Made available in DSpace on 2016-12-08T15:50:03Z (GMT). No. of bitstreams: 1 PGMS11DA003.pdf: 2953340 bytes, checksum: bbaae7a8b0e4fdd162058cd82f79cea9 (MD5) Previous issue date: 2011-08-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Under conservation soil tillage, the effectiveness of crop residues in reducing water erosion decrease if the mulch is transported by runoff and/or if the runoff furrows the soil. This phenomenon is called mulch failure, characterizing the critical slope length, i.e., the distance on the ground from which the flood gains sufficient shear stress to overcome the resistance to transport the mulch and/or the resistance of the soil to furrow. The objectives of this study were to define critical slope lengths and critical shear stress in two sowing directions under different types and doses of crop residues, in no-till. The field work was conducted from May 2009 to May 2011, on a Nitosol (Alfisol) in Santa Catarina, Brazil, in experimental units with dimensions of 3.5 x 11 m, and mean slope of 0.144 m m-1. Sowing directions transverse (contour) and parallel (up-and-down) to the slope were tested using maize (Zea mays), wheat (Triticum aestivum) and soybean (Glycine max) mulches at doses of 50 and 100% of the total residue produced. During the research, simulated rainfall tests were performed using a rotating-boom rainfall simulator, with rain intensity of 65 mm h-1 and 90 min of duration, which was time required to achieve the constant runoff rate. At the end of 90 min of rain, without disconnecting the rainfall simulator were applied increasing levels of extra flow of clean water at the upper part of the plots, simulating additional runoff from longer slopes. The mulch failure was evaluated based on the theory of erosion, using the relationship between erosion rate (Dp) x runoff rate (qm), sediment concentration in runoff (C) x runoff rate (qm) and runoff velocity (V) x runoff rate (qm). Moreover, the mulch failure was observed visually when it occurred. In all treatments were found the critical slope lengths, and, in general, contour sowing and higher dose of crop residues increased the critical slope length and critical shear stress in relation to the up-and-down sowing and the lowest crop residue dose, respectively. Such lengths and critical stress ranged from 35 to 155 m and 1.9 to 7.4 N m-2, respectively. The theory of erosion, the point of failure was identified jointly analyzing the relationships Dp x qm and C x qm. The relationship V x qm was not a good indicator of failure. The visual failure could be identified for maize and soybean residues, while for wheat it was not clearly distinct / Nos preparos conservacionistas de solo, a eficácia dos resíduos culturais na redução da erosão hídrica diminui se os resíduos forem transportados pela enxurrada e/ou se a enxurrada sulcar o solo. A esse fenômeno se denomina falha dos resíduos, caracterizando a existência de comprimento crítico de declive, ou seja, a distância no terreno a partir da qual a enxurrada adquire tensão cisalhante suficiente para superar a resistência do resíduo ao transporte e/ou a resistência do solo ao sulcamento. Os objetivos do trabalho foram definir comprimentos críticos de declive e a tensão crítica de cisalhamento em duas direções de semeadura direta, sob diferentes tipos e doses de resíduos culturais. O trabalho foi desenvolvido em campo, entre maio de 2009 e maio de 2011, sobre um Nitossolo Bruno aluminoférrico húmico, em São José do Cerrito (SC), usando unidades experimentais com dimensões de 3,5 x 11 m, com declividade média de 0,144 m m-1. Foram testadas as formas de execução de semeadura direta no sentido transversal (em contorno) e paralelo ao declive (na pendente), sobre os resíduos culturais de milho (Zea mays), trigo (Triticum aestivum) e soja (Glycine max), nas doses de 50% e 100% do total produzido para cada um deles. Foram realizados testes de chuva simulada com o uso de simulador de chuva de braços rotativos, na intensidade de chuva planejada de 65 mm h-1 e, com duração de 90 min cada um, tempo este necessário para se obter a taxa constante de enxurrada. Ao final dos 90 min de chuva, sem desligar o aparelho simulador de chuva, foram aplicados níveis