Biochar, a carbon (C)-rich material produced by the pyrolysis of organic residues, is frequently used as a soil amendment to enhance soil fertility and improve soil properties in tropical climates. However, in temperate agriculture, the impact of biochar on soil and plant productivity remains uncertain. The objective of this review is to give an overview of the challenges and opportunities of using biochar as an amendment in temperate soils. Among the various challenges, the type of feedstock and the conditions during pyrolysis produces biochars with different chemical and physical properties, resulting in contrasting effects on soils and crops. Furthermore, biochar aging, biochar application rates, and its co-application with mineral fertilizer and (or) organic amendments add further complexity to our understanding of the soil-amendment-plant continuum. Although its benefits on crop yield are not yet well demonstrated under field studies, other agronomic benefits of biochar in temperate agriculture have been documented. In this review, we proposed a broader view of biochar as a temperate soil amendment, moving beyond our current focus on crop productivity, and instead target its capacity to improve soil properties. We explored biochar’s benefits in remediating low-productive agricultural lands and its environmental benefits through long-term C sequestration and reduced nutrient leaching while curtailing our reliance on fertilizer input. We also discussed the persistence of beneficial impacts of biochar in temperate field conditions. We concluded that biochar displays great prospective to improve soil health and its productivity, enhance plant stress resilience, mitigate greenhouse gas emissions, and restore degraded soils in temperate agriculture.

Acidification and metal mobility may present challenges in soil receiving paper mill biosolids (PB). Co-applying biochar and PB could help prevent these issues, but its effect must be assessed. The objective of this 224 d incubation study was to evaluate the effect of amending two acidic soils, a clay and sandy loam, with two PB types varying in pH (PB1, pH = 7.80; and PB2, pH = 4.51) co-applied with three rates (0%, 2.5%, and 5% w/w) of pine (Pinus strobus L.) biochar on soil pH and macro- (P, K, Ca, and Mg) and micronutrients (Cu, Zn, Fe, and Mn). In both soils, co-applying biochar and PB significantly increased soil pH and extractable K concentration compared with PB-only application, whereas amending with PB significantly increased soil extractable P concentration compared with the unamended soil. In comparison with PB only, co-applying 5% biochar and PB decreased extractable Cu concentration in both soils and extractable Fe concentration in the sandy loam soil. This study showed that co-applying biochar and PB can be more beneficial to agricultural soils than application of PB alone by supplying nutrients and helping prevent metal toxicity by raising pH, especially in acidic sandy soils.

A greenhouse trial assessed the effects of biochar and vermicompost as partial substitutes of conventional growing media on leafy vegetables’ yields and changes of NH₄⁺-N and NO₃⁻-N in growing medium and leachates. Six growing media mixtures [(a) coir, (b) coir + biochar, (c) coir + vermicompost, (d) peat, (e) peat +vermicompost, (f) peat + biochar] combined with three nitrogen (N) rates [0% (0 g N·pot⁻¹), 50% (0.5 g N·pot⁻¹), and 100% (1.0 g N·pot⁻¹) commercial recommendation] were arranged in a split-plot design with three replicates. On average, the yield gap between 100% N and 50% N was improved when biochar and vermicompost were used as substitutes of coir (32% and 28% vs. 49%) and peat (14% and 18% vs. 27%). The concentrations of NH₄⁺-N in the leachates for peat + biochar varied between 17.20 and 1.00 mg·L⁻¹. The concentrations of NO₃⁻-N in the leachates varied between 130.0 and 1.0 mg·L⁻¹ for coir + vermicompost, and 60 and 1.0 mg·L⁻¹ for peat + vermicompost. The residual NO₃⁻-N in peat + biochar growing media and the leachates did not match the changes observed for NH₄⁺-N, and the much lower residual NH₄⁺-N indicates possible NH₄⁺-N retention by biochar and loss through volatilization in the early growth stages. Our results show that partial substitution of peat with biochar and coir with vermicompost maintained acceptable crop yield at 50% N due probably to N supply by vermicompost and decreased residual mineral N and loss by biochar in the leachates which could be beneficial for the environment.

