La rétrodiffusion associée aux effets de géométrie de surface à des angles d’incidence élevés (62°—76°) et pour quatres angles azimutaux (Q0, 3Q0, 60° et 90°) a été étudiée pour des champs de maïs du Québec (Canada) à l’aide de 3 images du ROS-C du Centre canadien de télédétection. Selon les conditions de drainage des champs, le couvert végétal apporte une plus ou moins grande contribution à la rétrodiffusion. L’effet de géométrie de surface est nettement plus prononcé (amplitude 3,2 dB) pour les champs de maïs sans drainage souterrain que ceux ayant un drainage souterrain (1,5 dB). Le contraste entre ces deux types de champ est rattaché aux différences de pente du couvert végétal ainsi qu’aux variations de biomasse.

Failure of slopes adjacent to the UK transport infrastructure causes delays and these are expensive assets to repair and maintain. Understanding the processes that lead to failure will assist asset managers both now and in the future in the context of a changing climate. The EPSRC-funded multidisciplinary FUTURENET project investigated the effect of climate change on the resilience of the UK transport network and this thesis is a part of that project considering the weather patterns leading to slope failures along transport infrastructure slopes within the UK. To that end a series of slope failure case studies were investigated to understand the processes leading to failure. These were compiled using nationally held datasets as well as news reports. This research used data from the FUTURENET partners that hold national data sets and asset management information. This shows the wide reaching remit of a multidisciplinary collaborative project such as FUTURENET, but also highlights the limitations of datasets collected and used for very specific purposes and not necessarily suited to wider research. From these case studies a suite of slope failure weather thresholds were developed. These thresholds consider the antecedent period, water content within the slope through the soil moisture deficit and triggering rainfall through comparison to the long term average rainfall. Consideration was given to possible future weather using weather event sequences (WESQs), possible weather patterns for 2050 derived from the UKCP09 climate projection data. By considering these possible weather patterns with the slope failure thresholds a picture of a possible future was evaluated.

The application of the crop water stress index (CWSI) method to irrigation scheduling is enhanced by knowledge of the relationship between CWSI and soil water potential (SWP) and how this relationship is affected by soil texture. A study using the same cultivar of cotton on three different soils was conducted in southern Arizona over a single growing season. Detailed data were collected of CWSI and soil moisture content for several treatments that scheduled irrigations at threshold CWSI values. CWSI was correlated with soil water potential values calculated from pressure plate determined moisture release curves. Spatial variability of soil characteristics necessitated use of average rather than plot specific moisture release curves. Analysis showed a linear CWSI-SWP relationship that varied greatly with soil depth and study site. The study concluded that soil profile average SWP alone does not normalize the CWSI between sites with different soil textures.

