Effects of Biochar Amendment and Nitrogen Fertilizer on RVA Profile and Rice Grain Quality Attributes

Improving rice production in modern agriculture relies heavily on the overuse of chemical fertilizer, which adversely affects grain quality. Biochar (BC) application is well known for enhancing rice yield under reduced nitrogen (N) application. Therefore, we conducted a two-year field experiment in 2019 and 2020 to evaluate RVA profile characteristics, grain milling, and appearance qualities under four BC rates (0, 10, 20, 30 t ha^-1) in combination with two N levels (135 and 180 kg ha^-1). The results showed that BC at 30 t ha^-1 along with 135 kg N ha^-1 improved rapid visco-analyzer (RVA) profile attributes, including peak viscosity (4081.3), trough viscosity (3168.0), break down (913.3), final viscosity (5135.7), and set back (1967.7). Grain yield, grain rain length, milled rice rate, percent grains with chalkiness, amylose, and starch content were improved by 27%, 23%, 37%, 24%, 14%, and 8%, respectively, in the plots treated with the combination of 30 t BC ha^-1 and 180 kg N ha^-1. A positive coefficient of correlation was observed in RVA profile, milling, and apparent quality of rice with soil properties. These results suggested that BC at 20 to 30 t ha^-1 in combination with 135 kg N ha^-1 is a promising option for enhancing grain yield, RVA profile, appearance, and milling quality.