becomes a part of the plant structure. As carbon dioxide gas is continually given off to the atmosphere by the decomposition of plants, by all forms of combustion. and from many other sources, the supply of carbon is unlimited.

Hydrogen composes a large proportion of the atmosphere. Its function seems to be that of diluting the oxygen. This gaseous element is taken into the plant through the leaf pores and enters largely into the composition of the carbon compounds. As a very large proportion of the air is composed of hydrogen its supply does not concern the farmer.

Oxygen also exists in the atmosphere as a gas and its supply is inexhaustible. It enters into the composition of the carbon compounds and is taken into the plants through the leaves.

Food Supplied Through Root System-All other elements of plant food are supplied to the plant through the root system from the soil. With one exception they are all supplied to the plant directly from the soil, which acts as a storehouse of plant food. The exception to this rule is nitrogen, which is in part taken from the atmosphere, where it exists as a gas, through the agency of leguminous plants. Tubercles are formed on the roots of the leguminous plants. through the action of certain organisms. In the building of these tubercles, the organisms take the nitrogen directly from the air and work it into the composition of the plants. When the tubercles decay, the nitrogen is left in the soil, where it can be used by succeeding crops. In this way, by the growth of leguminous crops, the store of nitrogen in the soil is increased. For this reason it has become the general practice among corn farmers to so rotate their crops that a leguminous crop, as clover, cowpeas or soy beans, is

grown frequently enough to insure a sufficient supply of nitrogen for the development of the corn crop.

The corn plant needs an abundance of the three important ingredients of all fertilizers-nitrogen, phosphorus and potash. The nitrogen develops a large growth of stalks, the phosphorus and potash are especially necessary in the growth of the seed. If any one of these three elements is lacking, the result is a dwarfed plant and small yield. The most important element, because it is most easily lost and is most expensive to buy in the form of commercial fertilizers, is nitrogen. Most of the prairie soils have an abundant supply of nitrogen. However, by continued cropping. the store of available nitrogen is used up and the effect is easily seen in the growth of the plants on such exhausted soils.

For instance, at the Illinois experiment station one-half acre has grown twenty-four successive crops of corn without the aid of commercial fertilizers or any kind of manure or special soil treatment. The result has been a gradual decrease in yield. By comparing the growth of the plants on this half acre with plants grown on rotated and manured fields, a very great difference can be seen at any time during the life of the plant. In the first place the young plants are not thrifty. They do not start off vigorously. Corn planted at the same time on well-fertilized plats comes up two weeks earlier. The plants do not have the dark green, healthy color of plants grown in soils rich in nitrogen, and the leaves are a plain green streaked with yellow. The stalks never equal in size those of the same variety grown on rich soils. They are weak, spindling, and have a dwarfed appearance as though the climate had been unfavorable to their development. During dry seasons the leaves curl and the plant seems to suffer excessively from the lack of

an abundance of water. Further, the plants seem to be more easily affected by insect and fungous pests and quickly succumb to any unfavorable circumstance.

When potash or phosphorus is lacking in the soil, the ears do not fully develop or mature. In soils which have a large amount of nitrogen and too little potash or phosphorus, the stalks become abnormally large while the ears are small and usually poorly filled. By correcting the proportions of nitrogen, potash and phosphorus, through manuring and other treatment of the soil, an otherwise unproductive section may be made to yield maximum crops of corn.

METHODS OF OBTAINING

NITROGEN

The cheapest and best method of obtaining nitrogen is by means of leguminous crops. Of such plants common red clover, cowpeas, soy beans and alfalfa are most generally used in all sections of the United States. These crops add large supplies of nitrogen to the soil and provide great yields per acre of valuable food for animals. They not only are a source of the supply of plant food for the soil, but have a valuable mechanical effect on the soil. Their extensive and deep root systems bring plant food from the subsoil to the surface soil, where it may be used by future crops. They loosen and break up the hard subsoil so that the roots of the corn plants can penetrate this portion of the soil and secure plant food. The roots of the leguminous crops remaining in the soil decay and add to the humus.

Clover has been grown in this country as a part of the crop rotation for many years, but not until the last fifteen years has it come into general use as a soil fertilizer. There are several varieties, adapted to different conditions of soil and climate, and for various uses. Of these varieties the mammoth red, the medium

red and the white clovers are most generally grown. The medium red clover is the variety which is usually used as a fertilizer for corn land.

The methods of seeding clover vary with the section of the country in which the clover is grown. There are three general methods of seeding for fertilizing purposes: I, with nurse crop; 2, alone, and 3, in corn after the last cultivation. Of these methods, the seeding with some nurse crop is in most general use.

The kind of nurse crop varies with the agriculture of the country. In the great corn belt of Illinois, Iowa, Kansas and Nebraska, seeding clover with oats is the most common and universal practice.

In this case the land is prepared for oats, usually by disking crosswise of the corn rows, if the land was previously in corn, then seeding the oats, and disking the field again the other way. This seedbed is then

harrowed once with the ordinary floating harrow and the clover seeded, after which it is harrowed again crosswise of the previous harrowing. This method of preparing the seedbed provides a firm soil for the growth of the oats, which is to be desired, and also gets the ground into the best possible shape for the growth of the clover crop. In such cases the oats should be seeded medium to thin, as a very dense growth of oats would interfere with the growth of the clover crop. With the ordinary varieties of oats, a seeding of one and one-half to two bushels of wellcleaned seed is sufficient. This will give a good crop of oats, protect the clover and not interfere with the growth of the plants.

In this way a stand of clover can be secured without losing a crop from the field, an important consideration to the ordinary farmer. The clover seed is small and consequently contains little plant food. Therefore it must be seeded shallow in order that the

young plants may reach the surface, yet deep enough to get sufficient moisture for the best germination. It is extremely difficult to get good clover seed. Very frequently the vitality of the seed has been injured by cutting too early or by improper harvesting and drying. If the seed is moist it is liable to heat, an injurious process to the vitality of the seed.

Clover seed is very likely to be mixed with noxious weed seed. This weed seed is often of such a size and shape that it is impossible, or at any rate difficult, to separate it from the clover seed. For instance, buckhorn grows very much like the clover plant and matures seed about the same time. The seed is about the same diameter as the clover seed, and boat-shaped. In screening the clover seed these boat-shaped buckhorn seeds tip up and go through the clover screen, making it necessary to secure special cleaners. Other