• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 149
  • 125
  • 44
  • 24
  • 9
  • 4
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 421
  • 90
  • 85
  • 66
  • 50
  • 47
  • 45
  • 39
  • 35
  • 28
  • 26
  • 24
  • 23
  • 22
  • 21
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Physicochemical and Compositional Etiology of In Vivo Microcracks in Human Cortical Bone Tissue

Wasserman, Nicholas 02 September 2004 (has links)
No description available.
42

Muscle Morphology, Function and Bone Mineralization in Girls with Turner's Syndrome / Musculoskeletal System in Turner's Syndrome

Dent, Jennifer January 1991 (has links)
The purposes of this research were i) to compare skeletal muscle development, function and bone mineralization in girls with Turner's syndrome (TS) (n=7) and healthy control girls (n=13), and ii) to examine the effects of growth hormone (GH) and estrogen (E2) therapy on musculoskeletal variables using a case study approach in two TS girls and one healthy control. Anthropometric measurements included: height, body mass, percent fat, and muscle and bone cross-sectional areas and muscle density from computed axial tomography. Evoked peak twitch torque (TT), maximal voluntary strength (MVC), contractile properties and motor unit activation (MUA) were determined for the elbow flexors (EF), plantar flexors (PF) and the knee extensors (KE). Total body and segmental bone mineral content (BMC) and density (BMD) were measured with dual photon absorptiometry. Dietary intake and participation in physical activity were assessed from questionnaires. Absolute strength (TT and MVC) for the TS patients was lower than that of the control girls' for EF, PF and KE and could not be accounted for by differences in muscle density, contractile properties, MUA, diet or level of physical activity. There were no significant differences in evoked and voluntary strength corrected for muscle area and lever length between the TS and control girls. Total body, leg and trunk BMC were lower in the TS girls compared to the controls; however, when normalized for body mass and bone width, total body BMC (g/kg) and BMD respectively were comparable between the TS and control girls. Growth hormone therapy increased height and lean mass, and reduced adiposity. All measures of arm strength increased but leg strength (PF & KE) was reduced. These may reflect the lack of GH effects on the leg muscle or possibly a detraining effect from the subject's withdraw! from a skating program. Growth hormone therapy resulted in increased leg BMC which may reflect a lag time between bone growth and subsequent mineralization. Estrogen therapy resulted in increased muscle area, fat mass and strength at all 3 muscle groups. The latter may be due to the laying down of muscle proteins as a result of estrogen therapy. The lack of major changes in BMC or BMD probably reflects the short duration of the follow-up period. Further studies are required with larger numbers for longer treatment periods in order to make conclusive statements about the effects of hormonal therapy on muscle function and bone mineralization in Turner's patients. / Thesis / Master of Science (MS)
43

Mulches in smallholder maize systems in the Limpopo Province of South Africa: untangling the effects of N through experimentation and simulation.

