Abstract:Nitrogen(N) fertilizer is one of the most important factors affecting grain yield in rice. The experiment investigated the effect of nitrogen application on the variation characteristics of the contents of three nitrogen forms［assimilable nitrogen(AN), functional nitrogen(FN), and structural nitrogen(SN)］ in different organs using two rice varieties of cold Japonica (Songjing 6 and Songjing 9) as test materials. The results showed that nitrogen levels affected AN and SN contents in the functional leaves and stems significantly, and varied with the varities, while it had slight effect on the AN and SN contents in grains. Nitrogen application rate had more significant influence on the FN content in function leaves and grains than in stems of two varieties. For both varieties, AN contents in functional leaves and stems presented a single peak curve with the growth process, and reached the maximum at the filling stage; while AN content of grains showed a “high-low-high” variation tendency. FN contents in different organs of both varieties were increased with the growth process generally, but the FN contents of leaves and stems decreased gradually in later filling stage. In grains, FN content of Songjing 9 was higher than that of Songjing 6SN contents in leaves and stems of both varieties (except N0, N100 and N200 treatment of Songjing 9) increased firstly and then decreased, and it reached the maximum at anthesis stage; SN content in grains showed a slow downward trend from anthesis to maturity; SN contents in leaves and stems of Songjing 9 were higher than that of Songjing 6The AN contents in the functional leaves and stems for whole growing stages (except booting stage) and the SN,FN contents of grains were significantly positively correlated to the yield.