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The effect of oxygen on the composition and microbiology of red wineDu Toit, Wessel Johannes 03 1900 (has links)
Thesis (PhD(Agric) (Viticulture and Oenology))--University of Stellenbosch, 2006. / The winemaking process involves different complex chemical and biochemical
reactions, which include those of oxygen (O2). Oxygen can come into contact with the
wine through various winemaking procedures and can be used by the winemaker to
enhance the quality of red wine. In wine, the main substrates for oxidation are
phenolic molecules, which form quinones. These can influence the sensory
characteristics of the wine. O2 can be used in fresh must to remove oxidisable
phenolic molecules through a process called hyper-oxidation and can also be added
to fermenting must to enhance the fermentation performance of yeast. Controlled O2
additions during ageing can lead to the wine’s colour being increased and the
astringency of the wine decreased. This is due to the formation of acetaldehyde from
the oxidation of ethanol, which induces the polymerisation of tannin and anthocyanin
molecules. The addition of too much O2 to wine can, however, lead to unwanted
over-oxidation, with certain off-odours being formed. It can also enhance the growth
of unwanted spoilage microorganisms, such as Brettanomyces and acetic acid
bacteria. Although research on O2 in wine was started many years ago, many
questions still remain. These include the general effect of O2 on the sensory and
phenolic profile of red wine especially and the microbiology of wine during ageing. An
effective way of measuring oxidation, especially in red wine must also be developed.
In the first part of this study, the effects of O2 and sulfur dioxide (SO2) additions
on a strain of Brettanomyces bruxellensis (also known as Dekkera bruxellensis) and
Acetobacter pasteurianus were investigated. Epifluorescence microscopy and plating
revealed that the A. pasteurianus strain went into a viable but non-culturable state in
the wine after prolonged storage under relative anaerobic conditions. This state,
however, could be negated with successive increases in culturability by the addition
of O2, as would happen during the transfer of wine when air is introduced. The A.
pasteurianus strain was also relatively resistant to SO2, but the B. bruxellensis strain
was more sensitive to SO2. A short exposure time to molecular SO2 drastically
decreased the culturability of the B. bruxellensis strain, but bound SO2 had no effect
on the culturability or viability of either of the two types of microorganisms. Oxygen
addition to the B. bruxellensis strain also led to a drastic increase in viability and
culturability. It is thus clear that SO2 and O2 management in the cellar is of critical
importance for the winemaker to produce wines that have not been spoiled by
Brettanomyces or acetic acid bacteria. This study should contribute to the
understanding of the factors responsible for the growth and survival of
Brettanomyces and acetic acid bacteria in wine, but it should be kept in mind that
only one strain of each microorganism was used. This should be expanded in future
to include more strains that occur in wine.
The second part of this study investigated the effect of micro-oxygenation on four
different South African red wines. It was found that the micro-oxygenation led to an
increase in the colour density and SO2 resistant pigments of the two wines in which micro-oxygenation was started just after the completion of malolactic fermentation. In
one of these wines, a tasting panel preferred the micro-oxygenation treated wines to
the control. In the other two red wines, in which the micro-oxygenation was started
seven months after the completion of malolactic fermentation, very little colour
increase was observed. One of these two wines was also matured in an oak barrel,
where the change in phenolic composition was on par with the treated wines. A
prolonged period of micro-oxygenation, however, led to this wine obtaining an
oxidised, over-aged character. Micro-oxygenation and maturation in an oak barrel
also enhanced the survival of acetic acid bacteria and Brettanomyces in this wine.
Micro-oxygenation can hence be used by the wine producer on young red wines to
enhance the quality of the wine, but should be applied with care in older red wines.
Future research into micro-oxygenation should focus on whether it can simulate an
oak barrel. More research into the effect of micro-oxygenation on the sensory profile
of the wine is needed.
As mentioned, the addition of O2 can lead to oxidative degradation of wine. The
brown colour in wine is often used as an indication of oxidation, but oxidative aromas
can be perceived before a drastic increase in the brown colour has been observed in
red wine.
