Long-term Soil Carbon Sequestration Research Articles

Soil carbon dynamics in perennial biomass crops on marginally productive cropland in southern Canada

Predicting changes in soil organic carbon (SOC) in perennial biomass crops using process-based models provides a greater understanding of land management impacts on climate mitigation through long-term soil carbon sequestration. The objective of this study was to predict long-term SOC dynamics in different perennial biomass crops [miscanthus (Miscanthus giganteus L.), switchgrass (Panicum virgatum L.), willow (Salix miyabeana L.)] as compared to secondary regrowth vegetation (successional site) and a row crop system. The century model accurately predicted SOC when simulated values were compared to measured field data. Average SOC stocks over the 162-year simulation period to 20 cm, were highest in miscanthus (8521 g C m−2), followed by the successional site (6877 g C m−2), switchgrass (6480 g C m−2), willow (5448 g C m−2) and lowest in the row crop system (3995 g C m−2). Higher SOC stocks in the miscanthus than the successional site indicates that, despite frequent biomass harvest, perennial biomass crops can accumulate higher carbon in soil than when a marginally productive cropland is left to undergo secondary regrowth. However, this depends on the crop species, since the miscanthus was the only biomass crop that reached pre-cultivation (1911) SOC stock of 8288 g C m−2. Moreover, the perennial biomass crops enhanced SOC in the slow fraction, whereas row crops depleted SOC in this fraction. This indicates the vital contribution of perennial biomass crops in long-term SOC sequestration and their role in climate change mitigation, especially when grown on marginally productive croplands.

Carbon Sequestration Potential of Manure-Derived Hydrochar Aided by Secondary Stabilization.

Hydrothermal carbonization (HTC) is a process that produces a carbon-rich solid from wet organic materials through the application of heat and pressure. Carbonized solids, previously correlated to long-term soil stability, may be considered for carbon sequestration through incorporation into soil. Chars produced by pyrolysis are known for exceptional stability in soil, but pyrolysis is expensive when applied to wet biomass, such as manure. Chars produced from manure by HTC show considerably improved potential for carbon sequestration relative to untreated manure, although not as great as that of chars produced by pyrolysis. This study focuses on producing and evaluating chars by HTC paired with pyrolysis and different methods of chemical oxidation for long-term carbon sequestration in soil. It is shown that a two-step process of pyrolysis following HTC produces a char that outperforms those produced by either individual process (HTC or pyrolysis) in carbon yield, carbon content, and, more importantly, soil carbon sequestration potential. It was found that acid-catalyzed HTC followed by pyrolysis resulted in a char with a 13% increase in carbon yield, a 51% increase in carbon content, and an atomic O/C ratio 64% smaller than the char produced by conventional pyrolysis.

A review of climate change mitigation and agriculture sustainability through soil carbon sequestration

As a result of human activities such as burning fossil fuels, organic materials, and engaging in unsustainable land practices, atmospheric carbon dioxide (CO2) levels have been steadily rising, heightening worldwide concerns about climate change. It is expected concentrations to grow and changes in CO2 sequestration in agricultural soils as a result of the industrial revolution's acceleration of CO2 emissions. These emissions have been intensified by changes in land use, such as cutting down trees, burning biomass, altering farming operations, draining natural wetlands, and using the wrong methods for managing soil. The present study utilized the systematic literature review method to investigate soil carbon sequestration options as a possible means of reducing the impact of climate change and improving agriculture sustainability. As a result of soil degradation and poor management, soil organic carbon (SOC) levels have decreased, which in turn has increased atmospheric CO2 levels. But cutting-edge land application and modern agricultural management methods have the ability to reduce CO2 emissions. Several methods exist for replenishing depleted SOC, such as repurposing marginal lands for restoration purposes, advocating for reduced or zero-tillage methods in conjunction with cover as well as residue crops, and introducing nutrient cycling through composting, manure usage, and other environmentally friendly approaches to managing soil and water. One holistic approach to fighting climate change is long-term soil carbon sequestration. Soil carbon sequestration offers a comprehensive and efficient strategy for reducing the impact of climate change by recharging depleted soils, increasing biomass production, cleaning surface and underground water sources, and compensating for CO2 emissions through fossil fuels. Soil carbon sequestration presents an exciting opportunity for management of the problems caused by contemporary changes in the environment, and the adoption of these novel approaches is essential for meeting these issues.

