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Processes and effects of root-induced changes to soil hydraulic propertiesScanlan, Craig Anthony January 2009 (has links)
[Truncated abstract] Root-induced changes to soil hydraulic properties (SHP) are an essential component in understanding the hydrology of an ecosystem, and the resilience of these to climate change. However, at present our capacity to predict how roots will modify SHP and the consequences of this is limited because our knowledge of the processes and effects are highly fragmented. Also, current models used to investigate the relationship between plants and root-induced changes to SHP are based on empirical relationships which have limited applicability to the various and often contrasting ecosystems that occur. This thesis focuses specifically on the quantifying the processes by which roots modify SHP and developing models that can predict changes to these and the water balance. Both increase and decreases in saturated hydraulic conductivity have been attributed to the presence of roots. In general, decreases occur when the root system is relatively young, and increases occur when the roots senesce and begin to decay, creating voids for water flow. The evidence available suggests that the change in pore geometry created by roots is the dominant process by which roots modify SHP because they are more permanent and of a greater magnitude than changes to fluid properties or soil structure. We first quantified the effects of wheat roots on SHP of a coarse sand with a laboratory experiment where we measured changes in both SHP and the root system at 3, 5, 7 and 9 weeks after sowing (weeks). ... The main message that can be drawn from this thesis is that root-induced changes to SHP are dynamic, and dependent upon the combination of soil texture, connectivity of root-modified pores and the ratio of root radius to pore radius. Consequently, root-induced changes to the water balance have the same dependencies. The work in this thesis provides a significant first step towards improving our capacity to predict how roots modify soil hydraulic properties. By defining the range for the parameters used to predict how the soil is modified by roots, we are able to make quantitative assessments of how a property such as hydraulic conductivity will change for a realistic circumstance. Also , for the first time we have measured changes in soil hydraulic properties and roots and have been able to establish why a rapid change from a root-induced decrease to increase in Ks occurred. The link between physiological stage of the root system, and the changes that are likely to occur has implications for understanding how roots modify SHP: it may provide an effective tool for predicting when the switch from a decrease to increase occurs. Further work is required to test the validity of the assumptions we have made in our models that predict changes to SHP. While we have endeavoured to define the parameter space for those parameters that we have introduced, there is still some uncertainty about the connectivity of root-modified pores. Also, the parameterisation of the soil domain with roots is based upon work that measures 'fine' roots only which may not provide a true representation of the effect trees and perennial shrubs have on SHP. It is inevitable that root-induced changes to SHP will affect the fate of solutes in the soil, and temporal dynamics of root-induced changes to these may be particularly important for the timing of nutrient and pesticide leaching.
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Soil development, plant colonization and landscape function analysis for disturbed lands under natural and assisted rehabilitation /Setyawan, Dwi. January 2004 (has links)
Thesis (Ph.D.)--University of Western Australia, 2005.
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The distribution of vesicular-arbuscular mycorrhizal fungi in the Savanna regions of Nylsvley Nature Reserve in relation to soil fertility factorsDames, Joanna Felicity January 1991 (has links)
Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Science, School of Botany, 1991 / The vegetation of the Nylsvley Nature Reserve situated in the Northern Transvaal, South Africa.
is a semi·arid savanna dominated by Burkea qfricana and Eragrostis paUensf interspersed with
patches of Acacia s_pp.and E, ie/t(lnumni(.ma. The Butkea savanna is established on soil which is
naturally low in phosphorus while the A,,;acia savanna is established on soU with higber phosphorus
levels. Spnres of vesictdar~arbusculat mycorrhizal (VAM) fungi Were extracted from soil samples
by wet 8i:¢ving and sucrose ("mttifugation after which they.· were enumerated .and identified.
Thirteen VAM species were isolated from the savanna regions. The population was composed of
three Gloltlus spp .• four .4cQulosp()ra spp., one .Gigaspora sp., three Scutel!ispora spp. and tWQ
species of uncertain identity. Root samples were cleated. and stained with acidic glycerol·tcypan
blue and assessed for mycoufMal colonization.
Significant positive correlations were indicated. between spore densities ar.d mycorrhizal root
infection. The total 81)01:'e popUlation was negntively correlated wiUlavailuble P, organic C, K. Ca.
