Because of the dynamic nature of shrinking and swelling of soils that are classified as Vertisols, partitioning of rainfall into infiltration and runoff in a Vertic watershed is more temporally and spatially unique than in most other watersheds. Hydrology models that account for realistic representation of crack dynamics are rarely used because the spatial and temporal patterns of cracking across a catena and under different land uses are poorly understood. The objectives of the study were to 1) determine if variability in soil cracking on a Vertisol catena, having the same soil and land cover, could be explained by shrink-swell potential of the soil and changes in soil water content; 2) characterize the temporal and spatial variability of the shrinkage of a Vertisol under different land uses; and 3) determine the relationship between specific volume and water content of soils, particularly between saturation and field capacity. The research was conducted in Vertisol catenae of the Houston Black and Heiden soil series. The catenae were located within the USDA-ARS Grassland, Soil and Water Research Laboratory, Riesel Texas. Soil samples were taken to characterize the general properties of the soils. In situ bi-weekly measurements of vertical soil movements and soil water contents were made over a two-year span. Because shrink-swell potential was high at most landscape positions, soil water content was the primary factor driving the spatial and temporal variability of soil shrinking and swelling. The measured relationship between the amount of soil subsidence and water loss generally agreed with what would be theoretically expected. Maximum soil subsidence was 120 mm in the grazed pasture, 75 mm in the native prairie, and 76 mm in the row cropped field. Shrinkage of the whole soil was not equidimensional, and the study generally indicates more horizontal shrinkage than vertical shrinkage. Laboratory analysis showed an appreciable change in volume of soils between saturation and field capacity, suggests a layer of soil layer can subside up to 4% while drying from saturation to field capacity, which indicates the common laboratory measure of shrink swell potential does not capture the complete shrink-swell behavior of soils.

In Southern Manitoba, potato producers are experiencing wetter and drier conditions within the soil profile during the growing season leading to poor quality and inconsistent yields. Russet Burbank Potato cultivar was grown in Southern Manitoba on fine sandy loam soil in a two year (2013-2014) study using two water management treatments: (i) overhead irrigation and (ii) no-irrigation. The main objectives of the study were (i) to assess the impact of overhead irrigation on water table depth and potato yield (ii) to estimate the shallow groundwater contribution to potato water requirement through upward flux (iii) to track the nitrogen dynamics within the potato root-zone under overhead irrigation and no-irrigation scenarios (iv) to examine the effects of no-irrigation and overhead irrigation system at critical growth stages on marketable yield and quality of potatoes. In 2013, water was applied using a linear move irrigation system and in 2014 a rain gun irrigation system was used for the irrigated treatment. Volumetric soil water content, precipitation, irrigation depth, water table depth, nitrate concentration and electrical conductivity in potato root-zone, groundwater electrical conductivity, weather variables, total potato yield, marketable yield, and quality parameters were measured. The total yield was not significantly different between the two treatments in both years. The marketable yield of the irrigated treatment (36.89 MT/ha) was 20% higher (p = 0.017) compared to the non-irrigated treatment (30.74 MT/ha) in 2013. However, no significant difference was found between the irrigated (39.0 MT/ha) and non-irrigated (43.7 MT/ha) treatments in 2014. Potato yields from both treatments were significantly correlated with the average groundwater depth. Water balance analysis within the root-zone during rainy and rain-free periods showed that nitrate rich groundwater may have contributed to some of the crop water demand. The lack of rainfall and high temperature during tuber initiation and tuber bulking stages resulted in the accumulation of high concentration of nitrates within the root-zone by the late release of nitrates from the polymer-coated urea and the upward migration of groundwater containing 55 ppm and 70 ppm of nitrates in the 2013 and 2014 growing seasons, respectively. Overhead irrigation was found to be economically advantageous to produce better quality potatoes with higher marketable yields.