In recent decades, there has been a growing interest in the recycling of organic materials such as paper mill biosolids (PB) and biochar for use as soil amendments. However, the benefits of co-application of PB and biochar and its effects on soil phosphorus (P) availability remain unknown. An incubation study was conducted on two acidic soils to assess the effect of two PB types (2.5% w/w) co-applied with three rates (0%, 2.5%, and 5% w/w) of pine (Pinus strobus L.) biochar on soil P fractions. An unfertilized control and a mineral NP fertilizer were used as a reference. Soil P fractions were determined by Hedley procedure after 2 and 16 wk of incubation. Material fractionation indicated that the PB containing the highest total P and the lowest Al content had the highest proportion of labile P, whereas most P in the biochar was in a stable form. The incubation study revealed that the P-rich PB increased P availability in both soils to a level comparable to mineral fertilizer at the end of the incubation. The addition of biochar to PB, however, did not affect soil P availability, but the highest rate induced a conversion of P fixed to Al and Fe oxides towards recalcitrant forms, particularly in the sandy loam soil. We conclude that co-applying biochar and PB could be more beneficial than application biochar alone and soils amended with such a mixture would be expected to release part of their P slowly over a longer period of time.

Warmer atmospheric temperatures (eT) will increase plant nutrient uptake, and elevated atmospheric CO₂ (eCO₂) is expected to enhance plant growth, whereas a multicomponent eTeCO₂ effect should also be beneficial for agroecosystems. Our goal was to understand if single- (eT, eCO₂) or multicomponent (eTeCO₂) climate effects, predicted for southern Ontario, Canada, will affect soybean and soil properties differently when soil is amended with manure and biochar (MB) or with manure, nitrogen (N) fertilizer, and biochar (MNB) compared with the addition of manure and N fertilizer (MN). We hypothesized that biochar regulates climate effects and causes soybean and soil properties to be similar to ambient climate conditions than soil without biochar. However, soil amended with biochar functioned independently of single- or multicomponent climate effects. Soybean pod and shoot biomass, shoot height, and shoot:root ratio were greater (p < 0.05) with eT. eCO₂ increased (p < 0.05) shoot biomass coinciding with an increase (p < 0.05) in nutrient uptake and uptake efficiency. All climate effects decreased (p < 0.05) soluble carbon (C), available N (NH₄⁺ and NO₃⁻), and the C/N ratio but increased (p < 0.05) orthophosphate. Amendment type MNB decreased (p < 0.05) soil microbial biomass carbon, but climate effects did not affect microbial biomass (p < 0.05). However, climate effects influenced how C and N were accessed by microbes in all amendment types, shifting (p < 0.05) microbial community structure, species richness, and diversity. We rejected our hypothesis and concluded that biochar amended soil does not strongly influence soybean and soil properties, and it does not provide a greater ability for soybeans and soil to cope with climate effects.

Renewable materials including coir, biochar, and composts are investigated worldwide in the horticultural industry to partially substitute peat in growing media. In this study, we assessed the effects of biochar and vermicompost as partial substitution of peat and compared these peat-based growing media with coir in terms of NH₄⁺-N and NO₃⁻-N content, CO₂-C and N₂O-N emissions and their microbial biomass carbon and nitrogen. Six growing media mixtures (peat; peat + biochar 9:1 v/v; peat + vermicompost 9:1 v/v; coir; coir + biochar 9:1 v/v; coir + vermicompost 9:1 v/v) replicated three times were incubated in growth chambers during a 60 d period. At day 0 of incubation (DAI), peat amended with biochar retained around 12.81% of NH₄⁺-N compared with peat alone. The concentrations of NO₃⁻-N peaked at 275 mg·kg⁻¹ at 33 DAI for peat and 552 mg·kg⁻¹ at 46 DAI for coir amended with vermicompost. The substitution of peat with biochar resulted in large CO₂-C [2070 μg CO₂-C·g⁻¹ dry weight (DW)] and N₂O-N (62.78 μg N₂O-N·g⁻¹ DW) emissions, but not coir. The substitution of coir with vermicompost increased N₂O-N emissions at a much lower level (47.53 μg N₂O-N·g⁻¹ DW) than peat (111.82 μg N₂O-N·g⁻¹ DW). Our results showed that supplements of vermicompost in peat and coir improved N supply which could benefit plant growth, while substituting part of peat with biochar increased CO₂-C and N₂O-N emissions. In contrast, no effect of biochar was observed with coir, which is beneficial for the environmental footprint of short-cycle growing crops.

