Effect Of Different Biochars Research Articles

Biochars assisted phytoremediation of polycyclic aromatic hydrocarbons contaminated agricultural soil: Dynamic responses of functional genes and microbial community

A biochar-intensified phytoremediation experiment was designed to investigate the dynamic effects of different biochars on polycyclic aromatic hydrocarbon (PAH) removal in ryegrass rhizosphere contaminated soil. Maize and wheat straw biochar pyrolyzed at 300 °C and 500 °C were amended into PAH-contaminated soil, and then ryegrass (Lolium multiflorum L.) was planted for 90 days. Spearman's correlations among PAH removal, enzyme activity, abundance of PAH-ring hydroxylating dioxygenase (PAH-RHDα), and fungal and bacterial community structure were analyzed to elucidate the microbial degradation mechanisms during the combined remediation process. The results showed that 500 °C wheat straw biochar had higher surface area and more nutrients, and significantly accelerated the phytoremediation of PAHs (62.5 %), especially for high molecular weight PAH in contaminated soil. The activities of urease and dehydrogenase and the abundance of total and PAH-degrading bacteria, which improved with time by biochar and ryegrass, had a positive correlation with the removal rate of PAHs. Biochar enhanced the abundance of gram-negative (GN) PAH-RHDα genes. The GN PAH-degraders, Sphingomonas, bacteriap25, Haliangium, and Dongia may play vital roles in PAH degradation in biochar-amended rhizosphere soils. Principal coordinate analysis indicated that biochar led to significant differences in fungal community structures before 30 days, while the diversity of the bacterial community composition depended on planting ryegrass after 60 days. These findings imply that the structural reshaping of microbial communities results from incubation time and the selection of biochar and ryegrass in PAH-contaminated soils. Applying 500 °C wheat straw biochar could enhance the rhizoremediation of PAH-contaminated soil and benefit the soil microbial ecology.

Effects of Different Biochars and the Impact of Heavy Metals on Growth and Yield of Amaranthus at Zagyuri Irrigation Field Tamale, Ghana

Effects of Different Biochars and the Impact of Heavy Metals on Growth and Yield of Amaranthus at Zagyuri Irrigation Field Tamale, Ghana

The effects of different biochars on Caenorhabditis elegans and the underlying transcriptomic mechanisms.

Different biochars have diverse properties, with ambiguous effects on soil nematodes. This study investigated how aspen sawdust (ABC), bamboo powder (BBC), maize straw (MBC) and peanut-shell biochars (PBC) affected Caenorhabditis elegans via culture assays and RNA-seq analysis. The results showed that biochars derived from different agricultural materials varied significantly in physicochemical properties, and PBC produced more volatile organic compounds (VOCs) to attract C. elegans than ABC, BBC and MBC. Moreover, worms in ABC experienced the worst outcomes, while worms in PBC experienced milder impacts. Nematode body length decreased to 724.6 μm, 784.0 μm and 799.7 μm on average in ABC, BBC and MBC, respectively, compared to the control (1052 μm) and PBC treatments (960 μm). The brood size in ABC, MBC, BBC and PBC decreased 41.1%, 39.4%, 39.2% and 19.1% compared to the control, respectively. Furthermore, the molecular mechanisms of biochar-induced developmental effects on C. elegans were explored. Although several differentially expressed genes (DEGs) were different among the four biochars, worm phenotypic changes were mainly related to col genes (col-129; col-140; col-40; col-184), bli-6, sqt-3, perm-2/4, cdk-8, daf-16 and sod-1/2/5, which are associated with cuticle collagen synthesis, eggshell formation in postembryonic growth and rhythmic processes. Our study suggests that different properties of biochars could be crucial to soil nematodes, as well as the worms' biochemical changes are important for the health in agriculture soil.

