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- The Farm That Won't Wear Out - 3/9 -
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 chlorids 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.
Liming the Soil
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.
THE NITROGEN PROBLEM AND
ITS ECONOMICAL SOLUTION
IN THE previous chapter emphasis has been laid upon the fact that plants as well as animals must have food, and that the neglect or ignorance of this factor in American agriculture has led to soil depletion and land ruin on vast areas, especially in the older states.
It has been shown that of the ten essential elements of plant food, five are provided by natural processes without the intervention of man; that, of the remaining five, potassium is the most abundant in normal soil, but requires liberation by good systems of farming; that ground natural limestone is the ideal material with which to supply calcium and to prevent or correct soil acidity; and that if dolomitic limestone be used magnesium is also supplied in suitable form for plant food, Thus only nitrogen and phosphorus remain for consideration.
Keeping in mind that systems of permanent profitable agriculture in America must be founded upon an intelligent understanding of the foundation principles involved, let us pray for strength to acknowledge the truth and cease trying to deceive ourselves. 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; and yet there is a method by which it can be secured not only without money but with profit in the process. The percentage of nitrogen in normal soils decreases with depth, so that subsoils are almost devoid of nitrogen. This would be more generally understood if it were known that the supply of soil nitrogen in humid countries is contained only in the organic matter.
This organic or vegetable matter consists of the partly decomposed residues of plants, including the roots and fallen leaves which may accumulate naturally, and the green manure crops, crop residues and farm manure which may be supplied in farm practice. Thus the nitrogen of a soil is measured approximately by its content of organic matter; and, vice versa, the percentage of nitrogen is an approximate measure of the organic matter, because nitrogen is a regular constituent of the organic matter normally contained in soils. Consequently if the organic matter of a soil is reduced the supply of nitrogen is also reduced.
In the most depleted soils nitrogen is usually the most deficient element, although it may not be the only deficiency. Thus in the depleted "Leonardtown loam," which occupies such extensive areas of land in Southern Maryland, near the District of Columbia, and which has been to a large extent agriculturally abandoned after one or two centuries of farming, only 900 pounds of nitrogen are found in the plowed soil of an acre--that is, in 2,000,000 pounds of surface soil, corresponding to about 6-2/3 inches an acre. This total amount if made available would be sufficient for only six such crops of corn as are actually produced on our best land in good seasons, and yet it is four times as much as is contained in an equal weight of the subsoil.
The average prairie land of the Corn Belt contains only 5000 pounds of nitrogen in the plowed soil of an acre 6-2/3 inches deep, whereas a 100-bushel crop of corn removes 150 pounds of nitrogen from the soil. A simple computation shows the supply in the plowed soil to be sufficient for only 33 such crops. Even the 100-bushel crop of corn per acre is known to have been produced in many places on exceptionally rich land, and yet the ten-year average yield in the United States is only 25 bushels to the acre.
200 Per Cent for Nitrogen
On Broadbalk Field at Rothamsted, England, wheat has been grown on the same land every year for about two-thirds of a century. As an average of the sixty years, 1852 to 1911 the yield was 12.6 bushels an acre on unfertilized land, 14.6 where mineral plant food was annually applied, 20.3 where nitrogen salts alone were used, and 37 where both nitrogen and mineral plant food were applied.
During the thirty years, 1882 to 1911 the average yields were 11.7 bushels an acre on the unfertilized land, 14 with minerals, 18.7 where only nitrogen salts were used, and 38 where both nitrogen and minerals were regularly supplied.
These absolute data from the oldest agricultural experiment station in the world should help us to understand why the ten-year average yield of wheat is 33 bushels an acre for all of Great Britain, 37-1/2 for England alone, and only 14 for the United States.
The application of nitrogen increased the yield of wheat by 24 bushels an acre--from 14 to 38 bushels--as an average of the last thirty years, following an average increase of 26.3 for the nitrogen
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