The third part of this study was to assess the possible use of Fourier Transform
Infrared Spectroscopy (FTIR) to measure the progression of oxidation in Pinotage red
wines. Three wines were used in this study and clear separation between the control
and aerated wines was observed by using Principle Component Analysis (PCA).
Sensory analysis of these wines confirmed this observation, with a reduction
especially in berry fruit and coffee characters and an increase first in potato skin and
then acetaldehyde aroma characters as the oxidation progressed. PCA analysis also
revealed that in certain wines the visible spectrum of light did not indicate the
progression of oxidation as sensitively as with the use of FTIR. This also correlated
with the inability of the panel to observe a drastic colour change. FTIR should be
further investigated as a possible means of monitoring oxidation in wine and this
study should be expanded to wines made from other cultivars as well.
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Studies on the wastage of export grapes : with special reference to that caused by Botrytis cinerea, Pers.Du Plessis, S. J. January 1935 (has links)
Thesis (PhD(Agric)--Stellenbosch University, 1935. / No Abstract Available
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Morphological and anatomical responses to plant growth regulators of abscised shoot apices of grapevines (vitis) in in vitro culture and heat inactivation of grapevine fanleaf viruses in apicesGoussard, P. G. (Pieter Gabriel) 03 1900 (has links)
Thesis (PhD) -- Stellenbosch University, 1984. / No abstract available
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Grapevine (Vitis vinifera L., cv. Pinotage) responses to water deficit modulated by rootstocksSerra Stepke, Ignacio M. 12 1900 (has links)
Thesis (PhD(Agric))--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Water scarcity is a key limiting factor for viticulture in dry regions. Traditionally drought
sensitive varieties have the potential to grow in dry areas, however in most situations, through
the use of rootstocks. Drought-tolerant rootstocks are expected to improve grapevine response to
water deficit by improving the water uptake and transport and by reducing the water loss in
leaves by root-to-shoot signalling. The mechanisms of rootstocks’ tolerance to drought are not
yet fully understood. The main aim of this study was to improve the understanding of the
rootstock/scion-cultivar interaction in the regulation of grapevine water use and leaf stomatal
behaviour. Irrigated field vines without any water constraint were compared to rain-fed
grapevines subjected to moderate water constraint. To better manage vine water status, reduce
variability, and compare more rootstocks, greenhouse trials were also conducted where plants
were well watered or subjected to severe water constraints. Pinotage grapevines (Vitis vinifera
L.) grafted onto 110 Richter, 140 Ruggeri and 1103 Paulsen rootstocks were used for field
experiments whereas Pinotage grapevines grafted onto 99 Richter, 110 Richter, 140 Ruggeri,
1103 Paulsen and Ramsey were used for greenhouse experiments. Our study suggested the
influence of rootstocks on scion-cultivar water status and leaf stomatal size and density and gas
exchange of the scion, implying an influence on water uptake and transport and a tight regulation
of the stomatal conductance. Our data supported the hypothesis that the influence of rootstock in
response to drought seemed to be higher under increasing water deficit up to a point where the
plant water status is the main driver of the stomatal conductance and therefore photosynthesis
regulation, considering the plant water status thresholds. In addition, the results suggested that
stomatal development is affected by light, drought and possibly by rootstocks. Nevertheless, it is
still not clear how the rootstock affects stomatal development and the link with scion-cultivar
water use. It seems that the transpiration rate of leaves is more related to stomatal size than
density. Thus one possible mechanism of Pinotage leaf adaptation to water constraints was
structural during leaf growth, with a reduction in pore size to reduce plant water loss. The results
showed that the rootstock is regulating the cultivar's stomatal size (anatomical changes during
leaf growth) and functioning (stomatal regulation) through a complex signalling process. The
effect of light on stomatal development is interesting in the context of canopy microclimate and
canopy manipulation (choice of the vine architecture vs canopy size, in the context of climate
change versus the possible increase in drought and water scarcity). The use of rootstocks is a
long term investment which aims to provide resistance to soil pests and pathogens and to confer
to the scion-cultivar drought and salt tolerance. The use of drought tolerant rootstocks is actually one of the most relevant practical solutions in dry terroir – units and in situations where water
availability is limited. The understanding of the physiological and genetic mechanisms which
govern scion-cultivar drought tolerance/behaviour induced by rootstocks is critical in terms of
rootstocks choice in interaction with the scion-cultivar and is critical to assist breeding programs
to create/select drought tolerant rootstocks.
