IT IS an old saying that "any fool can farm," and this was almost the truth when farming consisted chiefly in reducing the fertility of new, rich land secured at practically no cost from a generous Government. But to restore depleted soils to high productive power in economic systems is no fool's job, for it requires mental as well as muscular energy; and no apologies should be expected from those who necessarily make use of technical terms in the discussion of this technical subject, notwithstanding the common foolish advice that farmers should be given a sort of "parrot" instruction in almost baby language instead of established facts and principles in definite and permanent scientific terms. The farmer should be as familiar with the names of the ten essential elements of plant food as he is with the names of his ten nearest neighbors. Safe and permanent systems of soil improvement and preservation may come with intelligence—never with ignorance—on the part of the landowners.
When the knowledge becomes general that food for plants is just as necessary as food for animals, then American agriculture will mean more than merely working the land for all that's in it. This knowledge is as well established as the fact that the earth is round, although the people are relatively few who understand or make intelligent application of the existing information.
Agricultural plants consist of ten elements, known as the essential elements of plant food; and not a kernel of corn or a grain of wheat, not a leaf of clover or a spear of grass can be produced if the plant fails to secure any one of these ten elements. Some of these are supplied to plants in abundance by natural processes; others are not so provided and must be supplied by the farmer, or his land becomes impoverished and unproductive.
Two elements, carbon and oxygen, are contained in normal air in the form of a gas called carbon dioxid, and this compound is taken into the plant through the breathing pores, which are microscopic openings located chiefly on the under side of the leaves. Some plants have more than a hundred thousand breathing pores to the square inch of leaf surface.
When plants or plant products are burned or decomposed the carbon of the combustible material—grass, wood, coal, and so forth—unites with the free oxygen of the atmosphere to re-form the carbon dioxid, which thus returns as a gas to the air. Even the food taken into the animal system, after being digested and carried into the blood, is brought, into contact with the oxygen of the air—which also passes into the blood through the cell walls of the lungs—and a form of combustion takes place, the heat generated serving to warm the body while the carbon dioxid passes back into the lungs and is exhaled into the open air.
By these circulation processes the supply of carbon dioxid in the atmosphere is renewed and maintained without any special effort on the part of man. Hydrogen is one of the elements of which water is composed. Water is taken into the plant through the roots, carried through the stems to the leaves, and there, under the influence of chlorophyll, sunlight and the life principle, the carbon, oxygen and hydrogen are made to unite into some of the most important plant compounds, such as the sugars, which are later transformed into starch and fiber.
Though these three elements constitute the larger part of the mature agricultural plant they are no more necessary for plant growth than the seven which are supplied by the soil. Iron is one of the essential elements of plant food; but the amount required by plants is so small and the amount contained in the soil is so large that soils have never been known to become deficient in iron. Though sulfur is found in plants in very appreciable amounts and is known to be essential to plant growth, it is evident that plants do not need so much sulfur as they often contain, some of it being taken up and merely tolerated, as is the case with all of the sodium and silicon found in plants, neither of these being required for normal growth, although commonly found in plants in very considerable amounts. The supply of sulfur in normal soils is not large; but, with the combustion and decay of organic materials—coal, wood, grass, leaves, and so forth—sulfur passes into the air and is brought back to the soil dissolved in rain or absorbed by direct contact of soil and air. Thus under normal conditions the supply of sulfur naturally provided is ample to meet the needs of the staple farm crops, although there are some plants, such as cabbage, for example, which may possibly be benefited by fertilizing with sulfur.
But there are five other essential elements of plant food, and these require special consideration in connection with permanent soil fertility. They are potassium, magnesium, calcium, phosphorus and nitrogen. There are also five important points to be kept in mind in relation to each of these elements: (1) the soil's supply, (2) the crop requirements, (3) the loss by leaching, (4) the methods of liberation, and (5) the means of renewal.
The neglect of one or more of these important points in relation to one or more of these five elements has reduced the fertility of most cultivated soils in the United States, has greatly impoverished the older farm lands, and has brought agricultural abandonment to millions of acres in the original thirteen states. On the other hand, intelligent attention to these same factors will bring restoration and high productive power to such lands.
