The platinum microelectrode technique for measuring oxygen flux in soils has been reviewed. Shortcomings in the existing technique and instrumentation have been discussed. The new instrumentation, electrode standardization and measurement techniques developed enable the method to be used with confidence in unsaturated soil systems. Measurements of oxygen flux index in four soil samples showed a very highly significant regression relationship between oxygen flux index and air space within the range 3 - 15% air space on each soil. There was no significant difference in the regression relation between soils. A field penetrometer, designed to measure the presence and strength of subsurface pans in field soils has been described. Measurements with the penetrometer on three depth of ploughing treatments (100, 230 and 355 mm) on tillage trials at four sites with different clay contents showed that hard layers were present on all the treatments. Except on the shallowest ploughing depth treatment on the fine-textured soil, where the pan was 225 mm below the nominal ploughing depth, the hard layers were present between a few mm and 150 mm below the nominal ploughing depth, and had strengths of between 16 and 24 bars. The theory and factors affecting measurement of soil strength with needle penetrometers have been investigated. The design and operation of a laboratory penetrometer used to measure soil strength under closely controlled laboratory conditions has been discussed. Physical factors likely to affect root growth, viz. soil texture, air space, bulk density, soil strength and available moisture, have been measured in a comprehensive range of undisturbed cores taken from the four tillage trials. High soil strength is considered as being the soil physical factor most likely to restrict root growth in these soils. Physical factors affecting soil strength have been investigated. Soil strength is shown to be highly dependent upon bulk density, matric potential and soil texture. The hard pans shown to exist in all the tillage trial soils exhibit many of the characteristics of tillage pans, but their existence cannot be attributed exclusively to the ploughing depth treatments imposed in the tillage trials. Rather, the pans have resulted from a combination of interacting factors, including the previous history of the soils, the imposed tillage treatments, crop, and climatic factors. A study of some of the data from the literature on root growth and soil strength shows that root growth is severely restricted by soil strengths of the order of 20 to 30 bars. In order to determine whether root growth was being restricted in the tillage trials, root profiles were extracted from one of the trials. These showed that the pans severely restricted root growth. Analysis of maize yield data from the tillage trials showed that on the three coarse-textured sites yield increased with increased depth of ploughing, and that there was a marked seasonal effect, ploughing depth having a relatively greater effect on maize yield in dry seasons than in wet. On the fine-textured site, however, where no pan existed near the surface in the shallow ploughed treatment, the ploughing depth effect was not significant, nor was there any marked seasonal effect of ploughing depth on maize yield. Evidence presented shows that the pans, by restricting root growth are reducing the amount of water available to the plant. This effect is greater in dry seasons, and in soils with low available water . / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1976.

Concerns have been raised on the deterioration of heather moorland due to management in the UK. A study was therefore conducted on the impacts of moorland management on the soils and hydrology of a catchment on Dartmoor. Soil moisture was measured gridwise using TDR on 19 occasions. At 23 sites within this grid, physical properties of the topsoil were obtained. At three locations, tensiometer nests were installed, recording soil suction at 10 cm depth intervals. At the catchment scale, stream discharge and rainfall were recorded. Grazing densities within the watershed were estimated and the observed patterns were related to vegetation types. Results from the TDR grid showed that in dry conditions, soil moisture patterns are heterogeneous in contrast to a more uniform pattern in wet periods. A threshold soil moisture content of about 0.60 cm3 cm-3 divides the two conditions. The exponential relationship between average hillslope soil moisture content and stream discharge also revealed the division between wet and dry states. A regression analysis showed that during dry conditions, the vegetation plays a significant role in determining the soil water status. During wet conditions, topography becomes more important. In these conditions, the soil water movement is mainly lateral, whereas in the dry state, this is vertical in the soil profile. Tensiometer data showed that most soil water movement is in the topsoil. Analyses suggested that soil moisture under vegetation classes associated with higher grazing pressures is higher in similar topographic conditions. Soil bulk density is higher and the total porosity is lower near the soil surface. This suggests that less rainfall is required to reach the soil moisture threshold and water will be transported laterally down the slope. A heather burning experiment revealed that the direct effect of temperature is shallow. Soil moisture levels do not change over the course of the burn. However, in dry situations during summer, soil moisture contents under burned plots are higher than under unburned vegetation probably due to reduced transpiration. If this effect is similar at the hillslope scale, when the soil is wetting up, the soil moisture threshold value could be reached at an earlier stage and accelerated lateral water movement could be the result. It can be concluded therefore, that moorland management could accelerate water movement on the hillslopes causing higher discharge peaks in wet periods and consequently low flows in summer. However, the effects are subtle and encouraging vegetation heterogeneity could play a role in buffering water to prevent loss to the stream.

Bibliography: p. 291-301. / xxxii, 301 p. : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Basic hypothesis is that improved water use efficiency of rainfed crops can be achieved by adoption of tillage and sowing practices and crop rotation systems which improve surface and subsurface soil structure to increase the accession of rainfall and availability of soil water. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1997?

Thesis (Ph.D.)--University of California, Davis, 2005. / (UnM)AAI3191201. Source: Dissertation Abstracts International, Volume: 66-10, Section: A, page: 3746. Adviser: Richard Howitt.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7212. Adviser: Tim R. Ellsworth. Includes bibliographical references (leaves 152-162) Available on microfilm from Pro Quest Information and Learning.

Thesis (M.S.)--University of North Carolina Wilmington, 2008. / Includes appendixes Title from PDF title page (viewed May 26, 2009) Includes bibliographical references (p. 47-49)

Thesis (M.Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves. Also available in print.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 123-139). Also available via the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Typescript. Vita. Description based on print version record. Includes bibliographies: leaves 144-147 ; 175-176.

Thesis (Ph. D.)--Syracuse University, 2003. / "Publication number AAT 3113254."