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Organic matter in sodic soils : its nature, decomposition and influence on clay dispersionNelson, Paul Netelenbos. January 1997 (has links) (PDF)
Bibliography: leaves 147-170. Aims to determine the influence of sodicity on the nature and decomposition of organic matter; and the influence of organic matter and its components on the structural stability of sodic soils.
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Studies on the nutritional value of the oils and mesocarp of avocado (Persea americana) and impact of soil quality on elemental composition.Reddy, Mageshni. January 2011 (has links)
This study covered both the Hass and Fuerte varieties of avocado pears. The quality of
extracted avocado oil produced by different extraction techniques was assessed to determine
the effect the extraction method had on the nutritional and storage value of the oil. While
microwave extraction produced the highest yield of oil (70.0 %), supercritical fluid extraction
produced oil with a wider range of fatty acids. Although the Hass variety produced a higher
oil yield, oil extracted from the Fuerte variety was shown to have a higher monounsaturated
fatty acid to saturated fatty acid ratio, which makes the latter oil more beneficial to health.
Oils of the Fuerte variety also possessed a higher concentration of co-extracted metals, which
makes it more susceptible to lipid oxidation. The overall choice for the most efficient
extraction method was microwave extraction as it produced the highest yield and quality of
oil.
The impact of soil quality on elemental uptake into locally grown avocado fruit sampled from
six different locations was determined. Of the 14 selected metals investigated, avocado fruit
was found not to accumulate Cd, Co, Cr, Pb and Se. Generally, the concentration of elements
in both varieties of fruit was in the order of Mg > Ca > Al > Zn > Fe > Mn > Cu > Ni > As.
Relative bioaccumulation plots were used to establish the essential and non-essential
elements for normal growth of avocado fruit. It was found that the plant has an involuntary
uptake mechanism for As due to similarity in ion species to P, which is an essential element.
The impact of soil quality parameters pH, cation exchange capacity and soil organic matter
were determined and their impact on plant-soil interactions was analysed. Statistical analysis
revealed a plethora of metal interactions at the plant-soil interface. However, the plant was
still seen to control uptake of specific elements such as Cu, Fe and Ca, due to its
physiological requirements. CEC was found to have a greater effect on availability of
elements than pH and SOM. Geoaccumulation indices indicated moderate enrichment of Pb
in soils; however this result had no bearing on the elemental uptake of the fruit at all sites.
Comparisons to recommended dietary allowances (RDAs) for human diet reveal the average
contribution of avocado to be 70% and 45% for Cu and Mn, respectively. Low levels of As
was found in fruit which warrants continued monitoring of this element in the plant due to its
similarity to P. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2011.
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Organic matter in sodic soils : its nature, decomposition and influence on clay dispersion / by Paul Netelenbos Nelson.Nelson, Paul Netelenbos January 1997 (has links)
Bibliography: leaves 147-170. / x, 170 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Aims to determine the influence of sodicity on the nature and decomposition of organic matter; and the influence of organic matter and its components on the structural stability of sodic soils. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1998?