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The interference potential of nine selected South African spring wheat cultivars with selected weed speciesNambili, Julia Nghituvali 12 1900 (has links)
Thesis (MScAgric (Agronomy))--Stellenbosch University, 2008. / The development of herbicide resistance in weeds is one of the major factors hampering
profitable crop production worldwide. In South Africa resistance to herbicides in weeds is also
a big problem, in particular in the Winter Rainfall Region of the country. The lack of sufficient
different mode of action herbicide groups that can be rotated in these conditions necessitate the
implementation of integrated weed management programmes to curb the development and
spread of herbicide resistance. One of the alternative physical weed management strategies is
to maximize crop competition to the weed population. One aspect of such a strategy is to plant crop cultivars that have greater interference potential than others.
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'n Ondersoek na die ontstaan van onkruiddoderweerstand in Bromus diandrus RothFourie, Johan Hendrik Petrus 04 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Ripgut brome (Bromus diandrus Roth.) is a weed that causes great problems
in the most wheat and grain producing areas and also in livestock practices.
Until recently (1995) there were no registered chemicals for the management
of ripgut brome in wheat, in South Africa. After the registration of sulfosulfuron
and iodosulfuron + mesosulfuron for the management of ripgut brome in
wheat, these two herbicides were widely used and in the case of wheat
monocultures, it was used repeatedly. During the last few years, reports of
ripgut brome that were suspected to be resistant to these chemicals,
increased. With the development of herbicide resistance it is of great
importance to investigate methods to confirm resistance and also to control it.
The goal of this study was firstly, to confirm resistance in ripgut brome and
secondly to compare growth and development of resistant ripgut brome
popualtions to that of susceptible ripgut brome populations. The dormancy of
Bromus seed was also investigated as were effective methods to break seed
dormancy. Lastly, quicker methods to confirm resistance were investigated.
A short summary of the experiments follows.
In the first experiment the degree of resistance of three different ripgut brome
populations were determined, by using the pot spray method. One population
each of B. pectinatus and B. rigidus were also included in the study. The
seed of the Bromus populations were germinated after which it was planted in
plastic pots and were placed in the glasshouse until the three to four leaf
stage. Subsequently the plants were treated with the following four herbicides:
sulfosulfuron, iodosulfuron + mesosulfuron, imazamox and haloxyfop-R
methyl ester, at seven concentrations namely, the recommended dosage, one
quarter, one half, twice, four times and eight times the recommended dosage.
After six weeks the percentage survival and the dry mass of the plants were
determined. Results showed that the three ripgut brome populations had
different degrees of resistance to sulfosulfuron and iodosulfuron +
mesosulfuron, varying from no resistance to moderate resistance to strong
resistance. There was no resistance to imazamox and haloxyfop-R methyl ester. The B. rigidus population exhibited strong resistance or tolerance
(natural resistance) to the two sulfonylureum herbicides.
In the second experiment the seed of the same Bromus populations were
germinated and planted in plastic pots that were filled with three litres of river
sand to determine the growth, development and seed production of the plants.
The number of leaves for each plant as well as the plant height were
measured weekly, until the plants became reproductive. The two resistant
populations grew much faster than the susceptible population and they also
produced taller plants. The susceptible population produced more leaves, but
seed production was delayed considerably. This probably relates more to the
plant’s adaptation to their enviroment, than to adaptation due to resistance.
