A field lysimeter experiment was conducted on a sandy loam soil during the 1990 and 1991 growing seasons. The experiment tested the effects of different watertables on soybean yields, and on moisture distribution and nitrogen concentration of the soil profile. The watertable depths were 40, 60, 80, and 100 centimeters (cm). / Yields were measured in terms of number of beans per plant, number of pods per plant, number of beans per pod, and seed protein content at harvest. / Soil samples collected at depths of 30 and 70 cm from the soil surface were analyzed for moisture content and NO$ sb3 sp-$-N and NH$ sb4 sp+$-N concentrations. / The experimental results showed that controlled watertable management increased the yield and decreased soil NO$ sb3 sp-$-N levels. The best results from the watertables tested were found to be at 60 and 80 cm. This is suggested as the range of watertable depths that should be maintained for optimum soybean production.

A computer model simulating moisture migration in soil from a drip source considering root water extraction (RWE) was developed. The model was formulated using Continuous System Modeling Program (CSMP). / A two-dimensional non-linear unsaturated transient flow equation was solved using the principle of mass conservation and Darcy's law on soils of dwarf-apple orchards located in southwestern Quebec. A finite axisymmetric cylinder with homogeneous, isotropic and non-swelling soil was considered for the simulations. No flow conditions across the boundaries of the cylinder were fixed. The initial soil moisture contents in the soil profile observed in the field were input for the simulations. / The macroscopic approach was used to compute RWE as a function of (THETA), Z and t. The RWE was assumed to be equal to evapotranspiration (EP) which was estimated using temperatures and the solar radiation index of the location. / The moisture contents in the soil profile observed at the termination of emitter discharge were in close agreement with the simulated values. The soil moisture distribution was found to depend on the amount of water remaining in the soil and soil moisture retention characteristics. It is independent of the rate of emitter discharge, the depth of root zone and method of application.

A well-managed irrigation scheduling system needs a rapid, preCIse, simple, costeffective and non-destructive soil water content sensor. The PRl profile probe and Diviner 2000 were used to determine the timing and amount of irrigation of three cover crops (Avena sativa L., Secale cereale L. and Lolium multiflonlm Lam.), which were planted at Cedara, KwaZulu-Natal. The PRl profile probe was first calibrated in the field and also compared with the Diviner 2000. For the calibration of the PRl profile probe the factory-supplied parameters (aJ = 8.4 and ao = 1.6) showed good correlation· compared to the soil-estimated parameters (aJ = 11.04 and ao = 1.02). The factorysupplied parameters gave a linear regression coefficient (r2 ) of 0.822 and root mean square error (RMSE) of 0.062. The soil-estimated parameter showed a linear regression coefficient of 0.820 with RMSE of 0.085. The comparison between the soil water content measured using the PR1 profile probe and Diviner 2000 showed a linear regression coefficient of 0.947 to 0.964 with a range of RMSE of 0.070 to 0.109 respectively for the first 100 to 300 mm soil depths. The deeper depths (400, 600 and 1000 mm) showed a linear regression coefficient ofO.716to 0.810 with a range of 0.058 to 0.150 RMSE. These differences between the shallow and deeper depths could be due to soil variability or lack of good contact between the access tube and the surrounding soil. To undertake irrigation scheduling using the PRl profile probe and Diviner 2000, the soil water content limits were determined using field, laboratory and regression equations. The field method was done by measuring simultaneously the soil water content using the PR1 profile probe and soil water potential using a Watermark sensor and tensiometers at three depths (100, 300 and 600 mm) from a 1 m2 bare plot, while the soil dries after being completely saturated. The retentivity function was developed from these measurements and the drained upper limit was estimated to be 0.355 m3 m-3 when the drainage from the pre-wetted surface was negligible. The lower limit was calculated at -1500 kPa and it was estimated to be 0.316 m3m,3. The available soil water content, which is the difference between the upper and lower limit, was equal to 0.039 m3 m,3. In the laboratory the soil water content and matric potential were measured from the undisturbed soil samples taken from the edge of the 1 m2 bare plot before the sensors were installed. Undisturbed soil samples were taken using a core sampler from 100 to 1000 mm soil depth in three replications in 100 mm increments. These undisturbed soil samples were saturated and subjected to different matric potentials between -1 to -1500 kPa. In the laboratory, the pressure was increased after the cores attained equilibrium and weighed before being subjecting to the next matric potential. The retentivity function was then developed from these measurements. The laboratory method moved the drained upper limit to be 0.390 m3 m,3 at -33 kPa and the lower limit be 0.312 m3m-3 at -1500 kPa. The regression equation, which uses the bulk density, clay and silt percentage to calculate the soil water content at a given soil water