Thesis (doctoral)--Swedish University of Agricultural Sciences, 2001. / Includes bibliographical references.

Thesis (Ph.D.)--Murdoch University, 2008. / Thesis submitted to the Faculty of Sustainability, Environmental and Life Sciences. Includes bibliographical references (leaves 118-134)

The effects of controlled environment strategies on the yield and quality of cherry tomato fruit production were studied between April, 2003 and September, 2004 at The University of Arizona Campus Agriculture Center; Tucson, AZ. Two cultivars of cherry tomato (Lycopersicon esculentum Mill. var. cerasiforme) planted at 2.2 plants m-2 were grown hydroponically in coconut coir and drip fertigated with a low EC (2.4 dS m-1), high EC (4.5 dS m-1), mid day relief of high EC (2.4 dS m-1 or 4.5 dS m-1 over a 24 h period) or night time super high EC treatment (12 dS m-1). From April to October, 2003, the effects of mid day relief of high EC on cherry tomato fruit yield and quality were determined. From February through September, 2004 the effects of super high EC treatment, horizontal air flow (HAF) fan operation and/or delayed fertigation on cherry tomato fruit cracking were studied.

The following body of research provides a detailed overview of the interactive effects of biocontrol agents and environmental factors and how these influence both the host plant and pathogen populations within hydroponic systems. Pythium and other zoosporic fungi are pathogens well suited to the aquatic environment of hydroponics. Motile zoospores facilitate rapid dispersal through fertigation water, resulting in Pythium becoming a yield reducing factor in most hydroponic systems and on most crops. With increasing trends away from pesticide use, biocontrol is becoming an ever more popular option. Unfortunately, much of our knowledge of biocontrol agents and their formulation can not be directly transferred to the widely differing environments of hydroponic systems. Paulitz (1997) was of the opinion that if biocontrol was to be successful anywhere, it would be in hydroponics. This is primarily due to the increased ability, in hydroponics, to control the growing environment and to differentiate between the requirements of the pathogen versus those of the host plant and biocontrol agent. Key environmental factors were identified as soil moisture, root zone temperature, form of nitrogen and pH. A review of the literature collated background information on the effects of biocontrol agents and environmental manipulation on plant growth and disease severity in hydroponic systems. A commercial formulation of Trichoderma (Eco-T(R1)) was used as the biocontrol agent in all trials. Dose responses in Pythium control and plant growth stimulation in lettuce were first determined using a horizontal trough system (closed system). In such systems optimum application rates were found to be lower than in field application (1.25x10[to the power of 5] spores/ml). This is probably because Trichoderma conidia are not lost from the system, but re-circulate until being transported into the root zone of a host plant. No significant growth stimulation was observed, although at high doses (5x10[to the power of 5] and 2.5x10[to the power of 5] spores/ml) a significant reduction in yield was recorded. Possible reasons for this growth inhibition are suggested and a new theory is proposed and investigated later in the thesis. In an open system of cucumber production (drip irrigated bag culture) no statistically significant results were initially obtained, however, general trends still showed the occurrence of positive biocontrol activity. The initial lack of significant results was mostly due to a poor knowledge of the horticulture of the crop and a lack of understanding of the epidemiology behind Trichoderma biocontrol activity. These pitfalls are highlighted and, in a repeat trial, were overcome. As a result it could be concluded that application rates in such systems are similar to those used in field applications. Management of soil moisture within artificial growing media can aid in the control of Pythium induced reductions in yield. A vertical hydroponic system was used to determine the interactive effects