at once harrowed in. The ground should be stirred again before seeding. The application of one ton per acre every 4 to 6 years is advised for Illinois uplands.

Marl. This consists essentially of carbonate of lime. Often considerable amounts of organic matter, sand and clay are also present. It originated in the breaking down of fresh water shells. Its action is more slow and "mild" than that of lime. It has been "regarded rather as an amendment than a fertilizer." Its chief functions are in improving the tilth, neutralizing acidity, and promoting nitrification, besides supplying lime. The marls of New Jersey also contain potash and phosphoric acid.

Nitrate of Soda.-Trade in this as a fertilizer began between 1830 and 1840. The supply is limited. In 1860 all estimates showed that it would last nearly 1,500 years. By 1900 these estimates had fallen to less than 50 years, and the world's markets were annually consuming nearly 1,500,000 tons, the United States requiring about 15 per cent of this amount. It is by far the most expensive fertilizer in use, and it is the best carrier of nitrogen.

Potash. The main sources are wood ashes, and, since 1860, the products furnished by the potash industry at Stassfurt, Germany. Several forms are imported from Germany, each containing a different but correctly warranted quantity of this fertilizer. Nearly 500,000 tons are imported annually by the United States. This is over half the product. Since 1860, the Stassfurt salts have been almost the only source of concentrated potash. Good wood ashes contain perhaps 10 per cent of potash. They were long used without the real reason of their value being known. Besides potash, ashes often contain considerable lime. Hartlib gave 23 fertilizers and means of fertilizing the ground, and among them were included lime, marl, ashes and chalk.

Gypsum or Land Plaster.-Those who are experimenting with this material report varied results. It has long been used, however, and the most reliable conclusions seem to be: (1) That gypsum has undoubted fertilizing value on many soils; (2) that its chief value depends on three processes: (a) Preservation of ammonia and perhaps other nitrogenous forms;

(b) decomposing potash and phosphorus-bearing silicates, liberating these two elements for plant-food; (c) affecting soils physically, making them granulated, or loose and mellow; (3) and that it decomposes sodium carbonate and thus breaks up the so-called "black-alkali."

Common Salt.-This has also been used as a fertilizer for at least several decades. In the eighties it was a common practice in England to sow salt in the early spring on wheat land that was too rich, the idea being that a larger deposit of silica in the stalk would result, enabling the wheat to stand better. While it has been found a valuable agent for increasing the yield of barley, it is of less importance in raising wheat.

Miscellaneous Fertilizers.-A great many other materials have been used to a greater or less extent as fertilizers. Among them are: Animal products, as wool waste and the refuse of modern slaughterhouses, blood, bone, hair, horn, hoof, etc., which with fish, manure and sulphate of ammonia from the gas works, are still the main sources of nitrogen applied to crops; swamp muck, marsh mud, sea-weed, sludge, poudrette, potassium, cottonseed meal, rape-cake, burnt clay, charred peat, soot and green manuring crops. The latter are simply plowed under, a practice widely followed in the United States, especially with alfalfa and other legumes. Where stock can be raised, green crops and cottonseed meal have nearly as great a value for fertilizer after feeding as before, and yield the additional intermediate product of milk or beef.

It is interesting to note that the aborigines taught the early settlers of New England the value of fish as a fertilizer. Fish or fish waste should be composted. Quicklime is used in France. Fish compost readily yields its elements to growing crops, consequently it should be applied in the spring, and not deeply covered. Sludge is the precipitant of sewage, and poudrette is the same reduced to a dry powder. A part of their value lies in the germs of nitric ferment which they contain. Some 40 tons of wheat straw leached and burned on the soil contribute to it 8 pounds of phosphorus and 680 pounds of potassium, besides the nitrogen leached into the soil before the straw was burned. This immensely increases the yield of wheat. Mulching with straw does not seem to be of any benefit to wheat, whether applied for fertilizing or for winter protection.

Description

Fertilizing by Irrigation. To show the fertilizing value of irrigation waters, some analyses are given below.

COMPOSITION OF IRRIGATION WATER.