Where these five elements were supplied regularly to land on the Rothamsted Experiment Station the average yield of wheat for the thirty years, 1852 to 1881, was 35.9 bushels an acre, while 13.6 was the average yield of similar unfertilized land; and during the next thirty years—1882 to 1911—the corresponding average yields were 38 bushels an acre on the fertilized land, and 11.7 bushels where no plant food was applied. These statements are not mere opinions, but determined facts whose accuracy stands unquestioned.
On another field at Rothamsted, England, the average yield of barley for the same sixty years was 43 bushels an acre where nitrogen, phosphorus and calcium were regularly applied, 42.6 where all five elements—including potassium and magnesium—were added, but only 14.3 on unfertilized land.
On still another Rothamsted experiment field, where a four-year crop rotation of turnips, barley, clover (or beans) and wheat has been practiced since 1848, the yield of turnips in 1908 was 717 pounds an acre on unfertilized land and 35,168 pounds where the five important elements of plant food had been regularly applied once every four years—for the turnips only—since 1848. In 1909 the barley yielded 33.4 bushels an acre on the fertilized land, but only 10 bushels where no plant food was applied. The yield of clover in 1910 was 8590 pounds an acre on the land fertilized for turnips, but only 1949 on the unfertilized land. The wheat following the clover with no other fertilizer produced 24.5 bushels an acre in 1911, but 38 bushels where plant food is always applied for turnips grown three years before.
These are the established facts from the longest accurate record, and thus the most trustworthy data the world affords; and when one hears promulgated the very pleasing doctrine that the rotation of crops will maintain the fertility of the soil it is time to remember that "to err is human."
Of the four important mineral elements, potassium is by far the most abundant in common soils. Thus, as an average of ten residual soils from ten different geological formations in the eastern part of United States, two million pounds of subsurface soil were found to contain:
Potassium 37,860 pounds
Magnesium 14,080 pounds
Calcium 7,810 pounds
Phosphorus 1,100 pounds
Even the depleted, and to some extent abandoned, gently undulating upland "Leonardtown loam," which was farmed for generations and which, according to the surveys of the Federal Bureau of Soils, covers 41 per cent of St. Mary's County, Maryland, and more than 45,000 acres of Prince George's County—still contains in two million pounds of surface soil—corresponding to the plowed soil of an acre about 6-2/3 inches deep:
Potassium 18,500 pounds
Magnesium 3,480 pounds
Calcium 1,000 pounds
Phosphorus 160 pounds
The brown silt loam prairie soil of the early Wisconsin glaciation is the most common type of the greatest soil area in the Illinois Corn Belt. Two million pounds of this surface soil contain as an average:
Potassium 36,250 pounds
Magnesium 8,790 pounds
Calcium 11,450 pounds
Phosphorus 1,190 pounds
The older gray silt loam prairie, the most extensive soil of Southern Illinois, contains in two million pounds of soil:
Potassium 24,940 pounds
Magnesium 4,690 pounds
Calcium 3,420 pounds
Phosphorus 840 pounds
These data represent averages involving hundreds of soil analyses, and they emphasize the fact that normal soils are rich in potassium and poor in phosphorus. This is to be expected, for most soils are made from the earth's crust, and normal soils should bear some relation in composition to the average of the earth's crust, which contains in two million pounds 49,200 pounds of potassium and 2,200 pounds of phosphorus, as shown by the weighted averages of analyses involving about two thousand samples of representative rocks, reported by the United States Geological Survey.
The plant food required for one acre of wheat yielding 50 bushels, one acre each of corn and oats yielding 100 bushels, and one acre of clover yielding four tons, includes for the total crops:
Potassium 320 pounds
Magnesium 68 pounds
Calcium 168 pounds
Phosphorus 77 pounds
If only the grain, including a yield of 4 bushels an acre of clover seed, is considered, the straw, stalks and hay being returned to the soil—either directly or in farm fertilizer—then the loss per acre from four years of cropping as above would be as follows:
Potassium 51 pounds
Magnesium 16 pounds
Calcium 5 pounds
Phosphorus 42 pounds
The average annual loss by leaching from good soils in humid sections is known by the results of many analyses to be about as follows per acre:
Potassium 10 pounds
Calcium 300 pounds
Phosphorus 2 pounds
The average annual loss of magnesium in drainage water from good soils is probably 30 pounds or more an acre, but the data thus far secured are inconclusive with respect to that element.
