Spelling suggestions: "subject:"soils, salts ono."" "subject:"soils, salts onn.""
91 |
ESTIMATION OF EVAPOTRANSPIRATION AND IRRIGATION UNIFORMITY FROM SUBSOIL SALINITY (ARIZONA).HASSAN, HESHAM MAHMOUD. January 1985 (has links)
Irrigation uniformity, efficiency, leaching fraction, salt and water ages, and evapotranspiration rate were estimated from subsoil salinity data for three cotton fields in Arizona. The estimation of these parameters was based on the assumption of steady-state water and salt flow through the crop root zone. The levels of salt concentration in the irrigation water were 21.3, 11.5, and 11.6 meq/L for Fields 1, 2, and 3, respectively. Two of these fields were furrow irrigated, and the third was subsurface drip irrigated. Each field was sampled for salt concentrations to a depth of 1.5 m at 10-15 sites. A total of 514 soil samples were collected. Significantly lower salt concentrations were observed in the soil profiles in Fields 1 and 2 compared to Field 3, but lower variations in the salt concentrations were observed in Field 3 compared with Fields 1 and 2. These variations in salt concentration could be due to restricted water movement within the soil profile caused by stratified soil. Since a soil-water extract model indicated little or no chemical precipitation of salt within the soil profile, there was no need to correct the data for chemical effects. The calculated irrigation uniformity was highest in Field 3 and lowest in Field 1. This may be related to more accurate land leveling in field 2 than Field 1. The irrigation efficiencies were 83.0%, 89.0%, and 80.0% for Fields 1, 2, and 3, respectively. The correlation coefficient between the ages of salt and water was 0.98, 0.99, and 0.97 for Fields 1, 2, and 3, respectively. Leaching fraction was highest in Field 3 and lowest in Field 2. Mean actual ET calculated from the Blaney-Criddle method were 372, 314, and 308 mm for Fields 1, 2, and 3, respectively. Mean ET calculated from the salinity data were 1,250, 1,590, and 1,140 mm for Fields 1, 2, and 3, respectively. Statistically significant correlation coefficients were, however, found between both methods of estimating ET. These values were 0.97, 0.86, and 0.93 for Fields 1, 2, and 3, respectively.
|
92 |
Leaf-litter and microsite on seedling recruitment in an alley-planted E. sargentii and Atriplex spp. saline agricultural systemFarrell, Claire January 2008 (has links)
[Truncated abstract] In order to assess the sustainability of mixed plantings on saline land, this thesis examined the importance of leaf-litter trapping and microsites on recruitment in a salt affected alley-belted (tree/shrub) agricultural system in Western Australia. Located in the low rainfall region (MAR <330 mm) of the wheatbelt, the 60 ha site consists of concentric rows of Eucalyptus sargentii trees with mounded (6 - 11 cm high) 10 -15 m inter-rows of Atriplex spp. Sustainability of this system and fulfilment of productive and ameliorative functions is dependant on successful recruitment (perennials). Although the present study site was conducted on farmland in a Mediterranean-type climate, low annual rainfall and spatial arrangement of perennial shrubs and trees, allow useful comparisons to be made with naturally occurring banded semi-arid systems and vice-versa. Of key interest were leaf-litter redistribution and trapping by tree and shrub rows and whether litter-cover/microsites facilitated/interfered with seedling recruitment (establishment, growth and survival). Litter from the tree row, redistributed by prevailing winds and rain, accumulated adjacent to saltbush seeding mounds, creating a mosaic of bare and littered areas across the site (total litter 10 t/ha over 22 months). Accumulated litter was hypothesized to differentially influence seasonal soil abiotic parameters (depending on litter-cover density) including; salinity, water availability, infiltration rates, water repellency and temperature. These abiotic conditions were also hypothesized to vary between tree and shrub microsites. Biotically, recruitment at this site was also hypothesized to be determined by interactions (positive and negative) between perennial components and understorey annuals/perennial seedlings. Accumulation of litter and resultant heterogeneity was influenced by shrub morphology, microtopography, wind direction and distance from litter source, with increased litter on the leeward sides of hemispherical Atriplex undulata shrubs and shrubs closest to tree rows. ... The importance of tree/shrub microsites varied seasonally, with no influence in winter due to moderate temperatures and increased water availability. In warmer months saltbush mid-row microsites were most favourable for seedling recruitment due to moderate litter-cover; reducing salinity, temperatures and increasing infiltration; and reduced root-competition/shading by the tree row. Tree microsites also directly inhibited seedling recruitment through increased salinities and water repellency. However, trees also indirectly facilitated recruitment in adjacent areas through provision of leaf-litter. As litter-trapping and recruitment patterns at this site mirror those found in semi-arid natural and artificial systems, the results of this study provide useful insights into creating appropriate mimics of low rainfall natural banded woodland and chenopod shrublands. Saltbush seeding mounds, shrub morphology and litter were key components for litter trapping and recruitment heterogeneity at this site. In this tree/shrub alley planting, where litter quantities directly influence vegetation cover densities, future saline plantings need to consider appropriate tree/shrub row spacings and orientation for efficient resource (seeds, litter and water) capture.