The market for small fruits (grapes, blueberries, strawberries, and raspberries) is valued at more than $100 million CAD per year in Quebec, Canada. Wood-based biochar is an amendment that improves soil quality, which may boost small fruit growth and production. The objective of this research was to determine if wood-based biochar could increase the yield and quality of grape, blueberry, strawberry, and raspberry in southern Quebec. We evaluated the fruit yield as well as the quality parameters like average fruit weight, fruit firmness, color, juice pH, total soluble solids, total phenolic content, and antioxidant activity. Field trials were established on commercial farms with grape, blueberry, strawberry, and raspberry production systems in plots that received wood-based biochar and no biochar in spring (April–May). Small fruits were harvested at their ripening stage for yield and quality evaluation in the fall (July–October). Biochar application did not improve yield and quality parameters of small fruits, except it gave a marginally higher yield of grape (3.7 vs. 4.4 t·ha⁻¹, P = 0.08) and a higher average fruit weight of strawberry (11.9 vs. 13.2 g, P < 0.05). There was no difference in the quality of the fruit from biochar-amended and control plots in the first year of biochar application, possibly because the quality parameters are affected more by weather conditions, handling, and storage than by soil quality. This work suggests that wood-based biochar (<5 t·ha⁻¹) has a limited first-year impact on small fruit yield and quality in southern Quebec, Canada.

Biochar has the potential to sequester carbon and mitigate greenhouse gas emissions, and it may also contribute nutrients for plant growth in temperate climates. Nutrient availability in biochar-amended soil was assessed in a 338 d incubation study. The clay soil prepared with 4% w/w (dry basis) compost or without compost, then amended with wood-based biochar made at different pyrolysis temperatures [maple bark (Acer saccharum) at 400 (M400), 550 (M550), and 700 °C (M700)] on a dry-rate basis of 5% (w/w). After moistening the soil mixture to 44% volumetric soil water content (equivalent to 70% water-filled pore space), soil mixtures were incubated in the dark at 22 °C. Soil was sampled at days 9, 16, 23, 44, 86, 23 170, and 338 of the incubation. Biochar amendment increased the Mehlich-3 phosphorus, potassium (K), magnesium, and copper concentrations, and reduced the Mehlich-3 aluminum and iron concentrations at each sampling date, and M400 had the most significant effect on Mehlich-3-extractable nutrient concentrations. Compost addition also increased the amounts of extractable nutrients. These results suggested that M400 and carbon-rich compost promoted microbial growth and mineralization in amended soil. In addition, soil mixed with compost and amended with biochar had more Mehlich-3-extractable K than when compost or biochar was applied alone, probably due to greater growth and activity of soil K-solubilizing microorganisms. Overall, our study indicated that co-application of wood-based biochar and compost could improve soil fertility in temperate regions by increasing the availability of most plant macronutrients and micronutrients.

