A MEASURE OF CROPPING INTENSITY∗

The measurement of agricultural intensity is fundamental to an understanding of spatial organization of agriculture. This paper develops a new index of cropping intensity from land use data. The length of time for which a crop stays in the field, a factor ignored in other indirect measures of cropping intensity, has been incorporated in the new index. To illustrate the method, cropping intensity in India is measured, mapped and discussed. Differences between the patterns derived from the new index and the traditional index are noted and explained.     

基于MODIS数据的2001—2018年中国耕地复种指数反演研究

耕地复种指数的持续稳定关乎国家粮食安全战略,实时高效地获取复种指数时空演变的详细过程信息具有重要意义。论文基于2001—2018年500 m分辨率的MODIS09A1影像数据,利用小波谱顶点的快速自动检测方法获取了全国复种指数的时空分布图,并采用Mann-Kendall检验、启发式分割算法等方法开展了全国复种指数变化形式的时空演变规律及驱动机制研究。结果表明：全国耕地复种指数稳中有升,复种指数均值从2001年的1.14上升至2018年的1.30。全国6%的耕地面积复种指数发生显著变化(约13.5万km²),相当于一个安徽省的面积。复种指数增加面积约占变化面积的2/3,复种指数下降面积约占变化面积的1/3。其中,复种指数增加的面积主要来源于黄土高原区、甘新区的休耕转为单季以及黄淮海区单季转双季,且集中在2004—2013年。2013年至今,全国复种指数仍呈增加趋势,黄淮海区单季转双季的面积保持持续增加是重要的影响因素。复种指数下降的面积主要来源于2009—2013年长江中下游平原区的双季转单季。保持黄土高原区、甘新区的耕地有效种植面积以及黄淮区耕地的双季种植面积,适当抑制长江中下游地区耕地复种指数的下降态势,对于稳定耕地复种指数、确保粮食安全具有重要意义。     

Changes of multiple cropping in Huang-Huai-Hai agricultural region,China

Multiple cropping index (MCI) is the ratio of total sown area and cropland area in a region, which represents the regional time intensity of planting crops. Multiple cropping systems have effectively improved the utilization efficiency and production of cropland by increasing cropping frequency in one year. Meanwhile, it has also significantly altered biogeochemical cycles. Therefore, exploring the spatio-temporal dynamics of multiple cropping intensity is of great significance for ensuring food and ecological security. In this study, MCI of Huang-Huai-Hai agricultural region with intensive cropping practices was extracted based on a cropping intensity mapping algorithm using MODIS Enhanced Vegetation Index (EVI) time series at 500-m spatial resolution and 8-day time intervals. Then the physical characteristics and landscape pattern of MCI trends were analyzed from 2000–2012. Results showed that MCI in Huang-Huai-Hai agricultural region has increased from 152% to 156% in the 12 years. Topography is a primary factor in determining the spatial pattern dynamics of MCI, which is more stable in hilly area than in plain area. An increase from 158% to 164% of MCI occurred in plain area while there was almost no change in hilly area with single cropping. The most active region of MCI change was the intersection zone between the hilly area and plain area. In spatial patterns, landscape of multiple cropping systems tended to be homogenized reflected by a reduction in the degree of fragmentation and an increase in the degree of concentration of cropland with the same cropping system.     

南方水稻复种指数变化对国家粮食产能的影响及其政策启示

中国南方地区水稻生产的变化对国家粮食安全具有重要影响。本文利用Landsat数据提取1990-2015年南方地区水稻种植制度分布及变化,并分析其对粮食产能的影响。结果表明：① 1990-2015年,水稻复种指数从148.3%下降到129.3%,双季稻改种单季稻（“双改单”）损失的播种面积为253.16万hm²,区域上以长江中下游地区变化最为突出。南方地区水稻种植制度整体呈现由北向南“双退单进”的变化格局;② 1990-2015年,“双改单”导致全国水稻产量减少6.1%,粮食产量减少2.6%。水稻主产区湖南省和江西省以及经济发展较好的浙江省因“双改单”水稻减产幅度较大,均超过13%;③ 充分利用“双改单”稻田的粮食产能相当于新增耕地223.3万hm²,为2001-2015年通过土地整治项目新增耕地总量的54%,是2016-2020年全国新增耕地规划目标的1.7倍,可节省约1674.4亿元新增耕地开垦费用。因此,与其追求低质量的“新”耕地,不如充分利用已有的高质量“旧”耕地,政府应转变耕地占补平衡的考核方式,将因提高复种指数增加的播种面积纳入补充指标。     