The susceptible population was collected from a natural environment, while
the others were collected from wheat fields.
In the third experiment the seed dormancy of the Bromus populations was
investigated. The effect of different treatments on the dormancy of the seed
was also investigated. The treatments that were applied were gibberrellic
acid, fumigation with ammonia gas and an ammonia treatment combined with
a cold treatment. Seed dormancy in all populations was short-lived and the
cold treatment was an effective way of stimulating fresh seed to germinate.
The last experiment was performed to develop a quicker method for the
evaluation of resistance in Bromus spp. In this experiment the petridish
method was investigated. Only sulfosulfuron and iodosulfuron + mesosulfuron
were used, because resistance to them was proven earlier. Different
concentrations of the herbicides were applied to the dishes with the seed and
were exposed to a cold treatment before being placed in a germination
chamber. The seed in al the treatments germinated and it was decided to let
the seed grow for two weeks in the petri dishes to observe whether the
herbicides may have a detrimental effect on the growth of the small seedlings.
After two weeks there were no differences between treatments and the
experiment was terminated. The study showed that resistance is present in some of the Bromus
populations and that there are biological differences between populations with
different degrees of resistance. However, the fact that the susceptible
population comes from a completely different environment than the other
populations, complicate matters and further studies are required to obtain a
clearer picture. / AFRIKAANSE OPSOMMING: Predikantsluis (Bromus diandrus Roth.) is ‘n onkruid wat in die meeste koringen
garsproduserende gebiede, asook in sommige vee praktyke, probleme
veroorsaak. Tot redelik onlangs (ongeveer 1995) was daar in Suid-Afrika
geen middels geregistreer wat predikantsluis in koring kon beheer nie. Nadat
sulfosulfuron en iodosulfuron + mesosulfuron vir predikantsluisbeheer in
koring geregistreer is, is die twee middels op groot skaal, en in die geval van
koring monokultuurstelsels, aanhoudend toegedien. Gedurende die afgelope
paar jaar is berigte ontvang dat beheer van predikantsluis met die middels nie
meer so doeltreffend is nie, moontlik as gevolg van onkruiddoderweerstand
wat ontwikkel het. Met die ontstaan van onkruiddoderweerstand is dit
belangrik om praktyke en maniere te vind om weerstand vinniger te bevestig
en doeltreffend te bestuur. Die doel van hierdie studie was eerstens om
weerstand in predikantsluis te bevestig en tweedens om die groei en
ontwikkeling van plante afkomstig van vermoedelike weerstandbiedende
predikantsluis populasies te vergelyk met plante uit ‘n vatbare populasie. Die
saadproduksie en dormansie van die saad is ook ondersoek asook effektiewe
metodes om dormansie te breek. Laastens is ondersoek ingestel na ‘n
vinniger manier (petribakkie metode) om weerstand te bevestig. Hieronder
volg ‘n oorsig oor die vier eksperimente wat uitgevoer is.
In die eerste proef is die mate van weerstand van drie verskillende
predikantsluis populasies bepaal, deur van die gewone potspuit metode
gebruik te maak. Daar is ook een populasie elk van Bromus pectinatus en
vermoedelik Bromus rigidus ingesluit in die studie. Die sade van die
verskillende populasies is toegelaat om te ontkiem en daarna is dit in
plastiese potjies geplant en in ‘n glashuis geplaas totdat die drie tot vier
blaarstadium bereik is. Die plante is daarna gespuit met die volgende vier
middels: haloksifop-R-metielester (Gallant Super), imasamoks (Cysure),
iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor), teen sewe
konsentrasies elk, nl. teen die aanbevole dosis, asook teen een kwart van,
een helfte van, twee keer, vier keer en agt keer die aanbevole dosis. Na ses
weke is die persentasie oorlewendes en die droëmassa van die plante bepaal. Resultate het getoon dat die drie predikantsluis populasies
verskillende grade van weerstand teen die twee sulfonielureums
(sulfosulfuron en iodosulfuron + mesosulfuron) toon, dit wil sê van geen tot
matig tot sterk weerstandbiedend. Daar is egter geen weerstand teen
haloksifop-R-metielester (Gallant Super) en imasamoks (Cysure)
waargeneem nie. Die B. rigidus populasie het sterk weerstand of toleransie
(natuurlike weerstand) teen die sulfonielureum middels getoon.
