Incentive systems for food quality control with repeated deliveries: Salmonella control in pork production

This paper presents a dynamic principal-agent analysis of incentivesystems for Salmonella control. The European Union will requireSalmonella testing from 2008. On the basis of the producer'sperformance history in controlling Salmonella, the incentivesystems analysed determine quality premiums to the producer,testing frequencies for hogs delivered, as well as charges tothe producer for testing and penalties. Using cost estimatesand technical parameters, we evaluate two dynamic incentivesystems. We also assess the impact of ownership structure onperformance. The more efficient incentive system economiseson testing costs by reducing the probability of testing in responseto a favourable production history and is preferred under allownership structures.     

Estimating Intertemporal Preferences for Natural Resource Allocation

In this article, we show how the degree of risk aversion, discounting, and preference for intertemporal substitution for a natural resource manager can be structurally estimated within a recursive utility framework. We focus on the management of a reservoir in California, and test the data for consistency with a recursive utility model specification versus standard time-additive separability. The results show that the data are consistent with a risk-averse manager with recursive preferences. The data also reject time-additive separability, with or without risk aversion, such as the standard constant relative risk aversion utility model. The improvement in model fit when recursive preferences are used is notable.     

Habitat and Open Space at Risk of Land-Use Conversion: Targeting Strategies for Land Conservation

Funds available to purchase land and easements for conservation purposes are limited. This article provides a targeting strategy for protecting multiple environmental benefits that includes heterogeneity in land costs and probability of land-use conversion, by incorporating spatially explicit land-use change and hedonic price models. This strategy is compared to two alternative strategies that omit either land cost or conversion threat. Based on dynamic programming and Monte Carlo simulations with alternating periods of conservation and development, we demonstrate that the positive correlation between land costs and probability of land-use conversion affects targeting efficiency using parcel data from Sonoma County, California.     

Optimal management of a flammable forest providing timber and carbon sequestration benefits: an Australian case study*

In deciding to keep or fell a forest stand given its age, the risk of loss of timber through wildfire is an important consideration. If trees also have value from sequestration of carbon, another effect of fire is the unplanned loss of stored carbon. Factors affecting the decision to keep or fell trees, and how much to spend on fire protection, are investigated using stochastic dynamic programming, using carbon sequestration in stands of mountain ash in Victoria as a case study. The effect of treating sawlogs as a permanent carbon sink after harvesting is explored.     

Spatial Dynamics of Water and Nitrogen Management in Irrigated Agriculture

Dynamic optimization of crop production with nonuniform irrigation and nitrogen carryover and leaching is considered. A production function system with thresholds, plateau maximum, and yield reduction is estimated from experimental data; rapid convergence to a steady-state is observed. Spatial variability implies a 40% increase in applied water and a six-fold increase in nitrate emissions, while dynamic optimization has more modest impacts. Nitrate emission control is accomplished primarily through reduced applied water, illustrating a strong cross-policy effect. Significant levels of water conservation and nitrate pollution control are achieved at relatively low cost with traditional irrigation systems and baseline conditions.     

土地利用现状遥感更新外业调查方法研究

以河南省偃师市为例,研究了土地利用现状遥感更新外业调查的方法。首先对原始影像进行预处理与校正,制作正射影像图;利用动态规划法确定最优调查路径;在严格的精度控制基础上,采用实地调绘的方法,分别调查境界与权属、地类图斑、线状地物、零星地类、耕地坡度与田坎系数。结果证明：外业调查能有效地解决内业判读过程中出现的多种问题。     

Managing Urban Deer

Conflicts are emerging between humans and wildlife populations adaptable to the high density of humans found in urban and suburban areas. In response to these threats, animal control programs are typically designed with the objective of establishing and maintaining a stable population. This article challenges this view by studying the management of urban deer in Irondequoit, NY. Pulsing controls can be more efficient than steady-state regimes under a wide range of conditions in both deterministic and stochastic environments, but potential gains can be dissipated by management constraints. The effect of citizen opposition to lethal control methods is also investigated.     

Stochastic Rangeland Use under Capital Constraints

The stocking density on Kazakhstan's extensive rangelands is well below traditional levels. To analyze dynamic flock performance, we develop a stochastic dynamic programming model for livestock systems with stochastic forage production. The model contains continuous five state and 12 control variables, allowing improved characterization of the biophysical relationships and economic tradeoffs inherent in such systems. Most Kazakhstan herders have restricted access to capital. The model indicates that the cost of capital strongly affects flock size and productivity. We conclude that capital constraints are important to explaining the current low stocking density. Improving capital markets in rural areas warrants policy attention.     

水肥一体化技术的环境效应与经济效应分析——基于山东省苹果种植户的调研数据

目的 绿色农业技术的环境与经济收益核算,对于推进技术应用、解决农业面源污染问题和实现生态文明建设具有重要的参考价值。究竟绿色农业技术有没有顺利实现农户的经济目标与社会的环境目标？现有研究诸多争议与困惑。方法 文章以水肥一体化技术为例,基于山东省649份苹果种植户的实地调查数据,借助内生转换模型,从微观层面探讨了水肥一体化技术的环境效应和经济效应。结果 （1）总体来看,农户采纳水肥一体化技术实现了节肥增收的目的。（2）采纳水肥一体化技术后,样本农户能够节约化肥施用量11.79%~20.98%,提高农产品收入8.15%~9.07%。（3）不同规模农户采纳水肥一体化技术的节肥增收效应存在显著差异。对于采纳水肥一体化技术的规模户而言,其化肥减量作用强度明显高于小规模农户。与此同时,采纳水肥一体化技术只对规模户有明显的农产品增收作用。结论 注重完善市场流通机制下农产品质量监督体系,使绿色农产品能够获得质量溢价的收益。同时创建有利于水肥一体化技术推广应用的土地规模条件,获得规模化带来的节肥增收效应。推动外部性内部化补偿制度实施,政府对具有正外部性行为的农户给予补偿。     

基于种养业融合的大兴安岭农垦种养结构优化研究

[目的]种养业协调发展是促进我国农业供给侧结构性改革的重要方面。文章以大兴安岭农垦的种养业结构优化为研究对象,针对大兴安岭农垦种养业结构发展失衡等问题,构建了基于种养业协调发展的多目标线性规划模型。[方法]根据Matlab编程求解,模拟提出了该地区的种养业优化方案,并阐明了促进种养业协调发展的对策措施。[结果](1)通过优化调整,大兴安岭农垦种养结构得到优化,与2013~2015年平均相比,粮食作物种植面积减少2.26万hm~2,经济作物种植面积增加了1.97万hm~2,其中大豆种植面积减少1.16万hm~2,玉米种植面积减少1.96万hm~2,养殖业饲养规模大幅度增加,其中猪的养殖数量增加5.89倍,牛增加16.62倍,羊增加1.57倍,家禽增加了10.2倍。(2)通过优化调整,与2013~2015年平均水平相比,种养业综合效益显著提升,提高了48.81%,其中经济收益增加了93.92%,社会效益减少了6.06%,生态效益提高了6.13%,其中总化肥施用量减少13.15%,总作物需水量减少5.74%、相对生态价值降低0.77%。[结论]为进一步推进大兴安岭农垦种养业结构调整,迫切需要加强宣传,探索种养业结合发展新模式,加快废弃物处理新技术推广,制定扶持政策,促进种植业和养殖业形成良性循环。