Ranking Crop Yield Models: A Comment

This comment discusses key specification issues that may have affected the performance and, therefore, the ranking of parametric models that were compared in a recent AJAE article. A procedure to obtain the most flexible parametric model specification possible, given the particular probability distribution function on which the model is based is presented. These specifications also allow for standardized and, therefore, more valid comparisons across parametric models that are based on different probability distributions. Finally, the comment cautions against generalization of the rankings in that AJAE article and recommends that these more flexible specifications be adopted in future comparisons and applications.     

基于加权马尔柯夫链的粮食单产风险预测——以辽宁省为例

利用随机过程中的马尔柯夫链原理预测粮食单产风险问题。针对粮食年单产量为相依随机变量的特点,提出以规范化的各阶自相关系数为权,运用加权的马尔柯夫链来预测未来粮食年单产量变化状况,并以辽宁省26年统计资料为实例对该方法进行具体应用。     

A Comparative Evaluation of Yield Risk Reductions with Alternative Crop Insurance Programs in Manitoba

Three crop insurance programs are evaluated in terms of their effectiveness of yield risk reductions for 371 Manitoba farms. The examination is first conducted with a proposed index method, with which the relative yield risk reduction magnitude is calculated and compared for each farm under each alternative program. The generalized stochastic dominance (GSD) methodology is also used to provide an alternative analytical framework in analyzing producers’relative preferences among those alternatives by comparing the net yield distributions generated by each program for each farm. The results suggest that, given an actuarially sound basis, the filly individualized crop insurance (FI) program is the most favorable choice for risk-averse producers. The area coverage and individual indemnity program (IA) is generally the second best option. The full area crop insurance program (FA) is least preferred by risk-averse farmers.     

The Simultaneous Hedging of Price Risk, Crop Yield Risk and Currency Risk

This study analyzes the joint hedging decision of a Canadian firm in U S. based price and yield futures. The key results of this study are that jointly hedging price and yield can reduce more revenue risk than hedging only with price futures. For offshore hedgers, the evidence shows that foreign exchange risk is important and can be reduced by jointly hedging in the currency futures markets.
Nous analysons les décisions de couverture multiple d'une entreprise canadienne contre les risques afférents aux prix et aux rendement à terme. Les conclusions clés de l'étude sont qu'une couverture simultanée contre ces deux risques peut accorder une meilleure protection qu'une couverture établie seulement contre les risques des prix à terme. Pour ceux qui font affaire avec un pays étranger, l'expérience montre que le risque afférent au taux de change est important et qu'il est possible de le réduire en se couvrant en měme temps contre les risques affectant la valeur à terme de l'argent.     

Product Differentiation and Representative Agent Import Demand Systems: A Reconsideration and Reconciliation

Product differentiation is the fundamental assumption employed to supposedly generate the import demand systems found in the literature. This paper shows that the assumption of product differentiation does not generate the import demand systems found in the literature, unless two additional assumptions are made. A procedure is demonstrated for testing these assumptions. By showing and exploiting the formal relationship between the "old" theory of demand and the "new" (Lancaster) theory of demand, the results are applicable to any demand system.
La différentiation des produits est l'hypotèse fondamentale qui sous-tendrait les nombreux systèmes de demande à l'importation qu'on retrouve dans la bibliographie économétrique des vingt dernières années. Or dans le présent article, il est démontré que cette hypothèse n'est vraiment valable que si on la complète de deux suppositions auxiliaires. Une démarche est proposée pour tester ces deux propositions. En dégageant et en exploitant le rapport formel qui existe entre l'«ancienne>> théorie et la «nouvelle>> théorie (Lancaster) de la demande, on montre que les résultats peuvent s'appliquer à n'importe quel système de demande.     

投资项目财务评价参数测度方法及其应用--以种植业行业为例

本文运用资本资产定价模型和加权平均资本成本模型来测度投资项目财务基准收益率，其他财务评价参数的测度则是采用行业历史数据统计分析法，最后对测度结果进行分析并运用经验判断方法给出行业财务评价参数的建议值。     

Pre-Harvest Price Expectations for Corn: The Information Content of USDA Reports and New Crop Futures

This article examines the puzzle of why futures prices continue to react to USDA crop reports despite the fact that reports appear to be no longer newsworthy, that is, provide no better production estimates than private forecasts. The information value of reports is measured in terms of their influence on rational agents' harvest-time corn price expectations, which are uncovered using a Hamilton-type modeling approach. Results show that reports are still newsworthy, as they would contribute to agents' price expectations if released a day early. Thus futures price reactions, which closely reflect price expectations, are rational and consistent with efficient markets hypothesis.     

Producers Get Squeezed up the Farming Food Chain: A Theory of Crop Portfolio Composition and Land Use

There are a number of seemingly contradictory trends in the structure of American agriculture. For example, total revenues from agriculture in the United States continue to increase nearly every year, yet the total acreage of land in farms continues to decrease. This article presents an explanation using portfolio theory that is consistent both with the trends and with rational behavior of individual producers. The results have implications for commodity markets, land prices, and, in the long run, for the economic viability of American production agriculture.     