In die tweede proef is saad van dieselfde Bromus populasies ontkiem en
oorgeplant in plastiese potte gevul met 3 liter riviersand om die groei en
ontwikkeling en saadproduksie van die plante te evalueer. Die aantal blare
per plant en hoogte van die plante is weekliks bepaal totdat die plante
reproduktief geraak het. Hierna is die metings gestaak om te voorkom dat die
saadproduksie van die plante benadeel word. Die resultate het getoon dat die
twee weerstandbiedende predikantsluis populasies vinniger groei as die
vatbare populasie en ook langer plante vorm, terwyl die vatbare populasie
vinniger en meer blare vorm, maar langer neem om saad te vorm. Hierdie
waarnemings hou egter waarskynlik meer verband met die oorsprong van die
populasies as met die graad van weerstandbiedendheid. Die vatbare
populasie is versamel in natuurlike veld vêr van enige landerye terwyl die
ander populasies almal uit graanlande afkomstig is.
In die derde proef is saaddormansie van die Bromus populasies ondersoek.
Daar is ook ondersoek ingestel na verskillende behandelings om dormansie
te breek. Die behandelings wat toegepas is, is ‘n gibberelienesuur
behandeling teen verskillende konsentrasies, beroking met ammoniak vir
verskillende tye en ‘n ammoniak behandeling tesame met ‘n koue
behandeling. Die resultate het getoon dat saaddormansie van die Bromus
populasies van korte duur is, maar dat kouebehandeling effektief is om
ontkieming van vars saad te stimuleer.
Die vierde proef is uitgevoer om vas te stel of daar vinniger evaluasiemetodes
is vir die evaluasie van weerstand in Bromus spp., deur van die petribakkie
metode gebruik te maak. In hierdie proef is slegs die middels iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor) gebruik, omdat daar ‘n
mate van weerstand teen hulle waargeneem is in die eerste proef. Die
middels is teen verskillende konsentrasies in petribakkies gevoeg, tesame
met die sade en toe blootgestel aan ‘n kouebehandeling voordat dit in ‘n
ontkiemingskabinet geplaas is vir ontkieming. Die sade in al die behandelings
het ontkiem en daar is besluit om die saailinge uit die ontkiemingskabinet te
haal en vir twee weke te laat groei sodat daar bepaal kon word of die middels
‘n effek op die groei van die plantjies het. Na twee weke kon geen verskil in
die groei van die plantjies waargeneem word nie en die proef is beëindig.
Die studie het getoon dat daar wel weerstand in sommige van die Bromus
populasies voorkom, en dat biologiese verskille voorkom tussen
predikantsluis populasies met verskillende grade van weerstand. Die feit dat
die vatbare populasie uit ‘n heeltemaal verskillende omgewing kom as die
ander populasies, maak definitiewe afleidings moeilik. Daar sal opvolgstudies
uitgevoer moet word om van die onduidelikhede op te klaar.
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Invloed van bemesting op die opbrengs en kwaliteit van uie (Allium cepa L.)Langenhoven, Petrus 03 1900 (has links)
Thesis (MScAgric (Agronomy)--University of Stellenbosch, 1999. / The Western Cape is one of the most important onion producing regions in South
Africa. It is well suited for the production of intermediate daylength onion cultivars.
Annually about 2500 ha are planted with a yield of about 120 000 tons. Only 9 000 tons
was exported in 1998 and of these 9 000 tons 4.9% was rejected due to poor quality. In
South Africa there are no guidelines for the production of intermediate daylength onions.
