According to what two rules may we apply mineral manures?

What course would you pursue to raise potatoes on a soil containing a very little phosphoric acid and no potash?]

1st. Those which are used as food by plants. It will be recollected that the _ash_ left after burning plants, and which formed a part of their structures, has a certain chemical composition; that is, it consists of alkalies, acids, and neutrals. It was also stated that the ashes of plants of the same kind are always of about the same composition, while the ashes of different kinds of plants may vary materially. Different parts of the same plant too, as we learned, are supplied with different kinds of ash.

For instance, _clover_, on being burned, leaves an ash containing _lime_, as one of its princ.i.p.al ingredients, while the ash of _potatoes_ contains more of _potash_ than of any thing else.

In the second section (on soils), we learned that some soils contain every thing necessary to make the ashes of all plants, and in sufficient quant.i.ty to supply what is required, while other soils are either entirely deficient in one or more ingredients, or contain so little of them that they are unfertile for certain plants.

[Would you manure it in the same way for wheat?

Why?]

From this, we see that we may pursue either one of two courses. After we know the exact composition of the soil--which we can learn only from correct a.n.a.lysis--we may manure it with a view either to making it fertile for all kinds of plants or only for one particular plant. For instance, we may find that a soil contains a very little phosphoric acid, and no potash. If we wish to raise potatoes on such a soil, we have only to apply potash (if the soil is good in other particulars), which is largely required by this plant, though it needs but little phosphoric acid; while, if we wish to make it fertile for wheat, and all other plants, we must apply more phosphoric acid as well as potash. As a universal rule, it may be stated that to render a soil fertile for any particular plant, we must supply it (unless it already contains them) with those matters which are necessary to _make_ the ash of that plant; and, if we would render it capable of producing _all_ kinds of plants, it must be furnished with the materials required in the formation of _all kinds of vegetable ashes_.

It is not absolutely necessary to have the soil a.n.a.lyzed before it can be cultivated with success, but it is the _cheapest_ way.

[How is the fertility of the soil to be maintained, if the crops are _sold_?

What rule is given for general treatment?

Give an instance of matters in the soil that are to be rendered available by mineral manures?]

We might proceed from an a.n.a.lysis of the plant required (which will be found in Section V.), and apply to the soil in the form of manure every thing that is necessary for the formation of the ash of that plant. This would give a good crop on _any_ soil that was in the proper _mechanical_ condition, and contained enough organic matter; but a moment's reflection will show that, if the soil contained a large amount of potash, or of phosphate of lime, it would not be necessary to make an application of more of these ingredients--at an expense of perhaps three times the cost of an a.n.a.lysis. It is true that, if the crop is _sold_, and it is desired to maintain the fertility of the soil, the full amount of the ash must be applied, either before or after the crop is grown; but, in the ordinary use of crops for feeding purposes, a large part of the ash will exist in the excrements of the animals; so that the judicious farmer will be able to manure his land with more economy than if he had to apply to each crop the whole amount and variety required for its ash. The best rule for practical manuring is probably to _strengthen the soil in its weaker points, and prevent the stronger ones from becoming weaker_. In this way, the soil may be raised to the highest state of fertility, and be fully maintained in its productive powers.

2d. Those manures which render available matter already contained in the soil.

[How may silica be developed?

How does lime affect soils containing coa.r.s.e particles?

How do mineral manures sometimes improve the mechanical texture of the soil?]

Silica (or sand), it will be recollected, exists in all soils; but, in its pure state, is not capable of being dissolved, and therefore cannot be used by plants. The alkalies (as has been stated), have the power of combining with this silica, making compounds, which are called _silicates_. These are readily dissolved by water, and are available in vegetable growth. Now, if a soil is deficient in these soluble silicates, it is well known that grain, etc., grown on it, not being able to obtain the material which gives them strength, will fall down or _lodge_; but, if such measures be taken, as will render the sand soluble, the straw will be strong and healthy. Alkalies used for this purpose, come under the head of those manures which develope the natural resources of the soil.

