Abstract: Exploring the effects of reducing nitrogen application combined with different active organic materials on the allocation patterns and stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) in various rice organs can provide a theoretical basis for the efficient nutrient management of highquality rice production in Qianxi, Guizhou Province. An experiment with five treatments was set up, including conventional fertilization (F), 20% nitrogen reduction (CF), 20% nitrogen reduction combined with commercial organic fertilizer (OM), 20% nitrogen reduction combined with biochar (B), and 20% nitrogen reduction combined with both commercial organic fertilizer and biochar (BOM). We examined the effects of different fertilization treatments on the yield, quality, and C∶N∶P stoichiometry of rice. The results showed that compared with F treatment, the grain and straw yields of OM, B, and BOM treatments increased by 9.7%-24.6% and 3.6%-13.0%. Rice yield was the highest in BOM treatment. Plant height, effective spike number, and 1000grain weight of BOM treatment were the highest, which were 98.43 cm, 25.42 spikes and 31.43 g, respectively. Compared with CF treatment, the protein, total starch, and reducing sugar contents of BOM treatment were increased by 11.4%, 4.7% and 25.0%, respectively, while the amylose content decreased by 8.2%. In terms of nutrient uptake and utilization efficiency, the accumulation of N, P, and K in BOM treatment increased by 39.8%, 32.9% and 33.8%, respectively, and the partial factor productivity of nitrogen fertilizer and nitrogen uptake efficiency increased by 54.0% and 74.8%, respectively. Compared with F treatment, C∶N and C∶P in each part of the rice plants were significantly decreased in OM, B, and BOM treatments, while N∶P was significantly increased in grain and straw. The grain and straw yield, protein content, the partial factor productivity of nitrogen fertilizer, and nitrogen uptake efficiency were significantly positively correlated with the N∶P ratio of rice grains. Under nitrogen reduction conditions, the combined application of organic materials with varying carbon stability effectively regulates the stoichiometric balance of C∶N∶P in rice, enhances nitrogen uptake and use efficiency, and ultimately improves rice yield and quality.

Key words: rice, biochar, commercial organic fertilizer, yield, quality, nutrient uptake and utilization, stoichiometric characteristics