Biochar-fertilizer interaction modifies N-sorption, enzyme activities and microbial functional abundance regulating nitrogen retention in rhizosphere soil

Deciphering the differences of bacterial communities between high- and low-productive wheat fields using high-throughput sequencing

Microbial communities have been demonstrated to be essential for healthy and productive soil ecosystems. However, an understanding of the relationship between soil microbial community and soil productivity levels is remarkably limited. In this study, bulk soil (BS), rhizosphere soil (RS), and root (R) samples from the historical high-productive (H) and low-productive (L) soil types of wheat in Hebei province of China were collected and analyzed by high-throughput sequencing. The study highlighted the richness, diversity, and structure of bacterial communities, along with the correlation networks among different bacterial genera. Significant differences in the bacterial community structure between samples of different soil types were observed. Compared with the low-productive soil type, the bacterial communities of samples from the high-productive soil type possessed high species richness, low species diversity, complex and stable networks, and a higher relative abundance of beneficial microbes, such as Pseudoxanthomonas, unclassified Vicinamibacteraceae, Lysobacter, Massilia, Pseudomonas, and Bacillus. Further analysis indicated that the differences were mainly driven by soil organic matter (SOM), available nitrogen (AN), and electrical conductivity (EC). Overall, the soil bacterial community is an important factor affecting soil health and crop production, which provides a theoretical basis for the targeted regulation of microbes in low-productivity soil types.

Investigation of the effects of biochar amendment on soil under freeze‒thaw cycles and the underlying mechanism

Biochar (BC) is widely utilized as a soil amendment; however, for widely distributed seasonally frozen soils, the effect of BC on soil and the optimal utilization of BC during the freeze‒thaw process are still unclear. In this study, the effects of freeze‒thaw aged biochar (FT-BC) and BC on soil properties and wheat cultivation were systematically investigated, and the underlying interaction mechanism between BC and soil was explored. The results show that FT-BC dramatically reduces the adverse effects of freeze‒thaw cycles on soil, enhances wheat growth, and increases dry matter yield by 17.5 %, which is mainly attributed to the ability of FT-BC to maintain soil structure, reduce water loss rates to below 0.20 g/h, and decrease nitrogen leaching by more than 20 % during freeze‒thaw cycles. Additionally, fresh BC had a greater effect on the fixation of cadmium than FT-BC in the soil, reducing its accumulation in wheat by 22.5 %. Multiple characterizations revealed that the freeze‒thaw process increased the porosity and specific surface area of FT-BC, providing more sites for water and nitrogen adsorption, whereas the dissolved organic matter released from fresh BC had a better ability to trap cadmium. These findings provide insights into the interactions between BC and soil components during the freeze‒thaw process and suggest the optimized utilization of fresh BC and FT-BC for different soil repair purposes.

Comparing combined application of biochar and nitrogen fertilizer in paddy and upland soils: Processes, enhancement strategies, and agricultural implications

Recently, biochar and N fertilizers have been used to tackle low N use efficiency (NUE) in crops across diverse environmental conditions. The coupling of biochar and N fertilizer may impact crop N utilization through different pathways in various soil types. However, there is currently a lack of comprehensive assessment of how coupling effects specifically influence N utilization in paddy and upland crops. We conducted a meta-analysis of 175 peer-reviewed studies to assess the responses of soil properties and crop traits in paddy and upland fields under coupling effects. The results indicate that NUE (+26.1 %) and N uptake (+15.0 %) in paddy fields increase more than in upland fields (+23.7 % and +8.0 %, respectively), with the coupling effect providing NH4+ predominantly for rice and NO3- for upland crops. NH4+ increases in paddy fields (+6.9 %) but decreases in upland fields (-0.7 %), while microbial biomass carbon (MBC) decreases in paddy fields (-2.9 %) and increases in upland fields (+36.0 %). These findings suggest that coupling effects supply soil inorganic nutrients in paddies and affect microbes in uplands, thereby positively affecting crop N utilization. Specifically, the greatest increase in paddy crop yield and N use efficiency occurs when the ratio of N fertilizer to biochar exceeds 1.5 %, and in uplands, it manifests when applying 10-20 t·ha-1 of biochar and <150 kg·ha-1 N fertilizer. In conclusion, this meta-analysis explores the differential effects of biochar and N fertilizer coupling in different arable land types, offering novel insights into the utilization strategies of biochar in agricultural fields.

Synthesis of struvite-enriched slow-release fertilizer using magnesium-modified biochar: Desorption and leaching mechanisms

To improve the retention and slow-release abilities of nitrogen (N) and phosphorus (P), an 82 %-purity struvite fertilizer (MAP-BC) was synthesized using magnesium-modified biochar and a solution with a 2:1 concentration ratio of NH4+ to PO43- at a pH of 8. Batch microscopic characterizations and soil column leaching experiments were conducted to study the retention and slow-release mechanisms and desorption kinetics of MAP-BC. The slow-release mechanism revealed that the dissolution rate of high-purity struvite was the dominant factor of NP slow release. The re-adsorption of NH4+ and PO43- by biochar and unconsumed MgO prolonged slow release. Mg2+ ionized by MgO could react with PO43- released from struvite to form Mg3(PO4)2. The internal biochar exhibited electrostatic attraction and pore restriction towards NH4+, while magnesium modification and nutrient loading formed a physical antioxidant barrier that ensured long-term release. The water diffusion experiment showed a higher cumulative release rate for PO43- compared to NH4+, whereas in soil column leaching, the trend was reversed, suggesting that soil's competitive adsorption facilitated the desorption of NH4+ from MAP-BC. During soil leaching, cumulative release rates of NH4+ and PO43- from chemical fertilizers were 3.55-3.62 times faster than those from MAP-BC. The dynamic test data for NH4+ and PO43- in MAP-BC fitted the Ritger-Peppas model best, predicting release periods of 163 days and 166 days, respectively. The leaching performances showed that MAP-BC reduced leaching solution volume by 5.58 % and significantly increased soil large aggregates content larger than 0.25 mm by 24.25 %. The soil nutrients retention and pH regulation by MAP-BC reduced leaching concentrations of NP. Furthermore, MAP-BC significantly enhanced plant growth, and it is more suitable as a NP source for long-term crops. Therefore, MAP-BC is expected to function as a long-term and slow-release fertilizer with the potential to minimize NP nutrient loss and replace part of quick-acting fertilizer.

Improvement and the relationship between chemical properties and microbial communities in secondary salinization of soils induced by rotating vegetables

Choosing a good crop rotation plan helps maintain soil fertility and creates a healthy soil ecosystem. However, excessive fertilization and continuous cultivation of vegetables in a greenhouse results in secondary salinization of the soil. It remains unclear how crop rotation affects Yunnan's main place for vegetable growing in the greenhouse. Six plant cultivation patterns were chosen to determine how different rotation patterns affect the chemical properties and the soil microbial communities with secondary salinization, including lettuce monoculture, lettuce-large leaf mustard, lettuce-red leaf beet, lettuce-cabbage, lettuce-romaine lettuce, and lettuce-cilantro (DZ, A1, A2, A3, A4, and A5). The results showed that all treatments increased the proportion of nutrients available in the soil, and the effect of the A1 treatment was the most significant compared to the monoculture mode. The high-throughput sequencing findings revealed that distinct crop rotation patterns exerted varying effects on the microbial communities. Microbial community diversity was significantly lower in the monoculture than in the other treatments. The number of microbial operational taxonomic units OTUs was significantly higher in the crop rotation modes (P < 0.05), and the A1 treatment had larger numbers and diversity of bacterial and fungal OTUs (Shannon's and Simpson's) than other treatments (P < 0.05). Prominent bacterial and fungal communities were readily observable in the soils planted with rotational crops. Proteobacteria had the highest relative abundance of bacteria, whereas Ascomycota was the most abundant fungus. The principal coordinate analysis at the OTU level separated soil bacterial and fungal growth communities under the different treatments. Among the six treatments, The first two axes (PC1 and PC2) described 46.44 % and 42.42 % of the bacterial and fungal communities, respectively. Network-based analysis showed that Bacteroidota and Gemmatimonadota members of the genus Bacteroidota were positively correlated with Proteobacteria. Members of Ascomycota and Chytridiomycota exhibited positive relationships. These results extend the theoretical understanding of how various crop rotation patterns affect soil chemical properties, microbial community diversity, and metabolic functions. They reveal the beneficial effects of crop rotation patterns on enhanced soil quality. This study provides theoretical guidance for the future enhancement of sustainable agriculture and soil management planning.

Nitrogen (N) "supplementation, slow release, and retention" strategy improves N use efficiency via the synergistic effect of biochar, nitrogen-fixing bacteria, and dicyandiamide

Irrational nitrogen (N) fertilizer management and application practices have led to a range of ecological and environmental problems that seriously threaten food security. In this study, an effective N fertilizer management strategy was established for improving N fertilizer utilization efficiency (NUE). Biochar, N2-fixing bacteria (Enterobacter cloacae), and a nitrification inhibitor (dicyandiamide, DCD) were simultaneously added to the soil during maize cultivation. The goal was to increase soil ammonium nitrogen content and NUE by regulating the relative abundance, enzyme activity, and functional gene expression of N conversion-related soil microbes. Biochar combined with E. cloacae and DCD significantly increased soil N content, and the NUE reached 46.69 %. The relative abundance of Burkholderia and Bradyrhizobium and the activity of nitrogenase increased significantly during biological N2 fixation. Further, the abundance of the nifH gene was significantly up-regulated. The relative abundance of Sphingomonas, Pseudomonas, Nitrospira, and Castellaniella and the activities of ammonia monooxygenase and nitrate reductase decreased significantly during nitrification and denitrification. Moreover, the abundance of the genes amoA and narG was significantly down-regulated. Correlation analyses showed that the increase in soil N2 fixation and the suppression of nitrification and denitrification reactions were the key contributors to the increase in soil N content and NUE. Biochar combined with E. cloacae and DCD synergistically enabled the supplementation, slow release, and retention of N, thus providing adequate N for maize growth. Thus, the combination of biochar, E. cloacae, and DCD is effective for mitigating the irrational application of N fertilizers and reducing N pollution.