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The moisture content of road foundations plays an important role in the durability of the pavement and the driving comfort of the road. After a pavement has been completed, gradual moisture changes occur in the foundations until equilibrium conditions can be reached, and this can have negative results if expansive clays, for example, are present in the foundation. Pre-wetting of the foundation material is seen as a method to minimilize moisture changes after construction, but if the pavement was already completed, it would be very difficult to change or alter the moisture content in the foundation, because water could then only be applied to the shoulder areas of the road and horizontal infiltration in the soil is exceptionally slow. The research which is reported in this account was undertaken to determine whether the process of electro-osmosis could be applied to accelerate water infiltration underneath covered areas, as in, for example, road foundation layers. Electro-osmosis, if found to be successful, has various advantages, of which the most important is that it can be applied without stopping the normal operations of the road. This research was carried out on a mixture of G5 material (TRH14 classification) and fine material in the form of clay with a low plasticity. Firstly, tests were performed to determine the percentage of fines required. It was found that, if too little fines were present infiltration did not occur, because moisture could flow freely through the openings between the rough aggregate. Electro-osmosis also had no effect on the rate of flow. The allocated amount of fines required to fill sufficient openings was about 30% (TRH14 classification of mixture is G10). Free flow was stopped and true infiltration occurred. Simultaneously, the rate of infiltration could be accelerated with electro-osmosis. Furthermore, a two-dimensional model of a road was constructed with electrodes placed on both sides, with the aim to determine the infiltration pattern controlled by electro-osmosis and what the effect of the initial moisture content would be on the process. Water was introduced to the one side of the model road and the wetting of the foundation was investigated. If the electric current for electro-osmosis was switched off, the infiltration was mainly vertical, as expected, but with the current switched on, there was an obvious acceleration of infiltration in the horizontal direction. As in the case of the initial tests, it was found that electro-osmosis was not very successful to accelerate horizontal infiltration at low percentages of fines. Furthermore, it was obvious that electroosmosis was also more effective if the initial moisture content of the soil was low. Low amounts of fines and high initial moisture contents had rather the electroosmotic flow of water passing underneath the road as a result instead of infiltration acceleration, with the result that the moisture content did not change much. The research thus showed that electro-osmosis is a possible manner in which moisture could be conducted into the foundation layers of roads to increase the moisture content if the appropriate amount of fines and moisture content were present in the foundation material. Further research could still be carried out and the materials in each case should be practically evaluated before this method could be continued with. / AFRIKAANSE OPSOMMING: Die voginhoud van padfondamente speel ’n belangrike rol in die duursaamheid van die plaveisel en die rygerief van die pad. Nadat ’n plaveisel voltooi is, vind daar geleidelike vogverandering in die fondamente plaas totdat ewewigstoestande bereik is, en dit kan nadelige gevolge inhou indien uitsettende kleie byvoorbeeld in die fundament teenwoordig is. Voorafbenatting van die fondamentmateriaal word gereken as ’n metode om vogveranderinge na konstruksie te minimeer, maar indien die plaveisel reeds voltooi is, is dit baie moeilik om die voginhoud in die fondament te verander of beheer omdat water dan slegs buite die skouerareas van die pad toegedien kan word en horisontale infiltrasie in grond uiters stadig is. Die navorsing waaroor hierin verslag gedoen word, is onderneem om te bepaal of die proses van elektro-osmose aangewend kan word om waterinfiltrasie onder bedekte areas, soos byvoorbeeld padfondamentlae, te versnel. Elektro-osmose, indien dit suksesvol blyk te wees, hou verskeie voordele in, waarvan die belangrikste dat dit aangewend kan word sonder om die normale bedryf van die pad te staak. Die ondersoek is uitgevoer op ’n mengsel van G5 materiaal (TRH14 klassifikasie) en fynstof in die vorm van klei met ’n lae plastisiteit. Eerstens is toetse uitgevoer om die persentasie fynstof wat nodig is, te bepaal. Daar is bevind dat, indien te min fynstof teenwoordig is, infiltrasie nie plaasvind nie aangesien water vryelik deur die openinge tussen die growwe aggregaat kan vloei. Elektro-osmose het ook geen effek op die vloeitempo gehad nie. Die aangewese hoeveelheid fynstof om genoegsame openinge te vul was ongeveer 30% (TRH14 klassifikasie van mengsel is G10). Vrye vloei is dan gestuit en ware infiltrasie het plaasgevind. Terselfdertyd kon die tempo van infiltrasie versnel word met elektro-osmose. Voorts is ’n twee-dimensionele model van ’n pad gebou, met elektrodes aan weerskante geplaas, met die doel om te bepaal of die infiltrasiepatroon deur elektro-osmose beheer kon word en wat die effek van beginvoginhoud op die proses sal wees. Water is aan een kant van die modelpad ingevoer en die benatting van die fondament bestudeer. Indien die elektriese stroom vir elektroosmose afgeskakel was, was die infiltrasie hoofsaaklik vertikaal, soos verwag, maar met die stroom aangeskakel was daar duidelike versnelling van infiltrasie in die horisontale rigting. Net soos in die geval van die aanvanklike toetse is bevind dat elektro-osmose nie baie suksesvol was om horisontale infiltrasie te versnel by lae persentasies fynstof nie. Dit het verder geblyk dat elektro-osmose ook meer effektief was indien die aanvanklike voginhoud van die grond laag was. Lae hoeveelhede fynstof en hoë aanvanklike voginhoude het eerder elektroosmotiese deurvloei van water onderdeur die pad tot gevolg gehad as infiltrasieversnelling, met die gevolg dat die voginhoud nie veel verander het nie. Die navorsing het dus getoon dat elektro-osmose ’n moontlike wyse is waarop water in die fondamentlae van paaie ingevoer kan word om die voginhoud te verhoog indien die geskikte hoeveelheid fynstof en voginhoud in die fondamentmateriaal teenwoordig is. Verdere navorsing kan nog uitgevoer word en die materiale van elke geval sal prakties evalueer moet word voordat met die metode voortgegaan kan word.