potential, estimated the drained upper limit to be 0.295 m3m-3at -33 kPa and the lower limit 0.210 m3 m,3 at -1500 kPa. Comparison was made between the three methods using the soil water content measured at the same soil water potential. The fieldmeasured soil water content was not statistically the same with the laboratory and estimated soil water content. This was shown from the paired-t test, where the probability level (P) for the laboratory and estimated methods were 0.011 and 0.0005 respectively at 95 % level of significance. However, it showed a linear regression coefficient of 0.975 with RMSE of 0.064 when the field method was compared with the laboratory method. The field method showed a linear regression coefficient of 0.995 with RMSE of 0.035 when compared with the estimated method. The timing and amount of irrigation was determined using the PR1 profile probe and Diviner 2000. The laboratory measured retentivity function was used to define the fill (0.39 m3 m-3 ) and high refill point (0.34 m3 m-3 ). The soil water content was measured using both sensors two to three times per week starting from May 29 (149 day of year, 2002) 50 days after planting until September 20 (263 day of year) 11 days before harvesting. There were five irrigations and twenty rainfall events. The next date of irrigation was predicted graphically using, the PRl profile probe measurements, to be on 3 September (246 day of year) after the last rainfall event on 29 August (241 day of year) with 8 mm. When the Diviner 2000 was used, it predicted two days after the PRl profile probe predicted date. This difference appeared since the Diviner 2000-measured soil water content at the rooting depth was slightly higher than the PRl profile probe measurements. The amount of irrigation was estimated using two comparable methods (graphic and mathematical method). The amount of irrigation that should have been applied on 20, September (263 day of year) to bring the soil water content to field capacity was estimated to be 4.5 hand 23 mm graphically and 5.23 hand 20 mm mathematically. The difference between these two methods was caused due to the error encountered while plotting the correct line to represent the average variation in soil water content and cumulative irrigation as a function of time. More research is needed to find the cause for the very low soil water content measurements of the PRI profile probe at some depths. The research should be focused on the factors, which could affect the measurement of the PRl profile probe and Diviner 2000 like salinity, temperature, bulk density and electrical conductivity. Further research is also needed to extend the non-linear relationship between the electrical resistance of the sensor and soil water potential up to -200 kPa. This non-linear equation of the Watermark is only applicable within the range of soil water potential between -10 and -100 kPa. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

Accurate estimation of reference evaporation is necessary for the estimation of actual evaporation for irrigation and water resource management purposes. Estimation of reference evaporati~n using the Penman-Monteith method using automatic weather station (AWS)measurements requires the available energy to be accurately estimated. The available energy of short grass of 0.12 m was measured using a component net radiometer and soil heat flux plate measurements at the Faculty of Sciences and Agricultural (Agrometeorological station, University of Natal, Pietermaritzburg, latitude ~29.79 oS, longitude ~ 30.95 °E, altitude ~ 650 m). In an attempt to evaluate the accuracy of commonly used procedures of estimating available energy, estimates of net irradiance (from net long wave irradiance and reflection coefficient estimate) and soil heat flux density were compared to the actual measurements. The linear approximation of atmosphere minus crop surface emittance based on air temperature was compared with measured net long wave irradiance and similar empirical formulations. The underestimation of the measured net long wave irradiance was observed using the linear approach. Furthermore, a plot of measured clear sky net long wave irradiance and air temperature showed a logarithmic relation. The estimated reflected solar irradiance was overestimated for the reference crop. The measured soil heat flux density was observed to vary not only with net irradiance but also with cloudiness, wind speed and soil water content. The soil heat flux density measured with plates was noticed to follow the measured net irradiance. The sensitivity of Penman-Monteith latent heat estimate was investigated for the use of estimated reflection coefficient and soil heat flux density as well as ignored soil heat flux density. Results showed the latent heat estimate to be greater when soil heat flux density was ignored. Reduced set assumptions of Penman-Monteith were assessed usmg the microclimatic measurements. The grass reference evaporation estimate using estimated water vapour pressure from the pervious day minimum air temperature and approximated wind speed were found to be seasonal and procedure dependent. The hourly-reduced set estimate of reference evaporation was in good agreement with the grass Penman-Monteith estimate. The estimated daily water vapour pressure underestimated the daily grass Penman-Monteith estimate. The sensitivity of the reduced set reference evaporation estimate was compared for the