The world is undergoing tremendous changes, and food security is encountering major challenges in China and even the world. In order to systematically study globalization and explore its new patterns, new issues and new paths for food security, we interviewed ten distinguished professors from different fields and discussed hot topics, including the potential for increasing farmland production, agricultural water and soil resources and food production, food waste, international agricultural product trade, stable supply of key agricultural product, global agricultural food system, dual circulation pattern and corporate actions, global food production and consumption, international food security governance, and cutting-edge research on food safety. The result shows that the global agricultural food system has entered an era of complexity and high risk. International food security governance is facing challenges in terms of resources, binding force and action power. We are facing an increasing pressure of import dependent agricultural products to ensure stable supply. It is necessary to deepen supply-side reform and strengthen demand-side management so as to guarantee national food security. New changes have taken place in globalization. This will test China's ability to deepen agricultural opening-up, participate in global food security governance, and achieve national food security. In the face of complex international and domestic situations, for better national food security governance, it is necessary to adhere to system thinking and coordinate domestic and international markets. It is also very important to target the entire industry chain, emphasize risk control, and handle the relationship between the government and the market. Furthermore, researchers need to explore the internal relationships and specific mechanisms between food security and other important issues, such as food systems, ecosystems, high-quality development goals, agricultural opening-up, and new dual-circulation development patterns. This could provide a scientific reference for establishing and improving the national food security strategy of "featuring self-sufficiency based on domestic grain production, guaranteed food production capacity, moderate imports, and technological support" in the New Era.

当今世界正面临“百年未有之大变局”,中国与全球的粮食安全面临重大挑战。为了系统认知全球化与粮食安全的新格局、新问题和新路径,邀请了十位来自不同专业领域的知名专家,就耕地增产潜力、农业水土资源与粮食生产、食物浪费、国际农产品贸易、重点农产品保供稳供、全球农业食物系统、双循环与企业行动、全球粮食生产与消费、国际粮安治理、粮食安全研究前沿等领域进行了一对一的交流访谈。访谈结果表明：全球农业食物系统进入复合型高风险时代,国际粮安治理面临资源、约束力、行动力等方面的挑战,凸显国家粮食安全尤其是进口依赖型农产品的保供稳供压力,需要加强国内农业供给侧改革与需求侧管理。全球化发生新变化,考验中国深化农业对外开放、参与全球粮安治理、实现国家粮食安全的能力水平。面对复杂的国际国内形势,国家粮食安全治理需要坚持系统思维、统筹国内国际、瞄准全产业链、强调风险管控、处理好政府与市场关系,进一步深入研究食物系统和粮食安全、生态系统和粮食安全、高质量发展与粮食安全、农业对外开放与粮食安全、双循环新格局与粮食安全等方面的具体方式路径,为新时期建立健全“以我为主、立足国内、确保产能、适度进口、科技支撑”的国家粮食安全战略提供科学参考。

Rapid population growth and environmental deterioration make ensuring food security with lower environmental costs fundamental to realizing sustainable development in China and other developing countries. The conceptual framework used in this paper integrates the major consequences of intensive agricultural land use and the diverse objectives of policymakers and farmers. It also offers an operational approach, based on farmers' diverse performance in grain production and farmland productivity, to assess food production and environmental impacts under foci-differentiated scenarios. Using data from farmer household surveys, soil surveys, land use images, and statistical yearbooks, this approach was tested using a regional case in China. The results indicate that, among all farmer types, the medium-scale farmers had a better comprehensive performance for grain production for yield, fertilizer and pesticide inputs, labor productivity, and sustainability. Therefore, grain yields can be increased and environmental costs reduced simultaneously through the use of policy instruments that encourage the transformation of trapped farmers into medium-scale farmers and balancing the proportion of single and double cropped rice. In addition, and in order to reduce grain losses caused by natural disasters and to prevent environmental degradation, robust policy measures should be developed to avoid the currently predominant cropping patterns that erode biodiversity.Copyright © 2018 Elsevier Ltd. All rights reserved.

Geopolitical competition between China and the United States has been intensifying, and uncertain events such as COVID-19 and extreme weather and climate occur frequently. The national strategy, which relies on two types of resources and two markets to ensure national food security, is facing challenges. Based on statistical data and literature viewpoints, this paper focuses on the main problems facing China's food security in the context of opening-up and how to ensure China's food security. The results show that: (1) China has made remarkable achievements in improving domestic food security, but with huge economic and resource environmental costs of food supply, and the increasing risks of stable food supply and access. The government is exploring practical ways for the achievement of food security in the era of globalization. (2) Agricultural opening-up can affect food supply, access, utilization and stability. The current opening-up has promoted the country's food supply, but it has not yet achieved stable and competitive food security. Agricultural opening-up still has a broad foundation for mutual benefit and win-win effect, while it is also facing greater uncertainty, which tests China's ability to deal with the challenges of globalization in food sector. (3) National food security governance is very important to food security. This paper recommends that we should adopt a self-sufficiency strategy with production capacity highlighted, a food security strategy for the entire industry chain to enrich the content of food, and a higher level of agricultural opening-up strategy, which will help to achieve the goal of national food security.

