PRELIMINARY INVESTIGATIONS ON AN ARTIFICIAL SOIL AGGREGATE USED IN BOTANICAL EXPERIMENTS: INITIAL GRAIN SIZE, REFLECTIVE SPECTROSCOPY, AND TRANSMISSION ELECTRON MICROSCOPY RESULTS
Caliper measurements of individual particles indicate that the dimensions of aggregate are modified by washing with unwashed aggregate having mean short axis length of 1.76 mm and mean long axis length of 4.33 mm and a 2.65 aspect ratio. Washed aggregate has mean short axis length of 1.68 mm and mean long axis length of 3.32 mm and a 2.12 aspect ratio, likely resulting in higher porosity for washed aggregate and lower and more flat packed porosity for dry aggregate. Reflective spectra of dry and wet samples were obtained and are dominated by hydroxyl features and oxidized iron features. Spectra of samples are heavily impacted by addition of water content, indicating that reflective spectra or hyperspectral imaging could be used to monitor surface moisture content in experiments. Initial transmission electron microscopy investigation on particles indicates that there are two dominant clay-sized particle types, a vermiculitic phyllosilicate and amorphous silica. Vermiculitic particles are characterized by compositions having Na, K, Mg, Al, Si, Ti, Fe and minor Mn and electron diffraction shows some turbostratic stacking. Amorphous silica particles are dominated by Si with minor Al, Fe and K and have few or no diffraction spots. Further investigations on other properties and how the washing and mechanical treatments impact cation exchange, the pore environments, and ultimately rhizosphere ecology are warranted.