Mg, and pH. ~'tldividual specles differed markedly from the population as a whole in their bltemctions with.,soil facrots, these wem. examined using linear regressions. The VA;M root
colonization as assessed b)! the mycorrhizal % WassigIlfijcant!y negativr1v: (forrelated with P white.
the frequency % was. negatively correlated. Wilh P and K. .The inter-relatidhs!;tips 'between the
d.ifferentVA1\i ,species and enviro~~eiita1 factors were further explored using prinCipal com'ponent
ana,lyt;ls. the population structure and the factors affecting the population ate discussed.
..bltemctions with.,soil facrots, these wem. examined using linear regressions. The VA;M root
colonization as assessed b)! the mycorrhizal % WassigIlfijcant!y negativr1v: (forrelated with P white.
the frequency % was. negatively correlated. Wilh P and K. .The inter-relatidhs!;tips 'between the
d.ifferentVA1\i ,species and enviro~~eiita1 factors were further explored using prinCipal com'ponent
ana,lyt;ls. the population structure and the factors affecting the population ate discussed. / MN (2017)
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Soil chemical and physical properties and their influence on the plant species richness of arid South-West AfricaMedinski, Tanya January 2007 (has links)
Thesis (MScConsEcol (Conservation Ecology and Entomology)--University of Stellenbosch, 2007. / Understanding the drivers and mechanisms of changes in plant richness is a basis for making scientifically sound ecological predictions and land use decisions. Of the numerous factors affecting plant richness, soil has a particularly large influence on the composition and structure of terrestrial flora. Infiltrability is one of the most important factors determining soil moisture, and therefore is of particular interest in semi-arid ecosystems, where water is one of the most limiting resources. Other soil properties, such as clay + silt content, electrical conductivity (EC) and pH may also influence plants. Heterogeneity of these properties creates niches with specific conditions, which in turn affects spatial distribution of plants. An understanding of the relationships between plant richness and soil properties is, however, incomplete. The present study has two main foci. Firstly, relationships between plant richness and soil infiltrability, clay + silt, EC and pH (H2O) were investigated, and secondly, due to the strong influence of infiltrability on plant richness, further investigations were undertaken to improve the understanding of the role of particle size fractions, EC of the soil solution and exchangeable sodium percentage (ESP) on infiltrability. This study only concentrated on the surface 2 cm thick soil layer (known as pedoderm).
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From the foothills to the crest: landscape history of the southern Manzano Mountains, central New Mexico, USA since 1800Huebner, Donald James 28 August 2008 (has links)
Not available / text
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Arsenic in plants important to two Yukon First Nations : impacts of gold mining and reclamation practicesNicholson, Heather Christine 05 1900 (has links)
This project examines arsenic in plants growing near closed or reclaimed gold
mines located in the traditional territories of two Yukon First Nations. A total of 238 soil
and plant samples (comprising 9 different species) were collected from Mt. Nansen,
Arctic Gold and Silver, and Venus Mine tailing properties. At each property, samples
were collected near the suspected point source of contamination, approximately 1 -3 km
away, and from background sites. Species were chosen for their ethnobotanical
significance to the Little Salmon/Carmacks and the Carcross/Tagish First Nations,
based on interviews with Elders and other knowledgeable people. Total and inorganic
arsenic concentrations were determined using ICP-MS and AAS instrumentation, and
organic arsenic concentrations were calculated from the difference.
Uptake of arsenic by plants was low compared to soil arsenic concentrations. In
both plants and soil, the arsenic form was predominantly inorganic. Concentrations in
berries at all three sites were low or undetectable, and are therefore considered safe to
eat under Health Canada tolerable daily intake guidelines for inorganic arsenic.
At Mt. Nansen, the lichen "caribou moss" (Cetraria/Cladina spp.), Bolete
mushrooms (Leccinum spp.), and the medicinal shrubs willow (Salix spp.) and Labrador
tea (Ledum groenlandicum/L. decumbens spp.) had high mean arsenic concentrations
around point sources or at sites up to 1.5 km away. These localized high
concentrations will not likely affect foraging animals, given their constant movement.
However, Carmacks residents could avoid gathering all species with elevated arsenic
around the Mt. Nansen mining property until reclamation is complete.
