Integration of biochar with nitrogen in acidic soil: A strategy to sequester carbon and improve the yield of stevia via altering soil properties and nutrient recycling

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.

Unraveling the synergistic effect of biochar and potassium solubilizing bacteria on potassium availability and rapeseed growth in acidic soil

Potassium (K) is an essential macronutrient for plant growth. However, its bioavailability is low in acidic soils. Excessive K fertilization deteriorates the soil health, thus highlighting the need for sustainable alternatives. In previous studies, biochar application has been proven to be an effective amendment. Meanwhile, various potassium solubilizing bacteria (KSB) have been identified in soil that contributes to K bioavailability. However, their interaction under combine (co) application in acidic soil and its effects on K availability remain poorly understood. Therefore, a pot experiment was conducted to investigate the synergistic effect of co-application of rice straw biochar (BC) and KSB consortium on K availability to promote rapeseed growth. The treatment plan consisted of CK (control), recommended K fertilizer, 2 % BC (2 % w/w), KSB consortium, KSB consortium + 2 % BC (2 % w/w). Results of soil analysis conducted after crop maturity showed that co-application of 2 % BC and KSB consortium significantly improved the soil pH and organic matter contents by 0.62 and 12.52 units respectively, relative to CK. Meanwhile, soil available nutrients were greatly enhanced, as available K content increased by 52.1 %, which indicated that co-application of 2 % BC and KSB consortium could facilitate the better conversion of different forms of soil K and make it available for plant uptake. Furthermore, it also improved extracellular enzymatic activities (26.7-71.6 %) and soil bacterial community (Actinobacteriota and Firmicutes). These improvements greatly enhanced plant biomass (46 %) and yield (31 %). Overall results proved that co-application of 2 % BC and KSB effectively enhanced K availability for sustainable plant growth. Still, there is a need to identify the most efficient KSB strains that, in conjugation with BC, reduce the K fertilizer usage.

Biochar Addition Reduces the Effect of High Nitrogen on Soil-Microbial Stoichiometric Imbalance in Abandoned Grassland on the Loess Plateau of China

Progressively higher atmospheric nitrogen (N) deposition increasingly affects soil ecosystems' elemental cycling and stability. Biochar (BC) amendment has emerged as a possible means of preserving soil system stability. Nevertheless, the pattern of soil-microbial nutrient cycling and system stability in response to BC after high N deposition in ecologically sensitive regions remains uncertain. Therefore, we investigated the effects of high N (9 g N·m-2·a-1), BC (0, 20, 40 t·ha-1), and combinations of the treatments on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), microbial entropy (q MB), and stoichiometric imbalance (Cimb:Nimb:Pimb). We found that high N addition decreased topsoil (0-20 cm) TP, C:N, q MBN, and Cimb:Nimb values and increased TN, C:P, N:P, q MBP, Cimb:Pimb, and Nimb:Pimb values. However, BC addition increased 0-40 cm soil q MBC and Nimb:Pimb values and decreased q MBN, Cimb:Nimb, and Cimb:Pimb values. Meanwhile, high BC additions attenuated BC's promotion of soil-microbial nutrients. We observed that a mixture of high N and BC increased the 0-40 cm SOC and TP content, promoted the accumulation of MBN and MBP in the subsoil (20-40 cm), and decreased the topsoil Cimb:Pimb and Nimb:Pimb values compared to high N additions. The impact of high N and BC additions on N and P elements varied significantly between the different soil depths. In addition, redundancy analysis identified C:N, MBC, MBN, and C:P as pivotal factors affecting alterations in soil q MB and stoichiometric imbalance. Overall, adding BC reduced the negative impacts of high N deposition on the stability of soil-microbial systems in the Loess Plateau, suggesting a new approach for managing ecologically fragile areas.

