Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 535-571). Available also in a digital version from Dissertation Abstracts.

Tang Chi Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 104-121) and index. / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgements --- p.v / Table of Contents --- p.vii / List of Tables --- p.x / List of Figures --- p.xi / List of Plates --- p.xii / Chapter Chapter One --- Introduction / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Conceptual Framework --- p.3 / Chapter 1.3 --- Objectives and Significance --- p.5 / Chapter 1.4 --- Structure of the Thesis --- p.7 / Chapter Chapter Two --- Literature Review / Chapter 2.1 --- Impacts of Soil Erosion on Agriculture --- p.8 / Chapter 2.2 --- Farmland Shortage Problems in the Reservoir Region --- p.10 / Chapter 2.3 --- Terracing Systems in China --- p.11 / Chapter 2.4 --- Contour Hedgerows --- p.13 / Chapter 2.5 --- Sustainable Agriculture and its Development in China --- p.18 / Chapter Chapter Three --- Study Area / Chapter 3.1 --- The Three Gorges Reservoir Region --- p.22 / Chapter 3.2 --- Geographical Settings of Zigui County --- p.23 / Chapter 3.2.1 --- Geographical and Administrative Location --- p.23 / Chapter 3.2.2 --- Geology and Geomorphology --- p.24 / Chapter 3.2.3 --- Soils --- p.25 / Chapter 3.2.4 --- Climate --- p.25 / Chapter 3.2.5 --- Hydrology --- p.26 / Chapter 3.3 --- Socioeconomic Conditions of Zigui County --- p.26 / Chapter 3.3.1 --- Demography --- p.26 / Chapter 3.3.2 --- Educational Attainments --- p.27 / Chapter 3.3.3 --- Economic and Social Development --- p.27 / Chapter 3.4 --- Environmental Problems in Zigui and the Reservoir Region --- p.28 / Chapter Chapter Four --- Cost-benefit Analysis of Contour Hedgerows / Chapter 4.1 --- Introduction --- p.30 / Chapter 4.2 --- Methodology --- p.32 / Chapter 4.2.1 --- Trial Plot Design --- p.32 / Chapter 4.2.2 --- Cost-benefit Analysis --- p.35 / Chapter 4.2.3 --- Identification and Valuation of Costs --- p.35 / Chapter 4.2.4 --- Identification and Valuation of Benefits --- p.37 / Chapter 4.2.5 --- Discount Rate --- p.37 / Chapter 4.2.6 --- Time Horizon --- p.37 / Chapter 4.2.7 --- Cost-benefit Criterion --- p.38 / Chapter 4.3 --- Results and Discussion --- p.38 / Chapter 4.3.1 --- Investment Costs and Operating Costs --- p.38 / Chapter 4.3.2 --- Replacement Costs --- p.39 / Chapter 4.3.3 --- Benefits --- p.42 / Chapter 4.3.4 --- Net Present Values (NPVs) --- p.44 / Chapter 4.3.5 --- Sensitivity Analysis --- p.47 / Chapter 4.4 --- Conclusion --- p.48 / Chapter Chapter Five --- A Questionnaire Survey of the Comparative Performance of Various Farming Systems / Chapter 5.1 --- Introduction --- p.50 / Chapter 5.2 --- Methodology --- p.52 / Chapter 5.2.1. --- Sampling Method --- p.52 / Chapter 5.2.2. --- Questionnaire --- p.52 / Chapter 5.2.3. --- Analytical Technique --- p.53 / Chapter 5.3 --- Results and Discussion --- p.54 / Chapter 5.3.1. --- Background of Households and Farming Systems --- p.54 / Chapter 5.3.2. --- Net Returns --- p.57 / Chapter 5.3.3. --- Inputs of Inorganic Fertilizers and Organic Manure --- p.61 / Chapter 5.3.4. --- Labour Inputs --- p.64 / Chapter 5.3.5. --- Characteristics of Hedgerow Management --- p.65 / Chapter 5.4 --- Conclusion --- p.66 / Chapter Chapter Six --- An Interview Study of the Perception of Contour Hedgerows / Chapter 6.1 --- Introduction --- p.68 / Chapter 6.2 --- Methodology --- p.70 / Chapter 6.3 --- Results and Discussion --- p.72 / Chapter 6.3.1 --- Familiarity with Hedgerows --- p.72 / Chapter 6.3.2 --- Hedgerow Acceptance in Usage --- p.74 / Chapter 6.3.3 --- Factors of Hedgerow Implementation --- p.79 / Chapter 6.3.4 --- Variation of Agricultural Inputs and Outputs --- p.83 / Chapter 6.3.5 --- Values of Indigenous Knowledge --- p.86 / Chapter 6.3.6 --- Implications for Hedgerow Extension --- p.88 / Chapter 6.4 --- Conclusion --- p.90 / Chapter Chapter Seven --- Conclusion / Chapter 7.1 --- Summary of Findings --- p.92 / Chapter 7.2 --- Synthesis of the Study --- p.95 / Chapter 7.3 --- Limitations of the Study --- p.100 / Chapter 7.4 --- Suggestions for Further Studies --- p.101 / Bibliography --- p.104 / Appendix I: Structured Questionnaire --- p.122 / Appendix II: Interview Guide for Hedgerow Users --- p.131 / Appendix III: Interview Guide for Non-hedgerow Users --- p.134 / Appendix IV: Interview Guide for Government Officials --- p.137 / Appendix V: Index --- p.140 / "Appendix VI: Publication-Cost-benefit Analysis of Contour Hedgerow in the Three Gorges Region (Published in ´ب´بResources Science´ح，Vol26 Supplement,pp. 132-136)" --- p.145

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