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Teores de carbono e nitrogênio dos solos de duas microbacias hidrográficas com diferentes usos da terra no município de Ibiúna-SPSantos, Ana Cecilia Arroyo [UNESP] 23 February 2012 (has links) (PDF)
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santos_aca_me_bauru.pdf: 1622232 bytes, checksum: 0a62a2ba673d2a818995495f22beee4a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / Estudar a qualidade do solo é um instrumento que apóia o conhecimento das consequências causados do uso dos solos, dando suporte à tomada de decisões no planejamento do desenvolvimento futuro das regiões. O objetivo deste estudo foi determinar os teores de carbono (C) e nitrogênio (N), assim como dos isótopos 'delta'13C e 'delta'15N de áreas com diferentes usos do solo. A área de estudo está localizada em Ibiúna-SP e compreende duas microbacias: do Rio Paiol e do Rio Sorocabuçu. São áreas que registram atividade agrícola, tanto agricultura convencional (Sorocabuçu) como a agricultura orgânica (Paiol). Usando 100 amostras de solo, previamente coletadas em áreas com diferentes tipos de cobertura (Vegetação Natural Remanescente (VNR), pastagem, reflorestamento, agricultura), foram medidos os teores de C e N e a relação isotópica 12C/13C e 14N/15N, no laboratório do CENA-USP. No laboratório da UNESP, do Campus Sorocaba, quantificou-se o C lábil através da oxidação por Dicromato de Potássio. Os maiores teores de C e N nas duas bacias ocorreram para a classe VNR. Para as outras classes de cobertura, a ordem de concentração, em termos decrescentes, tanto para o C como o N foi: reflorestamento > pastagem > agricultura, para ambas as microbacias. Os dados de 'delta'13C indicaram valores médios de -26,22% e -26,95%, respectivamente para as microbacias Sorocabuçu e Paiol. Os dados sobre 'delta'15N mostram maiores valores, em ambas as bacias, para solos manejados para agricultura ou silvicultura (8,25% para a microbacia Paiol e 8,75% para microbacia Sorocabuçu) em relação aos solos cobertos com VNR (6,5% e 6,21% respectivamente, para as microbacias Paiol e Sorocabuçu). O C lábil apresentou valores maiores para VNR, com 1,65% e 2,00% para as microbacias Paiol e Sorocabuçu respectivamente, em... / Studying the soil quality is a tool that helps the knowledge concerning the consequences of the land cover change over the soil. This supports the decisions making for many regions. The goal of this research was to determine the levels of carbon (C) and nitrogen (N), as well as, the concentration of the isotopes 'delta'13C and 'delta'15N of soils from areas with different land cover classes. The study area is located in Ibiuna - SP and encompasses two watersheds: Paiol and Sorocabuçu. In such watersheds occurs the agriculture, conventional (Paiol) and organic (Sorocabuçu). Using 100 previously collected soil samples from area covered with Natural Remmant Vegetation (NRV), pasture, reforesting or agriculture, we measured the concentration of C and N, as well as the isotopic signature ('delta'13C and 'delta'15N), in laboratory of the CENA-USP. In the Unesp laboratory, we determined the C lability, through the oxidation by Potassium Dichromate. The highest C and N concentration for both watersheds were to the VNR. For other land cover classes, the C and N concentration followed the decreasing sorting, for the two watersheds: reforestation > pasture > agriculture. 'delta'13C values ranged from -26,22%, respectively, for the Sorocabuçu and Paiol waterheds. 'delta'15N isotopes showed greatest values, in both watershed, for solis managed for agriculture or reforestation (8.25% for the Paiol and 8.75% for Sorocabuçu) in relation to land covered with NRV (6.50% and 6.21% respectively, for Sorocabuçu and Paiol). The labile C presented greatest values for VNR class, with 1.65% and 2.00% for Paiol and Sorocabuçu watersheds, respectively, compared with those obtained for other land uses, especially pasture in the two waterheds. We identified statistically significant difference among the land cover classes for both watersheds for... (Complete abstract click electronic access below)
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Espécies de brássicas no controle de fitopatógenos habitantes do soloMoccellin, Renata 28 February 2011 (has links)