Selection of Suitable Organic Amendments to Balance Agricultural Economic Benefits and Carbon Sequestration

Long-term excessive use of fertilizers and intensive cultivation not only decreases soil organic carbon (SOC) and productivity, but also increases greenhouse gas emissions, which is detrimental to sustainable agricultural development. The purpose of this paper is to identify organic amendments suitable for winter wheat growth in the North China Plain by studying the effects of organic amendments on the economic benefits, carbon emissions, and carbon sequestration for winter wheat fields and to provide a theoretical basis for the wide application of organic amendments in agricultural fields. The two nitrogen rates were N0 (0 kg ha-1) and N240 (240 kg ha-1), and the four organic amendments were straw, manure, mushroom residue (M R), and biochar. The results showed that, compared to N0, N240 significantly increased the yield by 244.1-318.4% and the organic carbon storage by 16.7-30.5%, respectively, but increased the carbon emissions by 29.3-45.5%. In addition, soil carbon stocks increased with all three types of organic amendments compared to the straw amendment, with the biochar treatment being the largest, increasing carbon storage by 13.3-33.6%. In terms of yield and economic benefits, compared to the straw amendment, the manure and biochar amendments increased winter wheat yields by 0.0-1.5% and 4.0-13.3%, respectively, and M R slightly decreased wheat yield; only the economic benefit of the M R amendment was greater than that of the straw amendment, with an increase in economic benefit of 1.3% and 8.2% in the 2021-2022 and 2022-2023 seasons, respectively. Furthermore, according to the net ecosystem productivity (NEP), N0 was the source of CO2, while N240 was a sink of CO2. The TOPSIS results showed that N240 with a mushroom residue amendment could be recommended for increasing soil carbon stocks and economic benefits for winter wheat in the NCP and similar regions. Low-cost M R can increase farmer motivation and improve soil organic carbon, making a big step forward in the spread of organic materials on farmland.

Removal of environmental pollutants using biochar: current status and emerging opportunities

In recent times, biochar has emerged as a novel approach for environmental remediation due to its exceptional adsorption capacity, attributed to its porous structure formed by the pyrolysis of biomass at elevated temperatures in oxygen-restricted conditions. This characteristic has driven its widespread use in environmental remediation to remove pollutants. When biochar is introduced into ecosystems, it usually changes the makeup of microbial communities by offering a favorable habitat. Its porous structure creates a protective environment that shields them from external pressures. Consequently, microorganisms adhering to biochar surfaces exhibit increased resilience to environmental conditions, thereby enhancing their capacity to degrade pollutants. During this process, pollutants are broken down into smaller molecules through the collaborative efforts of biochar surface groups and microorganisms. Biochar is also often used in conjunction with composting techniques to enhance compost quality by improving aeration and serving as a carrier for slow-release fertilizers. The utilization of biochar to support sustainable agricultural practices and combat environmental contamination is a prominent area of current research. This study aims to examine the beneficial impacts of biochar application on the absorption and breakdown of contaminants in environmental and agricultural settings, offering insights into its optimization for enhanced efficacy.

Biochar application alters soil metabolites and nitrogen cycle-related microorganisms in a soybean continuous cropping system

Biochar application is a promising practice to enhance soil fertility. However, it is unclear how field-aged biochar affects the soil metabolites and microbial communities in soybean fields. Here, the rhizosphere soil performance after amending with biochar addition rates at 0 (CK), 20 (B20), 40 (B40), and 60 t ha-1 (B60) was examined via a five-year in-situ field experiment based on a soybean continuous cropping system. Untargeted metabolomics and metagenomics analysis techniques were applied to study the regulatory mechanism of biochar on soybean growth from metabolomics and N cycle microbiology perspectives. We found that the contents of soil total N (TN), available N (Ava N), NH4+-N, and NO3--N were significantly increased with biochar addition amounts by 20.0-65.7 %, 3.6-10.7 %, 29.5-57.1 %, and 24.4-46.7 %, respectively. The B20, B40, and B60 triggered 259 (236 were up-regulated and 23 were down-regulated), 236 (220 were up-regulated and 16 were down-regulated), and 299 (264 were up-regulated and 35 were down-regulated) differential metabolites, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and topology analysis demonstrated that differential metabolites were highly enriched in seven metabolic pathways such as Oxidative phosphorylation and Benzoxazinoid biosynthesis. Moreover, ten differential metabolites were up-regulated in all three treatments with biochar. Biochar treatments decreased the Nitrospira abundance in soybean rhizosphere soil while increasing Bradyrhizobium abundance significantly in B60. Mantel test revealed that as the biochar addition rate grows, the correlation between Nitrospira and soil properties other than NO3--N became stronger. In conclusion, the co-application of biochar with fertilizers is a feasible and effective way to improve soil N supply, even though biochar has undergone field aging. This work offers new insights into the variations in soil metabolites and microbial communities associated with N metabolism processes under biochar addition in soybean continuous cropping soils.