Sphagnum increases soil’s sequestration capacity of mineral-associated organic carbon via activating metal oxides

Sphagnum wetlands are global hotspots for carbon storage, conventionally attributed to the accumulation of decay-resistant litter. However, the buildup of mineral-associated organic carbon (MAOC) with relatively slow turnover has rarely been examined therein. Here, employing both large-scale comparisons across major terrestrial ecosystems and soil survey along Sphagnum gradients in distinct wetlands, we show that Sphagnum fosters a notable accumulation of metal-bound organic carbon (OC) via activating iron and aluminum (hydr)oxides in the soil. The unique phenolic and acidic metabolites of Sphagnum further strengthen metal-organic associations, leading to the dominance of metal-bound OC in soil MAOC. Importantly, in contrast with limited MAOC sequestration potentials elsewhere, MAOC increases linearly with soil OC accrual without signs of saturation in Sphagnum wetlands. These findings collectively demonstrate that Sphagnum acts as an efficient ‘rust engineer’ that largely boosts the rusty carbon sink in wetlands, potentially increasing long-term soil carbon sequestration.

Evidence for the formation of fused aromatic ring structures in an organic soil profile in the early diagenesis

The presence of fused aromatic ring (FAR) structures in soil define the stability of the recalcitrant soil organic matter (RSOM). FAR are important skeletal features in RSOM that contribute to its extended residence time. During the early diagenesis, FAR structures are formed through condensation and polymerization of biomolecules produced during plant residue and microbial product decay. Molecular level characterization of the RSOM extracted from an organic soil profile gives important insights into the formation of FAR. Advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, including recoupled long-range C–H dipolar dephasing experiments on extracted humic acids (HA) showed that they contain diagenetically formed FAR different from charcoal and lignin. Peaks characteristic of FAR are observed at all depths in the soil profile, with a greater prevalence observed in the HA extracts from the clay soil layer at the bottom. In the clay soil layer, 78% of the aromatic carbon was non-protonated, and this was 2.2-fold higher than the topsoil. These data further strengthen our understanding of the humification process that could occur in early diagenesis and help explain the importance of incorporating diagenesis as an important phenomenon for long-term carbon sequestration in soil.

Trade-offs in carbon-degrading enzyme activities limit long-term soil carbon sequestration with biochar addition.

Biochar amendment is one of the most promising agricultural approaches to tackle climate change by enhancing soil carbon (C) sequestration. Microbial-mediated decomposition processes are fundamental for the fate and persistence of sequestered C in soil, but the underlying mechanisms are uncertain. Here, we synthesise 923 observations regarding the effects of biochar addition (over periods ranging from several weeks to several years) on soil C-degrading enzyme activities from 130 articles across five continents worldwide. Our results showed that biochar addition increased soil ligninase activity targeting complex phenolic macromolecules by 7.1%, but suppressed cellulase activity degrading simpler polysaccharides by 8.3%. These shifts in enzyme activities explained the most variation of changes in soil C sequestration across a wide range of climatic, edaphic and experimental conditions, with biochar-induced shift in ligninase:cellulase ratio correlating negatively with soil C sequestration. Specifically, short-term (<1year) biochar addition significantly reduced cellulase activity by 4.6% and enhanced soil organic C sequestration by 87.5%, whereas no significant responses were observed for ligninase activity and ligninase:cellulase ratio. However, long-term (≥1year) biochar addition significantly enhanced ligninase activity by 5.2% and ligninase:cellulase ratio by 36.1%, leading to a smaller increase in soil organic C sequestration (25.1%). These results suggest that shifts in enzyme activities increased ligninase:cellulase ratio with time after biochar addition, limiting long-term soil C sequestration with biochar addition. Our work provides novel evidence to explain the diminished soil C sequestration with long-term biochar addition and suggests that earlier studies may have overestimated soil C sequestration with biochar addition by failing to consider the physiological acclimation of soil microorganisms over time.