It is very important to have fertiliser guidelines, because optimal yields of good quality
can be achieved with a good fertiliser program. Produce with exceptional quality can
boost exports and at the same time stabilize local markets. However fertilisers are very
expensive and could be damaging to the environment ifused incorrectly.
To produce fertiliser guidelines N, P and K field trials were planted at three
differen~ localities (Koue Bokkeveld, Stellenbosch and Caledon). The localities were
chosen according to the difference in climate and soil texture, and these are important
onion growing areas. The minimum and maximum temperature for the Koue Bokkeveld,
Stellenbosch and Caledon was 11123, 12/25 and 13/27 °C respectively. At all the
localities 3 nitrogen-, 4 phosphorus- and 4 potassium levels were used. Treatments were
factorially arranged in a randomised block design, with two replicates. At Stellenbosch a
N fertiliser trial was planted with four N levels and four N application methods. The
treatments were factorially arranged in a completely randomised block design, with three
replicates. N, P and K was applied as limestone ammonium nitrate, single superphosphate
and potassium sulphate. Marketable and unmarketable bulbs were quantified at harvest.
Weight loss during storage was determined over a six month period and storage disorders
were evaluated.
It was clear that high N levels, especially on soil with a high potential for
releasing N, had a negative effect on yield and keeping quality. At Caledon a significant
reduction in yield took place with the highest N level. High N levels also had a
significant effect on weight loss at Stellenbosch and Caledon. The same trend with high
N levels occurred in the N fertiliser trial. Weight loss was increased with the late
application ofN in the growing season. In spite of the fact that the P levels were high (58
- 66 mg.kg-I) in the different soils, the onions reacted very well to phosphorus fertiliser.
As a result of the higher P levels there was more foliage in the leaf canopy and the bulbs
were larger. This P reaction only occurred in the Koue Bokkeveld and at Caledon. At
Stellenbosch yield was not improved with P fertilisation and bulbs were of poor quality.
The highest P level resulted in the greatest weight loss in storage. K had an effect where
the K status and clay content of the soil was low. High potassium levels improved yield
and keeping quality remarkably in the Koue Bokkeveld. Some interactions also occurred.
The percentage unmarketable bulbs were influenced by a P and K interaction. An
increase in double bulbs was responsible for the increase in the percentage unmarketable
bulbs. At the lowest P level, higher K levels decreased the percentage unmarketable
bulbs. Alarming proportions were reached when high K levels were combined with the
highest P level. The P and K interaction also had an effect on the percentage sprouting. K
did not have any effect' on sprouting at low P levels. A combination of the highest P level
and the lowest K level produced the highest percentage sprouting. The interaction
between N and P, like the P and K interaction had an effect on the percentage sprouting.
The highest N level in combination with the highest P level increased the percentage
sprouting significantly.
The N, P and K field trials showed that the optimum N level is less than 130 kg
N.ha-l on a soil with 16 % clay. On a sandy soil it can be as high as 160 kg N.ha•l The
optimum P level varied from 30 to 130 kg P.ha-l Where a poor P reaction was observed
the Ca and S status in the soil was low. It is possible that the drastic P reaction with
superphosphate (10.5 % P, 20.3 % Ca, 12.1 % S) in the Koue Bokkeveld can be a result
of the application of Ca and S. On the shale soil at Caledon, with a K status of 288
mg.kg-\ the optimum K level is less than 75 kg K.ha-l On the sandy soil of the Koue
Bokkeveld, with a K status of 43 mg.kg•l
, the optimum K level was 200 kg K.ha•l
. The N
fertilisation trial was done on a soil with an optimum N level of 115 kg N.ha-l (10 %
clay). It was demonstrated that the standard N application method (40 % N with planting
and the rest divided in three equal applications of 20 % N on 2, 4 and 7 weeks after
planting) is still an acceptable practice.
