A quantitative analysis of the effects of nitrogen on the growth, development and yield of oilseed rape

SUMMARY Two experiments carried out in 1968 and 1969 are described which examined, through growth and yield analysis, the effect of nitrogen on the growth of oilseed rape. The results of the second experiment, when 0, 105·5 and 211·0 kg N/ha were compared, are presented and discussed. The application of nitrogen increased the yields of seed and oil, principally through increased production of seeds by a larger number of pods. However, the application of nitrogen had little effect on average pod weight or average seed weight. Crop growth rates were increased by the application of nitrogen and reached their highest levels during the period of pod development when the leaf areas had declined to very low levels. The order of effects of nitrogen (N 2 > Nl > NO) was similar for LAI, number of pods per plant and number of seeds per pod and it is likely that the effect of nitrogen was achieved indirectly through an increase in the supply of assimilates to the flowers and young pods. This suggests that the maintenance of a large and photosynthetically efficient leaf area during the period of flowering is necessary for high yields in this crop. The results also suggest that once pods are macroscopic they produce much of the assimilates needed for their own growth. The implications of these findings with regard to both practice and further research are discussed.