The influence of date of origin of the shoot and level of nitrogen on ear size in three perennial grasses

SUMMARY In plants of S.24 ryegrass, S.215 meadow fescue and S.37 cocksfoot grown in the field, or with controlled nutrition in the glasshouse, ear size decreased the later the date of origin of the shoot between October and March, before flowering in late spring. The smaller ear size in shoots arising at successively later dates resulted from decreased numbers of primary branches in the ear, and also from the development of fewer florets on each branch. The decrease in number of primary branches was correlated with a decrease in number of unexpanded leaf primordia accumulated at the shoot apex before reproduction. No effect of nitrogen on ear size was detected when nitrogen was added as ‘Nitro‐chalk’ to plants growing one yard apart in the field. In contrast, plants receiving the smaller rates of nitrogen in the glasshouse generally developed ears with fewer florets on each lateral branch. Lack of nitrogen also decreased the number of primary branches in ears of ryegrass and prevented many shoots of all three varieties from flowering.