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1.
This paper is concerned with a farmer's decision on the timing of nitrogen fertilizer application. Analytical models are developed to determine the necessary conditions for the optimal timing of the application of nitrogen fertilizer. The models, coupled with an estimated cotton yield function, are used to assess a farmer's decision on the optimal application timing of nitrogen fertilizer in cotton production. The empirical results explain various observed application timings of nitrogen fertilizer being used in cotton production in Mississippi, USA, and provide an estimate of the cost to a farmer when he or she must comply with a restriction on the timing of the application of nitrogen fertilizer.The views expressed are those of the authors, and do not necessarily represent the policies of the US Department of Agriculture or the views of other US Department of Agriculture staff members 相似文献
2.
Wen-yuan Huang Russ W. Keim Yao-chi Lu N. D. Uri Terry Kelley 《Environmental Geology》1998,34(2-3):116-127
The economic and environmental consequences of soil nitrogen tests can have significant impacts on agricultural production.
Some of these are explored here. The pre-side-dress soil N-test is evaluated for a hypothetical farmer growing corn at the
ARS Sustainable Agriculture Demonstration Farm site in southern Maryland. For a farmer not currently using a soil N-test,
adoption of this technology can lead to the enhancement of net farm income and the reduction in nitrogen loss to the environment.
This will transpire only if the farmer is currently underestimating nitrogen carryover by more than 25% or applying nitrogen
fertilizer based solely on an expected plateau-yield goal.
Received: 13 February 1997 · Accepted: 13 May 1997 相似文献
3.
This paper is directed at providing an integrated framework that a regional authority should use when assessing the potential impacts of any policy initiative directed at improving groundwater quality. In particular, a policy model is developed relying on three decision components (a farm-level production decisions model, a household decisions model and a regional policy decision model) where the objective is one of identifying the trade-offs that a regional authority will be confronted with as it strives to balance the preferences of farmers and households while endeavoring to maximize net economic welfare. The basic rule developed indicates that the regional authority must choose a policy whereby any increase (decrease) in regional income is just equal to the decrease (increase) in net benefits to households.The views expressed are those of the authors and do not necessarily represent the policies of the U.S. Department of Agriculture or the views of other U.S. Department of Agriculture staff members. 相似文献
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河口地区感潮河段水动力过程复杂,为在突发水污染事故中合理制定精细化应急方案,基于环境流体水动力模型（EFDC）从水动力学角度对不同水文条件下深圳河口水域突发水污染事故的影响范围、时间及程度进行了数值模拟分析,提出了一种判断河口海湾地区主导水动力因素的分析方法。采用基于傅里叶变换的频谱分析法对事故中污染物输移扩散的主要影响因子进行了准确识别,并采用单因变量多因素方差分析法进行了印证。结果表明,潮流是感潮河段水动力过程的主要驱动因素,但在突发水污染事故中,深圳河各断面特征污染物浓度变化与陆地径流关系密切,径流是感潮河段内突发事故中特征污染物输移的主导动力因素。 相似文献
6.
Marielle Medeiros de Souza Maria do Carmo Cauduro Gastaldini Glaucia Ghesti Pivetta 《Environmental Earth Sciences》2017,76(24):833
Diffuse or nonpoint source (NPS) pollution results in different pollutant concentrations, which depend on river catchments, land use and precipitation events and may vary along a single event. This study aimed to assess NPS pollution loads of organic matter, nutrients, bacteria and heavy metals in four river catchments associated with different types of land use in Southern Brazil. Cluster analysis was used to identify similarities between basins and main component analysis (PCA) to identify the main variables that characterize diffuse pollution in each basin. The use and occupation of the soil were determinant in the formation of the clusters. The basins with rural characteristics formed one group, whereas the basin with urban characteristic generated another group. PCA suggests that changes in the water quality of the catchments in this study can be explained by organic pollutants and farming activities. The Rancho do Amaral catchment, with 55.8% of native forest, displayed the lowest NPS pollution load for all tested parameters. The Alto da Colina catchment, with the largest urban area and largest agricultural land use (50%), showed the highest NPS for all variables in the study, even though it has the smallest area. The differences in pollutant loads can be attributed to the intense degradation processes associated with anthropic activities, such as urbanization, agricultural activity and the discharge of effluents, which are different for each catchment. 相似文献
7.
《Geoforum》2016
This article examines the post-emancipation contests over agricultural land in the South Carolina Lowcountry – the coastal region surrounding the port city of Charleston – in the context of recent theorizations of plantation geographies and the racial politics of the US Department of Agriculture (USDA). In the aftermath of slavery, freedpeople in the Lowcountry were remarkably successful in securing control over their labor and access to land. The measure of relative autonomy that came with these gains spurred enormous anxiety for white elites, however, who realized that black control over land and labor threatened to upend the region’s racial hierarchy. I argue that plantation geographies persist through the white monopolization of land, and suggest that successfully challenging this historical trajectory depends on challenging liberal modes of improvement. 相似文献
8.