Liquid hog manure (LHM) and solid cattle manure (SCM) co-applied with biochar could beneficially influence soil nitrogen (N) and phosphorus (P) dynamics. A split-plot design was used at two sites (Brown and Black) in Saskatchewan to assess LHM and SCM (100 kg N·ha⁻¹) applied alone or in combination with biochars (8 Mg carbon·ha⁻¹) produced using slow or fast pyrolysis. Crop growth and nutrient uptake, along with fertilizer ¹⁵N recovery, were followed over four years in a cereal–oilseed rotation. Crop growth on the Brown soil was more responsive to the treatments than the Black soil, reflecting lower fertility of the Brown soil. The manure and biochar, applied alone or in combination, had little impact on available soil P. Manure and biochar effects on crop growth and nutrient uptake were attributed to temporal effects on soil N immobilization–mineralization influencing plant-available soil N. A negative impact of the fast pyrolysis biochar on growth and plant uptake was observed and attributable to its greater labile-carbon content, which likely promoted soil N immobilization. Synergism observed between SCM and the slow pyrolysis biochar may reflect enhanced net SCM-N mineralization and increased water-holding capacity. The majority (55%–80%) of plant ¹⁵N recovery occurred during the first year, with 86% of fertilizer ¹⁵N conserved within the soil–plant system after four years. Greater (40%) plant ¹⁵N recovery without biochar addition, coupled with increased (38%) soil ¹⁵N recovery with added biochar, suggests biochar-related immobilization and (or) sorption in the biochar-amended soils.

Amending croplands with forest residues may help in restoring soil properties in fields subject to intensive land management. Despite their known benefits when applied separately, co-application of wood biochar with paper mill biosolids (PB) has seen little investigation under field conditions. A study was initiated in Québec, QC, Canada, to determine the effect of a single application of wood biochar with and without PB on the nitrogen (N) and phosphorus (P) availability of two pH-neutral to alkaline loamy soils. Biochar at 0, 10, and 20 Mg dry weight·ha⁻¹ and PB at 30 Mg wet weight·ha⁻¹ were applied before planting of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] in 2018. Residual effect of this co-application was determined under soybean and corn in the subsequent year. In both years, corn received supplemental N and P from mineral fertilizers according to local agronomic recommendations. Co-applying biochar and PB reduced soil NO₃-N availability in the year of application and decreased corn yield by 1.0 Mg·ha⁻¹ compared with biochar or PB applied alone, but these amendments did not affect soybean yields. In the following year, the previous biochar addition increased soybean yield by 0.6 Mg·ha⁻¹ but had little effect on corn. For both years, biochar addition induced a large increase in soil Mehlich-3 P. This study revealed that wood biochar positively impacted P status of these soils but was not a source of N to crops even when co-applied with PB.

Soil amended with biochar is expected to produce less nitrous oxide (N₂O), although this may depend on nitrate (NO₃-N) availability. Our objective was to determine how pine wood biochar, slow pyrolyzed at 500 °C, affects N₂O production in soil having different denitrification potentials with variable NO₃-N concentrations under controlled laboratory conditions. Sandy loam surface soils (0–30 cm, pH 5.7) and sandy clay loam subsurface soils (40–60 cm, pH 5.6) were amended with four biochar rates (0, 10, 20, and 30 g·kg⁻¹), two nitrogen fertilizer rates (0 and 100 mg·kg⁻¹ NO₃-N) and two acetylene levels (0% and 10% headspace), arranged as a full factorial. Soil moisture content was adjusted to 80% water-filled pore space, and flasks were incubated at 20 °C for 30 h. Headspace gas was collected from each flask at 25, 26, 28, and 30 h. There was a significant reduction in N₂O production with an increasing rate of biochar in the surface soil but not in the subsurface soil. On average, less N₂O was produced in the subsurface soil than in the surface soil. As the NO₃-N concentration was not a limiting factor for denitrification, the most likely explanation was that denitrifier activity was influenced by the availability of soluble organic carbon in the soil–biochar mixtures. We recommend further study of the coupled carbon–nitrogen transformations during denitrification to understand how biochar influences soil N₂O production in sandy loam soils.

Soil moisture level is crucial to soil phosphorus (P) availability; however, there is no quantitative research on the relation between soil P availability and moisture level. In addition, biochar application could also alter soil P availability at different moisture levels. In this study, a 16 d soil incubation experiment was conducted at a laboratory scale to analyze the effects of soil moisture and P fertilization regimes (P-laden biochar fertilizer and conventional mineral P fertilizer) on soil P availability and fractionation. The results showed that soil P availability was positively correlated with soil moisture level (Pearson coefficients ranged from 0.46 to 0.91). High moisture level would lead to less amount of P in readily available fractions under P-laden biochar application. However, even with less P in readily available fractions, P-laden biochar could maintain soil P availability (117.7 mg P·m⁻²) at a similar level as the conventional P fertilizer (116.1 mg P·m⁻²).

