Effect of agronomic management on rice grain quality Part II: Nitrogen rate and timing

Background and objectives In temperate rice growing regions, the application of nitrogen (N) fertilizer is often split into two applications to reduce the risk of cold-induced sterility associated with high N uptake. This strategy involves a basal N application applied pre-permanent water (PW) and the second application following panicle initiation (PI). Split N application generally increases crop yield, however, data describing the impact on grain quality are relatively sparse. The objective of this study was to determine the effect of the split N method on grain quality parameters. We analyzed grain quality under various pre-PW and PI N rates. Findings N applied pre-PW increased head rice yield (HRY; the percentage of grain that remains whole or at least 75% of the original length after milling) in all tested cultivars, however, the effect of splitting the same total N rate into two doses on HRY was cultivar specific. N rate applied pre-PW also showed a positive and negative relationship with milled grain yellowness (b*) and brightness (L*), respectively. The effect of N on amylose content was cultivar specific. The changes in quality parameters through pre-PW N application were associated with protein content. However, total protein content did not correlate as strongly with quality parameters in the split treatments compared with the single-dose treatments. Analysis of protein composition revealed N rate and timing affected protein composition, which had significant impacts on quality parameters, and the effects were cultivar specific. Conclusion These results indicate altering the nutritional management of rice changes the protein composition affecting grain quality parameters. Significance and novelty This study demonstrates the importance of N rate and timing of application in regard to grain quality and the significant role protein composition plays in quality characteristics.