我国农村水环境非点源污染研究进展 总被引：8，自引：0，他引：8
农业非点源污染是导致水质污染最主要原因之一。我国农村非点源污染研究之初采用的研究方法主要有两种，一种是应用与水文模型紧密相关的模型来模拟和估算非点源污染负荷；另一种是通用土壤流失法。最近又提出了一种简便易用的流域非点源污染负荷估算方法－平均浓度法。将农业非点源污染负荷与3S技术结合、与水质模型对接用于流域水质管理成为农业非点源污染研究的新生长点。近年来，农村非点源污染研究也开始探索非点源污染负荷与河流水质模型接口问题。 相似文献
9.
US billion-dollar weather and climate disasters: data sources, trends, accuracy and biases 总被引：5，自引：4，他引：1
This paper focuses on the US Billion-dollar Weather/Climate Disaster report by the National Oceanic and Atmospheric Administration’s National Climatic Data Center. The current methodology for the production of this loss dataset is described, highlighting its strengths and limitations including sources of uncertainty and bias. The Insurance Services Office/Property Claims Service, the US Federal Emergency Management Agency’s National Flood Insurance Program and the US Department of Agriculture’s crop insurance program are key sources of quantified disaster loss data, among others. The methodology uses a factor approach to convert from insured losses to total direct losses, one potential limitation. An increasing trend in annual aggregate losses is shown to be primarily attributable to a statistically significant increasing trend of about 5 % per year in the frequency of billion-dollar disasters. So the question arises of how such trend estimates are affected by uncertainties and biases in the billion-dollar disaster data. The net effect of all biases appears to be an underestimation of average loss. In particular, it is shown that the factor approach can result in a considerable underestimation of average loss of roughly 10–15 %. Because this bias is systematic, any trends in losses from tropical cyclones appear to be robust to variations in insurance participation rates. Any attribution of the marked increasing trends in crop losses is complicated by a major expansion of the federally subsidized crop insurance program, as a consequence encompassing more marginal land. Recommendations concerning how the current methodology can be improved to increase the quality of the billion-dollar disaster dataset include refining the factor approach to more realistically take into account spatial and temporal variations in insurance participation rates. 相似文献
10.
我国在国民经济持续高速发展的同时也承受着能源消耗和环境恶化的巨大压力,水泥行业是耗能、排污大户,面临技术升级和节能减排的重大课题和历史任务。天津水泥工业设计研究院有限公司一直致力于我国水泥工业开发和提供新技术和新装备,推动我国水泥工业走资源节约型、环境友好型的新型工业化道路。近年来的新成果主要在新一代烧成节能技术、无球磨粉磨节能技术、余热发电技术、水泥工业处置工业废弃物和城市生活垃圾以及减少水泥生产有害粉尘和气体的排放等方面,代表了我国新型干法水泥生产技术和装备的先进水平。 相似文献
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M. ?mietanka J. Brzozowski D. ?liwiński K. Smarzyńska Z. Miatkowski M. Kalarus 《Frontiers of Earth Science》2009,3(2):175-181
Poland, like other EU countries, is obliged to implement the Water Framework Directive (2000/60/WE) by the end of 2015. The
main objective of the Directive is to provide normative quality of all water resources (surface, underground and coastal sea
waters). To reach this goal, reduction of water pollutant emission to the environment is needed. Our project focuses on pollution
from agricultural sources which share in global pollution, which is high and growing. This is due to both intensification
of agricultural activities and ignoring Agricultural Good Practice Code rules by farmers. In view of the above, this project
is expected to provide analysis of selected catchments; especially those exposed to agricultural pollution risk, and propose
adjustment strategies for new trends, still keeping in mind environment protection.
Our project concerns the area further called “sensitive area” (according to the rules of Regional Water Management Board in
Warsaw). A part of Zglowiaczka river catchments in central Poland was defined as sensitive area (125.3 km2) where reduction
of nitrogen and phosphorus run-off from agricultural land to water resources is especially needed. This is a typical agricultural
district characterized by good soil quality (predominance of black swampy soil with deep and fertile humus layers). Due to
this, it is the first and foremost high quality agricultural land, and almost forestless. The main topic of the research,
with the use of the SWAT model, is to propose different means for reduction of migration of P and N to surface waters. Another
problem is retention of water for actual and future irrigations. After model verification, calibration and validation, several
climatic changes and reclamation strategies will be tested and simulated by the model to find the most effective and profitable
solutions.
The project focuses on supporting administration and self-governmental organization in the implementation of effective strategies
of catchments management based on a modeling approach. This method enables analysis of trends and early warning system against
excessive pollution load. Enhancement of the ecological education level and activation of local population for implementation
of EU directives are also very important factors. 相似文献
13.
Natural Hazards - Agriculture is an important component of national economy in China, and agricultural production is also an important source of greenhouse gas emission. Based on the methods of... 相似文献
14.