Sasa, Seshuhla Rebinah January 2010 (has links)
In Limpopo Province of South Africa, poor soil fertility and low crop yields are serious problems facing resource poor smallholder farmers. A survey of over 60 farmers in 2 villages (Gabaza and GaKgoroshi) found that most of the smallholder farmers were women (68%), elderly (50% above 68 years of age) and had not attended school or only attended up to the primary level (80%). Very few farmers kept livestock (usually in small numbers) and most grew cereal and legume crops (on 1ha of land) for home consumption and livestock feed, with legumes being planted on 13% of the land. The study showed that 80% of farmers were not fully aware of the benefits of legumes in fixing nitrogen (N) and improving yield. A field study at the survey village of Gabaza found that the application of fertiliser N and grass mulch combination and fertiliser N plus guarbean mulch significantly increased plant height and maize shoot growth at 4 and 8 weeks after planting. However, when grass mulch was without N fertiliser, there was no increase in maize growth relative to the control (0N). A farming systems simulation model (Agricultural Production Systems sIMulator - APSIM) was used to simulate this field study as well as over the long-term (1971 to 2008). Simulation analysis showed poor average maize yield (<3000 kg ha⁻ ¹) with the application of grass residues even when used with 30 kg N fertiliser. However, the application of guarbean residues as mulch with or without N fertiliser and as green manure increased maize yields to >4000 kg ha⁻ ¹. Simulation showed that the grass mulch with or without the addition of N fertiliser reduced water stress and soil water evaporation but increased N stress during the reproductive phase of the crop in most seasons. When guarbean mulch was used as green manure by itself, or mulch plus N fertiliser, N stress was reduced but water stress and soil water evaporation were increased which could have been due to faster decomposition of legume mulch as compared to grass mulch. Addition of N fertiliser reduced N stress to maize but increased water stress and soil water evaporation similar to the guarbean mulch because of high soil evaporation. APSIM analysis clearly showed the importance of N x soil water interactions in determining maize growth and yield at Gabaza. Therefore, two studies were undertaken in the laboratory in Australia to determine the dynamics of carbon (C) and N where residues of different qualities [canola (C:N 43), wheat (26), pea (9) and mucuna (14)] were applied to clay loam (Tarlee) or sandy (Waikerie) soils. In experiment 1, where residues were incorporated into the two soils, the cumulative CO₂-C evolution for the wheat and canola treatments at the end of the incubation period were fairly similar but significantly higher than for pea, mucuna and the control. In general, the application of residues increased microbial biomass C more than the control, with highest increases up to 1.48 and 1.56 mg C g⁻ ¹ soil for canola and wheat in Tarlee soil, respectively and 0.82 mg C g⁻ ¹ soil for pea in Waikerie soil. Even though the Tarlee soil showed greater C release than Waikerie soil, the C turnover from the residues between the 2 soils was not significantly different except for pea residues. Canola and wheat residues were found to immobilise N whereas N content increased in both soils with the application of legumes (pea and mucuna). In experiment 2, mucuna, pea and wheat residues were either incorporated or applied as surface mulches on Waikerie soil. Initially the CO₂-C release was higher for incorporated than mulched residues and CO₂-C released was higher for pea residues. However, at the end of the incubation more CO₂-C was released with the application of wheat residue indicating differences between residue types in the pattern of soil respiration. Microbial biomass C was higher for incorporated than mulched residue treatments; pea residue showed the highest biomass C for incorporated (0.78 mg C g⁻ ¹ soil) whereas mucuna had the highest microbial biomass (0.11 mg C g⁻ ¹ soil) treatments. The method of residue application resulted in a significant difference in C turnover between residues, with pea residue showing significant increase in C utilisation than mucuna and wheat. The pea residues, which had the lowest C:N, increased soil mineral N more than other treatments in both incorporated and mulched treatments. Lower mineralisation of N observed in residues of high C:N ratio compared to the control could be due to immobilisation of N. Therefore, understanding the nutrient dynamics of different crop residues could play an important role in the management of residues in different soil types. Based on these results it can be concluded that legume residues have the potential to improve soil fertility and crop yields in dryland farmers’ fields in Limpopo. Extension programs aimed at increasing farmers’ knowledge of the benefits of N fixation by legumes may increase their adoption and thereby improve soil fertility and maize yield. / Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010
44

