Effects on dry weight and nitrogen content of grains of semi-dwarf and tall varieties of winter wheat caused by decreasing the number of grains per ear

The number of grains in ears of six varieties of winter wheat growing in the field was decreased by removing the top half of the ear 6 days after anthesis (halving). In the semi-dwarf varieties Hustler, Sentry and Hobbit, and in the taller varieties Armada and Flanders, the mean dry weight per grain in the lower six spikelets of halved ears was about 23% greater than the dry weight of grains in the comparable part of intact ears. In Maris Huntsman the increase in grain size amounted to only 13%. Halving increased the number of grains in the semi-dwarf varieties but not in the others. Consequently, the increases caused by halving in the total weight of grain in the lower six spikelets ranged from 41% in Hustler and Hobbit to 7% in Maris Huntsman. Halving increased the amount of nitrogen in the grain of the lower half of the ear similarly in all varieties, and relatively more than it increased dry weight. So nitrogen per cent dry weight of grain was increased, especially in Armada, Flanders and Maris Huntsman which responded least in dry weight. The uptake of nitrogen into the stem plus ear after anthesis was unaffected by halving. Most of the nitrogen that normally moved to the upper grains accumulated in the lower grains of halved ears. More nitrogen moved into the grain of intact ears of tall than of semi-dwarf varieties after anthesis, because there was greater uptake of nitrogen into the shoot from the roots.