Biochar and Organic Fertilizer Co-Application Enhances Soil Carbon Priming, Increasing CO2 Fluxes in Two Contrasting Arable Soils

Biochar soil amendments, along with non-tillage agriculture, are often proposed as a strategy for carbon sequestration. It is still questionable how the quality of biochar might influence the priming effect on soil organic matter and whether the addition of unprocessed organic amendments will affect biochar stability. In the study, six different biochars and three exogenous organic matter sources were added to two distinct arable soils. CO2 emission was monitored for 100 days of incubation and CO2 flux was estimated. Results showed that biochar increased soil CO2 fluxes. The highest peaks, up to 162 µg C-CO2 h-1 100 g-1, were recorded in treatments with food waste biochars, suggesting that they serve as a source of easily available carbon to soil microbes. Co-application of raw organic materials (manure and fresh clover biomass) enhanced CO2 emission and carbon losses, especially in sandy soil, where 0.85-1.1% of total carbon was lost in the short-term experiment. Biochar properties and content of labile C can stimulate CO2 emission; however, in a long-term period, this contribution is negligible. The findings of our study showed that more attention should be paid to priming effects caused by the addition of exogenous organic matter when applied to biochar-amended soils.

Deashed Wheat-Straw Biochar as a Potential Superabsorbent for Pesticides

Biochar activation methods have attracted extensive attention due to their great role in improving sorptive properties of carbon-based materials. As a result, chemically modified biochars gained application potential in the purification of soil and water from xenobiotics. This paper describes changes in selected physicochemical properties of high-temperature wheat-straw biochar (BC) upon its deashing. On the pristine and chemically activated biochar (BCd) retention of five pesticides of endocrine disrupting activity (carbaryl, carbofuran, 2,4-D, MCPA and metolachlor) was studied. Deashing resulted in increased sorbent aromaticity and abundance in surface hydroxyl groups. BCd exhibited more developed meso- and microporosity and nearly triple the surface area of BC. Hydrophobic pesticides (metolachlor and carbamates) displayed comparably high (88-98%) and irreversible adsorption on both BCs, due to the pore filling, whereas the hydrophilic and ionic phenoxyacetic acids were weakly and reversibly sorbed on BC (7.3 and 39% of 2,4-D and MCPA dose introduced). Their removal from solution and hence retention on the deashed biochar was nearly total, due to the increased sorbent surface area and interactions of the agrochemicals with unclogged OH groups. The modified biochar has the potential to serve as a superabsorbent, immobilizing organic pollutant of diverse hydrophobicity from water and soil solution.

Characterization and Sodium Cations Sorption Capacity of Chemically Modified Biochars Produced from Agricultural and Forestry Wastes

Excessive amounts of sodium cations (Na⁺) in water is an important limiting factor to reuse poor quality water in agriculture or industry, and recently, much attention has been paid to developing cost-effective and easily available water desalination technology that is not limited to natural resources. Biochar seems to be a promising solution for reducing high loads of inorganic contaminant from water and soil solution, and due to the high availability of biomass in agriculture and forestry, its production for these purposes may become beneficial. In the present research, wheat straw, sunflower husk, and pine-chip biochars produced at 250, 450 and 550 °C under simple torrefaction/pyrolysis conditions were chemically modified with ethanol or HCl to determine the effect of these activations on Na sorption capacity from aqueous solution. Biochar sorption property measurements, such as specific surface area, cation exchange capacity, content of base cations in exchangeable forms, and structural changes of biochar surface, were performed by FTIR and EPR spectrometry to study the effect of material chemical activation. The sorption capacity of biochars and activated carbons was investigated by performing batch sorption experiments, and adsorption isotherms were tested with Langmuir's and Freundlich's models. The results showed that biochar activation had significant effects on the sorption characteristics of Na⁺, increasing its capacity (even 10-folds) and inducing the mechanism of ion exchange between biochar and saline solution, especially when ethanol activation was applied. The findings of this study show that biochar produced through torrefaction with ethanol activation requires lower energy demand and carbon footprint and, therefore, is a promising method for studying material applications for environmental and industrial purposes.

Wheat Straw Biochar as a Specific Sorbent of Cobalt in Soil

There is an urgent need to search for new sorbents of pollutants presently delivered to the environment. Recently biochar has received much attention as a low-cost, highly effective heavy metal adsorbent. Biochar has been identified as an efficient material for cobalt (Co) immobilization from waters; however, little is known about the role of Co immobilization in soil. Hence, in this study, a batch experiment and a long-term incubation experiment with biochar application to multi-contaminated soil with distinct properties (sand, loam) were conducted to provide a brief explanation of the potential mechanisms of Co (II) sorption on wheat straw biochar and to describe additional processes that modify material efficiency for metal sorption in soil. The soil treatments with 5% (v/w) wheat straw biochar proved to be efficient in reducing Co mobility and bioavailability. The mechanism of these processes could be related to direct and indirect effects of biochar incorporation into soil. The FT-IR analysis confirmed that hydroxyl and carboxyl groups present on the biochar surface played a dominant role in Co (II) surface complexation. The combined effect of pH, metal complexation capacity, and the presence of Fe and Mn oxides added to wheat straw biochar resulted in an effective reduction of soluble Co (II), showing high efficiency of this material for cobalt sorption in contaminated soils.