A careful consideration of the trustworthy data clearly reveals the fact that potassium is very abundant in normal soils, while phosphorus is relatively very deficient; and, all things considered, calcium—and probably magnesium—is of much greater significance than potassium, from the standpoint of the maintenance of usable plant food in the soil. It should be noted, too, that certain crops which are exceedingly important for economic systems of permanent agriculture require very large amounts of calcium as plant food. Thus a four-ton crop of clover hay takes about 120 pounds of calcium from the soil, or the same amount as of potassium; while such a crop of alfalfa requires about 145 pounds of calcium, but only 96 pounds of potassium. When it is known that the abandoned "Leonardtown loam" still contains in two million pounds of surface soil 18,500 pounds of potassium and only 1000 pounds of total calcium, the significance of these chemical and mathematical data must be apparent.
Probably there has never been a greater waste of time and effort in the name of science than in the endeavor to determine the "available" plant food in soils. The almost universal assumption has been that the plant food in the soil exists in two distinct conditions, "available" and "unavailable," and that the determination of the "available" plant food would reveal both the crop-producing power of the soil and the fundamental fertilizer requirements for the improvement of the soil for crop production.
After ascertaining the total stock of plant food in the plowed soil, the next important question is not how much is "available," but rather how much can be made available during the crop season, year after year. In other words we must make plant food available by practical methods of liberation, by converting it from insoluble compounds into soluble and usable forms; for plant food must be in solution before the plant can take it from the soil. For the present, space is taken only to emphasize the value of decaying organic manures in the important matter of making plant food available; and attention is also called to the fact that the decomposition of the organic matter of the soil—including both fresh materials and old humus—is hastened by tillage and by underdrainage, which permit the oxygen of the air to enter the soil more freely, oxygen being a most active agent in nitrification and other decomposition processes of organic matter, as well as in the more common combustion of wood, coal, and so forth.
In rational systems of general farming the supply of any element which is normally very abundant may be renewed from the subsoil by even the very slight erosion which occurs on all ordinary lands in humid sections. This statement applies to iron and potassium, and often to magnesium.
If two million pounds of normal surface soil contain 30,000 pounds of potassium, one inch an acre would contain 4500 pounds of that element; and if a third of this—1500 pounds—were removed by cropping and leaching before its removal by surface washing, then two-thirds of a century could be allowed for the erosion of one inch of soil, with crop yields of 50 bushels of wheat, 100 bushels of corn and oats, and 4 bushels of clover seed to the acre, provided the stalks, straw and clover hay were returned to the land, either directly or in farm manure. This amount of surface washing is likely to occur on land sufficiently undulating for good surface drainage, provided the land is plowed and cultivated as frequently as would be required for a four-year rotation as suggested above. Where hay, straw, potatoes, root crops or common market garden crops are sold, very much larger amounts of potassium leave the farm than in grain farming or live-stock farming, and in such cases potassium must ultimately be purchased and returned to the soil, either in commercial form or in animal manures from the cities.
There are some soils, however, which are not normal—soils whose composition bears no sort of relation to the average of the earth's crust; such, for example, as peaty swamp soil or bog lands, which consist largely of partly decayed moss and swamp grasses. These soils are exceedingly poor in potassium, and they are markedly and very profitably improved by potassium fertilizers, such as potassium sulphate and potassium chloride—commonly but erroneously called "muriate" of potash.
Thus, as an average of triplicate tests each year, the addition of potassium to such land on the University of Illinois experiment field near Manito, Mason county, increased the yield by 20.7 bushels more corn to the acre in 1902, by 23.5 in 1903, by 29 in 1904 and by 36.8 in 1905; and the proceedings of the midsummer session of the Illinois State Farmers' Institute for 1911 report that the use of $22,500 in potassium salts on the peaty swamp lands in the neighborhood of Tampico, Whiteside county, increased the value of the corn crop in 1910 by $210,000, the average increase for potassium being about 30 bushels of corn to the acre.