Lead Isotope Geochemistry Of Pb-zn Deposits From Eastern Taurides, Turkey

Ceyhan, Nuri 01 December 2003 (has links) (PDF)
This study is concerned with the Pb-isotope compositions of galena samples from Pb-Zn occurrences in southern Turkey. The purpose is to i) provide chronologic information for ore deposition, ii) investigate the likely source(s) of lead in ore deposits, and iii) examine the possible control of tectonic setting and crustal basement on Pb-isotope compositions. The data used in the study belongs to the deposits located in Taurides (Zamanti, KahramanmaraS, Malatya, Elazig, Bitlis), with additional data from Nigde Massif and Hakkari Area. The mineralizations are dominantly carbonate-hosted Pb-Zn deposits formed as fracture and karst fillings and, in some places, parralel to bedding. Ore minerals are mainly Zn-oxides and minor Zn, Pb-sulphides. The Pb-isotope compositions, as evaluated in terms of their configuration with respect to reference crustal growth curves and reference isochrons on conventional Pb-isotope diagrams, point to U/Pb ratios greater than average crustal values (and close to the Western Mediterranean Crustal Growth Curve) for all the deposits, indicating upper crustal source for Pb. However, some of the deposits (AfSin-KahramanmaraS / Oreks, D&uuml / ndarli, AgcaSar and skarn type deposits to the south of &Ccedil / adirkaya in Zamanti (Kayseri-Adana) / Keban-Elazig) appear to have magmatic inputs in their genesis. Relatively old deposits are likely Paleozoic (Cafana-Malatya and T&uuml / rksevin-KahramanmaraS), Late Paleozoic-Early Mesozoic (Kalek&ouml / y-Zamanti) and Mesozoic (Hakkari) in age. The rest of the deposits (most of the occurrences in Zamanti, Nigde, KahramanmaraS, Elazig and Bitlis) are likely of Cenozoic age. The Pb-isotope compositions are, in general, similar to those from other occurrences in the Mediterranean Belt.
45

Mulches in smallholder maize systems in the Limpopo Province of South Africa: untangling the effects of N through experimentation and simulation.

Sasa, Seshuhla Rebinah January 2010 (has links)
In Limpopo Province of South Africa, poor soil fertility and low crop yields are serious problems facing resource poor smallholder farmers. A survey of over 60 farmers in 2 villages (Gabaza and GaKgoroshi) found that most of the smallholder farmers were women (68%), elderly (50% above 68 years of age) and had not attended school or only attended up to the primary level (80%). Very few farmers kept livestock (usually in small numbers) and most grew cereal and legume crops (on 1ha of land) for home consumption and livestock feed, with legumes being planted on 13% of the land. The study showed that 80% of farmers were not fully aware of the benefits of legumes in fixing nitrogen (N) and improving yield. A field study at the survey village of Gabaza found that the application of fertiliser N and grass mulch combination and fertiliser N plus guarbean mulch significantly increased plant height and maize shoot growth at 4 and 8 weeks after planting. However, when grass mulch was without N fertiliser, there was no increase in maize growth relative to the control (0N). A farming systems simulation model (Agricultural Production Systems sIMulator - APSIM) was used to simulate this field study as well as over the long-term (1971 to 2008). Simulation analysis showed poor average maize yield (<3000 kg ha⁻ ¹) with the application of grass residues even when used with 30 kg N fertiliser. However, the application of guarbean residues as mulch with or without N fertiliser and as green manure increased maize yields to >4000 kg ha⁻ ¹. Simulation showed that the grass mulch with or without the addition of N fertiliser reduced water stress and soil water evaporation but increased N stress during the reproductive phase of the crop in most seasons. When guarbean mulch was used as green manure by itself, or mulch plus N fertiliser, N stress was reduced but water stress and soil water evaporation were increased which could have been due to faster decomposition of legume mulch as compared to grass mulch. Addition of N fertiliser reduced N stress to maize but increased water stress and soil water evaporation similar to the guarbean mulch because of high soil evaporation. APSIM analysis clearly showed the importance of N x soil water interactions in determining maize growth and yield at Gabaza. Therefore, two studies were undertaken in the laboratory in Australia to determine the dynamics of carbon (C) and N where residues of different qualities [canola (C:N 43), wheat (26), pea (9) and mucuna (14)] were applied to clay loam (Tarlee) or sandy (Waikerie) soils. In experiment 1, where residues were incorporated into the two soils, the cumulative CO₂-C evolution for the wheat and canola treatments at the end of the incubation period were fairly similar but significantly higher than for pea, mucuna and the control. In general, the application of residues increased microbial biomass C more than the control, with highest increases up to 1.48 and 1.56 mg C g⁻ ¹ soil for canola and wheat in Tarlee soil, respectively and 0.82 mg C g⁻ ¹ soil for pea in Waikerie soil. Even though the Tarlee soil showed greater C release than Waikerie soil, the C turnover from the residues between the 2 soils was not significantly different except for pea residues. Canola and wheat residues were found to immobilise N whereas N content increased in both soils with the application of legumes (pea and mucuna). In experiment 2, mucuna, pea and wheat residues were either incorporated or applied as surface mulches on Waikerie soil. Initially the CO₂-C release was higher for incorporated than mulched residues and CO₂-C released was higher for pea residues. However, at the end of the incubation more CO₂-C was released with the application of wheat residue indicating differences between residue types in the pattern of soil respiration. Microbial biomass C was higher for incorporated than mulched residue treatments; pea residue showed the highest biomass C for incorporated (0.78 mg C g⁻ ¹ soil) whereas mucuna had the highest microbial biomass (0.11 mg C g⁻ ¹ soil) treatments. The method of residue application resulted in a significant difference in C turnover between residues, with pea residue showing significant increase in C utilisation than mucuna and wheat. The pea residues, which had the lowest C:N, increased soil mineral N more than other treatments in both incorporated and mulched treatments. Lower mineralisation of N observed in residues of high C:N ratio compared to the control could be due to immobilisation of N. Therefore, understanding the nutrient dynamics of different crop residues could play an important role in the management of residues in different soil types. Based on these results it can be concluded that legume residues have the potential to improve soil fertility and crop yields in dryland farmers’ fields in Limpopo. Extension programs aimed at increasing farmers’ knowledge of the benefits of N fixation by legumes may increase their adoption and thereby improve soil fertility and maize yield. / Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010
46