Influence of Organic and Inorganic Fertilizers on Tea Growth and Quality and Soil Properties of Tea Orchards' Top Rhizosphere Soil

Organic-based fertilizers have been ratified to be effective in ameliorating tea growth and the fertility of soil. However, the effect of integrated fertilization on tea growth and quality and the chemical properties of the soil in tea gardens are unclear. To address this, from 2020 to 2021, five different treatments were carried out in the greenhouse of the Tea Research Institute, Hangzhou, CAAS, including CK (control), NPK (chemical fertilizers), RC (rapeseed cake), NPK+B (chemical fertilizer + biochar), and NPK+RC, to investigate the effects of different fertilizations on soil chemistry and tea growth and quality. The results indicated that NPK+B and NPK+RC significantly improved the different amino acid and catechin concentrations in the young shoots, stems, and roots of the tea compared to the CK. The plant growth parameters, e.g., the plant height, no. of leaves, mid-stem girth, and fresh weights of stems and leaves, were significantly increased with integrated fertilization (NPK+B and NPK+RC) compared to the CK and solo organic and inorganic fertilizers. The chlorophyll contents (Chl a, Chl b, and Chl a+b) were generally higher with NPK+RC than with the CK (37%, 35%, and 36%), RC (14%, 26%, and 18%), and NPK (9%, 13%, and 11%) treatments. Integrated fertilization buffered the acidic soil of the tea garden and decreased the soil C:N ratio. NPK+RC also significantly increased the soil's total C (31% and 16%), N (43% and 31%), P (65% and 40%), available P (31% and 58%), K (70% and 25%), nitrate (504% and 188%), and ammonium (267% and 146%) concentrations compared to the CK and RC. The soil macro- (Mg and Ca) and micronutrients (Mn, Fe, Zn, and Cu) were significantly improved by the RC (100% and 72%) (49%, 161%, 112%, and 40%) and NPK+RC (88% and 48%) (47%, 75%, 45%, and 14%) compared to the CK. The chlorophyll contents and soil macro- and micronutrients were all significantly positively correlated with tea quality (amino acids and catechin contents) and growth. These results indicated that integrated fertilization improved the soil nutrient status, which is associated with the improvement of tea growth and quality. Thus, integrated nutrient management is a feasible tool for improving tea growth, quality, and low nutrient levels in the soil.

Factors regulating interaction among inorganic nitrogen and phosphorus species, plant uptake, and relevant cycling genes in a weakly alkaline soil treated with biochar and inorganic fertilizer

To highlight how biochar affects the interaction between inorganic nitrogen species (ammonium nitrogen, nitrate nitrogen, and nitrite nitrogen: NH4+-N, NO3¯-N, and NO2¯-N) and phosphorus species (calcium phosphate, iron phosphate, and aluminum phosphate: CaP, FeP and AlP) in soil and plant uptake of these nutrients, walnut shell (WS)- and corn cob (CC)-derived biochars (0.5 %, 1 %, 2 %, and 4 %, w/w) were added to a weakly alkaline soil, and then Chinese cabbages were planted. The results showed that the changes in soil inorganic nitrogen were related to biochar feedstock, pyrolysis temperature, and application rate. For soil under the active nitrification condition (dominant NO3¯-N), a significant decrease in the NH4+-N/NO3¯-N ratio after biochar addition indicates enhanced nitrification (excluding WS-derived biochars at 2 % and 4 %), which can be explained by the most positive response of ammonia-oxidizing archaeal amoA to biochar addition. The CC-derived biochar more effectively enhanced soil nitrification than WS-derived biochar did. The addition of 4 % of biochars significantly increased soil inorganic phosphorus, and the addition of CC-derived biochars more effectively increased Ca2P than WS-derived biochars. Biochars significantly decreased plant uptake of phosphorus, while generally had little influence on plant uptake of nitrogen. Interestingly, NO2¯-N in soil significantly positively correlated with total phosphorus in both soil and plant, and significantly negatively correlated with phoC, indicating that a certain degree of NO2¯-N accumulation in soil slightly facilitated plant uptake of phosphorus but inhibited phoC-harboring bacteria. The NO3¯-N in soil significantly positively correlated with Ca2P and Ca8P, while the NH4+-N/NO3¯-N ratio significantly negatively correlated with Ca10P and FeP, indicating that the enhanced nitrification seemed to facilitate the change in phosphorus to readly available ones. This study will help determine how to scientifically and rationally use biochar to regulate inorganic nitrogen and phosphorus species in soil and plant uptake of these nutrients.

Effect of different types of biochar on soil properties and functional microbial communities in rhizosphere and bulk soils and their relationship with CH4 and N2O emissions

Biochar as an agricultural soil amendment plays vital roles in mediating methane (CH4) and nitrous oxide (N2O) emissions in soils. The link between different types of biochar, bulk soil, and rhizosphere microbial communities in relation to CH4 and N2O emissions is being investigated in this study. The rice pot experiment was conducted using biochar at two temperatures (300°C and 500°C) in combination with three biochar levels (0, 2, 10% w/w). Soil properties and the abundance of genes associated with CH4 and N2O emissions from both rhizosphere and bulk soils were investigated. The study also aimed to examine the structure of microbial communities (pmoA, nosZ) in rhizosphere and bulk soils whereas CH4 and N2O emissions were monitored while growing rice. Results showed that biochar at 300°C and 10% incorporation significantly increased the CH4 emissions by up to 59% rise compared to the control group. Random Forest analysis revealed that the ratio of mcrA/pmoA along with the abundance of mcrA from both rhizosphere and bulk soils, the abundance of AOA, TN, DOC, and the community composition of pmoA-harboring microorganisms from both bulk and rhizosphere soils were important predictors of CH4 emissions. Therefore, the ratio of mcrA/pmoA in rhizosphere soil and the abundance of AOA in bulk soil were the main factors influencing CH4 emissions. Variation Partitioning Analysis (VPA) results indicated that the effects of these factors on bulk soil were 9% of CH4 emissions variations in different treatments, which contributed more than rhizosphere soils' factors. Moreover, random forest analysis results indicated that the abundance of AOB in bulk soil was the most important predictor influencing N2O emissions. The VPA result revealed that the factors in rhizosphere soil could explain more than 28% of the variations in N2O emissions. Our study highlights that rhizosphere soil has a more significant effect than bulk soil on N2O production. Our findings further the understanding of the link between bulk and rhizosphere attributes, and their impact on CH4 and N2O emissions in paddy soils. In summary, we recommend the application of biochar at 500°C and 2% incorporation rate for agricultural production in the area.

Biochar Decreases Fertilizer Leaching and Promotes Miscanthus Growth in Saline-Alkaline Soil

Biochar has been widely reported to improve soil conditions and affect plant growth. However, its effectiveness is limited by soil type and production technology. Considering the application effect of biochar in saline alkali soil, there is currently a lack of in-depth mechanism explanations in the research. Therefore, we designed an experiment to explore the effect of biochar on plant growth in saline alkali soil and conducted soil column experiments in a greenhouse environment using composite inorganic fertilizer (NPK). The results showed that biochar significantly affected the distribution of soil nutrient content at different depths, with a significant increase in fertility levels in the surface and middle layers and a decrease in fertility levels in deep soils. Compared to using fertilizers alone, the combined use of biochar and fertilizers further expands the enrichment effect and significantly reduces the leaching of fertilizers into deeper layers. At the same time, the application of biochar also improved soil properties, including an increase in electrical conductivity and organic matter content, as well as an increase in soil enzyme activity. On the other hand, the application of biochar also increases the activity of antioxidant enzymes and the content of osmoregulation substances in plants, reducing the environmental stress that plants are subjected to. Therefore, our results indicate that biochar can reduce the leaching of fertilizers into deep soil layers, improve soil properties, and promotes the growth of Miscanthus in saline alkali soils.

Legume-grass mixtures increase forage yield by improving soil quality in different ecological regions of the Qinghai-Tibet Plateau

Introduction

Information on the relationship between soil quality and forage yield of legume-grass mixtures in different ecological regions can guide decision-making to achieve eco-friendly and sustainable pasture production. This study's objective was to assess the effects of different cropping systems on soil physical properties, nitrogen fractions, enzyme activities, and forage yield and determine suitable legume-grass mixtures for different ecoregions.

Methods

Oats (Avena sativa L.), forage peas (Pisum sativum L.), common vetch (Vicia sativa L.), and fava beans (Vicia faba L.) were grown in monocultures and mixtures (YS: oats and forage peas; YJ: oats and common vetch; YC: oats and fava beans) in three ecological regions (HZ: Huangshui Valley; GN: Sanjiangyuan District; MY: Qilian Mountains Basin) in a split-plot design.