of soil moisture and Trichoderma. This system was used because it allowed for separate irrigation regimes at all 36 stations, controlled by a programmable logic controller (PLC). With lettuce plants receiving optimum irrigation levels, no significant reduction in yield was observed when inoculated with Pythium. However, after Pythium inoculation, stresses related to over- or under-watering caused significant yield losses. In both cases, Trichoderma overcame these negative effects and achieved significant levels of disease control, especially under higher soil moisture levels. Growth stimulation responses were also seen to increase with increasing soil moisture. Similar results were obtained from strawberry trials. These results show that Pythium control is best achieved through the integration of Trichoderma at optimum soil moisture. However, where soil moisture is above or below optimum, Trichoderma serves to minimize the negative effects of Pythium, providing a buffering capacity against the effects of poor soil moisture management. Pythium, root zone temperature and form of nitrogen interact significantly. In greenhouse trials using horizontal mini troughs with facilities for heating or cooling recirculating water, nitrate fertilizer treatments resulted in statistically significant results. Lettuce growth was highest at 12°C, although no significant differences in yield were observed between 12-24°C. Pythium was effective in causing disease over the same temperature range. Pythium inoculation did not result in yield reduction at 6 and 30°C. Trichoderma showed a slight competitive advantage under cooler temperatures (i.e., 12 degrees C), although significant biocontrol occurred over the 12-24 degrees C range. Ammonium fertilizer trials did not generate statistically significant data. This is possibly due to complex interactions between root temperature, ammonium uptake, and competitive exclusion of nitrification bacteria by Trichoderma. These interactions are difficult to replicate over time and are probably influenced by air temperature and available light which are difficult to keep constant over time in the system used. However, the data did lead to the first clues regarding the effects of Trichoderma on nitrogen cycling as plants grown with a high level of ammonium at high temperatures were seen to suffer more from ammonium toxicity when high levels of Trichoderma were added. In further trials, conducted in the recirculating horizontal mini trough system, it was determined that Trichoderma applications resulted in an increase in the percentage ammonium nitrogen in both the re-circulating solution and the growing medium. This was a dose-related response, with the percentage ammonium nitrogen increasing with increasing levels of Trichoderma application. At the same time an increase in ammonium in the root tissue was observed, corresponding with a decrease in leaf nitrate levels and an increase in levels of Cu, Na, Fe and P in leaf tissue. In independent pot trials, populations of nitrifying bacteria in the rhizosphere were also seen to decrease with increasing Trichoderma application rates. This led to the conclusion that the increase in ammonium concentration was as a result of decreased nitrification activity due to the competitive exclusion of nitrifying bacteria by Trichoderma. The possibility that Trichoderma functions as a mycorrhizal fungus and so increases the availability of ammonium for plant uptake is not discarded and it is thought that both mechanisms probably contribute. Water pH provides the most powerful tool for enhancing biocontrol of Pythium by Trichoderma. Trichoderma shows a preference for more acidic pHs while Pythium prefers pHs between 6.0 and 7.0. In vitro tests showed that Trichoderma achieved greater control of Pythium at pH 5.0, while achieving no control at pH 8.0. In greenhouse trials with the recirculating horizontal mini trough system, yield losses resulting from Pythium inoculation were greatest at pH 6.0 and 7.0, with no significant reduction in yield at pH 4.0. Biocontrol activity showed an inverse response with greatest biocontrol at pH 5.0. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2003.

