In the use of the cultures, also, failure is almost certain where the directions are not carefully studied and intelligently followed.
SWEET CLOVER SOIL USED TO INOCULATE ALFALFA FIELDS
The discovery in Illinois that inoculation of the soil for alfalfa was necessary in certain places and not in others suggested the theory that bacteria living on some other, probably native, plant were identical with the alfalfa bacteria. Investigations led to satisfactory evidence that this was the case and that the native plant was the ordinary Sweet clover (Melilotus alba). The [illustration] facing page 230 shows the results of a series of pot culture experiments made at the University of Illinois and reported in Bulletin No. 94 by Prof. Cyril G. Hopkins. The four photographs were made five, six, seven and eight weeks, respectively, from the time of planting. Alfalfa seed were planted in each of the five pots, in carefully prepared soil practically free of combined nitrogen, and at the same time four of the five pots were inoculated as follows:
Pot No. 1.—Not inoculated.
Pot No. 2.—Inoculated with bacteria obtained from infected alfalfa soil.
Pot No. 3.—Inoculated with bacteria obtained from alfalfa root tubercles.
Pot No. 4.—Inoculated with bacteria obtained from infected Sweet clover soil.
Pot No. 5.—Inoculated with bacteria obtained from Sweet clover root tubercles.
The results indicate that the same effect is produced upon the growth of the alfalfa by the nitrogen-gathering bacteria obtained from Sweet clover as by those from the older alfalfa, and seem to prove that infected Sweet clover soil can be used for the inoculation of alfalfa fields. Investigations have shown that 100 pounds of thoroughly infected soil to the acre is sufficient to produce a satisfactory inoculation within one year from the time it is applied.