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排序方式: 共有313条查询结果,搜索用时 183 毫秒
51.
西南涌是广东佛山一条重要的纳污河流,其水质长期未能稳定达标。与大部分的城市被污染的内河涌不同,西南涌的主要污染来自于农业生产。本文对西南涌污粢的成因进行了分析。提出了西南涌治污的短期策略和长期策略。 相似文献
52.
The primary goal of the paper is to show the validity of investing capital in fertilizer–mining companies, both from a market return perspective for individual or institutional investors, or from a hedging standpoint for insurance companies and other economic actors exposed to inflation risk and high agricultural commodity prices. After providing some elements on the fertilizer market and describing the joint dynamics of corn, wheat and fertilizer prices over the last decade, we analyze an exhaustive sample of listed fertilizer producing companies over the years January 2004–December 2012. We show that their shares generated quite good returns over the whole period and extremely high ones during the years January 2004–December 2007, both in absolute terms and compared to their betas. We also exhibit that these returns display higher sensitivities to major agricultural indexes than to the World Bank Fertilizer Index, making the hedging argument quite compelling. 相似文献
53.
提出建立农业面源污染动态监控系统的技术构思,构筑了“辽宁省农业面源污染动态监控系统”的功能及运行机制的构架,阐述了推进此动态监控系统完善的研究方案与系统实施的保证措施。 相似文献
54.
文中简要叙述了农村能源是农业生态系统和农业环境保护的重要内容之一。指出新疆农村能源缺乏,结构不合理,热效率低,浪费大等,是造成新疆干旱地区生态环境不断恶化的主要原因之一。加强领导,提高能源意识,制定能源发展规划,大力发展农村能源产业和大力营造薪炭林,并增加农村商品能源供应,积极开发利用新能源,解决农村能源建设资金问题。 相似文献
55.
56.
Global emissions trading allows for agricultural measures to be accounted for the carbon sequestration in soils. The Environmental Policy Integrated Climate (EPIC) model was tested for central European site conditions by means of agricultural extensification scenarios. Results of soil and management analyses of different management systems (cultivation with mouldboard plough, reduced tillage, and grassland/fallow establishment) on 13 representative sites in the German State Baden-Württemberg were used to calibrate the EPIC model. Calibration results were compared to those of the Intergovernmental Panel on Climate Change (IPCC) prognosis tool. The first calibration step included adjustments in (a) N depositions, (b) N2-fixation by bacteria during fallow, and (c) nutrient content of organic fertilisers according to regional values. The mixing efficiency of implements used for reduced tillage and four crop parameters were adapted to site conditions as a second step of the iterative calibration process, which should optimise the agreement between measured and simulated humus changes. Thus, general rules were obtained for the calibration of EPIC for different criteria and regions. EPIC simulated an average increase of +0.341 Mg humus-C ha−1 a−1 for on average 11.3 years of reduced tillage compared to land cultivated with mouldboard plough during the same time scale. Field measurements revealed an average increase of +0.343 Mg C ha−1 a−1 and the IPCC prognosis tool +0.345 Mg C ha−1 a−1. EPIC simulated an average increase of +1.253 Mg C ha−1 a−1 for on average 10.6 years of grassland/fallow establishment compared to an average increase of +1.342 Mg humus-C ha−1 a−1 measured by field measurements and +1.254 Mg C ha−1 a−1 according to the IPCC prognosis tool. The comparison of simulated and measured humus C stocks was r2 ≥ 0.825 for all treatments. However, on some sites deviations between simulated and measured results were considerable. The result for the simulation of yields was similar. In 49% of the cases the simulated yields differed from the surveyed ones by more than 20%. Some explanations could be found by qualitative cause analyses. Yet, for quantitative analyses the available information from farmers was not sufficient. Altogether EPIC is able to represent the expected changes by reduced tillage or grassland/fallow establishment acceptably under central European site conditions of south-western Germany. 相似文献
57.
F. Le Ber C. Lavigne K. Adamczyk F. Angevin N. Colbach J.-F. Mari H. Monod 《Ecological modelling》2009
Neutral landscape models are not frequently used in the agronomical domain, whereas they would be very useful for studying given agro-ecological or physical processes. Contrary to ecological neutral landscape models, agricultural models have to represent and manage geometrical patches and thus should rely on tessellation methods. We present a three steps approach that aimed at simulating such landscapes. Firstly, we characterized the geometry of three real field patterns; secondly, we generated simulated field patterns with two tessellation methods attempting to control the value of some of the observed characteristics and, thirdly, we evaluated the simulated field patterns. For this evaluation, we considered that good simulated field patterns should capture characteristics of real landscapes that are important for the targeted agro-ecological process. Real landscapes and landscapes simulated using either a Voronoi or a rectangular tessellation were thus compared when used as input data within a gene flow model. The results showed that neither tessellation method captured field shapes correctly, thus leading to over or (small) under estimation of gene flow. The Voronoi tessellation, though, performed better than the rectangular tessellation. Possible research directions are proposed to improve the simulated patterns, including the use of post-processing, the control of cell orientation or the implementation of other tessellation techniques. 相似文献
58.
Novel lightweight composite foams based on recycled polypropylene reinforced with cellulosic fibres obtained from agricultural residues were prepared and characterized. These composites, initially prepared by melt-mixing recycled polypropylene with variable fibre concentrations (10-25 wt.%), were foamed by high-pressure CO2 dissolution, a clean process which avoids the use of chemical blowing agents. With the aim of studying the influence of the fibre characteristics on the resultant foams, two chemical treatments were applied to the barley straw in order to increase the α-cellulose content of the fibres. The chemical composition, morphology and thermal stability of the fibres and composites were analyzed. Results indicate that fibre chemical treatment and later foaming of the composites resulted in foams with characteristic closed-cell microcellular structures, their specific storage modulus significantly increasing due to the higher stiffness of the fibres. The addition of the fibres also resulted in an increase in the glass transition temperature of PP in both the solid composites and more significantly in the foams. 相似文献
59.
Extractable atrazine and its metabolites (hydroxyatrazine, deethylatrazine and deisopropylatrazine) were evaluated in agricultural
soils from the temperate humid zone (Galicia, NW Spain) under laboratory conditions. The experiment was performed with five
soils with different properties (organic C, soil texture and atrazine application history), both unamended and treated with
atrazine at field application rate. Measurements of the atrazine compounds were made at different time intervals (1, 3, 6,
9 and 12 weeks) during a 3-month incubation period. Results showed that only hydroxyatrazine was detected in the extractable
fraction of the unamended soils, with values remaining relatively constant throughout the incubation period. Atrazine addition
notably increased the concentration of the parent compound and its degradation products; deisopropylatrazine and hydroxyatrazine
were the main metabolites detected in the extractable fraction of the treated soils, whereas deethylatrazine was not detected.
After 7 days incubation, values of total extractable residues, expressed as percentage of initially added atrazine, ranged
from 75 to 86% (25–68% of atrazine, 7–11% of hydroxyatrazine and 9–57% of deisopropylatrazine). The values decreased rapidly
during the first 3 weeks of incubation, showing values of 2–8% in soils with higher atrazine application and from 28 to 30%
in soils with lower application history. At the end of the incubation, 2–8% of total extractable residues were still detected
(0–4% of atrazine, 2–3% of hydroxyatrazine and 0–2% of deisopropylatrazine), indicating a residual effect of atrazine addition.
These variations in the extractable fraction indicated that most added atrazine was rapidly degraded, especially in soils
with higher application history. 相似文献
60.