Selenium, as an essential trace element, is intricately linked to the onset and progression of numerous diseases due to deficiencies in selenium intake. Selenium compounds exhibit tumor specificity and can efficiently inhibit the growth of tumor cells, making them potential candidates for cancer treatment. Nevertheless, given its status as one of the most widely consumed crops globally, increasing the selenium content in rice could prove advantageous in alleviating the prevailing issue of selenium intake deficiency, particularly in China. This review explored the regulatory role of selenium in rice growth, the regional distribution characteristics of soil selenium content in various rice-growing regions in China, and the impact of cultivation practices on selenium fortification in rice, aiming to suggest improved rice cultivation management strategies to enhance the capacity for rice selenium biofortification. The findings revealed that: (1) In Northeast and North China, characterized by alkaline soils and severe selenium deficiency, it is advisable to moderately decrease the duration of flooding, elevate the soil redox potential, and apply organic and nitrogen fertilizers in a judicious manner. (2) In Southwest China, which is characterized by acidic soils, alternating wet and dry irrigation should be employed, and the biofortification of selenium can be facilitated by applying lime and foliar spraying of selenium fertilizer. (3) In the south-central region of China, distinguished by acidic soils and double-cropped rice, it is recommended that intermittent or alternating wet and dry irrigation be employed, and the reasonable application of organic, silica, and selenium fertilizers is advocated. (4) In the northwest region, characterized by slightly alkaline soil and mild selenium deficiency, it is recommended to implement various water management practices, including shallow water during the seedling stage, deep water during the booting stage, and wet grain filling. Additionally, a rational application of nitrogen, phosphorus, and potassium fertilizers, along with foliar application of selenium fertilizer, should be employed. (5) Cultivating selenium-enriched, high-yielding, and high-quality rice varieties proves to be an effective strategy in addressing selenium deficiency. In conclusion, the unique characteristics of diverse rice-growing regions in China indicate that suitable water management, fertilization techniques, and varietal selection practices can effectively enhance the selenium content in rice, thereby maximizing the nutritional requirements for selenium.

The incorporation of aquaculture feed within a rice–crayfish coculture system significantly enhances nitrogen cycling, thereby diminishing the reliance on chemical fertilizers. However, this benefit is often overlooked in practice, and farmers continue to use large quantities of chemical fertilizers to maximize production, resulting in excessive soil fertility and water nitrogen pollution. Thus, avoiding nitrogen pollution in rice–crayfish coculture systems has become a pressing issue. In this study, we conducted a two-year experiment with two rice cultivars, and a 33.3% reduction in nitrogen fertilizer in a rice–crayfish coculture system (RC), to systematically analyze the overall nitrogen balance, rice nitrogen nutrition, and soil fertility, as compared with a rice monoculture system (RM). Our findings revealed the following: (1) Under the 33.3% reduction in nitrogen fertilizer, the nitrogen surplus in the rice–crayfish coculture system was comparable to that in the rice monoculture, and was controlled at an environmental safety level. (2) Nitrogen utilization efficiency and the accumulation of nitrogen in the rice–crayfish coculture were comparable to those in the rice monoculture. The nitrogen cycle in this system was able to provide the nitrogen required for rice growth after nitrogen fertilizer reduction. (3) The rice–crayfish coculture significantly improved the overall soil fertility and the effectiveness of soil nitrogen nutrition. Furthermore, cutting off the application of nitrogen fertilizer after the mid-tillering stage effectively controlled the total nitrogen content in soil after rice maturity. In conclusion, reducing nitrogen fertilizer in a rice–crayfish coculture system is feasible and beneficial. It ensures rice production, reduces the risk of excessive nitrogen surplus and surface pollution, and promotes a greener, more environmentally friendly paddy field ecosystem.

