Combined Impacts of Nitrogen Forms, Rice Husk Biochar, and Water Regime on Purple Rice Yield and Grain Quality

Purple rice contains beneficial bioactive compounds, but the concentrations can be influenced by the growing conditions. This study investigated the interactive effects of water regime, biochar amendment, and nitrogen (N) sources on the yield and grain quality of purple rice. Purple rice grown under flooded conditions combined with biochar and urea or ammonium demonstrated significant increases in grain yield and yield components such as plant height, number of spikelets per panicle, and the percentage of filled grains compared to non-flooded conditions. Nitrate consistently resulted in the lowest yields and grain quality, especially under non-flooded conditions and with no added biochar. Grain anthocyanin concentration was highest under flooded conditions, with the maximum observed with biochar and nitrate application and with ammonium application without biochar. In contrast, the grain phenol content and antioxidant capacity were maximized by the biochar and water applications. The findings indicate that rice husk biochar can improve productivity without altering the color shade of purple rice. Combining flooding, biochar, and ammonium or urea improves the agronomic performance of purple rice, though the impact on nutritional qualities is more complex.