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    Water and solutes in soil : hydraulic characterisation, sustainable production, and environmental protection : application for the degree of Doctor of Science from Massey University, Palmerston North, New Zealand
    (Massey University, 2002) Clothier, Brent E
    The soil of the rootzone, the fragile and fertile interface between the atmosphere and the subterranean realm, is characterised by massive transfers of water and solutes. Our understanding of the biophysical transport processes into, and through, soil has been enhanced by the research endeavours of the applicant, Brent Euan Clothier. Dr Clothier, a 1977 Ph.D. graduate of Massey University, has developed tools and techniques that increased the acuity of our vision of transport processes of water and solutes in soil, as well it has sharpened our ability to hydraulically characterise those mechanisms for the purpose of modelling and risk assessment. His research has also enhanced our understanding of how these biophysical processes affect sustainable agriculture, environmental protection, and the bioremediation of contamination. These endeavours are grouped, in this thesis, into four overlapping areas of research: • Processes and properties of water movement into and through soil • Processes and properties of solute movement through soil • Root uptake processes and sustainable irrigation • Plants, groundwater protection and bioremediation of contaminated soil. The key elements of these four themes, and their contribution to knowledge, form Chapters 2-5 of this thesis. Dr Clothier's awards, honours, and impact are discussed in Chapter 6.
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    Solute movement associated with intermittent soil water flow : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1991) Tillman, Russell Woodford
    The movement of nutrients within the root zone of orchard crops is important in determining both fruit yield and quality. Currently much of the research on solute movement in field soils concerns movement of chemicals to ground water. Little attention has been paid to smaller scale movement. In this study the movement of solutes in response to intermittent soil water flow was investigated in columns of repacked silt loam in the laboratory and in a similar soil in the field. In the laboratory study a 5mm pulse of a solution of potassium bromide and urea in tritiated water was applied to columns of repacked soil, left for three or ten days, and then leached with 30 mm of distilled water. Twelve days after the solute pulse was applied, the distributions of water, tritiated water, applied and resident nutrients and pH were measured. The bulk of the bromide and tritiated water was moved to between 50 and 1 50 mm depth in both water treatments. As the nitrogen applied in urea was mainly in the form of ammonium after three days, the water applied then caused little movement of nitrogen. But the water applied after 10 days caused the nitrogen, now in the form of nitrate, to move in a similar fashion to the bromide. The soil solution anion concentration determined the amount of cations leached. Calcium and magnesium were the dominant cations accompanying the nitrate and bromide downwards. The added potassium remained near the soil surface. Given the soil hydraulic properties, the behaviour of water and solutes could be simulated by coupling the water flow equations with the convection-dispersion equation, and by using solute dispersion , diffusion and adsorption parameters derived from the literature. The model assumed the Gapon relationship for cation exchange, and that hydrogen ion production during nitrification reduced the effective cation exchange capacity. It was able to simulate closely the experimental data. Two field experiments were conducted. The first involved application of a 5 mm pulse of potassium bromide solution followed by 50 mm of water to pasture plots of contrasting initial water content. Twenty-four hours later core samples of soil were collected and the distribution of water and bromide measured. Bromide applied to initially dry soil was much more resistant to leaching than bromide applied to moist soil. The second experiment lasted 12 days and was essentially an analogue of the laboratory experiment. The final nutrient distributions however differed considerably from those obtained in the laboratory, due to non-uniform flow in the structured field soil. Coupling a mobile-immobile variant of the convection-dispersion model with a description of the water flow provided a mechanistic model. When combined with the submodels developed in the laboratory study describing nutrient interactions and transformations, this model successfully described the solute movement under the four different field regimes of water and solute application. Evaporation and plant uptake, and diffusion between mobile and immobile phases emerged as key processes affecting nutrient movement. It is suggested some control over nutrient movement is possible by varying the relative timing of water and fertiliser applications.
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    Solute transport in a layered field soil : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1992) Snow, Valerie Olga
    Although concern about the effects of movement of chemicals through soil has brought about a need for greater understanding of solute transport, the question as to where best to focus the research effort remains open. Initially a philosophical fram ework was presented that described in a general sense how research into solute transport has been conducted. It was argued that we must combine modelling with experimentation for effective progress in understanding, and that the efforts in field versus lab experimentation and process- versus nonm echanistic modelling should be balanced. Currently there is a need for more field experimentation, but the preferred direction of the modelling effort is less clear. Both process-based and non-mechanistic models are considered in order to deduce the effect of soil layering on solute transport. Field experiments were carried out on a soil consisting of three layers of distinct texture. This soil was instrumented with porous cup samplers at four depths at twenty sites. There was also a 2 m2 lysimeter within the plot. In the first experiment irrigation was used to supplement rainfall in order to leach a surface application of solid KCl through the soil. Porous cup samples of the soil solution were collected on numerous occasions and soil cores less often . The experiment of the following year was similar in design except that no irrigation was used. Finally, in the third year, the Iysimeter was instrumented with porous cup samplers and the same experimental design repeated on a smaller scale. A convection-dispersion (CDE) model was applied to the lysimeter data. This was successful, provided that the surface soil and assumed Dirac delta solute input were not included in the calibration. Layering within the profile appeared to have little effect on solute transport. The transport porosity was revealed to be two-thirds of the water-filled porosity, thus a substantial part of the water-filled porosity did not transport solute. The CDE modelling of the field data was not particularly successful, probably due to the spatially variable nature of solute transport and water application. The Aggregated Mixing Zone (AMZ) model was also used. This model subdivided the transport porosity i nto convective and dispersive components, and also allowed for non-interacting flow paths. Although the AMZ model was conceptually appealing, parameterisation of the model was found to lack discrimination. Little further understanding of solute transport was gained from this model. Textural differences in the soil seem to be overwhelmed by both small-scale heterogeneity of water application and solute movement in the soil, especially near to the surface. It was apparent that processes occurring in the surface soil require much more attention than they have been afforded in the past. Both process-based modelling and field experimentation will increase our understanding of solute transport. It also seems that an increased effort in improving measurement techniques will be advantageous.