|
93 |
Effects of irrigation-induced salinity and sodicity on soil chemical and microbial properties and sugarcane yield. / ThesisRietz, Diana Nicolle. January 2001 (has links)
The effects of irrigation-induced salinity and/or sodicity on sugarcane yield, and two growth parameters, namely stalk height and number of nodes per stalk , were investigated on a sugarcane estate in the Zimbabwean lowveld. The effects of soil salinity and/or sodicity on the size, activity
and metabolic efficiency of the soil microbial community was also studied. Furrow-irrigated fields which had a gradient in soil salinity and/or sodicity which increased from the upper to lower ends of the fields were selected for this study. This gradient was recognized by decreasing sugarcane
growth down from the upper to the lower ends and the appearance of salt on the soil surface at the lower ends of fields. Sugarcane growth was classified as either dead, poor, satisfactory or good; and soil samples (0-0 .15 m, 0.15-0 .3 m, 0.3-0 .6 m and 0.6-0.9 m) were taken from each of these areas. Soils from under adjacent areas of undisturbed veld were also sampled. Sugarcane
growth and yields in micro-plots of the various areas of the fields were measured. Foliar samples of sugarcane were taken at 22 weeks of age and analysed for nutrient content. Soil salinity and sodicity were quantified by measuring pH(water), electrical conductivity (ECe) and cation content of saturation paste extracts and the exchangeable cation content. From this information, the
sodium adsorption ratio (SARe)and exchangeable sodium percentage (ESP) were also calculated.
The calcareous, vertic soils in the study area under undisturbed veld were found to have high pH
values (8 to 9.5), very high exchangeable Ca and Mg concentrations and there was evidence of
accumulation of soluble salts in the surface 0.15 m. Under sugarcane production, irrigation induced
salinity and sodicity had developed. Under poor and dead sugarcane, high values for ECe,
SARe, and ESP were generally encountered in the surface 0-0 .3 m of the profile. In addition, the
pH values under sugarcane were often between 9 and 10 particularly in profiles where sugarcane grew poorly or had died. As expected, pH was positively related to ESP and SARe, but negatively related to ECe.
Measurements of aggregate stability by wet sieving, the Emerson dispersion test and the Loveday
dispersion score all showed that soils from the study sited tended to disperse and that dispersion
was most apparent where high ESP and SARe values occurred in association with elevated pH
values and relatively low ECe values. These measurements confirmed observations at the sites of
low infiltration rates and restricted drainage particularly on the lower ends of fields where sugarcane had died. In addition to the above measurements it was also observed that there was a rise in the watertable
under furrow irrigation and that the watertable was nearest to the surface at the lower ends of the
fields. In some cases the watertable was observed to be only 0.2 to 0.3 m from the surface. Thus,
death of roots due to anaerobic conditions could be occurring to a greater extent at the lower ends
of the fields. Another consequence of the high watertable was that these vertic soils were
observed to remain in a permanently swollen state. This limits air and water movement in the soil
profile as such soils need to be allowed to dry out and crack regularly so that macroporosity can be restored.
