Rice–crayfish continuous production system offers high economic and ecology benefits, which developed rapidly in China. To investigate the effects of different mechanical transplanting methods and planting densities on rice yield and quality, Nanjing 2728 was used to determine rice growth performance under mechanically transplanted carpet seedling (MTCS) with equal row spacing (30 cm) at five spacings and mechanically transplanted pot seedling (MTPS) with wide and narrow rows (23 + 33 cm) at five spacings. The results showed that MTPS presented significantly higher rice yields than MTCS as more spikelets per panicle. Rice yields of both mechanical transplanting methods first increased and then reduced with decreasing planting density, and its highest value was obtained at 77.9 × 10⁴ seedlings ha⁻¹. Compared with MTCS at the same stage, rice tiller dynamics of MTPS first increased and then decreased. Additionally, its dry matter accumulation per stem at jointing, heading, and maturity stages, leaf area index, photosynthetic potential, crop growth rate, and net assimilation rate were all significantly higher relative to MTCS. For each mechanical transplanting method, dry matter accumulation per panicle, leaf area index, photosynthetic potential, crop growth rate, and net assimilation rate from the sowing to jointing stages declined with decreasing planting density, while dry matter accumulation per stem and net assimilation rate from the heading to maturity stages increased. Compared with MTCS, MTPS significantly improved rice milling and appearance quality, decreasing density was also beneficial to rice milling and appearance quality, while grain content of amylose and protein were not sensitive to both transplanting method and planting density. Consequently, MTPS with 13.8 cm plant spacing is a suitable mechanical transplanting method for Nanjing 2728 to obtain better yield and quality under rice–crayfish continuous production system.

High temperature frequently occurs during rice’s early grain-filling period in the south of China, negatively affecting rice yield and quality and posing a major threat to local rice production. This experiment researched the influence of 3.5 °C warming during the first 20 grain-filling days on rice yield and quality and emphatically investigated the effects of the low-broadcast nitrogen fertilizer application level (LBN), high-broadcast nitrogen fertilizer application level (HBN) and foliar nitrogen fertilizer application (FN) at heading on the rice organ temperature, leaf photosynthesis, chlorophyll fluorescence, yield and grain quality, pasting and thermal properties under high temperature in 2020 and 2022, with a widely planted japonica rice variety, “Wuyunjing31”, in order to explore the practical mitigation measures for reducing the adverse impact of high temperature on rice productivity. The results showed that high temperatures during grain filling increased the rice plant temperature, damaged the chlorophyll fluorescence system and decreased the net photosynthesis rate. This led to a decline in the seed-setting rate and grain weight, resulting in a 7.0% and 13.9% yield loss in 2020 and 2022, respectively. In addition, high temperature caused a decline in the head rice rate and an increase in chalk occurrence and pasting temperature, thereby deteriorating rice grain quality. Under high temperatures, HBN enhanced the rice yield by 3.6% and 13.0% in 2020 and 2022, respectively, while FN enhanced the rice yield by 11.5% in 2022. The increase in yield was linked to the increased seed-setting rate and 1000-grain weight. LBN did not significantly affect the rice yield under high temperatures. The positive effects of nitrogen fertilizer measures on rice yield were associated with their role in lowering plant temperature and protection against the damage to the chlorophyll fluorescence system. All three nitrogen application measures generally improved rice milling quality and appearance quality under high temperature, with HBN generally showing the greatest impact. Under high temperature, LBN and FN tended to make the texture of cooked rice softer due to the decreased consistency, retrogradation enthalpy and retrogradation percentage, and this was closely associated with the decline in amylose content. In summary, nitrogen supplementation at the heading could efficiently mitigate the adverse impact of high temperature during the early grain-filling period on rice yield and quality.

Grain quality indicates rice commodity value. This research compared grain quality and physicochemical properties of premium japonica rice from three production regions, Yangtze River downstream of China (YRDCN), Northeast region of China (NECN) and Japan. Results showed that there were distinct quality and physicochemical characteristics variance among the three groups of japonica rice, while CVs of most quality parameters from low to high was Japan, YRDCN and NECN. YRDCN rice presented obvious lower apparent amylose content (AAC) and ratio of each chain-length sections of amylopectin, and showed higher protein contents especially glutelin and ratio in short and intermediate amylopectin molecules. Among three rice groups, YRDCN rice presented weaker appearance, whereas did not show inferior cooking and eating properties, which was primarily linked to lower AAC. Rice AAC and starch fine structure significantly correlated with pasting parameters, swelling power and solubility, while protein content had close relation with taste analyzer parameters. Results of this study indicated improvement direction for japonica rice of YRDCN, and also provided reference for consumers’ rice purchasing selection in accordance with individual taste preference.