中美地缘政治竞争加剧,新冠肺炎疫情、极端天气气候等不确定性事件频发,依托两种资源两个市场的国家粮食安全策略面临新的挑战。结合统计数据与文献观点,分析了新时期中国粮食安全面临的主要问题,研究了农业开放保障粮食安全的主要效用,探索了扩大对外开放背景下我国粮食安全的保障思路。结果表明：（1）中国粮食安全取得了显著成就,但也存在粮食供应的经济与资源环境代价巨大、粮食稳定供应与获取的风险加大等问题,需要在开放条件下创新粮食安全实现路径。（2）农业对外开放可影响粮食供应、获取、利用与稳定性,当前对外开放促进了国家粮食供应,但尚未实现稳定的食物安全、有竞争力的食物安全。农业对外开放仍有广泛的互惠共赢基础,同时也面临更大的不确定性,考验我国粮食领域应对全球化“危”“机”的治理能力。（3）国家粮食安全治理对于保障粮食安全至关重要,建议采取凸显产能的粮食自给战略、全产业链的食物安全战略与高水平的农业对外开放战略,确保粮食安全落实落地。

Agriculture is a source for three primary greenhouse gases (GHGs): CO(2), CH(4), and N(2)O. It can also be a sink for CO(2) through C sequestration into biomass products and soil organic matter. We summarized the literature on GHG emissions and C sequestration, providing a perspective on how agriculture can reduce its GHG burden and how it can help to mitigate GHG emissions through conservation measures. Impacts of agricultural practices and systems on GHG emission are reviewed and potential trade-offs among potential mitigation options are discussed. Conservation practices that help prevent soil erosion, may also sequester soil C and enhance CH(4) consumption. Managing N to match crop needs can reduce N(2)O emission and avoid adverse impacts on water quality. Manipulating animal diet and manure management can reduce CH(4) and N(2)O emission from animal agriculture. All segments of agriculture have management options that can reduce agriculture's environmental footprint.

China is currently the world's largest carbon emitter. As a large agricultural country, understanding the relationship between carbon emissions, economic growth and energy consumption in the agricultural sector can contribute to achieving the sustainable development of agriculture. Hence, this paper aims to investigate the relationship between carbon emissions, energy consumption and economic growth in the agricultural sector using a time series of data from China's main grain-producing areas during the period between 1996 and 2015. We first estimate the agricultural carbon emissions. And then based on the estimated results, we employ the autoregressive distributed lag (ARDL) model, the Granger causality test based on the vector error correction model (VECM), and impulse response and variance decomposition to test the relationship between carbon emissions, energy consumption and economic growth in the agricultural sector. The estimated results support the environmental Kuznets curve (EKC) hypothesis for agricultural carbon emissions in China's main grain-producing areas. Furthermore, agricultural energy consumption has both the short-run and the long-run negative impacts on agricultural carbon emissions. In addition, we find that there is a bidirectional causality between agricultural carbon emissions and agricultural economic growth in both the short-run and the long-run, and the unidirectional causalities are found to exist from agricultural energy consumption to agricultural carbon emissions and agricultural economic growth. Finally, several policy recommendations are offered to promote the sustainable development of agriculture in China's main grain-producing areas. (c) 2019 Elsevier B.V.

Environmental issues caused by agricultural production have attracted wide concern. Estimating environmental efficiency is an intuitive way to reflect the impact of agricultural production on ecological systems,which can make people realize the environmental costs of agricultural production and contribute to sustainable production. We used the Rural Fixed Point Observation（RFPO）dataset from 2004 to 2012 for China and adopted a stochastic frontier translog production function to estimate the environmental efficiency of China’s household grain production. A Tobit model was then used to identify the determinants of environmental efficiency. We found that the average technical efficiency and environmental efficiency are 0.802 and 0.489 respectively. A strong and positive association was also detected between these two efficiencies. The estimated average technical efficiency dropped slightly after taking environmental efficiency into account,while the relative magnitude of technical efficiency in three regions remains the same. We found that environmental efficiency varies greatly across regions and Central China has the highest efficiency while Eastern China the lowest. A decreasing trend along with time change in environmental efficiency was found for all three regions,indicating a deteriorating agricultural ecological system in China. Farmers with different scales also presented different environmental efficiency. Large-scale farmer’s environmental efficiency is higher than small-scale farmers. Environmental efficiency was also influenced by farmer characteristics,agricultural inputs,training and land fragmentation. In particular,older and well-educated farmers have higher environmental efficiency;larger scale farms and more labor input also contributed to lower pollution. Agricultural training,land fragmentation,and intensive use of fertilizers and pesticides have negative impacts on environmental efficiency.