Results expressed in parts per 1,000,000

The waters of the Nile seem to have the largest amount of nitrogen, 1.7 per cent, all the others having merely a trace. Some 24 acre-inches of Rio Grande water add to the soil about 1,075 pounds of potash, 116 pounds of phosphoric acid, and 107 pounds of nitrogen. The same amount of Delaware river water contains 741.08 pounds of materials, while the Mississippi, St. Lawrence, Amazon and La Plata rivers average 655.6 pounds of solid matter for every 24 acre-inches. As a rule sewage waters from the cities have the highest value for irrigation, and muddy river waters stand next. Waters containing sulphate of iron are positively injurious when applied to land. They usually issue from peaty or boggy swamps. While the fertilizing value of sewage waters is unquestioned, and while their use has been almost universally favored, objections have been made to them on other grounds. To say the least, they undoubtedly contain a hidden danger, and if used at all, it should be with the greatest of care. It has been claimed that "the use of sewage for fertilizing purposes is not to be commended because of the danger of contaminating the soil with 1 Rept. Mont. Exp. Sta., 1902, p. 62.

2 Exp. Sta. Record, V. 14, No. 11, p. 1057.

pathogenic ferments, which may subsequently infect the health of man and beast. These ferments may attach themselves to vegetables and thus enter the animal organism, or they may remain with a suspended vitality for an indefinite period in the soil and awaken to pernicious activity when a favorable environment is secured."

Vast stores of fertilizing materials are continually being washed from the earth by floods, and carried away by streams and rivers. The Seine river thus annually carries two million tons of silt, a greater weight than the merchandise which its waters transport. The Var carries seaward yearly 23,000 tons of nitrogen, and one cubic meter of water per second from this stream could be made to produce crops valued at 35,000 francs each year. The river Durance, an Alpine stream, annually carries silt, the fertilizing power of which is equal to 100,000 tons of stable compost or excellent guano. It would take 119,000 acres of forest trees to yield the carbon that this volume of silt contains.

FERTILIZER EFFECTS

Effect on Germination. In general, fertilizers never seem to aid in the germination of seeds, and may be harmful if used in large quantities. One per cent of muriate of potash, or of sodium nitrate, is very detrimental, whether applied directly, or mixed with the soil. Phosphoric acid and lime are much less injurious, and may be harmless if not used in excess. It is safest not to bring commercial fertilizers into immediate contact with germinating seeds, and the effect of chemicals applied to seeds before they are planted is no index of their action in this respect when used as fertilizers. When injury does result, it is chiefly to the young sprouts during the time between when they leave the seed coat and when they emerge from the soil, the seed being affected but slightly, if at all. Salts injurious to wheat seedlings have been given in the following order: Magnesium sulphate, magnesium chlorid, sodium carbonate, sodium sulphate and sodium chlorid. Different varieties of wheat vary in their ability to resist the same toxic salt, as does also one variety in different salts.

Effect on Yield and the Supply of Plant Food.-There seems to be a certain minimum yield of wheat which a soil will give

under continuous cropping and ordinary cultivation, and this yield can be increased by rotation of crops, and still more by improved methods of cultivation. Fertilizing is also a factor which generally increases the yield, whether utilized by itself, or in conjunction with other factors. The use of commercial fertilizers must, however, be accompanied by intensive methods of cultivation in order to be profitable, and now and then the returns seem to diminish with continued use. Mr. Whitney, chief of the bureau of soils in the United States department of agriculture, maintains that he never saw a case of soil exhaustion which was probably due to the actual removal of plant food. He considers the so-called worn-out soils of the United States due to conditions which make the plant food unavailable, and holds that the primary object of fertilizing is the adaptation of soils to any desired crop or crops. Fertilizing can also be practiced to force growth, even on rich soil. Texture and drainage of soils can be improved, the ratio of soil constituents balanced, and acidity neutralized. Attention is called to the facts that "the soils of India, which tradition says have been cultivated for 2,000 years, under primitive methods, without artificial fertilizing, still give fair returns. In Egypt, lands which have been cultivated since history began are as fertile as ever. In Europe there are records of cultivation of soils for

Tradition is not always scientific, however, and soil is not greatly taxed by such primitive methods of culture as have existed in India for 2,000 years. The sediment which is deposited by the waters of the Nile at every annual overflow is entirely adequate to maintain the fertility of the cultivated lands of Egypt, while fertilizing, improved methods of cultivation, and crop rotation have greatly increased the yield of European soils. On some of the fields in France 28 bushels of wheat are raised per acre where 17 bushels were raised 50 years ago. The soil of France is more fertile today than it was in the time of Cæsar. The fertility of the soil in Germany has increased proportionately. In England, land on which wheat was grown continuously for 50 years without fertilization yielded 12 to 13 bushels per acre, while adjacent plots to which fertilizers were applied averaged about 30 bushels per acre. Mr. 1 Industrial Commission, 10: clxxxviii, excii.