Efficient and quick yield prediction is of great significance for ensuring world food security and crop breeding research. The rapid development of unmanned aerial vehicle (UAV) technology makes it more timely and accurate to monitor crops by remote sensing. The objective of this study was to explore the method of developing a novel yield index (YI) with wide adaptability for yield prediction by fusing vegetation indices (VIs), color indices (CIs), and texture indices (TIs) from UAV-based imagery. Six field experiments with 24 varieties of rice and 21 fertilization methods were carried out in three experimental stations in 2019 and 2020. The multispectral and RGB images of the rice canopy collected by the UAV platform were used to rebuild six new VIs and TIs. The performance of VI-based YI (MAPE = 13.98%) developed by quadratic nonlinear regression at the maturity stage was better than other stages, and outperformed that of CI-based (MAPE = 22.21%) and TI-based (MAPE = 18.60%). Then six VIs, six CIs, and six TIs were fused to build YI by multiple linear regression and random forest models. Compared with heading stage (R² = 0.78, MAPE = 9.72%) and all stage (R² = 0.59, MAPE = 22.21%), the best performance of YI was developed by random forest with fusing VIs + CIs + TIs at maturity stage (R² = 0.84, MAPE = 7.86%). Our findings suggest that the novel YI proposed in this study has great potential in crop yield monitoring.

Machine transplanting technology of biodegradable films has solved the problems of the higher cost of artificial film and the serious environmental pollution of polyethylene film residue. Previous studies have shown the positive impact of mulching on mitigating global warming potential. However, the mechanisms underlying the association between greenhouse gas emissions and the bacterial community structure in paddy field soil with biodegradable film mulching (BM) still remain limited. In this study, greenhouse gas emissions and the associated bacterial community in non-mulching, biodegradable mulching in a paddy field in Eastern China were analyzed over the 2019 and 2020 rice growing seasons. Rice mulching cultivation significantly inhibited CH₄ emissions from a rice paddy, mainly due to the significant reduction in methane emission peaks. Film mulching significantly increased the diversity of the bacterial community as revealed by 16S rRNA gene sequencing. The relative abundance of methanogens was decreased, while the relative abundance of methanotrophs was increased in the paddy soil due to the BM treatment, with the change pattern basically consistent with CH₄ emissions. The N₂O emissions during the growth period showed a pronounced downward trend. However, the total abundance of bacteria involved in nitrification and denitrification was higher under BM. Mulching cultivation improved the soil nutrient availability and significantly increased the yield by 5.0%. BM inhibited the greenhouse gas emission intensity (GHGI) of the paddy field by 46.9%. Film mechanical transplanting could promote yield increases and significantly mediate the warming potential (GWP) of greenhouse gases in the paddy fields of the Middle-Lower Yangtze Area. The rational use of film mechanical transplanting would play a role in carbon neutrality in paddy fields. This study provided a theoretical basis for paddy field emission reduction and sustainable agricultural development.

Determination of the optimal fertilization method is crucial to maximize nitrogen use efficiency and yield of different rice cultivars. Side-deep fertilization with controlled-release nitrogen, in conjunction with machine transplanting and subsequent topdressing, was applied to Indica–japonica hybrid rice ‘Yongyou1540’ (YY1540) and indica hybrid rice ‘Tianyouhuazhan’ (TYHZ). Four nitrogen treatments were applied in 2018 and 2019: traditional nitrogen application with quick-release nitrogen (T₁), single-dose deep fertilization at transplanting with 100% controlled-release nitrogen (T₂), and deep fertilization of 70% controlled-release nitrogen and topdressing of 30% quick nitrogen at tillering (T₃), or at panicle initiation (T₄). Side-deep fertilization reduced the fertilizer application frequency without causing yield loss, T₄ enhanced the yield of YY1540 by increasing the number of productive tillers and number of spikelets per panicle compared with T₁, T₂ and T₃. The yield of TYHZ showed no significant difference among treatments. The T₄ treatment decreased the number of tillers at the tilling peak stage and increased the percentage productive tillers and number of differentiated spikelets. Compared with the other treatments, T₄ increased dry matter accumulation and leaf area index during panicle initiation and grain ripening, and contributed to enhanced nitrogen uptake and nitrogen utilization in YY1540. On average, nitrogen uptake and utilization in YY1540 were highest in T₄, but no significant differences among treatments were observed in TYHZ. Dry matter accumulation and nitrogen uptake from panicle initiation to heading of YY1540 were correlated with number of spikelets per panicle, but no significant correlations were observed for TYHZ. Supplementary topdressing with quick-release nitrogen at the panicle initiation stage was required to increase yield of indica–japonica hybrid rice, whereas single-dose deep fertilization with controlled-release nitrogen is satisfactory for the indica hybrid cultivar.

The rapid development of new roots in transplanted rice (Oryza sativa L.) is crucial for shortening the returning green time of seedlings and accelerating tillering. Root regeneration plays an important role in enabling seedlings to resume normal growth and produce effective spikes after root injury. This study aimed to investigate the dynamic changes in new root production and the growth of seedlings of different varieties after root cutting in addition to the key physiological factors. We utilized hydroponics to set up four different time treatments to observe the occurrence of root systems in various rice seedling varieties after root cutting; we also measured related physiological indexes to further analyze the results. This study found that changes in aboveground nutrient, energy, and hormone levels in seedlings are critical for the growth of new roots after cutting. A morphological analysis showed that the root germination force of Zhongzao 39 (ZZ39) was stronger than Jiazao 311 (JZ311) before shearing and weaker after shearing. Physiological and biochemical analyses revealed that both ZZ39 and JZ311 experienced a decrease in their aboveground nitrogen and phosphorus content after root cutting. Soluble sugar content and starch content were found to decrease to their lowest levels after two days of root shearing. Furthermore, both varieties showed a significant increase in aboveground indole-3-acetic acid (IAA) content after two days of root shearing, and the IAA content in new roots was also higher. The results indicate that higher levels of hormones in seedlings with cut roots can enhance the transportation of nutrients and carbohydrates from the stems and leaves to the roots, leading to improved growth and the production of new roots. Additionally, the accumulation of IAA in damaged roots can also positively impact this process. This study found significant differences in the regeneration of rice seedling roots after cutting depending on the variety. We identified key physiological characteristics that affect new root generation, which provides a scientific basis for identifying strong root regeneration varieties and developing cultivation measures to promote new root growth in rice.

Due to rainfall, closed weeding of paddy fields and other reasons, submergence stress often occurs during the germination and emergence stages of direct-seeded rice (Oryza sativa L.), which leads to intensified anaerobic respiration, accelerated consumption of stored nutrients, difficulty in germination of rice seeds, uneven emergence of seedlings and varying yields. Recent advances in the understanding of phytohormone interaction and the regulation of signaling pathways in crops have increased the feasibility of modulating responses to phytohormones in crop plants to enhance adaptation to environmental changes. In this review, we summarize recent advances and progress in the understanding of the regulation of phytohormone signaling pathways and their interactions with diverse internal and external signaling cues under submergence. We also discuss how these physiological modulations of phytohormones and their abundant signaling crosstalk can be applied to enhance the submergence tolerance of direct-seeded rice during germination through the manipulation of seedling morphogenesis and the fine-tuning of stress responses. Finally, we discuss how complex phytohormone signaling pathways could regulate the metabolism of stored nutrients, anaerobic respiration and energy supply in submerged direct-seeded rice seeds, thereby improving their submergence tolerance. This review hopes to provide a basis for studies of the tolerance mechanisms of submerged direct-seeded rice and the promotion of the simplified direct-seeded rice cultivation model.