Effect of Nitrogen Application Rate and Timing on Grain Yield and Protein Content of the Bread Wheat Cultivar ‘Minaminokaori’ in Southwestern Japan

Abstract

The effect of nitrogen (N) application rates at active tillering and anthesis on grain yield and protein content of a bread wheat cultivar, ‘Minaminokaori’, was examined in the field study conducted in Fukuoka, Japan. Number of spikes, leaf area index (LAI), and SPAD value at anthesis increased significantly (P < 0.05) with increasing N application rate at active tillering. Grain yield also increased significantly (P < 0.05) because of the increased number of spikes. However, grain yield did not increase significantly (P > 0.05) with increasing N application rate at anthesis. The slope of the relationship between N application rate at active tillering and grain yield was about 3 times that of the relationship between N application rate at anthesis and grain yield. These results indicate that N application at active tillering is more effective than N application at anthesis for increasing grain yield. Increasing N application rate at active tillering and anthesis generally increased grain protein content. However, the slope of the relationship between N application rate at anthesis and grain protein content was about 2 times that of the relationship between N application rate at active tillering and grain protein content. These results indicate that N application at anthesis is more effective than N application at active tillering for increasing grain protein content. The interaction between N application rates at active tillering and anthesis was significant (P < 0.05) for grain protein content. With the application of 4 g N m–2 at active tillering, grain protein content increased linearly at a rate of about 0.5% per 1 g N m–2 (from 10.9% to 14.0%) with increasing N application rate (from 0 to 6 g N m–2) at anthesis. However, the rate of increase in grain protein content with increasing N application rate at anthesis was greater with 0 g N m–2 at active tillering than that with 4 g N m–2 at active tillering, whereas that with 8 g N m–2 at active tillering was smaller than that with 4 g N m–2 at active tillering. Application of 8 g N m–2 at tillering resulted in the highest SPAD value at anthesis; this was followed by the results for 4 and 0 g N m–2. Therefore, the SPAD value may be an important trait to decide N application rate at anthesis.