Results

The results showed that the forage yield decreased with increasing altitude, with an order of GN (3203 m a.s.l.; YH 8.89 t·ha-1) < HZ (2661 m; YH 9.38 t·ha-1) < MY (2513m; YH 9.78 t·ha-1). Meanwhile, the forage yield was higher for mixed crops than for single crops in all ecological regions. In the 0-10 cm soil layer, the contents of total nitrogen (TN), microbial biomass nitrogen (MBN), soil organic matter (SOM), soluble organic nitrogen (SON), urease (UE), nitrate reductase (NR), sucrase (SC), and bacterial community alpha diversity, as well as relative abundance of dominant bacteria, were higher for mixed crops than for oats unicast. In addition, soil physical properties, nitrogen fractions, and enzyme activities varied in a wider range in the 0-10 cm soil layer than in the 10-20 cm layer, with larger values in the surface layer than in the subsurface layer. MBN, SON, UE, SC and catalase (CAT) were significantly and positively correlated with forage yield (P < 0.05). Ammonium nitrogen (ANN), nitrate nitrogen (NN), SOM and cropping systems (R) were significantly and positively correlated with Shannon and bacterial community (P < 0.05). The highest yields in the three ecological regions were 13.00 t·ha-1 for YS in MY, 10.59 t·ha-1 for YC in GN, and 10.63 t·ha-1 for YS in HZ.

Discussion

We recommend planting oats and forage peas in the Qilian Mountains Basin, oats and fava beans in the Sanjiangyuan District, and oats and forage peas in Huangshui valley. Our results provide new insights into eco-friendly, sustainable, and cost-effective forage production in the Qinghai Alpine Region in China.

Clean water production from plastic and heavy metal contaminated waters using redox-sensitive iron nanoparticle-loaded biochar

The unceasing release of tiny plastics (microplastics and nanoplastics) and their additives, like metal ions, into the aquatic systems from industries and other sources is a globally escalating problem. Their combined toxic effects and human health hazard are already proven; hence, their remediation is requisite. This study utilised the nano-zerovalent iron-loaded sugarcane bagasse-derived biochar (nZVI-SBC) for simultaneous removal of Nanoplastics (NPs) of different functionality and size along with metal ions (Ni2+, Cd2+, AsO43-, and CrO42-). Batch and column experiments were conducted, and the results showed an efficient removal of contaminants with maximum sorption of carboxylate-modified NPs of size 500 nm (qmax = 90.3 mg/g) among all three NPs types. Significant removal was observed in Cd2+ in case of cations and CrO42- in case of anions with qmax = 44.0 and 87.8 mg/g, respectively. Kinetics and the isotherm modelling better fitted the pseudo-second-order kinetic model and Sips isotherm model, respectively for both NPs and metal ions. The designed material worked well in pH range of 4-8, ionic strength 1-20 mM and in complex aqueous matrices, with >90% removal. FTIR, zeta potential and the imaging analysis of the reaction precipitates confirmed the electrostatic attraction, pore retention and complexation as the potential mechanisms for removing NPs, whereas, XPS studies confirmed the reduction co-precipitation and surface complexation as the possible mechanism for removing metal ions. High values of attachment efficiency factor calculated from colloidal filtration theory (CFT) validated the experimental results and justified the high sorption of carboxylate modified 500 nm NPs particles. The synthesized material successfully removed both NPs of varying size and functionality and metal ions simultaneously with significant efficacy in complex environmental samples proving the broad applicability of material in realistic environmental conditions and different types of water treatment processes.

The Inhibiting Effects of High-Dose Biochar Application on Soil Microbial Metagenomics and Rice (Oryza sativa L.) Production

Biochar is usually considered as an organic improver which can improve soil and increase crop yields. However, the unrestricted application of biochar to normal-fertility farmland will cause chemical stress on crops and affect agricultural production. At present, the effects and mechanisms of high-dose applications of biochar on rice (Oryza sativa L.) production and soil biological characteristics have not been fully studied. In this greenhouse pot experiment, combined with soil microbial metagenomics, three treatments in triplicates were conducted to explore the responses of rice production, soil chemical properties, and soil biological properties to high-dose applications of biochar (5%, w/w) prepared using peanut waste (peanut hulls and straw). The results show that peanut hulls, with a loose texture and pore structure, are a raw material with stronger effects for preparing biochar than peanut straw in terms of its physical structure. In a rice monoculture system, high-dose applications of biochar (5%, w/w) can slightly increase the grains per spike, while significantly inhibiting the spike number per pot and the percentage of setting. High-dose applications of biochar also have significant negative effects on the diversity and stability of soil bacterial and archaeal communities. Moreover, the microbial metabolism and nutrient cycling processes are also significantly affected by changing the soil carbon/nitrogen ratio. This study discusses the response mechanisms of rice production and soil biology to high-dose biochar applications, and complements the understanding of irrational biochar application on agricultural production and land sustainability.

Iron-modified biochar reduces nitrogen loss and improves nitrogen retention in Luvisols by adsorption and microbial regulation

Nitrogen (N) loss poses a great threat to global environmental sustainability. The application of modified biochar is a novel strategy to improve soil nitrogen retention and alleviate the negative effects caused by N fertilizers. Therefore, in this study iron modified biochar was used as a soil amendment to investigate the potential mechanisms of N retention in Luvisols. The experiment comprised five treatments i.e., CK (control), 0.5 % BC, 1 % BC, 0.5 % FBC and 1 % FBC. Our results showed that the intensity of functional groups and surface structure of FBC was improved. The 1 % FBC treatment showed a significant increment in soil NO₃^--N, dissolved organic nitrogen (DON), and total nitrogen (TN) content by 374.7 %, 51.9 %, and 14.4 %, respectively, compared with CK. The accumulation of N in cotton shoots and roots was increased by 28.6 % and 6.6 % with 1 % FBC addition. The application of FBC also stimulated the activities of soil enzymes related to C and N cycling i.e., β-glucosidase (βG), β-Cellobiohydrolase (CBH), and Leucine aminopeptidase (LAP). In the soil treated with FBC, a significant improvement in the structure and functions of the soil bacterial community was found. FBC addition altered the taxa involved in the N cycle by affecting soil chemical properties, especially for Achromobacte, Gemmatimonas, and Cyanobacteriales. In addition to direct adsorption, the regulation of FBC on organisms related to N-cycling also played an important role in soil nitrogen retention.

Biochar-extracted liquor stimulates nitrogen related gene expression on improving nitrogen utilization in rice seedling

Introduction

Biochar has been shown to be an effective soil amendment for promoting plant growth and improving nitrogen (N) utilization. However, the physiological and molecular mechanisms behind such stimulation remain unclear.

Methods

In this study, we investigated whether biochar-extracted liquor including 21 organic molecules enhance the nitrogen use efficiency (NUE) of rice plants using two N forms (NH4 +-N and NO3 --N). A hydroponic experiment was conducted, and biochar-extracted liquor (between 1 and 3% by weight) was applied to rice seedlings.

Results

The results showed that biochar-extracted liquor significantly improved phenotypic and physiological traits of rice seedlings. Biochar-extracted liquor dramatically upregulated the expression of rice N metabolism-related genes such as OsAMT1.1, OsGS1.1, and OsGS2. Rice seedlings preferentially absorbed NH4 +-N than NO3 --N (p < 0.05), and the uptake of NH4 +-N by rice seedlings was significantly increased by 33.60% under the treatment of biochar-extracted liquor. The results from molecular docking showed that OsAMT1.1protein can theoretically interact with 2-Acetyl-5-methylfuran, trans-2,4-Dimethylthiane, S, S-dioxide, 2,2-Diethylacetamide, and 1,2-Dimethylaziridine in the biochar-extracted liquor. These four organic compounds have similar biological function as the OsAMT1.1 protein ligand in driving NH4 +-N uptakes by rice plants.

Discussion

This study highlights the importance of biochar-extracted liquor in promoting plant growth and NUE. The use of low doses of biochar-extracted liquor could be an important way to reduce N input in order to achieve the purpose of reducing fertilizer use and increasing efficiency in agricultural production.

Mixed legume-grass seeding and nitrogen fertilizer input enhance forage yield and nutritional quality by improving the soil enzyme activities in Sichuan, China

Information regarding relationships between forage yield and soil enzymes of legume-grass mixtures under nitrogen (N) fertilization can guide the decision-making during sustainable forage production. The objective was to evaluate the responses of forage yield, nutritional quality, soil nutrients, and soil enzyme activities of different cropping systems under various N inputs. Alfalfa (Medicago sativa L.), white clover (Trifolium repens L.), orchardgrass (Dactylis glomerata L.), and tall fescue (Festuca arundinacea Schreb.) were grown in monocultures and mixtures (A1: alfalfa, orchardgrass, and tall fescue; A2: alfalfa, white clover, orchardgrass, and tall fescue) under three N inputs (N1: 150 kg ha^-1; N2, 300 kg ha^-1; and N3: 450 kg ha^-1) in a split plot arrangement. The results highlight that A1 mixture under N2 input had a greater forage yield of 13.88 t ha^-1 year^-1 than the other N inputs, whereas A2 mixture under N3 input had a greater forage of 14.39 t ha^-1 year^-1 than N1 input, but it was not substantially greater than N2 input (13.80 t ha^-1 year^-1). The crude protein (CP) content of grass monocultures and mixtures significantly (P < 0.05) increased with an increase in the rate of N input, and A1 and A2 mixtures under N3 input had a greater CP content of 18.91% and 18.94% dry matter, respectively, than those of grass monocultures under various N inputs. The A1 mixture under N2 and N3 inputs had a substantially greater (P < 0.05) ammonium N content of 16.01 and 16.75 mg kg^-1, respectively, whereas A2 mixture under N3 had a greater nitrate N content of 4.20 mg kg^-1 than the other cropping systems under various N inputs. The A1 and A2 mixtures under N2 input had a substantial higher (P < 0.05) urease enzyme activity of 0.39 and 0.39 mg g^-1 24 h^-1 and hydroxylamine oxidoreductase enzyme activity of 0.45 and 0.46 mg g^-1 5 h^-1, respectively, than the other cropping systems under various N inputs. Taken together, growing legume-grass mixtures under N2 input is cost-effective, sustainable, and eco-friendly, which provide greater forage yield and improved nutritional quality by the better utilization of resources.