Sugarcane yield, stalk height and number of nodes per stalk were not significantly related to ECe.
Sugarcane yields were, however, significantly correlated with ESP and pH while stalk height and
number of nodes were negatively correlated with ESP, SARe and pH. These results suggested
that sodicity was a more limiting factor for sugarcane growth than salinity. Foliar analysis of leaf
tissue did not reveal substantial differences in macro- or micro-nutrient content between good and
poorly-growing sugarcane.
It was concluded that the gradient of decreasing sugarcane growth down the furrow-irrigated fields, with crop death at the lower ends, was the result of a combination of factors. That is, the
watertable had risen due to over-irrigation and it was nearer the surface at the lower ends of the fields. Due to capillary rise of salts, this resulted in sodic and sometimes saline-sodic conditions
in the surface soil. These conditions could limit plant growth through ion toxicities, plant water
stress and inhibition of root growth and function and physiological processes. These would be
induced by the high pH and high salt, Na and HC03- concentrations in soil solution. Poor
physical conditions associated with sodicity and the continually swollen state of the soils
presumably limited infiltration and aeration in the surface soil, and probably restricted root
growth. In addition, it is likely that the high watertable limited effective crop rooting depth to
about 0.2 m at the lower ends of the fields. The net result was that sugarcane died at the lower
ends. A negative effect of soil salinity and/or sodicity was also observed on the soil microbial
population. Significant negative correlations were obtained with ECe SARe and ESP with
microbial biomass C and microbial activity (as measured by FDA hydrolytic activity or arginine
ammonification rate). The activity of enzymes involved in C (P-glucosidase), P (phosphatase) and
S (arylsulfatase) mineralization and potential nitrogen mineralization (as determined by aerobic
incubation) were also negatively correlated with these factors, with the exception of arylsulfatase
activity and ESP. All the above mentioned microbial population measures were also positively
correlated with soil organic C content, besides potential nitrogen mineralization. The metabolic
quotient, which provides an indication of stress and efficiency of the microbial community,
increased considerably with increasing salinity and sodicity and decreased with soil organic C.
Thus, increasing salinity and/or sodicity resulted in a smaller, more stressed, less efficient
microbial community, while the turnover rate and cycling of C, N, P and S also decreased. It was
concluded that salt affected soil not only causes a decline in sugarcane yield through raising the concentration of soluble salts in soil solution, but also has a detrimental effect on microbial activity and on mineralization of soil organic C, N, Sand P. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.
|
94 |
Multiscale prediction of saline-sodic land degradation processes in two South Australian regions.Thomas, Mark January 2007 (has links)
Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / In this thesis, the distribution of saline-sodic properties forming part of a complex pattern of soils in two varied upland agricultural regions in South Asutralia were predicted at multiple scales using DSM and allied approaches. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1283986 / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2007
|
95 |
Multiscale prediction of saline-sodic land degradation processes in two South Australian regions.Thomas, Mark January 2007 (has links)
Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / In this thesis, the distribution of saline-sodic properties forming part of a complex pattern of soils in two varied upland agricultural regions in South Asutralia were predicted at multiple scales using DSM and allied approaches. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1283986 / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2007
|
96 |
Water- en soutbalanse van geselekteerde besproeide gronde van die benede Bergrivier opvanggebiedEngelbrecht, Hendrik Nicolaas 04 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: A study was conducted between 2000 and 2002 in the lower Berg River catchment of
the semi-arid Western Cape Province to investigate the effect of irrigation
developments (wheat fields to table grapes) on the quality of the Berg River as well as
the sustainability of these developments. This study was necessitated by the
mineralisation of both the Breede and Berg River, probably due to irrigation together
with the higher pressure on these water resources from the growing demand for fresh
water from the Cape Town metropolitan area.
