Nitrogen in Plant Parts of Seven Spring Wheat Varieties at Successive Stages of Development 1

Nitrogen content of leaves and stems, head chaff, and grain was determined for seven spring wheat varieties on five sampling dates at two locations near Bozeman, Montana, in 1966. Nitrogen percentages in the chaff were at about the same levels as the nitrogen percentages in stems and leaves, and each decreased with successive sampling dates at nearly the same rate. Grain nitrogen percentages were similar at the late flowering and milk stages, but showed a significant increase by the dough stage. The amount of nitrogen translocated from top growth to grain averaged 66.2% under irrigation and 74.8% on dryland. Varietal differences in grain nitrogen percentages could not be attributed to differences in the percentage of total nitrogen that was translocated from top growth to the grain. Nitrogen increases in the total top growth from first to last sampling date were 85.1 kg/ha under irrigation and 20.1 kg/ha on dryland. Correlation coefficients at the irrigated and dryland locations of —0.88 and —0.93, respectively, for grain nitrogen percentages vs. the grain to straw ratio, and 0.89 and 0.92 for grain nitrogen content vs. total top yield indicate that grain nitrogen percentages are closely associated with top growth. These r values suggest that grain nitrogen percentages decrease as the grain to straw ratio becomes larger.