鄱阳湖区2004-2010年水稻种植制度时空变化(英文)

Rice cropping systems not only characterize comprehensive utilization intensity of agricultural resources but also serve as the basis to enhance the provision services of agro-ecosystems.Yet,it is always affected by external factors,like agricultural policies.Since 2004,seven consecutive No.1 Central Documents issued by the Central Government have focused on agricultural development in China.So far,few studies have investigated the ef-fects of these policies on the rice cropping systems.In this study,based upon the long-term field survey information on paddy rice fields,we proposed a method to discriminate the rice cropping systems with Landsat data and quantified the spatial variations of rice cropping systems in the Poyang Lake Region(PLR),China.The results revealed that:(1) from 2004 to 2010,the decrement of paddy rice field was 46.76 km2 due to the land use change.(2) The temporal dynamics of NDVI derived from Landsat historical images could well characterize the temporal development of paddy rice fields.NDVI curves of single cropping rice fields showed one peak,while NDVI curves of double cropping rice fields displayed two peaks an-nually.NDVI of fallow field fluctuated between 0.15 and 0.40.NDVI of the flooded field during the transplanting period was relatively low,about 0.20±0.05,while NDVI during the period of panicle initiation to heading reached the highest level(above 0.80).Then,several temporal windows were determined based upon the NDVI variations of different rice cropping systems.(3) With the spatial pattern of paddy rice field and the NDVI threshold within optimum tem-poral windows,the spatial variation of rice cropping systems was very obvious,with an in-creased multiple cropping index of rice about 20.2% from 2004 to 2010.The result indicates that agricultural policies have greatly enhanced the food provision services in the PLR,China.     

Mapping cropping intensity trends in China during 1982–2013

Long range continuous monitoring information of cropping intensity is useful for sustainable agricultural management but still limited. This study filled this information gap through delivering spatiotemporal continuous datasets of cropping intensity in China during the past 30 years. Cropping intensity data were derived by a wavelet features-based method based on the long-term weekly global EVI2 (Enhance Vegetation Index with two bands) at 0.05° spatial resolution (5 km) from 1982 to 1999 and 8-day composite 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance products from 2001 to 2013. The remote-sensing estimated images in 2013 agreed well with field survey data (overall accuracy = 91.63%) and the national agricultural census data (r² = 0.89). Results revealed that the cropping intensity remarkably increased during 1982–1999 but slightly declined during 2001–2013. The overall cropping intensity increased from 1.34 in the 1980s to 1.41 in the 1990s, and then dropped to an average of 1.36 after 2000. From 1982 to 1999, approximately 93,225 km² single-cropped areas changed to double-cropping, primarily those located in the North China plain. However, 39,883 km² double-cropped areas were turned back into single-cropping areas from 2001 to 2013, principally located in the North China plain, the Middle-lower Yangtze River plain, and the hill regions of the southern Yangtze River. This reverse trend of cropping intensity was due to combined effects from the corresponding reverse variations in agricultural population, increasing agricultural mechanical power, positive agricultural policy. The agricultural duty free policy has only immediate effects on stabilizing cropping intensity in croplands with more favorable biophysical conditions.     

An explanation of labor migration and grain output growth: Findings of a case study in eastern Tibetan Plateau

Although there has been rapid rural-urban migration in rural China since the 1980s, the total grain production of China saw a continuous increase. As of today, the relationship between labor migration and grain output growth remains partial and contradictory. The main aim of this empirical study is to examine some specific measures adopted by peasants to deal with labor shortage and maintain grain output growth. Using tracking survey, participatory rural appraisal methods, and land plot investigation, we investigate 274 households and 1405 arable land plots in four villages in two stages in Jinchuan county, southwestern China. The results show that continuous emigration of labor from the four villages caused the abandonment of a small amount of land, decreased labor intensity, and reduced multiple cropping index, shifting from “corn-wheat” multiple cropping pattern to the “corn” cropping pattern, which means labor shortage in some households. At the same time, owing to surplus labor in the villages, the peasants utilize a series of means to offset the negative impacts of labor migration on grain output, such as cropland transfer, labor exchange in the busy seasons, and the substitution of capital and technology for labor. The econometric analysis also shows that labor migration boosts grain production. This study provides a reasonable explanation of grain output growth under rural-urban migration.     

