An essential step in producing "drinking" water is to precipitate the suspended and dissolved colloids through the addition of flocculents such as lime, ferric chloride, aluminium sulphate and/or poly-electrolytes. The by-product of this process is termed water treatment sludge (WTS) and contains mainly silt, clay and some organic matter. Previously this material was disposed of in landfill but more recently, alternative methods for its disposal are being evaluated. A potential disposal option is land treatment. In this system of waste disposal the inherent properties of the soil are used to assimilate the waste. Although the effect of the land disposal of WTS on soil chemical quality is gaining increasing research attention, few studies have investigated the effects on soil physical quality. This study was originally commissioned by a local water utility to evaluate the effects of the land disposal of sludge produced at their works, on soil quality. At this plant organic polymers are used to both flocculate the material and to thicken the sludge in the water recovery process. Fresh sludge has a consistence approaching that of slurry but dries to angular shaped aggregates of extremely high strength. Nevertheless, sludge aggregates comprise a network of micro-pores and channels and are therefore porous. Because of these properties, the potential use of WTS as a soil conditioner was considered.. Since lime, gypsum and polyacrylamide are wellrecognised soil conditioners, these were included as reference treatments in the study. Two field trials (Brookdale and Ukulinga) and laboratory experiments were designed to investigate the influence of WTS on soil in terms of water retention, hydraulic conductivity, evaporation, aeration, aggregation and strength. Seven rates of WTS are represented at the . Brookdale trial but research efforts were concentrated on the 0, 80, 320 and 1280 Mg ha' treatments. WTS was also applied as a mulch (without incorporation into the soil) at the 320, 640 and 1280 Mg ha" level. Gypsum was applied at rates of 5 and 10 Mg ha", lime at 2 and 10 Mg ha' and anionic polyacrylamide at 15 and 30 kg ha'. At the Ukulinga trial, WTS was mixed with the upper 0.2 m of the soil at rates of 0, 80, 320 and 1280 Mgha'. Only the high rates of gypsum, lime and anionic polyacrylamide being tested at the Brookdale trial are represented at the Ukulinga trial. All treatments in this study were maintained fallow. The laboratory study features an additional two soils to those from the field experiments, chosen to produce a range in clay contents. WTS influenced several soil physical properties. Soil bulk density decreased following the addition of sludge to soil. This caused an increase in porosity (particularly macro-porosity) and therefore water retained at saturation, but only of statistical significance at the 1280 Mg ha" level. Equally an increase in water retention at the wilting point (-1500 kPa matric potential) also occurred, owing to the high microporosity of sludge aggregates. Despite these effects very little change in both the plant available and readily available water content occurred. Neither, gypsum nor lime caused any significant change in water retention. Aslight improvement was noted on the polyacrylamide treatment at the Brookdale site but this effect did not persist for very long after the trial was established. Although in situ field measurements were influenced strongly by natural spatial variability, WTScaused a marked increase in the saturated hydraulic conductivity (Ks). The reasons for this relate to the higher porosity and the inherently stable nature of the sludge aggregates, which imparts a more open structure to the soil and reduces the extent of pore blockage. This finding was corroborated in a laboratory study in which strong positive correlations between sludge content and Ks was found. The water retention curve and saturated hydraulic conductivity was used to predict the unsaturated hydraulic conductivity function (Kw)using the RETe computer model of van Genuchten et al., 1991. The results showed a decrease in Kw on the sludgeamended treatments the extent of which increased with sludge content. This finding was tested in an evaporation study conducted under controlled environmental conditions. More water was conserved on the sludge-amended treatments than the control, because of its lower Kw. The application of the sludge as a mulch was more effective in conserving water than incorporating the sludge with soil. The air-filled porosity at field capacity (-10 kPa matric potential) of the sludge-amended soil remained within a favourable aeration range of 10-15%, which suggests that aeration should not be a limiting factor for plant growth. Air-permeability nevertheless improved substantially. Attempts at using the size distribution of dry soil aggregates to evaluate the influence of the sludge on aggregation proved unsuccessful. Saturated soil paste extracts for selected soil depths beneath the mulch layers at the Brookdale trial, nevertheless, showed significant increases in Ca2+ and Mt+ concentrations, which is encouraging from a soil stability perspective. Due to the inherently strongly aggregated nature of this soil, no meaningful change in aggregate stability, however, was measured. Significant improvements in soil stability were, nevertheless, found when fresh sludge was mixed with soil. If the sludge is not allowed to dry fully beforehand the polymer that it contains remains active and available for bonding of the soil particles together. Upon drying, these polymers become irreversibly attached to the soil substrate and win not become reactivated even upon re-wetting of the soil. This also explains why sludge aggregates found below only a few centimetres of the soil surface maintained their strongly aggregated nature. This suggests that although WTS consists of mainly silt and clay, the risk of this constituent fraction becoming released and clogging water conductive soil pores are, at present, low. Despite the high strength of the sludge aggregates the penetrometer soil . strength (PSS)within the tilled layer was non-significantly different from the control treatment. Below the tilled layer, however, the PSS on the sludge-amended treatments were lower owing mainly to wetter soil conditions. The research completed to date suggests that land treatment as an environmentally acceptable disposal option for water treatment sludge shows promise since soil conditions tend to be improved. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2001

