EFFECT OF NITROGEN APPLICATION ON RECONSTRUCTION OF NITROGEN-COMPOUNDS DURING THE MATURATION STAGE IN SEVERAL FIELD CROPS

The effect of nitrogen application on the process of nitrogen distribution and retranslocation during the maturation stage was investigated in the field for rice, spring wheat, maize, soybean and potato. 1. The yield of the harvesting organs reached a peak at 100 kg N/ha (100 N) in potato and at 300 kg N/ha (300 N) in rice, spring wheat, maize, and soybean. In soybean, the yield was the same at 0 kg N/ha (0 N) and at 100 N, but it increased with the increase of the level of nitrogen application from 100 N to 300 N. 2. The amount of nitrogen accumulated in the plant increased with the increase of the level of nitrogen application up to 300 N in rice, soybean and potato and up to 600 N in spring wheat and maize. 3. The harvest index of dry weight was stable regardless of the level of nitrogen application, but that of nitrogen showed a decrease at 300 N and 600 N in all the crops except for soybean. 4. The proportion of each fractionated nitrogen compound was not altered by nitrogen application in the leaves and the harvesting organs of all the crops. Although it was also stable between 0 N and 100 N in the stems, the proportion of ethanol-soluble nitrogen to total nitrogen increased with the level of nitrogen application from 100 N to 300 N in the stems of all the crops except for soybean. 5. The proportion of free amino acid nitrogen and/or nitrate nitrogen in the stems increased with the increase of the level of nitrogen application in all the crops, and that of amides in the stems also increased to some extent. On the other hand, it was quite stable in the leaves and the harvesting organs. Based on the above results, it is suggested that, though the amount of nitrogen accumulated in the plant increased and the pattern of nitrogen distribution changed with the level of nitrogen application, the mechanism for the reconstruction of the nitrogen compounds in the leaves and harvesting organs was stable regardless of the level of nitrogen application in all the crops.