From hemp grown on carbon-vulnerable lands to long-lasting bio-based products: Uncovering trade-offs between overall environmental impacts, sequestration in soil, and dynamic influences on global temperature

In this study, the potential of carbon storage in soil combined with mitigation via bio-based products is investigated for the case of 100 years of hemp cultivation on carbon-vulnerable land (CV-lands) in France. The originality of this study lies in the coupling of soil organic carbon (SOC) simulations (over 100 years of hemp cultivation) with consequential life cycle assessment (LCA) to investigate the mitigation potential of different environmental impacts, and the coupling with dynamic LCA to investigate the long-term effects on global warming. When hemp stems (straw) are left on the ground, SOC increases of 25.8 t ha−1 are observed over 100 years. However, the greenhouse gas (GHG) emissions that result from diverting the initial land use to hemp cultivation cannot be compensated for and, therefore, this scenario cannot mitigate global warming or most other impacts. Two long-lasting product scenarios were studied: insulation boards in buildings and car panels, both involving the production of hemp concrete as co-product. Our study shows that, even though no additional long-term carbon sequestration in soil could be achieved, both scenarios ensured a long-term climate benefit well beyond 2100, mostly because of carbon sequestered in the hemp-based products but also as a result of avoided fossil-based products. Uncertainty analyses reveal that the yield is the most influential parameter, inducing significant uncertainties in all scenarios and most impact categories. According to the overall results obtained, the car panel scenario is the most promising pathway with the lowest environmental impacts and the highest potential for long-term global warming mitigation; this is in part due to the reduction of fuel consumption during the use phase.

Sequestration potential of phytolith occluded carbon in China's paddy rice (Oryza sativa L.) systems

Phytolith-occluded carbon (PhytOC) is resistant to decomposition and, if crop residue biomass is incorporated into soil, has a significant potential for long-term soil carbon sequestration. However, the magnitude and spatial distribution of rice straw PhytOC sequestration remain unclear. Here, we used 279 samplings from nine provinces across China to establish the relationship between soil nutrients availability and rice straw phytoliths concentration, thereby predicting annual PhytOC sequestration of Chinese rice systems. The results suggest that rice straw phytoliths sequester about 0.26 Tg CO2 per yr (8.7 kg CO2 ha−1 yr−1) in China. Great variability of PhytOC exists across the region depending on rice variety. If rice varieties that occluded little PhytOC were replaced by ones with the highest PhytOC concentration, the sequestration rate might be increased to 0.83 Tg CO2 yr−1 (27.7 kg CO2 ha−1 yr−1). The distribution pattern shows that 51% of rice straw PhytOC sequestration can be attributed to the Middle-Lower Yangtze Plain due to its vast rice production. PhytOC sequestration is a crucial mechanism of global biogeochemical carbon sink, and practices such as appropriate fertilization application and selection of rice varieties with higher PhytOC concentration may alleviate climate warming.

Kinetics of C Mineralization of Biochars in Three Excessive Compost-Fertilized Soils: Effects of Feedstocks and Soil Properties

The aim of this work was to compare the carbon (C) mineralization kinetics of three biochars (Formosan ash (Fraxinus formosana Hayata), ash biochar; Makino bamboo (Phyllostachys makino Hayata), bamboo biochar; and lead tree (Leucaena leucocephala (Lam.) de. Wit), lead tree biochar) applied with two addition rates (2 and 5 wt %) in three excessive compost-fertilized (5 wt %) soils (one Oxisols and two Inceptisols), and to ascertain the increasing or decreasing effect of biochar and soil type in the presence of excessive compost. The study results of 400 days incubation indicated that, in general, the potential of the three biochars for C sequestration is similar in the three studied soils. The presence of excessive compost stimulated the co-mineralization of the more labile components of biochar over the short term (first two months). The potential of biochar addition for neutralizing soil pH and regulating the release of Al from soil for preserving soil organic carbon (SOC) might be the important mechanisms in biochar-compost interactions, especially in the presence of excessive compost. Overall, 5% application rate of three high temperature-pyrolysis biochars showed the less detriments to studied soils. In these incubations of biochar, excessive compost, and soil, it is a decreasing effect overall, that is, the enhanced storage of both biochar-C and SOC, which is expected as a long-term carbon sequestration in soil. The recorded direction and magnitude of effect, both are strongly influenced by biochar and soil type. When co-applied with excessive compost, the negative (reducing CO2 release) effect with increasing biochar application rates was eliminated.