Pyrolysis temperature determines the amendment effects of poplar residue‐derived biochars on reducing CO2 emission

AbstractPoplars and their hybrids are widely planted in both plantation forestry and agroforestry systems of the world. Along with the utilization and plantation management processes, a large amount of biomass residues are produced, but the relationship between biochar properties and soil CO2 emissions is largely unknown. Here, a laboratory incubation study was conducted to assess the effects of different biochars and their corresponding biomass residues on soil CO2 emissions during the 180 days of incubation. Poplar residue‐derived biochars were larger in the surface area and total pore volume but lower in nutrients and pH values than the rice straw‐derived biochar. Increasing pyrolysis temperature led to a decrease in the total nitrogen (TN) content of poplar leaf‐ and rice straw‐derived biochars, but enhanced the TN in the poplar twig‐ and poplar bark‐derived biochars. After 180‐day incubation, the total cumulative CO2 emission decreased by 33.1%–73.8% in the biochar amendments compared to their corresponding biomass residue addition, whereas the biochars derived from poplar twig and bark residues had more positive effects on reducing soil CO2 emissions, but depended on the pyrolysis temperature. Correlation analysis showed a significant and positive correlation between the CO2 emissions and TN content of bio‐based materials but the negative relationships to total carbon content and C/N ratio. Meanwhile the positive correlations of CO2 emissions to the surface area, t‐plot micropore area, and volume of the biochars were detected. Our results suggest that application of poplar twig‐ and poplar bark‐derived biochars has a great potential for mitigating global warming.

Manganese-modified biochar promotes Cd accumulation in Sedum alfredii in an intercropping system

Intercropping of crops with hyperaccumulators is a sustainable method to remediate contaminated soil without impeding agro-production. However, the function of engineered biochar in intercropping systems and its possible influence on cadmium (Cd) accumulation in hyperaccumulators remain unknown. A root box experiment on celery and Sedum alfredii with and without root separation was conducted in this study. Pristine and KMnO4-modified biochar (BCMn) were used to investigate the effects of different biochars on plant growth and Cd uptake in an intercropping system, as well as the influence of engineered biochar on Cd accumulation in hyperaccumulators. The results demonstrated that soil pH did not significantly vary with biochar application in the root separation treatment. However, BCMn significantly increased soil pH and thus reduced available Cd when the plant roots were not separated. Intercropping (no separation treatment) led to a 34% higher and 24% lower aboveground biomass of celery and S. alfredii, respectively, regardless of biochar addition. Compared with aboveground plant parts, plant roots exhibited more significant responses to biochar. Interestingly, intercropping may favour the phytoextraction of Cd by S. alfredii. In particular, the Cd uptake by S. alfredii roots substantially increased (118–187%), whereas that of celery roots decreased (51–71%) with BCMn addition, compared with other treatments. Moreover, after BCMn addition the accumulation of Cd in aboveground S. alfredii in the no separation treatment was 136% higher than that in the separation treatment. This was possibly related to the interaction of manganese (Mn) with Cd as well as the roots of S. alfredii. These findings provide new insights into the application of engineered biochar for phytoextraction, which is important for the efficient remediation of Cd-contaminated soils.

Improved methane production with redox-active/conductive biochar amendment by establishing spatial ecological niche and mediating electron transfer

The multifunctional roles of biochar as an additive in improving the performance of anaerobic digestion (AD) has not been perfectly understood. In this study, the effects of different biochars on AD and the enhanced mechanisms were explored. The CH4 productions were significantly improved with an increase of 45.9%, 28.3% and 16.5% by amendment with biochar pyrolyzed at 300℃ (BC300), 450℃ (BC450) and 600℃ (BC600), respectively. The tightly-bound communities were established on biochar at the initial stage of fermentation and functional microbes were selectively enriched/colonized in biochar-amended systems. Distinctive loosely-bound microbial communities were observed in BC300 and BC600 amended systems, among which electroactive Desulforhabdus and Clostridiales were the dominant bacteria. Biochar amendments also led to the formation of distinctive spatial ecological niches and the selection preference of microbes for specific spatial locations. These results provided new insights in revealing the potential mechanisms of enhanced AD performance by biochar amendment.