The critical role of biochar to mitigate the adverse impacts of drought and salinity stress in plants

Drought stress (DS) is a potential abiotic stress that is substantially reducing crop productivity across the globe. Likewise, salinity stress (SS) is another serious abiotic stress that is also a major threat to global crop productivity. The rapid climate change increased the intensity of both stresses which pose a serious threat to global food security; therefore, it is urgently needed to tackle both stresses to ensure better crop production. Globally, different measures are being used to improve crop productivity under stress conditions. Among these measures, biochar (BC) has been widely used to improve soil health and promote crop yield under stress conditions. The application of BC improves soil organic matter, soil structure, soil aggregate stability, water and nutrient holding capacity, and the activity of both beneficial microbes and fungi, which leads to an appreciable increase in tolerance to both damaging and abiotic stresses. BC biochar protects membrane stability, improves water uptake, maintains nutrient homeostasis, and reduces reactive oxygen species production (ROS) through enhanced antioxidant activities, thereby substantially improving tolerance to both stresses. Moreover, BC-mediated improvements in soil properties also substantially improve photosynthetic activity, chlorophyll synthesis, gene expression, the activity of stress-responsive proteins, and maintain the osmolytes and hormonal balance, which in turn improve tolerance against osmotic and ionic stresses. In conclusion, BC could be a promising amendment to bring tolerance against both drought and salinity stresses. Therefore, in the present review, we have discussed various mechanisms through which BC improves drought and salt tolerance. This review will help readers to learn more about the role of biochar in causing drought and salinity stress in plants, and it will also provide new suggestions on how this current knowledge about biochar can be used to develop drought and salinity tolerance.

Assessing the impact of biochar and nitrogen application on yield, water-nitrogen use efficiency and quality of intercropped maize and soybean

Introduction

Biochar (BC) and nitrogen (N) application have the potential to increase grain yield and resource use efficiency in intercropping systems. However, the effects of different levels of BC and N application in these systems remain unclear. To address this gap, the study is intended to ascertain the impact of various combinations of BC and N fertilizer on the performance of maize-soybean intercropping and determine the optimum application of BC and N for maximizing the effect of the intercropping system.

Methods

A two-year (2021-2022) field experiment was conducted in Northeast China to assess the impact of BC (0, 15, and 30 t ha^-1) and N application (135, 180, and 225 kg ha^-1) on plant growth, yield, water use efficiency (WUE), N recovery efficiency (NRE) and quality in an intercropping system. Maize and soybean were selected as materials in the experiment, where every 2 rows of maize were intercropped with 2 rows of soybean.

Results and discussion

The results showed that the combination of BC and N significantly affected the yield, WUE, NRE and quality of intercropped maize and soybean. The treatment of 15 t ha^-1 BC and 180 kg ha^-1 N increased grain yield and WUE, while that of 15 t ha^-1 BC and 135 kg ha^-1 N enhanced NRE in both years. Nitrogen promoted the protein and oil content of intercropped maize, but decreased the protein and oil content of intercropped soybean. BC did not enhance the protein and oil content of intercropped maize, especially in the first year, but increased maize starch content. BC was found to have no positive impact on soybean protein, but it unexpectedly increased soybean oil content. The TOPSIS method revealed that the comprehensive assessment value first increased and then declined with increasing BC and N application. BC improved the performance of maize-soybean intercropping system in terms of yield, WUE, NRE, and quality while N fertilizer input was reduced. The highest grain yield in two years was achieved for BC of 17.1-23.0 t ha^-1 and N of 156-213 kg ha^-1 in 2021, and 12.0-18.8 t ha^-1 BC and 161-202 kg ha^-1 N in 2022. These findings provide a comprehensive understanding of the growth of maize-soybean intercropping system and its potential to enhance the production in northeast China.

Influence of biochar-based urea substituting urea on rice yield, bacterial community and nitrogen cycling in paddy fields

BACKGROUND

There is an increasing understanding of the importance of biochar-based fertilizers in agroecosystems. However, no research has evaluated the effects of partial substitution of urea with biochar-based urea on rice yields and soil microbial communities. We therefore investigated the rice yields, bacterial communities, and gene abundance involved in nitrogen in silty clay and sandy loam soil paddy fields treated with urea (U), total substitution of urea with biochar-based urea (BSU), partial substitution of urea with biochar-based urea in basal and tillering fertilizers (BSU1), and partial substitution of urea with biochar-based urea in panicle fertilizers (BSU2).

RESULTS

Compared with U, applying biochar-based urea increased rice yields, with BSU2 having the most notable effect. Principal coordinate analysis revealed that bacterial communities treated with BSU2 in both soils were significantly different from those treated with U and BSU, most probably due to the decrease in pH caused by the decrease in the concentration of ammonium. The relative abundance of Subdivision3_genera_incertae_sedis, Azotobacter, Geobacter, Buchnera, and Terrimonas in silty clay soils and Saccharibacteria_genera_incertae_sedis and Geobacter in sandy loam soils significantly increased when treated with BSU2 and was positively correlated with rice yields, indicating that the improvements in rice yield were associated with changes in bacterial communities. Based upon amoA/narG related to nitrate accumulation and norB/nosZ related to nitrous oxide emissions, BSU2 enabled a lower risk of nitrate leaching and nitrous oxide emissions in both soils, in comparison with the U and BSU treatments.

CONCLUSION

The BSU2 treatment had a stronger yield-increasing effect than biochar-based urea alone and lowered the risk of nitrogen pollution, which is beneficial to the sustainable development of paddy fields. © 2022 Society of Chemical Industry.

Nitrogen retention potentials of magnesium oxide- and sepiolite-modified biochars and their impacts on bacterial distribution under nitrogen fertilization

Mitigating the loss and negative impacts of reactive N from fertilized soils remains a global environmental challenge. To optimize N retention by biochar, bamboo and pig manure biochars were modified as MgO- and sepiolite-biochar composites and characterized. Novel soil application of the modified biochars and their raw forms were comparatively evaluated for N-retention in a fertilized soil leached for 90 days in a column experiment. Changes in N-cycling-related enzyme and bacterial structure were also reported after 90 days. Results revealed low leaching losses of NH₄⁺, which reduced over time across all the treatments. However, while sole fertilizer (F) increased the initial and cumulative NO₃^- leached from the soil, the MgO-bamboo biochar (MgOBF) and sepiolite-bamboo biochar (SBF) treatments reduced leachate NO₃^- by 22.1 % and 10.5 % compared to raw bamboo biochar (BBF) treatment. However, 15.5 % more NO₃^- was leached from the MgO-pig manure biochar-treated soil (MgOPF) compared to its raw biochar treatment (PMBF) after 90 days. Dissolved organic N leached was reduced by 9.2 % and 0.5 % in MgOBF and SBF, as well as 15.4 % and 40.5 % in MgOPF and SPF compared to their respective raw forms. The total N of the biochars, adjustment of surface charges, cation exchange capacity, surface area, pore filling effects, and the formation of potential MgN precipitates on the modified-biochar surfaces regulated N leaching/retention. In addition, the modified biochar treatments reduced the hydrolysis of urea and stimulated some nitrate-reduction-related bacteria crucial for NO₃^- retention. Hence, unlike the raw biochar and MgOPF treatments, MgOBF, SBF, and SPF hold promise in mitigating inorganic-N losses from fertilized soils while improving the soil's chemical properties.

Deciphering biochar compost co-application impact on microbial communities mediating carbon and nitrogen transformation across different stages of corn development

Under current climatic conditions, developing eco-friendly and climate-smart fertilizers has become increasingly important.The co-application of biochar and compost on agricultural soils has received considerable attention recently.Unfortunately, little is known about its effects on specific microbial taxa involved in carbon and nitrogen transformation in the soil.Herein, we report the efficacy of applying biochar-based amendments on soil physicochemical indices, enzymatic activity, functional genes, bacterial community, and their network patterns in corn rhizosphere at seedling (SS), flowering (FS), and maturity (MS) stages.The applied treatments were: compost alone (COM), biochar alone (BIOC), composted biochar (CMB), fortified compost (CMWB), and the control (no fertilizer (CNTRL).The non-metric multidimensional scaling (NMDS) indicated total nitrogen (TN), pH, NO₃^--N, urease, protease, and microbial biomass C (MBC) as the dominant environmental factors driving soil bacteria in this study.The dominant N mediating genes belonged to nitrate reductase (narG) and nitronate monooxygenase (amo), while beta-galactosidase, catalase, and alpha-amylase were the dominant genes observed relating to C cycling.Interestingly, the abundance of these genes was higher in COM, CMWB, and CMB compared with the CNTRL and BIOC treatments.The bacteria network properties of CWMB and CMB indicated robust niche overlap associated with high cross-feeding between bacterial communities compared to other treatments.Path and stepwise regression analyses revealed norank_Reyranellaceae and Sphingopyxis in CMWB as the major bacterial genera and the major predictive indices mediating soil organic C (SOC), NH₄⁺-N, NO₃^--N, and TN transformation.Overall, biochar with compost amendments improved soil nutrient conditions, regulated the composition of the bacterial community, and benefited C/N cycling in the soil ecosystem.

