there is an educational value in the use of the separate ingredients, which is lost when mixed goods are employed. This fact has been aptly stated in a bulletin from the New York station at Geneva, as follows: "There is little of educational value in using an unknown mixture. To purchase intelligently unmixed fertilizing materials will ultimately lead in most cases to a well grounded knowledge of the science of agriculture. One will seek to know what the different forms of plant food are, what they do, from what source they can be obtained, and how he can use them to best advantage. He will become to some extent an investigator and will of necessity take a deeper interest in his work. His entire system of farming will be lifted to a higher plane, and his more intelligent labor will yield more profitable results."

CHAPTER XXII

INDIRECT FERTILIZERS

Soil Amendments.-There are a number of substances which are beneficial to the land under some conditions, although they add neither humus nor important quantities of plant food. Such substances have been called soil amendments, and the benefit derived from their use arises from the fact that they produce certain changes in the soil, which directly, or indirectly, promote plant growth. Some of these amendments contain small amounts of plant food, but their value is chiefly due to their secondary effect, and not that they add nitrogen, phosphoric acid or potash.

Lime an Important Indirect Fertilizer.-Lime is probably the most important substance of this class, and its use as a manure antedates the Christian era. Although lime has been employed as a fertilizer for so long a time, it is only in recent years that its action has been explained, and at the present time there remain for investigation many questions concerning the action of lime upon the soil.

In a few instances lime has a direct manurial value, for occasionally a soil is found which is so lacking in this substance that the crops are unable to obtain sufficient lime for a maximum yield. Such soils are rare, and in nearly every instance the good results from the use of lime are due to its indirect effect. The effects of lime may be considered to be of three kinds, i. e., physical, chemical and biological.

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Lime Improves Physical Condition of Soil.-Lime has a very marked effect on the physical condition of the soil. When added to the sandy soil it tends to make the soil more compact by partially cementing together the particles of sand, and thus makes the soil capable of retaining larger quantities of water. When

used on clay lands, on the other hand, lime makes the soil more mellow. A clay soil containing very little lime is made fine with greatest difficulty; it adheres to the implements used when wet, and cracks when allowed to dry. A soil rich in lime crumbles more easily, is readily brought into good tilth, and does not adhere to any appreciable extent to the implements. The addition of lime to a soil containing much clay makes the soil more friable, makes it possible for the

rains to percolate more easily through the soil, and overcomes the danger of puddling. The puddling of clay soils is due to the fact that the clay is composed of very small granules which fit so closely together that the water cannot pass between. When lime is added to the soil a number of these small particles become cemented together to form a much larger granule, and as the granules increase in size the spaces between them also become larger.

Any one can easily satisfy himself in regard to this valuable effect of lime on stiff clay by taking a sample of such clay, adding a little water, working it thoroughly, and then allowing it to dry, when it becomes as hard as a brick. If to another portion of the clay a little lime is added (say 12 per cent.), and this is moistened, mixed thoroughly, and allowed to dry, it will be found that a mere touch will cause it to crumble to pieces. There are other materials that have a somewhat similar effect on clay, but none are so efficient as lime. This granulated condition of clay soils, so easily accomplished by liming, is not readily destroyed but will last for some years.

Lime Makes Potential Plant Food Available.Lime is useful in making potential plant food available. Much of the potash of the soil, for instance, is locked up in insoluble compounds, and is not available to the plant. Lime may decompose these compounds, and thereby convert the potash into forms that the crop can use. Experiments have proved that when lime is applied to a soil originally poor in this constituent the plants grown are not only richer in lime, but also in potash. The use of lime, then, may for a time have a

similar effect to that of potash-containing manures, but it must be remembered that the lime does not supply potash, it merely makes that present in the ground available, and if the store of potash originally present is small, the soil will probably need liberal potash ma

Another home-made lime-kiln lined with sandstone. Limestone and coal are added each day at the top, and the burned lime raked out from the bottom

nuring at an earlier date because of liming. Caustic lime acts energetically upon organic matter, and its beneficial action on peaty or other soils containing large quantities of undecomposed vegetable matter may be partly due to this fact.

Lime Promotes Growth of Desirable Bacteria.Lime is valuable because it promotes the growth of desirable bacteria in the soil. It has been shown that