Wheat and maize-derived water-washed and unwashed biochar improved the nutrients phytoavailability and the grain and straw yield of rice and wheat: A field trial for sustainable management of paddy soils

A field experiment was carried out to evaluate the effects of different biochars on grain yield and phytoavailability and uptake of macro- and micro-nutrients by rice and wheat grown in a paddy soil in a rotation. Soil was treated with i) maize raw (un-washed) biochar (MRB), ii) maize water-washed biochar (MWB), iii) wheat raw biochar (WRB) or iv) wheat water-washed biochar (WWB) and untreated soil was used as control (CF). Inorganic fertilizers were applied to all soils while biochar treated soils received 20 ton ha−1 of designated biochar before rice cultivation in rice-wheat rotation. The WRB significantly (P < 0.05) increased rice grain yield and straw by up to 49%, compared to the CF. Biochar addition, particularly WRB, significantly increased the availability of N, P, K and their content in the grain (26–37%) and straw (22–37%) of rice and wheat. Also, the availability and grain content of Fe, Mn, Zn, and Cu increased significantly after biochar addition, particularly after the WRB, due to WRB water dissolved C acting as a carrier for micronutrients in soil and plant. However, the water-washing process altered biochar properties, particularly the water extractable C, which decreased its efficiency. Both wheat- and maize-derived biochars, particularly the WRB, are recommended to improve nutrients availability and to improve grain yield in the rice-wheat rotation agro-ecosystem. These results shed light on the importance of crop straw transformation into an important source for soil C and nutrients necessary for sustainable management of wheat-rice agro-ecosystem. However, with the current and future alternative energy demands, the decision on using crop biomass for soil conservation or for bioenergy becomes a challenge reliant on regulatory and policy frameworks.

Effects of Different Biochars, Activated Carbons and Redmuds on the Growth of Trifolium repens and As and Pb Stabilization in a Former Mine Technosol.

Soil pollution by metal(loid)s is an important issue in Europe, as it causes environmental and health problems. Therefore, remediation of these areas is needed. The success of phytoremediation process will depend on the ability of plants to implement, which can require the addition of amendments to the soil in order to improve soil conditions, immobilize pollutant and thus ameliorate plant growth. Amendments that can be used are biochar, activated carbon and redmuds, all of which have previously shown positive outcomes. The objectives of this study were to evaluate the effects of several amendments (biochars, activated carbons and redmuds) on (i) the soil physico-chemical properties of a former mine technosol contaminated by As and Pb, (ii) As and Pb immobilization and (iii) the growth of Trifolium repens. Results showed that amendment addition could ameliorate soil conditions, by reducing soil acidity (pH increased by 1.2 to 1.7 units) and immobilizing pollutants (85 to 99% of Pb immobilized); and improve plant growth (dry weight increased 1.5 to 2.5 times). However, not all amendments were beneficial to the soil and plant. For instance, the L27 activated carbon acidified soil pH, mobilized As and lowered plant growth. This study has allowed us to conclude that amendment effect is dependent on soil type, metal(loid)s and amendment properties, and it is thus necessary to choose the right amendment. Finally, amendments could be combined for better outcomes.

One-year monitoring of nitrogen forms after the application of various types of biochar on different soils

Biochar is a carbon rich product obtained from pyrolysis of biomass. The use of biochar as soil amendment has been boosted in the last years due to its possible influence on fertility, including its potential ability to lower mineral nitrogen losses, but specially for its potential to reduce greenhouse gases and to increase carbon sequestration in soil. However, the studies on the effects of biochar on nitrogen forms in soil are heterogeneous and contradictory. The present work aims to clarify this point by applying 6 different biochars (with different origin and production process) on 6 different soils (of different properties). The amendment corresponded to an agronomic addition rate of 30 Mg ha−1, together with the addition of urea at a 100 kg N per ha rate. Then those mixtures were incubated for one year at a 60% of the WHC. The samples were analyzed for nitrogen forms (Kjeldahl-N, ammonium-N, nitrate-N, nitrite-N, and microbial-N) at different incubation times (1 week, 1 month, 4 months and 1 year after the addition). The results showed that the effects of different biochars on the soil nitrogen forms were variegated, mainly attributable to soil properties, and to a lesser extent to the particular biochar used. Overall, the Kjeldahl-N (KN) decreased after the incubation time, and only the mixtures with N-rich biochars achieved slightly higher KN compared to controls. Also, biochars tended to induce a decrease in NH4+-N, and, especially, in NO3–-N. The biochars causing highest shifts on N inorganic forms were those produced from agronomic sources (olive and corn wastes) and the one from pine wood materials subjected to high pyrolysis temperature conditions.