The combined action of biochar and nitrogen-fixing bacteria on microbial and enzymatic activities of soil N cycling

This study aims to investigate the positive effects of the combined use of Enterobacter cloacae and biochar on improving nitrogen (N) utilization. The greenhouse pots experimental results showed the synergy of biochar and E. cloacae increased soil total N content and plant N uptake by 33.54% and 15.1%, respectively. Soil nitrogenase (NIT) activity increased by 253.02%. Ammonia monooxygenase (AMO) and nitrate reductase (NR) activity associated with nitrification and denitrification decreased by 10.94% and 29.09%, respectively. The relative abundance of N fixing microorganisms like Burkholderia and Bradyrhizobium significantly increased. Sphingomonas and Ottowia, two bacteria involved in the nitrification and denitrification processes, were found to be in lower numbers. The E. cloacae's ability to fix N₂ and promote the growth of plants allow the retention of N in soil and make more N available for plant development. Biochar served as a reservoir of N for plants by adsorbing N from the soil and providing a shelter for E. cloacae. Thus, biochar and E. cloacae form a synergy for the management of agricultural N and the mitigation of negative impacts of pollution caused by excessive use of N fertilizer.

Quantifying biochar-induced greenhouse gases emission reduction effects in constructed wetlands and its heterogeneity: A multi-level meta-analysis

Zero-waste biochar is an emerging tool for carbon neutralization, but the role of biochar in reducing greenhouse gases (GHGs) emissions from CWs were controversy and uncertainty. Yet, no previous study has integrated multiple research systems to quantitatively examine biochar-mediated GHGs emission reduction potential in CWs. Here we synthesized 114 studies to quantify biochar-induced declines ability of GHGs in the CWs by using the multi-level meta-analysis, reveal the variation of GHGs emission effect in different biochar-CWs and its response relationship with biochar, and identify the moderating variables that had a strong explanatory effect on the emission reduction effect of biochar. We showed that biochar remarkably affect CO₂ mitigation (p < 0.05), but has insignificant and heterogeneous effects on CH₄ and N₂O. Pyrolysis time, influent dissolved oxygen (DO), influent NO₃^--N concentration, hydraulic retention time (HRT) and wetland type can significantly affect the effect of biochar on CH₄ emission reduction. Particularly, the importance of HRT and wetland type was 0.89 and 0.85, respectively. Specially, the surface batch CWs modified by biochar could significantly promote the emission of CH₄ (p < 0.001), and the effect size was up to 89.59. For N₂O, biochar diameter, biochar addition ratio, influent COD/TN ratio, plant name, and removal efficiency of NO₃^--N/TN/COD were significant moderators. Among them, influent COD/TN ratio and plant name showed a stronger explanation. Planting Cyperus alternifolius L. significantly enhanced the N₂O emission reduction capacity by biochar (p < 0.001), and effect size was as low as -24.32. 700-900 °C biochar can promote CH₄ flux but inhibit N₂O flux. This study provides an important theoretical basis and valuable strategic guidance for more accurate estimation and improvement of synergistic emission reduction benefits between CH₄ and N₂O of biochar in CWs.

The addition of biochar and nitrogen alters the microbial community and their cooccurrence network by affecting soil properties

Biochar plays an important role in reducing the harmful environmental effects of inorganic nitrogen (N) fertilizers on agroecosystems, but the the impact mechanisms of biochar combined with N fertilizers on soil microorganisms are not clear enough. In this study, high-throughput sequencing was used to study the influences of three N fertilizer levels (0 (N0), 90 (N90) and 120 (N120) kg ha^-1) and two biochar levels (0 (B0) and 20 (B20) t ha^-1) on the soil microbial community and symbiotic network among microbial taxa in wheat fields. Compared to the control (B0N0), N fertilizer alone or combined with biochar significantly increased soil total N, available N, and organic matter in topsoil (0-20 cm), and the same results were found only in B20N120 treatment in subsoil (20-40 cm). In addition, bacterial and fungal diversity in topsoil were significantly increased and decreased by all N and biochar treatments, respectively. Moreover, soil bacterial and fungal community compositions also were also changed by N and biochar. Furthermore, biochar weakened the competition and cooperation among microorganisms in topsoil and subsoil, and the keystone species of networks were also changed by biochar. Redundancy analysis showed that soil total N, available N, available P, available K and pH were the main environmental factors driving the changes in bacterial and fungal community structures. These data indicated that the addition of N fertilizer and biochar could improve soil fertility by maintaining the stability of microbial community structures, which can provide reasonable guidance for the sustainable development of agriculture, such as maintaining dryland production.

Enhancing N uptake and reducing N pollution via green, sustainable N fixation-release model

The overuse of N fertilizers has caused serious environmental problems (e.g., soil acidification, excessive N₂O in the air, and groundwater contamination) and poses a serious threat to human health. Improving N fertilizer utilization efficiency and plant uptake is an alternative for N fertilizers overuses. Enterobacter cloacae is an opportunistic pathogen, also used as plant growth-promoting rhizobacteria (PGPR), has been widely presented in the fields of bioremediation and bioprotection. Here we developed a new N fixation-release model by combining biochar with E. cloacae. The efficiency of the model was evaluated using a greenhouse pot experiment with maize (Zea mays L.) as the test crop. The results showed that biochar combined with E. cloacae significantly increased the N content. The application of biochar combined with E. cloacae increased total N in soil by 33% compared with that of N fertilizers application. The N-uptake and utilization efficiency (NUE) in plant was increased 17.03% and 14.18%, respectively. The activities of urease, dehydrogenase and fluorescein diacetate hydrolase (FDA) was improved, the catalase (CAT) activity decreased. Analysis of the microbial community diversity revealed the abundance of Proteobacteria, Actinobacteria, Firmicutes, and Gemmatimonadetes were significantly improved. The mechanism under the model is that E. cloacae acted as N-fixation by capturing N₂ from air. Biochar served as carrier, supporting better living environment for E. cloacae, also as adsorbent adsorbing N from fertilizer and from fixed N by E. cloacae, the adsorption in turn slower the N release. Altogether, the model promotes N utilization by plants, improves the soil environment, and reduces N pollution.

Biochar application ameliorated the nutrient content and fungal community structure in different yellow soil depths in the karst area of Southwest China

The influence of biochar on the change of nutrient content and fungal community structure is still not clear, especially in different yellow soil depths in karst areas. A soil column leaching simulation experiment was conducted to investigate the influence of biochar on soil content, enzymatic activity, and fungal community diversity and structural composition. Three biochar amounts were studied, namely, 0%(NB, no biochar), 1.0%(LB, low-application-rate biochar), and 4.0% (HB, high-application-rate biochar). The results showed that biochar increased the pH value and the contents of soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP), and available potassium (AK) but reduced the microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN). Furthermore, this effect was enhanced with increasing biochar amount. Biochar was conducive to improving the nutrient availability in topsoil (0-20 cm), especially TN, AK, and MBN. Meanwhile, biochar affected the enzymatic activity, especially the sucrase activity. Biochar affected the diversity and structure of the fungal community, of which HB treatment had the most obvious effect. Among these treatments, Aspergillus, unclassified_Chaetomiaceae, Mortierella, Spizellomyces, Penicillium, Fusarium, and unclassified_Chromista fungal genera were the highest. Moreover, biochar inhibited the growth of harmful pathogens and increased the abundance of beneficial fungi in soil, and the effect was enhanced with increasing biochar amount and soil depth. Redundancy analysis (RDA) showed that AK was an important factor in yellow soil, although the main environmental factors affecting the fungal community structure were different in different soil depths. Overall, biochar had a positive effect on improving the land productivity and micro-ecological environment of yellow soil in the karst area.

Synthesis and application of starch-stablized Fe-Mn/biochar composites for the removal of lead from water and soil

Starch-stablized and Fe/Mn bimetals modified biochar derived from corn straw (SFM@CBC and SFM@CBC-350) were firstly prepared, characterized (FTIR, XRD, SEM, EDS, BET and XPS), and applied in Pb removal from water and soil. SFM@CBC and SFM@CBC-350 displayed highly effective adsorption performance of Pb²⁺ from wastewater with the maximum adsorption capacity of 170.91 mg g^-1 and 190.17 mg g^-1, respectively, which were much greater than that of FM@CBC (149.25 mg g^-1) and CBC (101.10 mg g^-1). Studies of adsorption kinetics, isotherms and thermodynamics indicated that the absorption of Pb²⁺ by SFM@CBC and SFM@CBC-350 was spontaneous and endothermic reaction, and it was controlled by monolayer chemisorption. The mechanism studies indicated that Pb²⁺ removal involved with multiple mechanism, including complexation (dominant process confirmed by XPS analysis), physical adsorption, electrostatic attraction, and cation exchange. The reusability test demonstrated that SFM@CBC and SFM@CBC-350 had very good stability and reusability. In addition, in order to further explore Pb removal performance of the modified biochar, SFM@CBC-350 was used in soil-ryegrass pot systems. Compared with the controls, the addition of SFM@CBC-350 reduced Pb content in soil and ryegrass, increased the biomass and total chlorophyll content, reduced the activity of antioxidant enzymes (CAT, SOD, MDA and POD) and ROS fluorescence intensity of ryegrass, thus alleviating Pb stress of ryegrass. Besides, the addition of SFM@CBC-350 could increase the richness and diversity of soil microorganisms, which was beneficial to the growth of ryegrass. Hence, SFM@CBC-350 has the potential of being used as a green, efficient and promising adsorbent in Pb removal from wastewater and soil.

