As one of the world’s principal food crops, rice sustains over half of the global population. With global climate change intensifying, the frequency of extreme high temperatures is increasing, posing significant threats to the growth and development, yield, and quality of rice, thereby jeopardizing global food security. This study reviews the impacts of high temperatures on rice at different developmental stages and summarizes previous research on heat tolerance cultivation techniques for rice. Currently, to enhance heat tolerance in rice, the following strategies were primarily adopted: (1) the exploration of heat-tolerant genetic resources and breeding of heat-tolerant varieties; (2) cooling through canopy temperature management via enhanced transpiration regulated by water management; (3) the scientific application of fertilizers to promote the accumulation of assimilates in rice; (4) the application of exogenous regulators to bolster the antioxidant capacity of rice. The implementation of these strategies not only helps to ensure rice yield and quality but also provides robust support for addressing the challenges that global warming poses to agricultural production.

This study investigated the differences in appearance quality among different soft japonica rice varieties based on grain shape, with a particular focus on the broad-ovate soft japonica rice varieties Nanjing 9108 and Nanjing 5718, as well as the slender soft japonica rice varieties Shangshida 19 and Jiahe 218, all sourced from the Yangtze River Delta. The results showed that the slender soft japonica rice varieties exhibited significantly superior appearance quality compared to the broad-ovate varieties. In the case of superior grains, the chalky grain rate of the broad-ovate soft japonica rice was 4307.79 percent higher than that of the slender varieties, and the degree of chalkiness was 8275.00 percent higher. For inferior grains, the chalky grain rate of the broad-ovate soft japonica rice was 238.34 percent higher than the slender varieties, and the degree of chalkiness was 339.96 percent higher. In contrast to the slender soft japonica rice, the broad-ovate varieties had a lower percentage of high-weight grains and a higher percentage of low-weight grains. Compared to the broad-ovate soft japonica rice, the slender varieties exhibited a faster grain-filling rate and shorter effective grain-filling days. Correlation analysis revealed that chalkiness had a significant negative correlation with grain length and aspect ratio. Simultaneously, chalkiness also showed a positive correlation with the number of effective grain-filling days while demonstrating a negative correlation with both the maximum and average grain-filling rates. The slender soft japonica rice exhibited a lower likelihood of developing chalkiness and higher grain-filling efficiency and developed a favorable grain weight distribution. These distinctive attributes significantly contribute to the superior appearance quality of the slender japonica soft rice.

To investigate the differences in carbon and nitrogen metabolism between superior and inferior grains of southern soft and non-soft japonica rice and their relationships with appearance quality, the metabolic characteristics and appearance quality of superior and inferior grains during the grain-filling stage were compared between the two rice types. The results showed that, compared with non-soft japonica rice, the activities of AGPase and GBSS in superior grains of soft rice were significantly lower, whereas the activities of SSS, SBE, and DBE were significantly higher. The amylose content decreased by 32.68–44.72%, while amylopectin increased by 7.27–10.73%. The limitation in carbon metabolism was more pronounced in inferior grains, and the non-structural carbohydrate content was 9.33–17.33% lower than that in superior grains. In terms of nitrogen metabolism, GS activity decreased whereas GOGAT activity increased in superior grains, resulting in a 6.28–8.38% increase in protein content. The protein content of inferior grains was 1.75–6.44% higher than that of superior grains. In addition, the chalky grain rate and chalkiness degree of superior grains in soft rice were 79.00–481.03% higher than those in non-soft japonica rice, while the increases in inferior grains ranged from 67.51% to 136.31%. Correlation analysis indicated that the chalky grain rate of superior grains was positively correlated with starch content during the early grain-filling stage, whereas the chalkiness degree of inferior grains was positively correlated with protein content. These results suggest that differences in carbon and nitrogen metabolism between grain positions are closely associated with the formation of appearance quality.

The effects of nitrogen (N) application rates and N topdressing at different leaf growth stages on the yield, N absorption, and utilization of japonica rice cultivar Nanjing 9108 were studied to screen the optimal N management mode for high yield and high N use efficiency. A field experiment was conducted from 2023 to 2024, with nine N regulation treatments (94–351 kg ha⁻¹) established through dynamic allocation of basal, tillering, and topdressing fertilizers. The results showed that with the increase of N application rate, the yield and N use efficiency of Nanjing 9108 first increased and then decreased. At a total N application rate of 270 kg ha⁻¹, the N6 treatment (basal N + tiller N + topdressing at the 13th leaf stage) demonstrated optimal overall performance, achieving the highest yield and N use efficiency. Topdressing at the 13th leaf stage (coinciding with young panicle differentiation) promoted spikelet differentiation and large panicle formation, increasing grains per panicle by 2.36–2.20% compared to other treatments under the same N rate. The N6 treatment exhibited enhanced N uptake and utilization: N accumulation increased by 39.27–67.12% during the elongating to heading stage and by 7.14–62.24% during heading to maturity, while N apparent efficiency and agronomic efficiency rose by 3.51–14.68% and 29.22–58.25%, respectively. At heading, the proportion of high-effective leaf area in N6 was 1.52–7.05% higher than in N4, N5, and N7 treatments, accompanied by a slower leaf area decay rate. These traits provided sustained photosynthetic support for dry matter accumulation in mid-to-late growth stages. Consequently, dry matter accumulation in N6 increased by 5.85–33.44% (elongating to heading) and 0.42–26.98% (heading to maturity), leading to a yield advantage of 3.8–17.2% over other treatments. In summary, the N management strategy combining basal, tiller, and 13th-leaf topdressing at 270 kg ha⁻¹ is most effective for achieving both high yield and high N efficiency in Nanjing 9108.

Silicon is an essential element for enhancing the yield, quality and lodging resistance of rice, which are mainly applied through a base application or foliar application during critical growth stages in current practice. The effect of foliar application of water-soluble silicon fertilizer at different growth stages on rice yield, quality and lodging resistance were studied to screen the optimal spraying period that enhances both high yield and lodging resistance. The experiment used “Nanjing9108 and Nanjing5718” as test materials; three treatment combinations were established, corresponding to the following spraying periods: tillering stage + elongation stage (Si1), tillering stage + elongation stage + grain-filling stage (Si2), elongation stage + grain-filling stage (Si3). Applying with plain water served as the control (CK). The results showed that a foliar application of silicon fertilizer significantly increased rice yields, with the Si2 treatment yielding the best results, increasing the yields of the NJ9108 and NJ5718 by 4.82–5.70% and 4.02–5.29%, respectively, over the two-year period. Foliar silicon fertilization significantly enhanced stem wall thickness and shortened the length of the basal internodes, thereby enhancing the lodging resistance of rice. The lodging resistance of the second basal internodes by 5.52–7.79% for NJ9108 and 4.80–7.15% by NJ5718, while that of the third basal internodes increased by 3.42–4.97% and 5.67–6.76%, respectively. In addition, silicon application treatments exhibited enhanced N uptake at maturity with increases of 6.19–13.56% and 5.37–13.86%, respectively. N use efficiency increased with the number of silicon applications. Silicon application during the grain-filling stage effectively delayed leaf senescence, providing sustained photosynthesis to support dry matter accumulation during the mid-to-late growth stages and further facilitating nitrogen transport and utilization. In summary, the synergistic application of silicon fertilizer during the tillering, elongation, and grain-filling stages is the most effective strategy for achieving the dual objectives of high yield and lodging resistance.