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The effect of trees and grass on soil aggregate stability in Potshini catchment, KwaZulu-Natal, South Africa.Mthimkhulu, Sandile Siphesihle. January 2011 (has links)
Long-term environmental quality is closely linked to maintaining soil quality. Therefore,
assessment of the effect of land use on soil chemical, physical and biological properties provides
fundamental information about soil sustainability. The role of vegetation on soil structural and
aggregate stability has received much attention over the last few decades. The loss of soil due to
erosion and reduction in organic matter due to change in vegetation is usually caused by invasion
of grassland by trees. The response of soils to land use depends on the inherent soil properties
and environmental conditions thus the effect of land use on soil stability is site specific. The
objectives of this study were to assess and compare soil aggregate stability under trees and in
open grassland from open-savannah woodland and nearby deeply eroded dongas (gullies).
Within the dongas, tree encroachment was expected to improve soil structural stability by
increasing the organic matter content. Results that were obtained from this study are aimed at
improving management of soil for smallholder and pastoral farming systems.
The study site was located at Potshini, KwaZulu-Natal Province, South Africa, about 18 km
south-east of Bergville. The vegetation of the area is classified as grassland biome. Acacia
sieberiana var. Woodii has encroached into the valley especially onto the eroded areas. Within
the study area itself the dominant parent materials are sandstone and dolerite, with colluvium
covering the lower slopes. The dominant soil was classified as Hutton form. Effects of different
vegetation types (grass and trees) on the soil structural stability was evaluated for their effects on
soil organic carbon (SOC), mean weight diameter, bulk density, root density, clay mineralogy
and some other chemical properties. For this study the site was divided into two areas i.e., the
donga (D) and the grassland (G). These were then each subdivided into two parts namely, donga
under a tree (DUT) with a corresponding open area (DOA), and grassland under a tree (GUT)
with its corresponding open area (GOA).
Three bulk samples were collected from each sampling area from 0 to 20 cm (topsoil only) using
a spade. Samples for bulk density were collected from 0 - 10 cm. For soil aggregate stability
determinations, samples were dried and sieved to collect soil aggregates between 2.8 and 5 mm.
Some of the bulk sample was analysed for SOC, pH, exchangeable bases, nitrogen and clay
mineralogy. For root biomass, soil samples were collected from 0 - 10 cm using a stainless steel
cylinder of 1766 cm3 volume. The type of vegetation affected the soil physical and chemical properties of the soil in the
investigated horizon (A horizon). Although the results were not significantly (p > 0.05) different,
the open area showed a positive effect on soil structural stability where higher soil aggregate
stability and root density were observed, as opposed to under trees in both donga and grassland.
Due to the non-significant differences observed in both donga and grassland, the effect of trees
and grass on the aggregate stability was considered as the positive effect. The bulk density
showed an unusual trend. Bulk density was higher in the open areas where high aggregate
stability was observed. From these results it was concluded that because trees have larger roots
than grass these are more effective in loosening the soil particles but less effective in stabilizing
the soil aggregates. In other words, the high amount of fine roots increased the soil stability
while large roots improved the loosening of the soil particles.
The amount of vegetation considerably affected all the physical and chemical soil properties
investigated. The SOC and root density was considerably higher under grassland compared to the
donga. The clay mineralogy differed between the donga and grassland. The donga soils had a
higher kaolinite content and amount of interstratified smectite/mica compared to grassland. The
presence of interstratified smectite/mica in the donga could cause lower aggregate stability due
to shrinking-swelling cycles during wetting-drying conditions. The effects of mineralogy have
been overridden by organic carbon in the grassland. From this study it was revealed that soil
aggregate stability is the product of interactions between soil clay minerals, and organic fractions
which are influenced by soil environment, land use and soil properties. This means that all the
factors involved in aggregate formation and their stabilization are interdependent. It is suggested
that factors that were driving the soil aggregate stability in the donga were different to the ones
in grassland. It is suggested that the aggregate stability was driven by inorganic factors i.e., clay,
clay mineralogy, bases and CEC in the donga while organic carbon and plants roots were
dominating in the grassland / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Rainwater harvesting systems and their influences on field scale soil hydraulic properties, water fluxes and crop production.Kosgei, Job Rotich. January 2009 (has links)
South Africa, in common with many parts of Sub-Saharan Africa, is facing increasing water
shortages. Limited available water arising from a low and poorly distributed rainfall, must
supply domestic, agricultural, industrial and ecosystem needs. Agricultural activities of
smallholder farmers, who largely occupy arid to semi-arid areas, are rainfall-driven as they do
not have the capacity to develop conventional water sources, such as boreholes and large dams.
