Harvey Washington Wiley

“ Of course, if a rock mass contains none of the constituents essential to plant growth, its resultant soil must by itself alone be quite barren. It does not absolutely follow, however, that those rocks containing the highest percentages of valuable constituents will yield the most fertile soils, since much depends on the manner in which they have been formed, the amount of leaching, etc., they may have undergone. Nevertheless, the study of the composition of the rocks in their relation to soils, is an extremely interesting and by no means unimportant one. ”

“ The only important plant food liable to be deficient in the soil which does not come under the influence of absorption is nitrogen in the form of salts of nitric acid, and nature has made a wide provision for this element by binding it in the form of organic bodies which nitrify but slowly, and by supplying each year a small quantity from the atmosphere. ”

“ The oxids of iron very commonly occur as such in rocks and soils, and play a very important part in organic life. The several oxids of iron very frequently determine the color of soils; as the iron in a soil is more or less oxidized, or as it is exposed more or less to access of air, the color of the soil changes. These oxids of iron also play an important part in the absorption capacities of soils for moisture and other physical conditions of soils, and also in the oxidation of organic matters in the soil. ”

“ All vegetable and animal material deposited in or on the soil contains more or less of these proteid or nitrogenous matters while the amount of nitric acid supplied in this way is probably represented entirely by the quantity in the organism of the plant or animal and unabsorbed at the time of its death. In other words it is not demonstrated that nitrates or nitrites are in any sense a special product of plant growth save in the case of nitrifying organisms themselves which are supposed to be of a vegetable nature. Animal organisms do not in any sense assimilate nitric nitrogen. ”

“ The action of water in reducing soil temperature is easily explained. In our latitude, we see the water in all its forms, solid, liquid, and gaseous, and we know that these forms are the direct result of temperature. The changing of water from the solid to the liquid or gaseous form is performed at the expense of heat; the more water evaporated from the soil the more heat must be used for the evaporation. Therefore, the more water contained in the soil at any given time the lower must be its temperature during subsequent exposure to sun heat because of the greater evaporation. ”

“ Use of a Solid Medium.—It may be justly claimed that the action of nitrifying organisms in a liquid is not to be compared with their action in a solid medium, such as a soil which is their natural habitat. It might be, therefore, that the inability of the nitrous organism to produce nitrates is due to the nature of the medium in which it is cultivated. Winogradsky in order to determine this question cultivated the organism in a solid medium of two kinds, first a silicate gelatin impregnated with an ammonium salt and second in sterilized earth. ”

“ Large quantities of organic matter do increase the amount of carbon dioxid, but the increase is not a proportional one, since a larger quantity of this gas in the air of a soil reduces the activity of the organisms which produce oxidation. Water and temperature have a greater influence on the oxidation, and act in an opposite direction to that of the organic matter. The amount of free gas in the soil affords no indication either of the intensity of the action of oxidation or of the amount of organic matter. ”

“ Mineralogical Examination of the Particles of Soil Obtained by Mechanical Analysis.—The principal object of the mechanical analysis of soils as has already been set forth is the separation of the soil into portions, the particles of which have the same hydraulic value. It is evident without illustration that particles of the same hydraulic value do not necessarily have the same size. The rate of flow of a liquid carrying certain definite particles does not imply that these particles are of the same dimensions. ”

“ It is as necessary to plant growth and development as water, phosphoric acid, lime, and potash, and far more costly. While a large quantity of nitrogen exists in the air in an uncombined state, it is, nevertheless, one of the least abundant of the elements of high importance in plant nutrition.
The conservation and increase of the stores of available nitrogen in the soil is one of the chief problems occupying the attention of agricultural chemistry. Nitrogen, which is not immediately available for the growth of plants, is conserved and restored by natural processes in various ways. ”

“ It has, however, now been demonstrated that a liquid may contain large numbers of nitro-bacteria and still produce no growth upon gelatin. However, for the organisms which accompany the nitro-bacteria in soils, it is regarded as certain that if no growth on gelatin is produced by them they are absent. Therefore in the case of a solution which has been seeded with a soil, if it can be brought to such a state as to produce no growth on gelatin, it may be safely assumed that it contains no bacterial organisms save those which are capable of producing nitrites or nitrates. ”

“ It is, therefore, fair to assume that the fixation of free nitrogen is a function of chemical activity quite independent of ordinary plant life and that the leguminous plants take no further part in this process than that of providing in their radical development a favorable nidus for the growth of the nitrifying organism. ”

“ Silicon never occurs in the free state, but combined with oxygen it forms silica, which constitutes more than one-half of the earth’s crust. The oxid of silicon occurs in the very common form of quartz, and likewise, as silicate of alumina, lime or magnesia. Silicon forms an essential part of many minerals, such as the feldspars, amphiboles, pyroxenes, and the micas, besides being an essential ingredient of many other minerals. ”

“ It is known, for example, that wood oxidizes much more rapidly around a rusty nail than where it is simply exposed to the air, the iron oxid acting as a carrier between the oxygen of the air and the organic matter. In a sandy soil, on the contrary, where there is usually less moisture and much freer circulation of air, the iron compounds have more oxygen and usually have a light yellow color. ”

“ When a soil is only slightly moist the water clings to its grains in the form of a thin film. When these soil particles are brought together the films of water surrounding them unite, one surface being in contact with the soil particles and the other exposed to the air. If more water enter the soil the film thickens until finally, when the point of saturation is reached, all the space between the soil particles becomes filled with water, and surface tension within the soil is thus reduced to zero. Gravity then alone acts on the water and with a maximum force. ”

“ In general, far the largest part of soil nitrogen, excluding the atmosphere diffused in the pores of the soil, is found in the organic state and is derived from the débris of animal and vegetable life and from added fertilizers. As ammonia, the nitrogen can only be regarded as in a transition state, arising from the processes of decay, or incomplete nitrification. As nitric acid, it is found as a completed product of nitrification, or as the result of electrical action. ”

“ Coefficient of Evaporation.—At an ordinary room temperature in the shade, samples of soil, if they are subjected to experiment in tolerably thin layers have nearly an equal coefficient of evaporation. That is, the absolute quantity of water evaporated in a given time is almost entirely conditioned upon the magnitude of the surface exposed and the temperature of the surrounding air. Only when exposed in conditions as nearly as possible natural in thin layers to the action of the sunlight and shade do the soils show their peculiarities in respect of the evaporation of moisture. ”

“ Carbon as an elementary substance occurs as diamond and graphite and in an impure form as anthracite and bituminous coals. In peats and mucks carbon is the chief constituent. This substance is also contained in the organic matters of the soil known as humus, and the relation of the carbon to nitrogen often throws important light upon the amount and character of the nitrogenous matters. In composition with oxygen it forms the chief food of growing plants, the carbon of the carbon dioxid of the air being elaborated into the tissue of the plants and the oxygen returned to the atmosphere. ”

“ The first group of silicates is doubtless of greater importance to vegetable life than the second since it would, doubtless, give up its alkalies with greater ease. This distinction is, however, arbitrary. It is, in fact, impossible to place on one side the soluble and on the other the insoluble silicates. This distinction represents only the unequal degrees in the speed of decomposition of the different silicates contained in the primitive rocks under the influence of atmospheric agents, the soil being nothing more than the products of the decomposition of these rocks with vegetable mold. ”