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field culture, appear to be the following; viz. 1st, To render thesubstances lodged in the soil, which may be injurious to vegeta-tion, harmless or useful; 2d, To give the soil the proper consis-tence for the reception of vegetable roots, and for receiving, pre-paring, and distributing water for their nourishment; 3d, To fa-cilitate the decomposition of putrescible matter, and to renderits hydrogen and carbon soluble in water, so as to furnish food togrowing vegetables.
1st, The injurious substances, which may be lodged in the soil,are the orange oxid of iron, described in the first Section, andsome of the acids. Iron, it has been already said, is very pre-valent in nature, and occurs in different states in the soil; andthe injurious effect of the orange oxid has been previously ad-verted to. The sterility occasioned by its excess is very exten-sive ; and many fields in which the different species of earths areproperly blended, are made sterile by its prevalence. Its pre-sence is discoverable by the dull yellow colour of the soil whenit is dry. This oxid is now known to be the red oxid combinedwith carbonic acid ; and of course this combination must bethe cause of its noxious quality. The application of quick lime,therefore, which has a stronger affinity for that acid, should takeit from the oxid, and “ heal the soil: ” and, that such is the fact,has been proved by a careful experiment. * To apply lime withefficacy to such soils, the land being reduced to small particlesby summer ploughing and harrow ing, the lime should be spreadas soon as it can be slacked to a manageable state, immediatelymixed by harrowing into the surface, and more fully mixed byanother ploughing, before the lime become effete. In this man-ner, many fields might be rendered more productive, providedthey be judiciously treated afterwards.
The impossibility of disengaged acids remaining in the soil,frequently turned over and exposed to the rain, has been alreadystated. But in wild grounds recently broken up, fragments ofmartial pyrites, of sulphate of iron and alumine, muriate of iron,&c. it is said have been found. These, as they decompose in theair, emit acids deleterious to growing plants. Lime, applied asabove, absorbs and neutralizes the acids, and thus renders themharmless. But there are many vegetables possest of acids whichretard their putrefaction. Lime, whether quick or effete, de-prives these vegetables of their acids, and facilitates their de-composition. In these ways, and, from any thing which is yetknown of it, in no other, does lime convert substances in thesoil from being injurious to be harmless or useful.
2d, The second purpose mentioned for the application of limeto the soil, was to give it a consistence more favourable to ferti-lity. Lime, in specific gravity, in the proportion of water it
* See Naismith’s Elements of Agriculture, p. 534.