Rice–crayfish rotation expanded rapidly in China, as it provides considerable profit and reduces pesticide application. This study investigated the impact of different mechanical transplanting methods and planting geometry on the yield and lodging resistance of an indica rice variety under a rice–crayfish rotation system in 2018 and 2019 in Hongze Lake district, using an excellent-quality variety Taoyouxiangzhan. Seedlings were mechanically transplanted using two mechanically transplanted carpet seedling (MTCS) with equal spacing (30 cm) at five spacings and mechanically transplanted pot seedling (MTPS) with wide and narrow rows (23 cm + 33 cm) at five spacings. The yield of MTPS was 8.3% higher across 2 years under the most optimum density than MTCS using the same density, mainly due to a significantly increased number of spikelets per panicle. Accompanied by the decrease in planting density, rice yield first increased and then decreased under each mechanically transplanting method, and reached the maximum in the A4 and B4 treatments (63.9 × 10⁴ seedlings ha⁻¹), respectively. Compared with MTCS, MTPS significantly increased the fresh weight of single stem, plant height, gravity center height, ear weight, length and area of the upper three leaves, so as to increase the bending moment at basal internodes by whole plant (WP), while it also increased the stem diameter, wall thickness and stem and leaf sheath dry weight per unit length of the second internode at the base, resulting in a significant increase in the force applied to break the base segment (F) and the bending moment of whole plant (M). The higher increase percentage in M than WP led to a decreased lodging index. The lodging index of both mechanically transplanting methods reduced with declined planting density in virtue of the improved breaking load of the basal internode, and it was primarily a result of increased stem diameter, wall thickness and plumpness of basal internode. The balance between the high yield and lodging resistance of Taoyouxiangzhan under a rice–crayfish rotation system can be realized at 63.9 × 10⁴ seedlings ha⁻¹, with MTCS at 15.7 cm plant spacing and MTPS at 16.8 cm. Generally, MTPS showed obvious advantages in yield and lodging resistance than MTCS.

In recent years, rice–crayfish integrated farming has expanded rapidly in the Hongze Lake district of China as the booming consumer market of crayfish. However, the current rice cultivation technology limits rice yield and the economic profits of rice–crayfish integrated farming, and the characteristics and farmers’ practices of rice culture under the rice–crayfish integrated farming system are unknown. To understand the present rice culture practices in rice–crayfish integrated farming by farmers and their perceptions and provide direction for improvement, a survey was carried out in 2019 and 2020 in Xuyi County, a representative region of rice–crayfish integrated farming in the Hongze Lake district of China, comprising 208 farmers engaged in RCIF, and detailed and complex information was obtained using face-to-face conversations. Based on the survey results, we found that farmers have limited knowledge of the rice cultivation request in a specific RCIF mode and well-suited rice varieties and mechanical transplanting equipment and corresponding techniques are lacking in RCIF. In addition, farmers had no reliable and scientific methods for the use of nitrogen fertilizers and pest management schemes. In accordance with the constraints mentioned above, we put forward the following suggestions for rice culture improvement: (i) the local agricultural extension department should strengthen the RCIF mode and extend techniques and training; (ii) researchers should develop RCIF-suited rice varieties, mechanical transplanters, and related seedling-raising methods; (iii) researchers should clarify the occurrence regularity of soil properties and rice pests with continuous RCIF practices and provide corresponding guidance for nitrogen application and pest control schemes.

Previous studies have mainly focused on cadmium (Cd) contamination in conventional rice monocultures, and no research on rice-crayfish coculture has been reported. In this study, a Cd-contaminated (0–30 mg kg⁻¹) rice-crayfish co-culture system was established by adding exogenous Cd. The results showed that the Cd concentration in each tissue of rice and each organ of crayfish increased with increasing soil Cd concentration. Specifically, the Cd concentration in each rice tissue was as follows: root > stem > leaf ≈ panicle > grain > brown rice, and the jointing and heading stages were critical periods for the rapid enrichment of Cd in the aboveground tissues of rice. The Cd concentration in each organ of crayfish was as follows: hepatopancreas > gut > gill ≈ exoskeleton > abdominal muscle. Cd was gradually enriched in the abdominal muscle after 30 days of coculture between crayfish and rice. Pearson’s correlation analysis showed that the soil’s total Cd concentration, available Cd concentration, and water Cd concentration were positively correlated with Cd content in various tissues of rice and various organs of crayfish, whereas EC and TDS in water were markedly related to rice stems, leaves, stalks, and small crayfish. According to the maximum limit of Cd in grain (0.2 mg kg⁻¹) and crustacean aquatic products (0.5 mg kg⁻¹) in China, the safe threshold of soil Cd for rice and crayfish under the rice-crayfish coculture system is 3.67 and 14.62 mg kg⁻¹, respectively. Therefore, when the soil Cd concentration in the rice-crayfish coculture system exceeds 3.67 mg kg⁻¹, the safety risk to humans through the consumption of food from this coculture system will increase. This study provides a theoretical basis for safe food production in a rice-crayfish coculture system using the established Cd pollution model.