Physiological responses of six sorghum (Sorghum bicolor (L.) Moench) hybrids and their respective parental lines were evaluated under high and low soil moisture conditions at Tucson, Arizona in 1980 and 1981. Apparent photosynthesis, transpiration, diffusive resistance, and temperature differential (ambient temperature minus leaf temperature) were measured under field conditions at weekly intervals. To measure apparent photosynthesis, a small plexiglas chamber was sealed over a section of leaf blade and gas was sampled with two syringes pulled at a 30 or 60 second interval. The gas samples were injected from the syringes into an infrared gas analyzer to measure CO(,2) concentrations. Transpiration, diffusive resistance, and temperature differential were measured with a steady state porometer. Regression analysis was used to compare the physiological performance of the germplasm sources over a wide range of environmental conditions. The physiological characteristics of the highest yielding sorghum hybrid in 1980 were the most stable across all environments. This hybrid was superior to both its male and female parent for all four physiological characteristics. In 1980, this hybrid was superior to the other hybrids in temperature differential and transpiration. The superior yielding hybrid had the highest mean apparent photosynthesis and the lowest mean diffusive resistance. All hybrids had higher yields than their respective male parents under both irrigation treatments. Thirty-five days after planting, the superior yielding hybrid had the greatest leaf, stem, and root dry weights. This hybrid also had the highest relative leaf area expansion rate. Heterosis for stomatal density was not observed either year. Regression analysis proved to be an effective tool for analyzing the sorghum germplasm over a diverse range of environmental conditions. By comparing the response of an individual germplasm against the mean response of the population under numerous environmental conditions, the slope, mean, and coefficient of correlation may be used to evaluate genotype-environment interactions.

Two laboratory experiments were conducted to study the effects of salt and nitrogen-sulfur compounds on the transformations of nitrogen in three Arizona soils. In the first experiment the effect of NaCl in concentrations of 0 to 1 m (molal) at moisture levels of 1/3 and 15 bars was studied in the Gila and Laveen loam soils. At 1/3 moisture nitrification of urea-¹⁵N and native soil nitrogen was appreciably reduced only at 1 m salt level. At 15 bars moisture, nitrification was almost completely inhibited by the 1 m salt concentration. Mineralization of soil nitrogen was reduced more by decreasing moisture than by increasing salt concentrations. Ammonia volatilization was increased by both salt and moisture stress and was associated with inhibition of nitrification. Slight effects of salt were observed on ¹⁵N immobilization and ¹⁵N recovery (including volatilization). In the second experiment nitrogen-sulphur combinations (¹⁵N labelled) of KNO₃, KNO₃ + S, urea, urea + S, APS (ammonia polysulfide) and Thiosul (ammonium thiosulfate) were studied at field capacity (FC) and 1.5 FC moistures. In the calcareous Gila soil nitrification was suppressed by the presence of sulfur at 1.5 FC moisture. Volatilization losses were appreciable only from APS. Immobilization of ¹⁵N was greatest from treatments with the higher sulfur rate (elemental S). Denitrification was slightly increased by sulfur at FC, however, at 1.5 FC dramatic losses occurred by denitrification (autotrophic in the presence of sulfur, especially with elemental S. The nitrifying ability of the slightly acid and coarse textured Sonoita soil was low. Nitrification was suppressed more by the presence of sulfur at both moistures. Ammonia volatilization was appreciable from APS followed by urea. ¹⁵N immobilization was high from urea followed by APS. Appreciable losses by denitrification occurred only with APS. The Sonoita soil showed a lower sulfur oxidizing power than the Gila with the only appreciable rate of oxidation from Thiosul followed by APS.

