Delayed Potassium Application Alters Protein Accumulation While Improving Eating Quality and Yield in Rice

Potassium plays a critical role in improving rice yield and quality; however, the effects of delayed K application on grain protein metabolism and eating quality remain unclear. This study evaluated four potassium fertilizer management modes designed with basal fertilizer: panicle fertilizer, with ratios of 10:0 (K1, control), 8:2 (K2), 6:4 (K3), and 4:6 (K4). Grain protein and protein fractions, free amino acids (FAA), key protein synthesis enzyme activities, starch RVA profile, taste value, processing and appearance quality, and yield were measured. With the delayed application of potassium fertilizer, grain GS, and GOGAT activities decreased by 3.15-7.67% and 6.92-13.06%, while GOT and GPT activities declined by 3.72-13.99% and 2.94-3.32% compared with K1. Consequently, FAA, albumin, globulin, prolamin, and glutelin contents all decreased, and grain protein content was significantly reduced, by 0.18-0.44 percentage points. In contrast, peak viscosity and breakdown increased, setback decreased, and taste value improved by 4.35-10.14%. Meanwhile, head rice rate increased, chalky grain rate and chalkiness decreased, and yield under K4 treatment increased significantly by 3.48%. Delayed potassium fertilizer application (K4 treatment) helps to reduce the activity of key enzymes involved in protein synthesis, decrease protein and its component contents, while simultaneously improving yield and eating quality.