Some sand soils, particularly residual sands, which often consist largely of quartz-silicon dioxid—are very deficient in potassium; consequently the experiments or demonstrations conducted by the potash syndicate at Southern Pines, North Carolina, show very marked increases from the use of potassium salts on such soil, although the result ought not to be used to encourage the use of such fertilizers on normal soils, which are exceedingly rich in potassium.
Even in soils abundantly supplied with potassium temporary use may well be made of soluble potassium salts when no adequate supply of decaying organic matter can be provided. For this purpose, kainit—which contains potassium and also magnesium and sodium in chlorides and sulfates—is preferred to the more concentrated and more expensive potassium salts. About 600 pounds an acre every four years is a good application. The kainit will not only furnish soluble potassium and magnesium but will also help to dissolve and thus make available other mineral plant food naturally present or supplied, such as natural phosphates. When the supply of organic matter produced in crops and returned either in farm manure or in crop residues becomes sufficiently abundant, then the addition of kainit may be discontinued on normal soil.
Thus, as an average of 112 separate tests covering four different years, on the Southern Illinois experiment field on worn, thin land, at Fairfield, the use of 600 pounds an acre of kainit once in four years increased the yield of corn by 10.7 bushels where no organic manure was used, and by only 1.7 bushels when applied with eight tons of farm manure.
In the form of ashes, marl or chalk, lime has been used as a fertilizer for thousands of years. It serves two very important purposes: to correct the acidity of sour soils and to supply calcium and sometimes magnesium as plant food. Burned lime has also been much used, but in more recent years the development of machinery for crushing and pulverizing rock—especially in cement manufacture—has made possible the production of pulverized natural limestone, and at much less expense than for caustic lime made by burning and slaking. Where ground limestone can be easily procured it takes the place of burned lime, and it produces better results at less expense, even though 1-3/4 tons of ground limestone are required to equal 1 ton of quicklime in calcium content and in power to correct acidity.
Furthermore, ground limestone can be applied in any amount with no injurious results, while caustic lime destroys the organic matter or humus of the soil, dissipates soil nitrogen, is disagreeable to handle, and may injure the crop unless applied in limited amounts or several months before the crop is to be planted.
The most valuable and trustworthy investigation on record in regard to the comparative value of burned lime and ground limestone has been conducted by the Pennsylvania Experiment Station. A four-year rotation of crops was practiced, including corn, oats, wheat and hay (clover and timothy) on four different fields, each crop being represented every year. After twenty years the results for the four acres showed that the land treated with ground limestone had produced 99 bushels more corn, 116 bushels more oats, 13 bushels more wheat and 5.6 tons more hay than the land treated with about an equivalent amount of burned lime. At the end of sixteen years the analysis of the soil showed that the burned lime had destroyed 4.7 tons of humus and had dissipated 375 pounds of nitrogen to the acre, as compared with the ground limestone, this loss being equivalent to 37-1/2 tons of farm manure.
Other trustworthy experiments by the Maryland and Ohio Experiment Stations confirm the Pennsylvania results in showing better crop yields when unburned lime carbonate was used; and more extensive experiments by the Tennessee Experiment Station also agree with the Pennsylvania data in regard to the destruction of organic matter and loss of soil nitrogen from the use of burned lime. If dolomitic limestone is used, magnesium as well as calcium is thus added to the soil.
Limestone need not be very finely pulverized. If ground so that it will pass through a ten-mesh sieve it is amply fine, assuming that the entire product is used, including the finer dust produced in grinding, and it is very possible that final investigations will show that the entire product from a quarter-inch screen is even more economical and profitable in permanent systems.
Limestone is quite easily soluble in soil water carrying carbonic acid. It is thus readily available; in fact, it is too available to be durable if very finely ground; and in humid sections the loss by leaching far exceeds that removed by cropping. In practical economic systems of farming about two tons an acre of ground limestone should be applied every four years, or corresponding amounts for other rotation periods.
The essential facts relating to potassium, magnesium and calcium and to the use and value of different forms of lime have been stated above, and they may be accepted with confidence for use in economic systems of farming on normal soils.
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