Co-application of biochar and nitrogen fertilizer promotes rice performance, decreases cadmium availability, and shapes rhizosphere bacterial community in paddy soil

Cadmium (Cd) contamination in soil has posed a great threat to crop safety and yield as well as soil quality. Biochar blended with nitrogen fertilizer have been reported to be effective in remediating Cd-contaminated soil. However, the influence of co-application of biochar and nitrogen fertilizer on the Cd bioavailability, rice yield and soil microbiome remains unclear. In this study, eight different treatments including control (CK), 5% biochar (B), 2.6, 3.5, 4.4 g/pot nitrogen fertilizers (N1, N2 and N3), and co-application of biochar and nitrogen fertilizers (BN1, BN2, BN3) were performed in a pot experiment with paddy soil for observations in an entire rice cycle growth period. Results showed single N increased soil available Cd content and Cd uptake in edible part of rice, while the soil available Cd content significantly decreased by 14.8% and 7.4%-11.1% under the B, BN treatments, and the Cd content in edible part of rice was significantly reduced by 35.1% and 18.5%-26.5%, respectively. Besides, B, N and BN treatments significantly increased the yield of rice by 14.3%-86.6% compared with CK, and the highest yield was gained under BN3 treatment. Soil bacterial diversity indices (Shannon, Chao1, observed species and PD whole tree index) under N2, N3 were generally improved. Cluster analysis indicated that bacterial community structures under BN treatments differed from those of CK and single N treatments. BN treatments enhanced the abundances of key bacterial phylum such as Acidobacteria, positively associated with yield, and increased the abundance of Spirochaetes, negatively correlated to soil available Cd and Cd uptake of rice. Furthermore, the regression path analysis (RPA) revealed that pH, organic matter (OM), alkaline hydrolysis of nitrogen (AHN) and available Cd were the major properties influencing Cd content in edible part of rice. Redundancy analysis (RDA) revealed that pH and available Cd played key role in shaping soil bacterial community. Thus, BN is a feasible practice for the improvements of rice growth and remediation of Cd-polluted soil.

Biochar impacts on the soil environment of soybean root systems

Biochar has been widely studied as a soil amendment, but little is known about the "biochar-freeze-thaw soil-crop root system" interface in seasonally frozen soil areas. In the second year after the application of biochar, we conducted research on the morphological characteristic indicators of the soybean root system and the nutrient migration of the soil in the root zone under different biochar application periods (spring and autumn mixed, autumn, and spring biochar application) and different biochar application rates (3 kg·m-2, 6 kg·m-2, 9 kg·m-2, and 12 kg·m-2). The effects of different biochar treatments on the growth and development of soybean roots were examined. The soil organic carbon, ammonium nitrogen and nitrate nitrogen contents of the soil were measured at different locations in the root zone, and the migration processes of these nutrients in the soil were explored. The conclusions drawn from the experiments are as follows. (i) The biochar application rate and application method together determine the root morphological characteristic indicators of soybean plants. During long freeze-thaw periods, the freeze-thaw cycles change the internal environment of the biochar-freeze-thaw soil complex. (ii) Biochar tends to move towards the root system, which can increase soil organic carbon content, but the effect of biochar on root characteristics is not caused by the change in soil organic carbon content. (iii) Biochar promotes nitrogen cycling in the soil and the migration of soil nitrogen to the root sheath, increasing the number of nitrogen compounds that can be directly absorbed and utilized by crops. (iv) From a comparison of the effects of various biochar treatments on crop roots and farmland soils, we suggest that the 9 kg·m-2 biochar application rate under spring and autumn mixed biochar application is the optimal treatment.

Field-applied biochar-based MgO and sepiolite composites possess CO2 capture potential and alter organic C mineralization and C-cycling bacterial structure in fertilized soils

Agricultural soils contribute a significant amount of anthropogenic CO₂ emission, a greenhouse gas of global environmental concern. Hence, discovering sustainable materials that can capture CO₂ in cultivated soils is paramount. Since the effect of biochar on C mineralization/retention in fertilized soils is unclear, we produced biochar-based MgO and sepiolite-nanocomposites with CO₂ capture potential. The field-scale impacts of the modified-biochars were evaluated on net C exchange rate (NCER) periodically for 3 months in fertilized plots. The effects of the modified-biochar on organic-C mineralization, the activities, and dynamics of C-cycling-related 16S rRNA which are unknown, were investigated. Results revealed an initial rapid and higher cumulative CO₂ emission from the sole fertilizer treatment (F). Unlike the biochar treatment (BF), the successful incorporation of MgO/Mg(OH)₂ nanoparticles into the matrix and surface of biochar, and the potential formation of MgCO₃ with soil CO₂, mitigated CO₂ emission, especially in the MgO-modified biochar (MgOBF), compared to the sepiolite-biochar treatment (SBF). Compared to F and BF, the higher C retention as MgCO₃ in the modified biochar treatments led to an increase in cellulase activity, stimulation of key C-cycling-related bacteria, and the expression of genes associated with starch, sucrose, amino sugar, nucleotide sugar, ascorbate, aldarate, cellulose, and chitin degradation, thus, increasing organic C mineralization. Among the modified-biochar treatments, higher C mineralization was recorded in SBF, resulting in increased cumulative CO₂ emission, despite its initial capture for up to 42 days. However, MgOBF was effective in capturing soil-derived CO₂, despite the increased C mineralization compared to biochar. The changes in soil moisture and temperature significantly regulated NCER. Also, the modified biochars positively influenced the distribution of C-cycling-related bacteria by improving soil pH and available nutrients. Among the modified biochars, the observed higher mitigation effect of MgOBF on NCER indicated that it could be preferably applied in agricultural soils.

Straw and straw biochar differently affect phosphorus availability, enzyme activity and microbial functional genes in an Ultisol

Crop straw is commonly returned back to agricultural fields to improve soil nutrient status. In order to compare the effects of straw returning modes (direct and carbonization returning) on the phosphorus (P) availability in acidic soils and explore possible chemical and microbial mechanisms, a pot experiment was conducted. The rice straw, canola stalk at the rate of 1% (w/w) and their corresponding biochar produced by the same amount of straw at 350 °C and 550 °C were used, and two-season crops (rice and soybean) were planted. Results indicated that the content of available P in biochar-treated soils was significantly higher than in the straw-treated soils owing to the biochar soluble P and increased pH. Straw returning increased the activities of urease, sucrase and catalase more than biochar. Biochar mode significantly increased the activity of alkaline phosphatase (ALP), while decreased the acid phosphatase (ACP) relative to the straw mode. Likewise, there were a significant rise in the copy number of phoD gene and a drop of phoC in the biochar mode. The P functional genes (phoD, gcd and pqqC) had the higher copy numbers in soils with biochar made at 350 °C. Similarly, biochar made at 350 °C improved the yields of rice and soybean more effectively. Therefore, straw returning modes affected the availability of P differently via chemical and microbial pathways and the ALP regulated by phoD played a crucial role in the conversion of P. Results demonstrated that biochar returning had a larger impact on the availability of P and developed the effectiveness of crop production than the straw returning directly.

Filtered mud improves sugarcane growth and modifies the functional abundance and structure of soil microbial populations

BACKGROUND

Exploring high-quality organic amendments has been a focus of sustainable agriculture. Filtered mud (FM), a sugar factory waste derived from sugarcane stems, could be an alternative organic amendment for sugarcane production. However, the effects of its application proportions on soil fertility, nutrient cycling, structure of soil bacterial and fungal communities, and the growth of sugarcane in clay-loam soils remain unexplored.

METHODS

Three application proportions of FM: (FM1-(FM: Soil at 1:4), FM2-(FM: Soil at 2:3), and FM3-(FM: Soil at 3:2)) were evaluated on sugarcane growth and soil nutrient cycling. High throughput sequencing was also employed to explore soil microbial dynamics.

RESULTS

We observed that FM generally increased the soil's nutritional properties while improving NO₃ ^- retention compared to the control, resulting in increased growth parameters of sugarcane. Specifically, FM1 increased the concentration of NH₄ ⁺-N, the N fraction preferably taken up by sugarcane, which was associated with an increase in the plant height, and more improved growth properties, among other treatments. An increase in the proportion of FM also increased the activity of soil nutrient cycling enzymes; urease, phosphatase, and β-glucosidase. High throughput sequencing revealed that FM reduced the diversity of soil bacteria while having insignificant effects on fungal diversity. Although increasing FM rates reduced the relative abundance of the phyla Proteobacteria, its class members, the Gammaproteobacteria and Betaproteobacteria containing some N-cycling related genera, were stimulated. Also, FM stimulated the abundance of beneficial and lignocellulose degrading organisms. These included the bacterial phyla Actinobacteria, Bacteroidetes, Acidobacteria, Chloroflexi, and the fungal phylum Ascomycota. The distribution of the soil microbial community under FM rates was regulated by the changes in soil pH and the availability of soil nutrients. Since FM1 showed more promise in improving the growth properties of sugarcane, it could be more economical and sustainable for sugarcane production in clay-loam soils.

Biochar-N fertilizer interaction increases N utilization efficiency by modifying soil C/N component under N fertilizer deep placement modes

The situation of imbalance application of nitrogenous fertilizers in maize production is a serious issue in China, and excessive nitrogen (N) application is hazardous to sustainable agricultural production and environment. In this experiment, two biochar levels (C0: 0, C1: 2 %), three different N rates (N1: 50, N2: 100, and N3: 200 mg kg^-1), and two fertilization methods (T: traditional N fertilizer application mode and D: deep N fertilizer placement mode) were set up to study the response of different treatments on maize yield, N uptake, and N use efficiency. Herein, we found that fresh and dry biomasses were increased by 292 % and 283 % under C1N3 treatment with the deep application of N fertilizer compared to the control treatment (without nitrogen fertilizers and biochar). According to structural equation modeling (SEM), soil physical and chemical properties, N component and C component in different soil layers were associated with biochar and N fertilizer treatment, especially at 20-40 depth. The combination of N fertilizer and biochar application promoted the effects of biochar on the improving NUE of plants. The biochar alleviated the loss of soil nitrogen (from 52.00 to 25.94 %) under traditional N fertilizer application. Overall, excessive input of N fertilizer not only promotes the growth of crops but also causes a waste of resources and environmental pollution. We suggest that combined application of biochar and N fertilizer could significantly reduce N loss, and improve root growth and N uptake, resulting in improving NUE by improving soil environment (pH, SOM, EC) and adjusting soil C/N component.

