结合Landsat 8和GF 1数据的冬小麦种植空间分布提取

[目的]为探讨多源中等分辨率数据在冬小麦种植时空分布上的应用。[方法]利用2017年冬小麦关键生育期的Landsat8 OLI(抽穗期)和时间序列的GF-1 WFV(2016—2017生育期)数据,在分析各个行政分区的地表覆盖状况、作物结构和地块破碎度差别的基础上,将行政区划分为3种类型不同的提取单元并建立了适合于各自分区的提取模型:(1)利用关键生育期的OLI数据,采用监督分类—神经网络方法提取结构单一、地块齐整的怀远县种植区;(2)基于WFV数据构建五河县及城区种植区的冬小麦全生育期NDVI时间序列曲线,根据NDVI的时间特征构建冬小麦提取的决策树分类模型提取结构较复杂、混合像元明显的五河县及城区种植区;(3)在对关键生育期OLI-NDVI数据合理分割的基础上,采用最大似然的面向对象分类法获取种植密集、地块破碎的固镇县种植区。[结果]提取结果采用混淆矩阵和当年度统计数据相结合的方法进行精度评价,结果表明:(1)怀远县提取出的冬小麦提取总体精度为97.91%,五河县及城区提取出的精度为97.62%,固镇县的精度为97.42%;(2)全区域冬小麦提取的总体精度为86.82%,Kappa系数为0.84。与当年度统计数据对比的结果表明:2017年蚌埠市的准确提取面积精度可达97.91%,提取面积数据小于蚌埠市统计年鉴提供的统计数据,与调查的实际种植地块基本一致。[结论]采用不同方法提取不同空间分布特征的冬小麦种植面积具有较好的精度,该方法可以为市域冬小麦面积提取提供技术参考。     

基于地块单元的冬小麦遥感估产方法研究

[目的]以高分时序遥感影像为基础数据源,结合土地承包经营权地块数据,对冬小麦遥感估产方法及其精度进行研究和分析。[方法]文章以河南省兰考县为研究区,采用2019年4―5月份的GF-1C和GF-6 2 m PMS遥感影像提取了研究区冬小麦种植空间分布,并在地块单元控制下对冬小麦种植面积进行了修正和精度验证。其最优提取结果的修正阈值为0.93,地块单元内冬小麦总体分类精度为95.66%,Kappa系数为0.89。利用3月7日至5月20日6期GF-1 WFV遥感影像序列NDVI和RVI与冬小麦种植地块单元数据进行空间统计,得出各冬小麦种植地块单元内NDVI和RVI均值,通过分析冬小麦测产地块单元内均值植被指数与产量间的敏感性,提出一种组合均值植被指数的冬小麦遥感估产模型构建方法,通过交叉验证法对不同的估产线性回归模型进行精度评价。[结果]由4个均值植被指数组合变量的多元线性回归模型为最佳,决定系数为0.922 0,预测误差为40.96 g/m~2,预测精度为93.13%。通过该模型得出兰考县冬小麦平均产量为6 047.25 kg/hm~2,较2017年河南省统计年鉴研究区冬小麦平均单产6 001 kg/hm~2有所提高,土地承包经营权地块内和地块外冬小麦总产量分别为2.76亿kg和4 650万kg。[结论]该方法实现了冬小麦估产结果以像元为单位向以地块单元为单位的转变,解决了模型构建时光谱信息与实测产量间对应问题,为利用国产高分卫星进行县域地块尺度遥感单产精准化估算提供了方法支撑。     

中国小麦生产的时空变异及区域优势分析

通过对1979～2002年小麦在中国粮食生产的产量和播种面积所占百分比的动态分析，论述了中国小麦在粮食生产中具有相对稳定的地位，而相对于其它粮食作物而言，小麦生产又具有较大的波动性的特征。对比分析五大气候生态区小麦单产、总产和播种面积，认为中国小麦生产具有空间上的相对稳定性和时间上的相对不稳定性，小麦生产的这种时空差异性造成了区域比较优势的时空变化。北方冬麦区和春麦区是发展小麦生产的重点地区。     

