Studies on Inoculated Soybeans: I. The Importance of Determining the Number and Size of Soybean Nodules for Evaluating Relative Efficiencies of Two or More Cultures 1

In testing.the efficiency of different cultures for the inoculation of soybeans at the Iowa Experiment Station, one of the first problems which demanded ~/ttention was that of devising a suitable classification of the inoculated plants for designating the various intensities or degrees ofnodulation. The need of such a classification iS apl~arent after a glance at the literature on ’soybean inoculationl With reference to numbers of nodules such terms as few, very few, numerous, large and numerous, small but numerous, very large and numerous, several scattered nodules, and sparse nodule formation are commonly found. With reference to the degree of inoculation such terms are recorde~l as fair, good, and very good, but more frequently either inoculated or uninoculated is used. In some cases the number of nodules, per plant is given, together with the average number per plant, but no mention is made of the size. In other instances the number of nodules is divided into two groups, namely, large and small, The great variation in size and numbers of nodules on soyUean plant roots is familiar to everyone. It see.ms, however, judging Prom the literature, that the real significance between different sizes of soybean nodules has beefl greatly underestimated, i Therefore, the first step was to establish, if possible, a definite relationship between nodules that vary markedly in size. Such information would tend to show whether or not the terms mentioned above are justified, and furthermore would possibly suggest a more accurate means of differentiating relative efficiencies of two or more cultures.