two values of approximated wind speeds. The assumption of 2 m S-1 wind speed gave a relatively better result. The sensitivity of the surface temperature energy balance (STEB) estimate of reference evaporation was investigated using two different atmospheric stability procedures. The evaporation estimate agreement and performance of the technique were found to vary depending on the stability correction procedure. The Monteith (1973) correction procedure was observed to be more sensitive to a higher surface-air temperature difference. The Monteith (1973) procedure was found to underestimate the reference evaporation and this resulted in a lower correlation coefficient. The uncorrected and Campbell and Norman (1998) stability corrected procedure of STEB estimate overestimated the reference evaporation but resulted in good agreement with actual reference evaporation. The use of estimated available energy using the STEB method resulted in a 7 % overestimate of measured available energy. Different designs of atmometers have been used to measure evaporation. The less expensive and simple ET_gageR (Model A and E) atmometer for daily evaporation measures were compared to grass-based and alfalfa-based Penman-Monteith and STEB estimate of reference evaporation. Two different evaporation surface covers used with the device allowed for the comparison to be made. Measurements using the canvas 30 ET-gage cover for grass reference evaporation were compared to grass based Penman-Monteith and STEB reference evaporation estimates. Correlation between the canvas 30 measures and Penman-Monteith estimates were good compared to the STEB estimate. The ET-gage canvas 54 measures were in a good agreement with alfalfa based Penman-Monteith reference evaporation estimate. There was, however, a slight time lag in ET-gage evaporation with ET-gage evaporation continuing accumulation when the reference evaporation was zero. The sensitivity of the ET-gage for microclimate variation was tested using the measurements made for two levels and three different microclimates. A shade measurement of reference evaporation was overestimated. The response of the ET-gage to one and two meter microclimate measures was similar to the short grass measurement. Furthermore, the ET-gage surface evaporation estimate using the STEB method showed equal response to the ET-gage surface for the microclimate measure and explained the possible cause of the lag of the ET-gage response. Accurate microclimate measurements is a requirement for the performance of the PenmanMonteith approach for the estimation of reference evaporation. The investment cost required for an AWS set up is high. Alternative options for gathering information of the microc1imate measurements required for calculating reference evaporation were assessed in terms of cost saving, accuracy and other advantages. A weather station system using a Hobo H8 logger (internal relative humidity and air temperature sensor and two external channels, one which was used for solar irradiance measurements) was found to be a cost-effective method for calculating the necessary microclimatic information for calculating reference evaporation. With this system reference evaporation was estimated with reasonable accuracy, at 16 % of the cost of normal AWS system. The use of an Event Hobo logger and an ET-gage was found to provide a reasonable estimate of reference evaporation. The use of the reduced set evaporation weather station was found to be unreasonable in terms of cost and accuracy. Air temperature and relative humidity were measured from different design of radiation shields and Stevenson screens. The use of home-made seven-plate plastic radiation shields provided a similar shield to radiation and ventilation compared to manufactured shields. At a low solar angle when wind speed was very low, all the radiation shields including the small Stevenson screens showed a higher air temperature difference relative to the standard Stevenson screen. The highest average difference of air temperature measurement was measured within the small Stevenson screen and metal-radiation shield. The home-made plastic radiation shield showed similar averages of air temperature and water vapour pressure difference compared to the six- and twelve-plate Gill radiation shields. The home-made metal radiation shield showed relatively higher deviation from the mean being cold at night time and hot during the day. More research is needed to explore the efficiency of the ET-gage evaporation from variety of microclimates to establish the cause of the overestimate under shade, to develop better relation of clear day net long wave irradiance and air temperature and the use of a wind speed sensor with Hobo H8 weather station system. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