Inibidor de nitrificação adicionado ao solo com cama de aviário e sua influência na dinâmica do nitrogênio e do carbono / Nitrification inhibitor added to soil with poutry manure influencing nitrogen and carbon dynamics

Ballem, Andressa 31 August 2012 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nitrification inhibitors can reduce the potential for environmental contamination of animal wastes, relatively to nitrate (NO3 -) leaching and nitrous oxide (N2O) emission. However, this strategy has not yet been sufficiently evaluated by research, especially with poultry litter (PL). Therefore, the objective of this study was to evaluate the effect of the product "Agrotain Plus" (AP), containing 81% of dicyandiamide (DCD), on the nitrification inhibition, ammonia (NH3) volatilization and carbon (C) and nitrogen (N) PL mineralization. Two laboratory experiments were conducted, using a Hapludalf soil collected in the 0-10 cm layer. In one experiment, conducted for 54 days, the treatments consisted of PL (4.7 Mg ha-1, dry basis) incorporated in the soil, without and with AP doses (3.5, 7.0 and 14 kg ha-1), and without PL or AP (control). In the other experiment, conducted for 69 days had all these treatments plus two additional treatments of CA on the soil surface, without and with AP (7 kg ha-1). The AP delayed NO3 - production in soil, and this inhibitory effect was more intense at the highest dose of AP (14 kg ha-1). NH3 volatilization occurred only when PL remained on the soil surface and was favored by the addition of AP. The AP addition increased PL C- and Nmineralization by 4 and 28%, respectively. The results of this study indicated that dicyandiamide (DCD), contained in the product Agrotain Plus, reduces the nitrification rate of PL ammonia in soil and could be a strategy to preserve the N of this organic material and reduce potential pollution of the environment. / Inibidores de nitrificação podem reduzir o potencial de contaminação ambiental de dejetos de animais, relativamente à lixiviação de nitrato (NO3 -) e à emissão de óxido nitroso (N2O). Todavia, essa estratégia não tem sido suficientemente avaliada pela pesquisa, especialmente com a cama de aviário (CA). Por isso, o objetivo do presente trabalho foi o de avaliar o efeito do produto Agrotain Plus (AP), o qual contém 81% de dicianodiamida (DCD), sobre a inibição da nitrificação, a volatilização de amônia (NH3) e a mineralização do carbono (C) e do nitrogênio (N) da CA. Foram conduzidos dois experimentos em laboratório, em solo da camada 0-10 cm de um Argissolo Vermelho Distrófico arênico. Num experimento, conduzido durante 54 dias, os tratamentos constaram da incorporação ao solo de CA (4,7 Mg ha-1, massa seca), sem AP e juntamente com as doses de 3,5, 7,0 e 14 kg ha-1 de AP, além de um tratamento sem CA e sem AP (testemunha). No outro experimento, conduzido durante 69 dias, além desses tratamentos havia dois com adição da CA na superfície do solo, com e sem adição de AP (7 kg ha-1). O AP, contendo DCD como inibidor da nitrificação, retardou o aparecimento de NO3 - no solo, sendo que esse efeito inibitório da nitrificação foi mais intenso na maior dose de AP (14 kg ha-1). A volatilização de NH3 ocorreu apenas quando a CA permaneceu na superfície do solo e foi favorecida pela adição de AP. A adição do AP aumentou a mineralização do C e do N da CA em 4 e 28%, respectivamente. Os resultados deste trabalho indicam que a dicianodiamida (DCD), contida no produto Agrotain Plus, reduz a taxa de nitrificação do N amoniacal da cama de aviário no solo e poderá constituir uma estratégia para preservar o N deste material orgânico, além de reduzir o seu potencial poluidor do ambiente.
47