T. T. Polgar J. K. Summers T. A. Cummins K. A. Rose D. G. Heimbuch 《Estuaries and Coasts》1985,8(2):125-135
An analytical method has been developed for evaluating the dependence of historical fish stock levels on estuarine pollutant loadings. Categorical time series regressions were used to derive preliminary relationships among previous levels of stock size, climatic variables, and pollution indicators. The analysis technique is used here to evaluate hypotheses on the effects of human population changes and dredging activity on stock histories of the Potomac estuary’s striped bass and American shad, for the period 1929 through 1976. Whereas climatic factors dominate striped bass dynamics compared to the two pollution variates tested, the American shad stock shows strong dependence on human population levels (but not on dredging activity) compared to climatic factors. Analyses of this type will be extended for examining the effects of specific pollutants on other important exploited stocks in five northeastern eatuaries. 相似文献
15.
Harold A. Perkins 《Geoforum》2011,42(5):558-566
The US Department of Agriculture Forest Service and the Wisconsin Department of Natural Resources coordinate the distribution of urban forestry grants to nonprofits and citizen groups. These granting agencies increased state funding during a period of neoliberal, fiscal austerity in order to channel ecosystem services provided by urban forests. Increased funding is an instance of rollout neoliberalism whereby the fiscally austere state builds market capacity to harness these services as part of an ecologically modernist agenda. A Gramscian perspective and data gathered from 20 in-depth interviews with foresters are used in this paper to theorize how rollout policy is deployed through urban forestry to extend market hegemony to new geographies. This is anything but a smooth process because the public’s perception of urban trees is highly varied. State bureaucracies must build civil sector capacity to educate people about the ecosystem services trees provide as market commodities. In doing so the state’s market-oriented regulatory legitimacy is consolidated through the apparently benign act of promoting urban forestry. This dialectical process limits participation in urban forestry because markets are inherently selective. Yet it potentially gives rise to an alternative political ecology of praxis beyond market ideology when grant recipients participate in the production of urban ecology and recognize their relationship with nature. 相似文献
16.
Antoinette M. Mannion 《GeoJournal》1993,31(4):347-354
Biotechnology is the manipulation of organisms to carry out specific processes. It has various applications that are relevant to many aspects of geography. At a fundamental level biotechnology is directed at manipulating energy flows, especially those in agriculture. Improved crop varieties, disease and pest control, as well as nutrient enhancement can all be achieved by biotechnology, culminating in increased agricultural productivity. There are significant environmental advantages though there are also constraints imposed by economic considerations. Mineral extraction, metal recycling and pollution abatement can also be improved by biotechnology which thus contributes to more efficient resource use and enhanced environmental quality. Food and fuel energy, notably biomass fuels, can also be so produced. The manifold implications of this technology for earth and social sciences thus require its inclusion in geographical studies. 相似文献
17.
云南个旧锡矿区大屯盆地土壤重金属污染与生态风险评价 总被引：9，自引：1，他引：8
土壤中的重金属直接影响农业安全生产,掌握不同耕地和土壤类型中重金属的污染程度可为削减生态风险提供依据。通过实地调查,对云南个旧锡矿区松树脚矿大屯盆地不同耕地和土壤类型的重金属含量,采用单因子指数法、内梅罗综合污染指数法进行污染评价,基于潜在生态危害指数法进行生态风险评价。结果表明,As、Cd、Cu、Cr、Ni、Pb和Zn七种元素中,As和Cd是大屯盆地农田土壤的主要污染因子,两者对污染程度的贡献率为97%,其中Cd的贡献率为68%;两者对生态风险的贡献率为87%。旱地重金属污染程度和生态风险大于水田,红壤中重金属的污染程度和生态风险大于红色石灰土。从空间来看,个旧大屯盆地重金属污染程度总体呈现从西南向东北逐渐降低的趋势。 相似文献
18.
生活垃圾填埋场渗滤液对潜层地下水污染的实验模拟分析——以北京北天堂垃圾填埋场为例 总被引：7，自引：0，他引：7
通过对北京市西郊南部北天堂垃圾填埋场渗滤污染组分在含水介质中运移的室内模拟实验分析，揭示了有机污染物等污染组分在含水介质中的运移转化规律，即有机污染物等污染组分在微生物的作用下得到降解；通过阻滞因子和水化学迁移率的计算，得出该含水介质对污染组分的阻滞能力较好。可用水化学迁移率粗略预测不同污染质锋面达到指定地点的时间，为垃圾填埋场地底部防渗层的设计和渗滤液对地下水污染程度的预报提供依据。 相似文献
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The Environmental benefits and costs of conservation tillage 总被引：1，自引：0，他引：1
Every production practice, including conservation tillage, has positive or negative environmental consequences that may involve
air, land, water, and/or the health and ecological status of wildlife. The negative impacts associated with agricultural production,
and the use of conventional tillage systems in particular, include soil erosion, energy use, leaching and runoff of agricultural
chemicals, and carbon emissions. Several of these impacts are quantified. The conclusions suggest that the use of conservation
tillage does result in less of an adverse impact on the environment from agricultural production than does conventional tillage
by reducing surface water runoff and wind erosion. Additionally, wildlife habitat will be enhanced to some extent with the
adoption of conservation tillage and the benefits to be gained from carbon sequestration will depend on the soil remaining
undisturbed. Finally, further expansion of conservation tillage on highly erodible land will unquestionably result in an increase
in social benefits, but the expected gains will be modest. 相似文献