Flow injection analysis offers distinct advantages in reproducibility, flexibility, sample throughput and cost performance. Since it was introduced in 1975, there are more than 10 000 publications to date. The present study focuses on the development of process analysers for the determination of nitrogen compounds (namely, nitrate, nitrite and protein), nickel, and phosphate in various combination in samples originating from various fields, such as foodstuffs, water, and fertilisers. Nitrite is potentially unstable; it decomposes with time under acidic medium with an increase in decomposition rate as the concentration of acid increases. Raman spectroscopy was employed as a means of determining the rate of decomposition of nitrite in solutions at various pH values. A simple method for the determination of nitrite in foodstuffs by flow injection analysis (FIA) is described. The foodstuffs containing nitrite are digested in a microwave oven and then treated with 1 moℓ/Q NH4CI solution at pH 9. The simultaneous determination of nitrate and nitrite in foodstuffs and water was also studied. Cadmium (coarse powder) was used to reduce nitrate to nitrite. The effect of pH, length of reductor column, and various types of cadmium reductor on the yield of nitrite are investigated. The flow injection method was developed for the spectrophotometric determination of nickel in cured meat. Dimethylglyoxime (DMG) in acetate buffer at pH 6.4 nickel forms a red complex which is measured at 475 nm. The effects of chemical and physical parameters in flow injection analysis were studied. A new bienzymatic amperometric sensor is proposed for the assay of proteins in milk. The sensor is based on two enzymes, namely, carboxypeptidases A and L-amino acid oxidase. The use of flow injection analysis and Raman spectroscopy for the determination of phosphate in foodstuffs and fertilisers, is also compared in this study. / Thesis (PhD (Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

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No description available.

Striga, a genus of obligate parasitic weeds in the family Orobanchaceae, has been identified as the most important biological factor limiting agricultural productivity in sub-Saharan Africa. Germination of Striga seeds is triggered by strigolactone root exudates from host plants. Strigolactones also induce hyphal branching in arbuscular mycorrhizal (AM) fungi, which are important for plant uptake of phosphorus in low phosphorus soils. Mechanisms of Striga resistance based on reduced strigolactone production may also convey resistance to AM fungi which would require higher inputs of phosphorus fertilizer to attain optimal crop growth. There is evidence for genetic differences in mycorrhizal responsiveness in other grain crops; therefore it is beneficial for breeders to be aware of these differences when developing Striga-resistant sorghum cultivars. This research aims to determine phosphorus and mycorrhizal responsiveness of sorghum genotypes important for or developed by breeders working on Striga resistance. Phosphorus response curves were determined for twelve sorghum genotypes using pasteurized low phosphorus soil amended to achieve four different phosphorus levels. Simple linear regression was performed on root and shoot dry weight data. Results indicate variability in phosphorus responsiveness within Striga resistant and susceptible genotypes. Seven of these genotypes were selected for continued research, which analyzed responsiveness to phosphorous and differences in mycorrhizal responsiveness in relation to reported mechanisms of Striga resistance. Treatments included three levels of phosphorus amendments and the addition of Funneliformis mosseae inoculum. All genotypes were strongly responsive to P amendment when grown without AM fungi and showed a decrease in responsiveness to P when inoculated with F. mosseae. Trends for all genotypes indicate a greater uptake of P, Zn, and Mg by mycorrhizal plants as compared to nonmycorrhizal plants. All seven genotypes were responsive to mycorrhizae, with a significant increase in biomass for all genotypes, especially at the lowest phosphorus level. The responsiveness to the mycorrhizal fungus does not appear to be directly related to the susceptibility of genotypes to the parasitic weed Striga. / Graduation date: 2012

