Nitrogen fertilization alters rice taste quality through layer-specific changes in protein and starch composition

Abstract

Nitrogen fertilizer application significantly affects the protein and starch distribution in rice grains, thereby influencing eating quality and overall grain quality. This study investigated different rice varieties—Conventional Indica Rice, Indica-Japonica Hybrid (Indica-leaning, Long Grain), Indica-Japonica Hybrid (Japonica-leaning, Short Grain)—under two nitrogen treatments (0 kg ha⁻¹ and 200 kg ha⁻¹). Grains were milled into four layers (L1–L4, representing 0°%–9°%, 9°%–14°%, 14°%–19°%, and 81°% of rice weight, respectively) to analyze their layered protein and starch content. High nitrogen fertilization increased protein content by 37.2°%–65.8°%, predominantly in the outer layers, and altered starch distribution. Under low nitrogen conditions, starch content in the third layer (L3) increased significantly by 74.02°%. However, high nitrogen fertilization increased milling intensity, reducing starch retention and taste quality, and causing up to a 14°% yield loss. These findings underscore the importance of optimizing nitrogen application and milling practices to balance eating quality, nutritional integrity, and yield.