Climate change impacts on investment in crop sowing machinery*

A model of investment in crop sowing machinery is applied to wheat production under current and projected climatic conditions at several locations in south‐western Australia. The model includes yield responses to time of sowing at each location given current and projected climatic conditions. These yield relationships are based on wheat growth simulation modelling that in turn draws on data from a down‐scaled global circulation model. Wheat price distributions and cost of production data at each location, in combination with the time of sowing yield relationships are used to determine a farmer's optimal investment in crop sowing work rate under each climate regime. The key finding is that the impacts of climate change on profit distributions are often marked, yet mostly modest changes in investment in work rate form part of the profit‐maximising response to climate change. The investment response at high versus low rainfall locations mostly involves increases and decreases in work rates, respectively. However, changes to investment in work rate within a broadly similar rainfall region are not always uniform. The impacts of climate change on investments in work rate at a particular location are shown to require knowledge of several factors, especially how climate change alters the pattern of yield response to the time of sowing at that location.     

Geography of crop yield skewness

Analysis of crop yield distributions provides insights into better understanding how natural resources shape agricultural productivity. This study seeks to provide a rigorous theoretical and empirical understanding of the effects of exogenous geographic and climatic factors on the first three moments of crop yields with focus on the third moment. We hypothesize that exogenous factors having beneficial effects on crop production should make crop yield distributions less positively or more negatively skewed. We employ a large crop insurance data set for corn, soybean, and wheat to find general support for our natural‐resources‐determines‐skewness hypothesis. The proposed statistical method optimally uses correlations between the first three moments. It significantly improves estimation performance over existing methods, including the linear moment model which has been commonly applied in the literature.     

Revealing the determinants of wheat yields in the Siberian breadbasket of Russia with Bayesian networks

Higher crop yields are critical to satisfy the rising global food demand. Russia holds untapped potential for increasing agricultural production because current grain yields are often far below the potentially attainable yields. Western Siberia is an important breadbasket in Russia, where wheat yields fall particularly short of their potential. Our goal was to assess the determinants of yield variations among farmers in the province of Altai Krai in Western Siberia. We conducted 67 structured in-person interviews with corporate farm managers and individual farmers about the potential determinants of wheat yields and complemented these data with 149 additional observations obtained from the provincial agricultural extension service. We used Bayesian networks (BNs) to represent the relationships between the explanatory parameters and contemporary wheat yields and to examine qualitative future scenarios of future yields. The results revealed higher yields on larger farms than on medium and small farms. Our results corroborated that the application of fertilizers and herbicides and the implementation of new equipment had large positive impacts on the yields. The scenario of higher future production costs and lower precipitation resulted in a yield reduction from 7.6 dt/ha to 5.3. Overall, our results suggest that policies aimed at increasing wheat yields should concentrate on the education of farmers and encourage higher input applications, particularly for small-scale farms. Additionally, policies should address concurrent challenges, such as a higher drought frequency, through the application of new equipment, seed material and tillage practices.     

An Evaluation of the Actuarial structure of manitoba crop Insurance Program and its Implications

Very little research has been done in evaluating the basic principles and assumptions of the actuarial structure for premium ratemaking in crop insurance programs. Therefore, the objectives of this study are: (a) to examine the Pearson probability distribution of actual crop yields as compared with an application of normal-curve theory to crop yields as compared with an application of normal-curve theory to crop yield distributions and in turn to crop insurance ratemaking which was suggested by Botts and Boles in 1958 [1]; (b) to evaluate the pure premium rates derived from estimated Pearson probability distributions for wheat yields in 14 crop districts of the province of Manitoba; and to establish an experience rating system for the crop insurance program based upon the estimated Pearson distribution of actual crop yields on the individual farm.     