近年来,农业生产带来的环境问题引起日益广泛的关注,而测算环境效率能直观反映农业生产对生态环境的影响,使人们清楚地认识到农业生产所付出的环境代价,进而推动中国农业生产向更具可持续性的方向转变。有鉴于此,本文基于2004-2012年全国农村固定观察点数据,采用超越对数随机前沿分析方法测算了中国农户粮食生产的环境效率,并用Tobit模型考察农户粮食生产环境效率的影响因素。研究结果表明：①全国范围内农户粮食生产的技术效率与环境效率均值分别为0.802和0.489,并且两种效率之间具有较高的相关性;②考虑环境效率后,中国粮食生产的技术效率均值出现了略微的下降趋势,但东部、中部、西部依次递减的趋势没有改变;③环境效率地区间差异明显,呈现出中部、西部、东部依次递减的趋势。而且随着时间变化,各地区的环境效率均呈现出递减趋势;④不同规模农户的粮食生产环境效率也存在差异,具体而言,大规模农户粮食生产环境效率普遍高于中小规模农户;⑤农户特征、农业生产要素、农业技术培训以及土地细碎化等因素均会影响粮食生产环境效率。

With the objective of reducing the large uncertainties in the estimations of emissions from crop residue open burning, an improved method for establishing emission inventories of crop residue open burning at a high spatial resolution of 0.25°×0.25° and a temporal resolution of 1month was established based on the moderate resolution imaging spectroradiometer (MODIS) Thermal Anomalies/Fire Daily Level3 Global Product (MOD/MYD14A1). Agriculture mechanization ratios and regional crop-specific grain-to-straw ratios were introduced to improve the accuracy of related activity data. Locally observed emission factors were used to calculate the primary pollutant emissions. MODIS satellite data were modified by combining them with county-level agricultural statistical data, which reduced the influence of missing fire counts caused by their small size and cloud cover. The annual emissions of CO2, CO, CH4, nonmethane volatile organic compounds (NMVOCs), N2O, NOx, NH3, SO2, fine particles (PM2.5), organic carbon (OC), and black carbon (BC) were 150.40, 6.70, 0.51, 0.88, 0.01, 0.13, 0.07, 0.43, 1.09, 0.34, and 0.06Tg, respectively, in 2012. Crop residue open burning emissions displayed typical seasonal and spatial variation. The highest emission regions were the Yellow-Huai River and Yangtse-Huai River areas, and the monthly emissions were highest in June (37%). Uncertainties in the emission estimates, measured as 95% confidence intervals, range from a low of within ±126% for N2O to a high of within ±169% for NH3. Copyright © 2016. Published by Elsevier B.V.

Due to the increasing environmental impact of food production, carbon footprint as an indicator can guide farmland management. This study established a method and estimated the carbon footprint of grain production in China based on life cycle analysis (LCA). The results showed that grain production has a high carbon footprint in 2013, i.e., 4052 kg ce/ha or 0.48 kg ce/kg for maize, 5455 kg ce/ha or 0.75 kg ce/kg for wheat and 11881 kg ce/ha or 1.60 kg ce/kg for rice. These footprints are higher than that of other countries, such as the United States, Canada and India. The most important factors governing carbon emissions were the application of nitrogen fertiliser (8-49%), straw burning (0-70%), energy consumption by machinery (6-40%), energy consumption for irrigation (0-44%) and CH emissions from rice paddies (15-73%). The most important carbon sequestration factors included returning of crop straw (41-90%), chemical nitrogen fertiliser application (10-59%) and no-till farming practices (0-10%). Different factors dominated in different crop systems in different regions. To identity site-specific key factors and take countermeasures could significantly lower carbon footprint, e.g., ban straw burning in northeast and south China, stopping continuous flooding irrigation in wheat and rice production system.

