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We designed two NGSS-aligned middle school classroom experiments to investigate the effects of biochar on plant growth and soil respiration. Biochar is a carbon-rich material, produced by heating organic matter under limited oxygen, that is added to soils to improve fertility, to promote plant growth, and as one possible strategy to help mitigate climate change. The experiments offer an ideal case study for students learning fundamentals of soil and plant interactions. Soils and biochar are accessible, are connected to global issues such as agriculture and climate change, and are the focus of ongoing research in soil science. These classroom experiments promote authentic science because students design replicated experiments, collect and analyze data, discuss variability in the data, and interpret their results in the context of recent research. [ABSTRACT FROM AUTHOR]

Biochar has been widely researched as an important technology for climate smart agriculture, yet work is still necessary to identify the magnitude of potential greenhouse gas ( GHG) mitigation and mechanisms involved. This study measured slow-pyrolysis wood-derived biochar's impact on GHG efflux, mineral N dynamics, and soil organic C in a series of two incubations across fertilized and unfertilized agricultural soils and soil moisture regimes. This research explored the magnitude of biochar's full GHG mitigation potential and drivers of such impacts. Results of this incubation indicate slow-pyrolysis wood-derived biochar has potential to provide annual emission reductions of 0.58-1.72 Mg CO2-eq ha−1 at a 25 Mg ha−1 biochar application rate. The greatest GHG mitigation potential was from C sequestration and nitrous oxide (N2O) reduction in mineral N fertilized soils, with minimal impacts on N2O emissions in unfertilized soils, carbon dioxide ( CO2) emissions, and methane ( CH4) uptake. Analysis of mineral N dynamics in the bulk soil and on biochar isolates indicated that neither biochar impacts on net mineralization and nitrification nor retention of ammonium ( [ABSTRACT FROM AUTHOR]

Climate change is predicted to increase climate variability and frequency of extreme events such as drought, straining water resources in agricultural systems. Thus, limited irrigation strategies and soil amendments are being explored to conserve water in crop production. Biochar is the recalcitrant, carbon-based coproduct of biomass pyrolysis during bioenergy production. When used as a soil amendment, biochar can increase soil water retention while enhancing soil properties and stimulating food webs. We investigated the effects of coupled biochar amendment and limited irrigation on belowground food web structure and function in an irrigated maize agroecosystem. We hypothesized that soil biota biomass and activity would decrease with limited irrigation and increase with biochar amendment and that biochar amendment would mitigate the impact of limited irrigation on the soil food web. One year after biochar addition, we extracted, identified, and estimated the biomass of taxonomic groups of soil biota (e.g., bacteria, fungi, protozoa, nematodes, and arthropods) from wood-derived biochar-amended (30 Mg ha−1) and nonamended soils under maize with limited (two-thirds of full) and full irrigation. We modeled structural and functional properties of the soil food web. Neither biochar amendment nor limited irrigation had a significant effect on biomass of the soil biota groups. Modeled soil respiration and nitrogen mineralization fluxes were not different between treatments. A comparison of the structure and function of the agroecosystem soil food web and a nearby native grassland revealed that in this temperate system, the negative impact of long-term conventional agricultural management outweighed the impact of limited irrigation. One year of biochar amendment did not mitigate nor further contribute to the negative effects of historical agricultural management. [ABSTRACT FROM AUTHOR]

Wildfire is a natural disturbance, though elemental losses and changes that occur during combustion and post-fire erosion can have long-term impacts on soil properties, ecosystem productivity, and watershed condition. Here we evaluate the potential of forest residue-based materials to rehabilitate burned soils. We compare soil nutrient and water availability, and plant recovery after application of 37 t ha−1 of wood mulch, 20 t ha−1 of biochar, and the combination of the two amendments with untreated, burned soils. We also conducted a greenhouse trial to examine how biochar influenced soil nutrient and water content under two wetting regimes. The effects of wood mulch on plant-available soil N and water content were significant and seasonally consistent during the three-year field study. Biochar applied alone had few effects under field conditions, but significantly increased soil pH, Ca, P, and water in the greenhouse. The mulched biochar treatment had the greatest effects on soil N and water availability and increased cover of the most abundant native plant. We found that rehabilitation treatments consisting of forest residue-based products have potential to enhance soil N and water dynamics and plant recovery following severe wildfire and may be justified where erosion risk or water supply protection are crucial. [ABSTRACT FROM AUTHOR]