crescentes de fluxo extra de água limpa na cabeceira das parcelas, simulando a enxurrada provinda de declives mais longos. Para identificação da falha dos resíduos, usou-se teoria de erosão, efetuando as relações entre taxa de erosão (Dp) x taxa de enxurrada (qm), concentração de sedimentos na enxurrada (C) x taxa de enxurrada (qm) e velocidade da enxurrada (V) x taxa de enxurrada (qm). Em adição, a falha dos resíduos foi avaliada visualmente. Detectou-se comprimento crítico de declive em todos os tratamentos, sendo que, de modo geral, a semeadura direta em contorno e a dose maior dos resíduos de milho, trigo e soja aumentaram o comprimento crítico e a tensão crítica de cisalhamento, em relação à semeadura direta na direção da pendente e à menor dose de resíduos, respectivamente. Tais comprimentos e tensões críticas variaram de 35 a 155 m e 1,9 a 7,4 N m-2, respectivamente. Da teoria de erosão, o ponto de falha foi melhor identificado analisando conjuntamente as relações Dp x qm e C x qm. A relação V x qm não foi um bom indicador da falha. A observação visual em campo indicou falha real dos resíduos de milho e soja, enquanto que para o de trigo, não houve clareza

Juniper (Juniperus spp.) encroachment into sagebrush (Artemisia spp.) and bunchgrass communities has reduced understory plant cover and allowed juniper trees to dominate millions of hectares of semiarid rangelands. Trees are mechanically masticated or shredded to decrease wildfire potential and increase desirable understory plant cover. When trees are masticated after a major increase in tree population density and associated decrease in perennial understory cover, there is a risk that invasive annual grasses will dominate because they are highly responsive to the increased resource availability that commonly follows removal of the main resource user. To determine if tree mastication increases resource availability and subsequently favors invasive annual or perennial grasses, we compared soil temperature, water, and nutrient microenvironmental conditions and seedling establishment and growth. We used the major rangeland weed, cheatgrass (Bromus tectorum L.), to represent invasive annual grasses and Anatone bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) A. Löve), a natural accession of native bluebunch wheatgrass, to represent the perennial grasses of the sagebrush-bunchgrass plant community. These comparisons were made between and within paired-adjacent masticated and untreated areas at three locations in Utah dominated by Utah juniper (Juniperus osteosperma (Torr.) Little). Juniper tree mastication generally increased resource availability with masticated areas having greater soil temperature, soil water availability, and soil N supply rates than untreated areas. Prior to juniper tree mastication litter mounds were not found to be resource islands probably because juniper trees themselves were using subcanopy soil water and nutrients. After juniper tree mastication and elimination of these predominant resource users, litter mounds served as resource islands with greater soil water availability and N supply rates than bare interspaces during the critical time for seedling establishment in spring. Plant growth followed in line with greater resource availability after tree mastication with masticated areas having more productive although fewer invasive-annual and perennial grass seedlings than untreated areas. These results suggest that increases in resource availability and warmer spring temperatures associated with mastication will not necessarily favor invasive annual over perennial grass seedling establishment. Resilience of the sagebrush-bunchgrass community to return to dominance after juniper control will likely be greatly influenced by how much of the sagebrush-bunchgrass community remains following tree control and the intensity of propagule pressure by invasive species. If only invasive annuals remain when the trees are treated then invasive annuals would be expected to dominate the post-treatment plant community especially with their ability to establish inside litter mounds unless they were also controlled and perennial grasses planted at the time of treatment.

No description available.