Magnetite Mineralization of the Hammondville Pluton: Poly-Phase Kiruna Type IOCG Magnetite-Apatite Deposits in the Lyon Mountain Granite

Geer, Phillip 18 December 2020 (has links) (PDF)
Recent mapping of the Eagle Lake Quadrangle, NY, coupled with whole-rock geochemistry and microscopy has offered insight into the petrogenesis of the magnetite-apatite deposits of the Hammondville mining district in the eastern Adirondack Mountains. This study provides insight into the magmatic history of the ca. 1060-1050 Ma Lyon Mountain Granite (Hammondville Pluton) which is intimately related to, and hosts the deposits in this area. Magnetite seams are commonly surrounded by well layered magnetite gneiss, which typically parallel the seams, although in some outcrops appear to be slightly truncated by them. Mineralization is generally concordant with the weak layering found throughout the rest of the pluton, and similarly lacks a pervasive metamorphic fabric. Sub-solidus deformation is recorded in some localized shear zones that occur in both the seams and host-granite indicating post-crystallization and post-mineralization deformation events. These episodes could have provided conduits for fluids responsible for growing younger zircon that past workers dated and interpreted as a separate time of mineralization. We conclude that magnetite mineralization likely occurred as separate magma, or magnetite rich fluid, injected into the Lyon Mountain Granite either as a syn-magmatic process, or while it was still a crystalline mush.
48

Evaluating organic and conventional management and nitrogen rate for effects on yield, soil and plant nutrient of tomato and pac choi grown under high tunnel and in the field

Elfar Altamimi, May January 1900 (has links)
Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Rhonda R. Janke / The goal of this study is to clarify the influence of organic fertilizer sources on vegetable crop yield under different production systems. This research hypothesized that organic soil amendments will produce healthy and vigorous plants with similar or higher yields while improving soil organic matter levels compared to conventional amendments. Applying organic fertilizer sources can be cost-prohibitive; moreover, synchronizing timing of crop nitrogen demand with soil plant available nitrogen is essential to maximizing yield and reducing nitrogen pollution to the environment. The objectives of this study are to evaluate yield in relation to soil fertility status at different fertility rates for organic and conventional management in field and high tunnel production systems, to measure plant nutrient status in crop petioles and compare it to available mineral N levels in soil at different growing stages, and to determine the effect of nitrogen availability of organic compared to conventional fertilization on plant available nitrogen and crop yield under both systems. A latin square experimental design was conducted from 2008 to 2010 at Kansas State University Research Center in Olathe KS to evaluate an organically managed vegetable rotation of tomato (Solanum lycopersicum L. ‘Bush Celebrity’) and pac choi (Brassica rapa L. ‘Mei Qing’) under three fertility rates; control, low (composted poultry manure), and high (composted poultry manure and fish hydrolyzate) in contrast with conventionally managed soils under two production systems (field and high tunnel). The effect of these four contrasting systems was measured on plant and soil nutrient status. All plots had cover crops of rye during the winter and buckwheat in the summer between pac choi crops. Soil nitrate-N (NO₃-N) and ammonium-N (NH₄-N) were measured, as well as petiole sap nitrate (NO₃⁻). In tomato, additional soluble fertilizers had no direct effect on yield in both field and high tunnel. Compost application had a positive effect on organic matter. In pac choi, additional liquid fertilizer helped organic field plots obtain maximum yield. Soil mineral nitrogen were affected by production system and fertility source, but statistical significance varied by crop and stage. Petiole sap reflected treatment regimens but not necessarily soil N status at each plant stage. The study also addressed long term management practices on organic and conventional available nitrogen. An incubation study on the soil at the conclusion of the field experiment explored the relationship between N mineralization from potentially mineralizable nitrogen (PMN) compared to Illinois Soil Nitrogen Test (ISNT) in control and pre-plant application fertility treatment for both field and high tunnel systems. The results indicated that ISNT concentration values for all soils were below the proposed value for corn crop suggested by (Khan, 2001). ISNT correlated with PMN with the stronger correlation being in field plots. ISNT also correlated with OM in field. Fertility rate showed a significant effect on total carbon and total nitrogen in organic systems of both field and high tunnel plots. This study supports composted poultry manure to improve the fertility status of the soil and to obtain a yield equal to that of conventionally managed soil.
49

