Land-use and land-cover dynamics in response to changes in climatic,biological and socio-political forces: the case of southwestern Ethiopia

Few studies of land-use/land-cover change provide an integrated assessment of the driving forces and consequences of that change, particularly in Africa. Our objectives were to determine how driving forces at different scales change over time, how these forces affect the dynamics and patterns of land use/land cover, and how land-use/land-cover change affects ecological properties at the landscape scale. To accomplish these objectives, we first developed a way to identify the causes and consequences of change at a landscape scale by integrating tools from ecology and the social sciences and then applied these methods to a case study in Ghibe Valley, southwestern Ethiopia. Maps of land-use/land-cover change were created from aerial photography and Landsat TM imagery for the period, 1957–1993. A method called `ecological time lines' was developed to elicit landscape-scale explanations for changes from long-term residents. Cropland expanded at twice the speed recently (1987–1993) than two decades ago (1957–1973), but also contracted rapidly between 1973–1987. Rapid land-use/land cover change was caused by the combined effects of drought and migration, changes in settlement and land tenure policy, and changes in the severity of the livestock disease, trypanosomosis, which is transmitted by the tsetse fly. The scale of the causes and consequences of land-use/land-cover change varied from local to sub-national (regional) to international and the links between causes and consequences crossed scales. At the landscape scale, each cause affected the location and pattern of land use/land cover differently. The contraction of cropland increased grass biomass and cover, woody plant cover, the frequency and extent of savanna burning, and the abundance of wildlife. With recent control of the tsetse fly, these ecological changes are being reversed. These complex patterns are discussed in the context of scaling issues and current conceptual models of land-use/land-cover change.     

社会力量参与公共文化服务建设的创新性动力机制研究

[目的/意义]鼓励和引导社会力量参与是政府提高公共文化服务保障水平的有效途径,提升社会力量参与公共文化服务建设质量,需要完善扶持社会力量发展的动力机制。[方法/过程]阐述社会力量参与公共文化服务建设动力机制的现状、动力机制的涵义与动力要素的类型,分析社会力量参与公共文化服务建设实践案例的先进典型做法。[结果/结论]结合案例分析,提出社会力量参与公共文化服务建设动力机制的优化策略,为推进公共文化服务的政社合作供给提供借鉴。     

新质生产力发展视角下山西省农机专业合作社提质增效优化研究

农机专业合作社发展离不开新质生产力的推动,而劳动者、生产关系、生产工具和生产要素创新性配置等,都是新质生产力形成过程中不可或缺的要素。该文采用文献研究、问卷调查,以及与农机专业合作社相关领域专家及负责人深度访谈交流的方式,从山西省农户调查、农业职业经理人经营能力和村镇银行信贷满意度调查3个视角对农机专业合作社提质增效进行分析研究,剖析产生问题的原因,提出深化联合社发展、构建新型服务模式,改革联合社人才选聘机制,充分发挥农业中介专业组织作用,以及优化农村金融贷款服务等促进农机专业合作社提质增效优化的建议。     

Effect of soil characteristics, seeding depth, operating speed, and opener design on draft force during direct seeding

Direct seeding practices that promote soil and water conservation and reduce input costs have become an increasingly accepted alternative to conventional tillage systems in western Canada. The objective of the present study was to determine the relative importance of soil characteristics, seeding depth, operating speed, and opener design on draft forces during direct seeding in central Saskatchewan. Draft was measured for nine different openers operated at 1–5 cm seeding depths and three ground speeds in four untilled Chernozemic soils that differed in soil moisture and/or texture. The average increase in opener draft for all fields was 4% for each km h⁻¹ increase in speed. Although the range in soil consistency was small, there was a 24% increase in draft in heavy clay compared to sandy loam soil. Draft force of the average opener increased by nearly 20% for each centimeter increase in seeding depth. However, highly significant interactions among most of the variables investigated indicated that the relative performance of openers was not consistent for the range of conditions evaluated. Large differences among the draft forces of different openers operated at different depths in soils with different consistencies were particulary noteworthy. For example, a 4.5-fold increase in the draft of a low versus a high draft opener operated at 1.25 versus 5.0 cm seeding depth at 7.5 km h⁻¹ in moist, heavy clay soil emphasized the large influence that opener design and seeding depth have on tractor power requirements and direct seeding input costs.     

收获期花生秧蔓切割锯盘设计与试验

为合理设计花生联合收获机切秧装置,在确定以旋转锯切为切秧方式的基础上,分析锯盘刀齿齿顶点和齿根点的运动特性,确定了锯盘的齿高、齿数、齿距等关键参数;通过对秧蔓切割时刀刃的受力分析发现合适的刀齿刃倾角可以减小工作时刀齿所受的阻力;建立了花生秧蔓的几何模型,并借助ANSYS/LS_DYNA进行关于盘厚、齿高、刃倾角的三因素三水平的切割仿真正交试验,试验以切割力为评价指标,确定了在盘厚5 mm、刃倾角20°、齿高17 mm为最优组合时,花生秧蔓的切割力最小为50 N;由自主设计的测力试验台所得试验值与仿真值的相对误差为3.24%,说明有限元仿真法对花生秧蔓切割力的测定是可行的。研究结果可为花生秧蔓切秧装置的设计和参数优化提供依据。     