CAPES / As brássicas possuem alto potencial de biofumigação, pois produzem gases tóxicos voláteis aos fitopatógenos habitantes do solo (FHS). Este trabalho objetivou testar três espécies de brássicas: Brassica juncea (mostarda), Brassica oleraceae (repolho) e Brassica napus (canola) no controle de três FHS: Sclerotium rolfsii, Rhizoctonia solani e Pythium aphanidermathum. Realizaram-se três ensaios, sendo o primeiro in vitro, constituído por doses: 0, 5, 10, 15, 20 e 25% de extrato de canola e mostarda. Cada Placa de Petri contendo meio de cultura recebeu um disco de BDA contendo micélio de um fitopatógeno. Na tampa foram colocados os extratos que serviram como base para a placa. Foram realizadas leituras do crescimento micelial. No segundo ensaio realizado em casa de vegetação, utilizou-se doses de 0, 30, 60, 90 e 120 t ha-1 de repolho triturado, em dois cultivos. Em sacos plásticos com sistema de vedamento foram colocados 500 g de solo e 10 g de substrato com P. aphanidermathum, recebendo em seguida as doses de repolho, com posterior fechamento e acondicionamento em BOD a 22ºC por 15 dias. Em seguida, o solo de cada saco foi distribuído em 16 células de bandejas de cultivo de mudas, semeandose uma semente de pepino por célula. O terceiro e último ensaio foi realizado a campo em dois cultivos, utilizando-se as doses de 0, 30, 60, 90 e 120 t há-1 de canola triturada. Em parcelas de 1 m2 incorporou-se substrato de areia e quirela de milho contendo P. aphanidermathum e a canola triturada 24 h após, com posterior cobertura com lonas dupla-face. Após a retirada das lonas foram coletadas amostras de solo para avaliar a sobrevivência do fitopatógeno e para a distribuição em bandejas, seguindo a mesma metodologia descrita no segundo ensaio. A sobrevivência foi realizada semeando-se cinco sementes de pepino em copinhos plásticos, com solo esterilizado, onde foi colocado 0,5 g de aveia e 15 g de solo retirado das parcelas. Foram realizadas avaliações de emergência e tombamento. Nas parcelas do campo, realizou-se a semeadura de 50 sementes de pepino. Para os três experimentos foram feitas avaliações de emergência, tombamento e peso seco das plântulas. Em todas as amostras de solo coletadas, foram realizadas avaliações da atividade microbiana, fertilidade do solo e condutividade elétrica. No primeiro ensaio todos os fitopatógenos reduziram o crescimento micelial pelo aumento das doses de canola e mostarda. No segundo e terceiro ensaios o repolho e a canola foram efetivos em todas as variáveis avaliadas. Estes substratos além de apresentarem efeito direto sobre o fitopatógeno, por meio da produção dos gases, o aumento da atividade microbiana e da condutividade elétrica,contribuindo de maneira indireta no controle do FHS testado. A concentração de potássio no solo aumentou com o aumento das doses de repolho e de canola, mostrando que os altos teores de potássio nos tecidos das brássicas contribuíram para o controle de P. aphanidermathum, além de servir como fertilizante orgânico para locais onde há deficiência de potássio. / The brassicas has high potential biofumigation and they produce toxic gases to volatile soilborne plant pathogens (SPP). This study intend to test three species of brassica: Brassica juncea (mustard), Brassica oleracea (cabbage) and Brassica napus (canola) in the control of three SPP: Sclerotium rolfsii, Rhizoctonia solani and Pythium aphanidermathum. We conducted three tests, the first in vitro, consisting of three treatments: 0, 5, 10, 15, 20 and 25% extract of canola and mustard. Each Petri dish containing culture medium received a disk of PDA containing mycelium of a pathogen. On the cover were placed extracts that were the basis for the board. Readings were taken of mycelial growth. In the second experiment conducted in a greenhouse, we used doses of 0, 30, 60, 90 and 120 t ha-1 cabbage shredded, in two crops. In plastic bags with sealing system were placed 500 g soil and 10 g of substrate with P. Aphanidermathum, then receiving doses of cabbage, with later closing and placing in chamber at 22 ° C for 15 days. Then the soil from each bag was distributed in 16-cell tray seedling cultivation, seeding a cucumber seed per cell. The third and final field test was carried out in two crops, using doses of 0, 30, 60, 90 and 120 t ha-1, canola crushed. In plots of 1m2 is incorporated in a sand and corn containing quirela P. Aphanidermathum and canola crushed after 24 h, with subsequent coverage with double-sided pads. After removing the pads we collected soil samples to assess the survival of the pathogen and for distribution in trays, using the same methodology described in the second test. The survival was performed sowing to five cucumber seeds in plastic cups with sterilized soil, where it was placed 0.5 g of oats and 15 g of soil taken from plots. We have made emergency and tip evaluations. At the plots of the field, we sow 50 seeds of cucumber. For the three experiments were made emergency evaluations, damping off and seedling dry weight. In all soil samples were evaluated microbial activity, soil fertility and electrical conductivity. In the first trial all pathogens reduced the mycelial growth by increasing doses of canola and mustard. In the second and third tests cabbage and canola were effective in all variables. Demonstrated that besides the direct effect on the pathogen through the production of gases, increased microbial activity and electrical conductivity contributed indirectly to control the SPP tested. The concentration of potassium in the soil increased with increasing doses, showing that high levels of potassium in the tissues of crucifers contributed to the control of P. Aphanidermathum, besides serving as an organic fertilizer to places where there is a deficiency of potassium.