Effect of three different types of biochars on eco-physiological response of important agroforestry tree species under salt stress

Soil reclamation through afforestation along with soil amendments is one of the most suitable practices to combat soil salinity while the use of biochar may have potential to ameliorate salt-affected soils. This study was designed to check effects of different biochars on the physico-chemical properties of soil and characteristics of three important agroforestry trees species: Eucalyptus camaldulensis, Vachellia nilotica and Dalbergia sissoo, in saline soils. Farmyard manure biochar (FYMB), sugarcane bagasse biochar (SCB), woodchips biochar (WCB) were applied (6% w/w) to check their effects on plants under saline conditions. Results revealed that FYMB was the best for promoting all growth and physiological parameters of three tree species while E. camaldulensis was the best suited species. Different types of biochars influenced the growth of agroforestry species differently as SCB showed better results for D. sissoo as compared to WCB but for V. nilotica and WCB was more effective than SCB. Trend of growth and other physiological attributes for E. camaldulensis and V. nilotica was FYMB > WCB > SCB > control whereas D. sissoo showed trend as FYMB > SCB > WCB > control. Biochar was helpful in improving physicochemical characteristics of saline soils by lowering values of soil EC and SAR but type of biochar has a differential effect on tree growth. Novelty statement: Biochar may be a potential source for the amelioration of salt affected soils while less is known about the effects of different types of biochars on the soil and eco-physiological response of important agroforestry trees species in saline soils. In this study, although all types of biochar ameliorated the soil conditions and enhanced the plant growth, but farmyard manure biochar was the most efficient treatment among three types of used biochars.

Effects of different biochars on physicochemical properties and immobilization of potentially toxic elements in soil - A geostatistical approach

The impact of different biochars (BCs) on the physicochemical properties and immobilization of potentially toxic elements (PTEs) in contaminated soil irrigated with industrial wastewater for the last three decades was studied. Furthermore, the efficacy of applied BCs in reducing geostatistical risks was also evaluated. For this purpose, BCs were prepared from green waste (Cynodon dactylon L.) for the first time at different pyrolysis temperature (400 °C, 600 °C and 800 °C), and amended the contaminated soil in pots with two different ratios of 2% and 5% (w/w) under controlled conditions. The BCs amended soil samples were analyzed after five months (equivalent to the life span of a wheat crop). The physicochemical impacts of applied BCs on the soil showed that the acidic soil was changed to basic. A tremendous increase in water holding capacity, cation exchange capacity, dissolved organic carbon, carbon, phosphorus and potassium contents was observed. The PTEs concentrations and geostatistical risks were significantly (p ≤ 0.05) decreased by all the BCs. Among them, BC prepared at 800 °C and applied at a ratio of 5% was showed the best effects by reducing the bioavailable concentrations of Cd, Pb, Cr, Ni, Cu, Mn, Fe, As, Co and Zn in 88%, 87%, 78%, 76%, 69%, 65%, 64%, 63%, 46% and 21%, respectively. Similarly, significant (p ≤ 0.05) reductions in geoaccumulation index, enrichment factor, contamination factor, and ecological risk were recorded. Therefore, BC prepared at 800 °C and applied at a ratio of 5% is recommended for soil remediation.

