Abstract
In this experiment, I investigated the effects of combinations of nitrogen fertilizer and temperature on the early growth of alfalfa under long-day conditions, using ^<15>N-labeled nitrogen. At 20/15℃, there was no difference between the NO_3 plot and NH_4 plot with respect to dry weight, total nitrogen content, and ^<15>N content. At 30/25℃, by contrast, values for all these three variables in the NH_4 plot were higher than those in the NO_3 plot. The relative specific activity (RSA) of ^<15>N in roots at 20/15℃ was comparable in the NO_3 plot and NH_4 plot. At 30/25℃, however, the RSA of ^<15>N in roots in the NH_4 plot was higher than that in the NO_3 plot. These results suggest that differences in the uptake of nitrogen fertilizer, or variations in the distribution of nitrogen to the roots may be responsible for the difference in the effects of NO_3 and NH_4 on the growth at 20/15 and 30/25℃.