Soil salinization threatens global agriculture, reducing crop productivity and food security. Developing strategies to improve salt tolerance is crucial for sustainable agriculture. This study examines the role of organic fertilizer in mitigating salt stress in rice (Oryza sativa L.) by integrating NDVI and metabolomics. Using salt-sensitive (19X) and salt-tolerant (HHZ) cultivars, we aimed to (1) evaluate changes in NDVI and metabolite content under salt stress, (2) assess the regulatory effects of organic fertilizer, and (3) identify key metabolites involved in stress response and fertilizer-induced regulation. Under salt stress, survival rate of the 19X plants dropped to 6%, while HHZ maintained 38%, with organic fertilizer increasing survival rate to 25% in 19X and 66% in HHZ. NDVI values declined sharply in 19X (from 0.56 to <0.25) but remained stable in HHZ (~0.56), showing a strong correlation with survival rate (R² = 0.87, p < 0.01). NDVI provided a dynamic, non-destructive assessment of rice health, offering a faster and more precise evaluation of salt tolerance than survival rate analysis. Metabolomic analysis identified 12 key salt-tolerant metabolites, including citric acid, which is well recognized for regulating salt tolerance. HTPA, pipecolic acid, maleamic acid, and myristoleic acid have previously been reported but require further study. Additionally, seven novel salt-tolerant metabolites—tridecylic acid, propentofylline, octadeca penten-3-one, 14,16-dihydroxy-benzoxacyclotetradecine-dione, cyclopentadecanolide, HpODE, and (±)8,9-DiHETE—were discovered, warranting further investigation. Organic fertilizer alleviated salt stress through distinct metabolic mechanisms in each cultivar. In 19X, it enhanced antioxidant defenses and energy metabolism, mitigating oxidative damage and improving fatty acid metabolism. In contrast, HHZ primarily benefitted from improved membrane stability and ion homeostasis, reducing lipid peroxidation and oxidative stress. These findings primarily support the identification and screening of salt-tolerant rice cultivars while also highlighting the need for cultivar-specific fertilization strategies to optimize stress resilience and crop performance. Based on the correlation analysis, 26 out of 53 differential metabolites were significantly correlated with NDVI, confirming a strong association between NDVI shifts and key metabolic changes in response to salt stress and organic fertilizer application. By integrating NDVI and metabolomics, this study provides a refined method for evaluating salt stress responses, capturing early NDVI changes and key salinity stress biomarkers. This approach may prove valuable for application in salt-tolerant variety screening, precision agriculture, and sustainable farming, contributing to scientific strategies for future crop improvement and agricultural resilience.

In the face of the current popular crayfish food culture, as well as the strong development trend of rice-crayfish farming (RCF), how to exploit their unique advantages to develop the RCF model is a direction of agricultural development in Hainan Province that deserves attention. In this paper, we systematically analyze the feasibility of developing RCF in Hainan Province by investigating the changes in RCF development in Hubei Province in recent years, combined with the current state of rice production and RCF trial data in Hainan Province. The results show that: 1) Using abandoned land to develop RCF contributes to the total rice production of Hainan Province. The rice yield of RCF in the late-season is 16.30% higher than that of rice monoculture (RM), but the rice yield of RCF is severely affected by the proportion of culture ditch. 2) Compared to RM, the RCF model can reduce the application of N fertilizer to a certain extent. The nitrogen partial factor productivity (NPFP) in the early- and late-season of RCF are 32.34% and 74.43% higher than those of the RM, respectively. 3) In Hubei, the RCF model has promoted the expansion of rice cultivation area. Therefore, introducing the RCF model in Hainan can help increase the area of the rice cultivation and land utilization while reducing the abandonment of arable land. 4) Drawing on the RCF model in Hubei, Hainan would expect to gain remarkable economic benefits, since anti-seasonal RCF has huge market prospects.

Organic fertilizer is utilized to improve the organic carbon levels in arable soils, which is helpful for soil quality improvement and crop yield increase. However, the after-effect of organic fertilizer varies among regions with different temperature and precipitation conditions, and the extent of the impact remains unknown. This study aimed to investigate the impact of varying temperature and rainfall conditions on the accumulation of soil organic carbon after organic fertilizer application. A meta-analysis of 168 peer-reviewed studies published between 2005 and 2022 involving a total of 464 trials was conducted. The following was discovered: (1) In the major grain-producing areas of China, there was a significant positive correlation (p < 0.01) between latitude and soil organic carbon content. Meanwhile, temperature and precipitation had a significant negative correlation (p < 0.01) with soil organic carbon content. (2) The increase in temperature inhibited the increase in soil organic carbon storage. The improvement effect of organic fertilizer application in the low-temperature areas was significantly increased by 60.93% compared with the mid-temperature areas, and by 69.85% compared with the high-temperature areas. The average annual precipitation affected the after-effect of organic fertilizer as follows: 400–800 mm > 400 mm > more than 800 mm. (3) The influence of climatic conditions on the after-effect of organic fertilizer was more significant depending on the specific tillage practice. To increase organic fertilizer use efficiency and eliminate greenhouse gas emissions, liquid organic fertilizers with abundant trace nutrients and amino acids, which take advantage of releasing nutrients more swiftly and have a better fertilization effect, could be an alternative to traditional organic fertilizers.