Biochar and Bioorganic Fertilizer Amendment Improved Soil Qualities and Altered Bacterial Communities in Quinoa Rhizosphere Soils of the Yellow River Delta

Co-Application of Biochar with Different Soil Amendments Regulates Bacterial Communities in Saline–Alkaline Soil and Promotes Oat Growth, Yield, and Quality

Soil salinization has become a major constraint on sustainable agricultural development and the improvement of crop productivity. However, the effects of biochar combined with different organic amendments on the microbial ecology of saline–alkaline soils and crop performance remain insufficiently understood. This study evaluated the effects of different amendment strategies, including sole applications of fulvic acid (FA), organic fertilizer (OF), and biochar (BC), as well as their combinations. Soil bacterial community composition, richness, and diversity, oat agronomic traits, hay yield, and forage quality indicators were assessed. Spearman correlation analysis and the Mantel test were employed to examine the relationships among soil physicochemical properties, microbial communities, and crop performance. Combined applications exerted stronger effects on modulating soil bacterial community composition than sole applications, while FA, BC, or their combinations significantly enhanced bacterial richness and diversity. Crop responses exhibited distinct functional differentiation among combined treatments. The biochar combined with fulvic acid (BC + FA) treatment showed the greatest potential for promoting oat growth and increasing yield, with plant height and stem diameter reaching 99.20 cm and 3.99 mm, respectively, and hay yield increasing by 48.5% compared with the control treatment. In contrast, the biochar combined with organic fertilizer (BC + OF) treatment significantly increased crude protein content (CP) and reduced acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents, indicating improved forage quality. Although the crude fat content was numerically higher under BC + OF, no significant differences were observed among treatments. Correlation analyses further revealed that changes in soil physicochemical properties were associated with variations in several dominant bacterial genera, which were correlated with oat agronomic traits and forage quality indicators. Overall, the combined application of biochar with fulvic acid or organic fertilizer improved saline-alkaline soil microbial characteristics and showed potential for enhancing forage oat yield and quality, with BC + FA primarily improving yield production and BC + OF mainly enhancing forage quality.

Organic and biochar-based fertilizers reshape bacterial communities and enhance fertility in acidic rubber plantation soils

Introduction Understanding the effects of different soil amendments on bacterial community structure and diversity in acidic rubber plantation soils is essential for biological remediation and the targeted restoration of these degraded systems. Methods In this study, a 2.5-year long field experiment was conducted in a second-generation 25-year-old rubber plantation at Dongfeng Farm in Jinghong City, southern Yunan, China. The experiment included five fertilization treatments: (1) unfertilized control (CK), (2) microbial fertilizer (T1), (3) biochar-based fertilizer (T2), (4) tobacco ash and oil cake organic fertilizer (T3), and (5) bio-organic fertilizer combined with polyacrylamide (T4). Soil samples were collected from the 0–20 cm layer in October 2022, and bacterial communities were analyzed using Illumina MiSeq high-throughput sequencing. Key environmental drivers were identified by integrating sequencing data with soil physicochemical properties. Results The application of soil fertilizers significantly altered the tested soil physicochemical properties and bacterial community composition. Compared with CK, T1 and T4 increased soil pH. T2 and T3 significantly enhanced soil organic matter, available phosphorus, and total nitrogen. In addition, T2 specifically increased exchangeable Ca2+ and Mg2+ concentrations and elevated the Chao1 richness index. Both T2 and T3 enriched beneficial taxa, including Proteobacteria and BradyRhizobium, while principal coordinate analysis (PCoA) revealed distinct shifts in bacterial community structure. The T4 treatment resulted in the most complex bacterial co-occurrence network. Mantel tests identified organic matter, total nitrogen, available phosphorus, and available nitrogen as the primary drivers of bacterial diversity. Further analysis using structural equation modeling indicates that soil conditioners alter bacterial community structure and diversity by influencing soil fertility and pH. Discussion Collectively, these findings demonstrate that organic matter, total nitrogen, available phosphorus, and available nitrogen serve as key environmental factors shaping bacterial community structure and diversity in acidic rubber plantation soils. Organic fertilizers and biochar have proven highly effective in enhancing soil fertility and buffering capacity, while significantly increasing the abundance of dominant bacterial taxa. Therefore, organic and biochar-based amendments should be prioritized as effective and sustainable strategies for restoring soil health and promoting continuous soil quality improvement in acidified rubber plantations.

