Biochar improves soil quality and wheat yield in saline-alkali soils beyond organic fertilizer in a 3-year field trial

Response of bacterial community structure in saline soils to the application of kitchen waste-derived fermented organic fertilizer

Saline soils, which inhibit plant growth and diminish soil functions such as carbon storage, present a significant challenge to agricultural productivity. Consequently, soil improvement is crucial for achieving sustainable agricultural development. Organic fertilizers, particularly those derived from kitchen waste, have shown potential in enhancing soil fertility and structure. However, the interaction between kitchen waste - derived fermented organic fertilizers and their impact on microbial diversity, community structure, and nutrient dynamics in saline soils remains an underexplored area within environmental research. In this study, microcosm experiments were conducted with saline soil samples. We examined the temporal changes in soil nutrient levels and microbial diversity after the application of inorganic and organic fertilizer for a 15-day period. The results demonstrated that short-term application of kitchen waste fermented organic fertilizer significantly increased the levels of organic matter (OM), total nitrogen (TN), hydrolyzed nitrogen (HN), total phosphorus (TP), available phosphorus (AP), and available potassium (AK); however, it also led to a reduction in microbial diversity within saline soils while simultaneously promoting the presence of beneficial microorganisms such as Photobacterium, Pseudoalteromonas, and Planococcus. The relative abundance of Bacillus increased from 0.34 to 35.22% in the COS (treatment with 30% organic fertilizer) treatment. The redundancy analysis demonstrated that, except for TK (total potassium), the physicochemical properties of the saline soils were positively correlated with the dominant bacterial community abundance under the BOS (treatment with 10% organic fertilizer) and COS treatments but negatively correlated with the salt-tolerant bacterial abundance under the CK (treatment with saline soil) and AIS (treatment with saline soil and inorganic fertilizer) treatments. In conclusion, the application of kitchen waste fermented organic fertilizer is a beneficial strategy for enhancing saline soil fertility, promoting the proliferation of beneficial microorganisms, and rehabilitating saline soils.

Biochar application improved soil properties, growth performances, essential oil, and rosmarinic acid content of Thymus vulgaris L. under salt stress

Nowadays, salinity is one of the most serious environmental problems affecting plant performance and metabolites. Biochar as a biological and sustainable amendment can be a valuable tool for improving soil health and plant growth traits under salinity stress and reducing its effects. The aim of this study was to investigate the effects of biochar (0, 1.5, and 3% by a mass percentage of the pot) on physicochemical properties and soil enzyme activity, as well as functional, physiological, and phytochemical traits of Thymus vulgaris L. under salinity stress (0, 2, 4, and 6 ds m-1 NaCl), were investigated. Biochar increases porosity, water-holding capacity, enzyme activity, phosphorus, and potassium nutrient content of the soil and reduces sodium uptake by the plant under salinity stress. Growth and performance traits were significantly increased under the influence of biochar and salinity conditions. The maximum fresh weight (104.87 g/plant) and dry weight (63.56 g/plant) of shoot were observed in the 3% biochar treatment in normal conditions. The highest content of essential oil (1.91%), thymol (63.51%), carvacrol (9.12%), and rosmarinic acid (15.05 mg/g DW) was observed at the highest levels of biochar and salinity. The activity of antioxidant enzymes and osmotic substances increased significantly (P < 0.01) in salinity conditions, which were reduced by adding biochar (P < 0.01). Generally, biochar as an organic and environmentally friendly material can be a suitable solution for increasing resistance to salinity in the garden thyme and enabling its cultivation and production in low-yielding and saline lands.

Recycled wheat straw biochar enhances nutrient-poor soil: Enzymatic kinetics of carbon, nitrogen, and phosphorus cycling

The recycling of waste wheat straw into biochar for soil improvement is a promising, sustainable strategy to enhancing nutrient-poor soils. Biochar application to soil has been shown to enhances the activity of key enzymes involved in nutrient cycling, such as invertase (INV), urease (URE), and alkaline phosphatase (ALP), which play roles in carbon (C), nitrogen (N), and phosphorus (P) cycling, as well as catalase (CAT), an enzyme with redox properties. However, the kinetic behavior of these enzymes remains largely unexplored. A 36-week laboratory study was conducted to evaluate the effects of biochar on enzyme kinetics in grey desert and aeolian soils including Michaelis-Menten constant (Km), maximum reaction velocity (Vmax), and catalytic efficiency (Vmax/Km). Results indicated that biochar application significantly increased soil pH, available phosphorus (AP), ammonium nitrogen (NH4+-N), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) while reducing nitrate nitrogen (NO3--N), which were identified as dominant factors influencing enzyme kinetic parameters. Enzyme activities related to C, N, and P cycling (excluding catalase) increased significantly at a biochar application rate of 4 % by mass. Changes in Km and Vmax for URE, INV, ALP, and CAT suggest that biochar influences enzyme kinetics through mechanisms such as adsorption, microenvironmental shifts, and allosteric modulation. An economic assessment identified 4 % biochar application as the optimal rate, yielding soil quality index (SQI) values of 0.53 and 0.65 for grey desert and aeolian soils, respectively. These findings suggest that biochar-amended soils exhibit improved fertility, highlighting the potential of biochar to enhance soil health.