Water and Salt balances of two dominant soil patterns (Glenrosa/Swartland and
Oakleaf/Hutton soil forms) from the catchment area were monitored at two localities.
Vineyard blocks of different ages in the same soil forms were used to study the effect
of irrigation over time. The electrical conductivity of the soil water extracts (ECe) was
measured three times over depth at the selected sites and the quality of irrigation and
drainage return-flow were monitored. Soil water storing capacities of these stony
(high rough fragment' fractions) soils were also characterised for more efficient
drainage quantity prediction.
Glenrosa/Swartland soils showed the highest ECe's (200-400 mx.m") that decreased
significantly after four to five years of irrigation and distribution became more
uniform over depth. These high salt concentrations were explained due to natural
occurrence of salts, mineral weathering and salts from the irrigation water.
Oakleaf/Hutton soils showed lower ECe's « 200 nfS.m") but they are subject to the
quality of the irrigation water, which is not that constant over years. Localised salt
accumulation was observed due to the irrigation method and became more prominent
over years. Drainage quantities were under predicted because of the big/high rough
fragment fractions and the occurrence of preferential-flow. This prohibited the
accurate calculation of the soil water house holding characteristics. It also led to the
under calculation of salt return-flow, but it was very evident that the most salt retumflow
occurred from the Glenrosa/Swartland soils. Effective irrigation management to
achieve and maintain optimal soil water levels and to reduce the negative impact of
high ECe's is essential for the sustainability of these irrigation developments. At
present it does not seem that the irrigation return-flow is causing dramatic
mineralisation of the lower Berg River, but it is a situation that must be monitored as
the developments extent and become older (come into production). It seems that
irrigation return-flow only has an influence on the quality of the river at the beginning
of such a development, but after about three years the influence directly correlates
with the quality of irrigation water and mineral weathering. / AFRIKAANSE OPSOMMING: 'n Studie is gedurende die jare 2000 tot 2002 in die benede Bergrivier opvanggebied
van die semi-ariede Wes-Kaap Provinsie gedoen om die effek van
besproeiingsontwikkelings (koringlande na tafeldruiwe) op die kwaliteit van die
Bergrivier se water, asook die volhoubaarheid van besproeiingslandbou te ondersoek.
Hierdie studie was genoodsaak deur toenemende versouting van beide die Breede- en
Bergrivier, waarskynlik a.g.v. besproeiing, tesarne met groter druk op hierdie
waterbronne van wee die groeiende aanvraag na vars water deur die Kaapstadse
metropool.
Water- en soutbalanse van twee dominante grondpatrone (Glenrosa/Swartland en
Oakleaf/Hutton grondvorms) binne die opvanggebied was by twee lokaliteite
gemoniteer. Wingerdblokke van verskillende ouderdomme binne dieselfde
grondvorms is gebruik om die effek van besproeiing oor tyd te ondersoek. Die
elektriese geleiding van die grondwaterekstrak (EGe) was drie maal op verskillende
dieptes by geselekteerde persele gemeet en die kwaliteit van besproeiingswater en
dreineringsterugvloei was deurgaans gemoniteer. Grondwaterstoringskapasiteite van
hierdie klipryke ( hoe 'growwe fragment fraksie) gronde was ook gekarakteriseer vir
meer doeltreffende voorspellings van dreineringshoeveelhede.
Glenrosa/Swartland gronde het die hoogste EGe's getoon (200-400 mx.m') wat na
vier tot vyf jaar se besproeiing aansienlik afgeneem het en meer uniform met diepte
versprei was. Die hoe soutkonsentrasies is veroorsaak deur die natuurlike voorkoms
van sout in die grond, minerale verwering en sout vanuit die besproeiingswater.