Effects of Selected Biochars Application on the Microbial Community Structures and Diversities in the Rhizosphere of Water Spinach (Ipomoea aquatica Forssk.) Irrigated with Reclaimed Water

The utilization of reclaimed water is one of the most important ways of alleviating the shortage of water resources for agricultural irrigation. As an effective disposal method for biomass waste, biochar has been widely used in the improvement and remediation of agricultural environments. However, few studies have been performed on the effects of biochar application on microbial community structures and pathogen abundances in rhizosphere soils irrigated with reclaimed water. Based on a pot experiment, high throughput sequencing technology and quantitative polymerase chain reaction (PCR) methods were used to investigate the effects of different biochars on the microbial community structure and diversity and pathogen abundance of rhizosphere soils irrigated with reclaimed water. The results showed that four different types of biochars had different effects on the soil nutrient status. Rice hull-derived biochar and rice straw-derived biochar resulted in significantly increased soil pH with reclaimed water irrigation, while peanut shell-derived biochar, rice straw-derived biochar, and wheat straw-derived biochar significantly increased EC values (P<0.05). The Sobs index, Shannon index, and Chao1 index of bacterial community in the rhizosphere soil significantly increased with rice straw-derived biochar treatment, while the Simpson index significantly decreased by adding peanut shell-derived biochar, rice hull-derived biochar, and wheat straw-derived biochar (P<0.05). There were differences in the relative abundances of bacterial communities in rhizosphere soils under different treatments. The dominant taxonomic groups at the phylum level were Proteobacteria, Actinobacteria, Chloroflexi, Bacteroidetes, and Acidobacteria. The dominant genera included Pseudomonas, Rheinheimera, Arthrobacter, Sphingomonas, and Aeromonas (relative abundance>5%). Redundancy (RDA) and heatmap analyses showed that the diversities and compositions of bacterial communities in rhizosphere soils in different treatments were closely related to soil EC values, organic matter, total nitrogen, and cadmium contents. Biochar application had no significant effect on the abundances of Aeromonas hydrophila and Bacillus cereus. Rice straw-derived biochar and peanut shell-derived biochar could significantly reduce the γ-Proteobacteria, while rice hull-derived biochar and wheat straw-derived biochar could significantly reduce the relative abundance of AOA (P<0.05). In conclusion, there were no obvious negative effects observed from reclaimed water irrigation on soil quality. Biochar application not only significantly improved the physicochemical properties of the soil, but also impacted the bacterial community structure and the abundance of the functional bacteria in the rhizosphere soil, which was closely related to the soil properties.

High pyrolysis temperature biochar reduced the transport of petroleum degradation bacteria Corynebacterium variabile HRJ4 in porous media

Biochar has been widely applied for the remediation of petroleum-contaminated soil. However, the effect of biochar on the transport of petroleum degradation bacteria has not been studied. A typical Gram-positive petroleum degradation bacteria-Corynebacterium variabile HRJ4 was used to study the effect of different biochars on bacterial transport and retention. Results indicated that the addition of biochar in sand was effective for reducing the transport of bacteria and poplar sawdust biochar (PSBC) had a stronger hinder effect than corn straw biochar (CSBC). The hindrance was more evident with pyrolysis temperature of biochar raised from 300°C to 600°C, which was attributed to the increase of specific surface area (309 times). The hindrance effect also enhanced with higher application rate of biochar. Furthermore, the reduction of HRJ4 transport was more obvious in higher (25 mmol/L) concentration of NaCl solution owing to electrostatic attraction enhancement. The adsorption of biochar to HRJ4 was defined to contribute to the hindrance of HRJ4 transport mainly. Combining the influence of feedstocks and pyrolysis temperature on HRJ4 transport, it suggested that specific surface area had the greatest effect on HRJ4 transport, and pore-filling, electrostatic force also contributed to HRJ4 retained in quartz sand column. At last, phenol transportation experiment indicated that the restriction of biochar on HRJ4 enhanced the phenol removal rate in the column. This study provides a theoretical basis for the interaction of biochar and bacteria, which is vital for the remediation of oil-contaminated soil and groundwater in the field.

