If lime is applied to the soil, and increases the amount of crops grown by furnishing a larger supply of inorganic matter, of course, the removal of inorganic substances from the soil will be more rapid than when only a small amount of crop is grown, and the soil will be sooner exhausted--not by the lime, but by the plants. In order to make up for this exhaustion, it is necessary that a sufficient amount of inorganic matter be supplied to compensate for the increased quant.i.ty taken away by plants.

Thus we see, that it is hardly fair to accuse the _lime_ of exhausting the soil, when it only improves its character, and increases the amount of its yield. It is the _crop_ that takes away the fertility of the soil (the same as would be the case if no lime were used, only faster as the crop is larger), and in all judicious cultivation, this loss will be fully compensated by the application of manures, thereby preventing the exhaustion of the soil.

[Is the purchase of marl to be recommended?

How is lime prepared for use? (Note.)

Describe the burning and slaking of lime.]

_Kind of lime to be used._ The first consideration in procuring lime for manuring land, is to select that which contains but little, if any _magnesia_. Nearly all stone lime contains more or less of this, but some kinds contain more than others. When magnesia is applied to the soil, in too large quant.i.ties, it is positively injurious to plants, and great care is necessary in making selection. As a general rule, it may be stated, that the best plastering lime makes the best manure. Such kinds only should be used as are known from experiment not to be injurious.

_Sh.e.l.l lime_ is undoubtedly the best of all, for it contains no magnesia, and it does contain a small quant.i.ty of _phosphate of lime_.

In the vicinity of the sea-coast, and near the lines of railroads, oyster sh.e.l.ls, clam sh.e.l.ls, etc., can be cheaply procured. These may be prepared for use in the same manner as stone lime.[AG]

_The preparation of the lime_ is done by first burning and then slaking, or by putting it directly on the land, in an unslaked condition, after its having been burned. Sh.e.l.ls are sometimes _ground_, and used without burning; this is hardly advisable, as they cannot be made so fine as by burning and slaking. As was stated in the first section of this book, lime usually exists in nature, in the form of carbonate of lime, as limestone, chalk, or marble (being lime and carbonic acid combined), and when this is burned, the carbonic acid is thrown off, leaving the lime in a pure or caustic form. This is called burned lime, quick-lime, lime sh.e.l.ls, hot lime, etc. If the proper quant.i.ty of water be poured on it, it is immediately taken up by the lime, which falls into a dry powder, called _slaked lime_. If _quick-lime_ were left exposed to the weather, it would absorb moisture from the atmosphere, and become what is termed _air slaked_.

[What is air slaking?

If slaked lime be exposed to the air, what change does it undergo?

What is the object of slaking lime?

How much carbonic acid is contained in a ton of carbonate of lime?

How much lime does a ton of slaked lime contain?

What is the most economical form for transportation?]

When _slaked lime_ (consisting of lime and water) is exposed to the atmosphere, it absorbs carbonic acid, and becomes carbonate of lime again; but it is now in the form of a very fine powder, and is much more useful than when in the stone.

If quick-lime is applied directly to the soil, it absorbs first moisture, and then carbonic acid, becoming finally a powdered carbonate of lime.

One ton of _carbonate of lime_ contains 11 cwt. of lime; the remainder is carbonic acid. One ton of _slaked lime_ contains about 15 cwt. of lime; the remainder is water.

Hence we see that lime should be burned, and not slaked, before being transported, as it would be unprofitable to transport the large quant.i.ty of carbonic acid and water contained in carbonate of lime and slaked lime. The quick-lime may be slaked, and carbonated after reaching its destination, either before or after being applied to the land.

[What is the best form for immediate action on the inorganic matter in the soil?

For most other purposes?]

As has been before stated, much is gained by slaking lime with _salt water_, thus imitating the lime and salt mixture. Indeed in many cases, it will be found profitable to use all lime in this way. Where a direct action on the inorganic matters contained in the soil is desired, it may be well to apply the lime directly in the form of quick-lime; but, where the decomposition of the vegetable and animal const.i.tuents of the soil is desired, the correction of _sourness_, or the supplying of lime to the crop, the mixture with salt would be advisable.

_The amount of lime_ required _by plants_ is, as was before observed, usually small compared with the whole amount contained in the soil; still it is not unimportant.

OF LIME.

25 bus. of wheat contain about 13 lbs.

25 " barley " 10 "

25 " oats " 11 "

2 tons of turnips " 12 "

2 " potatoes " 5 "

2 " red clover " 77 "

2 " rye gra.s.s " 30 "[AH]

[What is the best guide concerning the quant.i.ty of lime to be applied?

What is said of the sinking of lime in the soil?

What is plaster of Paris composed of?

Why is it called plaster of Paris?]

The amount of lime required at each application, and the frequency of those applications, must depend on the chemical and mechanical condition of the soil. No exact rule can be given, but probably the custom of each district--regulated by long experience--is the best guide.

_Lime sinks in the soil_; and therefore, when used alone, should always be applied as a top dressing to be carried into the soil by rains. The tendency of lime to settle is so great that, when cutting drains, it may often be observed in a whitish streak on the top of the subsoil. After heavy doses of lime have been given to the soil, and have settled so as to have apparently ceased from their action, they may be brought up and mixed with the soil by deeper plowing.

_Lime should never be mixed with animal manures_, unless in compost with muck, or some other good absorbent, as it is liable to cause the escape of their ammonia.

PLASTER OF PARIS.

_Plaster of Paris or Gypsum_ (sulphate of lime) is composed of sulphuric acid and lime in combination. It is called 'plaster of Paris,' because it const.i.tutes the rock underlying the city of Paris.

[Is it a const.i.tuent of plants?

What else does it furnish them?

How does it affect manure?

How does it produce sorrel in the soil?

How may the acidity be overcome?]

It is a const.i.tuent of many plants. It also furnishes them with sulphur--a const.i.tuent of the sulphuric acid which it contains.

It is an excellent absorbent of ammonia, and is very useful to sprinkle around stables, poultry houses, pig-styes, and privies, where it absorbs the escaping gases, saving them for the use of plants, and purifying the air, thus rendering stables, etc., more healthy than when not so supplied.

It has been observed that the extravagant use of plaster sometimes induces the growth of _sorrel_. This is probably the case only where the soil is deficient in lime. In such instances, the lime required by plants is obtained by the decomposition of the plaster. The lime enters into the construction of the plant, and the sulphuric acid remains _free_, rendering the soil _sour_, and therefore in condition to produce sorrel. In such a case, an application of _lime_ will correct the acid by uniting with it and converting it into _plaster_.

CHLORIDE OF LIME.

[What does chloride of lime supply to plants?

How does it affect manures?

How may it be used?

How may magnesia be supplied, when wanting?