Oakleaf/Hutton gronde het laer EGe's getoon « 200 mS.m-I
), maar hierdie gronde se
soutinhoud is ook onderhewig aan die kwaliteit van die besproeiingswater en
dreinering wat oor jare nie baie konstant was en nog is nie. Gelokaliseerde
soutaansarneling tussen wingerdrye is ook waargeneem a.g.v. die besproeiingsmetode
en dit word meer prominent oor jare. Dreineringshoeveelhede was onder-voorspel
a.g.v. die groot/hoe growwe fragment fraksies en voorkoms van voorkeurvloei, wat
die akkurate modellering van grondwaterhuishouding beperk het. Dit het ook daartoe
gelei dat soutterugvloei ondervoorspel was, maar dit was duidelik dat die meeste
soutterugvloei vanuit die Glenrosa/Swartland gronde plaasvind. Effektiewe
besproeiingsbestuur, om optimale grondwaterpeile te handhaaf en om negatiewe
effekte van hoe EGe te beperk, is noodsaaklik vir die volhoubaarheid van hierdie tipe
besproeiingsontwikkelings. Tans blyk dit nie of besproeiingsterugvloei drarnatiese
versouting van die benede Bergrivier veroorsaak nie, maar dit is egter 'n situasie wat
deeglik gemoniteer moet word soos wat ontwikkelings uitbrei en ouer word (in
produksie kom). Besproeiingsterugvloei het dus net aan die begin van so 'n
ontwikkelling 'n invloed op die EG van die rivier, maar na ongeveer drie jaar hou die
invloed direk verband met die kwaliteit van die besproeiingswater en minerale
verwenng.
|
97 |
Influence of clay content and salinity on the bioavailability and toxicity of metals (copper and zinc) to soil organismsOwojori, Olugbenga J. (Olugbenga John) 12 1900 (has links)
Thesis (PhD (Botany and Zoology))—University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Metal pollution is a problem of increasing global concern. It could arise from
industrial activities, as well as pesticide use in agriculture, among other sources. For
adequate protection of the soil ecosystem from metal toxicity, the bioavailability of
metals must be properly evaluated. A plethora of soil factors affect the bioavailability
of metals to soil organisms. These include pH, clay and organic matter contents,
salinity among others. While much is known about the influence of some of these
parameters, little is known on how clay content and salinity modify the bioavailability
of metals to soil organisms.
This study investigated the influence of clay content and salinity on
partitioning, uptake and toxicity of two essential metals (Cu and Zn) to the earthworm
Eisenia fetida in separate laboratory trials. Partitioning of the metals was evaluated
with 0.01 M CaCl2, DTPA (di-ethylene-triamine-penta acetic acid), and nitric acid
extractions. The metal content of worms was determined by acid digestion, while
growth, cocoon production, and mortality were used as endpoints showing toxicity to
metals and/or salinity. To test the validity of some of the laboratory results, a field
study was undertaken, using the earthworm Aporrectodea caliginosa. Further, the
study assessed the effect of salinity, using a battery of laboratory tests (acute, chronic
and avoidance tests) with natural and/or artificial soils on four species of organisms (a
collembolan Folsomia candida, a potworm Enchytraeus doerjesi and two earthworm
species E. fetida and A. caliginosa), representing different feeding patterns and
ecological roles in soil.
Results showed that with increased clay content, there was increased
availability of Cu in the substrate, and increased toxicity to E. fetida as shown by data
for mortality and growth. The situation with Zn was less significant at sub-lethal
concentrations but much so at lethal concentrations. DTPA and CaCl2 extracted
metals revealed changes in partitioning of Cu and Zn with changes in clay content,
but this trend was not always consistent. Both DTPA and CaCl2 revealed increased
availability of Zn in substrates with increased salinity. Salinity had an additive to
synergistic effect with Zn in toxicity to E. fetida. When combined with Cu, salinity
also increased the availability of Cu as shown by CaCl2 extracted fraction, and had
additive effect on toxicity of Cu to the earthworm. The field study did not succeed in in
iv
confirming the results of the laboratory study due to confounding role of flooding
after heavy rainfall and subsequent leaching of salts and Cu. The results of the
experiment on acute and chronic toxicity tests for NaCl on E. fetida showed LC50 of
5436 mg/kg NaCl and EC50 for growth and cocoon production of 4985 and 2020
mg/kg NaCl. These values showed that earthworms might be negatively affected in
many soils containing fairly moderate concentrations of salts. Similarly, A. caliginosa
could not survive in natural soil containing relatively low salt concentrations (EC =
1.62 dS/m) while reproduction was severely affected at lower EC value of 0.52 dS/m.