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The growing demand for forest products has enabled the increase in areas planted to trees in Brazil. Eucalyptus is a fast growing tree species being cultivated on a large scale; however, there is a controversy about the role of this plant on the dynamics of water in the soil where they are grown. In order to evaluate the effect that the replacement of native eucalypt causes the hydro-physical properties of soil, in infiltration, in storage and water availability in a sandy loam Alfisol, a study was conducted in the city of Santa Maria, in Experiment Station of FEPAGRO FORESTS. The forest was delineated into four areas: plantations of Eucalyptus grandis Will ex Maiden. 3 to 4 years of age, natural grassland 1, plantations of Eucalyptus saligna Smith 5 to 6 years of age, natural grassland 2. Soil samples were collected with preserved structure in layers of 0.00 to 0.10, 0.10 to 0.20, 0.20 to 0.30, 0.30 to 0.40 and from 0.40 to 0.50 m depth to determine the bulk density, pore size distribution, air permeability, saturated hydraulic conductivity and water retention curve. The soil water content was continuously monitored to 0.80 m depth, using an automated TDR. The substitution of natural grassland by eucalypt plantations do not negatively alter the bulk density, macroporosity, microporosity and total porosity, hydraulic conductivity of saturated soil and soil permeability to air. The soil use under natural grassland and eucalyptus contribute to the improvement of structural quality, because they favor the formation of continuous pores, important for an adequate aeration, water retention and conduction. The anthropic effect derived from the natural vegetation substitution, the natural grassland by eucalyptus plantations does not significantly alter the capacity of water storage in soil and does not reduce the amount of water available to plants. The total of water stored in the areas of natural grassland and eucalyptus, 69 and 63%, respectively, are in the range potential extracting plants, other words, readily available for utilization. The soil with sandy loam texture, along the year, suffers no adverse effect on water regime as a function of eucalyptus forestation compared to natural grassland and therefore, there is no exhaustion of soil water in places with eucalyptus monoculture. / A crescente demanda por produtos florestais tem propiciado o aumento das áreas com florestas plantadas no Brasil. O eucalipto é uma espécie florestal de rápido crescimento e é cultivada em larga escala, porém tem gerado polêmica devido às controvérsias existentes sobre o seu efeito na dinâmica da água do solo onde são implantados. Com o objetivo de avaliar o efeito que a substituição do campo nativo pelo eucalipto provoca nas propriedades físico-hídricas do solo, na infiltração, no armazenamento e na disponibilidade de água de um Argissolo de textura franco arenosa, realizou-se um estudo no município de Santa Maria, na Estação Experimental da FEPAGRO FLORESTAS. Foram utilizadas quatro áreas: povoamento florestal de Eucalyptus grandis Will ex Maiden. de 3 - 4 anos de idade; campo nativo 1; povoamento florestal de Eucalyptus saligna Smith de 5 - 6 anos de idade; campo nativo 2. Amostras de solo com estrutura preservada foram coletadas nas camadas de 0,00 a 0,10; 0,10 a 0,20; 0,20 a 0,30; 0,30 a 0,40 e 0,40 a 0,50 m de profundidade, para determinar a densidade, a distribuição de poros, a permeabilidade ao ar, a condutividade hidráulica saturada e a curva de retenção de água. O conteúdo de água do solo foi monitorado continuamente até a profundidade de 0,80 m, utilizando-se um TDR automatizado. A substituição do campo nativo pelo cultivo do eucalipto não altera negativamente a densidade, a macroporosidade, a microporosidade e a porosidade total, a condutividade hidráulica do solo saturado e a permeabilidade do solo ao ar. O uso do solo sob campo nativo e eucalipto contribuem para a melhoria da qualidade estrutural, pois favorecem a formação de poros contínuos, importantes para uma adequada aeração, retenção e condução de água. O efeito antrópico derivado da substituição da vegetação nativa, o campo nativo, por povoamentos de eucalipto não altera significativamente a capacidade de armazenamento de água no solo e não reduz a quantidade de água disponível às plantas. Do total de água armazenada nas áreas de campo nativo e de eucalipto, 69 e 63 %, respectivamente, encontram-se na faixa potencial extraível às plantas, ou seja, prontamente disponível para o seu aproveitamento. O solo de textura franco arenosa, ao longo do ano, não sofre efeito adverso sobre o regime hídrico em função do florestamento com eucalipto em comparação com a vegetação de campo nativo e, portanto, não ocorre esgotamento da água do solo em locais com monocultivo de eucalipto.