Biochar has been advocated as a method of sequestering carbon while simultaneously improving crop yields and agro-ecosystem sustainability. It can be produced from a wide variety of biomass feedstocks using different thermochemical conversion technologies with or without the recovery of energy coproducts, resulting in chars of differing quality and a range of overall system greenhouse gas ( GHG) mitigation outcomes. This analysis expands on previous sustainability studies by proposing a mechanistic life cycle GHG and economic operating cost assessment model for the coproduction of biochar and bioenergy from biomass residue feedstocks, with a case study for north-central Colorado presented. Production is modeled as a continuous function of temperature for slow pyrolysis, fast pyrolysis, and gasification systems. Biochar environmental benefits ( C sequestration, N2O suppression, crop yield improvements) are predicted in terms of expected liming value and recalcitrance. System-level net GHG mitigation is computed, and net returns are estimated that reflect the variable economic costs of production, the agronomic value of biochar based on agricultural limestone or fertilizer displacement, and the value of GHG mitigation, with results compared to the alternate use of char for energy production. Case study results indicate that slow pyrolysis systems can mitigate up to 1.4 Mg CO2eq/ Mg feedstock consumed, provided a favorable feedstock is utilized, production air pollutant emissions are mitigated, and energy coproducts are recovered. The model suggests that while financial returns are generally greater when char is consumed for energy (biocoal) than when used as a soil amendment (biochar), chars produced through high-temperature conversion processes will have greater GHG-mitigation value as biochar. The biochar scenario reaches economic parity at carbon prices as low as $50/ Mg CO2eq for optimal scenarios, despite conservative modeling assumptions. This model is a step toward spatially explicit assessment and optimization of biochar system design across different feedstocks, conversion technologies, and agricultural soils. [ABSTRACT FROM AUTHOR]

Char is a product of thermochemical conversion of biomass via pyrolysis, together with gas (syngas), liquid (bio-oil), and heat. Fast pyrolysis is a promising process for bio-oil generation, which leaves 10-30% of the original biomass as char. Char produced for soil application, is defined biochar ( BC), and it may increase soil C storage, and reduce soil emissions of greenhouse gases ( GHG), such as N2O and CH4 -potentially making fast pyrolysis bioenergy generation a C-negative system. However, differences in production conditions (e.g., feedstock, pyrolysis temperature and speed, post handling, and storage conditions) influence the chemical properties of BC and its net effect when added to soils. Understanding if fast pyrolysis BC can increase C sequestration and reduce GHG emissions will enable full assessment of the economic value and environmental benefits of this form of bioenergy. We characterized a BC produced by fast pyrolysis for bio-oil generation and examined GHG ( CO2, N2O and CH4) efflux, C partitioning using δ13C, and soil C sequestration across four temperate soils and five BC rates; 0%, 1%, 5%, 10%, and 20% w/w. The fast pyrolysis process created a highly aromatic, low N, ash-rich BC with a O : C ratio of 0.01, which we expected to be highly recalcitrant. Across soils, CO2 emissions increased linearly and N2O emissions decreased exponentially with increasing BC addition rates. Despite still being actively respired after 2 years, total BC-derived C- CO2 comprised less than the BC volatile C content (4%). Expressed as CO2 equivalents, CO2 was the primary GHG emitted (97.5%), followed by N2O. All GHG emissions were small compared to the total SOC sequestered in the BC. Fast pyrolysis produced a highly recalcitrant BC that sequestered C and reduced GHG emissions. The recovery and soil application of BC would contribute to a negative carbon balance for this form of bioenergy generation. [ABSTRACT FROM AUTHOR]

