This study evaluates the impact of using biogas slurry (BS) instead of nitrogen fertilizer (NF) on wheat soil, and aims to provide an optimized fertilization strategy for green wheat production. Five fertilization modes were tested: basal fertilizer only (CK), NF at the full-bearing stage (CF), BS at the jointing stage + NF at the grouting period (S1), NF at the jointing stage + BS at the grouting period (S2), and BS at the full-bearing stage (S3). Wheat yield in S3 treatment was not significantly different from CF (9632.57 kg·ha⁻¹), but significantly increased starch content by 23.39% (p < 0.05). Analysis of soil nutrient content showed that S3 treatment elevated ammonium nitrogen (AN) content by 98.30% during the harvest period and maintained the highest urease activity (686.45 μg·g⁻¹·d⁻¹). Microbial community analysis showed that the bacterial Shannon index under S3 treatment reached 7.09, and the abundance of Actinomycetes reached 39.40%. The fungal Simpson index was 0.02, lower than that of other treatments (p < 0.01). A comprehensive evaluation led to the conclusion that a complete replacement of BS with NF synergistically improves soil quick-acting nutrient levels, enhances soil enzyme activities, and sustains high microbial diversity, whilst maintaining wheat yield.

This study explored how top-dressed biogas slurry at winter wheat’s (Triticum aestivum L.) jointing stage (JS) and grain-filling period (GP) affects soil enzyme–microbe interactions, aiming to address nutrient supply–crop demand mismatches. A field experiment with five treatments (water [CK], chemical fertilizer [CF], and three biogas slurry topdressing regimes [S1–S3]) was conducted. Soil samples (0–20 cm) were collected at JS, flowering stage (FS), GP, and reaping period (RP) to analyze soil properties (total nitrogen [TN], available phosphorus [AP], available potassium [AK], soil organic matter [SOM], ammonium nitrogen [AN], pH), enzyme activities (urease [UE], neutral phosphatase [NP], sucrase [SC], catalase [CAT]), and microbial community abundance (via Illumina NovaSeq sequencing). Results showed biogas slurry altered enzyme activities, microbial structure (e.g., Actinomycetota, Ascomycota), and their interactions by regulating soil properties. JS application boosted Pseudomonadota and UE activity, GP application increased Ascomycota and CAT activity, and S3 had the most complex enzyme–microbe network, enhancing nutrient cycling. The analysis indicated that UE activity was strongly and positively correlated with several bacterial phyla (e.g., Planctomycetota, Verrucomicrobiota) (p < 0.01) and fungal phyla (e.g., Ascomycota) (p < 0.01).

Returning biogas slurry to fields is an important approach for the resource utilization of organic waste. It enhances soil fertility and crop growth, but its long-term effects on soil ecosystems need evaluation. A meta-analysis approach was employed to comprehensively assess the influence of biogas slurry application from multiple perspectives (soil enzyme activities, heavy-metal accumulation, microbial communities, and fundamental nutrients) across different time scales: short-term (3 years). The results demonstrate that the ecological effects of biogas slurry application exhibited a pronounced time-dependency. Specifically, short-term application (less than 1 year) significantly increased soil urease (23.0%) and sucrase activity (22.1%), along with organic matter and available nutrients. However, it also resulted in the rapid accumulation of heavy metals, including Hg and As. Under medium-term application, sucrase activity further surged (108.1%). Meanwhile, phosphatase activity and total potassium content decreased, and heavy-metal accumulation showed declining trends. Following long-term application, microbial richness substantially improved, but certain heavy metals (Cu, Zn and Cd) continued to accumulate. In summary, this study reveals distinct temporal-scale mechanisms by which field biogas slurry application regulates soil functions.