Again, much of the mineral matter in the soil is combined within particles, and is therefore out of the reach of roots. Lime, among other thing, has the effect of causing these particles to crumble and expose their const.i.tuents to the demand of roots. Therefore, lime has for one of its offices the development of the fertilizing ingredients of the soil.

3d. Those manures which improve the mechanical condition of the soil.

The alkalies, in combining with sand, commence their action on the surfaces of the particles, and roughen them--_rust_ them as it were.

This roughening of particles of the soil prevents them from moving among each other as easily as they do when they are smooth, and thus keeps the soil from being compacted by heavy rains, as it is liable to be in its natural condition. In this way, the mechanical texture of the soil is improved.

It has just been said that _lime_ causes the pulverization of the particles of the soil; and thus, by making it finer, improves its mechanical condition.

Some mineral manures, as plaster and salt, have the power of absorbing moisture from the atmosphere; and this is a mechanical improvement to dry soils.

[Name some mineral manures which absorb ammonia?]

4th. Those mineral manures which have the power of absorbing ammonia.

_Plaster_, _chloride of lime_, _alumina_ (_clay_), etc., are large absorbents of ammonia, whether arising from the fermentation of animal manures or washed down from the atmosphere by rains. The ammonia thus absorbed is of course very important in the vegetation of crops.

Having now explained the reasons why mineral manures are necessary, and the manner in which they produce their effects, we will proceed to examine the various deficiencies of soils and the character of many kinds of this cla.s.s of fertilizers.

CHAPTER IX.

DEFICIENCIES OF SOILS, MEANS OF RESTORATION, ETC.

As will be seen by referring to the a.n.a.lyses of soils on p. 72, they may be deficient in certain ingredients, which it is the object of mineral manures to supply. These we will take up in order, and endeavor to show in a simple manner the best means of managing them in practical farming.

ALKALIES.

POTASH.

[Do all soils contain a sufficient amount of potash?

How may its deficiency have been caused?

How may its absence be detected?

Does barn-yard manure contain sufficient potash to supply its deficiency in worn-out soils?]

_Potash_ is often deficient in the soil. Its deficiency may have been caused in two ways. Either it may not have existed largely in the rock from which the soil was formed, and consequently is equally absent from the soil itself, or it may have once been present in sufficient quant.i.ties, and been carried away in crops, without being returned to the soil in the form of manure until too little remains for the requirements of fertility.

In either case, its absence may be accurately detected by a skilful chemist, and it may be supplied by the farmer in various ways. Potash, as well as all of the other mineral manures, is contained in the excrements of animals, but not (as is also the case with the others) in sufficient quant.i.ties to restore the proper balance to soils where it is largely deficient, nor even to make up for what is yearly removed with each crop, except that crop (or its equivalent) has been fed to such animals as return _all_ of the fertilizing const.i.tuents of their food in the form of manure, and this be all carefully preserved and applied to the soil. In all other cases, it is necessary to apply more potash than is contained in the excrements of animals.

[What is generally the most available source from which to obtain this alkali?

Will leached ashes answer the same purpose?

How may ashes be used?]

_Unleached wood ashes_ is generally the most available source from which to obtain this alkali. The ashes of all kinds of wood contain potash (more or less according to the kind--see a.n.a.lysis section V.) If the ashes are _leached_, the potash is removed; and, hence for the purpose of supplying it, they are worthless; but _unleached_ ashes are an excellent source from which to obtain it. They may be made into compost with muck, as directed in a previous chapter, or applied directly to the soil. In either case the potash is available directly to the plant, or is capable of uniting with the silica in the soil to form silicate of potash. Neither potash nor any other alkali should ever be applied to animal manures unless in compost with an absorbent, as they cause the ammonia to be thrown off and lost.

[From what other sources may potash be obtained?

How may we obtain soda?

In what quant.i.ties should pure salt be applied to the soil?]

_Potash sparlings_, or the refuse of potash warehouses, is an excellent manure for lands deficient in this const.i.tuent.

_Potash marl_, such as is found in New Jersey, contains a large proportion of potash, and is an excellent application to soils requiring it.