Global ETD Search

261	Bioavailability of cadmium, copper, nickel and zinc in soils treated with biosolids and metal salts Black, Amanda January 2010 (has links) It is widely accepted that bioavailability, rather than total soil concentration, is preferred when assessing the risk associated with metal contamination. Despite this, debate continues on what constitutes a bioavailable pool and how to best predict bioavailability, especially in relation to crop plants. The overall aim of this thesis was to assess and validate measures of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) bioavailability in a range of soils amended with metal salts and biosolids. Six potential measures of bioavailability were investigated and compared: total metal; 0.04 M EDTA extraction; 0.05 M Ca(NO₃)₂ extraction; soil solution extracted using rhizon probes; effective solution concentration (CE) determined using diffusive gradients in thin films (DGT); and modelled free ion activities (WHAM 6.0). These were compared to shoot metal concentrations obtained from plants grown in three soils with contrasting properties treated with biosolids and metal salts. The first study involved a wheat seedling (Triticum aestivum) assay carried out under controlled environmental conditions on incubated soils treated with metal salts and biosolids. Results showed that the presence of biosolids resulted in increases of DOC, salinity, Ca and Mg in soil solution as well as total concentrations of Cu and Zn, dry matter was also adversely affected by increased levels of salinity. The addition of biosolids did not significantly alter the extractability or solubility of Cd, Cu, Ni and Zn although concentrations of Cd in shoots were significantly lower in plants grown in biosolids amended soils compared with unamended soils. The second study involved a field experiment that used 20 cm diameter by 30 cm deep soil monoliths of the same three soils treated with metals and biosolids, and perennial ryegrass (Lolium perenne) was grown for 24 months. Results revealed the addition of biosolids significantly increased the amount of DOC, salinity, Ca and Mg in solution. The presence of biosolids also significantly altered the bioavailability of Cd, Cu, Ni and Zn, as measured by soil solution, CE and free ion activity. However, this change had little effect on plant metal uptake. The length of time following treatment application had the greatest effect on soil chemistry and metal availability, resulting in pH decreases and increases in DOC, soil solution salinity, Ca and Mg. The free ion activities of each metal increased with time, as did soil solution Cd and Zn and CE-Cu, with results for Zn indicative of migration through the soil profile with time. Plant uptake of Ni and Zn also changed with time. Nickel concentrations in shoots decreased, while concentrations of Zn in shoots increased. The findings from the two studies demonstrated that biosolids increased the amount of DOC, salinity, Ca and Mg present in soil solution. In the lysimeter study measures of metal availability were affected in soils amended with biosolids, but this did not effect shoot concentrations. The overall predictive strengths of the six potential measures of bioavailability was investigated using results from the previously described experiments and related studies carried out by ESR and Lincoln University using nine different soils amended with combinations of biosolids and metal salts. Of the four metals Ni provided the strongest correlations between metal bioavailability and shoot concentrations, with 0.05 M Ca(NO₃)₂ extraction giving the strongest relationship for Ni concentrations in shoots (r² = 0.73). This suggests that the solubility of Ni is highly indicative of shoot concentrations and that Ca(NO₃)₂ is a robust measure of Ni bioavailability. In addition Ca(NO₃)₂ provided the best estimate of Zn bioavailability (r² = 0.65), and CE-Cd provided the best measure of Cd bioavailability, although it could only describe 47 % of shoot Cd concentration. Results for Cu were typical of previously described studies as assays of Cu availability are almost always poorly correlated with shoot concentrations, with total Cu having the strongest relationship (r² = 0.34). Methods based on the extractability and solubility of Cu in soils were poor indicators of Cu concentration in shoots. Overall, the addition of biosolids did not alter the outcome of these bioavailability assays, and results indicated that total metal concentrations present in the soils and biosolids matrix, plus length of time since soil treatment, had a greater affect on metal bioavailability. bioavailability soils cadmium copper nickel zinc ryegrass wheat biosolids Triticum aestivum L.
