|Abstract or Summary
- The purpose of this study was to evaluate differences between winter wheat varieties in response to nitrogen fertilizer. Seven nitrogen fertilizer rate x variety factorial experiments were conducted in several environments. Dry matter and nitrogen yields at boot, soft dough, and harvest and grain yield components were measured. The yield component data were evaluated in terms of storage capacity which is assumed to be proportional to kernels /rn² for a given variety. The kernels /m² was divided into two components, spikes /rn² and kernels/spike. The spikes /m² of each variety were closely related to the boot nitrogen yield, but not to boot dry matter yield or plant nitrogen content. Since the kernels/spike generally remained constant or increased as the boot nitrogen yield increased, the kernels/m² appeared to depend on the boot nitrogen yield. The variety Hyslop had high dry matter and nitrogen yields at boot stage of growth. This appears to allow it to have excellent storage capacity as measured by kernels /m² . Good growth by boot stage appears to lower the nitrogen fertilizer rate needed for maximum grain yields. The variety Nugaines had relatively low growth and nitrogen uptake by boot. This may be the reason why it needs a higher fertilizer rate than Hyslop to obtain adequate storage capacity (kernels/m² ). However; Nugaines had better growth after soft dough stage. At the dryland locations this may be due to slower depletion of the soil water. At the irrigated locations it may be due to greater late tillering. Hyslop and Nugaines differed in the pattern of yield component adjustment to improving environment. Hyslop mainly increased its average kernels/spike rather than spikes/m² . Nugaines had greater increases in spikes/m² but smaller increases in kernels/spike. This may be related to their different cuim sizes and tillering. Hyslop forms a few large culms early in the season, but Nugaines continues to tiller during stem elongation. Coulee was intermediate between Hyslop and Nugaines in patterns of growth over time and pattern of yield component adjustment to improving environment. It had good yields at moderate nitrogen rates, and high nitrogen rates did not appear to be needed for adequate storage capacity. Wanser consistently had low grain yields, which was due to low kernels/m² . Nitrogen fertilizer increased its height more than the shorter varieties and this was associated with reductions in kernels/spike: Thus the height growth of Wanser may compete with its ear development and cause poor storage capacity. Wanser had slightly greater grain nitrogen percentage than other varieties, but this was simply associated with its low grain yield. There were only small varietal differences in the percentage of plant nitrogen translocated to grain. However, environment and nitrogen fertilizer rate greatly affected this. The club wheat Paha yielded well but usually less than some other varieties. It had high dry matter and nitrogen yields, but after soft dough its dry matter yields decreased more than for other varieties. This indicated that it depleted soil moisture earlier than other varieties did. Tx65A1268, a short hard red winter wheat with prolific tillering and small culms, was included in. two experiments. It had the highest grain yield at the low rainfall site. This may be related to its early maturity. However, with irrigation it yielded poorly. This appeared to be due to poor storage capacity since there was no increase in kernels/spike with improving environment. Yamhill, an awnletted wheat, yielded well in the Willamette Valley, but not in eastern Oregon. Estimates of the recovery of fertilizer nitrogen were calculated from the increases in soft dough nitrogen yield caused by each increment of nitrogen fertilizer. At sites with excellent moisture supply the first fertilizer increment was incompletely recovered (44-66%), apparently due to immobilization associated with plant residue decay. With higher fertilizer increments which increased yields, fertilizer recovery values were near 100%. At low rainfall sites under fallow cropping recovery values were 38-56% and decreased with above optimum fertilizer rates. At eastern Oregon sites losses of nitrogen from the plant tops after soft dough ranged from 7-33% depending on variety, location, and fertilizer rate. At maturity the percentage of the total plant top nitrogen in the grain ranged from 60-81%. This percentage decreased with nitrogen fertilization, but was little affected by variety.