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The retention and availability of water in the soil are controlled by soil structure and its temporal variation is associated with the weather and the crops needs. Water also controls the aeration and soil penetration resistance, factors that are directly linked to root growth. The overall objective of this study was to evaluate the effect of management systems and soil compaction levels on soil physical properties to define the conditions that favor the retention, storage and availability of water to plants while maintaining aeration and soil resistance favorable to root growth. To meet these goals an experiment was set up in the experimental station of the Soils Department-UFSM. The area was under fallow and in 2002 year it was incorporated into the crop production under no-tillage. The treatments were: notillage (NT) no-tillage with compaction (NTC), subsoiling (Sub), chiseling (ESC) and conventional tillage (CT). The design was a randomized block design with four replications. Undisturbed soil samples were collected in the soil layers 0.0 to 0.05, 0.05 to 0.10 0.10 0,15; 0.15 to 0.20; 0.20 to 0.30, 0.30 to 0.40 and 0.40 to 0.50 m to determine the bulk density (BD), pore distribution, air permeability (Ka), saturated hydraulic conductivity (Ks) and the water retention curve. For the same layers, soil moisture (UV) was monitored continuously down to the layer of 0.30 m, using an automated TDR. In the other layers readings were taken weekly with a manual TDR. The penetration resistance (Rp) was determined at six points across the plant rows, under eight conditions of soil moisture. The maize parameters evaluated were the emergency, dry mass, root distribution at physiological maturity and yield. The NTC had a higher BD and lower total porosity (Pt) and macropores (Mac) down to 0.40 m depth. The ESC, Sub and the CT reduced the BD and increased Pt. The Ksat and Kl had little influence of the treatments, but showed positive correlation with Pt and negatively with Mac and Ds. The main benefit of tillage is the reduction of its resistance to penetration and improved soil aeration which allows for better root growth. No-tillage did not store more water for plants in relation to conventional tillage, subsoiling and chiseling. Soil compaction increased the water retention in densiest layer, but reduced the plant's ability to exploit the soil, by inhibiting root growth and reduce soil aeration. The compacted soil reached in less time and kept for longer time restrictive values of soil penetration resistance and air permeability. The dry matter production and grain yield of maize was not affected by managements and compaction levels, although some plant growth factors were outside the appropriate range indicated by the least limiting water range. / A retenção e a disponibilidade de água no solo são controladas pela sua estrutura e a sua variação temporal está associada às condições meteorológicas e à necessidade das culturas. A água também controla a aeração e a resistência do solo à penetração, que são fatores diretamente ligados ao crescimento do sistema radicular. O objetivo geral desse estudo foi avaliar o efeito de sistemas de manejo do solo e níveis de compactação sobre as suas propriedades físicas e definir as condições que possam favorecer a retenção, o armazenamento e a disponibilidade de água às plantas, mantendo a aeração e a resistência do solo favorável ao crescimento radicular. Para atender estes objetivos instalou-se um experimento na área experimental do Departamento de Solos da UFSM. A área utilizada estava sob pouso e, a partir de 2002, foi incorporada ao sistema produtivo, sob sistema de plantio direto. Os tratamentos estudados foram: plantio direto (PD); plantio direto com compactação adicional (PDc); escarificação profunda (Sub); escarificação superficial (Esc) e preparo convencional (PC). O delineamento foi em blocos ao acaso com quatro repetições. Amostras de solo com estrutura preservada foram coletadas nas camadas de 0,0 a 0,05; 0,05 a 0,10; 0,10 a 0,15; 0,15 a 0,20; 0,20 a 0,30; 0,30 a 0,40 e 0,40 a 0,50 m, para determinar a densidade (Ds), distribuição de poros, permeabilidade ao ar (Ka), condutividade hidráulica saturada (Ksat) e a curva de retenção de água. Nestas mesmas camadas, a umidade do solo (Uv) foi monitorada continuamente até a camada de 0,30 m, utilizando-se um TDR automatizado. Nas demais camadas as leituras foram feitas semanalmente com um TDR manual. A resistência do solo à penetração (Rp) foi determinada em seis pontos transversalmente às linhas de semeadura, sob oito condições de umidade do solo. Na cultura do milho avaliou-se a emergência, a massa seca, a distribuição radicular na maturação fisiológica e a produtividade. O PDc apresentou maior Ds e menor porosidade total (Pt) e macroporos (Mac) até 0,40 m de profundidade. A Esc, Sub e o PC reduziram a Ds e aumentaram a Pt. A Ksat e a Kl tiveram pouca influência dos tratamentos, mas apresentaram correlação positiva com Pt e Mac e negativa com Ds. O principal beneficio da mobilização do solo é a redução da sua resistência à penetração e a melhoria na aeração do solo, o que permite um melhor crescimento das raízes. O plantio direto não armazenou maior quantidade de água para as plantas em relação ao preparo convencional e a escarificação. A compactação do solo aumentou a retenção de água na camada mais adensada, mas reduziu a capacidade da planta explorar o solo, por dificultar o crescimento radicular e reduzir a aeração do solo. O solo compactado atingiu em menos tempo e manteve por mais tempo valores de resistência à penetração e de permeabilidade ao ar, considerados restritivos. A produção de massa seca e de grãos do milho não foi afetada pelos manejos e níveis de compactação, mesmo que alguns fatores de crescimento da planta estivessem fora da faixa adequada indicada pelo intervalo hídrico ótimo.