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Teores de carbono e nitrogênio dos solos de duas microbacias hidrográficas com diferentes usos da terra no município de Ibiúna-SP /Santos, Ana Cecilia Arroyo. January 2012 (has links)
Orientador: Alexandre Marco da Silva / Banca: Michel Brossard / Banca: Clayton Alcarde Alvares / Resumo: Estudar a qualidade do solo é um instrumento que apóia o conhecimento das consequências causados do uso dos solos, dando suporte à tomada de decisões no planejamento do desenvolvimento futuro das regiões. O objetivo deste estudo foi determinar os teores de carbono (C) e nitrogênio (N), assim como dos isótopos 'delta'13C e 'delta'15N de áreas com diferentes usos do solo. A área de estudo está localizada em Ibiúna-SP e compreende duas microbacias: do Rio Paiol e do Rio Sorocabuçu. São áreas que registram atividade agrícola, tanto agricultura convencional (Sorocabuçu) como a agricultura orgânica (Paiol). Usando 100 amostras de solo, previamente coletadas em áreas com diferentes tipos de cobertura (Vegetação Natural Remanescente (VNR), pastagem, reflorestamento, agricultura), foram medidos os teores de C e N e a relação isotópica 12C/13C e 14N/15N, no laboratório do CENA-USP. No laboratório da UNESP, do Campus Sorocaba, quantificou-se o C lábil através da oxidação por Dicromato de Potássio. Os maiores teores de C e N nas duas bacias ocorreram para a classe VNR. Para as outras classes de cobertura, a ordem de concentração, em termos decrescentes, tanto para o C como o N foi: reflorestamento > pastagem > agricultura, para ambas as microbacias. Os dados de 'delta'13C indicaram valores médios de -26,22% e -26,95%, respectivamente para as microbacias Sorocabuçu e Paiol. Os dados sobre 'delta'15N mostram maiores valores, em ambas as bacias, para solos manejados para agricultura ou silvicultura (8,25% para a microbacia Paiol e 8,75% para microbacia Sorocabuçu) em relação aos solos cobertos com VNR (6,5% e 6,21% respectivamente, para as microbacias Paiol e Sorocabuçu). O C lábil apresentou valores maiores para VNR, com 1,65% e 2,00% para as microbacias Paiol e Sorocabuçu respectivamente, em... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Studying the soil quality is a tool that helps the knowledge concerning the consequences of the land cover change over the soil. This supports the decisions making for many regions. The goal of this research was to determine the levels of carbon (C) and nitrogen (N), as well as, the concentration of the isotopes 'delta'13C and 'delta'15N of soils from areas with different land cover classes. The study area is located in Ibiuna - SP and encompasses two watersheds: Paiol and Sorocabuçu. In such watersheds occurs the agriculture, conventional (Paiol) and organic (Sorocabuçu). Using 100 previously collected soil samples from area covered with Natural Remmant Vegetation (NRV), pasture, reforesting or agriculture, we measured the concentration of C and N, as well as the isotopic signature ('delta'13C and 'delta'15N), in laboratory of the CENA-USP. In the Unesp laboratory, we determined the C lability, through the oxidation by Potassium Dichromate. The highest C and N concentration for both watersheds were to the VNR. For other land cover classes, the C and N concentration followed the decreasing sorting, for the two watersheds: reforestation > pasture > agriculture. 'delta'13C values ranged from -26,22%, respectively, for the Sorocabuçu and Paiol waterheds. 'delta'15N isotopes showed greatest values, in both watershed, for solis managed for agriculture or reforestation (8.25% for the Paiol and 8.75% for Sorocabuçu) in relation to land covered with NRV (6.50% and 6.21% respectively, for Sorocabuçu and Paiol). The labile C presented greatest values for VNR class, with 1.65% and 2.00% for Paiol and Sorocabuçu watersheds, respectively, compared with those obtained for other land uses, especially pasture in the two waterheds. We identified statistically significant difference among the land cover classes for both watersheds for... (Complete abstract click electronic access below) / Mestre
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Tillage and crop rotation impacts on soil, quality parameters and maize yield in Zanyokwe Irrigation Scheme, South AfricaNjaimwe, Arnold Ngare January 2010 (has links)
