RESPONSE OF THE SEMINAL ROOT ELONGATION TO NH4-NITROGEN IN SEVERAL RICE CULTIVARS

The aim of this study was to examine the effect of various NH4-nitrogen concentrations in culture solution on the seminal root elongation of the rice plant. Ten rice cultivars with differing adaptabilities for heavy manuring were grown in Kasugai rice culture solution at 30-degrees-C for 12 days. First, the nitrogen concentration was set at four levels, 0, 4, 40 and 240 mg L-1. In all the cultivars, seminal root elongation was exponentially inhibited with increasing nitrogen concentration and thus the inhibitory effect per unit increase of nitrogen concentration was much greater in the range of 0 to 4 mg L-1 than in the higher range. In a separate experiment, nitrogen concentration was set at six levels, 0, 0.4, 1, 2, 3 and 4 mg L-1. In this range, seminal root elongation was linearly inhibited with increasing nitrogen concentration. Comparing the cultivars, a clear trend was seen. The seminal root elongation of the rice cultivars, which are reputed for their low adaptability for heavy manuring, was more severely inhibited as nitrogen concentration increased compared to cultivars with high adaptability. Additionally, the seminal root axis length of the former cultivars tended to be greater than that of the latter cultivars when nitrogen concentration was at 0 mg L-1.