Nitrogen application practices to reduce cadmium concentration in rice (Oryza sativa L.) grains

Enhancing soil health to minimize cadmium accumulation in agro-products: the role of microorganisms, organic matter, and nutrients

Agro-products accumulate Cd from the soil and are the main source of Cd in humans. Their use must therefore be minimized using effective strategies. Large soil beds containing low-to-moderate Cd-contamination are used to produce agro-products in many developing countries to keep up with the demand of their large populations. Improving the health of Cd-contaminated soils could be a cost-effective method for minimizing Cd accumulation in crops. In this review, the latest knowledge on the physiological and molecular mechanisms of Cd uptake and translocation in crops is presented, providing a basis for developing advanced technologies for producing Cd-safe agro-products. Inoculation of plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi, application of organic matter, essential nutrients, beneficial elements, regulation of soil pH, and water management are efficient techniques used to decrease soil Cd bioavailability and inhibiting the uptake and accumulation of Cd in crops. In combination, these strategies for improving soil health are environmentally friendly and practical for reducing Cd accumulation in crops grown in lightly to moderately Cd-contaminated soil.

Foliar spraying of Zn/Si affects Cd accumulation in paddy grains by regulating the remobilization and transport of Cd in vegetative organs

The reduction of cadmium (Cd) accumulation in rice grains through biofortification of essential nutrients like zinc (Zn) and silicon (Si) is an area of study that has gained significant attention. However, there is limited understanding of the mechanism of Zn/Si interaction on Cd accumulation and remobilization in rice plants. This work used a pot experiment to examine the effects of Zn and Si applied singly or in combination on the physiological metabolism of Cd in different rice organs under Cd stress. The results revealed that: Zn/Si application led to a significant decrease in root Cd concentration and reduce the value of Tf Soil-Root in filling stage. The content of phytochelatin (PCs, particularly PC2) and glutathione (GSH) in roots, top and basal nodes were increased with Zn/Si treatment application. Furthermore, Zn/Si treatment promoted the distribution of Cd in cell wall during Cd stress. These findings suggest that Zn/Si application facilitates the compartmentalization of Cd within subcellular structures and enhances PCs production in vegetative organs, thereby reducing Cd remobilization. Zn/Si treatment upregulated the metabolism of amino acid components involved in osmotic regulation, secondary metabolite synthesis, and plant chelating peptide synthesis in vegetative organs. Additionally, it significantly decreased the accumulation of Cd in globulin, albumin, and glutelin, resulting in an average reduction of 50.87% in Cd concentration in milled rice. These results indicate that Zn/Si nutrition plays a crucial role in mitigating heavy metal stress and improving the nutritional quality of rice by regulating protein composition and coordinating amino acid metabolism balance.

Exploring the mechanism of Cd uptake and translocation in rice: Future perspectives of rice safety

Cadmium (Cd) contamination in rice fields has been recognized as a severe global agro-environmental issue. To reach the goal of controlling Cd risk, we must pay more attention and obtain an in-depth understanding of the environmental behavior, uptake and translocation of Cd in soil-rice systems. However, to date, these aspects still lack sufficient exploration and summary. Here, we critically reviewed (i) the processes and transfer proteins of Cd uptake/transport in the soil-rice system, (ii) a series of soil and other environmental factors affecting the bioavailability of Cd in paddies, and (iii) the latest advances in regard to remediation strategies while producing rice. We propose that the correlation between the bioavailability of Cd and environmental factors must be further explored to develop low Cd accumulation and efficient remediation strategies in the future. Second, the mechanism of Cd uptake in rice mediated by elevated CO2 also needs to be given more attention. Meanwhile, more scientific planting methods (direct seeding and intercropping) and suitable rice with low Cd accumulation are important measures to ensure the safety of rice consumption. In addition, the relevant Cd efflux transporters in rice have yet to be revealed, which will promote molecular breeding techniques to address the current Cd-contaminated soil-rice system. The potential for efficient, durable, and low-cost soil remediation technologies and foliar amendments to limit Cd uptake by rice needs to be examined in the future. Conventional breeding procedures combined with molecular marker techniques for screening rice varieties with low Cd accumulation could be a more practical approach to select for desirable agronomic traits with low risk.

Improving grain yield and nitrogen use efficiency of direct-seeded rice with simplified and nitrogen-reduced practices under a double-cropping system in South China

BACKGROUND

Enhancing grain yield and nitrogen use efficiency (NUE) of rice is of great importance for sustainable agricultural development. Little effort has been made to increase grain yield and NUE of direct-seeded rice under the double-cropping system in South China. Field trials were conducted during 2018-2020 with four treatments, including nitrogen-free, farmers' fertilization practice (FP), 'three controls' nutrient management (TC), and simplified and nitrogen-reduced practice (SNRP).

RESULTS

Grain yield under SNRP averaged 6.46 t ha-1 during the three years and was 23.0% higher than that of FP but comparable to that of TC. Recovery efficiency (REN ), agronomic efficiency (AEN ), and partial factor productivity (PFPN ) of nitrogen under SNRP increased by 12.0-22.7%, 159.3-295.0% and 94.6-112.5% respectively compared with FP. Harvest index and sink capacity increased by 7.3-10.8% and 14.9-21.3% respectively. Percentage of productive tillers (PPT) and biomass after heading increased by 24.0% and 104.5% respectively. Leaf nitrogen concentration at heading and nitrogen accumulation after heading increased by 16.3% and 842.0% respectively. Grain yield was positively correlated with PPT, sink capacity, harvest index, biomass and nitrogen accumulation after heading, REN , AEN , and PFPN .

CONCLUSION

Grain yield and NUE under SNRP were superior to those under FP and comparable to those under TC. Increase in sink capacity, higher PPT, more biomass and nitrogen accumulation after heading, and greater harvest index were responsible for high grain yield and NUE in SNRP with reduced nitrogen fertilizer and labor input. SNRP is a feasible approach for direct-seeded rice under a double-cropping system in South China. © 2023 Society of Chemical Industry.