In New Zealand, native shrubs are considered an important potential carbon-sink in disturbed or abandoned land (e.g., pastoral land that is unsustainable for long-term pastoral agriculture). However, the impact of varying environmental drivers on carbon uptake from photosynthesis and carbon loss from respiration of a developing shrubland remains uncertain. In this study, the effects of both temperature and soil water content (θ) on photosynthesis and respiration were examined under controlled growth cabinet and field conditions in a pasture grass and the native shrub, kānuka (Kunzea ericoides var. ericoides). The purpose of the investigation was to assess the combined impacts of varying temperature and θ on canopy processes and to disentangle the effects of θ on photosynthesis and respiration for the two different plant types. A controlled growth cabinet study (Chapter 2) showed that θ had a greater effect on the short-term temperature response of photosynthesis than the temperature response of respiration. The optimum value of θ for net photosynthesis was around 30 % for both kānuka and the grass. Statistical analysis showed that the temperature sensitivity of photosynthetic parameters was similar for both plant types, but the sensitivity of respiratory parameters was different. Reduction in θ induced an inhibition of photosynthetic capacity in both plant types. The response of respiratory parameters to θ was not related to substrate limitations, however available evidence suggests that it is likely to be a species dependent plant mechanism in regulating the cost of maintenance due to reduced photosynthate assimilation and decreasing energy supply to support the activity of respiratory enzymes. Results obtained from a field study (Chapter 3) showed that photosynthesis and respiration in the grass and kānuka were sensitive to seasonal changes in temperature and θ. Photosynthetic parameters showed little acclimation following changes in seasonal growth conditions. In contrast, respiratory parameters tended to acclimate more strongly. Respiratory acclimation to multiple environmental conditions was characterised by changes in temperature sensitivity and a shift in the response of respiration to temperature, demonstrating the involvement of both ‘Type I’ and ‘Type II’ acclimation in both plant types. The results from controlled growth cabinet and field studies were used to drive a leaf level model that integrates the responses of photosynthesis and respiration to changes in temperature and θ and incorporates acclimation using variable photosynthetic and respiratory parameters (Chapter 4). This model was used to estimate the annual canopy carbon exchange of the grass and kānuka in response to seasonal changes and to predict changes in canopy carbon exchange under varying future climate change scenarios. The model highlighted the importance of considering seasonally-acclimated parameters in estimating canopy carbon exchange of both plant types to concurrent changes in multiple environmental variables. The overall results support the conclusion that understanding the combined effects of environmental variables on canopy processes is essential for predicting canopy net carbon exchange of a pasture-shrub system in a changing global environment. It has been shown here that the rate of increase in photosynthesis with increasing θ is greater than that of respiration which results in a progressively greater apparent carbon gain at moderate values of θ. Moreover, the impact of lower values of θ, which reduced the apparent sensitivity of respiration to temperature, may effectively decrease the rate of respiration during warmer summer months and enhance thermal acclimation via downregulation of respiration. Therefore, considering the influence of soil water conditions on the temperature sensitivity of photosynthetic and respiratory model parameters has important implications for precisely predicting the net carbon exchange of a pasture-shrub system.

Surface mining of the Athabasca Oil Sands of Canada is occurring at an unparalleled rate resulting in large scale disturbances over vast areas. Soil water availability for plants is one of the key issues faced when reclaiming the landscape. A factor which limits the soil water availability is soil water repellency (SWR). Soil water repellency is found on both natural and disturbed sites in this region and can cause reduced infiltration, reduced soil water storage, enhanced runoff, increased preferential flow, and reduced ecosystem productivity. Effective characterization of SWR, determination of the causes of SWR and understanding how it affects soil pores and water flow are important for environmental management. The main objective of this study is to examine the effect of SWR and fungal hydrophobicity on soil water dynamics in Athabasca Oil Sands. This was accomplished by determining the relationship between the measurement of severity and persistence of SWR and the critical water content (CWC) where SWR is greatest between different soils in the region. Examining how the water conducting porosity and soil pores are affected by SWR. Developing methods to quantify fungal strains that cause SWR and testing of these fungal strains for their ability to alter the SWR and infiltration into soil. Results show that a high severity (Contact angle) of repellency does not necessarily denote long persistence (Water Drop Penetration Time) or high CWC in soils from the region. A high severity of SWR in larger diameter pores decreased the water conducting porosity due to the larger pore contribution to the total liquid flux. The modified microscopy approach and the alcohol percentage test (APT) resulted in improved characterization of fungal hydrophobicity. Fungal strains were classified as hydrophilic, hydrophobic and chrono-amphililic based on their surface properties from these measurements. The surface property of selected fungi strains can alter the SWR in both a repellent and wettable soil and can also change the water infiltration rate. This research highlights the importance of characterization of SWR, the effects on water flow, and how fungal hydrophobicity can alter the SWR and infiltration. This will aid in improving our understanding of SWR and improve remediation efforts on water repellent soils in the Athabasca Oil Sands region.

