No description available.

No description available.

Due to the complexity of nitrogen dynamics in the soil, tracer techniques are employed to estimate the fate and transport of nitrate in agricultural fields. This study was conducted to examine effects of N fertilization and landscape position on two-dimensional redistribution of bromide in a hummocky landscape, and to identify the landscape position with the greatest potential for solute loss using a dual application of Br- and 15N. The field data on Br- transport was also simulated using the HYDRUS models. The study was carried out near Brandon, Manitoba in 2007 and 2008, using two separate plots denoted as Site-2007 and Site-2008, respectively. The field plot was delineated into three landscape positions as upper (UPP), middle (MID) and lower (LOW) slope. Each landscape position received labelled K15NO3 at the rates of 0, 90 and 135 kg N ha-1, and KBr at the rate of 200 kg Br- ha-1. Site-2007 was seeded to canola while Site-2008 had winter wheat. Soil samples were taken in the fall and the following spring and were analyzed for Br-, NO3-N, total N, and isotope N ratio. Nitrogen fertilization reduced the downward movement of Br- in the soil profile, resulting in a greater lateral movement of Br- compared to the unfertilized plots. The greatest vertical and lateral movement of Br- occurred at the LOW slope. In the dual-tracer experiment, the smallest amounts of Br-, 15N, and NO3-N were measured in the soil at the LOW slope, while the greatest amounts were at the MID slope; indicating that solute loss was: LOW > UPP > MID. In the absence of crop uptake, Br- transport was identical to that of 15N. The simulation study showed that HYDRUS-1D model was inadequate to describe solute transport in the landscape, as HYDRUS-2D/3D reproduced the field data better than HYDRUS-1D. However, the 2D model did not reflect effects of landscape position and N fertility on Br- transport. Overall, the study confirmed the “Campbell hypothesis” which states that proper N fertilization reduces nitrate leaching. The field experiment and model simulation both showed that downward movement is the main pathway of solute loss in the landscape.

Graduation date: 1994

Typewritten / Bibiography: leaves 209-222. / iv, 223 leaves : ill. ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Botany, 1960

Universiẗat, Diss., 2002--Saarbrücken. / Erscheinungsjahr an der Haupttitelstelle: 2002.

Th. univ.--Sci.--Toulouse--I.N.P., 1980. N°: 8.

No description available.

No description available.

The application of nitrogen (N) fertilizers and manure to agricultural soil is essential for crop production, but has in turn introduced environmental impacts including: eutrophication, contamination of groundwater, freshwater acidification, and an increase in greenhouse gas emissions. The movement of nitrogen was observed following liquid swine manure applications at six fields in Winchester, ON employing controlled tile drainage and denitrifying bioreactors. The manure was mainly in the form of ammonium during application where it was transformed to other N species including nitrate and nitrous oxide (N2O) by microbial activity in soil. Large soil N2O fluxes occurred in fields throughout 2012 and 2013, and total N of soil in the fields was enriched in 15N, indicating denitrification. Soil nitrate was also leached and collected by drainage tiles, and a portion of the tile water was treated by denitrifying bioreactors. Previous studies have demonstrated that denitrification of nitrate in bioreactors elicits the production of N2O, which is emitted from the overlying soil surface and/or is released as dissolved N2O in tile effluent. In this study, it is found that a decrease in nitrate was associated with decreasing levels of nitrous oxide during a rain event, and no significant N2O flux was recorded above bioreactors throughout either year. The δ15N and δ18O signatures of nitrate did not change significantly following bioreactor treatment and did not exhibit the 15N and 18O enrichment that is characteristic of denitrification. The data demonstrates that the decrease in nitrate through the bioreactors was due to dilution, likely from the accumulation of rainfall in reactor beds employing controlled tile drainage. Further work is needed to examine the conditions under which dilution may occur in place of denitrification.