Comparison of plant Cd accumulation from a Cd-contaminated soil amended with biochar produced from various feedstocks.

The bioavailability of cadmium (Cd) in agricultural soils is a significant health concern due to the potential risk of human exposure via foods grown in Cd-contaminated fields. Biochar has been known to have a highly porous structure and high pH, as well as containing various functional groups; as such, it can immobilize heavy metals. Although it has found that biochar amendment in Cd-contaminated agricultural soils could be effective in reducing Cd bioavailability in previous studies, differences in plant Cd accumulation from Cd-contaminated soils amended with biochars produced from various types of biomass have not been fully discussed yet; we aimed to address this shortcoming in the present work. The soil investigated was an acid soil (pH 5.1) and had an elevated concentration of Cd (total Cd: 3.3 mg kg-DW-1). Six kinds of biochar were produced, i.e., from woodchips (Japanese cedar [CE] and Japanese cypress [CY]), moso bamboo (MB), rice husk (RH), poultry manure (PM), and wastewater sludge (WS), at a pyrolysis temperature of 600 °C. Biochars were incorporated into the Cd-contaminated soil at 3% (w/w) and pot experiments using Brassica rapa var. perviridis were conducted for 28 days in a growth chamber. The Cd concentrations in the above-ground portion of the plants were significantly decreased as a result of the incorporation of all biochars compared to the unamended soil, with reduction ratios following the order PM (78%) > > WS (31%) ≈ RH (29%) ≈ MB (28%) ≈ CY (26%) > CE (19%). Among all biochar-amended soils, soil pH and shoot biomass were highest for those amended with PM-derived biochar. These results suggest that in Cd-contaminated soils, PM-derived biochar may offer significant potential in reducing plant Cd accumulation due to the immobilization of soil Cd and an effect of dilution resulting from enhanced plant shoot biomass.

The Preliminary Study of Water-Retention Related Properties of Biochar Produced from Various Feedstock at Different Pyrolysis Temperatures.

Physicochemical properties of biochar, which are used as a soil amendment material in agricultural fields, are different depending on biomass feedstock and pyrolysis processes. In this study, we evaluated the influence of feedstock type and pyrolysis temperature on the water-retention related properties of biochar. Wood-chips [cedar (CE) and cypress (CY)]; moso bamboo (MB); rice husk (RH); sugarcane bagasse (SB); poultry manure (PM) and agricultural wastewater sludge (WS) were each pyrolysed at 400, 600 and 800 °C with a retention time of two hours. Scanning electron microscopy micrographs (SEM), hydrophobicity indices, pore-size distribution measured by mercury-intrusion porosimetry, water-retention curves (WRCs) and plant-available water capacities (AWCs) of the biochars were measured to evaluate their potentials as soil-amendment materials for improving soils' water-retention. As the pyrolysis temperature was increased, the hydrophobicity index decreased. On the other hand, pyrolysis temperature did not affect the distribution of micrometre-range pores, which are useful for plant-available water, of biochars. The AWCs of the biochars formed from CE, CY and SB were greater than those produced from other feedstocks, at 600 and 800 °C. Therefore, we can suggest that the biochars derived from wood-chips (CE and CY) and SB have greater potential for enhancing soils' water-retention.

Optimum soil frost depth to alleviate climate change effects in cold region agriculture.

On-farm soil frost control has been used for the management of volunteer potatoes (Solanum tuberosum L.), a serious weed problem caused by climate change, in northern Japan. Deep soil frost penetration is necessary for the effective eradication of unharvested small potato tubers; however, this process can delay soil thaw and increase soil wetting in spring, thereby delaying agricultural activity initiation and increasing nitrous oxide emissions from soil. Conversely, shallow soil frost development helps over-wintering of unharvested potato tubers and nitrate leaching from surface soil owing to the periodic infiltration of snowmelt water. In this study, we synthesised on-farm snow cover manipulation experiments to determine the optimum soil frost depth that can eradicate unharvested potato tubers without affecting agricultural activity initiation while minimising N pollution from agricultural soil. The optimum soil frost depth was estimated to be 0.28-0.33 m on the basis of the annual maximum soil frost depth. Soil frost control is a promising practice to alleviate climate change effects on agriculture in cold regions, which was initiated by local farmers and further promoted by national and local research institutes.

Biochar Impacts on Crop Productivity and Greenhouse Gas Emissions from an Andosol.

To assess the impacts of biochar application on crop productivity and global warming mitigation, a 4-yr field experiment was conducted in a well-drained Andosol in northern Japan. Wood residue-derived biochar (pyrolyzed at >800°C) was applied at rates of 0, 10, 20, and 40 Mg ha for potatoes, winter wheat, sugar beet, and soybeans cultivated in rotation, and CO, NO, and CH emissions from the soil and yield and quality of the harvested materials were measured. Biochar application, regardless of rate, had no significant impact on yield and quality of the harvested materials, except for soybean grain yield. It also had no effect on cumulative CO, NO, and CH emissions from the soil. Andosols are inherently highly porous, and biochar application increased soil porosity only at the highest amendment level. The small changes in soil properties and the recalcitrance of the biochar's C components probably account for the unchanged soil-associated greenhouse gas emissions and the minimal impact on crop yield and quality. Because soil CO emission was not increased, the net ecosystem C budget during the study period increased with the rate of biochar application from -3.55 ± 0.19 Mg C ha without biochar application to 4.89 ± 0.46, 13.4 ± 0.3, and 29.9 ± 0.4 Mg C ha at application rates of 10, 20, and 40 Mg ha, respectively; therefore, application of wood residue-derived biochar to an Andosol has great potential for mitigating global warming through enhanced soil C sequestration without sacrificing crop productivity.