F. candida and E. doerjesi could survive in the highest salinity soil (EC = 1.62 dS/m)
used in this study but their reproduction was severely affected from 1.03 dS/m.
Overall, it appears that of all the taxa used, earthworm species were the most sensitive
to saline stress and could proof useful in determining ‘safe levels’ of salt in
contaminated soils. The results of the avoidance test showed that A. caliginosa
avoided both natural and artificial saline soil containing concentrations lower than
those avoided by E. fetida.
The conclusion is that the influence of clay content and salinity on the
bioavailability of Cu and Zn depends largely on the metal in question, but generally
speaking, bioavailability and toxicity of the metals were reduced with increased clay
content while the opposite was true for salinity. If the species used in this study can be
seen as fairly representative of a wide range of soil organisms, the conclusion is that
salinisation of soil will be detrimental to most soil organisms at relatively low saline
concentrations. Given the role of beneficial soil organisms in several soil processes
which in turn contribute to soil fertility and sustainable use of land, it is recommended
that any farming practices that may lead to an increase in salt content of agricultural
soils should be discouraged. / AFRIKAANSE OPSOMMING: Metaalbesoedeling is ‘n probleem wat toenemende globale kommer
veroorsaak. Dit kan ontstaan as gevolg van industriële aktiwiteite sowel as van
plaagmiddelgebruik in die landbou en ander bronne.Ten einde die grondekostelsel
genoegsaam te beskerm, moet die biobeskikbaarheid van metale ge-evalueer word. ‘n
Verskeidenheid van grondfaktore be-invloed die biobeskikbaarheid van metale vir
grondorganismes Hulle sluit onder andere in pH, klei, organiese inhoud en
soutgehalte. Hoewel heelwat bekend is oor die rol van sommige van hierdie
parameters, is min bekend oor hoe klei en soutgehalte die biobeskikbaarheid van
metale vir grondorganismes kan modifieer. Hierdie studie het die invloed van kleiinhoud
and soutgehalte op die verdeling/partisie, opname en toksisiteit van twee
essensiële metale (Cu en Zn) vir die erdwurm Eisenia fetida in afsonderlike
laboratoriumproewe ondersoek. Kompartementele verdeling van die metale is geevalueer
deur middel van ekstraksie-metodes met 0.01 M CaCl2, DTPA (di-etileentriamien-
penta asysnsuur), en salpertersuur ekstraksies. Die metaalinhoud van wurms
is bepaal deur suurverterings en spektrofotometriese analises te doen terwyl groei,
kokonproduksie en mortaliteit van organismes gebruik is as gevoeligheidseindpunte
om toksisiteit van metale en soutgehalte aan te toon. Om die geldigheid van somige
van die laboratoriumresultate te toets, is ‘n veldstudie ook onderneem met die
erdwurm Aporrectodea caliginosa. Die effek van soutgehalte is verder ondersoek
deur ‘n battery van laboratoriumtoetse met vier spesies (‘n kollembool Folsomia
candida,’n potwurm Enchytraeus doerjesi en twee erdwurmspesies E. fetida en A.
caliginosa), wat verskillende voedingspatrone verteenwoordig.
Die resultate het getoon dat met toenmende klei-inhoud was daar ‘n toename
in die beskikbaarheid van Cu vir opname vanuit die substraat, asook ‘n toename in
toksisiteit vir E. fetida soos deur die gegewens vir mortaliteit en groei uitgewys. Die
situasie met Zn was minder betekenisvol by subletale konsentrasies en selfs baie
minder so by letale konsentrasies. DTPA en CaCl2 ge-ekstraheerde metale het
veranderinge in die partisie/verdeling van Cu en Zn uitgewys met verandering in
klei-inhoud, maar die tendens was nie altyd konstant nie. Beide DTPA en CaCl2
ekstraksie het toenemende beskikbaarheid van Zn in substrate uitgewys met
toenemende soutinhoud. Soutinhoud het ‘n additiewe/toegevoegde tot sinergistiese
vi
toksisiteitseffek saam met Zn vir E. fetida. In kombinasie met Cu het soutgehalte ook
die geskatte biobeskikbaarheid van Cu verhoog soos uitgewys deur die CaCl2, geekstraheerde
fraksie, en het ‘n additiewe effek gehad op die toksisitiet van Cu vir die
erdwurm.