262	Inoculation with Azospirillum brasilense associated with silicon applied to correct soil acidity and nitrogen rates in corn and wheat crops / Galindo, Fernando Shintate. January 2020 (has links) Orientador: Marcelo Carvalho Minhoto Teixeira Filho / Resumo: Alternative management practices are needed to minimize the need for chemical fertilizer use in non-leguminous cropping systems. The use of biological agents which can fix atmospheric nitrogen and promote plant growth has shown potential as an option to improve soil nutrient availability to grass crops. In recent years, studies investigating the effects of silicon (Si) have increased substantially, especially in grain crops. This increased interest in Si is likely due to the beneficial effects of Si application on plant resistance to abiotic and biotic stresses, reflecting on greater plant development. This research was developed to investigate if inoculation of corn and wheat with Azospirillum brasilense associated with Si can enhance nitrogen use efficiency (NUE) and improve plant nutrition and yield, leading to a greater economic profit. The study was set up in a Rhodic Haplustox under no-till system, located in Selvíria, state of Mato Grosso do Sul, Brazil. The field trial took place during the 2015/16 (November-March), 2016 (April-September), 2016/17 (November-March) and 2017 April-September) seasons, with corn and wheat crops in sucession (spring/summer and winter seasons for corn and wheat, respectively). Treatments were tested in a randomized completely block design with four replicates, arranged in a full factorial design 5 × 2 × 2 and included: i) five N application rates, as urea source, applied in side-dressing (0, 50, 100, 150 and 200 kg ha-1); ii) two liming sou... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor Biological nitrogen fixation on grasses Economic viability Nitrogen fertilization with urea Plant growth promoting bacteria Silicon use on grasses Zea mays L. Triticum aestivum L. Viabilidade economica. Adubação nitrogenada com ureia Uso de silício em gramíneas
263	Plant communities in organic and conventional agriculture - comparing local, landscape and regional effects / Ackerwildpflanzengesellschaften in ökologischer und konventioneller Landwirtschaft - die Bedeutung von Standort, Landschaft und Region Gabriel, Doreen 03 February 2006 (has links) No description available. 630 Landwirtschaft Veterinärmedizin Agricultural Sciences Ackerwildkräuter Ackerland Agrarumweltprogramme Beta Diversität Biodiversität Geographische Informationssysteme Getreide Landschaft Landschaftskomplexität Landschaftsökologie konventioneller Landbau ökologischer Landbau Naturschutz Insektenbestäubung räumliche Skala Samenbank Sameneinflug Unkräuter Winterweizen zeitliche Skala additive partitioning agri-environment schemes arable weeds arable crop beta diversity biodiversity cereal fields conventional farming community composition conservation functional scale geographic information system GIS insect pollination inter-annual variability landscape context landscape complexity landscape ecology organic farming seedbank seed rain spatial turnover temporal turnover Triticum aestivum winter wheat 48.16 YA
264	Spinnen in Agrarlandschaften und die biologische Kontrolle von Getreideblattläusen / Spiders in agricultural landscapes and the biological control of cereal aphids Schmidt, Martin H. 27 May 2004 (has links) No description available. Agricultural Sciences Ackerland Ausbreitung Biodiversität Biologische Schädlingsbekämpfung Blattläuse Brache Habitatpräferenz Grünland Landschaftsökologie Mulch natürliche Schädlingskontrolle Ökologischer Landbau Parasitoide Populationsdynamik Prädatoren Räuber-Beute Beziehung räumliche Skala Schlupfwespen Schwebfliegen Spinnen Störung Überwinterung Winterweizen 500 Naturwissenschaften Aphididae Aphidiidae Aphidoletes aphidimyza aphids arable crop Araneida biodiversity biological control dispersal disturbance fallow functional scale geographic information system GIS grassland habitat preference landscape ecology Linyphiidae mulch natural pest control organic farming overwintering parasitoid population dynamics predator Rhopalosiphum padi Sitobion avenae spiders Syrphidae Triticum aestivum trophic interactions wasps winter wheat 48.16 42.65 YA

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