Biochar can regulate methane (CH₄) emissions from paddy soils. However, the mechanism through which biochar conductivity influences methanogenesis in paddy soils remains unclear. In this study, biochar samples with varying conductivity levels were prepared by incorporating different amounts of graphene. The dissolved organic matter (DOM) derived from biochar was completely eliminated before its application. The addition of conductive biochar in the paddy soil system increased CH₄ production by enhancing the electron transfer rate (ETR), as demonstrated by a significant positive correlation between CH₄ production and ETR. Electrochemical experiments conducted after the removal of DOM from paddy soil demonstrated that biochar enhanced the ETR in paddy soils by facilitating the electron transfer of dissolved organic matter. Anthraquinone-2,6-disulfonate (AQDS), a common analogue for quinone- and hydroquinone-containing molecules in DOM, facilitates electron transfer and serves as a model for electrochemically active DOM. An experiment with biochar and AQDS confirmed that biochar enhanced the ETR of AQDS, supporting previous findings. Following incubation, methanogenic archaea showed no significant change in relative abundance across systems, demonstrating that that biochar enhanced methanogenesis solely via accelerated ETRs, without altering the microbial community composition. This study deepens our understanding of how biochar conductivity affects methanogenesis and offers scientific guidance for optimising the use of biochar in paddy soils. Graphical Abstract

In this work, Cu₂O nanoparticles were deposited on a carbon cloth cathode using a facile electrochemical method. The morphology of the modified cathode, which was characterized by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) tests, showed that the porosity and specific surface area of the cathode improved with longer deposition times. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) results showed that cupric oxide and cuprous oxide coexisted on the carbon cloth, which improved the electrochemical activity of cathode. The cathode with a deposition time of 100 s showed the best performance, with a power density twice that of bare carbon cloth. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) results revealed that moderate deposition of nano copper oxide on carbon cloth could dramatically reduce the charge transfer resistance, which contributed to the enhanced electrochemical performance. The mediation mechanism of copper oxide nanocatalyst was illustrated by the fact that the recycled conversion between cupric oxide and cuprous oxide accelerated the electron transfer efficiency on the cathode.

Red soil regions commonly experience land degradation and low nutrient availability. Excessive fertilizer use in recent years has intensified these challenges, necessitating scientifically informed fertilization strategies to ensure agricultural sustainability. To identify optimal fertilization strategies for maize cultivation in Yunnan’s red soil regions, this study conducted field experiments involving partial substitution of nitrogen fertilizer with organic manure to determine whether this approach improves soil health and boosts maize yield. Four treatments were compared in a randomized complete block design over one growing season: no fertilization (NF), soil testing and formula fertilization (STF), 15% organic fertilizer (swine manure) replacing nitrogen fertilizer (OF15), and 30% organic fertilizer replacing nitrogen fertilizer (OF30). The results indicated that substituting organic fertilizer for nitrogen fertilizer reduced soil acidification while increasing total phosphorus (TP) and available phosphorus (AP), thereby enhancing soil physicochemical properties. Maize grown under OF30 exhibited improved agronomic traits including plant height, stem diameter, ear height, and ear length. Additionally, the partial replacement of synthetic fertilizer with organic fertilizer notably increased maize yield and the weight of 100 grains, but there was no significant difference (p < 0.05) between OF15 and OF30. Moreover, the OF30 treatment generated the highest economic return of 25,981.73 CNY·ha⁻¹. Correlation and principal component analyses revealed that substituting organic fertilizer for nitrogen fertilizer notably influenced total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), and yield, with maize yield positively correlated with TP and AP content. This study presents evidence that replacing 30% of nitrogen fertilizer with organic fertilizer is a viable strategy to enhance soil health, maize productivity, and profitability in Yunnan’s red soil regions, providing a crucial scientific foundation to support sustainable agricultural development in the region.