Intensive tillage and monoculture cropping practices reduce soil C accumulation hence increasing soil vulnerability to chemical, physical and biological degradation. This study focussed on enhancing biomass production of wheat and oat winter cover crops as a means of increasing C sequestration in the low organic C soils of the central part of Eastern Cape Province. The specific objectives were (i) to evaluate the short-term effects of no till and cereal-fallow based crop rotations on; soil organic matter related parameters, pH and electrical conductivity, (ii) soil bulk density, water retention and aggregate stability, (iii) soil microbial biomass C and N, mineralizable N, soil respiration, and dehydrogenase enzyme activity, (iv) grain yield, soil nutrient concentration (N, P and K) and their uptake by maize, and (v) to identify soil parameters with high sensitivity to tillage under maize-fallow-maize, maize-wheat-maize and maize-oat-maize rotational cover cropping practices. The experiment was laid out as a split-plot arrangement in a randomized complete block design with 4 replicates. Tillage treatments (CT and NT) were applied on the main plots which measured 8 × 18 m while crop rotation treatments were applied in the subplots which measured 8 × 6 m. The rotation treatments were maize-fallow-maize (MFM), maize-wheat-maize (MWM) and maize-oat-maize (MOM). Weed control in NT plots involved preplant application of glyphosate to control mainly the grass weeds while post emergence weed management was done using Atrazine (485 atrazine and 15 g l-1 triazines). Initial weed control in CT plots was achieved through ploughing to a depth of 20 cm followed by disking while post emergence weed iii management was done by hand hoeing. Soil parameters measured were; (i) particulate organic matter (POM), soil organic carbon (SOC), total nitrogen (TN), pH and electrical conductivity (EC), (ii) soil bulk density (b), moisture at field capacity (FC), aggregate mean weight diameter (MWD) determined by fast wetting (FW), slow wetting (SW), mechanical breakdown by shaking (MB) and the stability index (SI), (iii) soil microbial biomass C (MBC) and N (MBN), mineralizable N (MN), soil respiration (SR), and dehydrogenase enzyme activity (DHEA). No-till increased POM and TN compared to CT in Lenye and Burnshill, respectively. The MWM and the MOM rotations increased TN relative to the MFM rotation in Lenye. The MWM and MOM rotations enhanced SOC relative to MFM in all sampled soil depths at Burnshill and similar observations were made under MOM rotation in the 5-20 cm depth in Lenye. The MWM and MOM rotations tended to depress soil pH relative to the MFM rotation in both sampled soil depths in Lenye while NT reduced soil pH relative to CT on the surface soil layer in Burnshill. Soil EC and pH varied with depth across tillage practices but both parameters remained within the ideal range for successful crop production over the study period. Soil stability index (SI) and aggregate MWD determined by FW, SW and MB were higher in Lenye compared to Burnshill. The MOM rotation enhanced the SI relative to MFM and MWM rotations at both sites. Scanning electron microscope (SEM) showed that more organic C was incorporated into the soil under NT and MOM rotation compared to CT and MFM rotation which had few organic coatings on the soil particles. Microbial properties varied with plant biomass input as influenced by tillage and type of rotational cover crop at both sites. Like in other past studies, NT showed higher levels of MBC, MBN, NM and SR at the soil surface layer compared to CT in Burnshill. No till increased MN iv relative to CT in both sampled soil depths in Lenye and resulted in higher DHEA compared to CT in Burnshill. The MOM rotation increased MBC, MBN, MN relative to MFM rotation especially within surface soil layer. Similar observations were made with respect to MN and SR in both sampled soil layers at Lenye. By contrast, the DHEA was higher under the MFM relative to the MWM and MOM rotations in Lenye but similar under the MFM and MOM rotations in Burnshill. Maize grain yield was not affected by both tillage and crop rotations but varied with cropping season. Comparable grain yields observed under the two tillage practices with similar fertilizer application rates indicated the advantage of NT over CT in saving on labour costs in maize production without compromising yields. High plant biomass retention under NT relative to CT contributed to high soil N and P levels under the former compared to the latter tillage practice especially on soil surface layer at both study sites. Principal component analysis (PCA) revealed that soil chemical and biological parameters closely linked to organic matter, namely SOC, MN, MBC and MBN showed the highest sensitivity to tillage and crop rotation treatments. Soil aggregate MWD determined by SW and b were the physical parameters which were highly altered by agronomic management practice. The MWM and MOM rotations were clustered together and clearly separated from the MFM rotation and this observed trend only applied to the 0-5 and 5-20 cm depths in Lenye site only. No till, MWM and MOM rotations enhanced POM, SOC and TN relative to CT and MFM rotation suggesting these practices have greater