Extracellular enzymes catalyze biogeochemical reactions in soil, cycling carbon and nutrients in agricultural systems. Enzymes respond quickly to soil management, including organic amendment inputs, such as biochar, a charcoal-like solid byproduct of bioenergy production. In a previous agricultural field trial, a pine biochar amendment caused an approximately 40% decrease in the enzyme activities of β-glucosidase (BG) and phosphatase (PHOS). The large surface area of the pine biochar has the potential to sorb nutrients and other organic molecules. To test if sorption caused decreased enzyme activity, we used a laboratory assay to quantify the activity of two sorbed enzymes: BG and acid PHOS, involved in the cycling of carbon and phosphorous. The enzymes were incubated with three solid phases: (1) the high surface area pine biochar, (2) the agricultural soil, and (3) a low surface area grass biochar, for an additional comparison. We quantified the sorbed enzymes at pH 6, 7, and 8, using a Bradford protein assay, and measured the immobilized enzyme activities via high-throughput fluorometric analysis. After sorption onto pine biochar, detectable BG and PHOS activity levels dropped by over 95% relative to the soil, supporting direct sorption as one mechanism that reduces enzyme activity in biochar amended soil. This laboratory assay demonstrated that sorption could account for the lack of priming of native soil organic matter and changes in soil phosphorous cycling after pine biochar addition. [ABSTRACT FROM AUTHOR]

Conversion of plant residues to biochar is an attractive strategy for atmospheric CO 2 emission mitigation and soil carbon (C) storage enhancement. However, our understanding of the factors controlling biochar persistence in soil is still limited, and generally based on biochar chemical recalcitrance. In addition to its chemical properties, biochar C decomposition might be limited by other factors, such as N and low molecular weight C compounds (LMW-C) availability. We presented results from a laboratory incubation experiment, where 4 atom% 13 C enriched biochar was added at a rate of 10% by weight to two different soils, with or without N and LMW-C additions. Sucrose was used as the LMW-C, and its 13 C natural abundance composition was manipulated, by mixing sucrose from sugar beet (C3) and from sugar cane (C4), to make it equal or dissimilar to the native soil organic carbon (SOC). This approach allowed partitioning the biochar-C from the ‘soil + LMW-C’ in the biochar amendment units and the LMW-C from SOC in the non-biochar amended units. Biochar-C, SOC and LMW-C were traced into CO 2 throughout the 112 day incubation and into microbial biomass C (MBC) and dissolved organic C (DOC) at the end of the incubation. Compared to LMW-C addition, N was a more significant factor stimulating biochar-C mineralization and biochar-C incorporation in microbial biomass. Biochar significantly decreased SOC mineralization and this negative effect was not influenced by N and LMW-C additions. Biochar addition promoted formation of SOC derived DOC; however, DOC accumulated in soil rather than being mineralized to CO 2 . According to our study, biochar was confirmed to be highly resistant to decomposition, and N or LMW-C availability did not affect the overall soil C sequestration potential of biochar. Biochar effects on soil DOC dynamics will need to be farther investigated in the field to better constrain the overall C sequestration potential of biochar. [ABSTRACT FROM AUTHOR]

Abstract Biochar is a high carbon material resulting from biomass pyrolysis that, when applied to croplands, can increase soil carbon and soil water retention. Both effects are of critical importance in semi-arid regions, where carbon decline and desertification are the main drivers of soil degradation. Since most environmental services provided by soil are mediated by belowground biota, effects of biochar on soil microbial and invertebrate communities must be evaluated under field conditions before its agricultural application can be recommended. We tested maize biochar for its mid-term effect on soil microbes and micro-arthropods of a Mediterranean vineyard. We applied biochar to three field plots with neutral sandy loam soils at a dose of 5 Mg ha−1. During two years, we monitored the abundance of functional groups of soil micro-arthropods and estimated the biomass of soil microbial groups. We also analyzed the δ13C value of microbial PLFA biomarkers to determine biochar-C utilization by each microbial group taking advantage of the δ13C natural abundance differences between the applied biochar and the soil. Biochar addition significantly reduced soil microbial biomass but did not alter the functional microbial diversity nor the abundance or biodiversity of soil micro-arthropods. The contribution of biochar-C to the diet of most microbial groups was very low through the monitoring period. However, two gram-negative bacterial groups increased their biochar-derived carbon uptake under extreme soil dryness, which suggests that biochar-C might help soil microbes to overcome the food shortage caused by drought. The decrease in microbial biomass observed in our experiment and the concomitant decrease of SOM mineralization could contribute to the carbon sequestration potential of Mediterranean soils after biochar addition. Graphical abstract Unlabelled Image Highlights • Application of biochar to Mediterranean vineyards reduced soil microbial biomass. • Biochar application at agronomic doses had no effect on soil micro-arthropods. • Microbial use of biochar was very low during the first two years after application. • Biochar may be utilized by soil microbes as an available C source during drought. [ABSTRACT FROM AUTHOR]

