Foliar spraying of rice with nitrogen: Effect on protein levels, protein fractions, and grain weight

Abstract

Grain yield and grain protein levels are usually negatively correlated. However, when the appropriate timing for nitrogen (N) supplementation is used, a significant increase in rice grain protein can be obtained without a corresponding decrease in grain yield. Increased N doses, equivalent to 40, 80, and 120 kg N ha^‐1, applied at 10 and 20 days after anthesis (DAA), led to 13, 27, and 18% increases in grain crude protein, respectively, compared to the control. The shoot weight of plants receiving foliar spray of N, did not differ significantly from that of untreated check plants, indicating that the extra N was utilized for other processes. The highest crude protein level (86.2 mg g^‐1) was obtained at 40+40 kg N ha^‐1, whereas the crude protein content, resulting from the highest N dose (60+60 kg ha^‐1), was only 80.0 mg g^‐1. Glutelin was the fraction that most contributed to the increase in grain protein content. A positive correlation between crude protein and glutelin level (r=+0.92^**) indicated that the increase in protein increased the quality of rice grains.