Agronomy

After years of cultivation, tea garden soils gradually become acidified and compacted. Liming to ameliorate soil acidification alters the soil microbial activity and community structure, ultimately affecting the soil nitrogen cycling and nitrogen use efficiency of tea plants. In this study, ammonium-preferring tea plants (Camellia sinensis) were cultivated in lime-amended soils across a pH gradient (pH 4.5, pH 5.5, pH 6.5, and pH 7.5) to assess the impacts of soil liming on the structure and composition of the rhizosphere microbial community. The results demonstrated that, as the soil pH increased, the diversity and richness of both bacterial and fungal communities exhibited a gradual decline. The biomasses of AOA and AOB were dominated in acid soils and alkaline soils, respectively. The abundance of Proteobacteria, Actinobacteria, and Bacteroidetes in pH 6.5 and pH 7.5 were 16.56–22.56%, 16.29–18.09%, and 1.65–4.52% times higher than those in pH 4.5 and pH 5.5 soils. Ascomycota and Basidiomycota were accounting for 89.93% of all the species. Across the rising pH gradient, the relative abundance of Ascomycota significantly increased by 9.64–20.49%, whereas Basidiomycota decreased by 1.11–15.01%. The RDA analysis results showed the soil pH was the main effect factor for the differences in the structure and composition of bacterial and fungal communities. This conclusion provides theoretical support for the optimization of acidic soil improvement techniques after long-term tea cultivation.

The atomization performance of the nozzle is a critical factor influencing the pesticide application efficiency and drift behavior of agricultural unmanned aerial spraying systems (UASSs). However, the underlying atomization mechanisms of such nozzles have not yet been fully elucidated. In this study, a Particle Image Velocimetry (PIV) system was employed to evaluate the liquid sheet breakup mode, breakup length, droplet size distribution, and velocity distribution of a fan-shaped nozzle used in UASSs. Experiments were conducted under a series of spray pressures (ranging from 0.10 to 0.50 MPa, with an increment of 0.05 MPa) using sodium dodecylbenzenesulfonate (SDS) surfactant solutions at four concentrations (0%, 0.2%, 0.5%, and 1.0%). The results demonstrated that both the SDS surfactant and spray pressure significantly influenced the liquid sheet breakup process and atomization behavior. High concentrations of surfactant solution had a pronounced effect on the surface tension of the spraying liquid, delaying the onset of liquid sheet breakup, enlarging the overall droplet size distribution, and reducing the droplet velocity components along the X-axis and Y-axis. Conversely, higher spray pressures facilitated liquid sheet breakup, decreased the overall droplet size, and increased the droplet velocity distribution. This study provides fundamental experimental data for quantifying the effects of solution surface tension and spray pressure on the atomization performance of fan-shaped nozzles. These data provide systematic support for the evaluation of nozzle atomization performance.

Acidic agricultural soils are frequently challenged by co-occurring heavy metal contamination and greenhouse gas (GHG) emissions. While biochar is widely used for integrated remediation, the specific role of silicon (Si) in modulating its effectiveness in cadmium (Cd) stabilization and nitrous oxide (N₂O) mitigation remains insufficiently understood. This study evaluated the co-remediation efficacy of two types of high-Si (bamboo leaves, ML; rice straw, RS) and two types of low-Si (Camellia oleifera leaves, CL; Camellia oleifera shells, CS) biochar, produced at 450 °C, within a Cd-contaminated and nitrogen-fertilized acidic soil. Results from a 90-day incubation showed that while all biochar effectively immobilized Cd, the low-Si CL biochar exhibited a superior stabilization efficiency of 66.2%. This enhanced performance was attributed to its higher soil organic carbon (SOC) and moderate dissolved organic carbon (DOC) release, which facilitated robust Cd²⁺ sorption and complexation. In contrast, high-Si biochar was more effective in mitigating cumulative N₂O emissions (up to 67.8%). This mitigation was strongly associated with an elevated abundance of the nosZ gene (up to 48.1%), which catalyzes the terminal step of denitrification. Soil pH and DOC were identified as pivotal drivers regulating both Cd bioavailability and N₂O dynamics. Collectively, low-Si biochar is preferable for Cd stabilization in acidic soils, whereas high-Si biochar is more effective at elevating pH and reducing N₂O emissions. These findings emphasize that optimizing co-remediation outcomes necessitates a targeted approach, selecting biochar based on the specific contamination profile and desired environmental benefits.