水稻时域散射特征分析及其应用研究

通过对肇庆试验区1996年和1997年获取的多时相、多模式雷达卫星（RADARSAT）数据分析，从图像上直接提取地物的后向散射系数，结合实地测量水稻的生长结构参数，建立了水稻生长模型，分析了不同生长周期（从80天到120－125天）4种类型水稻的时域散射特性。利用1997年4月至7月获取的7景标准模式雷达卫星数据，对试验区内三个县和两个行政区共5000km^2面积范围内的作物进行分类和水稻产量预估算，水稻类型分类及面积量算精度达91％。结果表明：利用雷达遥感数据进行水稻种植面积量算和估产需要水稻生长期间三个时相的数据，即插秧期、抽穗期、收割前期。若能够获得多参数雷达图像，可以用插秧期和收割前期的两个时相图像来代替上述的三个时相图像同样可以达到种植面积量算和估产的效果。这一结果充分说明多时相雷达卫星数据对我国南方水稻长势监测及估产具有明显优势和潜力。     

3S技术在晚稻长势监测中的综合应用研究

以江西省为试验区，探讨用RS－GIS－GPS技术监测作物长势的方法和途径。针对丘陵山区地形复杂、地块不成规模的情况，在GIS支持下，将数字高程数据、土地利用分类数据与GPS定位观测数据相结合，对NOAA／AVHRR进行判读，提取反映双季晚稻长势的植被指数，用该指数与GPS定位观测资料及地理信息数据进行监督分类监测苗情，并用迭代自组织分析法进行无GPS定位观测资料时相应时相的NOAA／AVHRR的长势监测。研究结果表明，选用的地理信息数据（数字高程数据、土地利用分类）与GPS定位观测资料相结合提高NOAA／AVHRR数据的利用效果是适合的和切实可行的。     

广西两系杂交稻制种安全期气候分析

根据两系杂交水稻制种对气象条件的要求 ,利用广西 80多站的气象资料 ,统计分析了广西各地两系杂交水稻制种的安全期 ,提出了广西杂交水稻安全制种应注意的一些气候问题     

NUMERICAL SIMULATION OF METHANE EMISSIONS FROM RICE PADDY FIELDS IN THE YANGTZE DELTA OF CHINA*

A numerical simulation model is presented in this paper,which comprises the processes of crop growth,soil organic carbon decomposition,and methane emissions in agroecosystems.Simulation results show that the model can simulate the main process of methane emissions well,and the correlation coefficient between the simulated values and observed data is 0.79 with 239 samples,which passed a significance test of 0.01.The average error of methane emission simulation in whole growth period is about 15%.Numerical analysis of the model indicates that the average temperature during rice growth period has much impacts on methane emissions,and the basic trend of interannual methane emissions is similar to that of average temperature.The amount of methane emissions reduces about 34.93%,when the fertilizer is used instead of manure in single rice paddy.     

Factors Affecting Methane Emission from Rice Paddies

A comparative study of rice paddies and the uncovered water field in Taoyuan(Hunan) showed that methane emission from rice-vegetated paddy fields in 1993 was different from that in 1992(I,e,lower in rates and irregular in pattern).Climate has obvious influence on methane emission .And ebullition made a considerable contribution to the total flux of methane emission from rice paddies (45%).This implies that the intensification of paddy cultivation of rice might not be,as was proposed,the main con-tributor to the observed gradual increasing of atmospheric methane.24-hour automatic measurements of atmospheric temperature,air temperature and methane concentration in the static sampling boxes revealed that temperature,in addition to fertilization and irrigation style,is one of the most important factors that control the emission of methane from rice paddies.     

A meta-analysis of global crop water productivity of three leading world crops (wheat,corn, and rice) in the irrigated areas over three decades

