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-- 1. On a soil low in organic matter that has not previously borne leguminous crops. 2. If the legumes previously grown on the same land were devoid of nodules, of “nitrogen knots,” thus showing the need of the nodule-forming bacteria. 3. When the legume to be sown belongs to a species not closely related to one previously grown on the same soil. For instance, soil in which Red clover forms nodules will often fail to produce nodules on alfalfa when sown with the latter crop for the first time. _When Inoculation May Prove Advantageous._--Inoculation may prove advantageous-- 1. When the soil produces a sickly growth of legumes, even though their roots show some nodules. If the cultures introduced are of the highest virility, their use will often result in a more vigorous growth. 2. When a leguminous crop already sown has made a stand, but shows signs of failing, owing to the absence of root nodules. The use of the culture liquid as a spray or by mixture with soil and top-dressing may save the stand if other conditions are favorable. _When Inoculation is Unnecessary._--On the other hand, inoculation is unnecessary and offers little prospect of gain-- 1. When the leguminous crops that are usually grown are producing up to the average, and the roots show nodules in normal abundance.