Grain nitrogen concentration differences among three sorghum hybrids with similar grain yield

The differences in grain nitrogen (N) concentration among 3 sorghum (Sorghu m bicolor (L.) Moench) hybrids with similar grain yield were examined under N-limiting conditions in relation to the availability of assimilate and N to grain. Several manipulation treatments [N fertiliser application, lower leaves shading, thinning (reduced plant population), whole canopy shading, canopy opening, spikelet removal] were imposed to alter the relative N and assimilate availability to grain under full irrigation supply. Grain N conc entration increased by either increased grain N availability or yield reduc tion while maintaining N uptake. Grain N concentration, however, did not decrease in the treatments where re lative abundance of N compared with assimilate was intended to be reduced. The minimum levels of grain N concentration differed from 0.95% (ATx623/RTx 430) to 1.14% (DK55plus) in these treatments. Regardless of the extent of v ariation in assimilate and N supply to grain, the ranking of hybrids on gra in N concentration was consistent across the manipulation treatments. For t he 3 hybrids examined, higher grain N concentration was associated with hig her N uptake during grain filling and, to a lesser extent, with higher N mo bilisation. Hybrids with larger grain N accumulation had a larger number of grains. There was no tradeoff between grain N concentration and yield, sug gesting that grain protein concentration can be improved without sacrificin g yield potential.