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 principal 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 quantity 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 analysis—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 analyzed 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?