Effect of different biochars on acid soil and growth parameters of rice plants under aluminium toxicity

Biochar is known to decrease the soil acidity and in turn enhance the plant growth by increasing soil fertility. Major objective of the present work was to understand the effect of biochar treatment on alleviation of soil aluminium (Al) toxicity and its role in enhancing plant growth parameters. Soil incubation study was conducted to understand the effect of biochar (Eucalyptus wood, bamboo, and rice husk) on soil pH, soluble and exchangeable Al in soil with and without Al addition. Another independent pot experiment with rice crop (Oryza sativa L. var. Anagha) was carried out for 120 days to examine the effect of biochars on soil properties and growth parameters of rice plants. Wood biochar application to soil at 20 t ha−1 was found to be highly consistent in decreasing soil acidity and reducing soluble and exchangeable Al under both studies. We conclude that wood biochar at higher dose performed better in reducing soluble and exchangeable Al in comparison to other biochars indicating its higher ameliorating capacity. However, rice husk biochar was effective under Al untreated soil, indicating the role of Si-rich biochars in enhancing plant growth.

Evaluation of nickel stabilization in a calcareous soil amended with biochars using mathematical adsorption models

ABSTRACT Batch adsorption experiments were performed to investigate the effect of different biochars (corn straw biochar (S-CSB), wheat straw biochar (S-WSB), rice husk biochar (S-RHB) and licorice root pulp biochar (S-LRB) each at 3% w/w) application on the kinetics, isotherms and thermodynamic parameters of nickel (Ni) adsorption onto a calcareous soil. The kinetics of Ni adsorption as a function of time was evaluated by seven different kinetic models. Also, the equilibrium adsorption data of Ni were analyzed by the Freundlich, Langmuir, and Temkin adsorption models. Two-constant rate model was best for the description of Ni adsorption kinetic and the S-CSB had the greatest adsorption rate of Ni (a = 841.5 (mg Ni kg−1 h−1)b and b= 0.030 [(mg Ni kg−1)]−1) among all the soil treatments. The Freundlich isotherm model had the best fit for the Ni equilibrium adsorption data, indicating multilayer adsorption. The maximum adsorption capacity of Ni (Qm) was increased by the addition of all the biochars to the soil and the highest amount was observed in S-CSB treatment (1.683 mg Ni g−1). This was mainly attributed to the CSB properties such as high amounts of CaCO3 and phosphorus. The Ni adsorption process onto the calcareous soil was endothermic, spontaneous and irreversible in nature according to the thermodynamic parameters (ΔG, ΔH and ΔS). In conclusion, it seems that the S-CSB was the best treatment for Ni immobilization in the calcareous soil.

Dynamic Effects of Different Biochars on Soil Properties and Crop Yield of Acid Farmland

To investigate the dynamic effects of biochars produced from different biomass materials on farmland soil acidity, exchangeable cations, phosphorus nutrient, and crop yield, a field experiment was performed on acid paddy soil. Five types of biochars-rice straw biochar (RSB), maize straw biochar (MSB), wheat straw biochar (WSB), rice husk biochar (RHB), and bamboo charcoal (BCB)-were applied to farmland soil at mass fraction of 0.1%. No biochar addition was used as control treatment (CK). The soil physicochemical properties and crop yields were analyzed after harvesting rice, rapeseed, and corn crops. Results indicated that the addition of biochars could effectively increase soil pH and exchangeable cations and reduce exchangeable acid content, but the effects decreased with time. The biochars increased the content of exchangeable K+, Ca2+, and Mg2+ and decreased the exchangeable Na+ content in soils. The biochars increased the contents of organic matter (SOM), available phosphorus, total phosphorus, and inorganic phosphorus (Al-P and Fe-P). Compared with the control treatment, biochars significantly (P<0.05) increased the yields of rice, oil seed, and maize crops. Rice husk biochar (RHB) had the best effect in improving acid soil physicochemical properties and increasing crop yield.

Effect of different biochars on soil moisture retention and nutrient release pattern

Soil incubation study in pots was carried out to study the effect of three different biochars on soil moisture retention percentage. The treatments involve three doses of maize biochar (MB), cotton biochar (CB) and prosopis biochar (PB) @ 2.0 t ha-1 (2T), 3.0 t ha-1 (3T) and 4.0 t ha-1 (4T), respectively besides a control and Farm Yard Manure @ 12.5 t ha-1. Significantly higher moisture per cent was noted in treatments of higher doses of all the biochars in second and third day of incubation. The significant increase in moisture per cent was noted in PB 4 T incubated pot, which was followed by CB 4T. The reduction in moisture per cent was noted with lower doses of biochar irrespective of source. Results of another incubation study with different biochars with varied doses, to find out nutrient release pattern revealed that the available N, P and K was higher at the start of incubation in control, where as in later days of incubation N, P and K availability was higher in Prosopis Biochar 4T after 70 days of incubation which was followed by cotton biochar 4T.