Follow-up trials are being done to determine the exact optimum level of
fertilisation.
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The effect of Phosphorus on the growth, plant mineral content and essential oil composition of Buchu (Agathosma betulina)De Villiers, Chris Johan 12 1900 (has links)
Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2007. / An increase in the demand of buchu (Agathosma betulina) oil has lead to an increase in the commercial cultivation of buchu in fields and also in hydroponic systems. A nutrient solution for hydroponically grown buchu is still required to ensure optimal growth and yield. ASNAPP (Agribusiness in Sustainable Natural African Plant Products) South Africa has done some trials to achieve optimal EC and pH in the nutrient solution. Phosphate concentrations in the nutrient solution might play a significant role due to reports by a variety of researchers on the sensitivity of Protea plants to phosphate. Buchu and Proteas are both part of the Fynbos biome and are found in regions with similar soil (sandy soils with a low pH and mineral contents) and climatic conditions.
Two separate experiments were conducted to determine the effect of increasing phosphate concentrations (ranging from 0.00 to 1.40 me L-1) in the nutrient solution on buchu growth. The first experiment was done in a plastic covered structure with a pad and fan and the objective of this trial was to determine the effect of increasing phosphate concentrations in the nutrient solution on the general growth, biomass production, oil composition, mortality rate and chemical composition of the buchu plants. The second experiment was done in a glasshouse with mechanical temperature control and the aim of this trial was to determine the response of buchu to increasing concentrations of P at two different root temperatures. A chemical analysis of the plants was done and the general growth, yield and root mass were recorded to determine the response of buchu plants to the phosphate and temperature treatments.
In the greenhouse experiment an optimum growth and yield response of buchu plants was found at a phosphate concentration of 0.7 me L-1 in the nutrient solution. Phosphate concentrations lower or higher than 0.7 me L-1 lead to a decrease in growth and yield. An increase in the phosphate concentration in the nutrient solution lead to a general increase in N, P, K, Ca, Mg and B content in the buchu plants and a decrease in Fe content. The mortality rate of the buchu plants increased with an increase in the phosphate concentration from 0.0 to 1.4 me L-1 in the nutrient solution. The phosphate concentration in the nutrient solution only made a significant difference on one major component of the buchu oil which was Ψ-Diosphenol, but no general trend with Ψ-Diosphenol content and P concentration could be found and the significant difference in Ψ-Diosphenol observed in this trial may only have been due to genetic variation between the plants.
The effect of the different root temperatures in the glasshouse experiment was very clear. The buchu plants grown at the high root temperature (20°C) produced a higher yield and better overall growth than the plants grown at lower (10°C) temperatures. The buchu plants grown at 20°C had a significantly higher N, K, Na and B content than plants grown at 10°C. Buchu plants grown at 10°C showed no significant response in terms of growth and yield to the phosphate concentration in the nutrient solution, but plants grown at 20°C exhibited growth and yield peaks at phosphate concentrations of 0.35 and 1.4 me L-1. The peak observed in the plants growth at high phosphate concentrations is unexplainable and can possibly be ascribed to the limitation of the plants per experimental unit and/or amount of replications. The increase in P concentration in the nutrient solution caused a general increase in N, P and K content in the buchu plants. A significant interaction between the phosphate concentration and root temperature was observed for the P, Mn en Zn contents of the plants which meant that the buchu plants respond differently towards phosphate concentrations at different root temperatures.
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The influence of different production systems, planting densities and levels of shading on the yield, quality and growth potential of ‘Chandler’ strawberry plants (Fragaria ananassa) grown in coirDe Villiers, Johannes Jacobus 12 1900 (has links)
Thesis (MScAgric (Agronomy))--Stellenbosch University, 2008. / The use of hydroponic strawberry production systems is increasing worldwide.
Although higher planting densities are possible in vertical production systems, these
higher planting densities may have a negative effect on individual plant yield and fruit
quality due to lower light levels when compared to conventional (horizontal)
production systems. Optimum planting densities will for this reason be affected by
light intensities inside the greenhouse and configuration of the vertical production
systems.
