AN OLD-NEW THEORY
The inoculation of soil, like many other lately exploited theories, has no doubt been known for hundreds of years. There are evidences that it was practiced in England at least a century ago, and it is thought to be an old custom among the Chinese. Some space was given to “soil inoculation” in a preceding chapter, attention there being devoted to the simple methods of infecting soil with bacteria.
IMPORTANT DISCOVERIES
Some twenty years ago a German scientist, Nobbe, discovered that the small nodules found on the roots of the leguminous plants contained bacteria that took nitrogen from the air and transferred it to the plant. It had been known that cultivated soils were rapidly losing their original supply of nitrogen and there seemed no practicable way of restoring it in sufficient quantity. Commercial nitrogen costs fifteen cents per pound and the expense of applying it to the land to equalize the loss from an ordinary farm crop is almost equal to the value of a crop. Hence, the discovery that the legumes were nitrogen-gathering, by means of these bacteria, was hailed as one of the greatest of the age. With millions of pounds of nitrogen over his land there seemed now a method whereby the farmer could utilize some needed portions of it. The bacteria live in tubercles upon the roots of various leguminous plants, such as Red clover, Sweet clover, Bur clover, alfalfa, cowpeas, garden peas, vetches and beans. These tubercles are the home of the bacteria, minute forms of vegetable life, too small to be seen with the naked eye. The legumes have no power in themselves to draw nitrogen from the air, yet these bacteria seem to have the power to absorb the free nitrogen and cause it to combine with other elements, forming nitrates or other assimilable compounds suitable for plant food. It has also been demonstrated that, as a rule, there are different species of these bacteria for different species of legumes.
After German scientists had made their discoveries, one of the existence of these bacteria on the roots of the legumes and another that in the laboratory, these organisms could be bred and multiplied, they seemed unable to develop them of sufficient vigor to survive any general distribution. At this point Dr. George T. Moore of the United States Department of Agriculture, hit upon a plan of cultivating them in a way by which they could be preserved for many months, and he also gave them a much greater power. This nitrogen-fixing power was so developed that seeds soaked in the solution, it is claimed, sprouted and produced plants in sand that possessed no nitrates. He then found that these bacteria when grown upon nitrogen-free media will retain a high activity for a long time, if carefully dried out and then revived in a liquid medium. He also devised a plan by which they could be mailed to any part of the world and arrive in perfect condition.
Most experiment station men have given to Dr. Moore great credit for his discoveries and have tried, with rather marked success, his method of nitro-culture; on the other hand a few have been opposed to the method from the beginning and are still opposed. It would seem that the tests made prove that nitro-culture does introduce bacteria when directions are followed.
Of course if a farmer’s soil has the alfalfa bacteria, it is not necessary to use any system of inoculation. If Sweet clover or Bur clover is growing in the vicinity, or if alfalfa is thriftily growing near without the aid of inoculation, it is hardly necessary to make there further efforts for the introduction of bacteria.
SUGGESTIONS FROM THE DEPARTMENT OF AGRICULTURE
In a preceding chapter the opinion was expressed that in most states, and in most localities in those states, inoculation was unnecessary because bacteria were already present; yet it is true that these bacteria are present, if at all, in varying quantity. If comparatively few are present, any method of inoculation that will introduce more into the soil, to hasten the growth of the tubercles and promote the gathering of nitrogen, will be helpful. The fact is, we know as yet comparatively little of all there is to be learned about this wonderful principle. It is altogether probable that the use of nitro-culture is as practicable and as free from objections as the use of inoculated soil, especially from distant and unknown fields. In one of its bulletins the United States Department of Agriculture has summarized its advice as to inoculation as follows:
When Inoculation is Necessary.—Inoculation is necessary—