potential to improve soil chemical properties compared to intensive tillage and maize monoculture based production practices. Reduced soil b under MOM rotation and improved SI under NT compared to MFM and CT, respectively v indicate that these practices have the potential to improve degraded soils. Although not significantly different, NT values for MBC, MBN, MN, SR and DHEA were higher compared to CT indicating the potential of the practice to improve soil biotic activity relative to conventional tillage practices. No till enhanced surface soil nitrate N and extractable P compared to CT at both sites revealing the long-term potential of NT in improving the supply of these essential plant nutrients compared to CT. Principal component analysis showed that SOC, MN, K, P, MBC, MBN, soil aggregate MWD determined by SW and b were the most sensitive parameters to tillage and crop rotations. Therefore, these parameters could constitute the minimum data set for assessments of the impact of selected CA practices on soil quality attributes.
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Weed Management and Soil Quality Outcomes of Non-Chemical Weed Control TacticsBeamer, Kenneth Paul January 2018 (has links)
In the Northern Great Plains (NGP), weed management within organic systems remains a challenge. Experiments were conducted at two distinct sites in North Dakota to investigate effects of deep mulch no-till (NT) on soil quality indices, weed densities, and weed seedbank densities. We hypothesized that alfalfa mulch no-till and arbuscular mycorrhizal fungi (AMF) inoculant would be associated with reductions in weed densities and improvements to soil quality and vegetable yield. NT treatments were associated with reductions in weed densities and time required for weeding, with improvements in soil quality, such as increased AMF biomass, and yield for snap pea, onion, beet, and butternut squash compared to tilled treatments. Our findings suggest deep mulch no-till using alfalfa residue may be a viable option for small-scale organic vegetable producers in the NGP. Additional research is required to determine costs associated with sowing, harvesting, baling, and applying alfalfa mulch compared to tilling.
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Reciprocal relationships between vegetation structure and soil properties in selected biomes of South AfricaMills, A. J. 12 1900 (has links)
Thesis (PhD) -- Stellenbosch University, 2003. / Please refer to full text to view abstract. / ENGLISH ABSTRACT: The effects of different land use practices on soil quality in South Africa were
investigated in five contrasting biomes, with a particular emphasis on the tendency of
soils to crust and soil C content. Soil quality is a nebulous concept and its
applicability in the South African landscape is scrutinised. A wide range of chemical
and physical soil properties were examined. The tendency of soils to crust was
assessed using modulus of rupture, water dispersible clay and a new method of
laboratory infiltration which was verified with rainfall simulation. Crusting was
greater in bare, exposed soils than soils under vegetation and varied with soil parent
material. Differences in crusting are explained by factors relating to clay dispersion
such as clay mineralogy, soil C, labile or readily oxidisable C, concentration of
soluble salts, soil texture and exchangeable Na percentage (ESP). Results from longterm
bum plots in savanna and grassland revealed that annual burning can increase
the tendency of soils to crust. Greater crusting in burnt plots is ascribed to greater
dispersion of clay, which in tum is attributed to a decline in soil C, a decline in EC
and an increase in ESP. The loss of nutrients from burnt plots over time is ascribed to
removal of ash in surface runoff. Calcium, Mg, and K were lost more readily than Na
probably because plants take up these nutrients in greater concentration than Na. The
net effect was an increase in ESP. Crusting on burnt plots may be self-perpetuating,
because increased runoff is likely to incsease the loss of soluble salts. Removal of
vegetation due to cultivation, grazing or burning reduced soil C at all sites. Mean soil
C in the 0-1 cm layer of unburnt plots in the Kruger National Park was more than
three times greater than in burnt plots (2.7 vs 0.8%). The difference in soil C between
treatments decreased with depth and illustrated that sampling to depths greater than a
few centimetres can obscure effects of land use. The top few centimetres of soil have
a disproportionate effect on soil infiltrability and nutrient cycling. This layer was
named the pedoderm. Tree cover on burnt plots in the southern Kruger Nationa--l- Park
is highly variable, and was hypothesised to be a function of herbivory pressure.
