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21.
K.A.S. Murshid 《Journal of Agrarian Change》2015,15(4):480-498
This paper explores the unaddressed question of how the large, complex paddy‐rice market in Bangladesh is able to transform itself and evolve, in the face of changing risks and incentives, into a better‐functioning market system. It notes significant but opposing trends over two decades in different areas, particularly in terms of market structure, trade circuits and exchange relations. Evidence of a sharp decline in tied transactions points to the growing importance of impersonal exchange. The underlying causes of these changes are explored, with particular reference to microfinance, remittances, rural roads and mobile telephony. 相似文献
22.
[目的]快速、准确地诊断水稻叶片氮素营养状况,为水稻氮肥精准管理提供依据。[方法]以江西省农科院8种不同施肥处理的晚稻为研究对象,于主要生育期同步测定了水稻冠层光谱反射率及叶片全氮浓度(Leaf Nitrogen Concentration,LNC),系统分析了原始光谱反射率、一阶微分光谱、\"三边\"参数以及由350~1 350nm两两波段组合的差值(SD (Rλ1,Rλ2))、比值(SR (Rλ1,Rλ2))及归一化(ND(Rλ1,Rλ2))光谱指数与水稻LNC的相关关系,筛选出敏感参数,并以之为自变量构建了水稻LNC的传统预测模型,另外构建不同指标个数的多元线性与BP神经网络模型,并对模型进行验证。[结果](1)水稻LNC与一阶微分光谱在751nm处的相关性最高(r=0. 822);(2)\"三边\"参数中的红边面积SDr与LNC的相关性较高(r=0. 687);(3) 750nm附近的红边波段与近红外波段差值组合、550nm附近的绿光波段与近红外波段的比值及归一化差值组合与水稻LNC的相关性较高,以SD (R752,R751)、SR (R534,R1 350)和ND (R534,R1 349)表现最好,相关系数分别为0. 827、-0. 790和0. 788;(4)传统回归模型中以SD(R752,R751)构建的一元线性模型最佳(RC2=0. 665、RV2=0. 750、RMSEV=0. 4%、RPD=2. 034);(5)利用5个指标((R'751、SDr、SD (R752,R751)、SR (R534,R1 350)、ND (R534,R1 349))经逐步回归筛选出的2个指标SD ((R752,R751)和SR (R534,R1 350))构建预测水稻氮素的BP神经网络模型,预测效果最佳,其验证参数值分别为R2=0. 859、RMSEV=0. 302%和RPD=2. 669。[结论]基于单指标构建的传统线性模型计算过程简单但精度略低,而基于2个指标(SD (R752,R751)、SR (R534,R1 350))构建的BP神经网络模型预测精度高于该2指标构建的多元线性模型,表明在指标适合的情况下,BP神经网络对氮素具有较好的预测能力,是一种快速准确估算水稻叶片全氮浓度的方法。 相似文献
23.
[目的]气候变化对我国粮食生产造成巨大损失,传统农业保险存在较多问题,天气指数农业保险作为金融创新工具,成为转移农业天气风险的有力路径。[方法]文章在分析降雨量指数保险合约设计思路的基础上,依照天气指数保险合约定义,选取稻谷生长期每日降水的累积降雨量作为天气指标,采用经济—气候模型和湖北省78个县市的面板数据,按风险区域分别设计了干旱指数保险合约和暴雨灾害指数保险合约。[结果]虽然湖北省全省累积降水的影响总体是负向的,但累积降水量对稻谷单产在十堰、襄阳等干旱区域的边际影响是正向的、显著的,累积降水量在暴雨集中区域江汉平原地区、咸宁市及辖内县市,有着显著的负向影响。[结论]气候变化对粮食生产的影响显著,根据面板数据的估计结果,有必要按不同的风险区域分别设计天气指数保险合约。该文的研究在天气指数保险设计方面做出了一定的探索,进一步使天气指数保险合约成为转移农业天气风险的有力创新工具。 相似文献
24.
Efficiency and Technical Change in the Philippine Rice Sector: A Malmquist Total Factor Productivity Analysis 总被引:1,自引:0,他引:1
Chieko Umetsu Thamana Lekprichakul Ujjayant Chakravorty 《American journal of agricultural economics》2003,85(4):943-963
Regional differences in total factor productivity, efficiency, and technological change in the Philippine rice sector are examined for the post-Green Revolution era. Malmquist productivity indices were constructed for 1971–90 and were decomposed into efficiency and technological change. The average annual Malmquist productivity growth was only slightly positive. Productivity growth was negative during the early 1970s, and was followed by a period of positive growth. Growth was negative again in the late 1980s. The period of positive growth coincided with the introduction of new rice varieties while the declines are likely to have been caused by intensification of rice production in lowland farming systems. Certain regions such as Central Luzon, Western Visayas, and Southern and Northern Mindanao had higher rates of technological change than others. This may be due to higher investments in infrastructure and education, increased adoption of tractors, and a better agroclimatic environment. 相似文献
25.
We employ a non‐parametric approach, data envelopment analysis, to estimate the technical and irrigation efficiency of rice farms in the Punjab Province of Pakistan. We use a cross‐sectional dataset of 80 rice growers, including 45 tube‐well owners and 35 water buyers. Mean technical efficiency scores show that tube‐well owners and water buyers are operating at fairly high efficiency levels, indicating that access to technology is not a major constraint. However, irrigation inefficiency is pronounced, with water buyers being more inefficient than tube‐well owners. A bootstrap truncated regression is used to investigate the determinants of technical and irrigation efficiency. We suggest that groundwater management policies should be designed to address efficiency enhancing factors such as knowledge of crop water consumption requirement, better credit opportunities, outreach extension services and training programs. 相似文献
26.
The present paper describes the benefits and costs, in qualitative terms, of managing food price instability in Asia in the context of promoting economic growth and poverty reduction to improve food security. The experience of Asian governments in actual practice with price stabilization is discussed in the context of managing an efficient transition to market‐mediated food security. Recent experience in Indonesia, where a sharp increase in rice prices (caused by a ban on rice imports) pushed 4 million people into poverty, provides continued motivation for the analytical story in this paper. 相似文献
27.
炎帝神农氏与湖南稻作农业的起源 总被引:1,自引:0,他引:1
炎帝神农氏是中华民族的始祖,也是稻作农业的创始人。据史实记载,炎帝神农氏在上古代农业方面作出了突出贡献。特别在史前稻作农业方面的贡献尤其突出。据现代考古发掘表明,与炎帝神农同时代的稻作农业非常发达。综合分析史实记载、历史传说、民俗民风和现代考古等都在很大程度上相互应证,形成了一条符合逻辑的证据链条。这些证据链条无一不指向长江中下游的两湖和湘江流域。特别是湖南境内的洞庭湖平原及湘江流域更是稻作农业的核心地。现代考古发掘也有力地证明了南稻北粟的学说和中国南北文化的差异。也有力批驳了南蛮之地的邪说,事实上,在远古时代,南方的文明在一定程度上先于并且胜过北方文明。南方也是中华文明的摇蓝。 相似文献
28.
生态标志型水稻要素资源需求与经济效应分析 总被引:1,自引:0,他引:1
基于对调查数据的处理,主要研究生态标志型水稻与常规水稻在投入品需求、成本收益及生产效率等方面的差异及其影响因素,以期把握我国生态标志型水稻生产规律. 相似文献
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