Urbanisation is characterised by mass migration of people to urban areas and conversion of land from rural to urban land uses. Changes in population dynamics have led to half the world’s population living in urban areas; in developed countries, urban dwellers account for three-quarters of the total population. Though populations have shifted from rural to urban areas, people continue to rely on their environment, and trees in particular, for tangible and intangible benefits alike. A great deal of factual and anecdotal knowledge supports the role of trees for ecological, social, and economic well-being. In spite of this, during urbanisation, previously vegetated land is converted to housing, roads, or utility corridors, all of which are necessary to support growing populations. This thesis investigates tree growth in these modified urban landscapes, in particular, the effects of pavements on urban trees. Pavements are truly pervasive, covering more than half of all land in highly developed urban areas. Their durability and strength are of great importance to transportation, but large-scale soil sealing is not without consequence. Pavements affect the hydrologic cycle, soil and air temperature, and nutrient cycling. Because of their effect on the surrounding environment, pavements inherently affect remnant or planted trees. They are believed to negatively affect tree growth and survival, thereby compromising the ecological, social, and economic benefits otherwise derived from the urban forest. In recent times, porous pavements have been increasingly installed in favour of impervious pavements. Porous pavements are perceived to be an environmentally-sound alternative to standard impervious pavements. This thesis begins by reviewing the literature concerning porous pavement’s effect on underlying soil and urban vegetation, thus illustrating the scarcity of empirical data describing the effect of porous pavement on tree growth. A greater understanding of porous pavement’s impact on the surrounding environment is needed, if its installation is to continue. With this aim in mind, this thesis describes an experiment in Christchurch, New Zealand, which monitored the impacts of porous and impervious pavement on underlying soil conditions, and subsequent tree growth. The experiment comprised 50 Platanus orientalis trees planted in an augmented factorial design, which consisted of controls and four treatments. Trees were split evenly amongst plots, such that ten replicates existed per treatment. The pavement treatments measured 2.3m by 2.3m, and were based on the combination of pavement type (2 levels: porous, impervious) and pavement profile design (2 levels: +/- subbase compaction and gravel base). The resulting four treatments were impervious concrete pavement (IP), impervious concrete pavement with compacted subbase and gravel base (IP+), porous concrete pavement (PP), and porous concrete pavement with compacted subbase and gravel base (PP+). From December 2007 to March 2009, data were collected to determine the effect of these treatments on soil moisture, aeration, pH, and nutrient concentration. Final tree height, stem diameter, shoot and root biomass, and root distribution were also measured at the conclusion of the experiment. Results of this experiment indicated that the effects of pavement porosity on soil moisture and aeration were dynamic, varying with season and soil depth. Increased soil moisture beneath porous pavements resulted from rapid infiltration following precipitation. This decreased the duration of plant stress resulting from drought. Relative to bare soil, paved plots had consistently greater soil moisture, likely because pavements reduced evaporation. The inclusion of a gravel base in the profile design limited capillary upflow, which resulted in lower soil moisture under pavements designed with a gravel base. Soil aeration was significantly lower beneath pavements relative to unpaved plots. This is likely related to greater soil moisture beneath pavements. Finally, soil pH increased beneath pavements, in particular beneath porous pavements. Though all growth parameters increased for trees surrounded by porous, rather than impervious pavement, this occurred only in the absence of a compacted subgrade and gravel base. Evidently, the impact of the compacted subgrade superseded the impact of pavement porosity. Furthermore, root growth was relatively shallow beneath pavements, likely due to favourable soil moisture directly beneath pavements. This research highlights (i) the dramatic effect of pavements on underlying soil conditions; (ii) that pavements do not inherently limit tree growth; (iii) that porous pavements can conditionally improve tree growth; and (iv) that soil compaction limits potential benefits resulting from porous pavements.