Effects of Below Ground Controlled Injections of CO2 on Microbial Respiration of Soil Planted With Wheat (Triticum aestivum L.)

Abstract

Below-ground carbon dioxide (CO₂) emissions occur naturally at CO₂ springs, but the risk of occurrence at other sites will increase as geologic CO₂ storage is implemented to help mitigate climate change. This investigation examines the effect of controlled injection of below ground CO₂ emission on wheat plant and soil microbial respiration where spring wheat (triticum aestivum L.) was grown. The study involved setting up eight (8) experimental plots (each 2.5 x 2.5m) for the growth of spring wheat. The experimental plots labelled A1 - A8 (A1, A6 and A7 were gassed plots while A2, A3, A4, A5 and A8 were used as control plots). Soil CO₂ concentration was increased by the release of concentrated CO₂ gas from a source point 60 cm below the soil for eight (8) weeks at the rate of 1L^-1 via tubes into the soil when wheat was grown.  Five plots were used as control, while three plots were used as treatment plots with a regulated meter gas supply. The variability of CO₂ concentrations was determined by a revised 2D method known as Barholing using a geotechnical Instruments GA2000 gas analyser to map CO₂ at 30 cm depth across each plots. This was used to measure the dispersion of CO₂ throughout the plots. This method which produced contour plots of spatial variation shows the rate of dispersion of soil gas in the treated plots. The concentrations of CO₂ at the centre of the plots were different, showing values up to 70% CO₂ but reduced rapidly from the centre to plot borders. No significant changes in microbial biomass or carbon utilisation were observed (at P>0.05), but a trend towards reduced microbial respiration was apparent in the gassed plots.