The demand for timber products in South Africa, and consequently afforestation, is increasing. There exists, however, abundant experimental evidence that trees utilise more soil water than other dryland crops. Because water is limited in South Africa, decision makers therefore currently face the challenge of determining a socially, and economically acceptable afforestation management plan to enable the reconciliation of increased timber demand with scarce water supply. This challenge, and the subsequent decisions that need to be made, may be accomplished by making use of suitable simulation models to predict the impacts of the forest hydrological system on water resources. Currently, these impacts are assessed through an Afforestation Permit System (APS) which is based on a model now acknowledged to have become outdated. In this dissertation an enhanced ACRU Forest Decision Support System (FDSS), now called the ACRU Forest model, is developed and proposed as a tool for modelling forest hydrological impacts on water resources. Research for this study included a literature survey, fieldwork at two locations, viz. at forest irrigation trials at Mkuze in northern KwaZulu-Natal, and at forest site preparation trials near Ugie in the Eastern Cape, as well as the evaluation, for purposes of model development, of a series of workshops. Results from the fieldwork experiments show that large tree water use potentials are possible if water is not limiting, although a water supply threshold exists at about 1400mm.annum-1, above which diminishing growth returns occur. Furthermore, trees display improved growth on more intensive forest site preparations, but at the expense of higher water usage rates. A series of workshops which had as the main objective the extraction of expert knowledge by stimulating responses to prepared questions and by constructive discussion on relative issues pertaining to forest hydrological modelling, yielded valuable information. This information, together with that gleaned from the literature, the fieldwork and a new Quaternary catchment database for South Africa, was used to develop the ACRU Forest model. The PC-based ACRU Forest model has the potential to aid decision makers by providing an initial indication of the impacts of afforestation on water resources, within a matter of minutes. An example of the model's application is used to demonstrate its operation, relative accuracy and its potential benefits in simulating hydrological responses to afforestation. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.

A study was conducted in 2004 and 2005 to determine the effect of liquid hog manure fertilization on greenhouse gas emissions from the surface of a grassland pasture in south-eastern Manitoba. The objectives of this research were to determine the effects of manure application, itstiming and soil moisture on greenhouse gas emissions from pasture soil, cattle dung and urine patches. Nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) emissions were determined from grassland soil surface, and from cattle dung and artificial urine patches. Liquid hog manure treatments were no manure (Control); 153 kg ha-1 of available-nitrogen (N) (two year average) in spring (Spring); and 149 kg ha-1 as half-rate applications in fall and spring (Split). Four field experiments were conducted on grassland plots. The static-vented chamber technique was used to estimate gas emission rates. Two of the experiments focused on the effects of manure application timing and soil moisture on greenhouse gas emissions from the grassland soil surface. The other two experiments focused on the effects of manure application and soil moisture on greenhouse gas emissions from cattle dung and artificial urine patches. Fresh cattle dung was collected from steers grazing adjacent pastures receiving the same three manure treatments. Artificial cattle urine treatments were generated by converting blood urea concentrations of the steers into urine-N concentrations. Manure application increased (P≤0.01) cumulative N2O emissions from the grassland soil surface with Control, Split and Spring treatments averaging 7, 43 and 120 mg N2O-N m-2, respectively. Of the two manure treatments, the Spring treatment emitted higher (P≤0.10) N2O emissions than the Split treatment. Soil moisture was a major factor influencing the quantity and type of greenhouse gas emissions, with saturated areas emitting CH4 during warm periods, whereas drier areas emitted N2O. Nitrous oxide emissions from these dry areas were higher in manure-treated plots. Spring application increased root density by 45% in the top 5 cm of soil compared to the Control. An increase in soil organic carbon with root density may offset any increase in greenhouse gas emissions caused by manure treatment. Cattle dung from Split and Spring treatments had higher cumulative N2O emissions (30 and 82 mg N2O-N m-2, respectively) compared to dung from Control pastures (6 mg N2O-N m-2) over two study years. Dung from the Spring treatment emitted more N2O (P≤0.01) than the other two treatments. All cattle dung patches emitted CH4 after deposition though unaffected by manure treatment. Artificial urine having highest N concentration had greater (P≤0.05) cumulative N2O emissions (690 mg N2O-N m-2) than urine with the lowest N concentration (170 mg N2O-N m-2). Drier soil locations emitted more N2O from cattle dung and artificial urine patches than wetter areas. This study demonstrated that Split application of liquid hog manure to grassland emitted less N2O than a complete application in spring. Moisture greatly affected the location of N2O and CH4 emissions. Drier areas emitted more N2O than wetter ones. Particularly, the findings indicate a need to assess grassland on periodically saturated soils as sources rather than sinks for CH4. Application of manure increased greenhouse gas emissions from cattle dung and urine patches with urine potentially having the greatest impact because of their higher emissions of N2O. An increase in root growth seems to offset greenhouse gas emissions from manure application.

