Gaseous movement in soil varies with soil's physicochemical properties and biochemical oxygen demand. Diffusivity patterns of four different types of soil (sand, silt, sandy silt, and clay) were examined and sand have shown the highest rate of diffusivity increase with the decreasing soil moisture content. Raw cow manure was then added to the sandy soil at four different rates 0, 20,40, and 80 Mg/ha. Depletion of soil oxygen and changes of carbon dioxide and ammonia for different concentrations were compared against the control. The oxygen depletion or carbon dioxide and ammonia accumulation reached the highest level at initial 16 hour followed by gradual reversal to a steady state. A significant amount of oxygen depletion was noticed with the different concentration levels. Oxygen depletion had shown an oscillatory behavior towards zero. Among different concentrations that of 40 Mg/ha showed the highest oscillatory behavior, but the shortest time was required to recover its original oxygen level. Thus the 40 Mg/ha application of organic matter is seems to be the optimum level for sandy soil.

Thesis (M.S.)--Oregon State University, 1995. / Typescript (photocopy). Includes bibliographical references (leaves 59-64). Also available on the World Wide Web.

No description available.

No description available.

No description available.

Gaseous transport through soil in the presence of soil microorganisms has been investigated. More recently, modeling of gaseous transport in the unsaturated zone has been investigated. However, the problem of mathematical model of oxygen and carbon dioxide transport through soil, as affected by the climatic conditions, the transport of soil water, and the biological activities, has not been studied. The problem of time-dependent diffusion of oxygen and carbon dioxide through plant canopy and soil system, as affected by the infiltration and evaporation of soil water and the rate of consumption of oxygen and production of carbon dioxide by plant leaves and roots and soil microorganisms was studied, using a one-dimensional mathematical model. This model consists of four sets of non-linear partial differential field equations, which describe the time-dependent simultaneous transport of water, heat, oxygen, and carbon dioxide through the soils. Finite difference methods were used to find the approximate solutions for the four sets of non-linear partial differential field equations. The field equations for the transport of water and heat were approximated by using the implicit scheme. The field equations for the transport of oxygen and carbon dioxide were approximated by using the explicit scheme. A computer program was written in Fortran code to conduct the simulations of the mathematical model. Simultaneous transport of water, heat, oxygen, and carbon dioxide through the unsaturated Indio loam soil, through the compacted and the non-compacted soil during infiltration, redistribution, and evaporation of soil water was evaluated. Diffusion of oxygen and carbon dioxide within the canopy and soil system was examined. Several different functions for the root elongation and the root oxygen consumption rates were used. Root elongation rate was chosen to depend on oxygen or carbon dioxide concentrations, in addition to being a function of time. Root oxygen consumption rate was assumed to be a function of root age, in addition to being a function of oxygen or carbon dioxide concentrations. Results illustrate that the behaviors of the simultaneous transport of water, heat, oxygen, and carbon dioxide were well predicted by the model. / Graduation date: 1991

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 155-168). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--University of Toledo, 2007. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science in Biology, Ecology-track." Bibliography: leaves 68-78.

No description available.

Globally, an estimated 25% of the CO2 and 90% of the N2O is believed to come from agroecosystems. The objective of this study was to investigate the dynamics of the below-ground CO 2 and N2O concentrations and efflux in corn and soybean systems. In our field study, changes in the below-ground concentrations of CO 2 and N2O were closely related to seasonal changes in soil moisture, with the first two months of the growing season being particularly critical to the production of these gases. Tillage significantly increased CO2 content in the soil profile, however, this effect was greater in the soybean plots than in the corn plots. In our greenhouse studies, an average of about 79% of the soil respiration in corn came from rhizosphere respiration, compared to an estimated 58% in the case of soybean. Specific rhizosphere respiration was significantly higher in soybean (0.29 mg C g -1 root h-1) than corn (0.09 mg C g-1 root h-1), which supports previous observations made with regards to slower-growing plants (e.g. soybean) having relatively higher root respiration than faster growing plants. We observed a nonsignificant difference between N2O efflux in the soybean-planted soil and unplanted bulk soil, which is in contrast to the perception that legumes could stimulate more N 2O production from the soil by increasing the N pool through N 2 fixation. While corn had the greatest uptake of fertilizer N, N 2O efflux in corn pots was higher (2.84 mug N pot-1 h-1) than the soybean pots (0.06 mug N pot-1 h-1). In the laboratory setting, denitrification in the microaggregates proceeded at about 4.4 to 39.6 times higher rate than in large macroaggregates, small macroaggregates or the bulk soil, and showed the greatest response to high moisture levels (80% WFPS).