Physico-hydraulic properties of sugarcane bagasse-derived biochar: the role of pyrolysis temperature

The study of biochar properties has received increasing attention by the scientific community in recent years. This study aimed to identify the most environmentally-relevant physico-hydraulic characteristics of slow-pyrolysis sugarcane bagasse-derived biochar prepared at temperatures of 300 (BC300), 400 (BC400), 500 (BC500), and 600 °C (BC600) and comparing the properties to those of the sugarcane bagasse (BG). The real density (RD) of biochar samples significantly increased from 1.42 to 1.64 g cm−3 as pyrolysis temperature increased from 300 to 600 °C. BG and BC600 showed the lowest and the highest N2 adsorption, specific surface area, total pore volume, microporosity, and adsorption energy, respectively. The average pore diameter of resultant biochars decreased with increasing pyrolysis temperature. The adsorption behavior of biochars was more like mesoporous materials, and the hysteresis effect increased with raising the pyrolysis temperature. Biochars were hydrophilic and were able to immediately absorb water, while BG showed hydrophobic properties with contact-angle (θ) of 107.6°, ninety-degree surface tension (γ90°) of 35.0 mN m−1 and solid–air surface tension (γs) of 8.7 mN m−1. The pore-size-distribution (PSD) curve based on water adsorption data gives clearly better results about large PSD responsible for water and solute transport than N2 adsorption. Thereby, it seems that high RD biochars may have high residency time and be more suitable for carbon-sequestration purposes. Biochar produced at low temperature (BC300) may improve nutrient-availability and crop productivity in acidic/alkaline soils, whereas high-temperature (BC600) may enhance long-term soil carbon-sequestration. Biochars produced at intermediate temperature (BC400 and MC500) seems be better in improvement of soil hydraulic properties associated with plant growth.

Determining organo-chemical composition of sugarcane bagasse-derived biochar as a function of pyrolysis temperature using proximate and Fourier transform infrared analyses

New research findings on biochar applications attracted considerable international attention as it offers environmentally sustainable solutions. This paper has focused on identifying the most important organo-chemical characteristics of slow pyrolysis bagasse-derived biochar as a function of pyrolysis temperature using proximate and Fourier transform infrared analysis. Therefore, a biochar thermosequence was produced by the pyrolysis of biomasses at 300, 400, 500, and 600 °C in a carbonization furnace. Organo-chemical transformations of biomasses during heating were followed by using chemical, proximate, and Fourier transform infrared (FTIR) analysis. The results can be summarized as follows. (1) Mass loss on ignition and oxidizable organic carbon content, respectively, decreased from 81.13 to 56.22% and 33.31 to 17.05% with increasing pyrolysis temperature from 300 to 600 °C. (2) The molar ratios of O/C, N/C, and H/C tended to decrease with increasing pyrolysis temperature. (3) Aromaticity equivalent (Xc) increased from 2.44 to 2.59 with increasing pyrolysis temperature from 300 to 600 °C. (4) The results of FTIR spectroscopy introduced the 1800–1100 cm−1 zone, related to oxygenated functional groups (OFGs), as region with most marked differences. (5) Results revealed an increase in the point of zero charge (pHpzc) with increasing pyrolysis temperature, indicating a decrease in the acidic OFGs and increase in the basic functionality. (6) Total acid functional groups concentration decreased from 9 to 5.8 mmol g−1 (based on Boehm titration) as the pyrolysis temperature decreased from 600 to 300 °C, while total basic functional groups concentration increased from 0.8 to 4.1 mmol g−1. (7) The cation exchange capacity, determined using NH4+ exchange, increased from nearly 18 to 105 cmolc kg−1 biochar as the pyrolysis temperature increased from 300 to 600 °C. In general, biochar produced at low temperature (< 500 °C) may improve nutrient availability and crop productivity in acidic and alkaline soils and also be suitable for removal of inorganic pollutants, whereas high-temperature biochar (≥ 500 °C) may enhance long-term soil carbon sequestration and also be suitable for removal of organic pollutants.

