Effects of nitrogen supply on tillering dynamics and regrowth of perennial ryegrass populations.

In a glasshouse, three diploid and three tetraploid populations of Lolium perenne L. were grown to evaluate population differences in tillering, leaf extension and assimilate distribution between root and shoot.Three subsequent conditions were used: 1) two steady-state plant nitrogen concentrations (0.027 and 0.042 g N.g DM" 1 ), 2) changing nitrogen availability to zero, 3) changing nitrogen availability to a supra-optimal level.Populations were grown in monocultures and mixtures to investigate the correlation between monoculture and mixture performance.The highest yielding population yielded 40 % more cut herbage than the lowest yielding population.Its nitrogen uptake was 29 % higher and its organic nitrogen concentra tion was between 5 and 8.5 % lower.Population differences in mixtures were larger, but population order remained the same.It was therefore concluded that selection of populations for regrowth characteristics can best be done in mixtures.Stopping nitrogen application re duced tiller density and assimilate allocation to shoots.Both were restored to more than the original values after changing to a supra-optimal nitrogen availability.Analysis of tillering in terms of leaf appearance and site filling showed a negative genetic correlation between the two factors.A simulation model was developed to evaluate the relative importance of tiller density, leaf expansion and assimilate partitioning for regrowth.