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    A study of the leaching of non-reactive solutes and nitrate under laboratory and field conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1992) Magesan, Gujjaiah Nanjaiah
    Leaching of solutes such as nitrate from soil to surface water and groundwater is of environmental and economic concern. Leaching experiments were conducted both in the laboratory using large intact soil cores (230 mm diameter; 250 mm depth) and in the field using a mole-pipe drained Tokomaru silt loam soil under pasture. In the laboratory experiments 'tracers' (tritium, bromide or chloride) were applied as pulse or step-change inputs to the soil surface during steady flow. A transfer function model, based on a probability density function (pdf), which characterised solute travel between inlet and outlet surfaces in terms of cumulative drainage, was used to predict solute movement. Using tracer model parameters, leaching of indigenous chloride was reasonably predicted, but the leaching of indigenous nitrate could not be modelled satisfactorily. This was apparently due to the dynamic nature and spatial variability of the biological transformations to which nitrate is subject in soil. In the field experiment solid sodium bromide and urea were applied in autumn 1990 to adjacent drained paddocks, each 0.125 ha in area. Soil, suction-cup and drainage samples were collected regularly during the drainage seasons of 1990 and 1991. The average amounts of drainage collected were 250 mm in 1990 and 320 mm in 1991, but the average amounts of nitrate leached were 47 and 20 kg N/ha, respectively. The results indicate the importance of source-strength for nitrate in N leaching loss. The nitrate-N concentration was around 35 g N m-3 in the early drainage, well above the WHO limit of 10 g N m-3, but dropped to around 2 g N m-3 later in the drainage season. About 8 % of the applied N, but 52 % of the applied bromide, was leached during the 1990 drainage season. This shows the important effect that biological reactions such as immobilization can have in reducing nitrate leaching. Comparisons were made between solute concentrations of suction-cup solution, soil extracted solution, and the drainage. For non-reactive solutes such as bromide (an applied solute) and chloride (an indigenous solute) die suction cup data provided better estimates of the solute concentration in the drainage than did the soil solution data. For nitrate, neither of these two measurements could estimate accurately solute concentrations in the drainage. The solute leaching data obtained in the field were modelled using transfer functions. The bromide and chloride data were used to calculate the pdf of solute travel times. For chloride, an exponential pdf fitted the data slightly better than a lognormal pdf, despite it having only one rather than two fitted parameters. The chloride pdf appeared to be similar for both 1990 and 1991. For bromide, the inferred pdf conformed to a log-normal distribution and was quite different from the pdf derived from the chloride data. It seems that assuming a pulse (Dirac delta) flux input for a surface-applied solid fertilizer is not valid, and that this is the reason for the discrepancy between the pdfs obtained using the bromide and chloride data. When the pdf derived from the chloride data was used to model nitrate leaching, the result was generally disappointing.
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    The convection dispersion equation -- not the question, the answer! : anion and cation transport through undisturbed soil columns during unsaturated flow : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1997) Vogeler, Iris; Vogeler, Iris
    Prediction of solute movement through the unsaturated zone is important in determining the risk of groundwater contamination from both "natural" and surface applied chemicals. In order to understand better the mechanisms controlling this water-borne transport, unsaturated leaching experiments were carried out on undisturbed soil columns, about 3 litres in volume, for two contrasting soils. One was the weakly-structured Manawatu fine sandy loam, and the other the well-aggregated Ramiha silt loam. Anion transport was satisfactorily described using the convection dispersion equation (CDE), provided that anion exclusion for the Manawatu soil, and adsorption for the Ramiha soil were taken into account. At water flux densities of about 3 mm h-1, a dispersivity of about 40 mm was obtained for the Manawatu soil, and a dispersivity of about 15 mm for the Ramiha soil. The difference was probably due to the contrasting structures of the two soils. Increasing the water flux density in the Manawatu soil to about 13 mm h-1 resulted in a slightly higher dispersivity of about 60 mm. Flow interruption resulted in a subsequent drop in the effluent concentration for the Manawatu soil but not in the Ramiha soil. This suggests that the lag time for transverse molecular diffusion from "mobile" to "immobile" water domains was important in the Manawatu soil, but not in the Ramiha soil. In both soils cation transport was described satisfactorily with the CDE in conjunction with cation exchange theory, providing that only 80% of the cations replaced by 1 M ammonium acetate were assumed to be involved in exchange reactions. Column leaching experiments were also carried out using a rainfall simulator and larger columns of about 22 litres of the Manawatu soil with a short pasture on top. Solid chemical was applied to both a dry and a wet soil surface. Neither the pasture nor the initial water content had a significant effect on solute movement. Slightly higher dispersivities of about 70 mm were found. Time Domain Reflectometry (TDR) was found to be valuable for monitoring solute transport in a repacked soil under transient water flow conditions. But in undisturbed soils TDR only proved to be accurate under steady-state water flow when absolute values of solute concentration were not sought. The CDE was thus found to satisfactorily answer the question of how to describe transport of non-reactive and reactive solutes under bare soil and under short pasture. This applied during both steady-flow and transient wetting.