_Feldspar_, _kaolin_, and other minerals containing potash, are, in some localities, to be obtained in sufficient quant.i.ties to be used for manurial purposes.

_Granite_ contains potash, and if it can be crushed (as is the case with some of the softer kinds,) it serves a very good purpose.

SODA.

[If applied in large quant.i.ties will it produce permanent injury?

In what quant.i.ties should salt be applied to composts? To asparagus?]

_Soda_, the requirement of which is occasioned by the same causes as create a deficiency of potash, and all of the other ingredients of vegetable ashes, may be very readily supplied by the use of _common salt_ (chloride of sodium), which consists of about one half sodium (the base of soda). The best way to use salt is in the lime and salt mixture, previously described, or as a direct application to the soil. If too much salt be given to the soil it will kill any plant. In small quant.i.ties, however, it is highly beneficial, and if _six bushels per acre_ be sown broadcast over the land, to be carried in by rains and dews, it will not only destroy many insects (grubs, worms, etc.), but will, after decomposing and becoming chlorine and soda, prove an excellent manure. Salt, even in quant.i.ties large enough to denude the soil of all vegetation, is never _permanently_ injurious. After the first year, it becomes resolved into its const.i.tuents, and furnishes chlorine and soda to plants, without injuring them. One bushel of salt in each cord of compost will not only hasten the decomposition of the manures, but will kill all seeds and grubs--a very desirable effect.

While small quant.i.ties of salt in a compost heap are beneficial, too much (as when applied to the soil) is positively injurious, as it arrests decomposition; fairly _pickles_ the manures, and prevents them from rotting.

[What is generally the best way to use salt?

What is nitrate of soda?

What plants contain lime?]

For _asparagus_, which is a marine plant, salt is an excellent manure, and may be applied in almost unlimited quant.i.ties, _while the plants are growing_, if used after they have gone to top, it is injurious. Salt has been applied to asparagus beds in such quant.i.ties as to completely cover them, and with apparent benefit to the plants. Of course large doses of salt kill all weeds, and thus save labor and the injury to the asparagus roots, which would result from their removal by hoeing. Salt may be used advantageously in any of the foregoing manners, but should always be applied with care. For ordinary farm purposes, it is undoubtedly most profitable to use the salt with lime, and make it perform the double duty of a.s.sisting in the decomposition of vegetable matter, and fertilizing the soil.

Soda unites with the silica in the soil, and forms the valuable _silicate of soda_.

_Nitrate of soda_, or cubical nitre, which is found in South America, consists of soda and nitric acid. It furnishes both soda and nitrogen to plants, and is an excellent manure.

LIME.

The subject of _lime_ is one of most vital importance to the farmer; indeed, so varied are its modes of action and its effects, that some writers have given it credit for every thing good in the way of farming, and have gone so far as to say that _all_ permanent improvement of agriculture must depend on the use of lime. Although this is far in excess of the truth (as lime cannot plow, nor drain, nor supply any thing but _lime_ to the soil), its many beneficial effects demand for it the closest attention.

[Do all soils contain enough lime for the use of plants?

What amount is needed for this purpose?

What is its first-named effect on the soil?

Its second? Third? Fourth? Fifth?

How are acids produced in the soil?]

As food for plants, lime is of considerable importance. All plants contain lime--some of them in large quant.i.ties. It is an important const.i.tuent of straw, meadow hay, leaves of fruit trees, peas, beans, and turnips. It const.i.tutes more than one third of the ash of red clover. Many soils contain lime enough for the use of plants, in others it is deficient, and must be supplied artificially before they can produce good crops of those plants of which lime is an important ingredient. The only way in which the exact quant.i.ty of lime in the soil can be ascertained is by chemical a.n.a.lysis. However, the amount required for the mere feeding plants is not large, (much less than one per cent.), but lime is often necessary for other purposes; and setting aside, for the present, its feeding action, we will examine its various effects on the mechanical and chemical condition of the soil.