青藏高原东部典型区的劳动力析出与粮食产量增长——2005和2010年的跟踪调查及其解释（英文）

Although there has been rapid rural-urban migration in rural China since the 1980 s, the total grain production of China saw a continuous increase. As of today, the relationship between labor migration and grain output growth remains partial and contradictory. The main aim of this empirical study is to examine some specific measures adopted by peasants to deal with labor shortage and maintain grain output growth. Using tracking survey, participatory rural appraisal methods, and land plot investigation, we investigate 274 households and 1405 arable land plots in four villages in two stages in Jinchuan county, southwestern China. The results show that continuous emigration of labor from the four villages caused the abandonment of a small amount of land, decreased labor intensity, and reduced multiple cropping index, shifting from "corn-wheat" multiple cropping pattern to the "corn" cropping pattern, which means labor shortage in some households. At the same time, owing to surplus labor in the villages, the peasants utilize a series of means to offset the negative impacts of labor migration on grain output, such as cropland transfer, labor exchange in the busy seasons, and the substitution of capital and technology for labor. The econometric analysis also shows that labor migration boosts grain production. This study provides a reasonable explanation of grain output growth under rural-urban migration.     

基于GIS和面板数据的城镇集聚能力极化现象研究——以东莞市为例

在潜力模型基础上,提出了伪潜力指数,将其应用于定量描述城镇集聚能力的极化过程,并分析城镇规模和交通条件对集聚能力的影响。为了消除时间段上存在着常数的变量问题,通过面板数据分析(Panel Data Analy-sis)验证研究结果。将该方法应用于分析东莞各镇区1997-2005年城镇集聚能力的空间特征及其变化,探讨城市内部是否存在极化现象。结果表明,镇区集聚能力在空间上存在聚类;集聚能力的变化使极化现象在全市范围内逐步加强,但在经济核心地带内部出现了反极化现象。综合城镇规模对集聚能力的提高更加显著,其空间格局奠定了集聚能力的空间分布状况,从而决定了经济发展要素流动的方向,产生极化现象。选取净迁入人口和实际利用外资情况建立面板数据模型,估计结果证明潜力指数计算结果与人口和资金的吸引呈正相关。     

Toward a Spatial Understanding of Staple Food and Nonstaple Food Production in Brazil

Brazilian agricultural census data at the municipal level are used to develop and map a simple index of staple food versus nonstaple food agriculture for Brazil over time (1996–2006). The results show spatial variation in the direction and degree of the shift toward or away from staple food cropping across Brazil. The index is presented as an important methodological step toward a systematic geographic understanding of crop share changes surrounding food versus fuel and other nonfood crop production.     

Farmer-based Rice Cropping Systems in the Poyang Lake Region,China: Analysis of Characteristics and Policy Implications

This paper examines the spatial characteristics of farmer/household behaviors in regional rice cropping systems (RCS), and the results provide necessary information for developing strategies that will maintain regional food security. Through field study and statistical analysis based on 402 households questionnaires finished in 2014-2015 in the Poyang Lake Region (PLR) of China, we arrived at two main conclusions. First, single- and double cropping rice were found across the study area, but showed a general distribution trend, with double cropping rice in the southeast part (especially in Jinxian county) and single cropping rice in the northwest (particularly in De’an county). Second, the household decisions concerning RCS varied in different parts of the PLR, but double cropping was the dominant type, with about 63.57% of the respondent households in the PLR cultivating double cropping rice. However, the multiple-cropping index of paddy rice was only 1.55. About 3% of interviewed households had altered their RCS during this period. Based on these findings, the local governments should guide farmers’ paddy field cultivation behaviors by increasing the comparative efficiency of rice production, promoting appropriate scale operations and land conversion, as well as optimizing rice growing conditions to improve the multiple cropping index and enhance food provision. Finally, land-use efficiency and more sustainable use of land resources should be improved.     

Using palaeoecological records to disentangle the effects of multiple stressors on floodplain wetlands

Ecosystems worldwide are subject to the deleterious effects of multiple anthropogenic stressors. Understanding and mitigating the effects of these stressors is difficult both because stressors are confounded in space and have the potential to act both synergistically and antagonistically. Palaeoecological approaches applied to systems where stressors may be confounded in space but not in time offer a way to explore the effects of multiple stressors. This multi-proxy study of sediment records from four floodplain lakes (billabongs) on a dryland river floodplain subject to grazing, commencing in the late 1800s, and irrigated cropping, commencing in the late 1900s, tests this approach. The results suggest that the effects of both grazing and irrigation on floodplain ecosystems can be detected in the pollen and diatoms preserved in sedimentary records of billabongs. For the pollen, these changes are inconsistent, but appear to reflect local shifts in dominance among major tree taxa and among key understorey plant families. For the diatoms, the changes were also not consistent across sites, but can be generalised as reductions in epiphytic diatoms and increases in planktonic and facultative planktonic taxa that likely reflect increased fluxes of sediments and nutrients and reduced flood frequency. Overall, the effects of grazing appear to have been greater than irrigated cropping. The results also show that the relative effects of grazing and irrigated cropping on floodplain and riparian vegetation and on diatom communities vary between billabongs, with some evidence that at least some of this variation relates to the level of hydrological connection to the mainstream. Finally, the study suggests that for the most part, grazing and irrigated cropping act antagonistically in the way they impact these floodplain ecosystems, a pattern that likely reflects a release from grazing pressure associated with the increase in irrigated cropping. Future applications of the approach should increase spatial and temporal replication and develop more sophisticated frameworks that account for temporal variation in driver intensity and proxy indicators of the specific stressors that influence ecosystem structure and function.     