Two experiments were conducted in a plastic cladded greenhouse, fitted with a wetwall
and fan cooling system, at the Department of Agronomy, University of
Stellenbosch, South Africa during the period of April 2007 to November 2007 (late
autumn to early summer). Mean daily maximum temperatures exceeded 26 oC during
most of the 14 week harvest period (22 August to 30 November 2007), while
photosynthetic active radiation (PAR), measured at 12h00 on cloudless days, inside
the greenhouse increased from about 200 μMol m-2 s-1 to about 460 μMol m-2 s-1
during this period. The first experiment compared the effect of two vertical production
systems (vertical system and ‘A-shape’ system), subjected to different planting
density (16.7, 23.3 and 33.3 plants m-2) and shading (0%, 20%, 50%) treatments, as
measured on selected yield, quality and growth factors. The second experiment
studied the effect of different planting density (3.3, 5.6 and 10 plants m-2) and shading
(0%, 20%, 50%) treatments on the same yield, quality and growth factors in a
conventional production system. A comparison with regard to these factors was also
made between the highest planting densities of the conventional-, vertical- and
‘A-shape’ system.
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The influence of different calcium levels, irrigation methods and storage temperatures on the yield, quality and growth potential of G0 mini-tubersDe Villiers, Andre Jaco 12 1900 (has links)
University of Stellenbosch. Faculty of Agrisciences. Dept. of Agronomy. / Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2007. / Calcium (Ca) is an important plant nutrient with many functions, such as strengthening of cell walls and maintaining membrane stability and cell integrity. A greenhouse experiment was conducted using an aeroponic production system, to evaluate the influence of different Ca: K & Mg ratios (consisting of a control [100% Ca], and three treatments in which the Ca levels were changed to 33%, 66% and 133% of the control, while the K and Mg levels were adjusted to compensate for the change in Ca) and two different irrigation methods (irrigation on roots only, and irrigation on roots and stolons) on tuber yield and mineral concentration. The treatment that received the highest Ca: K & Mg ratio had significantly more larger tubers than the lowest Ca treatment, although there was no significant difference in total tuber number between treatments. The high Ca treatment also had a significantly higher Ca concentration in the skin than the low Ca treatment. The site of irrigation did not have a significant effect on the total tuber number per plant, or on the Ca content of the tubers that were produced.
The tubers produced in the first experiment were divided into two weight classes, and stored at three different temperatures. The percentage weight loss during storage was determined by weighing the tubers before, and again after storage. The firmness of the tubers was also measured after storage. Tubers were then stored in a dark room at room temperature to allow sprouts to develop. The sprouts of each tuber were counted and weighed. Weight loss was the lowest for tubers stored at 3oC. Firmness of the tubers increased as the Ca: K & Mg ratio of the nutrient solution used during production was increased. Number of sprouts was the highest for tubers stored at 6oC. Sprout number was also significantly higher for the larger tubers compared to the smaller ones. Total sprout weight was the highest for the tubers stored at 6oC, and was also the highest for the larger tubers.
After sprouts started to develop, the tubers were planted again in the greenhouse, in sawdust and irrigated with a complete Steiner nutrient solution at 1.5 mS cm-1. After these plants were harvested, the leaf area and dry weight of the leaves were determined. The first generation tubers were counted and weighed. The only factor that had a significant influence on the growth of the plants, was the size of the seed tubers that were used. The larger seed tubers produced plants that had significantly higher leaf areas, dry weight of leaves, as well as higher yields than that of the plants produced from the smaller seed tubers.
From the results of this study, it can be concluded that Ca has a definite positive effect on the quality of seed potatoes as well as the size of the tubers that are produced. This study also supported that seed tubers should be stored at low temperatures, around 3oC, to maintain the highest quality, while larger tubers proved to out-yield smaller ones.
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