Data Aggregation Issues for Crop Yield Risk Analysis

With increased emphasis on risk management in agriculture and a lack of disaggregated or farm‐level yield time series, decision makers are often faced with having to make adjustments to temporal yield risk measures obtained from readily available but aggregated yield data. This paper provides some empirical evidence on what type of aggregation bias to expect when measuring temporal yield risk using yield observations averaged across a region relative to yield risk estimated from quarter‐section yield time series in wheat. This study highlights some of the challenges faced when estimating aggregation distortions in measuring yield risk defined by temporal variance, especially given the nature of the empirical data set used. Cluster analysis, visual examination of relative frequency distributions and mapping of yield risk clusters suggest that using a readily available, aggregate temporal yield risk measure has the tendency to underestimate yield risk observed at the quarter‐section level and that clear, geographic yield risk boundaries do not exist in municipalities or across larger areas in this study. Further research on crops more risky than wheat appears promising. Avec un plus grand intéret sur la gestion du risk dans l'agriculture et un manque de données détaillees ou bien de collections de séries temporelles sur les rendements, les décideurs sont souvent tenus d'apporter des correctifs aux measures du risk obtenues a partir des données de rendements qui sont disponibles. Cet artcle apporte une preuve empirique du type de biais lie a l'agrégation qui peut être présent dans le calcul du risk de rendement temporel obtenu a partir de rendements moyens de blé observés au niveau régional en comparaison du risk de rendement qui est estimé a partir de données basées sur des quart‐de‐sections. Cette étude met en exergue quelques uns des obstacles qui se présentent dans l'estimation de distosions liées a l'aggrégation dans le calcul du risk de rendement défini par la variance temporelle, speciallement étant donne la charactère empirique des données utilisées. L'analyse de groupe, l'examen visual de la distribution des fréquences relatives, et la cartographie de classes de risk de rendement suggèrent que l'utilisation de la measure du risk de rendement basée sur des données disponibles de risk aggrège temporel a tendence a sousestimer le risk de rendement observe au niveau des quart‐de‐sections et qu'il n'y a pas de frontières de risk de rendement certaines, géographiques qui existent entre les municipalités ou bien a travers les zones plus larges examinées dans cette etude.     

CHANGES IN CEREAL PRODUCTION AND YIELD VARIABILITY ON FARMS IN SOUTH EAST ENGLAND

Data from 16 wheat growers and 18 barley growers in South East England were investigated for changes in variability of production and yield between the periods 1964-74 and 1975-84. Sixteen per cent of the increase in variability of wheat production was due to changes in yield variances and covariances. The increase in variability of barley production was not statistically significant. Variability of yield increased for both wheat and barley. Wheat yields became more positively correlated between farms, but barley yields did not. The results for wheat were consistent with the hypothesis of an increase in the number of controlled factors in the production process. Particularly important was thought to be the use of fungicides in the control of many cereal diseases. Increased heterogeneity of the barley crop may have contributed to the decline in the number of between-farm correlations for that crop.     

基于光能利用率模型的河南省冬小麦单产估算研究

[目的]快速、准确估算空间尺度上作物产量,对于评价农田生态系统对气候变化的响应、制定科学合理的粮食政策、对外粮食贸易等具有重要意义。河南省冬小麦产量占全国1/4,准确估算河南省冬小麦产量对维护国家粮食安全具有重要作用。单产估算作为农作物估产中的关键技术,也是作物估产的难点之一。[方法]文章首先利用VPM(Vegetation Photosynthesis Model)估算冬小麦NPP(Net Primary Product),结合收获指数、冬小麦收获部分的含水量、含碳量、NPP分配到地上或地下部分比例等一系列符合该研究区的经验指数,进行河南省冬小麦单产估算研究,并分析了引起模拟误差的原因。[结果]模拟单产较实测单产低估4.4%(实测单产为6 810kg/hm~2,模拟单产为6 519kg/hm~2),但两者之间存在显著相关关系,两者相关系数的平方R2=0.70(n=50,p0.01)。通过与MODIS-GPP产品获得的冬小麦单产数据比较,基于VPM模型的模拟结果优于MODIS-GPP产品。[结论]基于VPM可快速、准确估算河南省空间尺度冬小麦单产,该方法具有较好的适用性。     

Is research on marginal lands catching up? The case of unfavourable wheat growing environments⋆