Marine microorganisms play a significant role in the cycling of nutrients in the open ocean through production, consumption, and degradation of organic matter (OM). Carbon (C), nitrogen (N), and phosphorus (P) are essential ingredients in every known recipe for life. However, the cycling of each of these elements proceeds at different rates such that the ratio of C:N:P can vary widely between particulate, dissolved, organic, and inorganic pools. To better understand the mechanisms controlling these transformations, this study investigated the bacterial remineralization of photosynthetically-derived organic matter derived from cultures of Trichodesmium IMS101, Thalassiosira weissflogii, Prochlorococcus MED4, and particulate material collected from the surface waters of an upwelling regime. Experiments were conducted at sea for a short duration (<6d) and in the laboratory for longer periods (<150 days). In all treatments, across experiments, we observed rapid and selective P remineralization independent of the type of organic material added. Full solubilization and remineralization of P typically occurred within a week. Conversely, N remineralization was slower, with only 39-45% of particulate N (PN) remineralized in shorter (6d) experiments and 55-75% of PN remineralized in <150d experiments. Nitrification was observed after 70-98 days depending on the remineralizing bacteria (isolated from either the Oregon coastal upwelling regime or the North Pacific Subtropical Gyre (NPSG). Notably, these events did not transform the full complement of ammonium to nitrate. This differential lability between N and P led to rapid changes in the N:P ratio of inorganic pools as organic matter was depolymerized by varying bacterial populations. The variable input of potentially limiting elements could have consequences for primary productivity and particle export. Finally, we observed that in short-term experiments with heterotrophic bacteria collected from the NPSG, the N:P ratio of remineralization (11 ± 2.2) was independent of the N:P of added organic material (5-23). This uniformity of inorganic ratios implies differential lability and N:P composition of residual semi-labile and refractory organic matter. Formation of refractory C and N rich organic matter, often termed the microbial pump, is a significant pathway for the transport and sequestration of elements in the aphotic zone of the ocean interior. The experimental results reported here suggest that differential supply of POM leads to rapid and preferential P remineralization, N:P remineralization independent of the N:P of added substrates, and variable N:P of residual organic matter. These findings help constrain our knowledge of elemental cycling in the marine environment. / Graduation date: 2013

Little is known regarding the effects of land use on soil organic matter and P status of South African soils. For that reason, the effects of the main agricultural land uses in the midlands region of KwaZulu-Natal [maize (Zea mays), sugarcane (Saccharum spp), annual ryegrass pasture (Lolium multiflorum), permanent kikuyu pasture (Pennisetum clandestnum), gum (Eucalyptus grandis) and pine (Pinus patula)] on soil organic matter content, microbial biomass C and P and inorganic and organic P pools derived from a modified Hedley P fractionation was investigated on two sites where the longterm history of land management was known. In comparison with undisturbed native grassland, permanent kikuyu pasture resulted in an increase in organic C, organic P and microbial biomass C and P. Maize and sugarcane production resulted in a decrease in organic C, organic P and microbial C and P. Under annual pasture, gum and pine forests, organic matter and microbial biomass concentrations remained similar to those under native grassland. Under native grassland, extractable organic P accounted for 50% or more of the total P content of soils but under agricultural management with regular applications of fertilizer P, there was an increase in the percentage of total P present as inorganic P. Agricultural management greatly affected the distribution of P among the various inorganic and organic P fractions. Resin-Pi and NaHC03-Pi (the potentially-available forms of Pi) showed similar trends with land use being greatly elevated under kikuyu pasture at both sites and sugarcane and maize at one site. This accumulated Pi was thought to have originated from recent fertilizer applications and possibly recently mineralized organic P. Trends for NaOH-Pi with land use differed greatly from those of the Resin- and NaHC03Pi fractions. Concentrations were notably high under maize and sugarcane production. Of the pools of soil organic P, the NaHC03-Po fraction was most greatly affected by land use, being elevated under kikuyu and decreased under maize and sugarcane. This supports the assertion that it is the NaHC03-Po fraction that is the most labile soil organic P pool. It was concluded that land use greatly affects soil organic C and P status, soil microbial biomass C and P contents, soil inorganic P concentrations and the distribution of P among the various P fractions. A short-term (8 weeks) laboratory incubation experiment was carried out to compare the effects of inorganic (KH2P04) and organic (cattle manure, poultry manure and maize crop residues) sources of P, applied at a rate equivalent to 30 kg P ha-1 , on soil inorganic and organic P fractions and the potential availability of soil P. Additional treatments consisted of lime [Ca(OHhl at 5 ton ha-1 and lime plus inorganic P. Applications of lime raised soil pH to a similar extent after 1, 4 and 8 weeks incubation. After 8 weeks, a small increase in soil pH was also noted for the cattle and poultry manure and maize residue treatments. For the inorganic P fractions, substantial treatment effects were observed only for the Resin-Pi fraction. The inorganic P source was more effective than the organic ones at increasing Resin-Pi after 1 and 4 weeks incubation and of the organic sources, cattle and poultry manure were more effective than maize residues. Resin-Pi concentrations generally increased between 1 and 4 weeks incubation but then declined rapidly between 4 and 8 weeks incubation. After 8 weeks incubation, treatment effects on Resin-Pi were small. Concentrations of NaHC03-Pi, dilute HCI-Pi and concentrated HCI-Pi all declined over the incubation period. There was no clear trend with incubation for NaOH-Pi although for the poultry manure and maize treatments, concentrations declined between 4 and 8 weeks incubation. In general, concentrations of NaHC03-Po were greater for organic than inorganic P sources after 8 weeks incubation suggesting microbial immobilization of P in these treatments. There were increases in NaHC03-Po and concentrated HCI-Po over the incubation period suggesting progressive immobilization of P from the Pi fractions that declined in concentration during the incubation. Concentrations of NaOH-Po were not greatly affected by incubation period. The lime treatments, however, had lower NaOH-Po concentrations than the others suggesting that liming may have stimulated microbial mineralization of Po. Residual-P concentrations increased over the incubation period. This was attributed to conversion of extractable Pi fractions into recalcitrant, non-extractable Pi forms and/or immobilization of Pinto intransigent organic forms. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