Caractérisation géochimique et isotopique dans un système d'altération complexe, du protolithe magmatique à la minéralisation Fe-Pb-Zn: le cas de la mine de Tamra (N. Tunisie)

Decrée, Sophie 23 May 2008 (has links)
L’objectif principal de cette thèse est de décrire et interpréter la mise en place des différents types de minéralisations présents dans le district minier de Nefza (NO de la Tunisie), qui constitue une région complexe et particulière du point de vue géologique dans ce pays. En effet, outre la présence de diapirs triasiques (commune à tout le Nord de la Tunisie), le district minier de Nefza est caractérisé par : (1) la mise en place d’épaisses nappes au Néogène qui forment le substratum sédimentaire régional, et (2) la présence d’une grande variété de roches magmatiques tant plutoniques que volcaniques, d’âge miocène (12,9 à 6,4 Ma),: - la granodiorite de l’Oued Bélif, qui est liée à l’évolution d’un magma calco-alcalin contaminé par la croûte ; - les rhyodacites de Aïn Deflaia, de l’Oued Bélif et du Jebel Haddada, qui résultent du mélange entre ce magma calco-alcalin et un magma de fusion crustale ; - les basaltes de Mokta el Hadid marquant la transition vers un magmatisme alcalin. A proximité des roches magmatiques – et en relation avec ces dernières – on observe différents types de minéralisation, riches en Fe, en Fe-Cu-Au, et en Pb-Zn. Parmi ces minéralisations, ce travail a permis de reconnaître : - un gisement (de volume réduit) de type « Iron Oxide Copper Gold » (IOCG), qui minéralise la brèche de l’Oued Bélif, datée du Miocène supérieur. Le minerai ferrifère (hématite et goethite), riche en F, Cu, REE, U et Au, cimente des clastes de taille variable et de nature principalement triasique ; - deux gisements (de volume modeste) de Pb-Zn, de type « sedimentary exhalative » (Sedex) qui prennent place dans lentilles carbonatées des bassins d’âge miocène supérieur de Sidi Driss et de Douahria. Les minéralisations syndiagénétiques (messiniennes) à galène, sphalérite sphérulitique et pyrite, remplacent : (1) des calcites riches en Fe-Mn et (2) des sulfates (barytine et célestine) qui remplacent eux-mêmes de façon précoce les carbonates (avant la mise en place des sulfures) ; - un gisement économique d’oxydes de Fe de type latéritique (mine de Tamra, minerais datés du Mio-Pliocène), qui résulte vraisemblablement de plusieurs épisodes de reconcentration du fer, en conditions pédogénétiques. Ce minerai enregistre également des apports hydrothermaux qui mènent, entre autres, à la précipitation de minéralisations riches en Mn, Pb, Zn et Ba. Ces unités géologiques sont étroitement liées au contexte géodynamique particulier du Nord de la Tunisie au Néogène. Ce dernier passe d’un régime compressif au Serravallien-Tortonien, qui voit la mise en place des roches magmatiques felsiques, à un régime extensif qui, à partir du Messinien (fini-Tortonien ?), se marque par la mise en place de basaltes et une augmentation du gradient thermique régional. Ce régime extensif favorise/active la circulation de fluides hydrothermaux et leur enrichissement en métaux au contact des formations constitutives du substratum régional. Ces fluides, mélangés aux fluides superficiels (localement riches en soufre au Messinien), mèneraient au dépôt de la plupart des minéralisations observées.
50

