The Percentage of Nitrogen in Different Parts of Soybean Plants at Different Stages of Growth 1

Chemical analyses of many crop plants show that as a rule the. percentage of nitrogen decreases with age, and consequently mature plants contain less nitrogen than young plants. Particularly is this true for plants belonging to the Gramineae. In the case of theLeguminosae, however, there is some evidence which shows that, although the percentage of nitrogen decreases during the early stages, the leg-ames gain in nitrogen during the later stages of growth and are much richer in nitrogen at matttrity than the nonlegnmes. This condition may be due primarily to the fact that in inoculated legumes there is a general transformation of the nitrogen from thenodules to the seeds of the plant. Whitings studied the relative percentages of nitrogenous compounds in the tops, roots, and nodules of soybeans at definite periods of growth. All the plants were grown in sand cultures. In one experiment ~he amount of nitrogen in the nodules increased until the plants were 50 days old. After this therewas a marked decrease in nitrogen until the final harvest when the plants were 74 days old. The amotmt of nitrogen in the roots followed the same general course as that in the. nodules. The tops gained in nitrogen up to the time when the plants were 67 days old, but after the next 7 days a very decided decrease in amount of nitrogen was noted. In two other experiments soybean plants were grown and harvested at different stages, the final harvest being made when the plants were 4z and 4~ days old, respectively. The tops, roots, and nodules showed successive gains in nitrogen for the various stages, the largest amount being formal in the plants representing the final harvest. The plants apparently were not grown long enough to follow any possible transformation of nitrogen from the nodules to the seeds.