Temporal changes of microbial community structure and nitrogen cycling processes during the aerobic degradation of phenanthrene

Phenanthrene (PHE) is frequently detected in worldwide soils. But it is still not clear that how the microbial community succession happens and the nitrogen-cycling processes alter during PHE degradation. In this study, the temporal changes of soil microbial community composition and nitrogen-cycling processes during the biodegradation of PHE (12 μg g^-1) were explored. The results showed that the biodegradation of PHE followed the second-order kinetics with a half-life of 7 days. QPCR results demonstrated that the bacteria numbers increased by 67.1%-194.7% with PHE degradation, whereas, no significant change was observed in fungi numbers. Thus, high-throughput sequencing based on 16 S rRNA was conducted and showed that the abundances of Methylotenera, Comamonadaceae, and Nocardioides involved in PHE degradation and denitrification were significantly increased, while those of nitrogen-metabolism-related genera such as Nitrososphaeraceae, Nitrospira, Gemmatimonadacea were decreased in PHE-treated soil. Co-occurrence network analysis suggested that more complex interrelations were constructed, and Proteobacteria instead of Acidobacteriota formed intimate associations with other microbes in responding to PHE exposure. Additionally, the abundances of nifH and narG were significantly up-regulated in PHE-treated soil, while that of amoA especially AOAamoA was down-regulated. Finally, correlation analysis found several potential microbes (Methylotenera, Comamonadaceae, and Agromyces) that could couple PHE degradation and nitrogen transformation. This study confirmed that PHE could alter microbial community structure, change the native bacterial network, and disturb nitrogen-cycling processes.

Insight to bacteria community response of organic management in apple orchard-bagasse fertilizer combined with biochar

Based on the sustainable development practice-zero growth in chemical fertilizer application, this article used bagasse organic fertilizer and rice husk derived biochar to investigate the response of soil bacterial community in apple orchard. Aimed at realize the soil quality improvement and biomass resource recovery to contribute agricultural and environmental sustainability. The co-trophic Proteobacteria was predominant in all the treatments (29-36 %) and enriched in non-nitrifying Alphaproteobacteria (9-11 %) and ammonia oxidant Betaproteobacteria (8-10 %), especially richest in bagasse fertilizer combine biochar treated soil. In addition, bacterial community variation was assessed by alpha and beta diversity, four treatments dispersed distribution and richer abundance observed in combined apply bagasse fertilizer and biochar treatment (3909.22 observed-species) than single application (3729.88 and 3646.58 observed-species). Biochar as microbial carrier combined organic fertilizer were established synergistic interaction and favorable to organic matter availability during sustainable agriculture. Finally, integrated biochar-bagasse fertilizer was richer than single organic or biochar fertilization in improving soil bacterial diversity, notably by promoting the metabolism of copiotrophic bacteria, nutrient cycling, plant growth and disease inhibit-related bacteria.

Biochar enhances the retention capacity of nitrogen fertilizer and affects the diversity of nitrifying functional microbial communities in karst soil of southwest China

Biochar is usually used as an agricultural soil amendment to improve soil nutrition availability and soil microbial environment. However, the effects of Moutai lees biochar on the migration and retention characteristics of nitrogen fertilizer and the changes of nitrifying microorganisms on yellow soil of southwest China are still not distinct. In this study, the migration distribution characteristics of nitrogen fertilizer, nitrogen retention capacity and microbial community structure were evaluated by a soil column leaching simulated experiment. Five application rates of biochar: 0%(BC₀), 0.5%(BC_0.5), 1.0%(BC_1.0), 2.0%(BC_2.0) and 4.0%(BC_4.0) were respectively tried. The results showed that the application of Moutai lees biochar has significantly increased the total nitrogen (TN) and nitrate (NN) contents in yellow soil, but it has also significantly decreased the microbial biomass nitrogen (MBN) content. When compared with the BC₀ treatment, it was found that the application of biochar increased nitrogen fertilizer retention rate (N_F) to 49.84%-95.23%. Moreover, high biochar application rates (2.0% and 4.0%) were also able to improve the N_F ratio, while low biochar application rates (0.5% and 1.0%) still had the risk of nitrogen leaching losses. Additionally, the application of biochar changed the bacterial community structure and the relative abundance of nitrogen-related microorganisms in yellow soil. Also, it was determined that Nitrite-oxidizing bacteria (NOB) played a major factor in affecting soil nitrogen, instead of ammonia-oxidizing archaea (AOA) and ammonium-oxidizing bacteria (AOB). Overall, research finally concluded that Moutai lees biochar decreased nitrite oxidation effect and changed ammoxidation to affect nitrogen nutrients availability in yellow soil and the biochar application rate of 4% has increased nitrogen fertilizer retention rate and decreased the risk of nitrogen leaching losses in yellow soil.

Full-scale municipal sludge pyrolysis in China: Design fundamentals, environmental and economic assessments, and future perspectives

The increasing amount of municipal sludge in China requires safe and effective management to protect human health and ensure environmental sustainability. Pyrolysis is a thermochemical process that decomposes organic matter at elevated temperature and under anaerobic conditions, and it has attracted an increasing attention in sludge treatment in the recent years. However, comprehensive environmental and economic assessment of sludge pyrolysis in China's context is rare, due to the small quantities of full-scale sludge pyrolysis plant. In this paper, we applied our design and operation parameters of full-scale sludge pyrolysis plants to generate the material and energy consumptions of the pyrolysis system under various of conditions, including sludge organic content and moisture content, system size, system energy distribution, and whether or not heat substitution is applied. Life cycle assessment and techno-economic assessment were then applied to investigate the environmental and economic performance of the system. Our results demonstrate the significant environmental and economic impacts associated with sludge properties and system size. Generally, sludge with higher organic content and lower moisture content requires less natural gas consumption, which leads to a simultaneous improvement of the system environmental and economic performance. The system economic performance is more sensitive to the system size, and centralized sludge handling using a larger pyrolysis system is more economic favorable. In the most ideal case, the average global warming potential and minimum sludge handling price of sludge pyrolysis could be as low as -32.5 kg CO₂-Eq/t DS and 188.8 $/t DS, respectively. Based on these results, we discussed the pathways that could be taken to further optimize the environmental and economic performances of the pyrolysis system.

Biochar-based fertilizer amendments improve the soil microbial community structure in a karst mountainous area

Biochar-based fertilizer amendment can improve soil properties partly due to stimulated microbial activities and growths. The karst ecosystem is prone to degradation and accounts for a large proportion of southwest China. Understanding of the response of the microbial community structure to biochar-based fertilizer application is of great significance in karst soil restoration. A field experiment located in southwest China was conducted in typical karst soil, and a high-throughput sequencing approach was used to investigate the effect of biochar-based fertilizer application on microbial community structure in karst soil. Field trials were set up for 24 months using the following treatments: control (CK), compost plus NPK fertilizer (MF), biochar (B), less biochar (half the quantity of biochar in B) plus compost and NPK fertilizer (B1MF), biochar plus compost and NPK fertilizer (BMF), and more biochar (double the quantity of biochar in B) plus compost and NPK fertilizer (B4MF). The results elucidated that BMF and B4MF treatments had higher contents of soil carbon and soil nutrients N, P, and K than the other treatments. Soil microbial abundance and diversity were significantly increased by biochar-based fertilizer amendments (BMF and B4MF), compared to CK (P < 0.05). BMF and B4MF treatments significantly increased the relative abundance of dominant microorganisms, compared to CK (P < 0.05). The difference in the composition of indicator microbes between each treated group indicated that soil amendments altered the microbial community structure. There was a strong correlation between soil properties (soil C-, N-, and P-fractions) and microbial community structure. Furthermore, network analysis revealed that the addition of biochar-based fertilizer increased the scale and complexity of the microbial co-occurrence network. To summarize, the application of biochar-based fertilizer enabled more keystone species in the soil microbial network to participate in soil carbon resource management and soil nutrient cycling, indicating that biochar-based fertilizer is beneficial for the restoration of karst-degraded soils.

Effects of Biochar Application on Enzyme Activities in Tea Garden Soil

Animal-manure biochar used as a sustainable amendment to garden soil has been widely applied, and the animal-manure pyrolysis temperatures would also have a regulatory effect on soil functions because of their affections on biochar physio-chemical properties. Here we studied the effects of different dosages of swine-manure biochar on tea garden soil functions, with the swine-manure pyrolysis temperature differed at 350 and 500°C. The results showed that the improvement of soil microbial biomass carbon and nitrogen and enzyme activities was closely related to the addition of 0.5-2% (biochar wt/soil wt) swine-manure biochar. Under different conditions of different carbon application rates and carbon type, the addition of 2% swine-manure biochar pyrolyzed at 350°C showed the best effects on soil enzyme activities and microbial biomass carbon and nitrogen contents. Compared to the control, after the addition of 2% swine-manure biochar, sucrase, phosphatase, catalase, and urease activities increased by 63.3, 23.2, 50.3, and 27.9%, respectively. Microbial biomass carbon and nitrogen contents also increased by 36.4 and 34.3%, respectively. Our study indicated that the effectiveness of using animal-manure swine-manure biochar as a sustainable amendment to soil would provide evidence of tea garden soil improvement and the environmental response to the usage of biochars.