In South Africa, clonal forestry of Eucalyptus and its hybrids has been implemented to increase the productivity on existing forestry lands and marginal sites and to facilitate the production of desired fibre types for timber processing operations. The cold-tolerant Eucalyptus grandis x E. nitens hybrids have produced consistently high yields, and are propagated clonally with limited success via a macro-cutting system currently in use for other hybrid species. The heart of vegetative propagation operations is the clonal hedge and its management, and nutrition in particular, is an important element of any vegetative propagation programme. However, achieving and sustaining an optimum nutritional balance in macrohedges is difficult in practice and, in order to accurately predetermine the optimum plant nutrition required all year round and to ensure optimal levels of rooting, a more controllable nutrient environment is essential. Hydroponics may facilitate this control of nutrition. At the same time it may be possible to manipulate the system to determine accurately what levels of each nutrient may contribute to the highest rooting and more importantly allow forest nursery managers to maintain those levels in a practical manner. The main aims of the present work were to obtain and compare cuttings and rooting yields from hydro-ramets in different hydroponic substrates and systems and to investigate the possible roles of essential nutrients on those parameters. Modified Nutrient Film Technique (NFT), ebb-and-flow and aeroponic tables were used in this study. The former consisted of eight individual gutters, allowing for eight different substrates to be tested simultaneously. One gutter was set up as an unmodified NFT table and the other seven gutters had gravel, Leca, peat, perlite, perlite: vermiculite mix, Rockwool® and sand as substrates; all were supplied with the same nutrient solution. Three commercial clones were used throughout these trials: GN107, GN156 and NHOO. Rooting results and data from plant elemental analyses indicated that certain elements (Ca, Cu, Zn, Mn and B) appeared to play a more important role in rooting than others (N, P, K, Mg, Na and Fe). It was also found that when comparing the hydroponic systems, the substrate and / or method of irrigation affected the availability and uptake of different nutrients, which in turn affected the rooting of coppice collected from those ramets. The rooting performance of coppice from the eight different substrates tested in the NFT system was compared. Within each of the four harvests undertaken, both clone and substrate had a significant effect on the rooting performance. However, when the four harvests were compared, only harvest number/time had a significant effect on the rooting performance of the cuttings derived from the hydro-hedges . For both the ebb-and-flow and aeroponics systems (where there was no substrate), only the clone had a significant effect on the rooting performance. In addition to this, the plants from the ebb-and-flow system produced the highest number of cuttings to be placed overall (7.9 cuttings per mother plant per harvest) while those from the gravel substrate had the highest rooting percentage overall (26.9 %). When combining these two factors into a success rate, the perlite substrate rated highest (1.7 rooted cuttings per mother plant per harvest). From a cost efficiency perspective, perlite was the most cost effective substrate, as it required the least initial capital outlay to produce one million rooted clones per year from a hydroponics system (R6 533 655). The plants in the perlite substrate also produced the highest number (6 700) of rooted cuttings per year from 1 000 mother plants with a low cost per plant (R2.33 per rooted plant). / Thesis (M.Sc.)-University of KwaZulu- Natal, Durban, 2004.

Wissenschaftler sind weltweit bereits seit geraumer Zeit darum bemüht, Lösungen für die praktikable Umsetzung einer urbanen Produktion frischer Gemüse zu erarbeiten. Die hydroponischer Anbauverfahren haben ein überdurchschnittlich hohes Potential, wenn es um die Einsparung von Produktionsmitteln geht. So können im Pflanzenbau gegenüber dem Freilandanbau bis zu 90 Prozent des eingesetzten Wassers durch geschlossene Kreisläufe eingespart werden. Diese Kreisläufe vermeiden zudem den Eintrag von Düngemittel in die Umwelt. Der geschützte Anbau in Hochhäusern sorgt für ein optimales Pflanzenwachstum ohne ungünstige Witterungseinflüsse. So ist nicht nur eine sichere marktnahe Produktion gewährleistet, es kann auch das ganze Jahr hindurch produziert werden. Transporte von Produkten aus weit entfernten Gegenden anderer Länder können somit vermieden werden. Hinzu kommt die Flächenersparnis und die damit hohe Flächenproduktivität führen. Dennoch zeigen erste Umsetzungsversuche auf, dass es noch einen hohen Grad an Forschungs- und Entwicklungsarbeit bedarf bis eine profitable Lösung für den Markt bereit steht. Insbesondere der hohe technische Aufwand und Energiebedarf erster Testanlagen sind hier als besondere Herausforderung anzusehen. In dem umfassend angelegten Forschungs- und Entwicklungsvorhaben mit dem Namen BrickBorn Farming – Nahrungsmittelproduktion in Gebäuden städtischer Gebiete sollen verschiedenste Aspekte weiterentwickelt und miteinander verknüpft werden.