Dynamics of soil organic carbon (SOC) content in stands of Norway spruce (Picea abies) in central Europe

Abstract: Norway spruce is the main forest tree species in the Czech Republic. Until now, little attention has been given in the literature to the dynamics of soil organic carbon (SOC) content under Norway spruce stands as a function of stand characteristics. The aim of this study is to estimate soil organic carbon (SOC) content and stock changes in organic and surface mineral soil horizons on forest sites with a dominant representation of Norway spruce. In the study area, a significantly higher content of SOC was found in the surface mineral soil horizon than in the organic soil horizon. In both soil horizons, there was evidence of an increasing trend of SOC with the increasing age of forest stands, a decreasing trend of SOC with increasing density of stocking and an increasing trend of SOC with increasing altitude. The relationship of SOC content with soil group (Podzol vs. non-Podzol) has also been demonstrated. The greatest potential for long-term carbon sequestration in soils was shown in older stands (101-190 years) dominated by Norway spruce with lower density of stocking, located in forest vegetation zones (altitude range: 1010-1225 m a.s.l.) where natural mountain Norway spruce forests currently occur. According to our results, Norway spruce stands may perform a stable function of carbon sequestration in the soil at these sites, especially in the mineral soil horizon.

Soil organic carbon content affects the stability of biochar in paddy soil

Recalcitrant biochar application appears to be a promising method to decelerate global warming through increasing long-term carbon sequestration in soil. Stability of biochar carbon (C), which is the major determining factor of C sequestration effect, depends mainly on biochar physiochemical characteristics and soil properties. However, little is known about biochar C stability in paddy soil. In this study, 13C labeled rice straw (RS) biochar produced at 500°C was incubated with five types of paddy soils to determine the key soil characteristics involved in biochar-C stability. Results showed that cumulative mineralization rates of RS biochar-C incubated with different paddy soils were relatively low (0.17–0.28%) during 390days of incubation. The cumulative mineralization rates of RS biochar-C increased with the increasing native soil total organic carbon (TOC) content. The estimated mean residence time (MRT) of stable C components of RS biochar in paddy soil, varying from 617 to 2829 years, decreased with the increase of soil TOC content. In addition, greater atomic O/C ratio and oxygen-containing functional groups were observed in biochar samples incubated in paddy soils with higher TOC content. These results suggest that RS biochar application could be an effective method for C sequestration in paddy soil. However, the stability of RS biochar in paddy soil would be significantly impacted by soil TOC content. From the perspective of long-term C sequestration, RS biochar is more suitable for applying in paddy soils with lower TOC content.

Biochar Treatment Resulted in a Combined Effect on Soybean Growth Promotion and a Shift in Plant Growth Promoting Rhizobacteria.

The application of biochar to soil is considered to have the potential for long-term soil carbon sequestration, as well as for improving plant growth and suppressing soil pathogens. In our study we evaluated the effect of biochar on the plant growth of soybeans, as well as on the community composition of root-associated bacteria with plant growth promoting traits. Two types of biochar, namely, maize biochar (MBC), wood biochar (WBC), and hydrochar (HTC) were used for pot experiments to monitor plant growth. Soybean plants grown in soil amended with HTC char (2%) showed the best performance and were collected for isolation and further characterization of root-associated bacteria for multiple plant growth promoting traits. Only HTC char amendment resulted in a statistically significant increase in the root and shoot dry weight of soybeans. Interestingly, rhizosphere isolates from HTC char amended soil showed higher diversity than the rhizosphere isolates from the control soil. In addition, a higher proportion of isolates from HTC char amended soil compared with control soil was found to express plant growth promoting properties and showed antagonistic activity against one or more phytopathogenic fungi. Our study provided evidence that improved plant growth by biochar incorporation into soil results from the combination of a direct effect that is dependent on the type of char and a microbiome shift in root-associated beneficial bacteria.