Effects of Applying Organic Amendments on Soil Aggregate Structure and Tomato Yield in Facility Agriculture

Amendment significantly improves soil structure and promotes crop growth. To combat soil degradation and low crop yields in facility agriculture, it is crucial to study the optimal application rate of amendments. This study analyzed the effects of biochar, vermicompost, and mineral-source potassium fulvic acid on the stability of aggregate structure, soil nutrient content, and tomato yield in cambisols, providing a theoretical basis for improving the soil quality of plastic greenhouses in Southern China. A pot experiment on tomato cultivation was carried out in yellow-brown soil in plastic greenhouses. The experiment included eight treatments: 1% biochar (B1); 3% biochar (B3); 5% biochar (B5); 3% vermicompost (V3); 5% vermicompost (V5); 0.1% mineral-source potassium fulvic acid (F1); 0.2% mineral-source potassium fulvic acid (F2); and the control condition without adding soil amendments (CK). The results showed that the biochar and vermicompost treatments effectively reduced soil bulk density and increased total soil porosity. Compared to the control, treatments with soil amendments significantly increased soil pH and had different effects on soil nutrients: F2 showed the most significant improvement in the content of available nitrogen, available phosphorus, and available potassium, with an increase of 133.33%, 834.59%, and 74.34%, respectively; B3 treatment had the highest increase in dissolved organic carbon (DOC), while B5 treatment had the highest organic matter content. Compared to the CK, the particle size of the biochar treatment was mainly 0.053~0.25 mm, while the V3, F1, and F2 mainly occurred with a particle size > 0.25 mm; and V3 has the best aggregate stability. Biochar, vermicompost, and mineral potassium fulvic acid can all promote tomato yield, with the F2 and V3 treatments having a yield increase effect of over 30%. Furthermore, Pearson's correlation analysis showed a highly significant positive correlation between geometric mean diameter (GMD) and mean weight diameter (MWD), water-stable macroaggregate content (R0.25), and a positive correlation between alkaline-dissolved nitrogen, available phosphorus, dissolved organic carbon content, and aggregate stability indicators. Adding 0.2% mineral-source potassium fulvic acid optimizes cambisols' properties, enhances aggregate formation and stability, boosts tomato yield, and shows great application potential.

Biochar Improves Yield by Reducing Saline-Alkaline Stress, Enhancing Filling Rate of Rice in Soda Saline-Alkaline Paddy Fields

Soda saline-alkaline stress significantly impedes the rice grain filling process and ultimately impacts rice yield. Biochar has been shown to mitigate the negative impacts of saline-alkaline stress on plants. However, the exact mechanism by which biochar influences the rice grain-filling rate in soda saline-alkaline soil is still not fully understood. A two-year field experiment was conducted with two nitrogen fertilizer levels (0 and 225 kg ha-1) and five biochar application rates [0% (B0), 0.5% (B1), 1.5% (B2), 3.0% (B3), and 4.5% (B4) biochar, w/w]. The results demonstrated that biochar had a significant impact on reducing the Na+ concentration and Na+/K+ ratio in rice grown in soda saline-alkaline lands, while also improving its stress physiological conditions. B1, B2, B3, and B4 showed a notable increase in the average grain-filling rate by 5.76%, 6.59%, 9.80%, and 10.79%, respectively, compared to B0; the time to reach the maximum grain-filling rate and the maximum grain weight saw increases ranging from 6.02% to 12.47% and from 7.85% to 14.68%, respectively. Meanwhile, biochar, particularly when used in conjunction with nitrogen fertilizer, notably enhanced the activities of sucrose synthase (SuSase), ADPG pyrophosphorylase (AGPase), starch synthase (StSase), and starch branching enzyme (SBE) of rice grains in soda saline-alkaline lands. Furthermore, rice yield increased by 11.95-42.74% in the B1, B2, B3, and B4 treatments compared to the B0 treatment. These findings showed that biochar improves yield by regulating ionic balance, physiological indicators, starch synthesis key enzyme activities, and the grain-filling rate in soda saline-alkaline paddy fields.

