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Graduation date: 1998

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Environmental Sciences." Includes bibliographical references.

Subsurface drainage affects water table fluctuation patterns by removing the excess water from the soil. The annual average water table depths of the drained (A) and undrained (D) regimes are 0.83 and 0.48 m from the soil surface respectively. Subirrigation continuously provides water to the upper soil by capillary rise. The annual water table depths of the subirrigated regimes (B and C) are 0.61 and 0.70 m respectively. It is found that there is a significant curvilinear correlationship between the drainage flow rate and the water table height above the drain. Soil drainable porosity of different regimes was investigated by using the soil water balance approach. The average drainable porosity of regimes A and B are 6.0% and 4.9% from water table rise, and 5.9% and 4.5% from water table drawdown , respectively. Subirrigation adversely affects the soil drainable porosity. Soil drainable porosity is often considered as a constant. However, the results of this study indicate that it varies with the water table height above the drain. In the case of water table drawdown, this dependence can be successfully expressed by a negative exponential equation. In the case of water table rise, the correlation is not as significant, but there is still a trend that the drainable porosity decreases with the increase of the water table height above the drain. Evapotranspiration (ET) is often neglected in soil water balance models for the drain-able porosity determination. This may result in some errors. In this study, the potential ET rate was computed by the Penman and Hargreaves methods. These two methods give very similar ET values for the studied area. It is assumed that actual ET equals to the potential ET rate when the ground water table is close to the soil surface. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

From a geomorphological point of view, and environments are characterised by complex process interactions and suites of landforms which can be sensitive to their controlling parameters. Relationships between sediment, moisture and soil crust characteristics are no exception. Field research and a programme of laboratory study were undertaken between 1993 and 1995 on the soils of the northern Badia of Jordan to advance knowledge on aspects of and zone soil dynamics, with a particular emphasis on crusting. The research focuses primarily on the effect soil crusts have upon the equilibrium of sediment dynamics at a hillslope scale and a ridge-furrow scale. The implications of the crust upon moisture storage within the surface layers of the soil are examined and the spatial characteristics which arise due to management practices and climate variables considered. A new, non-destructive dielectric technique to investigate moisture content in dryland soils has been developed and tested. Monitoring has taken place to examine the effects of irrigation upon the surface characteristics of the surrounding soil, with special reference to evaporation fluxes within a furrow and the associated precipitation of salts. The role of small-scale topography tends to be underestimated. Different types of crust have been studied from various topographic locations. Soil fabric and porosity have been studied, to increase understanding of micro-scale depositional and erosional processes. A new method of tracing' fine material through the upper soil profile has been developed. As crusts form, the tracer can be used to monitor the movement of fines, permitting a much clearer understanding of soil and water dynamics as a result of rainfall events.

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The physical state of the seedbed is of importance to the plant environment as it influences some important processes in the soil such as seedling emergence, water and solute transport, and ease of root penetration. This is affected to a large extent by tillage process, the tillage implement type and the geometry of the implement used. / A field experiment was carried out on a clay soil to determine the effect of the geometry of bladed tillage implements on some soil physical properties after tillage. The soil properties evaluated were bulk density, mean clod size distribution and total pore space after tillage and the extent of loosening achieved. / Implement parameters considered were blade width, rake angle and depth of operation of the implement. Two blade widths of 75 and 150 mm were evaluated in combination with three rake angles of 30, 60 and 90 degrees. Each tillage implement was drawn through the soil at four operating depths of 100, 150, 200 and 250 mm. / Larger rake angles were observed to result in larger mean aggregate sizes and greater bulk density reductions when compared to smaller rake angles. Greater reduction in bulk density was observed with the wider of the two blade widths evaluated. Mean clod size after tillage was also observed to be large for the wider of the two widths evaluated. Irrespective of width and rake angle, greater operating depths resulted in larger mean clod sizes and greater reductions in bulk density as compared to shallower operating depths. Fractal analysis showed the extent of fragmentation to be greater at shallower operating depths, hence the small mean clod sizes obtained.

Persistent soil compaction by heavy-axle-load vehicles is a growing concern for the long-term productivity of clay soils. For optimum soil management, however, we must be able to evaluate adequately soil structural damages. This study compares different methods of assessing soil structure as affected by compaction and subsoiling treatments in a clay soil under corn production. / The tests used were: total porosity as calculated from densimeter readings and from soil cores; structural porosity; water desorption characteristics; and soil profile examination. These tests were performed in three layers of 20 cm and evaluation was based on their practicality and their ability to differentiate between treatments and to correlate with corn yield. / The results confirm that total porosity is a poor indicator of compaction in the subsoil. In soil profile assessments, ped descriptions were preferable to examination of pores. Water content and saturation deficit at $-$4.0 and $-$100 kPa were the best indicators of treatments and plant response.

Thesis (Ph. D.)--Carleton University, 1996. / Also available in electronic format on the Internet.

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