Concern about NO$ sb3 sp-$-N leaching and groundwater pollution from monoculture corn (Zea mays L.) has prompted investigation of alternative production systems which reduce N leaching. Both intercrop systems and water table controls alone have been shown to increase nitrogen (N) uptake and reduce soil NO$ sb3 sp-$-N accumulation in cropping systems. There is a need to maintain crop productivity while reducing the potential for soil NO$ sb3 sp-$-N leaching into groundwater. However, there has been no information available regarding agronomic and physiological aspects of N and water management for monocrop corn and corn competing with annual Italian ryegrass (Lolium multiflorum Lam) in an intercrop system. A study was conducted in southwestern Quebec during 1993 and 1994. Nitrogen and dry matter components in the plant-soil system were determined. Intercropped corn grain yield did not differ from monocropped corn under high N fertility. At harvest, the corn-annual ryegrass intercrop system increased total aboveground N uptake by 77.2 and 50.7 kg ha$ sp{-1}$ when compared with the corn monocrop system in 1993 and 1994, respectively. The intercrop system reduced the amount of NO$ sb3 sp-$-N in the top 1 m of soil by 47% (92.3 kg N ha$ sp{-1}$) at harvest in 1993. Water table controls had little effect on corn yield, N use efficiency and soil NO$ sb3 sp-$-N accumulation over the two years of this study. Both plant establishment and weather conditions affected the ability of annual ryegrass to aid in the uptake of soil NO$ sb3 sp-$-N. The reproductive development of water stressed plants after silking was limited more by overall plant changes due to water stress than assimilate supply. The delivery of C (sucrose) and N ($ sp{15}$N urea) into corn plants via stem-injection showed that externally supplied C changed both the source strength (photosynthetic inhibition) and sink strength (decreased total grain production), while distribution of $ sp{15}$N was affected by p

Satellite observations provide information on land surface processes over a large spatial extent with a frequency dependent on the satellite revisit time. These observations are not subject to the spatial limitations of the traditional point measurements and are usually collected in a global scale. With a reasonable spatial resolution and temporal frequency, the Moderate Resolution Imaging Spectroradiometer (MODIS) is one of these satellite sensors which enables the study of land-atmospheric interactions and estimation of climate variables for over a decade from remotely sensed data. This research investigated the potential of remotely sensed land surface temperature (LST) data from MODIS for air temperature (Ta) and soil moisture (SM) estimation in New Zealand and how the satellite derived parameters relate to the numerical model simulations and the in-situ ground measurements. Additionally, passive microwave SM product from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) was applied in this research. As the first step, the MODIS LST product was validated using ground measurements at two test-sites as reference. Quality of the MODIS LST product was compared with the numerical simulations from the Weather Research and Forecasting (WRF) model. Results from the first validation site, which was located in the alpine areas of the South Island, showed that the MODIS LST has less agreement with the in-situ measurements than the WRF model simulations. It turned out that the MODIS LST is subject to sources of error, such as the effects of topography and variability in atmospheric effects over alpine areas and needs a careful pre-processing for cloud effects and outliers. On the other hand, results from the second validation site, which was located on the flat lands of the Canterbury Plains, showed significantly higher agreement with the ground truth data. Therefore, ground measurements at this site were used as the main reference data for the accuracy assessment of Ta and SM estimates. Using the MODIS LST product, Ta was estimated over a period of 10 years at several sites across New Zealand. The main question in this part of the thesis was whether to use LST series from a single MODIS pixel or the series of a spatially averaged value from multiple pixels for Ta estimation. It was found that the LST series from a single pixel can be used to model Ta with an accuracy of about ±1 ºC. The modelled Ta in this way showed r ≈ 0.80 correlation with the in-situ measurements. The Ta estimation accuracy improved to about ±0.5 ºC and the correlation to r ≈ 0.85 when LST series from spatially averaged values over a window of 9x9 to 25x25 pixels were applied. It was discussed that these improvements are due to noise reduction in the spatially averaged LST series. By comparison of LST diurnal trends from MODIS with Ta diurnal trends from hourly measurements in a weather station, it was shown that the MODIS LST has a better agreement with Ta measurements at certain times of the day with changes over