中国亚热带北界及其过渡带

本文根据亚热带热量指标构造了热量综合指数表达式,确定亚热带北界的具体位置、宽度和特征,分析过渡带内气候变量在时间上和空间上的内在联系。     

基于空间句法的扩张强度指数及其在城镇扩展分析中的应用

扩张强度指数（Expand Intensity Index, EII）是目前城市扩展数量特征研究的常用指标,用以表征城市扩张程度和速度,但该指标是从城市扩张的结果,即从城市用地面积变化角度对物质空间变化的简单描述与分析,忽略了人在空间中的感受,未能从城市扩张的动因角度揭示城市扩张特征,缺乏对城市外部空间形态演变模式的深入研究,不能反映人在城市扩展空间上的活动。本文从交通网络对城市扩张的驱动作用入手,基于空间句法,提出一种新的扩张强度指数——基于空间句法的扩张强度指数（Space Syntax Expand Intensity Index, SS-EII）,SS-EII包涵可反映空间集聚和离散程度的句法变量,可用于分析空间可达性的变化等情况。与传统扩张强度指数相比,SS-EII是基于空间句法从城市扩张的驱动力方面计算扩张强度,不仅关注城市扩张的结果,同时关注交通对城市扩张模式、方向的导向作用和人主观感知下城市空间的变化。将SS-EII应用于广东省棉湖镇2002-2014年期间的城镇扩展特征分析中,研究结果表明,SS-EII可用于分析比较建成区不同方向的扩张速率与建设状况,其计算结果与棉湖镇建成区实际扩张情况相符,与EII相关度R²达0.95以上。     

中国粮耕价值比与种植结构时空耦合演化及分区调控

耕地粮食产出价值与种植结构均深刻影响着国家粮食安全,探讨耕地粮食产出价值与种植结构的时空耦合变化,可理清两者关系,助力粮食安全保障能力的提升。本文以中国省级行政单元为研究对象,在深刻解读粮耕价值比和种植结构内涵的基础上,综合利用Simpson指数、耦合协调度模型和空间自相关等方法,分析2004—2020年中国粮耕价值比和种植结构耦合时空演化,以揭示其时空动态关系。结果表明：① 2004—2020年各省份粮耕价值比空间分布特征表现为“由北向南”和“由西向东”的双重递减态势;② 种植结构空间格局呈现由“胡焕庸线”沿线区域向两侧递减的空间分布形态,东北、华北和华东地区多样性递减明显;③ 粮耕价值比与种植结构耦合协调度介于勉强耦合协调与高度耦合协调之间,表现为规律性空间集聚,中西部及东北地区呈高高集聚,具有“匹配性优势”,东南沿海地区呈低低集聚,有待“匹配性改良”,总体表现为：“东北、中部高,东南部低”的态势。本文认为应依据要素空间集聚和扩散的分异特征,因区施策引导耕地粮食品质化与多元化协同演进,促进粮食结构与效益匹配发展。     

土壤含水量、种植模式和丁香酚对土壤微生物种群结构的影响

盆栽试验了田间持水量(45%、60%、75%)、种植模式和小麦根系分泌物丁香酚对小麦、蚕豆下土壤微生物种群结构的影响。结果表明:间作土壤中细菌、真菌和放线菌数量较单作加权平均有所减少,但间作化感促进作用和土壤微生物多样性均大于单作加权平均,且丁香酚对单作小麦和小麦间作蚕豆土壤微生物数量表现出明显的化感促进作用,在丁香酚处理下间作土壤中3种菌类数量较单作加权平均分别提高95.9%、8.8%和99.6%,但对单作蚕豆土壤微生物数量表现为化感抑制作用;随着供水水平的增加,单作小麦化感促进作用增强,单作蚕豆化感抑制作用减弱,间作化感促进作用在60%相对含水量以下随供水水平增加而增强,超过60%后随供水水平增加而减弱。丁香酚处理下间作土壤微生物多样性指数在小麦拔节期、灌浆期和成熟期比单作加权平均提高74.3%、96.1%和134.0%,且在单作小麦和间作群体下在60%相对含水量以下随供水水平增加而提高,超过60%后随供水水平增加而降低,单作蚕豆则随供水水平增加而持续降低。因此,利用间作和灌水水平的控制可充分挖掘根系分泌物对土壤微生物数量和多样性的化感促进作用。     

