. Soils, their properties and management. Soils. 428 SOILS : JPEOPEBTUSS AND MANAGEMENT the roots of many forest trees and known as myeorrhizal fungi have the abihty to fix atmospheric nitrogen, and that in some way the trees obtain a part, at least, of the nitro- gen so fixed. The growth of forests on poor, sandy soil containing practically no nitrogen has been urged as an example of this process. 350. Bacteria. — Of the several forms of microorgan- isms found in the soil, bacteria are the most important. In fact, the abundant and continued growth of plants on the soil is absolutely dependent
. Soils, their properties and management. Soils. 428 SOILS : JPEOPEBTUSS AND MANAGEMENT the roots of many forest trees and known as myeorrhizal fungi have the abihty to fix atmospheric nitrogen, and that in some way the trees obtain a part, at least, of the nitro- gen so fixed. The growth of forests on poor, sandy soil containing practically no nitrogen has been urged as an example of this process. 350. Bacteria. — Of the several forms of microorgan- isms found in the soil, bacteria are the most important. In fact, the abundant and continued growth of plants on the soil is absolutely dependent on the presence of bacteria, for through their action chemical changes are brought about which result in making soluble both organic and inorganic material necessary for the life of higher plants, and which, in part at least, would not otherwise occur. Bacteria are thus trans- formers, not producers, of fertility in the soil, although, as will be seen later, certain kinds of bacteria take nitro- gen from the air and leave it in the soil. With this excep- tion, however, they add no plant-food to the soil. It is their * action in rendering available to the plant ma- terial already present in the soil that constitutes their greatest present value in crop production. It is to their subtiiis; (/), ciostridmm pas- activity in conveying nitro- gen trom the air to the soil that we are indebted for most of our supply of nitrogen in virgin soils (see Fig. 59).. Fig. 59.—Some types of soil mi- croorganisms highly magnified, (a), nitrate formers; (6), ni- trite formers; (c), B. graveo- lens; (d), B. fusiformis; (e), Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lyon, T. L. (Thomas Lyttleton), 1869-1938; Fippin, Elmer O. (Elmer Otterbein), 1879-1949; Buckman, Harry Oliver, 1883-. New York, Macmillan
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