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【Objective】 The effect of temperature on plant development is often characterized by degree days or accumulated temperature. In this paper, we investigate how planting date affects accumulated temperature and the consequence for the yield of two ratooning rice varieties. 【Method】 The experiment was conducted in a rice field in Changsha, central Hunan province. It included two rice varieties: Y Liangyou 900 (YLY900), which has a long growth period, and Y Liangyou 911 (YLY911), which has a moderate growth period. The seeds of both varieties were sown on March 15 (B1), March 20 (B2), March 25 (B3), March 30 (B4), April 5 (B5), or April 10 (B6) to establish a planting date gradient. In each treatment, we measured physiological parameters including growth duration, yield component, and seed-setting rate to evaluate the physiological development of the crops. 【Result】 The average annual growth period of YLY911 was 215 days. Its first and regeneration seasons were eight and ten days shorter, respectively, than those of YLY900. Delaying the planting date shortened the vegetative growth period of the first season and reduced the total growth period of both seasons in both varieties. The variation in grain yield in the first and regeneration season, as well as annual yield of YLY911, followed a parabolic relationship, peaking in B2. Conversely, the yield of YLY900 decreased steadily as planting date was delayed. Yields in the first and regeneration season, as well as annual yield, were consistently higher in YLY911 than in YLY900. The primary factors affecting grain yields were the number of ears per unit area and the seed-setting rate. With delay in planting dates, the annual accumulated temperature for both varieties first increased and then declined, peaking in B2. The accumulated temperature in the first and annual seasons for YLY900 was significantly higher than for YLY911, while the accumulated temperature in the regeneration season was lower for YLY900 than for YLY911. Such differences in the regeneration season between the two varieties were statistically insignificant (p>0.05). 【Conclusion】 For ratooning rice in our studied area, the optimal planting date was March 15 for varieties with long growth period and March 20 varieties with moderate growth period.

【Objective】 Transplant is a cultivation commonly used in ratooning rice production in southern China and other eastern Asian countries. Its impact on rice growth and yield depends on a range of factors. This paper presents an experimental study of the effect of transplanting density on yield composition of different panicle-typed varieties. 【Method】 The field experiment compared three rice varieties: Tianyou Huazhan, Huiliangyou 898 and Yliangyou 900. The transplanting density treatments for all three varieties were the same: 1.5×104 points/hm2 (D1), 187 500 points/hm2 (D2), 225 000 points/hm2 (D3), 262 500 points/hm2 (D4), 300 000 points/hm2 (D5), and 337 500 points/hm2 (D6). In the experiment, we measured rice growth and its ultimate yield formation in each treatment. 【Result】 Transplanting density affected composition of both seasonal and annual rice yields significantly, but the effect varied with rice varieties. There was a lack of variety-planting density interaction on the yield. The variety Huiliangyou 898 had the highest seasonal and annual yields, strong coordination ability among yield factors, high seed setting rate; variety Tianyou Huazhan had strong tillering ability, high ear-setting rate and full panicle numbers per unit area. All these were significantly higher than those of the variety YLY900. The variety YLY900 had fast population growth rate and high grain numbers per panicle, but its tillering ability was poor, and ear-setting rate and low harvest index were low; it hence produced the lowest seasonal and annual yields. On average, the optimal transplanting density for the three varieties was D5, producing highest seasonal and annual yields, faster tillering rate and more tillers per unit area; it also significantly increased the panicle numbers and sink capacity, population growth rate, and dry matter accumulation. 【Conclusion】 Selecting rice varieties with panicle and grain for the initial season in ratooning rice production should consider its tillering ability to achieve high yield. For the three rice varieties we compared, the optimal transplanting density is 300 000 holes/hm2.

Mycotoxins often contaminate rice, which are the secondary metabolites of fungi. Ustiloxins, a type of mycotoxin that has often been overlooked, pose a significant risk to human health. Therefore, identifying and controlling the pollution of ustiloxins in rice is required. In this study, we examined the natural contamination of rice with ustiloxins and their link to climate conditions. A total of 300 paddy samples were collected from six regions in southern China, and concentrations of ustiloxins A, B, C, D, and F were analyzed by liquid chromatography–tandem mass spectrometry (LC-MS/MS). Results showed that the occurrence of ustiloxins A, B, C, D, and F in paddies was found to be 55.7%, 41.3%, 29.0%, 93.7%, and 96.7%, respectively. Ustiloxin A had the highest mean (177.8 µg/kg) and maximum (3620.9 µg/kg) concentration, followed, in order, by ustiloxins C, B, D, and F. Furthermore, ustiloxin levels were significantly different depending on their origin, with the highest concentration in rice from Changde and Yueyang. And the regional difference in ustiloxins was related to the diversity of climate. A positive correlation between ustiloxin occurrence and mean humidity and precipitation was found in July and August of different regions, while mean temperature indicated a negative dependence. This is an essential survey of the contamination of rice with ustiloxins throughout southern China. The influence of climatic conditions on ustiloxins contamination was evaluated for the first time in our study. Overall, the rice samples examined in this study exhibited a high distribution of ustiloxins, suggesting that regulatory limits and the establishment of maximum allowable levels of ustiloxins in rice are necessary. This study provides a basis and guidance for the pollution situation and control strategy of ustiloxins in China. [ABSTRACT FROM AUTHOR]