Herbivores tended to congregate on plots with the greatest clay, Zn and Mn content
and the lowest tree cover. It is suggested that soil properties determine the abundance
of herbivores after fire, which in tum affects tree cover. In the Eastern Cape,intensive stocking with goats transforms dense thicket to an open savanna. Soils from
goat-transformed sites had a greater tendency to crust than soils from intact thicket,
probably due to aggregate weakening associated with a decline in soil C. Mean soil C
content of intact thicket was almost double that of goat-transformed thicket (5.6 vs.
3% to a depth of 10 cm) and is exceptionally high for a semi-arid region. The
potential to sequestrate carbon in degraded thicket landscapes is thus considerable.
Managing the land for greater sequestration of C will have the added benefit of
increasing soil aggregate stability, reducing the tendency of soils to crust and
therefore increasing the rate of water infiltration through the pedoderm. The benefits
of such an approach have been recognised by specialists in soil conservation and rural
land use for many decades, based largely on empirical observation. The results of this
thesis provide a more quantitative basis for appreciating the effects of soil C across a
broad spectrum of South African biomes. / AFRIKAANSE OPSOMMING: Die invloed van verskillende landgebruikspraktyke op grondkwaliteit in Suid-Afrika
is in vyf kontrasterende biome ondersoek met spesifieke klem op die neiging van
gronde om korste te vorm en die grond koolstofinhoud. Grondkwaliteit is 'n vae
konsep en die toepassing daarvan in die Suid-Afrikaanse grondlandskap is noukeurig
ondersoek. 'n Wye reeks van chemiese en fisiese grondeienskappe is ondersoek. Die
neiging van korsvorming by gronde is beraam deur die gebruik van breukmodulus,
waterdispergeerbare klei en 'n nuwe metode van laboratorium-infiltrasie wat met
behulp van reënvalsimulasie gekontroleer is. Korsvorming was groter in kaal,
blootgestelde gronde as in gronde met 'n plantbedekking en het gewissel volgens
moedermateriaal. Verskille in korsvorming word verklaar deur faktore wat verband
hou met kleidispergering soos byvoorbeeld kleimineralogie, grondkoolstof, labiele of
maklik oksideerbare koolstof, konsentrasie oplosbare soute, grondtekstuur en
uitruilbare natriumpersentasie (UNP). Resultate van langtermyn brandpersele in
savanna en grasland het getoon dat jaarlikse brand die neiging tot korsvorming kan
verhoog. Meer korsvorming in brandpersele word toegeskryf aan groter
kleidispergering, wat waarskynlik verband hou met 'n afname in grondkoolstof, 'n
afname in elektriese geleiding (Be) en 'n toename in UNP. Plantvoedingstowwe
gaan oor tyd verlore uit brandpersele, waarskynlik deur die verwydering van as in
oppervlak afloop. Kalsium, Mg en K gaan meer geredelik verlore as Na, waarskynlik
omdat plante hierdie voedingstowwe in groter hoeveelhede opneem as Na. Die netto
effek is 'n toename in UNP. Korsvorming op brandpersele kan self instand gehou
word omdat verhoogde afloop die moontlike verlies van oplosbare soute kan verhoog.