A study of soil variability was performed on an 87 hectare area within a uniform mapping unit--Pima Clay loam-- at The University of Arizona Branch Experiment Station at Marana. The primary interest was with respect to soilwater parameters. From 36 sites selected by an unbalanced three-stage nested design, 180 core samples were collected at 30 cm depth intervals to 150 cm. In addition, 500 bulk samples were taken at the 60 cm depth on an equally spaced grid over a secondary sampling area of 96 by 76 meters. The measured parameters showed different patterns of spatial variation. For example, to estimate means within 10% for the 30 cm depth 5, 51, and 1,011 samples would be needed for bulk density, the porosity index, and the saturated hydraulic conductivity, respectively (using the 0.05 level of significance). Most of the other estimates for number of samples required were in a range of 50 to 100. Most coefficients of variation were between 10 and 50% with bulk density lower and saturated hydraulic conductivity higher. Variance components for the three stages obtained from the analysis of variance revealed that the variation among fields was smaller than within fields and sections for the majority of the measured parameters, their average relative contribution to the total variance being 25, 44, and 31%, respectively. Values of 15-bar moisture retention corresponding to the 500 bulk samples showed a frequency distribution close to the normal with a slight tendency toward skewness. Values of bulk density were normally distributed at each depth and on the combined 180 samples. The highly skewed distributed values of the saturated hydraulic conductivity proved to be normally distributed after a logarithmic transformation. The porosity index showed a nonconsistent distribution pattern at the different depths and a moderately skewed frequency distribution for the composite 180 samples. Close relationships were found between bulk density and per cent sand and silt. A highly significant correlation (significant at th 0.01 level) between 15-bar water retention and clay content existed. Values of the logarithm of the hydraulic conductivity showed a high degree of correlation with values of per cent pores drained at 50 millibars (correlation coefficients of high absolute values and significant at the 0.01 level). Particle size distribution exhibited a decrease of silt and clay and a corresponding increase of sand with depth. The average percentages of sand, silt, and clay at 30 cm depth were 23.3, 41.2, and 35.3, and at the 150 cm depth were 39.7, 35.6, and 24.7, respectively. A similar trend was revealed for bulk density which ranged from 1.42 at 30 cm depth to 1.57 g/cm³ at the 150 cm depth. Soil moisture release curves for each depth showed similar general shapes. The "porosity index" describing the moisture release curve in the low pressure range varied from 3.58 at 30 cm depth to 5.79 at the 150 cm depth. Mean values of the saturated hydraulic conductivity also tended to increase with depth--1.71 and 7.03 cm/hr at 30 and 150 cm depth, respectively. Comparison between the sampling scheme used and three-stage balanced designs revealed that at least two alternatives would be more effective in decreasing the variance of the mean, but they do not provide any degrees of freedom for the third stage. An apparent compromise was found to exist between the scheme used and the optimum unbalanced designs selected for efficient estimation of variance components for the majority of the measured parameters.

