Seiji Shimoda

Rapid change in soil C storage associated with vegetation recovery after cessation of cultivation

The total area of abandoned and fallow agricultural fields in Japan has been increasing annually. The change in agricultural land use can alter belowground carbon (C) stocks associated with changes in the types of plant species. The aim of this study was to investigate how the cessation of cultivation influenced the soil C storage in former agricultural fields. The study sites were previously used for rice (Poaceae, Oriza sativa L.) and wheat (Poaceae, Triticum L.) cultivation, and fallow management practices had been in effect for three years under three different conditions: two treatments involved mowing and either leaving the plant residue on the ground or removing the plant residue, while the third treatment involved simply abandoning the field. We found that the former paddy site invaded by rhizomatous perennial grasses had significantly higher soil C storage compared to former upland fields that was dominated by annual grass species. The cessation of cultivation increased soil C storage by about 1.3 times in former paddies, and decreased the content by 0.83–0.91 times in former uplands. The three-year total belowground production was 2.0–4.7 times greater in former paddies than former uplands for each management condition, suggesting that lower C input from the annual grasses caused a loss in soil C at the upland fields. Aboveground biomass removal of the perennial grasses strongly reduced C input, whereas the C input from their high belowground production led to the significant increases of soil C storage near the surface of the former paddies. Our studies indicate that high belowground productivity of perennial grasses can increase soil C storage after the cessation of cultivation.

Differences in CO2 and N2O emission rates following crop residue incorporation with or without field burning: A case study of adzuki bean residue and wheat straw

Abstract In the context of sustainable soil-quality management and mitigating global warming, the impacts of incorporating raw or field-burned adzuki bean (Vigna angularis (Willd.) Ohwi & Ohashi) and wheat (Triticum aestivum L.) straw residues on carbon dioxide (CO2) and nitrous oxide (N2O) emission rates from soil were assessed in an Andosol field in northern Japan. Losses of carbon (C) and nitrogen (N) in residue biomass during field burning were much greater from adzuki bean residue (98.6% of C and 98.1% of N) than from wheat straw (85.3% and 75.3%, respectively). Although we noted considerable inputs of carbon (499 ± 119 kg C ha–1) and nitrogen (5.97 ± 0.76 kg N ha–1) from burned wheat straw into the soil, neither CO2 nor N2O emission rates from soil (over 210 d) increased significantly after the incorporation of field-burned wheat straw. Thus, the field-burned wheat straw contained organic carbon fractions that were more resistant to decomposition in soil in comparison with the unburned wheat straw. Our results and previously reported rates of CO2, methane (CH4) and N2O emission during wheat straw burning showed that CO2-equivalent greenhouse gas emissions under raw residue incorporation were similar to or slightly higher than those under burned residue incorporation when emission rates were assessed during residue burning and after subsequent soil incorporation.

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 biochars 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.