This situation has led to persistent food shortages, low income and a lack of investments,
resulting in high dependency levels of which examples include over reliance on social grants,
household crop production that largely relies on external inputs and availability of cheap
unskilled labour. A growing global perception that water for agriculture has low value relative
to other value uses could further jeopardize the already over exploited agricultural water.
Developing economies such as South Africa are likely to favour, in terms of water allocation,
e.g. electricity generation through steam turbines relative to irrigation needs because industry
plays a more significant role in the economy.
While substantial scientific research has resulted in enhanced yields through in-situ water
harvesting and soil and water conservation, as well as crop and soil fertility management and
plant breeding, less work has been done to assess the impact of intermittent dry spells on crop
yield, particularly with regard to smallholders. Indeed, the interventions that have been
promoted to smallholders may provide little buffer against such events. In addition, the increase
in yield from many such efforts has been marginal and inconsistent, leading some to conclude
that semi-arid environments are hydrologically marginal, have no significant agricultural
potential and any attempts to intensify agricultural activities would lead to severe environmental
degradation.
This study investigated the rainwater harvesting and storage potential among rainfed farmers in
a summer-rainfall region of South Africa. The influences of this practice on soil hydraulic
properties, water fluxes and crop production is detailed in subsequent chapters.
Using historical meteorological data, this study commenced with an investigation of the factors
that influence the length of maize (Zea Mays L.) growing seasons notably the prevalence of
early season dry spells and late season low temperature which could be responsible for
persistent low maize yields amongst smallholder rainfed farmers (Chapter 2). An increasing
trend of dry spells was observed which was found to influence sowing dates and the length of
the growing season. The influence of no-tillage (NT) as an intervention to secure more root-zone soil moisture was
investigated in comparison to conventional tillage (CT) practices. Field experiments, with the
aim of quantifying the extent to which water productivity and yields can be improved among
smallholder rainfed farmers in the Potshini catchment, Thukela basin; South Africa (Chapter 8),
were conducted during both the dry and growing seasons from 2005/06 – 2007/08 seasons at
four sites with similar soil textural properties and slopes. Each site was developed as a runoff
plot and was fitted with moisture and runoff measuring devices. Meteorological parameters
were measured from a weather station installed nearby. A snapshot electrical resistivity survey
was used to compliment soil moisture profiling. The analyses of the different measurements
provided information on various water flow paths and potential downstream hydrological
effects (Chapter 3). The average cumulative runoff was 7% and 9% of seasonal rainfall in NT
and CT treatments over the three seasons.
Changes over time in soil hydraulic properties due to tillage were examined at two depths
through infiltration tests and determination of their bulk densities. These included changes in
steady state infiltration rate and hydraulic conductivity (Chapter 4), interaction between soil
infiltration and soil characteristics (Chapter 5) and water conducting porosity and water
retention (Chapter 6). In 50% of the sites, NT treatments showed significantly higher hydraulic
conductivity compared to CT treatments.
In response to an unexploited opportunity identified to produce vegetables in winter, an
assessment of the potential for runoff water harvesting systems using polyethylene lining as an
alternative cost-effective construction method for underground rainwater storage systems,
particularly in areas where groundwater levels fluctuate rapidly was undertaken (Chapter 7).
The process from conceptualization through design, construction and utilization of the stored
water is described and recommendations for the design and construction of such systems made.
Finally, various case studies which highlight the potential impact of improved soil profile
moisture storage, the additional benefits of water stored in tanks and recommendations for
tailored policies to support household food and income generation are made (Chapter 8). / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.
