|Abstract or Summary
- The response of cultivars of winter wheat to foliar applications of urea was examined for grain protein content, yield, and kernel hardness. The objectives of this study were to measure the effect of urea on these three traits in diverse environments and to explain how potential responses could occur by (1) determining potential uptake of N15 labelled urea from foliar application under greenhouse conditions using different cultivars, light duration, and soil fertility levels; (2) analyzing immature spike samples collected following foliar applications in the field during the flowering period; and (3) examining grain from primary and secondary tillers and from central and lateral florets within spikelets. Foliar applications significantly increased grain protein content over the control and standard topdressing treatment in most cultivars. For example, for a single cultivar at the Hyslop location in 1979-1980, protein percents of 11.18, 12.22, and 13.60 were obtained for the control, standard topdressing, and foliar urea treatments respectively. Generally, foliar applications of urea failed to increase grain yield over the control, and yield was significantly below the standard topdressing treatment. However, the combination of topdressed nitrogen with foliar sprays produced yields equal to topdressing alone while significantly increasing protein. Mean yields at the Wasco location of the topdressing treatment and the combination of topdressing and one foliar application were 4.05 and 4.04 T/ha, whereas the grain protein content averaged 9.34 and 10.45 percent respectively. Foliar applications of urea did not significantly alter kernel hardness. Significant cultivar x nitrogen treatment interactions were found for protein, yield, and hardness, and split applications of foliar nitrogen did not significantly change these results. A potential uptake of 29.2 to 61.4 percent of actual foltar applications was found with N15 labelled urea in a greenhouse experiment. A significant effect for light duration was observed with recovery values of 41.4 and 46.6 percent for 12 and 18 hour photo-periods respectively. The varieties Stephens and Centurk had a significant difference in uptake of 48.1 and 39.9 percent recovery respectively. Following urea sprays which were initially applied at the heading stage, nitrogen treatment differences were found within three weeks after anthesis. The ranking of treatments from immature spike analysis corresponded to grain protein analysis at harvest. Nitrogen treatments did not change the protein or hardness levels disproportionately for mature spikes in comparing grain from primary and secondary tillers or from central and lateral florets within the spikelets.