No description available.

In many situations, the upper layers of soil above the ground water table are in a state of unsaturated condition. Although unsaturated soils are found throughout the world, they are predominant in arid or semi-arid regions. In these areas, the soil water characteristic curve (SWCC) which relates the water content to the matric suction could be used as key tool to implement the mechanics of unsaturated soils into the designs of geotechnical structures such as dams, embankments, pavements, canals, and foundations. Several experimental techniques are available for determining the SWCC in a laboratory environment. However, these experimental techniques are expensive, time consuming typically requiring days or weeks, depending on the soil type, and demanding intricate testing equipment. Due to these reasons, there has been a growing interest to find other means for estimating SWCC and encourage the adoption of unsaturated soils mechanics in geotechnical engineering practice. Several methods exist to indirectly estimate the SWCC from basic soil properties. Some may include statistical estimation of the water content at selected matric suction values, correlation of soil properties with the fitting parameters of an analytical equation that represents the SWCC, estimation of the SWCC using a physics-based conceptual model, and artificial intelligence methods such as neural networks or genetic programming. However, many studies have shown that environmental effects such as temperature, soil structure, initial water content, void ratio, stress history, compaction method, etc. can also affect the SWCC. This means that the estimation SWCC from set of conditions may not reliably predict the SWCC in other conditions. Due to this reason, it is crucial for engineers involved with unsaturated soils to take into account all the factors that influence the SWCC. The two key objectives of the present thesis are the development of a method based on first principles, using the capillary rise theory, to predict the variation of the SWCC as a function of temperature, as well as developing a technique for the prediction of the fixed parameters of a well-known function representing the SWCC based on basic soil properties together with the moisture profile of a soil column subjected to a known temperature gradient. A rational approach using capillary rise theory and the effect of temperature on surface tension and liquid density is developed to study the relation between temperature and the parameters of the Fredlund and Xing (1994) equation. Several tests, using a Tempe cell submerged in a controlled temperature bath, were performed to determine the SWCC of two coarse-grained soils at different temperatures. A good comparison between the predicted SWCC at different temperatures using the proposed model and the measured values from the Tempe cell test results is achieved. Within the scope of this thesis, a separate testing program was undertaken to indirectly estimate the SWCC of the same two coarse-grained soils from the measurement of their steady state soil-moisture profile while subjected to a fixed temperature differences. The water potential equation in the liquid and vapor phases is used to analyses the steady state flow conditions in the unsaturated soil. A good comparison is obtained for the SWCC estimated using this technique with the SWCC measured used a Tempe cell submerged in a controlled temperature bath. The results of this study indicate that knowledge of the moisture content of a soil specimen under a constant thermal gradient and basic soil properties can be used to estimate the SWCC of the soil at the desired temperature.

An essential component for evaluating the performance of a mine site after its closure includes the tracking of water movement through mine waste such as tailings and overburden. A critical element of this evaluation is the measurement of the volume of water stored in the closure landform. The objective of this project was to design a time domain reflectometry (TDR) device that could be used to measure the volumetric water content of a soil profile to depths of 10 to 20 m. Upon completion of this project, the device will be integrated onto ConeTec’s cone penetration testing (CPT) shaft for initially monitoring Syncrude Canada Limited’s northeastern Alberta oil sands mine site. The objective of this project will be achieved through at least two phases of research and development; this thesis concentrates on the first phase. In this phase, research focused on prototype development through laboratory testing to determine appropriate TDR probe geometries and configurations that could be integrated onto a CPT shaft. Considerations also had to be made for protecting the integrity of the probe during field use and mitigating the effects of highly electrically conductive soils common in reclaimed mine sites. A number of different prototype designs were initially investigated in this research, leading to the development of a refined prototype for advanced testing. Testing for the project was carried out first in solutions of known dielectric constants and salinities, and then proceeded to soils with a range of known water contents and salinities. Good quality electrical connections were found to be crucial for generating waveforms that were easy to interpret; bad connections resulted in poor results in a number of cases. Decreased probe sensitivity was observed in response to increased rod embedment within the probe variants. A far greater decrease in sensitivity was seen in the results of the fully sheathed rods, although the sheathing was effective for extending the range of the probe in electrically conductive testing conditions. Despite poor results that were seen in some of the tests, overall the results were promising. In particular, results from the push-test showed that the probe was able to monitor changes in water content with depth.

