The New Student's Reference Work/Nitrogen-Gathering Crops
Nitrogen-Gathering Crops all belong to the family of leguminous plants or Leguminoseæ, having irregular, conspicuous flowers or clusters and seeds in pods. The bean and pea are good examples. The clovers do not seem at first sight to answer this description. All have abundant foliage, root deeply, and are remarkable for their ability to take pure nitrogen from the soil and store it up in form available as plant and animal food. This is done by means of germ-like organisms which grow inside of tiny lumps on the roots. These nodules can be seen by washing the earth from the roots of any of these plants, and range in size from that of a pin-head to that of a small pea. These nodules will not appear on clover roots if none of the germs exist in the soil. Such a soil can now be inoculated with the germs by applying a solution containing them. The germs are put up in dry form like yeast-cakes and can be obtained from the Department of Agriculture, and be dissolved to make the solution. The nitrifying action goes on best in well-ventilated soils. In poorly drained soils just the opposite process, denitrification, is apt to occur, reducing plant food to unavailable simple nitrogen. The subject of nitrifying bacteria is very complex, as they possibly also exert a fermenting influence on the minerals of the soil. Experiments have shown that an acre of cowpeas at the Louisiana Experiment Station produced 65 pounds of nitrogen, and an acre of crimson clover at Cornell University produced 156 pounds, 30 of which were in the roots. Other clovers produce a greater proportion in the roots, as the mammoth clover, with 78 pounds in the roots out of a total of 146 pounds. It grows best in wet soils that usually are deficient in nitrogen, and so leaves much in the soil when the tops are cut off. Red clover, the usual variety grown on loams and heavier clays, contained in the experiment, 40 pounds in the roots out of a total of 103 pounds. A low estimate of the market value of nitrogen is between 15 and 20 cents a pound. See Moore’s Soil Inoculation with Legumes and Wood’s Inoculation of Soil with Nitrogen-Fixing Bacteria, both bulletins of the U. S. Dept. of Agriculture.