Cette these etudie les effets de la conversion de la foret tropicale en parcelles agricoles, sur les emissions de n2o par les sols. Ce travail est realise a l’echelle du cycle cultural sur le dispositif experimental de combi (littoral guyanais), a l’aide de mesures in situ et de simulations (modele noe) des flux de n2o. La foret tropicale a ete comparee a des parcelles de foret converties en terres agricoles par la methode ‘chop-and-mulch’. La methode de deforestation ‘chop-and-mulch’ associe coupe mecanique de la vegetation, broyage puis enfouissement des residus forestiers dans le sol. Les terres agricoles etaient soient des parcelles de prairie non paturee soient des parcelles cultivees (maïs fertilise/soja) conduites en semis conventionnel (semis apres travail du sol, sans plante de couverture) ou en semis direct (sans travail du sol, avec plantes de couverture).Les principaux resultats de cette etude sont : le sol de la foret tropicale de combi est un faible emetteur de n2o ; la conversion par la methode ‘chop-and-mulch’ de cette foret en prairie ne conduit pas a une augmentation significative des emissions de n2o entre le 19eme et le 31eme mois suivant la conversion ; la conversion de la foret en parcelles cultivees induit une augmentation significative des emissions de n2o due a la fertilisation et a la modification des parametres edaphiques (densite apparente, temperature, humidite volumique) ; la technique sans travail du sol n’engendre pas de flux de n2o significativement plus eleves que la technique avec travail du sol ; l’introduction du phenomene d’hysterese hydrique dans le modele noe presente un reel potentiel pour l’estimation des emissions de n2o in situ. / This study investigates the effects of the conversion of tropical forest to cultivation on soil n2o emissions. The study was carried out over a complete crop cycle at the experimental site combi (french guianese coast). Nitrous oxide fluxes were obtained in the field and by conducting simulations with the noe model. Undisturbed tropical rainforest was compared to rainforest that had been converted to agricultural land using the ‘chop-and-mulch’ method. The ‘chop-and-mulch’ method is a fire-free method used for vegetation clearing combining the mechanical felling of trees with the mulching of small vegetation. Agricultural land included either mowed grassland or soybean/fertilised maize crop rotation. For croplands the two cultivation practices employed were: conventional seeding (using an offset disc harrow, without cover plants) or direct seeding (no till, with cover plants).The main results of this study are: rainforest soil at combi produced low n2o emissions; rainforest converted to mowed grassland using the 'chop-and-mulch’ method did not lead to a significant increase in n2o emissions between the 19th and 31st months after conversion; the conversion of rainforest to croplands induced a significant increase in soil n2o emissions due to the application of fertiliser and the modification of soil parameters (bulk density, temperature, volumetric moisture); n2o emissions from agricultural practices with no-till were no higher than those produced by conventional agricultural practices using an offset disc harrow; and, the introduction of an hydric hysteresis into the noe model constitutes a promising improvement to estimate in situ n2o emissions.

Les nématodes à galles demeurent l'un des problèmes les plus graves des ‎agriculteurs de serres du Liban et du Moyen-Orient. Dans le passé, la fumigation du sol au ‎bromure de méthyle a été considérée comme la meilleure mesure de contrôle contre ces ‎nématodes. Toutefois, à la lumière de l'élimination globale du bromure de méthyle, l'accès ‎aux alternatives efficaces et durables est devenu une nécessité essentielle.‎L'objectif de cette étude est d'évaluer l'efficacité des deux engrais verts, le radis ‎huileux (Raphanus sativus oleifera) et à la roquette (Eruca vesicaria sativa) appliquées ‎avec ou sans bâche en plastique, séparément et en combinaison avec Oxamyl, dans la ‎gestion des nématodes à galles en cultures de concombres de serre. En outre, cette étude ‎vise à évaluer la faisabilité financière de la technique de biofumigation avec les deux ‎cultures utilisées et de la rentabilité finale de ces engrais verts en termes de taux coût-profit ‎par rapport au bromure de méthyle.‎A cette fin, trois expériences sur le terrain ont été menées dans des serres ‎commerciales, situées sur la zone côtière du Liban.‎Dans les deux expériences A et B, des résultats cohérents ont été enregistrés en ‎termes de production de rendements significativement plus élevés et de la réduction des ‎populations de nématodes avec les engrais verts‎ utilisés avec ou sans bâche en plastique, ‎par rapport au témoin non traité.‎Quant aux résultats obtenus par les engrais verts‎ par rapport ‎ au bromure de ‎méthyle, dans l'expérience A, le rendement produit par le bromure de méthyle était ‎significativement plus élevé que celui du radis huileux avec bâche en plastique. ‎Cependant, la différence n'était pas significative entre la réduction de la population de ‎nématodes résultant du bromure de méthyle et celle du radis huileux avec bâche en ‎plastique. Les différences du rendement ainsi que la réduction des nématodes étaient ‎significatives entre le bromure de méthyle et le radis huileux sans bâche en plastique.