Both empirical and process-simulation models are useful for evaluating the effects of management practices on environmental quality and crop yield. The use of these models is limited, however, because they need many soil property values as input. The first step towards modelling is the collection of input data. Soil properties can be highly variable spatially and temporally, and measuring them is time-consuming and expensive. Efficient methods, which consider the uncertainty and cost of measurements, for estimating soil hydraulic properties form the main thrust of this study. Hydraulic properties are affected by other soil physical, and chemical properties, therefore it is possible to develop empirical relations to predict them. This idea quantified is called a pedotransfer function. Such functions may be global or restricted to a country or region. The different classification of particle-size fractions used in Australia compared with other countries presents a problem for the immediate adoption of exotic pedotransfer functions. A database of Australian soil hydraulic properties has been compiled. Pedotransfer functions for estimating water-retention and saturated hydraulic conductivity from particle size and bulk density for Australian soil are presented. Different approaches for deriving hydraulic transfer functions have been presented and compared. Published pedotransfer functions were also evaluated, generally they provide a satisfactory estimation of water retention and saturated hydraulic conductivity depending on the spatial scale and accuracy of prediction. Several pedotransfer functions were developed in this study to predict water retention and hydraulic conductivity. The pedotransfer functions developed here may predict adequately in large areas but for site-specific applications local calibration is needed. There is much uncertainty in the input data, and consequently the transfer functions can produce varied outputs. Uncertainty analysis is therefore needed. A general approach to quantifying uncertainty is to use Monte Carlo methods. By sampling repeatedly from the assumed probability distributions of the input variables and evaluating the response of the model the statistical distribution of the outputs can be estimated. A modified Latin hypercube method is presented for sampling joint multivariate probability distributions. This method is applied to quantify the uncertainties in pedotransfer functions of soil hydraulic properties. Hydraulic properties predicted using pedotransfer functions developed in this study are also used in a field soil-water model to analyze the uncertainties in the prediction of dynamic soil-water regimes. The use of the disc permeameter in the field conventionally requires the placement of a layer of sand in order to provide good contact between the soil surface and disc supply membrane. The effect of sand on water infiltration into the soil and on the estimate of sorptivity was investigated. A numerical study and a field experiment on heavy clay were conducted. Placement of sand significantly increased the cumulative infiltration but showed small differences in the infiltration rate. Estimation of sorptivity based on the Philip's two term algebraic model using different methods was also examined. The field experiment revealed that the error in infiltration measurement was proportional to the cumulative infiltration curve. Infiltration without placement of sand was considerably smaller because of the poor contact between the disc and soil surface. An inverse method for predicting soil hydraulic parameters from disc permeameter data has been developed. A numerical study showed that the inverse method is quite robust in identifying the hydraulic parameters. However application to field data showed that the estimated water retention curve is generally smaller than the one obtained in laboratory measurements. Nevertheless the estimated near-saturated hydraulic conductivity matched the analytical solution quite well. Th author believes that the inverse method can give a reasonable estimate of soil hydraulic parameters. Some experimental and theoretical problems were identified and discussed. A formal analysis was carried out to evaluate the efficiency of the different methods in predicting water retention and hydraulic conductivity. The analysis identified the contribution of individual source of measurement errors to the overall uncertainty. For single measurements, the inverse disc-permeameter analysis is economically more efficient than using pedotransfer functions or measuring hydraulic properties in the laboratory. However, given the large amount of spatial variation of soil hydraulic properties it is perhaps not surprising that lots of cheap and imprecise measurements, e.g. by hand texturing, are more efficient than a few expensive precise ones.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2007. / Härtill 3 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 4 uppsatser.