day and night. After estimation of Ta, the MODIS LST was applied to derive the near-surface SM using two Apparent Thermal Inertia (ATI) functions. The objective was to find out if more daily LST observations can provide a better SM derivation. It was also aimed to identify the potential of a land-atmospheric coupled model for filling the gaps in derived SM, which were due to cloud cover. The in-situ SM measurements and rainfall data from six stations were used for validation of SM derived from the two ATI functions and simulated by the WRF model. It was shown that the ATI function based on four LST observations has a better ability to derive SM temporal profiles and is better able to detect rainfall effects. Finally, the MODIS LST was applied for spatial and temporal adjustment of the near-surface SM product from AMSR-E passive microwave observations over the South Island of New Zealand. It was shown that the adjustment technique improves AMSR-E seasonal trends and leads to a better matching with rainfall events. Additionally, a clear seasonal variability was observed in the adjusted AMSR-E SM in the spatial domain. Findings of this thesis showed that the satellite observed LST has the potential for the estimation of the land surface variables, such as the near-surface Ta and SM. This potential is greatly important on remote and alpine areas where regular measurements from weather stations are not often available. According to the results from the first validation site, however, the MODIS LST needs a careful pre-processing on those areas. The concluding chapter included a discussion of the limitations of remotely sensed data due to cloud cover, dense vegetation and rugged topography. It was concluded that the satellite observed LST has the potential for SM and Ta estimations in New Zealand. It was also found that a land-atmospheric model (such as the WRF coupled with the Noah and surface model) can be applied for filling the gaps due to cloud cover in remotely sensed variables.

Unbound granular materials (UGMs) used in the base and sub-base layers of flexible pavements play a significant role in the overall performance of the structure. Proper understanding and characterization of the deformation behaviour of UGMs in pavement structures are, therefore, vital for the design and maintenance of flexible pavements. In this study, the resilient deformation (RD) and the permanent deformation (PD) behaviour of UGMs were investigated for the better understanding and improved modelling of these deformation characteristics. The study is based on a series of repeated-load triaxial (RLT) tests carried out on several UGMs commonly used in pavement structures. Here, the influences of stress level and moisture content - two of the most significant factors affecting the deformation behaviour of UGMs - were analysed. The effects of the grain size distribution and the degree of compaction were also considered. The study on the RD behaviour indicated that the resilient stiffness (MR)of UGMs increases with the increased bulk stress level, which can be satisfactorily described by the k-θ model. Moisture was found to negatively impact the MR as long as the deformation was mostly resilient with a negligible amount of accumulated PD. Analysis of the influence of moisture on the parameters k1 and k2 of the k-θ model showed that k1 decreases with increased moisture and k2 is relatively insensitive to moisture. Based on these observations, a simple model was developed for the impact of moisture on MR. The performance of this model was comparable to an existing moisture dependent MR model. In contrast, it was further observed that at the later stages of the RLT tests, after a relatively large number of load applications, the MR increased with increased moisture up to the optimum moisture content. This occurred when the RD was accompanied by a significant amount of PD. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. In this case k1 decreased, whereas k2 increased, with increased moisture. The existing MR-moisture model did not work for this behaviour. This suggests that the effect of PC on MRshould be considered in modelling. However, although not explored in this study, it may be possible to simulate this effect of increase in MR with increased moisture due to PC using the proposed model if k2 is expressed as a function of moisture. The PD characteristics of UGMs were investigated based on the multistage (MS) RLT test. In contrast with the single stage (SS) RLT test, the MS RLT test accounts for the effect of stress history and enables a comprehensive study of the material behaviour under cyclic stresses of various magnitudes. Since the existing PD models cannot be directly applied for the MS loading procedure, a general formulation based on the time hardening concept was derived that can be used to extend the models for the MS loading conditions. Based on this formulation, some of the current models were calibrated and their performance in predicting the PD