Toward a functional integration of anaerobic digestion and pyrolysis for a sustainable resource management. Comparison between solid-digestate and its derived pyrochar as soil amendment

The integration of different technologies acts as a leverage in boosting “circular economy” and improving resource use efficiency. In this respect, the coupling of anaerobic digestion with pyrolysis was the focus of this work. Solid-digestate obtained from anaerobic digestion was addressed to supply pyrolysis thus increasing the net energy gains and obtaining “biochar” (called “pyrochar” in our case) to be used as soil amendment alternatively to solid-digestate. The current interest on biochar is linked to its long-term soil carbon sequestration, thus contributing to global warming mitigation.A parallel detailed screening of the physical and chemical properties of both solid-digestate and pyrochar was performed, inferring their effects on soil quality. Results showed that while P and K are enriched in pyrochar, total N showed no significant differences. Heavy metals revealed higher concentrations in pyrochar, but always largely below the biochar quality thresholds. Pyrochar exhibited a higher surface area (49–88m2g−1), a greater water holding capacity (352–366%), and a more recalcitrant carbon structure. Both solid-digestate and pyrochar showed good soil amendments properties but with complementary effects. Although starting from the same biomass, being the original feedstock processed differently, their ability to improve the physical and chemical soil properties has proved to be different. While several other soil improvers of organic origin can substitute digestate, the important role played by biochar appears not-replaceable considering its precious “carbon negative” action.

The promise [and uncertainties] of Biochar

The promise [and uncertainties] of Biochar

Assessing humification and organic C compounds by laser-induced fluorescence and FTIR spectroscopies under conventional and no-till management in Brazilian Oxisols

Data on humification is important to assessing the rate and magnitude of soil carbon (C) sequestration. Thus, this study assessed the humification degree (HLIF) of soil organic matter (SOM) and the changes in functional C groups (aromatic-C and aliphatic-C) for contrasting land use and management practices (native vegetation (NV), conventional plow-based tillage (CT) and no-till (NT) systems) in sub-tropical and tropical Brazilian environments. Experiments were conducted at Ponta Grossa (PG) in Paraná State and Lucas do Rio Verde (LRV) in Mato Grosso State of Brazil. Laser-induced fluorescence (LIFS) and Fourier-transform infrared (FTIR) spectroscopies, were used on whole soil samples to 1-m depth, and on seven aggregate size classes (8–19, 4–8, 2–4, 1–2, 0.5–1, 0.25–0.5, 0.053–0.25mm) obtained by wet sieving of 0–5 and 5–10cm layers. Three functional C groups were selected based on FTIR: aliphatic-C1 (1404cm−1), aromatic-C (1632cm−1), and aliphatic-C2 (2852 and 2922cm−1). The HLIF was 3 to 5 times higher at the LRV site than at PG at all soil depths, indicating that selective preservation by aromaticity of SOM is the predominant mechanism in this environment. Relatively lower HFIL was observed in NT soils at both locations because of aggregation which protects most labile moieties. The depletion of C concentration in CT was related to the decrease in functional C groups (i.e., aromatic-C and aliphatic-C) and an overall increase in the humification degree, indicating that physical protection mechanisms are not sufficient to protect the labile fractions of OM. In contrast, the intensity of functional C groups under NT systems was similar to that in the soil under NV at both locations. A discriminant analysis of principal components clearly showed that soils at both locations can be clustered into three groups, corresponding to the three main land-use and management practices. Thus, soils under NV, NT, and CT differed significantly in terms of the composition of organic compounds, and in the interactions between inorganic and organic fractions. Land use changes modify the arrangement of organic compounds necessitating the diversification of agroecosystems and conversion to NT farming. Altogether, our results reveal that LIFS and FTIR are fast, efficient, and precise techniques for analyzing the degree of SOC humification, functional C groups, and hence the efficiency of NT cropping systems in promoting long-term carbon sequestration in soils.

