COMPARISON OF ROOT-GROWTH AND NITROGEN ABSORBING ABILITY BETWEEN GRAMINEAE AND LEGUMINOSAE DURING THE VEGETATIVE STAGE

Eight Gramineae crops (rice, spring wheat, barley, oat, maize, sorghum , redtop, and orchardgrass), and seven Leguminosae crops (soybean, fie ld bean, adzuki bean, lupin, pea, alfalfa, and red clover) were grown in a field. The characteristics of nitrogen absorption were parametriz ed as root size (root length or dry weight), root activity (specific a bsorption rate of nitrogen per unit root dry weight; SAR(N)), and phot osynthetic factors (crop growth rate (CGR), leaf area index and net as similation rate). The results were as follows. 1) The rate of nitrogen accumulation by plant (DELTAN) was highly correlated with the crop gr owth rate (CGR), and dry matter accumulation per unit amount of nitrog en accumulated in plant was lower in Leguminosae than in Gramineae. 2) In Leguminosae, the length or weight of root (root size) was generall y shorter or smaller than in Gramineae. However, SAR(N) of Leguminosae was higher than that of Gramineae. Therefore, the increase in the roo t size was considered to contribute more significantly to the increase in the shoot weight in Leguminosae compared to Gramineae. 3) Througho ut the growth, in Gramineae, SAR(N) and CGR were correlated with DELTA N, whereas in Leguminosae, LAI and CGR were correlated with DELTAN. Th us, nitrogen absorption was assumed to be basically regulated by the r equirement of nitrogen in shoot. 4) Root function was found to be diff erent among crops; in Gramineae at both early vegetative and late vege tative stages, SAR(N) was correlated with DELTAN, and in Leguminosae a t the early vegetative stage, the root size was correlated with DELTAN , then at the late vegetative stage, the root activity (SAR(N)) became an important factor for the control of DELTAN.