufactured therefrom are of primary importance to agriculture. The phosphoric-acid content of soils is mostly very small, and only a fraction of it is usually in an immediately available form. Hence for permanent productiveness, and especially for intensive farming or gardening, a cheap supply of phosphate fertilizers is of first importance in all soils and climates. ”

“ If we retain the straw on the farm and sell only the grain, the supply of potassium in the surface soil of Poorland Farm is sufficient to meet the needs of a fifty bushel crop of wheat per acre every year for nineteen hundred and twenty years, or longer than the time that has passed since the Master walked among men on the earth; whereas, the total phosphorus content of the same soil is sufficient for only seventy such crops, or for as long as the full life of one man. ”

“ His withering blight has fallen upon every living thing within his reach, himself not excepted; and his besom of destruction in the uncontrolled hands of a generation has swept into the sea soil fertility which only centuries of life could accumulate, and yet this fertility is the substratum of all that is living. It must be recognized that the phosphate deposits which we are beginning to return to our fields are but measures of fertility lost from older soils, and indices of processes still in progress. ”

“ As an average of the most common commercial fertilizers sold to the farmers in the Eastern and Southern States, the four hundred pounds would add to the soil seven pounds of nitrogen, fourteen pounds of phosphorus and seven pounds of potassium, while a single fifty-bushel crop of corn will remove from the soil ten times as much nitrogen, five times as much potassium, and nearly as much phosphorus as the total amounts applied in this six-year or seven-year rotation. ”

“ From the amounts of nitrogen, phosphorus and potassium applied annually to the cultivated fields of Japan and from the data in these two tables it may be readily seen that these people are now and probably long have been applying quite as much of these three plant food elements to their fields with each planting as are removed with the crop, and if this is true in Japan it must also be true in China. Moreover there is nothing in American agricultural practice which indicates that we shall not ultimately be compelled to do likewise. ”

“ Hensel declares that the current theory of fertilizing is wrong. Too much potash, phosphorus, and nitrogen, he says, are supplied to plants, and not enough lime, magnesia, silica, sulphur, or fluorine. The normal soil consists of weathered rocks. This is the best soil for plants, producing not only vigorous growth, but also edible parts of firm texture, resisting insects, and valuable and wholesome for food. ”

“ Nearly all the other ingredients are indispensable to the growth of plants, and if we should use manures containing nothing but nitrogen, phosphoric acid, and potash, the time would come when the crops would fail, from lack of a sufficient quantity of, perhaps, magnesia, or lime, sulphuric acid, or soluble silica, or iron. ”

“ The aim of fertilization, as a rule, is merely to increase crop production. But this may prove to be not merely shortsighted, it may turn out to be a social crime. It is criminal, indeed, as a great many diseases are directly traceable to incomplete and improper fertilization.
Let us face the effect of attempting to fertilize our fields with nothing more than stable manure, which, it is true, supplies phosphoric acid, potash and nitrogen. We know that phosphorus forms the foundation of nerves, and too much of it provokes nerve irritation in exact ratio to the deficiency of sulphur. ”

“ Nitrogen and phosphorus occur in the effluent from waste treatment plants, for they are present in human wastes and in detergents, and in dissolved form are little affected by standard treatment processes. And in the upper Basin a large part of the nutrient load in streams appears to be associated with sediment from the same diffused land runoff mentioned above, for they occur abundantly in manure, in synthetic fertilizers, in certain natural soils, and in decaying organic substances of many kinds. The health and growth of living things is dependent on these elements, of course ”

“ The very evident decrease in the fertility of those soils which have been under cultivation for a number of years, combined with the increased competition and the advanced price of labor, have convinced the intelligent farmer that the agriculture of the future must be based upon more rational practices than those which have been followed in the past. We have felt for some time that there was a place for a brief, and at the same time comprehensive, treatise on this important subject of Soil Fertility. ”