The agricultural soils of the Happy Valley-Goose Bay (HV-GB) region of Newfoundland and Labrador, Canada are Podzols that are converted from boreal forest and have limited productivity due to their sandy texture, acidity, low soil organic matter (SOM), cation-exchange capacity (CEC), and water and nutrient retention capacity. Although numerous studies advocate biochar for mitigating soil quality problems and enhancing agronomic productivity, there is limited information on managing biochar for boosting the productivity of Podzols under newly converted agricultural lands. A 5 year experiment evaluated the impact of eight biochar rates (0–80 Mg C·ha⁻¹) on soil properties including SOM, CEC, and availability of plant nutrients and metals in agricultural soils of HV-GB. Both immediate and long-term impacts were thus assessed. Biochar generally improved soil fertility indicators. Although the largest rates (40 and 80 Mg C·ha⁻¹) led to the greatest changes, significant changes were also found with rates as low as 10 Mg C·ha⁻¹. Increasing biochar rates had diminishing returns for quality parameters of soil. The impact of biochar decreased with time after application, but the largest rate led to longer lasting effects. Although biochar was incorporated in topsoil, its effects were also measurable in the subsoil, albeit with a temporal delay, usually of 1 year. Thus, given the diminishing returns of increasing biochar rates, and that beneficial effects diminish over years, it is advisable that biochar be added in smaller amounts immediately after conversion, as little as 10 Mg C·ha⁻¹, with regular supplementation as needed.

Ammonia (NH₃) volatilization from NH₃-based fertilizer and animal manure reduces their nitrogen (N) fertilizer value and is a source of environmental pollution. Mixing manure with biochar may lower NH₃ volatilization from manure by adding H⁺, adsorbing mineral N, or increasing N immobilization in microbial biomass. The objective of this study was to determine whether wood-based biochar could lower NH₃ volatilization from vented pails containing manure (liquid swine, dairy slurry, and solid poultry manure) or a urea ammonium nitrate solution (UAN). Two types of wood-based biochar (BlueLeaf and Dynamotive) were mixed with three types of manure and UAN fertilizer solution at 0, 2.5, 5, 10, and 25% biochar by volume in vented pails. After 21 d storage in an outdoor shaded area, the greatest NH₃ volatilization was from poultry manure, which had pH 9.4 on average and low water content regardless of the biochar source and application rate. There was less NH₃ volatilization from UAN fertilizer solution when mixed with 25% (v/v) of Dynamotive biochar compared with NH₃ volatilization from UAN fertilizer solution mixed with 0%–10% (%) of Dynamotive biochar, probably because pH decreased from 7.0 to 6.4 after 21 d contact. Mixing wood-based biochar with manure had no impact on NH₃ volatilization, suggesting that these biochar sources did not appreciably change the pH and N dynamics in stored manure after 21 d.

Tremendous benefits of biochar (BC) amendment to soil have been reported, including their role in alleviating the impact of salinity stress in plants. The aim of this study was to evaluate the effects of BC produced at 300 °C (BC300) and 700 °C (BC700) on the germination rate (GR) and selected growth characteristics of corn plants irrigated with salinized water over a growth period of 6 weeks. The experimental treatments included three biochar treatments: BC0 (control, without biochar addition), BC300, and BC700. The treatments also included three salinity levels of irrigation water: 0, 3, and 6 dS·m⁻¹. The biochar was applied at a rate of 3%. The GR decreased with increasing salinity level, which was more evident in the first week. This stress impact was reduced when treated with the BC700 relative to the saline treatments without BC. Both BC treatments demonstrated contrasting effects on corn growth, nutrient uptake, and Na⁺ and K⁺ content in plant tissue. The effect of BC700 treatment on plant height and root length was limited, but the impact of salinity stress on chlorophyll meter readings, chlorophyll fluorescence parameter (Fv/Fm), dry matter yield, and N and P uptake were largely mitigated. It also increased K⁺ and decreased Na⁺ content in plant tissue. However, the BC300 treatment adversely affected plant growth parameters at each salinity level. Overall, the BC produced at a higher temperature significantly alleviated the impact of salinity stress on plant growth characteristics, which is probably attributed to their higher surface area and porosity, enhancing their salt ion sorption capacity.

