PRODUCTIVITY OF HIGH-YIELDING CROPS .5. ROOT-GROWTH AND SPECIFIC ABSORPTION RATE OF NITROGEN

''Standard yield variety'' and ''high-yielding variety'' of rice, wint er wheat, maize, soybean, potato, beet, and sunflower were grown, and the relationship between root growth and absorption of nitrogen was st udied. To estimate the role of root in nitrogen absorption, nitrogen a bsorption rate (Delta N, g N m(-2) d(-1)) was parameterized into root dry weight (RW, g m(-2)) and specific absorption rate of nitrogen per root dry weight (SAR(N), Delta N RW(-1)). 1) Since during the vegetati ve growth stage, the correlation between Delta N and crop growth rate (CGR) was high, Delta N was under the control of shoot demand for nitr ogen, while during the early maturing stage, Delta N was well correlat ed with SAR(N) except for sunflower. Thus, Delta N at the vegetative g rowth stage was regulated by shoot growth (CGR), which was related to RW sometimes. Thereafter, Delta N was regulated by SAR(N) with the pro gression of growth 2) Based on the cluster analysis of SAR(N) or RW fo r Delta N, and correlation between Delta N and SAR(N) or RW, crops wer e classified into three groups: group (I), soybean, potato, and beet; group (II), rice, winter wheat, and maize; and group (III), sunflower. During the early maturating stage, Delta N of group (I) was regulated by mainly SAR(N), Delta N of group (II) was regulated by both SAR(N) and RW, and Delta N of group (III) was regulated mainly by RW. 3) SAR( N) remained high during the early maturation stage in the ''high-yield ing variety'' of crops.