Pesticide leaching from two Swedish topsoils of contrasting texture amended with biochar

The use of biochar as a soil amendment has recently increased because of its potential for long-term soil carbon sequestration and its potential for improving soil fertility. The objective of this study was to quantify the effects of biochar soil incorporation on pesticide adsorption and leaching for two Swedish topsoils, one clay soil and one loam soil. We used the non-reactive tracer bromide and the pesticides sulfosulfuron, isoproturon, imidacloprid, propyzamid and pyraclostrobin, substances with different mobility in soil. Adsorption was studied in batch experiments and leaching was studied in experiments using soil columns (20 cm high, 20 cm diameter) where 0.01 kg kg(-1) dw biochar powder originating from wheat residues had been mixed into the top 10 cm. After solute application the columns were exposed to simulated rain three times with a weekly interval and concentrations were measured in the effluent water. The biochar treatment resulted in significantly larger adsorption distribution coefficients (Kd) for the moderately mobile pesticides isoproturon and imidacloprid for the clay soil and for imidacloprid only for the loam soil. Relative leaching of the pesticides ranged from 0.0035% of the applied mass for pyraclostrobin (average Kd=360 cm3 g(-1)) to 5.9% for sulfosulfuron (average Kd=5.6 cm3 g(-1)). There were no significant effects of the biochar amendment on pesticide concentrations in column effluents for the loam soil. For the clay soil concentrations were significantly reduced for isoproturon, imidacloprid and propyzamid while they were significantly increased for the non-mobile fungicide pyraclostrobin suggesting that the transport was facilitated by material originating from the biochar amendment.

The effects of biochar on the physical properties of bare soil

ABSTRACTThe pyrolysis conversion of vegetable residues into energy and biochar, and its incorporation in agricultural soil, reduces CO2emission and provides a longterm soil carbon sequestration. Moreover, biochar application in soil seems to increase nutrient stocks in the rooting layer, improving crop yield. Compared with the numerous studies assessing the positive effect of biochar on yield, however, little research has been published elucidating the mechanisms responsible for the reported benefits. Few studies cited soil moisture as the key factor, attributing the increased yield to the higher soil water availability.The aim of this study was to investigate the effect of biochar on the physical and hydraulic properties of a bare Padana Plain (Cadriano, Bologna) agricultural soil. A preliminary plot experiment in 2009 explored the influence of 10 and 30 kg ha–1of biochar on soil moisture, without effects from plants. Results of the first experiment suggested using higher biochar rates in a similar experimental scheme. During the second experiment, 30 and 60 t ha–1doses were investigated. Soil water content, bulk density, electrical conductivity and soil water retention were measured. The comparison between treated soils and the control indicates that the biochar rate is directly correlated to electrical conductibility and inversely correlated with bulk density. The effect on the density of soil can be very positive in case of heavy soils. The dark colour of the char increased the surface temperature with respect to the control, while no differences were detected at 7·5 cm depth. No influences were found on other soil characteristics, including soil pH, moisture and water retention.

Carbon exchange by establishing biofuel crops in Central Illinois

Perennial grass biofuels may contribute to long-term carbon sequestration in soils, thereby providing a broad range of environmental benefits. To quantify those benefits, the carbon balance was investigated over three perennial grass biofuel crops – miscanthus ( Miscanthus × giganteus), switchgrass ( Panicum virgatum) and a mixture of native prairie plants – and a row crop control (maize–maize–soy) in Central Illinois, USA, during the establishment phase of the perennial grasses (2008–2011). The eddy covariance technique was used to calculate fluxes of carbon dioxide and energy balance components, such as latent and sensible heat fluxes. Whereas maize attained the highest maximal carbon uptake rates, the perennial grasses had significantly extended growing seasons, such that their total carbon uptake rivaled that of corn in the second growing season and greatly exceeded that of soy in the third growing season. To account for the removal of carbon through harvest, net ecosystem exchange of carbon (NEE) was combined with estimates of yields, resulting in the net ecosystem carbon balance (NECB). After 2.5 years, NECB for the maize/soybean plot was positive (a source of carbon), while the grasses were a sink of carbon. Continuous measurements over the next years are required in order to confirm whether miscanthus, switchgrass and prairie can sustain a long-term sink of carbon if managed for biofuels, i.e., if harvested annually.