Advances in research on effects of biochar on soil nitrogen and phosphorus

In the context of global research, soil non-point source pollution is becoming more and more severe. Biochar is used as a soil amendment to repair soil. Therefore, research on biochar has received extensive attention. According to relevant literature reports, biochar has strong adsorption performance, and according to its nature, it can improve the availability of nitrogen and phosphorus in crops and fix nitrogen and phosphorus in soil. Also, biochar can also improve soil structure and reduce the migration of N and P with soil media. The research mechanism of biochar is distinct. The article cites the results of the majority of researchers and explains the effects of different biochars. Biochar has a certain promoting effect on nitrogen, phosphorus adsorption, conversion and leaching. In the future, we should strengthen the prospect of biochar in the treatment of soil environment and sustainable development of the environment.

The effect of different biochars on the growth and water use efficiency of fenugreek (Trigonella foenum‐graecum L.)

AbstractIn two identical pot trials, we investigated the effect of different biochars on the growth and water use efficiency (WUE) of fenugreek (Trigonella foenum‐graecum L.) grown with and without water stress. Plants were grown in pots with and without biochar. Rice husk (RH), standard rice husk (SRH), standard wheat straw (SWS) or standard oilseed rape straw (SOS) biochars were added at a rate of 2% by weight. Irrigation was reduced from 80% of field capacity to 40% in half of the pots to create water stress when 50% of the plants flowered. No significant interaction was observed between irrigation and biochar treatments. Water stress resulted in smaller plants (11.5%), fewer pods (16.1%) and reduced 100‐seed weight (12.6%), seed yield (20.1%) and plant dry weight (55.0%). All standard biochars increased plant dry weight in a range of 18%−25% compared with the controls. There was no significant effect of biochar on the number of pods and seed weight. Only RH, SWS and SOS biochar increased the number of seeds pod−1 by 9.0%−14.5% compared with the controls regardless of water stress. RH and SOS biochars increased seed yield by 16.7 and 21.6%, respectively. RH, SWS and SOS biochar increased the WUE by 17.3%, 10.1% and 16.2% regardless of water stress, respectively. Based on the experiment, we recommend farmers to add biochar whatever type they have available. However, RH and SOS seem to be better than the others are, as they seem to be able to increase seed yield and WUE considerably.

Linking hydrophobicity of biochar to the water repellency and water holding capacity of biochar-amended soil

Biochar addition to soil may change the hydrophobicity of amended soil and influence soil hydraulic properties. Soil hydrophobicity, i.e. soil water repellency (SWR) can interrupt water infiltration and form preferential flow leading to a potential risk of soil erosion or groundwater pollution. Up to date, the effect of different biochars on soil hydrophobicity remains unclear and the association of SWR with soil hydraulic properties is still unknown. To link the biochar hydrophobicity to SWR and soil water holding capacity (WHC), the surface structure and chemical composition of 27 biochars with different feedstocks and pyrolysis temperatures were characterized, and the SWR and soil WHC of biochar-added soil were investigated. Carboxylic groups on the biochar surface, surface area and pore volume were mostly influenced by pyrolysis temperature, which suggested the dominant factor determining the severity of biochar hydrophobicity was pyrolysis temperature. Hydrophilic soil became hydrophobic after biochar amendment. A higher addition rate led to a stronger SWR of hydrophilic soil. Biochar addition increased soil WHC of hydrophilic soil with low total organic carbon (TOC) content. Biochar did not have significant influence on SWR and soil WHC of hydrophobic soil with high TOC content. It implied that the influence of biochar on SWR and soil hydraulic properties mainly depended on soil original hydrophobicity and TOC content. Therefore, the properties of biochar and influence on soil hydrophobicity and hydraulic properties should be considered before processing biochar application.