A Methodology for Farm-Level Economic Analysis of Soil Erosion Effects Under Alternative Crop Rotational Systems in Ontario

Multiperiod linear programming techniques are used to evaluate comparative profitabilities and soil erosion rates for corn grown monoculturally and in rotation with a) soybeans, b) soybeans and oats, c) barley, and d) alfalfa on moderately sloping land with medium loam soils in southern Ontario. Attention is focussed on the case of a highly leveraged recent entrant to farming with heavy debt servicing needs and potential cash flow constraints. Monocultural corn was found to be more profitable than any of the rotational systems, with corn-soybeans rotations the next most profitable and corn-barley rotations the least profitable. Corn-soybeans caused the highest soil erosion, followed by continuous corn, with corn-alfalfa rotations causing the least. Les techniques de programmation linéaire multipériode sont utilisées pour évaluer et comparer les niveaux de profit et les taux d' érosion de sols agricoles moyennement argileux pour des systèmes de production de grandees cultyres localiées dans le sud de l' ontario et produisant, soit du mais en régime de monoculture, soit du mais en rotation avec: a) du soja, b) soja et avoine, c) orge. et d) de la luzerne plantée sur des terrains à pentes modérées. L' analyse developpée dans cet article met l' accent sur des agriculteurs récemment installés, disposant de beaucoup d' actifs, mais également, ayant des besoins énormes d' emprunts et, par conséquent, soumis à des contraintes potentielles sur leurs cash-flows. Les résultats obtenus montrent que le système de production, mais-monoculture, est le plus viable de tous les systèmes etudies. Parmi les systemes de production reposant sur une rotation culturale, il s' avère que celui combinant maïs et soja vienne en seconde position, tandis que un régime cultural fondé sur une rotation maïs et orge donne les pires resultats. Pour ce qui concerne des taux d' erosion des sols, la rotation maïs-soja cause les plus gros dommages. ensuite suivie par le système de production, maïs-monoculture. Finalement, les taux d' erosion les plus faibles ont été obtenus pour la rotation culturale, maïs-luzerne.     

International and Institutional R&D Spillovers: Attribution of Benefits among Sources for Brazil's New Crop Varieties

Reported rates of return to agricultural R&D are generally high, but they are likely to be biased, particularly because of attribution problems—mismatching research benefits with costs. The importance of attribution biases is illustrated here with new evidence for Brazil. During 1981–2003, varietal improvements in upland rice, edible beans, and soybeans yielded benefits of $14.8 billion in present value (1999 prices) terms. Attributing all of the benefits to Embrapa, a public research corporation accounting for more than half of Brazil's agricultural R&D spending, the benefit-cost ratio would be 78:1. Under alternative attribution rules, the ratio drops to 16:1.     

A Statistical Analysis of Wheat Price Fluctuations in England: 1685–1850

For some commodities and time periods, the analysis of price fluctuations must necessarily rely on the existence of price data alone. A theory applicable in such circumstances is outlined for commodities that are storable, traded in open markets and subject to net supply shocks which are heterogeneously distributed across the months of the year. Market prices are predicted to vary autoregressively except at times when wheat stocks become negligible and observed market prices exceed threshold prices (which may themselves differ across months). The model is applied to a monthly time series of wheat prices for southern England from 1685 to 1850. The autoregressive parameter and the threshold prices are estimated, substantial empirical support being found for the models tested. Historical events from the late seventeenth century through to the continental wars in the late eighteenth and early nineteenth centuries are used to illustrate the mechanisms underlying the theory.     

从国内核心期刊文献统计分析透视森林公园研究的发展

以中国期刊全文数据库为资料来源,检索1992年1月～2011年12月期间在核心期刊发表的森林公园的文章,统计分析这些文献在时间、地区、发文期刊、作者、发文单位、被引用次数、内容等方面的情况,透视国内森林公园研究近20年的发展状况。     

橡胶农场经济发展状况评价的统计分析

本文根据橡胶农场经济发展状况和实证统计数据,运用因子分析和聚类分析方法,对2003年海南农垦79个橡胶农场的经济发展状况进行了评价和分类,为制订海南农垦经济发展战略提供参考。     

2013年国土资源领域科技论文统计分析

以2013年国土资源部相关机构发表科技论文为例(按第一作者的第一机构进行统计),基于科学引文数据库网络版(SCI-E)、中国科学引文数据库(CSCD)扩展版和中国地质文献数据库(GDS)3个数据库,利用文献计量统计方法,从科技论文的年度分布、机构分布、学科分布、期刊分布作者分布等情况进行了统计分析,并跟2012年的论文分布情况作了对比分析,从一个侧面了解国土资源部相关机构2013年度科研状况。     

Crop diversification in Thailand: Status,determinants, and effects on income and use of inputs