A study was initiated in 1989 to examine the effects of applying excess liquid hog manure with mineral fertilizers to corn and forage crops. Manure was applied yearly at twice the recommended level either in the spring, fall or a combination of both spring and fall applications. Mineral fertilizers were applied at recommended levels to plots receiving only mineral fertilizers and to manure treatment plots. Two control plots received no fertilizers. / During the summer of 1999, soil samples were taken at a depth of 0--2 cm and analysed using different phosphorus extractants. Six runoff events were sampled and analysed for different phosphorus fractions. / Strong correlations were found in corn plots between average dissolved reactive phosphorus concentrations in runoff and soil test phosphorus concentrations. Timing of manure application had a significant impact on both soil and runoff phosphorus concentrations. Runoff from forage plots had significantly higher concentrations of dissolved phosphorus, but phosphorus loads were greater from corn plots due to higher runoff volumes. Corn plots released significantly higher particulate phosphorus concentrations than forage plots because of higher sediment loads in runoff from corn plots.

Phosphorous concentrations exceed water quality guidelines in most of the major rivers in southern Quebec. The problem is particularly acute in the Pike River, which drains into the Missisquoi Bay of Lake Champlain, in southeastern Quebec. Elevated phosphorus concentrations can lead to a reduction in the palatability of drinking water, a decrease in diversity of aquatic life and loss of recreational opportunities. All of these problems have been observed in the Bay. / Two agricultural fields (the Marchand and Gagnon sites) located on the Pike River watershed, in southeastern Quebec were selected and equipped with instrumentation to measure and evaluate the partitioning of phosphorus between surface runoff and subsurface drainage, on a year round basis. The snowmelt event was the dominant surface and subsurface event for the 2000/2001 hydrological year. On the Marchand site surface flow data was incomplete as a result of a failure of the surface runoff flume. On both sites the IF 200 subsurface flow meters failed, which resulted in missing subsurface flow data during certain runoff events. Therefore, the majority of the comparisons made relate to the Gagnon site. / The 2000/2001 hydrological year was unusually dry, which resulted in a limited number of surface and subsurface runoff events. The annual depth of surface runoff for the Gagnon site was 87.5 mm/ha, of which only 0.2mm occurred outside the snowmelt event. The estimated depth of subsurface runoff of the snowmelt event at the Gagnon site based upon a water balance equation was 93.7 mm/ha, or 51.7% of the total volume that occurred on the Gagnon field during the snowmelt event. / The total phosphorus load in surface runoff for the spring snowmelt at the Gagnon site was 166.4 g/ha, whereas the estimated total phosphorus load in subsurface drainage was 98.2 g/ha, or 37.1% of the total load. Subsurface drains can therefore be a significant pathway for phosphorus losses.