Salt stress reduces the yield and quality of rice. It is of great significance to screen out salt-tolerant varieties for the development and utilization of saline land. The study was carried out on 114 rice varieties; first, seven varieties were selected and treated with different salt concentrations (0, 50, 85, 120, 155, 190, 225 mM), and seven traits, including germination energy, germination capacity, shoot length, root length, root number, plant fresh weight, and seedling vigor index, were measured. The salt concentration at which the sodium chloride injury index was 50% of the control was considered the optimal salt concentration. Second, 114 rice germplasms were carried out under an optimal salt concentration (120 mM). Then, principal component analysis, fuzzy function analysis, stepwise regression analysis, correlation analysis, and systematic cluster analysis were carried out on each parameter. There was a significant correlation between each parameter and the D-value, and the correlation coefficient between the seedling vigor index and D-value was the highest. D-value = − 0.272 + 1.335 × STI − SVI + 0.549 × STI − RN − 0.617 × STI-RL + 0.073 × STI − GE, R² = 0.986. Using this equation, the sodium chloride tolerance of rice in the germination experiment could be quickly identified. This study showed that the seedling vigor index was a reliable parameter to identify the salinity tolerance of rice varieties. Five groups were obtained by classification at a Euclidean distance of 5. There were 8 highly salt-tolerant cultivars, 23 salt-tolerant cultivars, 42 cultivars with moderate salt tolerance, 33 salt-sensitive cultivars, and 8 highly salt-sensitive cultivars. In this study, we found that Riguang was the most salt-tolerant rice variety, and Xiangxuejing15 was the most salt-sensitive variety.

Field experiments were performed in 2019 and 2020 to explore yield performance and biomass accumulation dynamics for different direct‐seeded rice methods after wheat straw return. The experimental treatments included two direct‐seeded rice methods (dry direct‐seeded rice and wet direct‐seeded rice) and two wheat straw return treatments (with and without wheat straw return). Wheat straw return had a negative impact on the yield and biomass of direct‐seeded rice. Compared with wet direct‐seeded rice, dry direct‐seeded rice was more negatively affected, with yield and biomass reduced by 6.7%–7.6% and 5.4%–6.5%, respectively. The yield loss was mainly associated with insufficient total spikelet numbers caused by reduced panicle numbers. A lower maximum tiller number caused by the restricted seedling tillering capacity was partly responsible for the inadequate panicle numbers in direct‐seeded rice after wheat straw return. Wheat straw return reduced the maximum and average rate of biomass accumulation, shortened the duration of effective biomass accumulation, and delayed the days to achieve the maximum rate of biomass accumulation for direct‐seeded rice. The negative effect of wheat straw return on direct‐seeded rice was concentrated mainly in the early stage; reduction in the average biomass accumulation rate in the early stage accounted for 61.1%–75.3% of the reduction in total average rate. Wet direct‐seeded rice had a higher average rate and amount of biomass accumulation at the early stage, a greater maximum tiller number, as well as a stronger photosynthetic ability and grain filling ability after heading, which contributed to improving panicle number and total spikelet number, ultimately increasing yield and biomass compared with dry direct‐seeded rice. These results demonstrate that wheat straw return reduced yield and biomass, mainly by inhibiting growth in the early stage of direct‐seeded rice. However, the wet direct‐seeding method decreased the losses in yield and biomass after wheat straw return.

To determine the combining effects of nitrogen application rate and planting density on rice yield and grain quality formation under salinity conditions, a field experiment was conducted in the coastal saline area using Oryza sativa L. cv. Nangeng 9108 from 2019 to 2020. The experiment was designed with six nitrogen rates (0, 210, 255, 300, 345, and 390 kg ha⁻¹; denoted as N0-N390, respectively) and two transplanting densities (334,000 and 278,000 hills ha⁻¹; denoted as D1 and D2, respectively). The results indicated that, with the increase of nitrogen input rate, the panicles number and spikelets per panicle increased first, subsequently decreased, and peaked under 300 kg ha⁻¹ N, whereas the filled-kernel rate and grain weight displayed a decreasing trend. The panicle number and grain weight were higher under D1 treatment compared to those under D2 treatment, while the spikelet number per panicle and the filled-kernel rate displayed an opposite trend. The grain yield displayed highest under N300D1 treatment among all treatments, accompanied by the highest agronomic N use efficiency, and the actual yield reached 8060.4 kg ha⁻¹ and 7869.8 kg ha⁻¹ in 2019 and 2020, respectively. Increased nitrogen application rate significantly improved the grain processing quality and nutritional quality, while reducing the appearance quality and cooking/eating quality. Higher transplant density was conductive to grain nutritional quality, but notably reduced the processing quality, appearance quality and cooking/eating quality. Overall, a combination of 300 kg ha⁻¹ nitrogen rate and 334,000 hills ha⁻¹ planting density was recommended for relatively higher rice yield and better grain quality in the saline area.

Because the current hybrid rice machine transplanting sowing quantity is too large and the high rate of missing hills or poor seedling quality during mechanical transplanting, the mechanized planting of hybrid rice is limited, which results in significant hindrance of large-scale planting of hybrid rice in China. In this study, a mixed sowing technology (replacement of a portion of hybrid rice seeds with conventional rice seeds) in seedling cultivation was adopted to determine the appropriate variety combinations and conventional rice sowing quantity using a variety combination experiment and sowing quantity experiments, respectively. The results of the variety combination experiment showed that combinations of Changyou 4 mixed with Nanjing 5055, and Yuanliangyou mixed with Yangdao 6 could reduce the sowing quantity of hybrid rice, improve the quality of machine transplanting, and not reduce the grain yield. The results of the conventional rice sowing quantity experiment showed that with the increase in conventional rice sowing quantity, the seedling quality, spikelet per panicle, and filled kernel percentage decreased, and the mechanical transplanting quality improved. Compared with pure sowing hybrid rice, the grain yield was not significantly different in the japonica rice treatment when the sowing quantity of Nanjing 5055 was more than 75 g/tray and Yangdao 6 was more than 60 g/tray. With the increase in conventional rice sowing quantity, the missing hill rate decreased significantly and the seedling density increased significantly, so that the panicle number was also improved, which might have compensated the reduction in seedling quality, spikelet per panicle, and filled kernel percentage. As a whole, 90 g Nanjing 5055 seeds mixed with 30 g Changyou 4 seeds per tray and 75 g Yangdao 6 seeds mixed with 30 g Yuanliangyou seeds per tray were suitable sowing quantities for mixed planting that could ensure strong seedlings and better mechanical transplanting quality, while reducing the cost (reduce the sowing quantity of hybrid rice and conventional rice) without reducing the grain yield.