ABSTRACT

The overarching goal of this study was to perform a comprehensive meta-analysis of irrigated agricultural Crop Water Productivity (CWP) of the world’s three leading crops: wheat, corn, and rice based on three decades of remote sensing and non-remote sensing-based studies. Overall, CWP data from 148 crop growing study sites (60 wheat, 43 corn, and 45 rice) spread across the world were gathered from published articles spanning 31 different countries. There was overwhelming evidence of a significant increase in CWP with an increase in latitude for predominately northern hemisphere datasets. For example, corn grown in latitude 40–50° had much higher mean CWP (2.45?kg/m³) compared to mean CWP of corn grown in other latitudes such as 30–40° (1.67?kg/m³) or 20–30° (0.94?kg/m³). The same trend existed for wheat and rice as well. For soils, none of the CWP values, for any of the three crops, were statistically different. However, mean CWP in higher latitudes for the same soil was significantly higher than the mean CWP for the same soil in lower latitudes. This applied for all three crops studied. For wheat, the global CWP categories were low (≤0.75?kg/m³), medium (>0.75 to <1.10?kg/m³), and high CWP (≥1.10?kg/m³). For corn the global CWP categories were low (≤1.25?kg/m³), medium (>1.25 to ≤1.75?kg/m³), and high (>1.75?kg/m³). For rice the global CWP categories were low (≤0.70?kg/m³), medium (>0.70 to ≤1.25?kg/m³), and high (>1.25?kg/m³). USA and China are the only two countries that have consistently high CWP for wheat, corn, and rice. Australia and India have medium CWP for wheat and rice. India’s corn, however, has low CWP. Egypt, Turkey, Netherlands, Mexico, and Israel have high CWP for wheat. Romania, Argentina, and Hungary have high CWP for corn, and Philippines has high CWP for rice. All other countries have either low or medium CWP for all three crops. Based on data in this study, the highest consumers of water for crop production also have the most potential for water savings. These countries are USA, India, and China for wheat; USA, China, and Brazil for corn; India, China, and Pakistan for rice. For example, even just a 10% increase in CWP of wheat grown in India can save 6974 billion liters of water. This is equivalent to creating 6974 lakes each of 100?m³ in volume that leads to many benefits such as acting as ‘water banks’ for lean season, recreation, and numerous ecological services. This study establishes the volume of water that can be saved for each crop in each country when there is an increase in CWP by 10%, 20%, and 30%.     

土壤-水稻系统中重金属元素与其他元素之间的相互作用

通过相关关系的统计分析,探讨了四川省61件水稻籽实及其根系土中重金属元素与其他元素间的相互关系。研究结果表明:①水稻籽实对重金属元素、微量元素、大量元素的富集系数差异很大,元素富集系数之间具有显著的相关性;②水稻籽实中重金属元素的含量与土壤中部分元素的含量之间存在着显著的相关关系;③水稻籽实重金属元素的含量与籽实中其他元素含量之间的相关关系显著。结合元素之间的相互作用对元素地球化学行为的影响,评价了作物籽实中重金属元素的危害程度,为土壤修复提供了新思路。     

大气环流对中国稻飞虱危害的影响及其预测

稻飞虱是中国和许多亚洲国家水稻生产上最重要的害虫。文中通过对上一年1月至当年8月74项大气环流特征量构建所有不同时段的组合,全面分析了大气环流特征量与中国稻飞虱发生面积率的相关关系。筛选出了影响中国稻飞虱发生面积率的关键环流特征因子52项,其对中国稻飞虱发生影响的重要次序为副热带高压类→极涡类→槽类→其他类;影响的时段主要为当年7—8月,其次为上年6月至当年6月。其中,副热带高压类、极涡类关键环流因子分别有35项和12项,占全部关键环流特征因子的67%和23%,在很大程度上决定着中国稻飞虱发生的面积。确定的直接影响中国稻飞虱发生的关键环流特征因子有11项,其中6项较好地表征了中国稻飞虱发生面积率轻、偏轻、偏重、重4个级别的气候特征。用直接影响中国气候的关键环流特征因子建立了当年3—9月的中国稻飞虱发生面积率月预测模式,每月初可以制作预报。该模式历史拟合效果较好,对2003年中国稻飞虱发生面积率的外延预报准确率分别达85.6%、90.5%、90.5%、90.4%、90.9%、93.2%、96.3%。同时,本研究还利用1—11月稻区月降水量、平均气温、日照时数所构建的所有不同时段的组合,分析了关键环流特征因子与稻区生态气象条件、中国稻飞虱发生面积率之间的关系。结果表明:三者之间相关密切,这种关系表现为大气环流通过影响稻区日照、气温和降水的变化导致稻飞虱发生条件的灾变,进而影响稻飞虱发生面积率。     

Toward an Ecological Explanation of Agricultural Unemployment in Bangladesh

Cultural ecology theoretical framework was found suitable to explain unemployment in agriculture in three villages in Bangladesh. Path analysis and multiple regression statistics were used to examine the direct, indirect, and total effects of eight independent human, social, environmental, and technology variables as well as their aggregate contribution on agricultural unemployment. The multiple regression model explains 86.2% of the total variation in unemployment in agriculture; they were followed by environmental constraints and labor saving technology variables.     

ESTIMATE OF METHANE EMISSIONS FROM RICE FIELDS IN CHINA BY CLIMATE-BASED NET PRIMARY PRODUCTIVITY

1INTRODUCTIONIrrigated ricefieldsarecharacterizedbylargespatialandtemporalvariationsin CH4 emissiontotheatmo-sphere.Accordingly,thereisagreatuncertaintyintheestimate ofCH4 emissionsfromricefields.GreateffortshavebeenmadetoestimatetheCH4 emissionsfromricefieldsandseveralapproacheshavebeendeveloped.TherepresentativemethodsincludetheIPCC(Inter-governmentPanelofClimateChange)region-specificemissionfactormethodandthemodelcalculationmethod.Toimprovethecalculationaccuracy,theIPCCmethodreq…