Recently, canopy temperature measurements and atmospheric vapor pressure deficits have been used to determine water stress in numerous plant species. A linear regression of the two parameters yields a crop water stress index (CWSI) baseline capable of determining a fraction of water stress between 0 (wet) and 100 (dry). Such a baseline was determined for one line of guayule (N396) in the spring of 1983 and used to determine time of irrigation for field plots. Three irrigation treatments were chosen based on CWSI measurements to aquire a relationship between rubber yield and water Stress. Treatments were irrigated when their respective CWSI measurements reached 0.30 (wet=1), 0.60 (medium=2), and 0.90 (dry=3). Duplicate tests were planted to determine if water delivery by drip irrigation differed from furrow irrigated plots. Very good correlations exist between rubber yield and seasonally averaged CWSI (r = 0.85). The interrelationship of rubber yield and total water applied was also high with r = 0.87. The highest rubber yield occurred in March in treatment 1 (wet) in the furrow irrigated field. Rubber yield was positively correlated with total water applied and inversely correlated with CWSI. Small differences were observed between the type of water delivery system used with similar treatments from both fields not being significantly different. The wet and medium treatments in both fields were about the same with the dry treatment being significantly different from the wet and medium treatments for total water applied. This indicates that guayule is not as sensitive to changes of 0.30 CWSI units as other species measured. Correlations between the CWSI and soil moisture deficits were very good with r=0.83 for 1983 and r=0.91 for 1984 indicating the CWSI can be used accurately to determine soil moisture deficits and vice-versa. A 0-stress moisture deficit range (0-SMDR) was determined for guayule where 0.0-2.26 and 0.0-4.58 cm (1983 and 1984, respectively) of water could be depleted from the soil profile before the plants showed stress as indicated by the CWSI. The 0-SMDR appears to be constant for a particular plant species in the same field for a particular year and may further define and standardize plant available soil moisture.

Soils darken upon wetting due to changes in the scattering properties of the individual soil particles. The objective of this research was to develop a procedure to map the distribution of wet soils using the radiance measurements acquired by a spaceborne imaging scanner. The soil-mapping procedure was designed for use in the regional exploration for ground water resources. The soil-mapping procedure was based upon the detection of reflectance changes in a comparison of Landsat 5 Thematic Mapper (TM) scenes acquired before and after a rain. The Stronghold watershed, which is situated on the western slopes of the Dragoon Mountains, Cochise County, Arizona, was chosen as the test site for the soil-mapping procedure. TM scenes depicting the watershed on 7 June 1985 and 14 November 1985 were used in the change-detection analysis. The region was dry at the time of the June overpass, the November overpass occurred two days after a rain. The recovery of reflectance from radiance requires knowledge of 1) the orientation of the surface relative to the sun and the satellite, 2) the exoatmospheric solar irradiance, 3) the atmospheric optical depth, and 4) the atmospheric path radiance. The orientation of the surface elements were defined through the use of a digital elevation model of the Stronghold watershed. The solar irradiance and atmospheric optical depth were obtained from the literature; the atmospheric path radiance was estimated from shadowed areas depicted in the images. Temporal changes in reflectance were detected by subtracting the November reflectance estimates from those recovered from the June radiance measurements. Changes significant at the 0.05 level were identified through use of the Student-t test. The identical significance level was used to identify temporal changes in the Perpendicular Vegetation Index, or PVI. A surface element was classified as an anomaly if there was a significant temporal change in reflectance with no attendant change in PVI. Field checks of the anomalies proved that wet soils could be mapped via the remote detection of changes in their reflectance. The majority of the false anomalies could be attributed to the disparity between the spatial resolutions of the radiance measurements and the topographic data.

The grain amaranths, Amaranthus cruentus and Amaranthus hypochondriacus have been promoted as grain-bearing plants of possible high productivity in saline or hot arid habitats. To investigate these claims, seeds of both species were germinated at 10, 15, 20, 25, 30, 35 and 40°centigrade. Germination percentage for both species was above 90% after four days at 20, 25, 30, and 35°C. Germination was negligible at 10 and 15°C and very low at 40°C. Seeds were germinated in isotonic solutions of PEG and NaCl at 0.0, -0.2, -0.4, -0.5, -0.6, -0.8, and -1.0 MPa osmotic potential at 30°C. Germination percentage was high in the range 0.0 to -0.4 MPa and dropped rapidly to zero in the -0.6 to -1.0 MPa range. Differences due to chemical effects were significant. Species differences were not. Radicles and hypocotyls were measured after six days in the above media. PEG was more inhibitory of seedling growth than was NaCl and generally inhibited A. cruentus more than A. hypochondriacus. This was also true of NaCl. All growth functions were slightly inhibited at 0.0 to -0.4 MPa and very inhibited above -0.6 MPa. PEG radically increased root/shoot ratio in both species.