The purpose of this study is to determine the effect of light quality on growth, carbon and nitrogen metabolism, and antioxidant defense system of rice seedlings. Six light conditions were employed, including white (W), red (R), blue (B), combined LED of R and B at 3:1 (R3B1), combined LED of R and B at 1:1 (R1B1), as well as combined LED of R and B at 1:3 (R1B3). Combined application of red light and blue light could promote the growth of rice seedling leaves and roots under low light stress to varying degrees, increase the photosynthetic area by increasing the leaf area, improve the root characteristics by increasing the root volume, and increase the dry matter accumulation of rice seedlings. In addition, the combination of red light and blue light could increase carbon and nitrogen metabolites in rice seedling leaves, regulate the expression of genes related to carbon and nitrogen metabolism and enzyme activity, and enhance the antioxidant enzyme activity of rice seedlings. These results indicate that red light and blue light directly have synergistic effects which can regulate the carbon and nitrogen metabolism of rice seedlings, promote the morphogenesis of rice seedlings under low light stress, and promote growth, which has never been reported in previous studies. This study is a new discovery in the application of light quality in crop production and provides new avenues to enhance crop stress resistance. However, further study is needed to explore the physio-biochemical and molecular mechanisms of light quality in crop production.

The purpose of this study is to determine the effects of red and blue lights on the photomorphogenesis and photosynthetic traits of rice seedlings. The rice seedlings were cultured with red light (R), blue light (B), combined red and blue lights (R3B1/R1B1/R1B3), and white light (CK) as the control. The combined application of red and blue lights could promote the growth of rice seedlings to varying degrees; enhance photosynthesis by increasing the seedling leaf area, chlorophyll content, and chlorophyll fluorescence; improve root characteristics by increasing root number, root volume, and root activity; and thus increase the dry matter accumulation of rice seedlings. In addition, the combination of red and blue lights could regulate the expression of genes related to photosynthesis in rice leaves, affect the activity of the Rubisco enzyme, and then affect the photosynthesis of rice seedlings. These results indicate that red and blue lights have direct synergistic effects, which can regulate the growth of rice seedlings and promote the morphogenesis of rice seedlings. The combined application of red and blue lights can be used to supplement the light in rice-factory seedling raising.

High‐density planting is a strategy employed to save resources in crop production, particularly in environmentally friendly double‐season rice (Orvza sativa L.) cropping, where it promotes high grain yield and reduces required nitrogen (N) input. We conducted a field experiment in 2014–2018 to detect the combined effect of increased seedling density and reduced N input on early rice grain yield and N use efficiency (NUE). The higher basic seedling with low N input treatment (T2) had an average grain yield of 7.01 t ha⁻¹, which was 16.3% greater than that of the control (CK). There was a strong linear relationship between grain yield and panicles m⁻² (R² = .82, P < .001). Grain yield increased significantly with above‐ground biomass before the full‐heading stage (R² = .79, P < .001), which in turn promoted an increase in panicles m⁻² (R² = .85, P < .001). Mean agronomic efficiency (AE) in the T2 treatment was 34.3 kg kg⁻¹ N, which was 48.1% higher than that in the CK treatment. Therefore, increasing seedling density from 62.5 to 176 seedlings number m⁻² while reducing inorganic N input in the early season resulted in significantly higher grain yield in hand‐transplanted rice production. Our results indicate that dense planting with N reduction could improve early rice grain yield and enhance NUE.

Gibberellic acid (GA₃) application after anthesis is an important practice in hybrid rice seed production, and it plays diverse roles in seed quality and seed yield. The main objective of this study was to determine (1) the effects of GA₃ application after anthesis on seed vigor and (2) the optimal GA₃ dosage applied to Indica hybrid rice seed production. Field experiments of different GA₃ dosages (15 g hm⁻² and 30 g hm⁻², respectively) after anthesis were conducted in 2016 and 2017, and seed vigor parameters, stigma vigor index, and seed yield were determined. We found that significant differences in seed vigor parameters by a standard germination test and a cool germination test were observed among different GA₃ dosages after anthesis. Compared with the water spraying treatment, the germination percentage (GP) increased by 2.5–6.3%, and the vigor index (VI) increased by 8.9–19.8% from GA₃ application after anthesis, respectively. Moreover, the stigma vigor index of the female parent was enhanced with an increasing GA₃ dosage, and there were significant increases (7.5–16.0%) between the water spraying treatment and GA₃ spraying treatments. There were positive significant relationships between the VI and stigma vigor index. Additionally, the seed yield of the GA₃ application with 30 g hm⁻² was 3.9% higher on average than that of the water spraying treatment. Therefore, our study suggests that seed vigor can be increased by GA₃ application after anthesis, and GA₃ application should be applied at a rate of 30 g hm⁻² to improve seed vigor and maintain seed yield in Indica hybrid rice seed production.

Using symbiotic farming methods [cover crops and chicken grazing (+ C)] in a winter fallow field, we found that the soil organic matter and total nitrogen of the + C treatment were 5.2% and 26.6% higher, respectively, than those of a treatment with cover crops and no chicken grazing (− C). The annual rice grain yield of the + C treatment was 3.8% higher than that of the − C treatment and 12.3% higher than that of the bare fallow field (CK), while the annual CH₄ emissions of the + C treatment were 26.9% lower than those of the − C treatment and 10.6% lower than those of the CK treatment. The 100-year global warming potential of the + C treatment was 6.2% lower than that of the − C treatment. Therefore, the use of winter cover crops and chicken grazing in a winter fallow field was effective at reducing CH₄ emissions and significantly improving soil nutrients and rice yield.

Elastic sowing dates (ESDs) are correlated with rice grain yield. ESD is the easiest factor for farmers to manipulate in mechanized large-scale farming. In this study, field experiments were conducted over a 2-year period to determine the effects of different sowing dates on growth duration, effective accumulated temperature, and yield attributes in two early- and late-season machine-transplanted rice cultivars. In early rice (ER), a delay in the sowing date led to decreased grain yield and shorter growth duration. In late rice (LR), delayed sowing led to significantly lower grain yield and prolonged growth duration. In LR, significantly positive correlations were detected between effective accumulated temperature in the post-heading stage and both filling ratio and yield. Reproductive redundancy increased markedly in LR, by 7.72% over a 5-day interval. We determined that the ESDs for LR were 10 days later than the control, and that of ER was recommend early sowing rather than late sowing. These findings suggest a new strategy to meet the demands of mechanized large-scale rice farming: the development of thermal sensitive high-yield long-duration ER cultivars and high-yield short-duration LR cultivars.