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Fertilizers For Different Crops

( Originally Published 1915 )

Fertilizers for Different Crops.—Much valuable information may be gathered from a series of lessons on special fertilizers for the different crops. While there is danger here, as in all of the work, that we may be too dogmatic, yet if we bear in mind that the science of fertilizers is new, that the aim in the work is to awaken keen interest, that some child who does not appear to be very bright may make a discovery here that will be of inestimable value, and that we make a partial failure of the work unless we lead the children to do most of the reading and talking—if we remember all this, we cannot fail to accomplish more good than bad in this series of lessons.

The man growing special crops would no doubt like to know just what fertilizer to use for each crop. This can be answered only by experiment. The chemical analysis of his soil gives the potential plant food only, but it tells little as to what is available for the plants at any given time. No man can tell offhand just what is the most economical fertilizer for a certain crop on a certain piece of land. A man should study the results which the land and the neighboring farms are giving and have been giving. He must always have a margin of profit coming his way. If the land is giving satisfactory results compared with other pieces of land in the neighborhood, it may be said to be getting about the right treatment, but when it is giving unsatisfactory results some change of treatment is necessary. If it is an orchard in sod and not giving good results, it may be best to plow it up and plow under some cover crops, such as cowpeas, soybeans, or rye and vetch. If the growth of trees or vines is strong and the leaves large and dark colored, it may be that there is relatively too much nitrogen, and then better fruit will follow liberal fertilizing with phosphorus and potash. Or the overgrowth of wood may be checked by seeding down for a time. Certainly, farmers need to be cautioned of the danger of spending their net incomes for commercial fertilizers and then again of the equal danger in the other direction of going for years with poor crops when a little of one or more fertilizers will bring splendid returns.

Two Theories of Soil Fertility.—There are two theories of soil fertility. These two theories have divided the soil specialists into two distinct and antagonistic schools. The first theory was announced some years ago by the great German scientist, Justin von Liebig. He found that the crops removed from the soil certain ingredients, and he believed that the soils could be made to produce indefinitely by mixing these ingredients and applying them to the soil again. His idea was that the field is like a great kettle into which we must put as much of each element as we take out if we do not wish to change the chemical contents. This theory is plausible, it is in harmony with what we learn and do in the chemical laboratories, and hence it is very generally accepted by laboratory men and by farmers who follow the laboratory scientists. Of course the theory is of value to the men who have commercial fertilizers to sell, and hence their advertising helps to keep the theory before the minds of the farmers. By this theory our lands are slowly and inevitably declining unless we put back as much as each crop takes off.

One thousand pounds of corn use about 8 pounds of nitrogen, 7 pounds of phosphoric acid, and 4 pounds of potassium. One thousand pounds of oats use 22 pounds of nitrogen, 8 pounds of phosphoric acid and 6 pounds of potassium. By the Liebig theory all that we have to do is to learn the percentages of the pure chemicals in the different fertilizers, and apply enough of each to take the place of what the crop takes off and we keep up the fertility of our soil. We find these percentages by looking at the tags on the sacks of fertilizers or the tables issued by our state examiners. We find the amounts of the different elements by referring to the tables in any standard book on soils or fertilizers. But there is danger here. There is great danger that the farmer will spend his net income for commercial fertilizers. The theory does not take account of the slow disintegration of the soil. The theory does not give sufficient recognition to the fact that the fields may be subject to erosion and hence the commercial fertilizer which we apply may be washed on to the field of the next neighbor or, worse, into the ocean.

To counteract these dangers, Professor Whitney of the United States Department of Agriculture announced his theory in the now famous sentence, " The resources of the soil are the one immutable asset of the nation. They may be impaired by abuse, but never destroyed." The followers of Professor Whitney throw the emphasis on the facts that the soil is constantly turning loose plant food, the legumes store nitrogen, the farmer may by bad farm practice so lock up his plant foods that they are unavailable for a year or more, that the farmer must be very careful when buying commercial fertilizers to keep the net profit on his side and not on the side of the man who sells the fertilizers, and lastly and most important, the chemical analysis of the soil as given above shows that there are enough chemicals present in most soils to produce maximum crops for one hundred years. This throws the emphasis on good farm practice rather than on restoring chemicals.

There is some truth in each theory. The farmer needs to know both, and he needs to know what the different chemicals do for his plants and where he may get the largest amount of each chemical for his money.

The Four Necessary Elements.—The scientists are agreed, that, of the ten or fourteen elements which a plant needs, at least one or more of three of them may be lacking. These three are nitrogen, potassium and phosphorus. Some of the scientists add a fourth element, calcium, but not all scientists think of calcium as a necessary plant food.