Verwydering van plantegroei deur bewerking, beweiding of brand het grondkoolstof
op alle plekke verlaag. Die gemiddelde grondkoolstof in die 0-1 cm laag van
ongebrande persele in die Kruger Nasionale Park was meer as drie maal groter as in --..
brandpersele (2.7 vs 0.8 %). Die verskil in grondkoolstof tussen behandelings neem
af met diepte wat daarop dui dat monsterneming tot dieptes groter as 'n paar
sentimeters die effek van landgebruik kan verberg. Die boonste paar sentimeters van
'n grond het 'n oneweredige invloed op infiltrasie en voedingstofsirkulasie. Hierdie
laag word die pedoderm genoem. Boombedekking op brandperseie in die suidelikeKruger Nasionale Park is hoogs variërend. Die hipotese was dat dit 'n funksie van
druk deur planteters is. Planteters neig om op persele met die hoogste klei, Zn- en
Mn-inhoud en die laagste boom bedekking te versamel. Daar word voorgestel dat
grondeienskappe die hoeveelheid planteters na 'n brand bepaal. Dit beïnvloed op sy
beurt weer die boombedekking. In die Oos-Kaap het intensiewe bokboerdery digte
bosruigtes verander na oop savannas. Gronde van bok-veranderde lokaliteite het 'n
groter neiging tot korsvorming as gronde van onveranderde bosruigtes, vermoedelik
as gevolg van verswakking van aggregate met 'n. afname in grondkoolstof. Die
gemiddelde grondkoolstof van onveranderde bosruigtes was byna dubbel soveel as die
koolstof van bok-veranderde bosruigtes (5.6 vs 3 % tot 'n diepte van 10 cm) en
buitengewoon hoog vir 'n semi-ariede streek. Die potensiaal vir koolstof sekwestrasie
in degradeerde bosruigte landskappe is dus aansienlik. Bestuur van land vir groter
sekwestrasie van koolstof het die bykomende voordeel van verhoogde grond
aggregaatstabilteit, verlaging van die neiging tot korsvorming en daardeur 'n
verhoging in die tempo van waterinfiltrasie deur die pedoderm. Die voordele van so
'n benadering is vir baie dekades deur spesialiste in grondbewaring en landelike
landgebruik herken. Dit was grootliks gebaseer op empiriese waarneming. Die
resultate van hierdie tesis bied 'n meer kwantitatiewe basis tot die verstaan van die
invloed van grondkoolstof oor 'n breë spektrum van Suid-Afrikaanse biorne.
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Assessment of cadium (Cd) and lead (Pb) contamination in the soils of pre-school facilities in the City of Cape TownNkoe, Nozi 'Mabafokeng January 2009 (has links)
Thesis (MTech (Environmental Health))--Cape Peninsula University of Technology, 2009. / In the last two centuries, the natural state of the environment has changed
significantly due to anthropogenic activities. With an estimated half-life of 15 -
1100 years for cadmium in soils, the metal remains a threat to the ecosystem. In
general, most soils contain <1 mg/kg, except those contaminated from discrete
sources or developed on parent materials with very high cadmium contents.
Anthropogenic lead in soil has several well recognized major sources, namely,
lead based paint, mining and smelting activities, manures, sewage sludge usage
in agriculture and contamination from vehicle exhausts. Since lead is a heavy
metal, over time it will settle down and build up in soil. The main aim of this study
was to determine the degree of cadmium and lead contamination of soil, in and
around selected pre-school facilities in the City of Cape Town (CCT). A number
of pre-school facilities, particularly those nearby heavy traffic, were selected in
the CeT. Natural soil and sand pit soil samples were collected and analysed for
cadmium and lead. Low soil moisture is normally associated with high pH, as
found in the present study. High pH values are in turn associated with low toxicity
of metal contaminants. Most urban populations rely heavily on motor vehicles
and vehicle-related pollution has been an increasing concern in recent years
(before 2006). Air pollution in the CCT is trapped by inversion layers. In this
study it has been found that cadmium is not a significant contaminant in the soils
of pre-school facilities in the CCT. The Cape Town administration area was
found to be the most contaminated with this metal. This study showed that the
Cape Town administration area also had the highest lead concentrations in pre-school soils in the CCT. This can be attributed to the higher density of industry
and traffic activities (study conducted pre-2006) in this area. There is a need for
further research to determine the relationship between soil metal concentrations
and blood metal levels, especially in children.
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