Zinc is a metal involved in structure of many enzymes, in the growth and differentiation of plants. Wheat is one of the most consumed cereals. Some wheat cultivars can&amp / #8217 / t deal with zinc deficiency and this situation not only reduces grain yield but also weakens the resistance of cereals to diseases and impairs the nutritional quality of the grain. Some wheat cultivars are not affected by zinc deficiency. In this study, &amp / #8216 / differential display&amp / #8217 / , used for determination differentially expressed genes between two samples, was performed. The most zinc efficient bread wheat cultivar Kira&ccedil / -66 was grown in hydroponics medium and samples were taken at different time periods. RNA isolations were done and differential display technique was performed. After examining the results, differentially expressed bands were selected and sequenced. DNA sequence analysis were done in available databases which showed that three of the bands were fragments of putative zinc transporters. In this study we have found threee putative gene fragments using differential display technique on zinc efficient plants grown under differeing zinc concentrations. These fragments showed homology with zinc transporter, ABC transporter and ADH (Alcohol Dehydrogenase). It is known that all of these three genes are involved in zinc efficiency mechanism. Further studies will be conducted on these gene fragments.

Licentiatavhandling (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2006. / Härtill 2 uppsatser.

Molecularly imprinted polymers (MIPs) are biomimetic sensing elements that combine the accuracy and highly specific binding affinity of a biosensor, with the robustness and reusability associated with artificial electrochemical sensors. This thesis investigates the application of a MIP sensor to address the challenge of phosphate detection in precision agriculture. Traditional chemical sensing approaches using portable electrochemical sensors display a significant cross-interference between inorganic phosphate and other nutrient ions. This is due to the low position of phosphate in the Hofmeister Selectivity Series for anions, its high electronegativity and its pH dependent structure, resulting in a molecule that is very difficult to detect. To address this challenge, a sensor was created by spin coating a phosphate selective MIP onto a substrate containing a series of electrodes. These electrode devices allowed for electrical measurements to be taken using an inductance, capacitance and resistance (LCR) testing station, and to observe the change in the materials dielectric constant as the binding sites become occupied by the target analyte. The devices underwent several design reiterations to produce an optimised setup consisting of 100 interdigitated chrome electrodes with a width of 1 μm and a separation distance of 1 μm on a quartz substrate. The final electrode design was used to carry out a nutrient cross-interference study across several polymer permutations. The purpose of this was to develop an optimised MIP formulation for binding specifically to inorganic phosphate ions. From this study, an optimal phosphate selective MIP was identified, based upon a binding site constructed from methacrylic acid around a diphenyl phosphate template molecule. During capacitance measurements, this MIP formulation demonstrated a clear preferential response to phosphate (1610 pF) over the average capacitance results observed following exposure to the competing nitrate (1286 pF) and sulphate (1212 pF) nutrients tested in the cross-interference study.

Agricultural practices face a difficult dilemma of producing enough food for a growing population and evolving to greatly diminish its large impact on the environment. Soilless cultures such as hydroponics has been put forth as an alternative solution due to the possibility of larger yields and, in some departments, less impact on the environment. This study sought to investigate if there are any statistically proven differences in biomass gain for Ocimum basilicum when growing hydroponically or in course sand with full nutrient treatment, as well as growing with a calcium deficiency. Key findings show that full nutrient treatment gathered few to none differences, whilst calcium scarcity resulted in greater biomass and greater leaf biomass when planted in sand, whilst the water culture displayed less chlorophyll degradation. Due to challenges in methodology the study would benefit from being undertaken again with greater scientific precision, but variants can also be explored such as different growing mediums and nutrient scarcities. Soil-based growing is considerably more forgiving to mistakes and errors rather than soilless cultures, and so, for the positive qualities of hydroponics (space efficiency, no runoff, more effective use of resources, no pesticides/herbicides, less transport, etc.) to be effectual, knowledge, experience and further investigation is required.