Interaction Between Sowing Date and Nitrogen Fertilization: Agronomic and Physiological Mechanisms Driving High Yield and Superior Grain Quality in Rice

ABSTRACT This study aims to balance yield and quality by selecting varieties and optimizing agronomic management practices. In 2023, field trials evaluated 35 new rice varieties for yield and grain quality. In 2024, four varieties with varying yield and quality performance underwent a split‐plot design for further investigation with two sowing dates (S1: 14th May and S2: 29th May) and two nitrogen (N) rates (N1: 120 and N2: 180 kg N ha −1 ). In 2023, the grain yield of these varieties ranged from 7.3 to 10.2 t ha −1 , with chalkiness degree 3.7%–29.0%. The selected variety Cheng Liang You (CLY607) in 2024 reached a peak yield of 9.3 t ha −1 with early sowing on 14th May and 180 kg N ha −1 . The increased yield was attributed to higher N uptake, improved grain filling percentage, increased biomass, and a higher harvest index. Delayed sowing resulted in lower daily radiation but maintained heat stress in a hot year of 2024, which reduced leaf area index (LAI) and biomass, lowered grain filling percentage and head rice rate, but increased chalkiness. Early sowing with a low N rate improved eating quality due to the reduced protein content and stabilized amylose levels, yet led to increased chalkiness. It also altered protein composition to more glutelin and less prolamin. On the contrary, a high N rate increased total protein content in grain but negatively affected rice taste quality. In conclusion, CLY607 showed high‐temperature tolerance for yield and quality; delaying sowing did not relieve the detrimental impact of high temperatures on crop yield and quality in extreme heat years; a high N rate increased resilience to high temperature by boosting yield and reducing chalkiness, but lowered eating quality.