Residues of Persistent Organic Pollutants (POPs) in Agricultural Soils Adjacent to Historical Sources of Their Storage and Distribution-The Case Study of Azerbaijan

The aim of this study was to identify and examine the levels of organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) in soil collected from the surroundings of historical pesticide storage facilities on former agricultural aerodromes, warehouses, and pesticide distribution sites located in the most important agricultural regions in Azerbaijan. The conducted research included determination of three groups of POPs (occurring together), in the natural soil environment influenced for many years by abiotic and biotic factors that could have caused their transformations or decomposition. In this study, soil samples were collected in 21 georeferenced points located in the administrative area of Bilasuvar, Saatly, Sabirabad, Salyan and Jalilabad districts of Azerbaijan. Soil chemical analysis involved determination of organochlorine compounds (OCP): hexachlorocyclohexanes (HCHs) (three isomers α-HCH, β-HCH and γ-HCH) and dichlorodiphenyltrichloroethanes (DDTs) (six congeners 2,4'DDT; 4,4'DDT; 2,4'DDE; 4,4'DDE; 2,4'DDE; and 4,4'DDE); polycyclic aromatic hydrocarbons (PAHs): 16 compounds from the United States Environmental Protection Agency US EPA list and, PCBs (seven congeners identified with the following IUPAC numbers: 28, 52, 101, 118, 138, 153, and 180). Our research showed that OCPs reached the highest concentration in the studied areas. The total concentrations of OCPs ranged from 0.01 to 21,888 mg∙kg^-1 with significantly higher concentrations of Σ6DDTs (0.01 μg kg^-1 to 21880 mg kg^-1) compared to ΣHCH (0.14 ng kg^-1 to 166.72 µg kg^-1). The total concentrations of PCBs in the studied soils was varied from 0.02 to 147.30 μg·kg^-1 but only PCB138 and PCB180 were detected in all analyzed samples. The concentrations of Σ16 PAHs were also strongly diversified throughout the sampling areas and ranged from 0.15 to 16,026 mg kg^-1. The obtained results confirmed that the agricultural soils of Azerbaijan contained much lower (up to by three orders of magnitude) concentrations of PCBs and PAHs than DDT. It is supported by the fact that PCBs and PAHs were not directly used by agriculture sector and their content results from secondary sources, such as combustion and various industrial processes. Moreover, the high concentrations of PAHs in studied soils were associated with their location in direct neighborhood of the airport, as well as with accumulation of contaminants from dispersed sources and long range transport. The high concentrations of pesticides confirm that deposition of parent OCPs have occurred from obsolete pesticide landfills.

Risk assessment of low-temperature biochar used as soil amendment on soil mesofauna

Biochar as a carbon-rich highly porous substance has been proposed for use in agriculture and horticulture as a soil amendment. One of the main concerns of this application of biochar is its potential contamination with heavy metals (HMs) and polycyclic aromatic hydrocarbons. The aim of this research was to access the environmental risk of biochar used as a soil amendment on soil mesofauna (mites and springtails). We conducted both field and laboratory experiments with the use of wood-chip biochar from low-temperature (300 °C) flash pyrolysis. Biochar was free from polycyclic aromatic hydrocarbons (PAH), and the concentration of all tested toxic compounds was very low or even under the level of detection. Both the results of field and laboratory studies show no toxic effects on soil mesofauna. In the field studies, the biochar application of 50 t/ha in maize and oilseed rape crops significantly increased the mean number of mesofauna. This change probably resulted from improved soil chemical properties (in particular organic carbon content and cation exchange capacity) upon biochar addition. The results of the avoidance test with the use of springtail species Folsomia candida showed the possible short-term toxicity risk from a dose of 5%. The results of the reproduction test indicate the negative response of F. candida from the rate of 25% (higher than the field dose, which corresponds to 10% in laboratory tests). The reason for the short-term toxicity might be the considerable increase in soil pH after biochar addition. To our knowledge, this is the first study that has looked so widely into the effect of biochar on soil mesofauna. We encourage further studies into the risk assessment of biochar on soil organisms in both a controlled laboratory environment and in the open field.

Lead isotopes and heavy minerals analyzed as tools to understand the distribution of lead and other potentially toxic elements in soils contaminated by Cu smelting (Legnica, Poland)

Surroundings of the Legnica Cu smelter (Poland) offer insight into the behavior of Pb and other metal(oid)s in heavily contaminated soils in a relatively simple site, where lithogenic and anthropogenic Pb contributions have uniform Pb isotope composition over the time of smelter activity. Distribution of metal(oid)s decreases asymptotically with depth and below 30 cm reaches concentrations typical or lower than those of upper continental crust. Usually, such distribution is interpreted as the decrease in anthropogenic Pb contribution with depth. However, calculations based on Pb isotopes indicate that anthropogenic Pb is probably distributed both as Pb-rich particles of slags and fly ashes and Pb-poor soil solutions. Generally, anthropogenic Pb constitutes up to 100 % of Pb in the uppermost 10 cm of the soils and comes often from mechanical mixing with slag and fly ash particles as well as their weathering products. On the other hand, lower soil horizon contains anthropogenic Pb in various forms, and at depths below 30 cm, most of anthropogenic Pb comes from soil solutions and can constitute from 1 to 65 % of the Pb budget. This is consistent with secondary electron microscope (SEM) analyses of heavy mineral particles showing that, in upper horizons, Pb, Cu, and Zn are contained in various particles emitted from the smelter, which show different stages of weathering. Currently, large portion of these metals may reside in the secondary Fe-hydro-oxides. On the other hand, in deeper soil horizons, anthropogenic Pb is probably dominated by Pb coming from leaching of slag or fly ash particles. Overall, metal(oid) mobility is a dynamic process and is controlled by the soil type (cultivated versus forest) and the composition and the structure of the metal-rich particles emitted from the smelter. High proportions of anthropogenic Pb at depths below 30 cm in some soil profiles indicate that Pb (and probably other metal(oid)s) can be transported down the soil profile and the present concentration of anthropogenic Pb depends on the availability of binding sites.