Biochar has been considered a stable additive for long-term soil carbon (C) storage and climate change mitigation. However, our understanding of the long-term interactions between aged biochar, soil organic C (SOC), and fresh low molecular weight C compounds (LMW-C) is still limited. In addition to the changes in the chemical properties of biochar and the SOC after aging, biochar stability and C sequestration potentials might be affected by the LMW-C availability. After 3.5 years of incubation, aged soils and aged soil-biochar mixtures (4 atom‰ 13 C enriched grass-derived biochar, 10% addition rate) of two different soil types were used in this study, with or without the addition of LMW-C. The 13 C natural abundance of the LMW-C was manipulated by mixing cane sucrose (C4) and beet sugar (C3) to make it different from or equal to the native SOC isotopic signature of the two soil types, which allowed the partitioning of the LMW-C and biochar C from the SOC in non-biochar and biochar addition treatments, respectively. We traced the 13 C in the cumulative CO 2 , microbial biomass C (MBC), and dissolved organic C (DOC) at the beginning and the end of the 28 days of incubation. Results indicated that this aged biochar was not as effective for SOC protection as it was when fresh. Aged biochar caused significant increases in the native SOC-derived CO 2 compared to non-biochar treatment during the 3.5 years of aging. Within the 28 days of incubation, aged biochar not only promoted the total CO 2 emission but also did not limit the priming effect of LMW-C on native SOC mineralization. SOC-derived DOC in the aged soil-biochar mixture was significantly higher than that in the aged soil, which further increased the SOC loss. A decline in the SOC stability with aged biochar might be associated with the attenuated sorption of SOC on aged biochar, the decline in bulk density with the high biochar addition rate, and a modified microbial community. The priming of aged SOC mineralization with the addition of LMW-C might be associated with the enhanced microbial N demand in aged soils and soil-biochar mixtures. The effect of aged biochar on the soil DOC and the effect of LMW-C on the aged biochar and SOC stabilities should be further investigated in field conditions, under continuous fresh C inputs, to better evaluate the effects of biochar on long-term SOC storage. [ABSTRACT FROM AUTHOR]

To mitigate negative impacts on crop yield from water-saving limited irrigation, we tested the effect of two organic amendments on soil moisture and nutrients. In an experimental maize field in northern Colorado, we tilled in conventional steer manure (30 Mg ha −1 ) and fast-pyrolysis pine-wood biochar (30 Mg ha −1 ). We quantified impacts on gravimetric soil moisture, total carbon and nitrogen, mineral nitrogen, available phosphorus, microbial biomass, and seven extracellular enzymatic activities (EEAs). Compared to the control, manure amendments increased gravimetric soil moisture by approximately 15%, total nitrogen by 10%, available phosphorus by 45%, and microbial biomass carbon by 15% ( p < 0.05). Relative to the control, biochar increased total soil carbon by 80% and altered EEAs ( p < 0.05). Biochar significantly increased α-1,4- glucosidase, β- d -cellobiohydrolase, and β-1,4- N -acetylglucosaminidase and significantly decreased β-1,4-glucosidase and phosphatase activities ( p < 0.05). Despite the effects on soil moisture, nutrient availability, and microbial dynamics, neither amendment significantly impacted maize yield under limited irrigation. Ongoing measurements will allow us to fully assess longer-term impacts on yield. [ABSTRACT FROM AUTHOR]