behaviour in MS RLT tests was compared. The investigation regarding the impact of moisture on PD showed that moisture significantly increases the accumulation of PD. Generally, materials with finer grading showed more sensitivity to moisture with regards to both PD and RD. To characterize the impact of moisture, moisture sensitivity of different grain size distributions and the impact of the degree of compaction on PD with reduced effort, a simple model was proposed. Unlike some of the well-performing existing models, this model can be calibrated using a single MS RLT test without requiring any separate static failure triaxial tests. This model was validated using the MS RLT test data with satisfactory results. The sensitivity of the parameters of this model was studied with respect to moisture content, degree of compaction and grain size distribution. Some reasonable trends for the sensitivity of the parameters to these influential factors were obtained, which suggests that these may be further developed to incorporate into the model. / <p>QC 20150325</p>

This thesis studied the influence of moisture content on the dynamic estimation of stiffness in wood of Pinus radiata D. Don. This is an important non-destructive measure for estimation of stiffness in standing trees, logs and lumber. Moisture content affects both acoustic velocity and density in the fundamental equation of dynamic MOE (DMOE = V²ρ, where V = acoustic velocity and ρ = density). Investigation included measurements with boards in the laboratory considering moisture contents below and above FSP as well as temperatures below and above 0°C. This also included field measurements of trees in contrasting climate sites and over different seasons including a long drought. Methods for measuring green density and moisture content and the patterns of variation of these parameters were also investigated. A secondary component of this thesis explored the wood quality and some mechanisms of tree response to water stress in two contrasting sites in terms or rainfall and water deficits in a region of Australia. The large increases in DMOE for frozen wood above the FSP (4.5 to 6 GPa) will limit the use of DMOE for grading logs in regions with freezing winters. Results from the experiment remeasuring young trees and the upper range of moisture content and temperatures above 0°C from the experiment with boards showed small to moderate variation in DMOE (0.1 to 1 GPa) which calls for further investigation on analytical procedures for adjustment of DMOE. Such procedures should consider that variations in acoustic velocity and density with changes in moisture content are not proportional and that there are counteracting effects between the two parameters. It remains to be investigated whether the typical variation (under normal climate conditions) in sapwood green density observed in our experiments has some implications for the use of DMOE. On the other hand, it is anticipated that the large differences along the stem and among stands in whole-section green density may bias DMOE measurements in logs for resource assessment. This also needs to be investigated. A comparison between acoustic velocity alone and DMOE for resource assessment under different scenarios is recommended. The study in two contrasting climate sites (high-altitude vs. warm-dry) in the Hume region of Forests NSW, Australia, including young (10-11 years) and mature trees (34 36 years) of radiata pine showed distinctive short and long-term responses of trees to cope with the water-limiting environment. In response to long-term water deficits the warm-dry site developed heartwood and thus reduced sapwood earlier and at faster rates than the high-altitude site. The onset of heartwood formation seemed to be triggered by some site threshold for water use as broadly indicated by the sapwood area/ha. The latter was consistently lower for the warm-dry site across the different stands. The warm-dry site also showed increased short-term responses to water stress and these were interpreted as seasonal mechanisms of the trees to cope with the limiting environment. The trees compensated for the lower available moisture and higher transpiration rates by lowering their saturation and disrupting water conduction at some points (cavitation). The inverse trends of cavitation spots and cavitation bands with height in the stem suggested the trees have different strategies to sacrifice conducting xylem depending on the position on the stem. Finally, it is suggested that saturation tended to fall to critical 'safe' levels as a result of water stress and this varied depending on age, site, and position in the stem. Significant decreases in DMOE and basic density were observed for the warm-dry site and were attributed to lower proportions of latewood due to lower rainfall for that site during the period of latewood formation. These showed no obvious association with any of the long-term water-stress traits (sapwood percentage and number of heartwood rings).