It is widely believed that the Green Revolution had very little effect in unfavourable or marginal environments. Many researchers have been concerned about the slow progress of technical change in marginal environments and the level of research resources allocated to these areas. This paper provides empirical evidence that there has been significant growth in wheat yield potential in marginal environments, especially during the post‐Green Revolution. International yield trial data, covering all major wheat growing environments from 1964 to 1999, were used in estimating the growth in wheat yield potential and changes in yield variability. The global database on wheat varietal adoption and yield gains based on estimated wheat yield growth rates were used to determine production increases due to wheat breeding research. Results show greater progress in shifting the wheat yield frontier in marginal areas, particularly in drought and high temperature environments. Furthermore, yield variability in marginal environments has notably declined, while it has increased slightly in favourable environments. While initial gains came from crossover of varieties from favourable environments, targeted breeding efforts have contributed significantly to more recent productivity growth in marginal environments. Increased production from marginal environments accounted for around 25% of the total wheat production increase in 1997. These findings show greater progress in wheat research and the huge potential of improving wheat productivity in unfavourable environments.     

RELATIVE VARIABILITY IN WHEAT YIELDS ACROSS COUNTRIES AND OVER TIME

Wheat yield variability is analysed in light of recent concern that rapid technological change has caused increased instability in world cereal production. The coefficient of variation of wheat yields is estimated for 57 countries from detrended data for various periods between 1951 and 1986. The coefficient of variation in wheat yields is shown to be determined by country size, moisture regime and temperature. Technological variables, such as level of adoption of high-yielding varieties and fertiliser dose, had no effect on differences in yield variability across countries. Analysis of yield variability for the same set of countries for three periods from 1951 to 1986 shows a general decline in yield variability since 1975 in developing countries. Analysis of wheat yield variability in India at the state and district levels confirms the analysis of country level data. The coefficient of variability of wheat yields in India in the period 1976-85 has fallen to less than half the level in the 1950s and this decline is statistically significant.     

振动润麦机对出粉率及润麦时间的影响

本文研究了高筋小麦、中筋小麦经振动润麦机润麦后经实验室磨粉机制粉和工厂实际加工生产制粉对小麦出粉率的影响.结果显示,与普通方式润麦相比,振动润麦方式均可有效缩短润麦时间,提高出粉率,中筋小麦润麦时间可缩短至10～14 h,高筋小麦润麦时间可缩短至12～16 h.     

基于文献计量法的强筋小麦研究现状分析

近些年随着强筋小麦在国民生活中的作用不断凸显,国家对强筋小麦的发展越来越重视。为了解我国强筋小麦研究现状并促进我国强筋小麦研究的进一步发展,本文以中国知网(CNKI)作为数据源,选取"强筋小麦"为检索词进行检索,采用文献计量法对强筋小麦相关文献的年份分布、作者、关键词、基金来源、载文期刊进行统计分析,结果表明近十年是我国强筋小麦研究的主要时期,研究多集中在强筋小麦的品质和产量两个方面。     

基于MODIS EVI时间序列的冬小麦长势监测

该文探讨了MODIS EVI序列与作物生长过程的互动规律,利用EVI序列分析影响冬小麦生长过程的气象因素。结果显示,冬小麦抽穗期EVI值及冬小麦返青期至收获期EVI积分值与作物产量之间有很好的相关性。冬小麦抽穗期EVI值与冬小麦产量的相关性体现了作物营养生长阶段的发育状况,可以利用抽穗期作物EVI早期预测作物产量;EVI曲线的积分值能综合反映作物整个生长发育过程,可以根据这一规律对农作物产量进行估算。冬小麦生育期内EVI均值与平均温度、降水量、日照时数相关性分析结果显示,温度和降水是冬小麦生长的主要限制因子,其中温度起主导作用。     

西北地区小麦增产潜力分析研究

文章通过对西北5省2000~2013年小麦生产情况、小麦高产创建取得的效益综合分析,结果显示:西北5省小麦种植面积持续下降,单产稳步提升,高产创建万亩片的效益远高于西北5省的平均单产。推广综合集成技术和加大投入是增产的关键,西北5省区小麦生产仍有很大的挖掘潜力。今后挖掘西北5省小麦增产潜力要依靠科学技术,加大优良新品种选育,建全新优品种的推广力度,改善农田基础设施,提高耕地产出能力,促进土地承包经营,推动生产全程机械化,持续加大投入,加强灾害预警与抗逆减灾技术研发,科学抗灾减损。提出要将高产田的种植技术推广应用到大田生产中,实现在现有种植面积不扩大的前提下,产量大幅度提高。为实现口粮绝对安全,需要进一步稳定供给,在挖掘科技潜力,扩大推广展示引导的基础上,探索多渠道的动态补贴机制,保障种粮主体的积极性。     

