Gil Won Kim

Evaluation of rice root oxidizing potential using digital image analysis

Abstract The aerenchymal transport of oxygen to rice roots has significantly influenced the anaerobic root zone of flooded paddy soils. Therefore, the visualization of redox dynamics may be useful to characterize rice root oxidation potentials and the dynamics of redox-influenced ions in the root zone of paddy soils. In order to investigate the interaction between root oxidation potential and Fe uptake of (a) six different rice cultivars (Oryza sativa L.; Chuchung, Dongjin, Ilmi, Junam, Nampyeong, and Samkwang) were monitored in a flooded paddy soil with the aid of rhizotron experiment throughout the vegetation period, (b) digital images of the root zone were taken at the important growing stages, and (c) rice Fe uptake was characterized simultaneously. The images were processed by image analysis to display the reduction and oxidation areas in the root zones, and the distinct areas which were colorized due to varying soil redox changes were localized and quantified. Oxidized areas were mainly observed in the surrounding active roots and in a distinct layer on the soil surface. The selected rice cultivars have shown significantly different root-oxidized areas at the same rice growing stage. Root-oxidized area was significantly and positively correlated with total Fe content of rice root, but negatively correlated with the inner root Fe content. Rice cultivars having higher root oxidation potential precipitated more Fe on the outer root surface in the form of Fe plaques. In conclusion, digital image analysis is an effective tool for evaluating the oxidizing potential of rice root under anaerobic soil condition.

Beneficial effect of compost utilization on reducing greenhouse gas emissions in a rice cultivation system through the overall management chain

Livestock manure application can stimulate greenhouse gas (GHG) emissions, especially methane (CH4) in rice paddy. The stabilized organic matter (OM) is recommended to suppress CH4 emission without counting the additional GHG emission during the composting process. To evaluate the effect of compost utilization on the net global warming potential (GWP) of a rice cropping system, the fluxes of GHGs from composting to land application were calculated by a life cycle assessment (LCA) method. The model framework was composed of GHG fluxes from industrial activities and biogenic GHG fluxes from the composting and rice cultivation processes. Fresh manure emitted 30MgCO2-eq.ha-1, 90% and 10% of which were contributed by CH4 and nitrous oxide (N2O) fluxes, respectively, during rice cultivation. Compost utilization decreased net GWP by 25% over that of the fresh manure during the whole process. The composting process increased the GWP of the industrial processes by 35%, but the 60% reduction in CH4 emissions from the rice paddy mainly influenced the reduction of GWP during the overall process. Therefore, compost application could be a good management strategy to reduce GHG emissions from rice paddy systems.

Stimulation of methane oxidation potential and effects on vegetation growth by bottom ash addition in a landfill final evapotranspiration cover.

The landfilling of municipal solid waste is a significant source of atmospheric methane (CH4), contributing up to 20% of total anthropogenic CH4 emissions. The evapotranspiration (ET) cover system, an alternative final cover system in waste landfills, has been considered to be a promising way to mitigate CH4 emissions, as well as to prevent water infiltration using vegetation on landfill cover soils. In our previous studies, bottom ash from coal-fired power plants was selected among several industrial residues (blast furnace slag, bottom ash, construction waste, steel manufacture slag, stone powder sludge, and waste gypsum) as the best additive for ET cover systems, with the highest mechanical performance achieved for a 35% (wtwt(-1)) bottom ash content in soil. In this study, to evaluate the field applicability of bottom ash mixed soil as ET cover, four sets of lysimeters (height 1.2m×width 2m×length 6m) were constructed in 2007, and four different treatments were installed: (i) soil+bottom ash (35% wtwt(-1)) (SB); (ii) soil+compost (2% wtwt(-1), approximately corresponding to 40Mgha(-1) in arable field scale) (SC); (iii) soil+bottom ash+compost (SBC); and (iv) soil only as the control (S). The effects of bottom ash mixing in ET cover soil on CH4 oxidation potential and vegetation growth were evaluated in a pilot ET cover system in the 5th year after installation by pilot experiments using the treatments. Our results showed that soil properties were significantly improved by bottom ash mixing, resulting in higher plant growth. Bottom ash addition significantly increased the CH4 oxidation potential of the ET cover soil, mainly due to improved organic matter and available copper concentration, enhancing methanotrophic abundances in soil amended with bottom ash. Conclusively, bottom ash could be a good alternative as a soil additive in the ET cover system to improve vegetation growth and mitigate CH4 emission impact in the waste landfill system.