1. It corrects acidity (sourness).

2. It hastens the decomposition of the organic matter in the soil.

3. It causes the mineral particles of the soil to crumble.

4. By producing the above effects, it prepares the const.i.tuents of the soil for a.s.similation by plants.

5. It is _said_ to exhaust the soil, but it does so in a very desirable manner, the injurious effects of which may be easily avoided.

[How does lime correct them?

How does it affect animal manures in the soil?]

1. The decomposition of organic matter in the soil, often produces acids which makes the land _sour_, and cause it to produce sorrel and other weeds, which interfere with the healthy growth of crops. Lime is an _alkali_, and if applied to soils suffering from sourness, it will unite with the acids, and neutralize them, so that they will no longer be injurious.

2. We have before stated that lime is a decomposing agent, and hastens the rotting of muck and other organic matter. It has the same effect on the organic parts of the soil, and causes them to be resolved into the gases and minerals of which they are formed. It has this effect, especially, on organic matters containing _nitrogen_, causing them to throw off ammonia; consequently, it liberates this gas from the animal manures in the soil.

3. Various inorganic compounds in the soil are so affected by lime, that they lose their power of holding together, and crumble, or are reduced to finer particles, while some of their const.i.tuents are rendered soluble. One way in which this is accomplished is by the action of the lime on the silica contained in these compounds, forming the silicate of lime. This crumbling effect improves the mechanical as well as the chemical condition of the soil.

4. We are now enabled to see how lime prepares the const.i.tuents of the soil for the use of plants.

[Inorganic compounds?

How does lime prepare the const.i.tuents of the soil for use?

What can you say of the remark that lime exhausts the organic matter in the soil?]

By its action on the roots, buried stubble, and other organic matter in the soil, it causes them to be decomposed, and to give up many of their gaseous and inorganic const.i.tuents for the use of roots. In this manner the organic matter is prepared for use more rapidly than would be the case, if there were no lime present to hasten its decomposition.

By the decomposing action of lime on the mineral parts of the soil (3), they also are placed more rapidly in a useful condition than would be the case, if their preparation depended on the slow action of atmospheric influences.

Thus, we see that lime, aside from its use directly as food for plants, exerts a beneficial influence on both the organic and inorganic parts of the soil.

5. Many contend that lime _exhausts_ the soil.

If we examine the manner in which it does so, we shall see that this is no argument against its use.

[How can lime exhaust the mineral parts of the soil?

Must the matter taken away be returned to the soil?]

It exhausts the organic parts of the soil, by decomposing them, and resolving them into the gases and minerals of which they are composed.

If the soil do not contain a sufficient quant.i.ty of absorbent matter, such as clay or charcoal, the gases arising from the organic matter are liable to escape; but when there is a sufficient amount of these substances present (as there always should be), these gases are all retained until required by the roots of plants. Hence, although the organic matter of manure and vegetable substances may be _altered in form_, by the use of lime, it can escape (except in very poor soils) only as it is taken up by roots to feed the crop, and such exhaustion is certainly profitable; still, in order that the fertility of the soil may be _maintained_, enough of organic manure should be applied, to make up for the amount taken from the soil by the crop, after liberation for its use by the action of the lime. This will be but a small proportion of the organic matter contained in the crop, as it obtains the larger part from the atmosphere.

The only way in which lime can exhaust the inorganic part of the soil is, by altering its condition, so that plants can use it more readily.

That is, it exposes it for solution in water. We have seen that fertilizing matter cannot be leached out of a good soil, in any material quant.i.ty, but can only be carried down to a depth of about thirty-four inches. Hence, we see that there can be no loss in this direction; and, as inorganic matter cannot evaporate from the soil, the only way in which it can escape is through the structure of plants.

[If this course be pursued, will the soil suffer from the use of lime?

Is it the lime, or its crop, that exhausts the soil?

Is lime containing magnesia better than pure lime?

What is the best kind of lime?]