Zhiling Gao

Biochar and plant growth-promoting rhizobacteria (PGPR) are promising for coastal saline–alkali soil remediation, but their combined effect is often limited by nutrient scarcity. This study investigated whether nutrient-laden biochar (saturated with livestock wastewater) synergizes with a PGPR inoculant (Paenibacillus mucilaginosus PM12) to enhance maize productivity by reshaping the rhizosphere microbiome. A field experiment included five treatments: control (CK), sheep manure biochar alone (BC), nutrient-laden biochar (NBC), BC + PGPR (MBC), and NBC + PGPR (MNBC). The MNBC treatment showed the most pronounced improvements, increasing maize yield by 52.5% compared to CK, while reducing soil pH by 0.30 units and enhancing soil organic matter, total nitrogen, and available phosphorus. Metagenomic analysis revealed that MNBC uniquely enriched beneficial genera (e.g., Nocardioides) and saprotrophic Basidiomycota, while suppressing pathogenic Fusarium. This restructuring elevated the genetic potential for nitrogen transformation, phosphorus solubilization, and carbon metabolism. Structural equation modeling identified increased soil available phosphorus and total nitrogen as the primary direct drivers of yield enhancement. The integration of nutrient-laden biochar and PGPR creates a synergistic system that reclaims saline–alkali soil by alleviating stress, supplying nutrients, and directing the assembly of a functional microbiome.

Urine-derived and plant-derived benzoic acid can accumulate within soil, and it likely changes the soil microbial community as well as N₂O emissions; however, its mechanism is not clear. This study conducted an incubation experiment to monitor N₂O emissions under low moisture (40% water-filled pore space (WFPS)) and high moisture (85% WFPS) conditions. Metagenomic sequencing and q-PCR methods were used to determine the link between N₂O emissions and the composition and functions of soil microbiota. Benzoic acid (BA) was found to significantly, yet dose-dependently, impact N₂O emissions; that is, low BA concentrations increased N₂O, whereas high BA decreased N₂O. However, this was only found under high moisture conditions. In contrast, BA had little impact on N₂O emissions under low moisture conditions. Under high moisture conditions, BA increased the gene copy number of bacteria and fungi, and decreased the ratio of bacteria to fungi. Similarly, BA significantly increased the abundance of denitrification functional genes, but reduced the (NirS + NirK)-to-NosZ ratio at the peak of emission. This is in agreement with the observation of the increased relative abundance of genes encoding N₂O reductase (EC 1.7.2.4) and NO₃⁻ heterotrophic reductase (EC 1.7.1.15, EC 1.7.2.2) in the metagenomic analysis. In summary, high concentrations of benzoic acid reduce N₂O emissions by promoting the reduction of N₂O. This study revealed the impact of BA on soil microbiota and highlighted the favorable conditions and underlying mechanism behind BA’s significant impact on soil N₂O emissions. This study’s novelty lies in the fact that it deepens our understanding of the complicated role of root exudates and metabolites of animals and plants in soil.

Identifying novel flocculants to improve the separation efficiency of dairy slurries is important to facilitate slurry recycling with a low carbon footprint. Two microcosm experiments were conducted to differentiate ammonia (NH₃), nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) emissions from liquid and solid fractions obtained using conventional (mechanical separator) and enhanced (flocculant + mechanical separator) solid–liquid separation (SLS) methods during the storage and soil application phases. Tannic acid (TA) was investigated as a potential flocculant in order to explore its effectiveness in reducing greenhouse gas (GHG) emissions during the storage and soil phases. Compared to the conventional SLS method, the employment of the enhanced SLS method reduced GHG emissions during the storage and soil application phases by 53.64% and 31.63%, respectively, thereby leading to an integrative mitigation of GHG emissions across the storage and soil application chain; however, it strongly increased NH₃ emissions by 70.96% during the soil application phase, demonstrating a higher risk of gaseous N loss. Meanwhile, large trade-offs in N₂O, CH₄, and NH₃ emissions between the solid and liquid fractions during the storage phase were observed, and the reduced CH₄ and NH₃ emissions during the storage phase were also partly offset by increased emissions during the soil application phase. In conclusion, enhanced separation technology using tannic acid as a flocculant can reduce GHG emissions from the management chain, with synergistic mitigation of CH₄ and N₂O, but the risk of increased NH₃ emissions requires further attention. This study may be helpful in mitigating GHG emissions and recycling plant-derived tannic acid in the circular agriculture context.

Application of organic manure on farmland is one of the most important tasks in agricultural recycling. However, few studies have investigated the potential impact of different solid–liquid separation (SLS) technologies on soil porosity and greenhouse gas (GHG) emissions as a result of the application of liquid fractions (LFs). A microcosm experiment was conducted to track the emissions of ammonia (NH₃), nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) from soils (1) without liquid manure application (CK), (2) with a raw dairy slurry (RM), (3) with the liquid fractions of mechanical solid–liquid separation (MS) technologies, and (4) with the LF of an enhanced solid–liquid separation technology including a flocculant (tannic acid, Ta) (MS + Ta). Soil porosities of different treatments were measured using computed tomography (CT). The saturated water conductivities of the RM and MS treatments were 53.38% and 78.63%, respectively, lower than that of the CK. The application of raw slurry and LFs reduced the gas diffusion due to the strong decrease in pore sizes >500 μm and increased gas emissions compared to the CK. Compared with RM, MS had greater N₂O and lower CH₄ emissions, whereas MS + Ta had lower NH₃ and N₂O emissions. MS had the greatest CO₂-e emissions, mainly owing to high N₂O emissions, followed by RM and MS + Ta. The implementation of a simple SLS led to an increase in nitrogen (N) loss and GHG emissions when the resultant LFs were applied to farmlands, whereas high emissions were reduced when a simple SLS was combined with a flocculant, such as Ta. Further research is required to elucidate the reduction mechanism and its effectiveness under field conditions.

The cultivation of silage crops is encouraged to enhance the connection between crop and livestock production in the North China Plain (NCP). A field experiment was designed to evaluate the ammonia (NH₃), nitrous oxide (N₂O), and methane (CH₄) emissions of five silage cropping systems, including triticale-summer maize (Tr-SuM), triticale-spring maize (Tr-SpM), triticale-double forage maize (Tr-DFM), double forage maize (DFM), and winter wheat-summer maize (WW-SuM), as well as their biomass- and crude protein-scaled emission intensities, with respect to NH₃ and greenhouse gas (GHG). The annual nitrogen (N) emissions through NH₃, N₂O, and CH₄ emissions of these systems were 13.43–23.77 kg ha⁻¹ (4.2–5.6% of N fertilizer input), 3.43–4.56 kg ha⁻¹ (0.75–1.08% of N fertilizer input) and 2.10–2.85 kg ha⁻¹, respectively. The total GHG emissions of these systems was dominated by the contributions of N₂O. Ranking these systems according to their biomass and crude protein production gave Tr-DFM > DFM > WW-SuM > Tr-SuM and Tr-SpM, their partial factor productivity was in the order of Tr-DFM > WW-SuM > Tr-SuM and Tr-SpM > DFM, and the order of their emission intensity was DFM > Tr-SuM > Tr-DFM > WW-SuM > Tr-SpM. In conclusion, the Tr-DFM needs to be further investigated for its suitability in the NCP, owing to its superior productivity and moderate emission intensities.