Following the national policy, the Department of Agriculture of Thailand has implemented a crop diversification program in several provinces of the country. This study, which was conducted in Nakhon Pathom Province, analyzed the extent of crop diversification and its determinants using primary information collected from 245 farm households using a structured questionnaire, and from selected farmer leaders and agricultural development officials. The study also assessed the effects of crop diversification on income and the inputs used. The findings of the study revealed that nearly three fourths of the land is still being used for rice mono-cropping, indicating little success in the promotion of the crop diversification program. Paddy fields, including farms for cultivating rice under mono-cropping and diversified system, still account for 90% of the total farmland in the country. The limited impact of the program on the farming sector is attributed primarily to the variation in land and labor resources available at the farmers’ disposal as well as soil suitability. The farmers’ attendance in training and interaction with farmer groups are the other influential factors. Although cropping diversification has provided attractive financial return particularly to the small farmers, it has also accelerated the use of inorganic fertilizers and pesticides. Broad policy instruments are therefore suggested for the effective implementation of future crop diversification programs in Thailand and perhaps elsewhere in Southeast Asia.     

供需视角下的农村信息传播:国内外研究述评与展望

伴随互联网+时代下信息的加速传播以及新媒介的不断涌现,农村地区的信息传播机制也在发生着深刻改变。农村信息传播在推动农业创新发展、解决农民信息不对称问题、缩小城乡信息鸿沟等方面的作用,已经得到国内外有关专家和学者的认同。本文基于对国内外农村信息传播相关文献的评价、分析和比较,从供需视角系统地梳理了国内外相关前沿研究的观点与成果。研究综述表明,在农村信息需求方面,国内外有关文献比较侧重于分析农村信息的类型、来源、获取渠道等内容,对农村信息受体的接受能力,及该接受能力对农村发展作用等的研究有待深入;农村信息供给层面的研究成果则多集中于分析农村信息的供给形式、供给平台和供给策略等,需要强化对农村信息供给适宜性和可行性的研究。通过对比国内外相关研究成果,笔者针对国内相关研究在理论、方法、策略等方面的不足,提出对农村信息传播的研究应引入多个学科的理论和方法,重点关注社会网络环境变化,聚焦个体行为逻辑、信息供需对接、传播策略优化,以及信息传播助推农村发展等主题。     

国土资源大调查统计数据质量与可靠性之我见

国土资源大调查是模拟市场运作的国家基础性、公益性、战略性地质工作,它的直接成果是国土资源大调查统计数据,就统计数据本身而言,质量和可靠性是衡量其使用价值的重要尺度.文章阐述了提高国土资源大调查统计数据质量与可靠性的必要性,分析了影响其质量与可靠性的因素,提出如何提高国土资源大调查统计数据质量的对策.     

Impact of Rising Energy Costs on Traditional and Energy Intensive Crop Production: the Case of Nicaragua

Fossil-based agricultural input price increases have shifted the competitive advantage from energy intensive agriculture to traditional agriculture in Nicaragua. A decline in output prices would make energy intensive agriculture uneconomical and reduce aggregate output of four major food crops, posing serious policy dilemmas for national development.
L'Agriculture Nicaraguaise a subi une augmentation du prix des facteurs de production issus d'énergie fossile, conduisant à un déclin de la compétitivité du secteur agricole "moderne" au profit du secteur traditionnel. Une diminution du prix des produits agricoles réduirait la rentalilité de I'agriculture "moderne" et entraînerait une chute de la production nationale des quatre principales récoltes, posant de sérieux dilemmes politiques pour le développement économique du pays.     

Structure of Public Support for National Agricultural Research Systems: A Political Economy Perspective

This paper initiates development of a set of stylized facts concerning the structure of public support for national agricultural research systems (NARS) within a neoclassical political economy framework. The aim is to place public funding of NARS in the broader context of the overall level of direct government assistance to agriculture. Using a newly constructed data set on NARS expenditures over the 1970-85 period, we observe a growing disparity in agricultural research intensity ratios, which measure the level of public support for NARS in relation to agricultural gross domestic production (Aggdp ) between low and high-income countries. This growing disparity appears to be driven by much larger increases in support for agricultural research by high-income countries, coupled with a significantly slower growth in the size of their agricultural sector, despite the propensity of low and middle-income countries to increase real support to agricultural research. As per-capita incomes rise the public agricultural expenditure ratio, which measures public expenditures on agriculture relative to the size of the agricultural sector, Aggdp , increases substantially. Public expenditures on agriculture were indexed on agricultural and non-agricultural populations to give a rough indication of the increasing incentives for rural 'distributional coalitions' to seek a redistribution of public expenditures in their favor. A relative research expenditure (rre ) ratio is developed, which measures the proportion of total public expenditure on agriculture spent on agricultural research. It provides an indication of the relative importance given to research on agriculture within the constraints imposed by overall public spending on agriculture. In contrast to the agricultural research intensity ratios, the rre ratios suggest that agricultural research appears to command as large a share of the public purse devoted to agriculture in low and middle-income countries as it does in high-income countries. Expectations derived from the neoclassical political economy literature that research may have fared relatively better in high compared with low-income countries were not supported by the data.