The application of biogas slurry in agriculture production is regarded as a sustainable method for mitigating the environmental impacts of fertilization. To investigate the effects of biogas slurry application on soil nitrogen loss and crop yield, a field plot experiment was conducted within a wheat–maize rotation system. This study assessed the effects of three levels of biogas slurry nitrogen substitution, 50% (BSF), 100% (BS), and 150% (EBS), on the yield of silage maize and wheat, nitrogen use efficiency, and soil nitrogen loss. The findings revealed that in the first year (characterized by high rainfall), the application of the biogas slurry led to increased NH₃ emissions and nitrogen leaching, resulting in a notable rise in the annual nitrogen loss. Additionally, it was observed that as the amount of applied biogas slurry increased, the nitrogen loss also rose correspondingly. However, in the second year (a period of drought conditions), despite the elevated NH₃ emissions from the biogas slurry, there was a significant reduction in nitrogen leaching, which resulted in reductions of 14.2% and 20.0% in annual nitrogen loss for the BSF and BS treatments, respectively, with comparable nitrogen input to the fertilizer treatment. Throughout both years, the application of biogas slurry did not decrease the yield of silage maize and wheat, and notably, the BS treatment even enhanced the crop nitrogen utilization efficiency. Compared with other nitrogen fertilizer treatments, the EBS treatment did not increase crop yield even with an increased nitrogen application rate; it also reduced the nitrogen utilization efficiency and N loss. In conclusion, employing biogas slurry to replace chemical fertilizer (equivalent nitrogen substitution) during drought years can enhance nitrogen utilization efficiency, reduce nitrogen loss, and sustain crop yield. When applying biogas slurry in years with substantial rainfall, effective measures should be implemented to mitigate nitrogen loss.

A large amount of vegetable waste generated by farms is currently damaging the environment and public health. Anaerobic fermentation is a mature technology that significantly contributes to the recovery of energy and resources from tail vegetables and the control of environmental pollution. However, most vegetable wastes have not been utilized due to poor performance of biogas production, lack of optimal solid contents, and multiple other reasons. Herein, the anaerobic digestion biogas production performance of tail vegetables treated with different total solid (TS) content was studied using solanaceous and leafy vegetables as raw materials. Results showed that there was no acidification in all trials except for treatment with TS of 6%. The optimal TS for anaerobic fermentation of vegetable waste was determined to be around 20% in terms of methane production and biogas production efficiency. The cumulative methane production per unit of volatile solids (VSs) reached 241.7 mL CH₄/g of VS, and the methane content was about 65% during the peak period of biogas production. Theoretically, the value of methane production based on anaerobic fermentation of tail vegetables is as high as 1.8 × 10¹³~4.6 × 10¹³ L in China. This research provides advice for screening specific and efficient parameters to promote the biogas production rate by tail vegetable anaerobic fermentation.

Anaerobic digestion is an important means to turn agricultural waste into resources and an important way to address the challenges in treating vegetable residues in China. In this study, the co-digestion of dairy manure with tomato residue was investigated to clarify the effect of the total solids (TS) of the digestion substrate on methane’s production and mechanism using the self-made anaerobic digestion device. The results showed that all treatments could rapidly ferment methane and that the daily methane production showed a trend of increasing first and then decreasing. The optimal concentrations of the digestion substrate for liquid anaerobic digestion (L-AD), hemi-solid-state anaerobic digestion (HSS-AD), and solid-state anaerobic digestion (SS-AD) were 10%, 18%, and 25%, respectively. Compared with SS-AD and HSS-AD, L-AD gas production peaked 3–6 days earlier. Treatment TS25 had the best cumulative methane production, reaching 117.4 mL/g VS. However, treatment TS6 had acid accumulation and a very unstable system. The cumulative methane production of SS-AD was higher than that of HSS-AD and L-AD. Firmicutes and Bacteroidetes were the dominant flora, and Methanoculleus, Methanosarcina, and Methanobrevibacter were the main archaeal groups. The TS significantly changed the microbial community composition of the digestion system, especially the low TS treatment. The results presented herein indicated that TS significantly changed the bacterial and archaeal community composition of the digestion system, and thus with the increase in TS from 6% to 25%, the methane yield increased.

Anaerobic digestion for biogas production represents a crucial approach to achieving the high-value utilization of agricultural solid waste. The adoption of multi-material co-digestion offers a viable solution to overcome the inherent constraints associated with single-substrate digestion, thereby significantly enhancing the efficiency of resource utilization. This study explored a co-digestion system using dairy manure and cucumber vines as substrates, uncovering how total solids (TS) influence the methane yield and microbial community characteristics. All treatments exhibited swift methane fermentation, with daily production initially increasing before declining. Cumulative methane production increased with the increasing TS contents. These results may be linked to pH value and the concentration of volatile fatty acids (VFAs). Except for the 6% TS treatment, digesters across different TS levels maintained a favorable final pH of 7.4–8.4, while VFA concentrations exhibited a downward trend as TS contents increased. The treatment with the highest TS concentration (25%) demonstrated superior performance, achieving the maximum volumetric methane yield. This yield was 1.6 to 9.1 times higher than those obtained at low (6–10%) and medium (12–18%) TS concentrations. Microbial community analysis revealed that during the peak methane production phase, Firmicutes and Methanoculleus were the predominant bacterial and archaeal phyla, respectively. The microbial community structure changed with different TS levels. This study offers valuable scientific insights for enhancing biogas production efficiency in co-digestion systems.