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The effects of compaction and residue management on soil properties and growth of Eucalyptus grandis at two sites in KwaZulu-Natal, South Africa.Rietz, Diana Nicolle. January 2010 (has links)
Concerns have been raised over the long-term site productivity (LTSP) of short rotation plantation forests, such as those of Eucalyptus, in South Africa. This is because diminished productivity of long rotation plantations overseas has been found to be generally due to decreases in soil porosity and organic matter. Since soil porosity and organic matter in plantations are mainly affected by soil compaction by harvesting machinery and residue management, the more frequent harvesting of short rotation plantations are of particular concern. Therefore the effects of soil compaction and residue management on soil properties at two sites, one a low organic carbon, sandy soil (Rattray), the other a high organic carbon, clay soil (Shafton) were investigated. The potential of early E. grandis productivity as an indicator of changes in soil properties at these sites was also evaluated. Three different levels of compaction (low, moderate and high) were applied to the sites by three methods of timber extraction, i.e. manual, logger and forwarder loaded by a logger, respectively. Three types of residue management, i.e. broadcast, windrow and residue removal were also applied. A factorial treatment design was used to ensure a resource-efficient study that allowed separation of main and interaction effects. Various soil physical and chemical properties were measured at intervals from before treatment implementation, until approximately 44, and 38 months after treatment implementation at Rattray and Shafton, respectively. Trees were planted at a commercial espacement at both trials, and their growth monitored over the same time period. In addition, to accelerate early growth, negate silvicultural variation, and determine changes in stand productivity with treatments, a portion of the treatment plots were planted at a very high density and harvested when these trees reached canopy closure at about six months of age. Moderate and high compaction treatments at both sites resulted in significant increases in penetrometer soil strength, and often in bulk density. Increasing residue retention decreased the compaction effects of machinery and, generally, increased the total quantity of nutrients contained in residues and soil. Changes in soil bulk density and organic matter as a result of the treatments in turn affected soil water characteristics, generally decreasing plant available water capacity with increasing compaction intensity and residue removal. Tree growth measurements showed that at both sites, tree productivity was negatively affected at some point by increasing compaction. In contrast, residue management only significantly affected tree growth at Shafton, initially increasing and later decreasing growth with residue removal. These variations in tree growth over time in response to treatments are most likely a result of changes in tree characteristics that occurred with age. In addition, trees did not always reflect changes in soil properties that may affect LTSP, most likely because these soil properties had not yet reached levels that would affect tree growth. It was therefore concluded that early tree growth is not always a good indicator of changes in LTSP, and that soil properties are a more reliable indicator. Plantation management practices that lead to soil compaction and residue removals will negatively impact LTSP in South Africa. However, variable responses of the two soils indicate that soils vary in their sensitivity to compaction and residue management. This therefore needs to be quantified across a range of major soil types in the South African forestry industry. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
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Incorporating the Canegro sugarcane model into the DSSAT V4 cropping system model framework.Jones, Matthew Robert. 31 July 2013 (has links)
Canegro is a leading sugarcane crop simulation model and has been used extensively in agronomic research and management. The model has been under development since the late 1980s at the South African Sugarcane Research Institute (SASRI). The Decision Support System for Agrotechnology Transfer (DSSAT) is a software package containing models for a wide range of field crops, and utilities for processing, storing and analysing model inputs and outputs. Canegro was included as part of version 3.1 of DSSAT in the mid-1990s. The SASRI Canegro model was subsequently developed further, but these changes were never integrated, nor incorporated, into DSSAT. DSSAT has also developed substantially, and as of version 4 adopted a modular Cropping System Model (CSM) structure, providing numerous scientific and practical advantages over previous non-modular versions. The DSSAT-Canegro v.3 model was not modified to use this modular structure.
Following recognition of the advantages offered by DSSAT and its modular CSM, a project was initiated to incorporate the Canegro model into the DSSAT CSM. The project entailed: (i) restructuring and integrating the current Canegro plant growth and development code into the DSSAT v4 CSM modular framework, making use of its generic modules for management, soil, weather and the energy balance; (ii) verification of DSSAT CSM Canegro model results against the current SASRI version of Canegro to ensure that the new model produced similar results to the original model, for a set of simulated situations; and (iii) evaluation of the new DSSAT CSM Canegro model against experimental datasets.
The new DSSAT v4 CSM Canegro model has been verified to behave identically to the SASRI Canegro model when the water balance is not modelled and growth can occur at climatic potential rates. When the water balance is simulated but where the crop is not stressed, near identical output is produced by both models. Under water-stressed conditions, some discrepancies appear between the two models, due to differences in the calculation of reference evaporation, soil surface evaporation and runoff. Validation of the new model against data from 16 experimental crops produced root mean squared errors of 6.62 t ha-1 for stalk dry mass and 3.59 t ha-1 for sucrose mass – very similar to published values for Canegro. This project has yielded a functional, well-documented, maintainable and user-friendly version of the Canegro model, which is available for universal use via the official release of the DSSAT v4.5. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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