Nitrogen.—Nitrogen is a very necessary plant food. It may be purchased in commercial fertilizers, (1) as nitrate of soda, mined in Chile, (2) ammonium sulphate, a by-product of the gas works, (3) dried blood and other products of the slaughter houses, (4) cotton seed meal and other plant refuse, and (5) as fish scrap. Nitrogen is very necessary for growth of leaves and stems. If you see a field with rank, dark-colored leaves you may be reasonably sure that there is plenty of nitrogen there. On the other hand, yellow leaves are apt to indicate a lack of nitrogen, though dry weather or water smothering of roots may be the cause of the unthrifty leaves. Nitrogen to induce a growth of stems and leaves is especially needed for pastures, for hay crops, silo corn, and such garden crops as lettuce, cabbage, endive, spinach, asparagus, etc.

Potassium.-Potassium is the element which we get• from potash. The cheapest source is wood ashes, decaying plant stems and disintegrating rock, especially feldspar. The commercial sources are muriate of potash, sulphate of potash and kainite from the mines of Germany. Potash is believed to be helpful, especially in the formation of the cell walls. Frequently orchards overfertilized with nitrogen may be made to bear fruit by feeding the trees more potash. So with strawberry beds and other small fruit patches. We are reasonably safe if we think of potash as necessary to the formation of large cell walls for fruit and seeds.

Phosphorus.—But we might have cell walls and little or nothing in them. We frequently find wheat making large, dark-colored stems and leaves and then setting large, heavy heads. But when harvest time comes, we find small, shrivelled seeds. What was the matter ? Evidently something was wanted to induce more cell activity until the seeds were filled. It is believed that phosphorus is principally useful in inducing cell activity. On most farms we seem to get better results from the application of phosphoric acid than from the application of any other commercial fertilizer. Phosphorus is applied in a form called phosphoric acid though it, like carbonic acid, is not an acid. The commercial forms of phosphoric acid are ground rock from Tennessee, South Carolina, Florida and some of the western states. The mines in the western states are not all available yet because of lack of railroad facilities.

Lime.—Experience teaches us that most soils cropped for any length of time may need lime. This may be for either of two reasons, the soil may have become sour or it may be lacking in calcium. Lime like other plant foods is constantly being leached and washed away. We may get lime in any one of three forms from ground or crushed limestone. If the stone be heated and the carbon dioxide driven off, we have caustic lime. If water be applied to the caustic lime, we have hydrated lime. If the crushed stone be ground and not heated in the kiln, we have ground limestone, which is the form preferred for agricultural purposes, though if the hauling be too expensive we may use the caustic form.

There are two stones which are sold as limestone. One is a calcium stone with. some 90 to 89 per cent of calcium in it. The other is a dolomite (calcium-magnesium) stone testing 40 to 50 per cent magnesia. Hall says the English farmers regarded this as injurious rather than beneficial, and Hilgard says, " An excess of magnesium over lime is injurious to most crops. But for neutralizing acid, the magnesia lime-stone does quite as well as pure calcium limestone."

Lime is especially beneficial to certain plants among which are clovers, alfalfa, beans, lettuce, celery, cauliflower, canteloupes, onions, asparagus, and cabbage. The following crops show little if any help derived from lime : cowpeas, alsike clover, sorrel, tomatoes, tobacco, watermelons, chestnut trees, black-berries, raspberries and rye.

Both caustic lime and magnesian lime are believed to be injurious to bacteria which grow on the roots of the clovers and alfalfa. But experiments have been tried where magnesian lime gave results equal to those obtained with pure calcium lime.

For some years there have been accumulating the results of many experiments and much speculation as to the relative functions and values of calcium and magnesium in animal and plant nutrition and growth. From these we gather the following: Both magnesium and calcium are necessary plant foods, either magnesian or calcium limestone will sweeten a sour soil, but beyond that the scientists do not agree.

Magnesium.—Magnesium is essential for the growth of plants, especially seeds. Magnesium is found in and used by growing stems and leaves, and, strange to say, it has the peculiar power to migrate in the growing plant from one part to another. It seems in some way necessary to prepare the way for the action of phosphorus and other elements. While magnesium is an essential element in plant and animal tissues yet there is very apt to be a sufficient quantity in all soils and feeds. And here comes the important thing for farmers to know, namely, that an excess of magnesium in the soil acts like a poison for most plants, and an excess of magnesium in the food acts like a poison for animals. Notice that the emphasis is on the excess of magnesium over calcium which, in most if not every case, acts as an antidote for the magnesium poison.

An excess of calcium for land may be obtained from a pure calcium limestone and an excess of calcium for an animal mava be obtained from the leaves of plants and from milk. Cows' milk is among the richest in calcium. What does this mean for the farmer ? It means that a very profitable way to make money is to feed the limestone to the soil, which gives it to plants, especially alfalfa, which in turn may be eaten by the cows. Lime-stone with 98 per cent of calcium in it may be spread on land for about five dollars per ton. Alfalfa which has in its ash about 34 per cent of calcium may be obtained in most markets for less than twenty dollars per ton. Milk which has in its ash about .16 per cent calcium sells at seventy-five or eighty dollars per ton.

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