Metabolic regulation in soil microbial succession and niche differentiation by the polymer amendment under cadmium stress

Cadmium (Cd) contamination seriously threatens the agricultural production, so exploring the response of soil microenvironment to amendments in Cd-contaminated soils is of importance. In this study, the mechanism of remediation of Cd-contaminated soil using the polymer amendment was studied in cotton flowering stage. The results showed that the concentration of Cd in cotton root and various Cd forms in Cd-contaminated soils were obviously high. High concentration of Cd, especially exchangeable Cd, could seriously affect the soil microenvironment. The root growth of cotton could be promoted, the carbon and nitrogen concentration and storage in soil were increased by 21.72-50.00%, while the exchangeable Cd concentration in soil were decreased by 41.43%, after applying the polymer amendment. In addition, the polymer amendment affected the soil microbial niche, increased the relative abundance of soil bacteria (Flaviaesturariibacter, Rubellimicrobium, and Cnuella), fungi (Verticillium and Tricharina), actinomycetes (Blastococcus and Nocardioides), and fungivores nematodes (Aphelenchus), and improved soil microbial metabolic functions (metabolism of nucleotides and carbohydrates). Therefore, this polymer amendment could be used to remediate severe Cd-contaminated soils, and the changes in the microbial and nematode communities help us understand the detoxification mechanism of the polymer amendment in Cd-contaminated soils.

Effect of mineral loaded biochar on the leaching performances of nitrate and phosphate in two contrasting soils from the coastal estuary area

Coastal estuary area is an important sink for the land-based or/and atmosphere-based nutrients, and is suffering a serious destruction derived from the intensifying human activities, which subsequently threatens the marine environment. Therefore, increasing soil retention capacities of nitrogen (N) and phosphorous (P) and reducing their leaching amount to sea water become a critical issue needed to be urgently addressed. In this study, a 38-day incubation and leaching experiment was conducted with two contrasting soils taken from the coastal estuary area, including the wetland and agricultural soils. Four kinds of biochars (BC), including one pure reed straw BC (BC₀), and three mineral loaded BCs produced through the co-pyrolysis of reed straw with CaO (BC_Ca), MgO (BC_Mg), and shell powder (BC_SP), respectively, were used to explore their effects on the leaching performances of nitrate-N and phosphate-P. The results demonstrated that the application of mineral loaded BCs could generally decrease the leaching amount of phosphate-P, while showed little effect on the nitrate-N leaching, compared to the controls. The positive improvement in soil nutrient retention capacity, mostly contributed by the increased adsorption on BC surface and into aperture, was suggested as the main mechanism for the decrease in nitrate-N and phosphate-P leaching. Compared to the agricultural soil, high clay content in the wetland soil could weaken the reduction potential in leaching losses of nitrate-N and phosphate-P derived from the newly introduced minerals with BC application. Furthermore, our results also indicated that the mineral loaded BCs may slow down the conversion rate of nutrients from organic forms to inorganic forms supported by the decreased enzymatic activity, which would be beneficial to the long term retention of nutrients in soil. Overall, based on the findings in the present study, the BC_Mg and Ca loaded BCs were respectively recommended for the wetland and agricultural soils.

The combined use of arbuscular mycorrhizal fungi, biochar and nitrogen fertilizer is most beneficial to cultivate Cichorium intybus L. in Cd-contaminated soil

We assessed Cichorium intybus L. (chicory) growth, nutrients and Cd uptake in the presence of arbuscular mycorrhizal fungi (AMF), biochar (BC) and nitrogen (N) fertilizer applications in experimental pot studies. Mycorrhizal colonization was improved by BC addition but not N addition. However, in the presence of AMF, BC and N had positive effects on shoot biomass and plants grown in the presence of all 3 components yielded the highest levels of shoot biomass compared to pair-wise combinations or individual components singly added. AMF inoculation also increased root biomass and this effect was apparent in the combinations that included AMF without BC. Fungal inoculation also led to increased contents of phosphorus (P), magnesium (Mg) and copper (Cu) in both chicory shoots and roots and potassium (K) and manganese (Mn) in roots. Moreover, in the presence of BC, AMF inoculation evidently enhanced the shoot Ca content. In contrast, the presence of AMF inhibited plant Cd absorption and BC addition further inhibited root Cd concentration following the AMF inoculation. Applying N fertilizer alone increased Cd transfering from soil to plants. However, when combined with use of AMF and BC, Cd toxicity to plants was reduced. This study demonstrated that AMF inoculation combined with BC and N fertilizer could improve chicory growth, nutrient absorption and reduction of Cd uptake in Cd-contaminated soil.

Different Responses of Soil Bacterial and Fungal Communities to 3 Years of Biochar Amendment in an Alkaline Soybean Soil

Biochar as a soil amendment has been regarded as a promising way to improve soil fertility. However, the response of microbial community after biochar and biochar compound fertilizer (BCF) application has not been thoroughly elucidated. This study evaluated the changes in abundance and composition of bacterial and fungal communities using quantitative real-time PCR (qPCR) and Illumina MiSeq amplicon sequencing. The field experiment ran for 3 years and comprised five treatments: chemical fertilizer as control (CK), straw-returning combined with chemical fertilizer (CS), low biochar application combined with chemical fertilizer (LB), high biochar application combined with chemical fertilizer (HB) and BCF. The results showed that biochar amendment results no changes in the abundance and diversity of bacteria in the bulk and rhizosphere soils. However, the abundance of soil fungi was significantly increased by biochar amendment (LB and HB). LB treatment significantly increased the fungal alpha diversity, while there was no significant change under HB. Furthermore, the dominant bacterial phyla found in the samples were Proteobacteria, Actinobacteria, and Acidobacteria. Biochar addition increased the relative abundance of Actinobacteria in both bulk and rhizosphere soils. The dominant fungal phyla were Ascomycota, Mortierellomycota, and Basidiomycota. The relative abundance of Ascomycota significantly decreased, but Mortierellomycota significantly increased in LB and HB. In addition, redundancy analysis indicated that the changes in bacterial and fungal communities are associated with soil properties such as SOC and TN, which are crucial contributors in regulating the community composition. This study is expected to provide significant theoretical and practical knowledge for the application of biochar in agricultural ecosystem.

Microbial mechanism of biochar addition on nitrogen leaching and retention in tea soils from different plantation ages

The effect of biochar additions on N leaching and retention in tea soils and its microbial mechanism are still unclear. In this study, effects of biochar additions at rates of 0, 3% and 6% on N leaching, N retention and microbial responses in two tea soils with 20- and 60-year plantation ages were investigated under application with ¹⁵N-labeled urea. The results showed that cumulative mass of leached NH₄⁺-N, NO₃^--N and TN was reduced by 20.9%-91.9%, 35.1%-66.9% and 40.0%-72.8% under biochar additions, respectively. The retention of TN in soil was increased by 1.2%-5.8% under biochar amendment. Fertilizer-N in the leachate was reduced by 28.8%-62.1%, while fertilizer-N retention in the soils was enhanced by 3.2%-23.9% with biochar application. Biochar addition of 6% showed the highest mitigation of N leaching and enhancement of TN retention across the two soils. Biochar additions increased soil microbial biomass and enzyme activities and changed the bacterial community composition, indicating that biochar addition increased the microbial N requirement, stimulated soil N cycling, including nitrification and denitrification processes, and enhanced microbial N immobilization in the tea soils. Those microbial responses to biochar addition were higher in 60-year-old soil relative to 20-year-old soil, leading to a higher enhancement of N retention and mitigation of N leaching. Soil pH was the prime factor that influenced soil microbes, and it strongly correlated with microbial biomass, enzyme activity, the relative abundance of dominant phyla and α-diversity indices. Therefore, the enhancement of microbial biomass, activity and shifts of bacterial community composition related to N cycling in response to biochar additions that increased the soil pH could be an important mechanism to better understand the biochar-induced N leaching mitigation and N retention enhancement in tea soils under different plantation ages.

Application of olive mill waste-based biochars in agriculture: Impact on soil properties, enzymatic activities and tomato growth

The olive oil industry is an important economic sector in Mediterranean countries. However, oil production is unfortunately accompanied by the generation of huge amounts of olive mill solid wastes (OMSW) and olive mill wastewater (OMWW). In the present study, a strategy is proposed for converting these olive mill wastes into biochar through pyrolysis, for their later use as an organic amendment in agriculture. Specifically, two biochars were prepared from the pyrolysis of OMSW at 500 °C, either alone or impregnated with OMWW (OMSW-B and I-OMSW-B). The characterization of the OMSW and I-OMSW samples and their derived biochars showed that the fixed carbon and ash contents in the feedstocks increased by 38% and 11% respectively for OMSW-B, and by 37% and 12% respectively for I-OMSW-B. Interestingly, the impregnation process significantly increased Na, P, K, Ca and Fe contents in the produced biochars. The effect of OMSW-B and I-OMSW-B amendments at different application dose (1%, 2.5% and 5% wt/wt) on the enzymatic activity of an agricultural soil was performed at laboratory scale with a pot test. The experimental results showed that phosphatase and urease activity increased with biochar application rate; amendment with I-OMSW-B at 1%, 2.5% and 5% enhanced the phosphatase activity by 63%, 142% and 285% and urease activity by 50%, 116% and 149%, respectively. On the other hand, dehydrogenase and protease activities were higher for the application rate of 2.5% biochar. Biochar amendment promoted tomatoes seedling growth after 10 weeks, which was highest in the application rates of 2.5% and 5% for both OMSW-B and I-OSMW-B. Thus, the produced biochars had great potential to be used as biofertilizers in agriculture.