In the past 10 years we have witnessed the beginnings of the study of soil ecology as a unified science, and the general realization by soil scientists, farmers, and land managers that many of the most important economic aspects of soil health are controlled by biological factors. This research focuses on alterations in a tropical soil microarthropod community under differing intensive agricultural protocols: native vegetation, pastures and cropland, during June, July and August 1998. The effect of pesticides in potato cultivation was also studied. In the Ecuadorean montane forest, 361 morphospecies of soil arthropods, were classified during the three sampling months. August was the month with highest abundance and diversity. Acari, Coleoptera, Collembola, Diptera and Homoptera were the most abundant orders present in all the three types of land management. The native vegetation had the most abundant and diverse representation of all soil arthropod taxa compared to the pastures and croplands. Coleoptera, Diptera, Diplopoda, Diplura and Hemiptera were significantly more diverse in native vegetation than in pastures and croplands. The most abundant functional groups were the fungivores, herbivores and predators. The abundance of functional groups was significantly higher in the native vegetation for predators, herbivores and detritivores. 115 morphospecies of soil arthropods were identified in the study of arthropod response to pesticides in a complete randomized potato plot. Seasonal effects were documented for Acari, Collembola, Diptera, and Homoptera. Predators were most abundant in July and fungivores decreased in September. Neither arthropod orders nor functional groups showed a significant change in abundance between different treatments. Only Homoptera showed an increase in its abundance in the third sampling date and only in the Antracol plots. The potato plants in the whole block showed poor productivity, suggesting that the whole system was stressed by the fungal pest. / Graduation date: 2000

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references (leaves 52-62). Also available on the World Wide Web.

Thesis (Ph.D.) in Ecology and Environmental Science--University of Maine, 2009. / Includes vita. Includes bibliographical references (leaves 147-157).

The occurrence of the cotton root rot fungus, Phymatotrichum omnivorum (Shear) Duggar, in sharply defined, localized areas in certain fields led to the suggestion that there may be a specific soil chemical factor which limits the spread of the fungus. The available sodium, potassium, calcium, and magnesium contents of infested and adjacent noninfested soils in 13 fields were determined and compared. At seven sites, there were no significant differences in cation contents of infested and adjacent noninfested areas (p = 0.05). Available sodium levels were higher in infested areas at three sites, and higher in noninfested areas at three sites. Potassium and calcium levels were higher in the infested area at one site, and higher in the noninfested areas at two sites. Magnesium levels were higher in the noninfested areas at three sites. Contrary to previous reports, the fungus was found to cause severe disease in soils with available sodium contents as high as 4.2 milliequivalents per 100 g soil. Applications of sodium chloride at rates ranging from 1800 to 4000 kg/ha did not reduce disease severity or increase yield significantly in ten field trials.

Two BSC based indicators for rangeland condition assessment are species composition and cover. While there is strong agreement that BSC composition is a good indicator, there is less agreement that BSC cover alone is a good indicator. Although BSC have been included in previous remotely- sensed studies, their spectral characteristics, and hence their contributions to remotely-sensed spectral signatures, are not well known. / Data collection methods were refined for suitable method selection, stratification and site characterization, and morphological/functional group classification. Cover data of BSC were collected using a 100m line-intercept method on the stratified land units and statistical analyses were based on the cover variance analyses. Spectra of BSC groups were collected and characterized for different remote sensing indices. Five grazing gradient models based on collected spectra were developed for the evaluation of BSC effect on remotely-sensed data. Both existing and newly developed remote sensing indices were examined for BSC detection. / Sampling for cover of BSC in the field showed that there is indeed a detectable change with distance from water, suggesting that BSC cover can be used as an indicator of rangeland condition, provided that appropriate stratification of the study sites is carried out prior to sampling, and spectral differences in morphological and functional groups are taken into account. / Spectral analysis of BSC components showed that different classes of organisms in the crusts have different spectral characteristics, an din particular, that the (commonly-used) perpendicular vegetation index (PD54) is not suitable for detecting BSC. On the other hand, ground-level spectral modelling showed that the Normalized Difference Vegetation Index (NDVI) and Soil Stability Index (SSI) did show a distinguishable contribution from BSC. / A procedure for detecting cover of BSC was developed for image taken during the period after an effective rain, in contrast to the normal practice of selecting images of dry surfaces for interpretation. / The most suitable interval appears to be 2-4 days after rain in late autumn, winter and early spring. Of the existing indices, the SSI is the best for estimating cover of BSC from Landsat images. However, eight new indices, specifically designed for detection of BSC were developed during the course of this work. The best results were obtained for indices using the middle-infrared bands. / These results are promising for application to rangeland monitoring and suggest that BSC cover is an important indicator of rangeland condition if appropriate stratification, classification and data-collection methods are used. The effects of BSC cover on a remotely-sensed method are considerable, and thus they can not be neglected during image interpretation. There are different phenological patterns for BSC, annual and perennial elements, thus there is the possibility for the selection of imagery based on each phenological stage to detect these elements. Application of certain indices such as the PD54 may create mis-estimation of land covers. Although some of the existing and newly developed indices had significant results for BSC cover estimation, there is a requirement for a standalone remotely-sensed method to conclude the best index. / This thesis considers various aspects of the use of ground-based methods and remote sensing of Biological Soil Crusts (BSC). They are mostly distributed in winter rainfall dominated areas such as those at Middleback Field Centre (MFC) in South Australia. They can be used potentially as an indicator of rangeland condition by estimating grazing pressure (trampling). / Thesis (PhDEnvironmentalManagement)--University of South Australia, 2007.