城市建设用地集约利用的碳排放效率分析

为研究城市建设用地集约利用度与其碳排放效率之间的关系,针对省际建设用地,构建城市建设用地集约利用评价指标体系,计算中国大陆30个省份的建设用地集约利用度;基于松弛测度的SBM模型,测算各省份建设用地集约利用的碳排放综合效率、技术效率与规模效率。结果表明:(1)城市建设用地集约利用程度与集约利用碳排放综合效率并不保持普遍一致;(2)建设用地集约利用度高的省份大多分布在东部地区;(3)区域建设用地集约利用碳排放技术效率不足是导致大多数省份综合效率偏低的主要原因,而规模效率不足对综合效率影响较小。     

甘肃省近30a来耕地空间动态变化与驱动力分析

通过采用主成分分析法与GM(1,1)模型,分析了近30 a来甘肃省耕地变化的总体趋势、空间差异、耕地复种指数的动态变化与耕地变化驱动力,并对未来耕地变化趋势进行了预测,结果表明:1978年以来,甘肃省耕地面积时增时减,总体呈递减趋势;各市(州)与全省耕地变化相比存在明显空间差异;耕地复种指数呈波动性上升,虽然总体水平在上升,但是耕地复种指数并不高,耕地利用程度有待提高;经济发展水平、人口因素、农业产业结构调整和农业现代化水平是耕地变化的主要驱动力;GM(1,1)预测分析表明在今后一段时间内,在影响因子不变的前提下,耕地面积将持续减少。     

不同种植方式下柽柳光合生理参数光响应特性研究

为选择合适的间套模式,在塔干沙漠南缘绿洲外围利用Li-6400光合作用仪对四种种植模式(行间混交、带状混交、块状混交、块状套作)下多年生多枝柽柳(Tamarix ramasissima ledeb.)的光合水分生理指标对有效光辐射(PAR)的响应进行测定。结果表明:(1)柽柳具有高光饱和点(679~822μmol·m^-2·s^-1)和高光补偿点(50.0~61.1μmol·m^-2·s^-1)。(2)不同的光照强度和种植方式对柽柳净光合速率有明显的影响(p<0.01),当0< PAR< 1500μmol·m^-2·s^-1,除胞间CO₂浓度(Ci)外柽柳的各项生理指标均随光照的增强而增加。(3) PAR>1500μmol·m^-2·s^-1后,块状套作和块状混交气孔导度(Gs)下降,行间混交和带状混交Gs则随光强增加而递增;带状混交下胞间CO₂浓度(Ci)和蒸腾速率(Tr)均随光强增加而递增,其他3种种植方式下Ci和Tr均呈递减或平稳趋势。(4) 4种种植方式下柽柳光响应曲线的特征参数存在着差异(P<0.05),带状混交下的光饱和速率、光饱和点、表观量子效率均最高,块状混交的暗呼吸速率最大,水分利用效率(WUE)随着光强的增强而逐步增大,依次表现为带状混交>块状混交>行间混交>块状套作。通过4种种植方式柽柳光响应特征的综合分析可知,带状混交下的柽柳具有高光合和高水分利用效率的特点,对于极端干旱的塔南地区而言,该种植方式下的柽柳生理特征表现出最好的适应性。     

河北省农用地利用集约度时空变异分析

我国人多地少, 农用地集约利用成为社会经济发展的客观要求。本文以河北省县( 市) 为 评价单元, 从投入强度、利用程度、利用效率和持续状况四个层面构建评价指标体系, 采用熵值法 确定指标权重, 综合指数法计算1985~2005 年河北省各县( 市) 的农用地集约度, 并进行农用地利 用集约度的时空变异分析, 以期为河北省农用地集约利用和持续发展提供政策依据。结果表明: 土地投入强度对农用地集约利用水平的影响较大, 各县( 市) 农用地集约利用水平表现出明显的 区域性差异, 农用地的投入强度和持续状况都表现出提高的趋势, 而农用地的利用程度和利用效 率则有所下降。