Transport and redistribution of nitrogen at late growth stagesin different oilseed rape cultivars

This paper used ¹⁵N tracer method in sand culture conditions to determine the physiological factors of N redistribution and its relationship with N utilization efficiency. The paper also studied the differences in N distribution, transshipment and loss under different N levels in different N-efficient oilseed rape cultivars. The results showed that different N levels had different outputs in terms of biomass, grain yield, grain N content, plant N content, plant total N, grain total N, harvest index, accumulated N and N harvest index of selected oilseed rapes. Under normal N level, oilseed rape cultivar "742" had higher biomass, grain yield, grain total N, harvest index and N harvest index than cultivar "814". However, rape cultivar "742" had lower grain N content, plant N content and plant total N than "814" at low N level. Oilseed rape cultivar "742" had higher plant N content, grain N content, harvest index and N harvest index at peduncle growth stage than "814". At harvest stage, however, "742" had lower biomass, grain yield, plant total N and grain total N than "814". ¹⁵N tracer method results showed decreasing N amount in vegetable organs and the proportions and redistributions of N in propagative organs were significantly different. Under different N levels, N decline in root and stem in cultivar "742" was higher than in "814". This difference was especially evident in the stems of the oilseed rape cultivars. Under normal N level, the proportions of N decline in roots and leaves were lower in cultivar "742" than in "814". However, the proportion of N decline in stems was much higher in cultivar "742" than in "814". Under low N level, the proportion of N decline in all vegetable organs was highest in cultivar "742". Under normal or low N levels, less N was redistributed to silique husk of cultivar "742" than in cultivar "814". However, more N was redistributed to grain of "742" than "814". T-test showed that the amounts of redistributed N were significantly different, except for silique husk under normal N level. This implied that N redistribution from vegetative organs benefited N use efficiency. Furthermore, with normal N level, N loss and proportion in oilseed rape cultivar "742" were higher than in "814", and the reverse was the case for low N level.