Tailored to the extremes: Quantile regression for index‐based insurance contract design

A new approach for weather index‐based insurance design based on Quantile Regression (QR) to condition the yield‐index dependency is developed and compared to standard regression technique. Three conceptual different risk measures, i.e., Expected Utility, Expected Shortfall and a Spectral Risk Measure, are used to evaluate the risk reducing properties of these contracts. Our findings show that QR is much more powerful in establishing the yield‐index dependency and lead for all risk measures to a higher risk reduction than the standard technique ordinary least squares (OLS). Thus, QR leads to a more efficient contract design, which is beneficial for both, the insurer (smaller remaining risk) and the insured (higher demand and willingness to pay). Our empirical application is based on a 31 years long time series of wheat yield data from Northern Kazakhstan.     

Econometric estimation of a global spillover matrix for wheat varietal technology

An econometric approach using international and national yield trial data is employed to estimate a spillover matrix for wheat varietal technology. The global spillover matrix is estimated based on international yield trial data from 1979–80 to 1987–88, that include 195 international trial locations and 209 wheat varieties. The locations were classified across countries using the CIMMYT's wheat megaenvironment system and varieties were classified by both their environmental and institutional origin. The model gave good explanatory power and confirmed the location specificity hypothesis, at least, for the varieties developed by national programs (NARS). The spillover matrix shows that NARS varieties developed in the home' environment generally perform better on average than varieties developed in other megaenvironments. Also, the matrix is not symmetric. CIMMYT varieties perform better on average in irrigated and high rainfall environments than NARS varieties developed for these environments. The yield advantage of CIMMYT varieties in many test megaenvironments indicates the potential of CIMMYT varieties to spill-over to these test megaenvironments. Results also indicate that national programs are efficient in selecting from among imported technologies. Analysis of international data is complemented by the analysis of country-level data for Pakistan and Kenya that confirms the above results. The country-level analysis, however, indicates that CIMMYT germplasm does not do so well in some sub-environments, such as the irrigated short-duration environment. The results of the spillover matrix have implications for the design of crop breeding programs both at the national and international levels. Information provided by the spillover matrix can be utilized by national programs to deploy their resources more efficiently by following a mixed strategy of direct importation of technology in some environments and local development of technologies in other environments which are unique to the country.     

Black Sea and World Wheat Market Price Integration Analysis

In 2008–10, Russia and Ukraine together exported an average of 29 million tons of wheat per year, and have become important players in the international wheat market. This research summarizes the short‐ and long‐run wheat price dynamics between Ukraine and Russia, and other major wheat exporters—the United States, European Union (EU), and Canada—from 2004 to 2010. Tests of market price co‐integration (Johansen maximum likelihood test and residual‐based tests) as well as threshold error correction techniques were performed for this purpose. The results suggest that Russian wheat prices were co‐integrated with EU and U.S. wheat prices but not with Canadian wheat prices. Ukrainian wheat prices were found to be co‐integrated with French wheat prices only. The estimated long‐run wheat price transmission elasticities were estimated to be equal to 1.04 between Russian and French (a representative country of the EU) wheat prices, 1.16 between Russian and U.S. wheat prices, and 1.05 between Ukrainian and French wheat prices. We also found the short‐term relationships between the co‐integrated series to be statistically significant. Price adjustments in all co‐integrated prices were found to be symmetric.     

Deregulation of the Australian Wheat Export Market: What Happened to Wheat Prices?

ABSTRACT

This report investigates whether deregulation of the Australian wheat export market induced a structural change in the price data generation process. We analyze the unit root properties of Western Australian wheat price series by testing for the possibility of single and double structural breaks. Daily spot prices for the period of May 20, 2003, to September 14, 2010 are used. We find the wheat price series has a unit root with two structural breaks but neither breaks coincides with the time when the Wheat Export Marketing Act 2008 came into effect on July 1, 2008. The implication of our results is that deregulation was not the main cause of structural breaks in the price series in the sample period.