The _mixing of soils_ is often all that is necessary to render them fertile, and to improve their _mechanical_ condition. For instance, soils deficient in potash, or any other constituent, may have that deficiency supplied, by mixing with them soil containing this constituent in excess. It is very frequently the case, that such means of improvement are easily availed of. While these chemical effects are being produced, there may be an equal improvement in the mechanical character of the soil. Thus stiff clay soils are rendered lighter, and more easily workable, by an admixture of sand, while light blowy sands are compacted, and made more retentive of manure, by a dressing of clay or of muck. [Why may the same effect sometimes be produced by deep plowing? What is absolutely necessary to economical manuring?] Of course, this cannot be depended on as a sure means of chemical improvement, unless the soils are previously analyzed, so as to know their requirements; but, in a majority of cases, the soil will be benefited, by mixing with it soil of a different character. It is not always necessary to go to other locations to procure the soil to be applied, as the subsoil is often very different from the surface soil, and simple deep plowing will suffice, in such cases, to produce the required admixture, by bringing up the earth from below to mingle it with that of a different character at the surface. * * * * * In the foregoing remarks on the subject of mineral manures, the writer has endeavored to point out such a course as would produce the "greatest good to the greatest number," and, consequently, has neglected much which might discourage the farmer with the idea, that the whole system of scientific agriculture is too expensive for his adoption. Still, while he has confined his remarks to the more simple improvements on the present system of management, he would say, briefly, that _no manuring can be strictly economical that is not based on an analysis of the soil, and a knowledge of the best means of overcoming the deficiencies indicated, together with the most scrupulous care of every ounce of evaporating or soluble manure_. FOOTNOTES: [AG] Marl is earth containing lime, but its use is not to be recommended in this country, except where it can be obtained at little cost, as the expenses of carting the _earth_ would often be more than the value of the _lime_. [AH] The straw producing the grain and the turnip and potato tops contain more lime than the grain and roots. [AI] See Working Farmer, vol. 2, p. 278. [AJ] Glycerine, etc. CHAPTER X. ATMOSPHERIC FERTILIZERS. [Are the gases in the atmosphere manures? What would be the result if they were not so?]