Nitrogen dynamics and biological response to dairy manure application

Bierer, Andrew M. 19 June 2019 (has links)
Animal manures are land applied in agronomic systems to supply essential crop nutrients and decrease dependency on chemical fertilizers. Liquid manures are traditionally surface broadcast to fields and sometimes incorporated to reduce odor and nutrient losses; however, incorporation is incompatible with no-till agriculture. Subsurface manure injection is a no-till compatible alternative application method which addresses these concerns, but likely changes the dynamics of nutrient cycling. Comparison of the two application methods has yielded mixed results and warrants further research. Therefore, the objectives of this research were to contrast the surface broadcast and subsurface injection of dairy slurry on nitrogen and carbon cycling, crop yield, and biologic responses to proxy soil health. In a forced air-flow laboratory incubation, manure injection reduced ammonia volatilization by 87% and 98% in a sandy loam and clay loam soil, respectively. The increased ammoniacal nitrogen recovery resulted in increases of soil nitrate of 13% for the sandy loam and 26% for the clay loam after 40 days of incubation. Microbial measurements were inconclusive in the laboratory. In 7 site-years of field study, soil nitrate was greater in 7 of 25 measurements under manure injection and 30% higher under injection on average during the corn pre side-dress nitrate test (PSNT) time. Soil nitrate sampling methods were assessed for fields injected with manure; a standard random sampling method had a coefficient of variation (C.V.) of 28% and was as equally repeatable as utilizing an equi-spaced distribution of cores taken across an injection band, C.V. of 30%. Both biological responses, carbon mineralization (C-min) and substrate induced respiration (SIR), were not different between application methods; both were highly variable and C-min was especially intensive logistically. Corn yield showed no consistent response to application method, but probably was not nitrogen limited. In 2 years of field study conducted on a university research farm injection resulted in greater 0-15cm soil nitrate levels than surface broadcast 1 week after application and persisted for 9 additional weeks. In injected plots, nitrate was concentrated in the injection band; nitrate movement was significant only 10cm lateral to the injection band but overall distribution fit well to a second degree polynomial, especially 2 and 4 weeks after application, R2>0.80. Evidence of leaching was observed in one year after receiving considerable rainfall in weeks 1 and 2 after application. When corn grain yield was averaged year over year, injection was 26% greater than the no- manure control, and 15% greater than surface application. Both biological metrics, C-min and microbial biomass, were stratified by depth; C-min was concentrated within the manure band leading to greater mineralization under injected applications. Microbial biomass was significantly higher under injection at the 15-30cm depth. Overall biological response to manure application method was inconclusive, however manure injection is superior to surface application in terms of nitrogen recovery. / Doctor of Philosophy / Animal manures supply nutrients essential to crop growth (notably nitrogen and phosphorous); liquid manures (pigs and dairy cattle) are commonly applied by spraying them on soils before tillage. Where no-tillage is used as a conservation measure subsurface injection can be used as an alternative to leaving manure on the soil surface. The purpose of this research was to assess nutrient cycling, crop yield, and soil health impacts of surface applied and injected dairy manure applications. Manure injection greatly reduces a nitrogen loss pathway, and as a result supplies more plant available nitrogen to the crop. Methods of soil sampling fields using injection were compared and a recommended sampling method was defined. Transport of a form of nitrogen vulnerable to movement in the ground was found to only travel 10cm away from where manure was injected. Transport of this form of nitrogen below the injection area was observed after abundant rainfall. Crop yields were sometimes higher under injection however, yields are also determined by factors other than nitrogen. Soil health was not repeatably improved under one application method, but microbial activity was greater at shallower soil depths.

Page generated in 0.1091 seconds