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Research study is conducted to compare the attachment of fecal coliforms to different soils and soil fractions and to assess the effect of bovine manure on fecal coliform attachment to soil and soil functions. It is found that the attachment to the coated sand particle is similar to the attachment to silt and clay.

While renewable biofuels can reduce negative effects of fossil fuel energy consumption, the magnitude of their benefits depends on the magnitude of N2O emissions. High variability of N2O emissions overpowers efforts to curb uncertainties in estimating N2O fluxes from biofuel systems. In this study, we explored (a) N2O production via bacterial denitrification and (b) N2O emissions from soils under several contrasting bioenergy cropping systems, with specific focus on explaining N2O variations by accounting for soil pore characteristics. Intact soil samples were collected after 9 years of implementing five biofuel systems: continuous corn with and without winter cover crop, monoculture switchgrass, poplars, and early‐successional vegetation. After incubation, N2O emissions were measured and bacterial denitrification was determined based on the site‐preference method. Soil pore characteristics were quantified using X‐ray computed microtomography. Three bioenergy systems with low plant diversity, that is, corn and switchgrass systems, had low porosities, low organic carbon contents, and large volumes of poorly aerated soil. In these systems, greater volumes of poorly aerated soil were associated with greater bacterial denitrification, which in turn was associated with greater N2O emissions (R2 = 0.52, p < 0.05). However, the two systems with high plant diversity, that is, poplars and early‐successional vegetation, over the 9 years of implementation had developed higher porosities and organic carbon contents. In these systems, volumes of poorly aerated soil were positively associated with N2O emissions without a concomitant increase in bacterial denitrification. Our results suggest that changes in soil pore architecture generated by long‐term implementation of contrasting bioenergy systems may affect the pathways of N2O production, thus, change associations between N2O emissions and other soil properties. Plant diversity appears as one of the factors determining which microscale soil characteristics will influence the amounts of N2O emitted into the atmosphere and, thus, which can be used as effective empirical predictors. Long‐term implementation of bioenergy systems with contrasting plant diversity influences microscale pore architecture, which then affects predictors of N2O production and emission. [ABSTRACT FROM AUTHOR]

Visualization of water in soil pores is challenging due to uncertainty in defining the grayscale threshold between the solid and liquid phases on X-ray CT images. This problem could be partly resolved by using a dual energy combined with contrast solutions (e.g Ba, I, Sr). The use of Iodide as a contrast is preferable due to less interaction of anions with the solid phase of soil minerals, and thus more uniform distributing the contrast in soil pores as compared to the distribution of cations. The use of contrasts, however, does not resolve entirely the thresholding problem, since in unsaturated soil KI occupies mostly pores which are considerably smaller than the resolution of scanner. To resolve this problem we developed a procedure for segmentation of X-ray CT images based on mass attenuation of iodide and its saturation of voxels on images. Unlike other methods, the threshold was not obtained from the shape of image histograms, but was calculated based on total iodide saturation derived from X-ray CT images and mass of iodide applied to the system. To test the approach a 10% KI solution was applied to the three soil aggregate fractions (< 0.05, 0.10–0.50 and 1.00–2.00 mm) of Typic Hapludalf soil. For the first testing set we added the solution to the pipette tips inserted into the soil to avoid the partial volume effect, whereas for the second set we added solution to the same soil to achieve 3 water content levels. The soil micro-columns were scanned at 33.269 and 33. 069 keV at Argonne National Laboratory (GeoSoilEnviroCARS magnet beam-line 13-BM-D). For segmentation we used the 16 thresholding methods available in ImageJ software along with proposed mass-based procedure. Results demonstrated that reliable estimation of the threshold cannot be achieved with the standard methods. The error of mass for the developed procedure varied from 3% to 7% of applied solution, and generally increased with decreasing size of the soil fraction. This was attributed to increasing partial volume effect with increasing volume of fine pores. [ABSTRACT FROM AUTHOR]

Soil microsites where newly added plant residue undergoes decomposition are the hotspots ofmicrobial activity, due to microbial utilization of organic matter as their energy sources. Thusthose sites often contribute to high emission of greenhouse gases such as carbon dioxide(CO2) and nitrous oxide (N2O). Although it is known that microbial activity anddecomposition are regulated by residue&#x2019;s chemistry, residue&#x2019;s interactions with soil physicalcharacteristics have been less understood. Specifically, soil pore size distributions could alsoalter the degree/type of microbial activity by regulating soil water and air pathways, includingO2 levels. In the past most of the plant residue incorporation studies focused onagronomic crops, while the crops that are currently proposed as feedstock for bioenergyproduction received less attention. For example, switchgrass is considered as one of thesustainable bio-energy crops due to its high yield, low input, and positive impact on soiland water conservation during the growth. Studying decomposition of switchgrasswould allow us to assess its environmental impact more thoroughly. Thus, the goalof this study is to: 1) investigate the rate of decomposition for switchgrass leafand root residues incorporated into soil with contrasting pore characteristics; 2)monitor CO2 and N2O fluxes from the soil with incorporated residue during thedecomposition; and 3) monitor O2 levels and spatial patterns of extracellular enzymes duringdecomposition. We built soil microcosms (d = 8 mm) with 2 g of soil and 2 mg of residue using soilmaterials with contrasting pore size distributions, namely with prevalence of &#x003C; 10 um and &#x003E;30 um pores. CO2 and N2O emission rates were measured during 21-day incubation, andcomputed micro-tomography was used to quantify residue decomposition at 7, 14, and 21days of incubation and moisture redistribution after the incorporation of plant residues.Additionally, oxygen micro-sensors and zymography technique will be applied to examinethe O2 and enzyme distributions (ongoing). Preliminary results showed that overall CO2 and N2O emissions were greater in soil withprevalence of &#x003C; 10 um pores rather than &#x003E; 30 um pores. However, presence of residues led togreater increases in N2O emissions from the soil with prevalence of &#x003E; 30 um pores than inthat with &#x003C;10 um pores. The increases of CO2 emissions due to the residue inputswere not significantly different among the two pore size treatments. The peak N2Oemission in control soil was reached on day 1, but peak emissions occurred onday 3-5 in the presence of residues. Greater residue decomposition took place inthe soil of &#x003E; 30 um than in &#x003C;10 um pore treatments. There were no significantdifferences in CO2 / N2O emissions between switchgrass root and leaf residues. [ABSTRACT FROM AUTHOR]