The chemical condition of a soil necessary to fertility (when reduced to its lowest terms, after separating the adventitious by means of a comparison of the reports of a great many analyses of soils, and of plants, and experiments with various fertilizers) appears to be this: The soil must contain silica, alumina, peroxide of iron, lime, magnesia, potash or soda, humic acid, and at least one of the three mineral acids, viz., phosphoric, or sulphuric, or muriatic. Also, there must be no salts of the heavy metals; also, the alkalies must be balanced with the acids, so that neither shall be in excess, thus making the soil exactly neutral.

The reduction by chemical equivalents of a great number of analyses of soils reported, both good and bad, has proved to me that neutrality is the most distinguishing characteristic of a fertile soil for ordinary field crops. This neutrality can be produced and made permanent without a previous analysis, without danger, at the smallest expense, and with exact precision, by pure lime, (or such as contains no magnesia,) in excess of all the acids in the soil. At the same time, this excess decomposes all the poisonous salts of the heavy metals, and makes them valuable fertilizers. It also liberates potash, and soda, and phosphoric acid from their compounds. The remaining excess of lime becomes a carbonate, as chalk, laid by in store; neutral and inert while not required, but still ready to neutralize any future increase of acid. Pure lime is the only substance that can be used artificially to produce these results. In natural soils this neutrality is produced by any of the four inorganic alkalies.

The above chemical conditions necessary to fertility can be produced by the five following simple, cheap, common applications, provided the ground be a fair loam, (or mixture of sand and clay,) and contain the ordinary amount of iron in any soluble form, although at present it may render the land barren by its poisonous condition as sulphate or phosphate. The proper quantities of the various applications must evidently vary according to the present condition of the soil. These can be ascertained by each culturist for his different grounds, by varying the amounts and noting the results. As a preliminary experiment, I suggest such quantities as I suppose will answer where the same substances are deficient in the soil, and at the same time not produce injurious excess where they are abundant at present.

1st. Pure Lime In Excess

One large application, to make an artificial limestone soil as a basis of operations, say 200 bushels per acre for ordinary land, and thence increasing, with the vegetable matter in the soil, up to 1,000 bushels or more for a drained swamp. The only danger in this application in excess is from magnesian stone lime. Shell lime is pure. A bushel measure means slaked, struck.

2d. Magnesian Stone Lime

A moderate quantity as food, every three or four years, say 50 bushels, and not to exceed 150 bushels, even for rich land.

3d. Gypsum (Plaster)

To supply sulphuric acid, say three bushels every three or four years; otherwise, twice as much "salt-cake".

4th. Common Salt

To supply chlorine (muriatic acid) and soda, say six bushels every three or four years.

5th. Decomposed Vegetable Matter

If in the form of barn-yard or other fermenting manure, it should not be applied within some months, either before or after fresh lime. An excess of fresh lime will expel all the ammonia from fresh manure, or any other ammoniacal compound, as guano, etc.; but if the vegetable matter be in the form of muck, or mud, or sods, or pumice from cider-mills, or rotten wood, bark, tan, or sawdust, then it should first be composted with lime to neutralize the acid before it is applied, unless it be for acid plants, as strawberries, cranberries, etc., where lime is said to be injurious, although necessary for field-crops and for fruit-trees.

Three of the inorganic constituents of plants are not supplied in the above, on account of the expense, viz., manganese, potash, and phosphoric acid. They may all be abundant, even in a barren soil. They may all be liberated and brought into use by the excess of lime; or they may all be absent In this condition we have evidence that we can have fertility without them. Thus manganese does not appear to be necessary when there is an abundance of iron. Potash is at times replaced by the other alkalies, lime, magnesia, and especially soda, which is almost identical with potash in its chemical action. Soda we apply in common salt, and also in salt-cake. Phosphoric acid is at times replaced by the other acids, (in a great measure at least.) We have humic acid in the vegetable matter, sulphuric acid in gypsum or in salt-cake, and muriatic acid (chlorine) in common salt.

It is, doubtless, better for plants to have a supply of every thing; and after the cheaper substances have been fully tried, then apply the more expensive fertilizers, and ascertain whether the increased fertility will pay for the increased expense. But in many cases they will now be found useless. Thus, the benefit from wood-ashes, soda-ash, potash, fresh manure, Peruvian guano, is frequently due solely to their alkaline action in neutralizing an acid soil well supplied with inorganics. This neutrality has already been produced by lime. So, again, where the soil contains sufficient phosphoric acid, the superphosphate of lime will have no effect, since gypsum gives us lime and sulphuric acid, the other two ingredients in superphosphate of lime.

For a partial improvement, magnesian stone lime is better than shell lime. It is cheaper per bushel, still cheaper per pound, and much cheaper in proportion to effect, since magnesia is more powerful than lime as 4.83 to 3.50. At the same time, it also furnishes magnesia as a food preferred by some plants. Thus the grain of Indian corn contains ten of magnesia to one of lime; but it can not be used freely, since an excess of burned magnesia will render the land permanently barren from excess of permanent alkali, unless counteracted by some acid, as fresh muck or old manure. Pure lime, on the contrary, soon becomes " mild or carbonated, as chalk, when freely exposed to the air, and hence may be used " in almost unlimited quantity, without any permanent injury. It is only a waste of money and a waste of time until the large excess becomes mild.