The inconsistent efficacy of biochar in mitigating agricultural greenhouse gas emissions remains a major barrier to its widespread adoption and the realization of its environmental benefits. This study aimed to develop a stable and efficient mitigation strategy by optimizing biochar physicochemical properties through urea-N activation (corn stover: urea mass ratios of 5:1 and 15:1). Five treatments were established: CK (control), GC (fertilization), GB (fertilization + raw biochar), GAB5 (fertilization + low-N activated biochar), and GAB15 (fertilization + high-N activated biochar). Mechanisms were elucidated by monitoring soil profile (0–20 cm) gas concentrations and surface fluxes, combined with a comprehensive analysis of soil physicochemical properties, enzyme activities, and microbial biomass. Results demonstrated that activated biochar, particularly GAB15, significantly reduced cumulative CO₂ (9.4%, p < 0.05) and N₂O (45.2%, p < 0.05) emissions and their concentrations in the 0–10 cm layer. This superior efficacy was linked to profound improvements in key soil properties: GAB15 significantly enhanced soil cation exchange capacity (CEC, increased by 17.3%, p < 0.05), NH₄⁺-N content (increased by 88.2%, p < 0.05), Mean Weight Diameter (MWD, increased by 13.0%), the content of water-stable aggregates > 0.25 mm (R_>0.25mm, increased by 57.3%) (p < 0.05), dissolved organic carbon (DOC), and the MBC (microbial biomass carbon)/MBN (soil microbial biomass nitrogen) ratio. Redundancy analysis (RDA) and structural equation modeling (SEM) revealed core mechanisms: CO₂ mitigation primarily stemmed from the physical protection of organic carbon within macroaggregates and a negative priming effect induced by an elevated MBC/MBN ratio; N₂O mitigation was attributed to weakened nitrogen mineralization due to enhanced aggregate stability and reduced substrate (inorganic N) availability for nitrification/denitrification via strong adsorption at the biochar–soil interface. This study confirms that urea-activated biochar produced at a 15:1 corn stover-to-urea mass ratio (GAB15) effectively overcomes the inconsistent efficacy of conventional biochar by targeted physicochemical optimization, offering a promising and technically feasible approach for mitigating agricultural greenhouse gas emissions.

Nutrient deficiency (nitrogen, phosphorus) strongly limited the productivity of the degraded coastal soils in the Yellow River Delta. Biochar (BC) is a kind of porous carbonaceous material. It has raised wide interests because of their multiple benefits in soil improvement. The effects of biochar on the retention of nitrogen and phosphorus varied with the types of biochar and soil properties. In this study, a maize straw derived BC was applied into a coastal salt-affected soil collected from the Yellow River Delta to investigate the response of soil nutrient using a three-month cultivating experiment with the simulated rainfall. The results showed that the addition of biochar reduced the content of NH4+-N and NO3--N in all-depth soil by 8.1–27.0% and 25.3–51.9%, respectively. The content of TP in 0-30 cm soil was significantly increased, while it had no significant effect on the content of TP in 30-60 cm soil. These findings would provide theoretical basis and technical support for developing feasible technologies for remediating degraded coastal wetland soil.

Micro-drip irrigation promotes high water and nutrient use efficiency in crops.We aimed to develop a new micro-drip irrigation technology that can reduce the effects of chemical fertilizer input on soil quality while maintaining agricultural productivity. There were four treatments: micro-drip irrigation with 240 (LF), 300 (MF), and 360 kg ha^-1 fertilization (HF) and subsurface drip irrigation (SDI) with 240 kg ha^-1 fertilization (CK). Micro-drip irrigation decreased N concentration around the roots by >24% compared with SDI, and increased the urease, alkaline phosphatase activities, and partial nitrogen productivity by 31.5%, 37.7%, and 22.1%, respectively. Although the HF treatment increased cucumber yield by 20%–45% compared with LF and MF, the urease and alkaline phosphatase activities decreased by 11.4%–15.3% and 11.5%–23.0%, respectively. Furthermore, the HF treatment significantly increased the N concentration around the roots. There was a negative correlation between soil enzymatic activities and N concentration. Overall, micro-drip irrigation mitigated the inhibition of soil enzymatic activities and increased nutrient uptake and cucumber yield. However, the negative effects of high fertilization on soil quality and N loss were unavoidable. The optimal fertilization level for greenhouse cucumber cultivations was 300 kg N hm^-2 under micro-drip irrigation.