High yield, good eating quality, and high N use efficiency for medium hybrid indica rice: From the perspective of balanced source-sink relationships at heading

High yield, good eating quality, and high nitrogen (N) use efficiency present challenges in cultivating medium hybrid indica rice. We hypothesized that balanced source-sink relationships are key traits for achieving high yield, good eating quality, and high N use efficiency in medium hybrid indica rice under suitable N management regimes. Three field experiments were conducted with two medium hybrid indica rice cultivars. Five distinct N application levels, designated as N0, N75, N150, N225, and N300, were used to investigate varying source-sink characteristics and their impact on yield, eating quality, and N use efficiency. The results indicated that the ratio of dry matter at the heading stage to the number of spikelets per unit area (DM/Spik. R) exhibited a significant decrease with increasing N application rates in both cultivars over three years, except for the cultivar HLY898 in 2021. Conversely, an increase in N application rates generally increased the ratios of accumulated N rate and leaf area at the heading stage to the number of spikelets per unit area (AN/Spik. R and LA/Spik. R) across the cultivars and experimental years. Only AN/Spik. R showed significant relationships with yield, eating score, and N partial factor productivity (PFPN). In addition, significant differences were observed among the three study years for DM/Spik. R and LA/Spik. R, but no significant difference was found for AN/Spik. R across the three study years. Moreover, both N concentration and nitrogen nutrition index (NNI) at heading had significant and linear relationships with AN/Spik. R. Further analysis revealed that the highest yield and maximum eating scores, constituting 92 % of the total, were achieved when AN/Spik. R reached 3.65 mg per spikelet. Correspondingly, the NNI was recommended as 0.93 at heading when 90 % of the highest yield and maximum eating scores were harvested. Additionally, 79 % of the highest yield and maximum PFPN were obtained when AN/Spik. R and NNI were approximate to 2.58 mg per spikelet and 0.78 at heading, respectively. These results suggest that moderate AN/Spik. R corresponding to mild N deficiency at heading could be a key source-sink indicator for the integrated regulation of high yield, good eating quality, and high N use efficiency in medium hybrid indica rice.