中国沼气发展的现状、驱动及制约因素分析

能源需求的急剧增加以及生态环境的日益恶化促使国家大力发展沼气事业。该文在总结中国沼气发展利用现状、技术以及相关政策的基础上,深入探讨了中国沼气发展的驱动及制约因素,并为未来中国沼气的健康持续发展提出了政策建议。研究表明:过去10 a中国沼气投资和建设快速发展、沼气综合和可持续发展利用模式不断创新、国家相关支持政策为中国沼气持续发展发挥了重要作用;在未来较长一段时期,中国沼气行业既面临能源需求增加、规模化养殖发展以及环境治理压力加大等因素的驱动,也面临适宜农户减少、融资渠道单一以及市场不健全、法规不完善等因素的制约。根据研究结果,该文提出了通过健全后续服务体系,完善相关政策法规等,促进中国沼气健康发展的政策建议。     

Temporal and spatial variability in root reinforcement of streambanks: Accounting for soil shear strength and moisture

Riparian vegetation exerts a number of mechanical and hydrologic controls on bank stability, which can affect the delivery of sediment to channels. Estimates of root reinforcement of soils have commonly been attained using perpendicular root models that simply sum root tensile strengths and consider these as an add-on factor to soil strength. A major limitation of such perpendicular models is that tensile strength and resistance is wrongly considered to be independent of soil type and moisture, and therefore variations according to these bank properties are omitted in conventional models. In reality, during mass failure of a streambank, some roots break, and some roots are pulled out of the soil intact; the relative proportions of roots that break or pull out are determined by a combination of soil moisture and shear strength. In this paper an equation to predict the frictional resistance of root–soil bonds was tested against field data collected at Long Creek, MS, under two soil moisture conditions. The root pullout equations were then included in the root-reinforcement model, RipRoot, and bank stability model runs for Goodwin Creek, MS, were carried out in order to examine the effects of spatial and temporal variations in soil shear strength and rooting density, on streambank factor of safety. Model results showed that at smaller root diameters breaking forces exceeded pullout forces, but at larger root diameters pullout forces exceed breaking forces. The threshold diameter between root pullout and root breaking varied with soil shear strength, with increasing soil shear strength leading to a greater proportion of roots failing by breaking instead of pullout. Root-reinforcement estimates were shown to reflect changes in soil shear strength, for example, brought about by variations in soil matric suction. Resulting Factor of safety (F_S) values for the bank during the period modeled ranged from 1.36 to 1.74 with 1000 grass roots/m², compared to a range of 0.97 to 1.37 for the non-vegetated bank. Root reinforcement was shown to increase bank stability under the entire range of soil moisture conditions modeled. However, the magnitude of root reinforcement varied in both space and time as determined by soil shear strength and soil moisture.     

“波特五力分析”视阙下的日本香菇产业发展特点研究

以"波特五力分析"理论为基础,结合实地调研结果和相关文献、统计数据,研究了日本香菇产业发展特点。认为影响日本香菇产业发展的外部因素呈现菌种品质稳定、替代食用菌增加、进口产品减少、消费市场预期萎缩的发展趋势,内部因素呈现鲜香菇供给量增加、市场集中度提升和外资生产主体增加的发展特点。建议我国应加强菌种知识产权保护力度,提升食用菌行业协会服务能力和加快开展工厂化生产技术研发。     

不同浓度NaCl胁迫对高粱幼苗SOD、POD酶活性的影响

用不同浓度的NaCl溶液,对5个高粱品种进行了苗期盐胁迫处理,测定了不同浓度盐胁迫下,不同品种幼苗叶片SOD、POD两种保护酶的活性。结果表明:随着盐胁迫的加剧,21A×R208、晋杂17 SOD活性变化为先升高而后下降;晋杂12则随盐胁迫的加剧活性逐渐上升;6A×R308、7A×R301两个品种的SOD活性逐渐下降。POD活性变化趋势较大。在盐胁迫过程中,21A×R208、6A×R308随盐胁迫的加剧POD活性先升高而后下降;7A×R301、晋杂12则随盐胁迫的加剧POD活性逐渐下降;晋杂17 POD活性则表现为先下降而后升高。由实验得出:21A×R208较其他品种耐盐性更强。     

基于“歧视经济学”的农村劳动力转移对城乡收入的影响

以＂歧视经济学＂的分析框架为基础,建立了一个农村劳动力向城市转移的模型,研究农村劳动力转移对城乡收入的影响。结果表明,农村劳动力向城市的转移能够提高城乡收入并在一定程度上缩小城乡收入差距,但由于我国城市资本存量远大于农村资本存量,农村劳动力转移并不能完全消除城乡收入差距。要提高我国农村的收入水平,缩小城乡收入的差距,政府必须双管齐下：一方面大力推动农村劳动力向城市的转移,改变目前城乡二元劳动力市场结构的状况;另一方面,加大对农村地区的投入,促进农村资本存量的增长,以便在劳动力转移的过程中进一步提高农村居民收入。