Two BSC based indicators for rangeland condition assessment are species composition and cover. While there is strong agreement that BSC composition is a good indicator, there is less agreement that BSC cover alone is a good indicator. Although BSC have been included in previous remotely- sensed studies, their spectral characteristics, and hence their contributions to remotely-sensed spectral signatures, are not well known. / Data collection methods were refined for suitable method selection, stratification and site characterization, and morphological/functional group classification. Cover data of BSC were collected using a 100m line-intercept method on the stratified land units and statistical analyses were based on the cover variance analyses. Spectra of BSC groups were collected and characterized for different remote sensing indices. Five grazing gradient models based on collected spectra were developed for the evaluation of BSC effect on remotely-sensed data. Both existing and newly developed remote sensing indices were examined for BSC detection. / Sampling for cover of BSC in the field showed that there is indeed a detectable change with distance from water, suggesting that BSC cover can be used as an indicator of rangeland condition, provided that appropriate stratification of the study sites is carried out prior to sampling, and spectral differences in morphological and functional groups are taken into account. / Spectral analysis of BSC components showed that different classes of organisms in the crusts have different spectral characteristics, an din particular, that the (commonly-used) perpendicular vegetation index (PD54) is not suitable for detecting BSC. On the other hand, ground-level spectral modelling showed that the Normalized Difference Vegetation Index (NDVI) and Soil Stability Index (SSI) did show a distinguishable contribution from BSC. / A procedure for detecting cover of BSC was developed for image taken during the period after an effective rain, in contrast to the normal practice of selecting images of dry surfaces for interpretation. / The most suitable interval appears to be 2-4 days after rain in late autumn, winter and early spring. Of the existing indices, the SSI is the best for estimating cover of BSC from Landsat images. However, eight new indices, specifically designed for detection of BSC were developed during the course of this work. The best results were obtained for indices using the middle-infrared bands. / These results are promising for application to rangeland monitoring and suggest that BSC cover is an important indicator of rangeland condition if appropriate stratification, classification and data-collection methods are used. The effects of BSC cover on a remotely-sensed method are considerable, and thus they can not be neglected during image interpretation. There are different phenological patterns for BSC, annual and perennial elements, thus there is the possibility for the selection of imagery based on each phenological stage to detect these elements. Application of certain indices such as the PD54 may create mis-estimation of land covers. Although some of the existing and newly developed indices had significant results for BSC cover estimation, there is a requirement for a standalone remotely-sensed method to conclude the best index. / This thesis considers various aspects of the use of ground-based methods and remote sensing of Biological Soil Crusts (BSC). They are mostly distributed in winter rainfall dominated areas such as those at Middleback Field Centre (MFC) in South Australia. They can be used potentially as an indicator of rangeland condition by estimating grazing pressure (trampling). / Thesis (PhDEnvironmentalManagement)--University of South Australia, 2007.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Agronomy and Farming Systems, 2002. / "September 2001" Includes bibliographical references (leaves 206-230).

Thesis (M.A.)--Carleton University, 2002. / Includes bibliographical references (p. 139-148). Also available in electronic format on the Internet.

Thesis (M. Appl. Sc.) -- Lincoln University, 2008. / Also available via the World Wide Web.

Thesis (Ph. D.)--Texas State University--San Marcos, 2009. / Vita. Includes bibliographic references (leaves 19-24, 46-50, 69-74, 97-101,127-131, 141-144). Also available on microfilm.