The present study investigated the effects of different integrated cultivation treatments on the yield, nitrogen agronomic efficiency (AEN), and growth performance of a ratoon rice system. A two-year field experiment was carried out during 2021–2022 using a randomized block design. Cultivation treatments included the farmers' practice model (control, CK), high-yield and high-efficiency model (T1), enhanced-high-yield and high-efficiency model (T2), and the no-N model (N0). The grain yield, yield components, root traits, and stubble characteristics were determined. The results showed that T2 treatment significantly increased the grain yield and AEN by 53% and 236%, respectively, compared with CK. Similarly, the stubble weight, non-structure carbohydrate contents, and the root attributes were significantly improved under T2 treatment. The correlation analysis suggested that ratoon rice yield and AEN was significantly and positively correlated with root weight (p < 0.01) and the stubble parameters including stubble weight (p < 0.01), starch content (p < 0.01), and soluble sugar content (p < 0.01). Additionally, a significant and positive correlation between root weight and stubble weight (p < 0.05) was determined in our study. Consequently, our work highlights the benefits of integrating planting density, nitrogen/water management, and other practices to achieve high AEN and grain yield of the ratoon rice by improving root trait and stubble characteristics of the main rice. [ABSTRACT FROM AUTHOR]

Summary: To clarify the combined effects of the cutting time and cutting height on ratooning ability and rice grain yield of the ratoon crop in the novel ratoon rice cropping, a field experiment was carried out to investigate the combined effects of harvesting time and the stubble-cutting height of the main crop on the growth duration, ratooning ability and grain yield of the ratoon crop. The growth period was shortened by 3.5 days on average when the harvesting time was 10 days ahead of time. On average, the growth duration was prolonged by 7 days per each decrease of 10 cm stubble height. Early harvesting and increasing stubble-cutting height greatly increased the grain yield of the ratoon crop. The highest grain yield was achieved at 10 days after flowering stage and a stubble height of 30 cm, which were 6916 kg·hm−2 for XLY900 and 7262 kg·hm−2 for YY4149, averaged across years. High rice yield of the ratoon crop was mainly depended on panicle numbers and grain-filling percentage, rather than spikelets per panicle. Increasing cutting height and the cutting time of the main crop ahead maintain more stubble biomass and nitrogen content. A significant positive correlation was observed between stubble nitrogen content and tillers-to-stubble ratio (TSR), as well as a significant positive relation was found between panicle-to-stubble ratio and TSR. Therefore, cutting 10 days after flowering stage of the main crop with 30 cm stubble-cutting height enhances ratooning ability due to higher stubble biomass and nitrogen content, and then increases rice yield of the ratoon crop. [ABSTRACT FROM AUTHOR]

Introduction: In recent years, with the rapid expansion of ratoon rice production in Hunan, a unique ratoon rice-based production system, forage-grain ratoon rice (FG-RR), has been newly developed. Ratooning rice is a season of rice harvested by utilizing the dormant buds on the rice stubble left after harvesting the first season of rice to sprout and grow. Therefore, the characteristics of stalks themselves are crucial for the production of ratoon rice. The cutting period and higher stubble height directly affect the characteristics of ratoon rice stubbles. Based on this, we conducted the following research., Methods: In 2021 and 2022, field experiments were conducted in central China to study the effects of different cutting periods and stubble height on the regeneration rate and nutrient content of ratoon crops. The treatments included two cutting periods (10 days after heading in the first season and 30 days after heading in the first season, respectively referred to as T10 and T30) and two stubble heights (10 cm and 30 cm, respectively referred to as H10 and H30)., Results: Compared with the T30H30 treatment, T10H10 and T10H30 increased grain yield by 48.1%, 41.7%, 73.1%, and 65.2% in the two-year ratoon seasons, while T30H10 reduced grain yield by 30.9% and 19.5% in the two years, respectively. Early cutting increased the panicles, spikelets per panicle, and filled grain rate to varying increase, while higher stubble height increased panicles but decreased spikelet panicle. On the one hand, early cutting and higher stubble height increased the dry and fresh weight, nonstructural carbohydrates (NSCs), organic carbon (C), and nitrogen content of rice stalks, thereby improving the regeneration rate of ratoon rice. On the other hand, early cutting and higher stubble height retention increased the accumulation of nitrogen in rice stubble throughout the entire growth period and facilitated the transport of nitrogen to the mature panicles., Discussion: Therefore, appropriate early cutting and higher stubble height retention are the keys to improving the grain yield and stability of ratoon rice., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Gai, Chen, Sun, Chen, Yang, Ren, Liu, Wang, Zheng and Tang.)