Die veldstudie kon nie die resultate van die laboratoriumstudie bevestig nie
weens die belemmerende rol van vloede na swaar reënneerslae en daaropvolgende
uitloging van soute en Cu. Die resultate van die eksperimentele ondersoek na die
akute en chroniese effekte van NaCl op E. fetida het ‘n LC50 van 5436 mg/kg NaCl
en EC50 vir groei en kokonproduksie van 4985 en 2020 mg/kg NaCl opgelewer.
Hierdie waardes het aangetoon dat erdwurms moontlik negatief beinvloed kan word
in baie gronde wat ‘n redelike gemiddelde konsentrasie van soute bevat. Soortgelyk
kon A. caliginosa nie oorleef in natuurllike grond wat relatief lae soutkonsentrasies
bevat het (EC=1.62 dS/m) nie terwyl voortplanting sterk ge-affekteer is by ‘n lae EC
waarde van 0.52 dS/m. F. candida en E. doerjesi kon oorleef in die grond met die
hoogste soutgehalte (EC= 1.62 dS/m) maar hulle voortplanting is ernstig geknou
vanaf 1.03 dS/m. In geheel blyk dit dat van allle taksa wat gebruik is, erdwurms die
sensitiefste was vir die stres wat deur soutgehalte veroorsaak is. Die kennis kan nuttig
wees in die bepaling van “veilige vlakke” van sout in gekontamineerde gronde. Die
resultate van die vermydingstoetse het getoon dat A. caliginosa beide natuurlike en
kunsmatig versoute gronde vermy het by konsentrasies wat heelwat laer was as dié
wat deur E. fetida vermy is
Die gevolgtrekking is dat die invloed van klei en soutgehalte op die
biobeskikbaarheid van Cu en Zn grootliks afhanklik is van die metale wat betrokke is
en dat biobeskikbaarheid en toksisiteit normaalweg verminder het met verhoogde
klei-inhoud, met die teenoorgestelde wat waar was in die geval van soutgehalte.
Indien die spesies wat in die studie gebruik is beskou kan word as redelik
verteenwoordigend van ‘n wye reeks van grondorganismes, is die gevolgtrekking dat
versouting van gronde nadelig sal wees vir meeste grondorganismes, selfs by relatief
lae soutkonsentrasies. In die lig van die rol wat nuttige grondorganismes speel in
verskeie grondprosesse wat bydraend is tot grondvrugbaarheid en volhoubare gebruik
van gronde, word dit aanbeveel dat enige boerderypraktyk wat mag lei tot verhoging
van die soutinhoud van landbougronde ontmoedig moet word.