‎Dans l'expérience B, aucune différence significative n'a été observée dans le ‎rendement ni la réduction de la population de nématodes entre aucun des deux engrais ‎verts‎ utilisés avec bâche en plastique et le bromure de méthyle. Ces différences étaient ‎significativement en faveur du bromure de méthyle uniquement lorsque le radis huileux a ‎été utilisé sans bâche en plastique.‎Dans l'expérience C, où Vydate (Oxamyl) a été appliqué à la dose de 1 litre par 1,000 ‎m2 à tous les traitements, il n'y avait pas de différence significative dans le rendement ni la ‎réduction de la population de nématodes entre chacun des deux engrais verts utilisés avec ‎ou sans bâche en plastique et le bromure de méthyle.‎L'analyse coût-profit menée sur tous les traitements appliqués dans les 3 ‎expériences a montré que dans tous les cas, tous les traitements appliqués, qu'ils soient ‎chimiques, non-chimique (avec ou sans bâche en plastique) ou en association ont produit ‎des bénéfices nets supérieurs au bromure de méthyle, même lorsque le rendement produit ‎par le bromure de méthyle était significativement plus élevée.‎L'utilisation du plastique pour couvrir les radis huileux a généralement produit de ‎meilleurs résultats en termes de production de rendements plus élevés, une meilleure ‎réduction des populations de nématodes à galles dans le sol, ainsi conduisant à des ‎augmentations raisonnables des profits nets.‎A la base de ces résultats et à la lumière de l'élimination globale du bromure de ‎méthyle, on peut conclure que l'utilisation du radis huileux et la roquette comme engrais ‎verts avec bâche en plastique peut être considéré comme un outil alternatif pour la gestion ‎des nématodes à galles dans la production de concombres de serre dans les conditions ‎libanaises.‎ / Root-knot nematodes remain one of the most serious problems faced ‎by ‎greenhouse farmers of Lebanon and the Middle East region. In the past, soil fumigation ‎with methyl bromide has been considered as ‎the best control measure against root-knot ‎nematodes. However, in the light of the global phase out of methyl bromide, finding ‎efficient and viable alternatives is an essential necessity.‎The objective of this study is to evaluate the efficacy of the two biofumigation ‎crops ‎Oil Radish (Raphanus sativus oleifera) and Arugula (Eruca vesicaria sativa) applied ‎with ‎and without plastic tarp, separately and in combination with Oxamyl in the ‎management of ‎the root-knot nematodes in greenhouse cucumber crops. Additionally, this ‎study aimed at ‎assessing the financial feasibility of the biofumigation technique with the ‎two cops used ‎and the final profitability of these green manure crops in terms of cost to ‎benefit ratio as ‎compared to methyl bromide.‎For this purpose, three field experiments were carried out in ‎commercial ‎greenhouses situated on the coastal zone of Lebanon.‎In both experiments A & B consistent results were recorded in terms of production ‎of ‎significantly higher yields and reduction of nematode population with the ‎biofumigation ‎crops used whether with or without plastic cover, as compared to untreated ‎fallow.‎As to the results achieved by the biofumigation crops with respect to methyl ‎bromide, ‎in experiment A yield produced by methyl bromide was significantly higher than ‎oil radish ‎with plastic cover. However, no significant difference was found between ‎reduction of ‎nematode population resulting from methyl bromide and oil radish with plastic ‎cover. ‎Difference was significant between methyl bromide and oil radish without plastic ‎cover in ‎both yield and reduction of nematodes.‎In experiment B no significant difference was observed in neither yield nor ‎reduction ‎of nematode population between any of the two biofumigation crops used with ‎plastic ‎cover and methyl bromide. These differences were significantly in favor of methyl ‎bromide ‎only when oil radish was used without plastic cover.‎In experiment C where Vydate (Oxamyl) was incorporated at the rate of 1 liter ‎per ‎‎1,000 m2 to all treatments, there was no significant difference in neither yield nor ‎reduction ‎of nematode population between any of the two biofumigation crops used with or ‎without ‎plastic cover.‎Cost-benefit analysis made on all treatments applied in the 3 experiments ‎showed ‎that in all cases, all treatments applied, whether chemical, non-chemical (with or ‎without ‎plastic cover) or in combination have produced higher net profits than methyl ‎bromide, ‎even when yield produced by methyl bromide was significantly higher.‎Use of plastic for covering oil radish has generally produced ‎better results in terms ‎of ‎production of higher yields, better reduction of soil ‎populations of root-knot nematodes‏‎ ‎and ‎‏leading to ‎‏reasonable increases of net profits.‎Based on these findings and in the light of global phase out of methyl bromide, ‎it ‎can be concluded that the use of oil radish and arugula as biofumigation crops with ‎plastic ‎cover can be considered as ‎an alternative management tool for the root-knot ‎nematode in ‎greenhouse cucumber ‎production under Lebanese conditions.‎