ABSTRACT The high basal fertilizer model is mismatched with the requirements of direct‐seeded rice during the germination stage in cold regions, which exacerbates the combined stress of low temperature and urea hydrolysis products, thereby limiting grain yield and nitrogen use efficiency. Using the low‐temperature‐tolerant cultivar “Jijing 305” as the experimental material, this study conducted an indoor controlled‐temperature culture experiment (16°C/20°C × urea levels of 0 (N0), 29.6 (N1), 59.2 (N2) mg kg −1 ) and a field nitrogen management experiment (with a total nitrogen application of 150 kg ha −1 , four modes were set: basal:tillering:panicle fertilizer = 0:0:0 (N 0:0:0 ), 2:4:4 (N 2:4:4 ), 4:3:3 (N 4:3:3 ), and 6:2:2 (N 6:2:2 )) to explore the rules of seed germination, seedling establishment, and yield formation in direct‐seeded rice. The results showed that at 16°C, the N1 treatment optimized the GA/ABA balance, promoted α‐amylase activity and soluble sugar accumulation, and enhanced the activities of hexokinase (HK), phosphofructokinase (PFK), and pyruvate kinase (PK), thereby significantly increasing the seed vigour index. At 20°C, the germination response exhibited a pattern characterized by the synergistic involvement of energy metabolism and hormonal regulation; however, the N2 treatment, despite a higher nitrogen supply, did not further improve the hormonal balance or vigour index. In the field experiment, compared with the N 4:3:3 and N 6:2:2 treatments, the N 2:4:4 treatment increased the seedling emergence rate by 6.72% and 17.46%, respectively, optimized the root architecture (increased root length, surface area, and dry weight, with decreased root diameter), and significantly increased the dry matter accumulation rate and total amount during the late growth stage. Ultimately, it synergistically increased the panicles, seed‐setting rate, and 1000‐grain weight, resulting in yield increases of 5.15% and 8.37% compared with N 4:3:3 and N 6:2:2 , respectively. In conclusion, under the conditions of this study, the regulatory effect of moderate urea on germination physiology exhibits significant temperature dependence, whereas reducing basal nitrogen and postponing topdressing optimizes root establishment and source‐sink relationships, providing a theoretical basis for stress‐resistant and stable‐yield cultivation of direct‐seeded rice in cold regions.
Gai et al. (Sun,) studied this question.