Co-pyrolyzed biochar enhances soil fertility and crop quality by modulating rhizosphere microbial functional modules

Biochar Exacerbates Nitrogen Loss in Drought-Affected Soil with Green Manure Application

The impact of biochar on N conversion in drought-affected soil with green manure application has not been systematically investigated. Therefore, this study examined the effects of biochar produced at 350 °C, 550 °C, and 750 °C (BC350, BC550, and BC750) on green manure (Medicago sativa L.) decomposition and N turnover in soil (Hapli-Udic Ferralosol) during a 60-day laboratory incubation experiment under different moisture conditions (45% or 65% soil water-holding capacity (WHC)). Due to low-temperature biochar (BC350) possessing hydrophilicity (thereby enhancing water retention) due to its surface oxygen-containing functional groups, while high-temperature biochar (BC750) relies on the aromatic conjugated π-electron system for electron transfer, both BC350 and BC750 promoted green manure decomposition and mineralization. Compared with green manure alone, co-application of BC350 and BC750 with green manure increased soil NH4+–N content by 5.58% and 38.37%, respectively. However, a significant total N loss (>11%) occurred under drought conditions. Partial least squares path modeling was used to elucidate the key driving pathways related to C and N sequestration in drought-affected soil with green manure and biochar co-application. The results indicate that the enhanced soil N loss could be attributed to both the biochar-induced rise in soil pH (>8%) and the drought-driven suppression of stable organic matter (e.g., >20% reduction in humus acid) and macroaggregate formation. This study demonstrates that although biochar addition can promote the decomposition of green manure to release available N, it may also exacerbate total soil N loss. Only under normal moisture conditions can the N released from green manure be converted into humus-associated N.

Physicochemical Characterization and Application of Cow Manure Biochar as a Substrate for Halophyte Growth and Coastal Soil

The physicochemical properties and applicability of cow manure biochar (CMB) as a soil conditioner and horticultural substrate amendment for halophyte growing on deteriorated coastal soils were assessed in this study. A typical commercial substrate (50% coco peat, 25% peat moss, 12% perlite, 7% vermiculite, and 6% zeolite) was used to compare elemental composition, thermal stability (TGA/DTG), surface morphology, pore structures (BET, FESEM), and functional groups (FT-IR) of CMB. In addition, 10% (w/w) CMB was added to coastal soils in the Saemangeum and Sinan-gun regions in order to assess changes in the physicochemical soil quality. In comparison to the commercial substrate, the analytical results showed that CMB had higher concentrations of essential mineral elements (such as K, Ca, P, Zn, and Na), a higher proportion of carbon (25.69%), and more accessible phosphorus (3490.97 mg/kg). Additionally, compared to the commercial substrate, CMB showed a nearly 19-fold larger specific surface area (77.53 m2/g) and increased micropore volume, suggesting better potential for soil aeration and water retention. Cultivating halophytes (Salicornia herbacea L. (glasswort) and Suaeda japonica Makino (seepweed)) in a 9:1 (v/v) substrate-to-CMB mixture for five weeks resulted in successful early germination and robust seedling establishment. Incorporating 10% CMB into coastal soils also substantially increased available phosphorus, total organic carbon (TOC), and organic matter (OM), demonstrating CMB’s effectiveness in enhancing nutrient availability and supporting soil carbon sequestration. All things considered, this study offers a practical framework for using biochar made from livestock manure as a sustainable substrate supplement to reclaim degraded coastal environments and advance biosaline agriculture.

Straw-Derived Synthetic Humic Acid Improves Soil Structure, Nutrient Availability, Humification, and Crop Productivity in a Compacted Alkaline Farmland of the Yellow River Floodplain

Sustainable crop residue management in alkaline agroecosystems is challenging due to trade-offs among carbon stabilization, nutrient availability, and microbial activity. To identify an optimal upcycling strategy for compacted alkaline farmland, a two-year wheat–maize rotation experiment in the Yellow River floodplain compared four treatments: no organic amendment (CK), direct straw return (CS), straw-derived biochar (CB), and straw-derived synthetic humic acid (CH). Results showed that CH produced the most balanced improvements across all dimensions. Compared to CK (pH 8.62) and CB (pH 9.16), CH significantly reduced soil pH to 8.03, enhancing alkaline buffering. CH achieved the highest available phosphorus (2.36 mg kg−1), macroaggregate proportion (19.40%), and microbial biomass carbon (91.77 mg kg−1). Enhanced humification was evidenced by superior HA content (5.82 mg kg−1) and an HA/FA ratio of 1.90 in the 0–20 cm layer. Agronomically, CH achieved the highest annual grain production (ATGP, 12.11 × 103 kg ha−1, comprising 5.65 × 103 kg ha−1 for wheat and 6.46 × 103 kg ha−1 for maize) and maximum Integrated Sustainability Score (ISS = 1.000). These findings suggest that converting straw into synthetic humic acid effectively bridges the gap between unstable raw residues and inert biochar, serving as a promising alternative pathway for improving soil structure, nutrient availability, and productivity in compacted, alkaline floodplain farmland.