EARTH. In an agricultural sense, earth is clay, saud, loam, peat, hog earth, etc., in a mixture seldom pure, comprising various soils adapted to the growth of plants. Mold, on the contrary, is humus earth, or that arising from the decomposition of barnyard manure, leaves, or other vegetable substances. Except pure sand, earth has tenacity to a greater or lesser degree, clinging together more or less when damp, according as sand predominates in its composition; mold, except when saturated with water, easily falls apart. Thus earth is divided into three classes : The more tenacious, as strong loams and clays; sandy soils, and humus; or mold. The loams contain the most humus, the sands the least. We have here tofore spoken of dry earth, especially dry clay, as a deodorizer. (See Deodorization.) The effect of the sun's rays on the temperature of the earth below the surface, the power of the soil in holding heat, its absorbent qualities, and power of taking up and holding moisture, and its disinte grability are among the most important uses of earths in the growth of plants, for upon these char acteristics the economy of vegetable life is chiefly due. (See article Soil.) Meteorology also exerts an important influence upon the productive capa bility of the earth. 1 n inquiring into the qualities of soils, the natural system would be to judge from the color, cohesion, consistence, their capa bility of holding moisture, the growth of vegeta tion, including the varieties, as adapted to various soils, etc. This was, in fact, the only means the ancients had of determining the value of soils. Nevertheless, this is by no means a critical test. The color of soils, in fact, is but a slight indica tion of their true value, some very dark soils being infertile, and some light-colored soils being quite fertile. In fact, it is but little more than 100 years ago since the physical properties of soils first commanded the attention of scien tific investigators. And really, the first investi gations were limited to the weight of soils, and their facility of absorbing water. Thacr, while he paid great attention to the physical properties of soils in his Analysis of Earths, did not sub mit them to a series of comparative experiments. It was not until 1816 that Schlibler, when appointed at Hoffwyl, professor of physics and chemistry applied to agriculture, that a real stride was taken. He asked himself the ques
tion: Where is the science I am expected to teach ? He found it did not exist. He then entered upon the study of agriculture as a physic ist, and sought the best means for determining and comparing the diverse physical properties of soils. He found that the specific weight of earth was always in relation to its power of retaining heat, and of drying quickly; that the facility for retaining water embraces that of absorbing the moisture and the oxygen of the air with rapidity, etc. The physical properties of arable soils, and the physical influences of the atmosphere, have a greater direct action upon vegetation than those properties and influences. purely chemical, because the first are anterior to. and serve as a basis for the last. Boussingault, proves how far this question was in its infancy in his day. He says: At an epoch which is not yet very far distant, it was believed that a close connection existed between the composition and the quality of arable soil. Numerous analyses soon modified tbis opinion by demonstrating that the mineral elements have not always the import ance which is attributed to them. Schtibler tried even to prove that the fertility of a soil depends a great deal more upon its physical pro perties, its aggregate condition, its aptitude for imbibition, etc , than on its chemical constitution. That which characterizes cultivable soil, whose base consists of disaggregated mineral sub stances, is the presence of organic remains more or less modified, such as humus and compost. Vegetable earth, properly called, results from this association. In regard to its intimate nature, we fear not to affirm that, in spite of its appar ent simplicity, we have still a very imperfect knowledge of it. This absorbing faculty, as mysterious as unexpected, which the soil exer cises on ammonia, lime, potash, and the salts of different bases, discovered by Thompson and Way, is a palpable proof of it. The chemical, composition and the physical properties do not admit of pronouncing upon the degree of fertil ity of earth. Direct observation is necessary. It is imperative to cultivate a plant in the soil, and ascertain its vigor and development. The analysis will be useful in determining the quantity and quality of assimilating elements. The memoir of Schfibler comprises one hundred pages. An.