Agricultural activities contribute to greenhouse gas emissions, but agroecosystems can also mitigate emissions by adding recalcitrant carbon sources such as biochar to soil. Our goal was to understand if greenhouse gas emissions decrease in soil amended with manure and biochar (MN) or with manure, nitrogen fertilizer, and biochar (MNB) than soil amended with manure and N fertilizer (MN) over the longer term. We hypothesized that biochar reduces the release of labile carbon and reactive nitrogen from organic amendments and nitrogen fertilizer, thereby reducing CO₂ and N₂O emissions and that soil temperature, moisture, and nitrogen availability are the strongest predictors for intra- and inter-annual variation in greenhouse gas emissions. Over three growing seasons, biweekly measurements of CO₂ and N₂O emissions were similar (P < 0.05) among treatments. Although input of labile carbon and reactive nitrogen was highest in MN and MB, cumulative CO₂ emissions were lowest (P < 0.05) in MNB. The availability of nitrogen from fertilizer caused greater cumulative N₂O emissions (P < 0.05) in MN and MNB. We found that soil temperature, moisture, and nitrogen availability regulated intraannual variability (P < 0.05) of CO₂ and N₂O emissions in all treatments, where emissions were greatest (P < 0.05) in the spring followed by summer and autumn. We accepted our hypothesis and concluded that, for cumulative emissions, biochar reduces the release of labile carbon and reactive nitrogen, but we rejected this hypothesis for biweekly emissions. We also concluded and accepted our hypothesis that soil temperature, moisture, and nitrogen availability regulated intraannual variation of CO₂ and N₂O in all treatments.

Many invasive species show allelopathic effects that contribute to competitive impacts on native vegetation for which few control measures exist. We investigated the potential for pyrolized organic material used as a soil amendment (“biochar”) to sorb allelochemicals and mitigate allelopathic effects on seed germination and early seedling development in three common invasive plants in Canada: garlic mustard (Alliaria petiolata), tree of heaven (Ailanthus altissima), and yellow sweetgrass (Melilotus officinalis). We hypothesized that biochars would mitigate effects on germination and early seedling development (radicle extension and cotyledon development) through sorption of allelochemicals. Laboratory assays of seed germination and early seedling development of two agricultural crops (Lactuca sativa and Raphinus raphanistrum) and two native grass species (Andropogon gerardi and Poa palustris) were conducted using water extracts from leaves. Seeds were treated with plant extracts exposed to four different biochars (red oak (Quercus rubra), jack pine (Pinus banksiana), shipping pallet and construction waste, and high-carbon wood ash) using a range of extract and biochar dosages. Treatment of allelopathic plant extracts by biochars significantly (p < 0.05) mitigated effects on seed germination for Alliaria and Melilotus. Effects on seed germination and early seedling development depended on extract concentration, biochar dosage, and the target species assessed. Controls treated with biochar leachate alone showed significantly (p < 0.05) increased germination for two of the biochars tested (jack pine biochar and high-carbon wood ash). Results indicated that biochars can mitigate allelopathic effects of invasive species through sorption of allelochemicals; however, this will be effective in only some cases.

Biochar is a source of stable organic matter being explored as a manure additive. A 64 d incubation experiment was conducted to quantify the short-term effect of manure (RM), biochar–manure (BM), raw biochar (BC), RM + BC, and BM + BC amendment on soil carbon (C) and nitrogen (N) mineralization. Manure increased CO₂-C emission rates, with the highest cumulative CO₂-C emissions being observed for RM + BC. Treatments with BM halted soil C mineralization, indicating manure-C stabilization. By contrast, neither RM nor BM affected soil N mineralization. Applying BM might benefit soil C sequestration by lowering CO₂-C emissions over the long term.