|
98 |
Western Australia's salinity investment framework : a study of priority setting in policy and practiceCleland, Jonelle January 2008 (has links)
In March 2002 the Western Australian Minister for Environment and Heritage adopted a policy framework to guide investment decisions on salinity management. Promoted as Western Australia's Salinity Investment Framework (or the SIF), it offered a set of principles for prioritising investment decisions that were generally grounded in economic theory. This represented a significant landmark in terms of the government's appreciation of the scale of salinity problem and its acknowledgement that a full turnaround in the situation was beyond the reach of both volunteers and the public purse. The evolution of the SIF policy, including an initial trial in the Avon Basin, provided an opportunity to evaluate pre-policy processes; observe policy on the run; and test stakeholder reactions to the investment principles embodied in the the SIF, as well as their reaction to its implied outcomes. The intention of the study was to highlight any barriers standing in the way of effectively implementing a policy to prioritise investments in salinity management and identify any novel approaches developed in an attempt to overcome them. The evaluation was multifaceted to incorporate retrospective and prospective modes of inquiry. The retrospective investigation involved the construction of a series of policy narratives using evidence from notes and minutes taken at SIF meetings, as well as other formal and informal documents. It systematically captured the influence of key people, events and decisions on the SIF up until June 2008. This evaluation highlighted the impact of (1) policy entrepreneurs; (2) time lags; (3) vertical silos, and (4) priority setting hierarchies. The prospective investigation involved the execution of a community survey featuring attitudinal questions, paired comparisons and a choice modelling experiment. The survey involved 269 personal interviews with rural landholders, townspeople and landcare officers across the Avon Catchment. It captured perceptions towards past funding strategies and proposals for future allocations and explored the nature of priority setting decisions in relation to trade-offs between: (1) the mix of assets protected; (2) the degree of risk; (3) the level of community involvement in the decision, and (4) the distribution of benefits. This evaluation highlighted the importance of (1) incentives and disincentives for change; (2) awareness of priority setting concepts; (3) the capacity of regional bodies; and (4) elements perceived to be crucial in priority setting.
|
99 |
The growth response of Eucalyptus grandis x e. camaldulensis to salt stress, ectomycorrhizae and endomycorrhizae double colonisationHengari, Simeon Ngaitungue 03 1900 (has links)
Thesis (MScFor (Forest and Wood Science))--University of Stellenbosch, 2007. / The study was undertaken to determine the potential physiological benefits to plants provided by the double colonisation of host plant roots by endomycorrhizal (AM) and ectomycorrhizal (ECM) fungi, when growing under normal and under salt stress conditions. Plants of the Eucalyptus grandis x E. camaldulensis clone were grown in a sterile soil with 0 and 75 mM NaCl and with or without infection with the fungi Glomus etunicatum (an AM fungus) and Pisolithus tinctorius (an ECM fungus). The Eucalyptus clone formed both ECM and AM in single and double inoculation. The mycorrhizal symbiosis did not provide any nutritional benefits to the hosts. The double colonisation had no effect on plant growth under normal growth conditions while single colonisations of AM and ECM reduced growth. Double colonisation reduced host plant specific leaf mass by 12% and increased total leaf area by 43% compared with the control under these growth conditions. This colonisation also reduced photosynthesis per leaf area by 29% compared with the control. The reduced photosynthesis of the double colonisation did not result in reduced plant growth because these plants may have had a high total plant photosynthesis because of their large total leaf area. The double symbiosis however did not reduce salt stress when host plants were exposed to 75 mM NaCl, while the AM fungus increased plant dry weight by 13% compared to the control. AM and ECM colonisation in the double colonised roots under salt stress was decreased by 18 and 43% compared to that in plants under normal growth. The reduced colonisation may have reduced the fungi’s abilities to be beneficial to the host plant. The double symbiosis is recommended based on the documented positive effects of this symbiosis to plant growth and the considered possible long-term benefits to host plants growing in saline soils.
|
100 |
Relationship of vegetation to salinity and sodicity in wetland meadows of the Chilcotin region of British ColumbiaMayall, Alison Christina January 1985 (has links)
This study investigates the relationships between vegetation and salinity and sodicity in wetland meadows in the Chilcotin region of British Columbia.
Eleven vegetation communities and one group of releves with no vegetation
were identified using cluster analysis. An exchangeable sodium per cent of 15 and an electrical conductivity of 4 mmhos/cm were found to be appropriate boundaries for distinguishing between saline and sodic tolerant and intolerant vegetation communities. Some salt tolerant species and communities occurred in fresh conditions; however, intolerant species and communities were rarely found in saline or sodic conditions. Most meadows have soils that are low in salts, but 20 per cent had a high electrical conductivity and 18 per cent had a high exchangeable sodium per cent. / Land and Food Systems, Faculty of / Graduate
|
Page generated in 0.0371 seconds