another series of experiments, one of the mineral elements; the crop secured in each experiment is found to be imperfect. Perfect growth is only reached when all the elements named are present. Pood obtained from the Atmosphere.-The leaves and roots are called organs of nutrition; the leaves take material from the air, the roots from the soil. The dry substance of a plant is made up chiefly of carbon, and the proper absorption of this element depends upon the activity of the leaves. The leaf is made up of rows of cells, placed side by side, which in the under portion are loosely held together, forming "air spaces" between them, and over the whole leaf there is a thin, transparent skin. This skin, called the " epidermis,'^is not entire, but is dotted with little holes called " stomata ; through these the atmospheric air passes freely into the cellular spaces in the leaf, and through the porous walls of the leaf cells, which contain a green substance called " chlorophyll." In these cells, containing chlorophyll, the carbonic acid of the air is broken up through the influence of light and warmth, and the oxygen set free and the carbon retained. This process is called "assimilation," and is active only during the daytime ; during the night the food, formed by day, undergoes a change, whereby it can be transferred in solution to the places where it is needed. Daylight, as also the presence of iron in the plant, is necessary for the formation of chlorophyll. In the daytime, growing plants purify the air by consuming the carbon ; in the night, the process is reversed, THE CONSTITUENTS OF PLANTS. 13 oxygen being then consumed. The quantity of oxygen set free by young plants is, however, greatly in excess of that consumed. The food directly supplied by the atmosphere is, therefore, chiefly carbon. The carbon absorbed by the plant, in connection with the hydrogen and oxygen of the water, forms starch, dextrine, sugar, fat, cellulose, substances serviceable in the growing plant, and to be stored away for future use in seeds, roots, and stems ; and the same elements, together with nitrogen and a little sulphur, form the albuminoids. All of these are vegetable substances with which we are familiar, and which are termed "organic.'' Pood obtained from the Soil.-Eoots are of two kinds,the " tap root,'' the chief use of which is to sustain the plant in an upright position; and the "fibrous root," which is engaged mainly in absorbing food from the soil. These roots are made up of cells, through the walls of which solid matter cannot pass ; all food absorbed by the root must be in solution. The surface membrane of the root, unlike that of the leaf, is not full of holes the absorption of solids is, therefore, impossible. The absorption of the solution by the root is obtained by means of what is called "diffusion." By this means water is absorbed, and, with the water, the dissolved food elements usually contained in the ash of plants. The absorption of food is, however, not confined to the taking up of ready formed solutions. The roo...
cowpea, soybeai}, vetch and clover in a rotation, and used as hay, are now recognized in part, and wherever used they result in largely increasing the amount of feed, without decreasing the total yield of corn, cotton or tobacco. An improved rotation, recommended by the Alabama Station, is (first year) corn with cowjieas planted between the corn rows in May or June; second year, fall-sown oats or wheat, followed by cowpeas in June; third year, cotton. The cowpeas, after the crop of small grains is removed, are usually cut for hay, but may be picked for seed, or pastured, or plowed under in January or February.
Nore than that, the baneful efiects do not stop here, for the nitrates as they are gradually formed from the organic matter of the soil are also attacked by the denitrifying bacteria, and their nitrogen is set free. In a word, then, the animal manure applied is not only useless of itself, but is harmful because of its destructive effects on the oxidized nitrogen derived from other sources. I t is quite apparent that the interests involved are of great moment, that 'Cl'agner's theory if it be borne out by practical experience vitally concerns the man of science, the practical farmer, and the world at large. It was in the hope of contributing something to the knowledge of the subject that these experiments were planned. The scope of the work included the study o f : I. The composition of the solid and liquid portions of con. manure, fresh. 11. The composition of the solid and of the solid and liquid portions of cow manure, leached. 111. The availability of the nitrogen in the solid and in the solid and liquid portions of cow manure, fresh. 11'. The availability of the nitrogen in the solid and in the solid and liquid portions of cow manure, leached. 1-. The relative availability of the nitrogen in the form of nitrate, of ammonia and of organic matter in dried blood. IT1. The effect of the use of the solid and of the solid and liquid portions of cow manure, fresh and leached, with nitrogen in the form of nitrate, of ammonia, and of organic matt e r. DESCRIPTIOK OF THE EXPERIMENTAL PI,.\KT. In order that the conditions of the experiment might conform as nearly as possible to those in actual practice, what is known as the "cylinder method" was adopted. The cylinders were made of galvanized iron, 23.5 inches i n diameter and 4 feet long, and were painted inside and out, to retard corrosion. The area of soil surface thus exposed was, therefore, 3 square feet, and its depth was such that the roots of the crop would be practically prevented from obtaining f,Jotl other than that contained within the cylinders. In order that the conditions for each cylinder might be uniform, the surface soil was first removed entirely, and the subsoil, a mixture of clay and ~2 n d. STUDIES IN DENITRIFICATION. 787 which was taken from the holes, was thoroughly mixed. The same weight of subsoil was then placed in each one, and thoroughly packed and brought to a uniform height, so as to permit of the addition of 8 inches of surface soil; 120 cylinders were used, divided into two groups of 60 each. Thus in each group there were 20 series of three each, A, B and C, enabling a triplication of crops in each case. DIAGRAM OF EXPERIMENT.
the beginning of the eighties of the last century. It was the introduction of Koch's^gelatin-plate method for the isolation of pure cultures that gave a powerful stimulus to bacteriologicah investigation.Koch was also among the first'' to make quantitative soil bacteriological studies and to show that the upper layers of the soil, whether taken from densely populated districts or from fields far removed from the city, contain enormous numbers of bacteria. The work of other investigators^has confirmed his results. On the whole, however, these quantitative studies have not been very fruitful in their practical application, though they have given us some interesting information as to the distribution and numbers of the bacteria in the soil, as well as their relation to changing climatic conditions.Frankel showed, for instance, that the number of bacteria rapidly diminishes with the increasing distance from the surface until they almost entirely disappear at depths below 3 meters. Similar results were obtained by Fiilles, who also noted quantitative differences in the bacterial content of forest, vineyard, meadow, and field soils and pointed out that certain species may suddenly appear in predominating numbers, and as suddenly disappear. These studies and others already referred to taught us, at least, that our arable soils are inhabited by vast numbers of microscopic beings, most of them located near the surface, changing in numbers with the changing nature of soil and season and exhibiting variable group relationships.After these preliminary studies the agricultural bacteriologists could not but recognize that the mere counting of the soil bacteria « Mitt. K. Gsndhtsamt. [Germany], I (1881), p. 1.b Ibid, pp. 34-36.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.