Influences of phosphorus-modified biochar on bacterial community and diversity in rhizosphere soil

Root-associated bacteria play a vital role in the soil ecosystem and plant productivity. Previous studies have reported the decline of bacterial community and rhizosphere soil quality in the cultivation of some medicinal plants (i.e., Pseudostellaria heterophylla). Phosphorus (P)-modified biochar has the potential to improve soil health and quality. However, its influence on the bacterial community and diversity in the rhizosphere of medicinal plants is not well understood. Therefore, this study aims to investigate the effects of P-modified biochar on the bacterial community and diversity in the rhizosphere of P. heterophylla. Soil samples were collected from the rhizosphere of 4-month P. heterophylla under control (no biochar), 3% unmodified and 3% P-modified biochar treatments, respectively. Compared with control and unmodified biochar treatment, P-modified biochar significantly increased the relative abundance of plant-beneficial bacteria (P < 0.05), particularly Firmicutes, Nitrospirae and Acidobacteria. The relative abundance of Bacillus, belonging to Firmicutes, was dramatically raised from 0.032% in control group to 1.723% in P-modified biochar-treated group (P < 0.05). These results indicate the potential enhancement of soil quality for the growth of medicinal plants. The application of biochar significantly increased bacterial richness and bacterial diversity (P < 0.05). P modification of biochar did not have significant effects on soil bacterial richness (P > 0.05), while it reduced Shannon and increased Simpson diversity index of soil bacterial communities significantly (P < 0.05). It indicates a decrease in bacterial diversity. This research provides a new perspective for understanding the role of P-modified biochar in the rhizosphere ecosystem.

Effects of biochar and vermicompost on growth and economic benefits of continuous cropping pepper at karst yellow soil region in Southwest China

Recently, biochar (B) and vermicompost (V) have been widely used as amendments to improve crop productivity and soil quality. However, the ameliorative effects of biochar and vermicompost on the continuous cropping of pepper under open-air conditions, particularly in the karst areas of southwestern China, remain unclear. A field experiment was conducted to study the effects of biochar and vermicompost application, alone or in combination, on the yield, quality, nutrient accumulation, fertilizer utilization, and economic benefits of continuous pepper cropping from 2021 to 2022. The experiment included six treatments: CK (no fertilizer), TF (traditional fertilization of local farmers), TFB (TF combined with biochar of 3000 kg·ha-1), TFV (TF combined with vermicompost of 3000 kg·ha-1), TFBV1 (TF combined with biochar of 1500 kg·ha-1 and vermicompost of 1500 kg·ha-1), and TFBV2 (TF combined with biochar of 3000 kg·ha-1 and vermicompost of 3000 kg·ha-1). Compared with the TF treatment, biochar and vermicompost application alone or in combination increased the yield of fresh pod pepper by 24.38-50.03% and 31.61-88.92% in 2021 and 2022, respectively, whereas the yield of dry pod pepper increased by 14.69-40.63% and 21.44-73.29% in 2021 and 2022, respectively. The application of biochar and vermicompost reduced the nitrate content and increased the vitamin C (VC) and soluble sugar content of the fruits, which is beneficial for improving their quality. Biochar and vermicompost application alone or in combination not only increased nutrient uptake but also significantly improved agronomic efficiency (AE) and recovery efficiency (RE). In addition, although the application of biochar or vermicompost increased production costs, the increase in yield improved net income (ranging from 0.77 to 22.34% in 2021 and 8.82 to 59.96% in 2022), particularly in the TFBV2 treatment. In conclusion, the use of biochar and vermicompost amendments had a positive effect on the productivity and economic benefits of continuous pepper cropping, and the co-application of biochar and vermicompost could be an effective nutrient management strategy for the continuous cropping of pepper in the karst mountain areas of southwest China.

Bioremediation of phenanthrene in saline-alkali soil by biochar- immobilized moderately halophilic bacteria combined with Suaeda salsa L

Polycyclic aromatic hydrocarbon (PAH) contaminated saline-alkali soil is commonly salinized and hardened, which leads to low self-purification efficiency, making it difficult to reuse and remediate. In this study, pot experiments were conducted to investigate remediation of PAH contaminated saline-alkali soil using biochar-immobilized Martelella sp. AD-3, and Suaeda salsa L (S. salsa). Reduction in phenanthrene concentration, PAH degradation functional genes, and the microbial community in the soil were analyzed. The soil properties and plant growth parameters were also analyzed. After a 40-day remediation, the removal rate of phenanthrene by biochar-immobilized bacteria combined with S. salsa (MBP group) was 91.67 %. Additionally, soil pH and electrical conductivity (EC) reduced by 0.15 and 1.78 ds/m, respectively. The fresh weight and leaf pigment contents increased by 1.30 and 1.35 times, respectively, which effectively alleviated the growth pressure on S. salsa in PAH-contaminated saline-alkali soil. Furthermore, this remediation resulted in abundance of PAH degradation functional genes in the soil, with a value of 2.01 × 10³ copies/g. The abundance of other PAH degraders such as Halomonas, Marinobacter, and Methylophaga in soil also increased. Furthermore, the highest abundance of Martelella genus was observed after the MBP treatment, indicating that strain AD-3 has a higher survival ability in the rhizosphere of S. salsa under the protection of biochar. This study provides a green, low-cost technique for remediation of PAH-contaminated saline-alkali soils.