Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references in end segment. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references in end segment. Also available on the Internet.

Thesis (M.Phil.) - University of Queensland, 2005. / Includes bibliography.

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: Cliff Montagne. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1998. / Typescript. Includes bibliographical references (leaves 24-29).

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Thesis (Ph. D.)--Rhodes University, 2004. / Title from PDF t.p. (viewed on May 2, 2006). Includes bibliographical references (p. 263-293).

Excessive ammonia (NH3) emission, originating largely from agriculture, can affect water, air and soil quality, and through these, endanger ecosystem and human health. Since NH3 emission is strongly dependent on temperature and also influenced by other meteorological variables, the question arises: how will NH3 emission alter in a changing climate? A way to address this question and predict the subsequent environmental consequences is to construct meteorology-driven models of NH3 emission from every agricultural source. Furthermore, NH3 emission is a highly localised and dynamic process. The focus of this thesis is NH3 emission from grazing. In the first stage a new process-based model for NH3 emission from a urine patch was developed. The GAG model (Generation of Ammonia from Grazing) is capable of simulating the TAN (total ammoniacal nitrogen) and the water content of the soil under a urine patch and also soil pH dynamics. In the second stage, GAG was applied to the scale of a grazed field, combining multiple simulations of the patch-scale model including both urine-affected and unaffected (“clean”) areas. The modelled NH3 fluxes were found to be in good agreement with the observations for both model types. The sensitivity of NH3 flux was assessed to various soil physical and chemical parameters for both the patch and the field scale models. It was found that ammonia volatilization from a urine patch could be influenced by the possible restart of urea hydrolysis after a rain event as well as carbon-dioxide emissions from the soil. Over the field scale, it was shown that the temporal evolution of the NH3 exchange flux was dominated by the NH3 emission from the patches within the field. The results also suggested that NH3 fluxes over the field in a given day could be considerably affected by the NH3 emission from urine patches deposited several days earlier. In the last stage of the work, a comprehensive sensitivity analysis was carried out with a special focus on temperature, for both versions of the GAG model. It was shown that due to the different governing dynamics over the patch and the field scale, the temperature-dependence of NH3 exchange is stronger over the field scale. It was also concluded that the temperature-dependence of NH3 exchange is stronger if the sinks of NH3 are stronger within the system. Finally, it was found, that Q10, a widely-used metric to express the relative increase of trace gas emissions over a range of 10 °C, is influenced by the length of the period of investigation and the initial value of the temperature range.

Made available in DSpace on 2015-01-26T13:21:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-02-24Bitstream added on 2015-01-26T13:31:04Z : No. of bitstreams: 1 000804433.pdf: 698887 bytes, checksum: af82de438cb8865e96506c2dcc5009b1 (MD5) / A ciclagem de nutrientes em pastos no Brasil é responsável pela maior parte dos nutrientes que entram no sistema, uma vez que a exploração tem como características a baixa utilização de insumos. O objetivo desse trabalho foi avalia a decomposição de serapilheira de Cynodon spp. cv Tfiton 85 manejado com índices de área foliar residual pastejados por ovinos. A decomposição da serapilheira foi avaliada através de sacos contendo quantidade conhecida de serapilheira durante os seguintes tempos de incubação, 0, 4, 8, 16, 32, 64, 128 e 256 dias. Foram avaliados o desaparecimento de massa seca, o comportamento do nitrogênio, fósforo, carbono, além da relação C:N. Houve uma maior taxa de desaparecimento nos primeiros 64 dias de incubação, seguido por uma fase lenta até o final dos 256 dias de incubação. Houve aumento na concentração do nitrogênio e do fósforo durante o período avaliado / The cycling of nutrients in pastures in Brazil is responsible for most of the nutrients entering the system, since the operating characteristics including low use of inputs. The aim of this study was to evaluate the decomposition of litter Cynodon spp. 85 hp Tfiton plied with residual leaf area indices grazed by sheep. Were evaluated by the decomposition of bags containing a known amount of litter during the following incubation times 0, 4, 8, 16, 32, 64, 128 and 256 days. The disappearance of dry mass were assessed, the behavior of nitrogen, phosphorus , carbon, addition of C:N. There was a higher rate of disappearance in the first 64 days of incubation followed by a slow phase until the end of the 256 days of incubation. There was an increase in the concentration of nitrogen and phosphorus during the study period