Estimation of the effect of grain production adjustment on the consumption of water and land resources will help to formulate the strategy for sustainable agricultural development. Since the mid and late 1990s, the proportion of corn in China's grain production has been obviously improved. Taking grain cropping structure without adjustment as the base scenario, and under certain grain output, the actual grain production adjustment in China during 1996-2015 has brought about the savings of water and land resources, accounting for about 4.2% and 3.7% of current demand in grain production respectively. The adjustment of grain production comes from grain demand structure change, which helps to alleviate the consumption pressure of water/land resources in grain production to some extent, though China's dietary transformation requires more agricultural resources. At the regional level, from the effect of structural adjustment on the demand for planting area, the savings in northern regions with relatively abundant arable land resources are significantly higher than those in the south. The area saving effect is higher in the northeast and northwest regions, and the least in southeastern coastal areas. From the effect of structural adjustment on the demand for water resources, the savings in northern regions are generally higher than those in the south, the highest in the northwest region with the highest drought degree, and the water saving effect in the middle and lower reaches of the Yangtze River is minimal. During the period, the output of regional grain crops has been widely affected by the change of cropping proportion, which is the indicator of the planting benefit and implies the change of consumption demand. Feed grain demand has increased more than rice and wheat rations, making the northern region suitable for corn planting become China's main grain production area. In the southern rice region, the demand for rice is relatively limited, and the regional production advantages of wheat, corn and soybeans are also lacking, which causes the relative stagnation of grain production in the south. To this end, in southern China, the recovery of grain production and full utilization of the potential of water/heat resources mainly depend on the consumption demand for rice and farmers' planting benefit. For the northern region, in order to reduce the amount of groundwater irrigation, it is necessary to rationally control the cropping area of rice and wheat and to adjust farming system according to the law of precipitation as far as possible.

粮食种植结构调整会影响农业资源的消耗需求。20世纪90年代中后期以来,玉米在我国粮食生产中的地位明显提升。以粮食种植结构无调整为参照情景,一定产量下,1996-2015年,在国家层面,因粮食种植结构调整对水土资源消耗的节省量约占现期需求量的4%左右。在区域层面,从结构调整对种植面积的减省效应看,耕地资源相对丰富的北方地区明显高于南方地区;从对水资源消耗的减省效应看,北方贫水区也普遍高于南方地区,干旱度最高的西北地区最高。期间区域分品种粮食生产广泛受到作物种植比例变化的影响。研究结果表明,要充分利用好南方水热资源,恢复水稻生产,主要取决于稻米需求及其种植效益,而北方地区则要尽可能按降水规律调整农作制度,合理控制水稻、小麦的种植面积。

This study calculated the agricultural carbon emissions in China during 1995-2010, as well as 31 provinces in 2010, based on 16 categories of major carbon source from agricultural land use, paddy field, livestock enteric fermentation and manure management. We found that China’s agricultural carbon emissions in 2010 were 286.7323 million tons (equal to 1051.3517 million tons of carbon dioxide), a 12.31% increase over 1995 resulting from agricultural land use, paddy fields, livestock enteric fermentation and manure management, which respectively produced carbon emissions of 98.3164 million tons, 121.8020 million tons, 50.9619 million tons and 15.6520 million tons and accounted for 34.29%, 42.48%, 17.77% and 5.46% of total agricultural carbon emissions. Emissions displayed an obvious‘up-down-up’phase-change characteristic, increasing from 1995-1999, decreasing from 2000-2003, and increasing again from 2004-2010. In lateral view, the regional difference was clear as the top 10 regions accounted for 59.61% of the total agricultural carbon emissions, while that of the last 10 regions was only 8.33%. Hunan province ranked first palace and produced 24.2451 million carbon emissions, while Tianjin ranked last and produced only 0.7726 million carbon emissions. As for the structure of agricultural carbon emissions, based on the differences of carbon emissions ration the 31 provinces were divided into four types (paddy field dominant, agricultural land use dominant, livestock enteric fermentation dominant and composite factors led). Agricultural carbon emission intensity across west China was highest, followed by the middle zone, and the east zone was lowest. Tibet province was the highest zone, its agricultural carbon emission intensity as high as 2931.74kilograms per ten thousand agricultural gross domestic product, while Shandong province was the lowest zone with an agricultural carbon emission intensity as low as 207.75 kilograms per ten thousand agricultural gross domestic product. On this basis we conducted Tapio decoupling in the analysis of the decoupling relationship between China’s agricultural carbon emissions and agricultural economic development and found that main types are the weak decoupling and strong decoupling. Based on the difference of elastic, the last 15 years were divided into two stages: the first stage from 1996-2000 included strong decoupling, expansion connection and weak decoupling; the second stage from 2001-2010 had concentration on strong decoupling and weak decoupling, indicating that some certain results have been achieved in agricultural carbon emission reduction during recent years.

本研究基于农地利用、稻田、牲畜肠道发酵和粪便管理等四方面16类主要碳源, 测算了我国1995年-2010 年期间以及31 个省(市、区)2010 年的农业碳排放量。结果表明:①2010 年我国农业碳排放总量为2 8673.23万t, 较1995年增加了12.31%。其中, 农地利用、稻田、肠道发酵和粪便管理所导致的碳排放量分别占农业碳排总量的34.29%、42.48%、17.77%和5.46%;分阶段来看, 呈现较为明显的“上升-下降-上升”的三阶段变化特征;②横向来看, 区域差异明显:农业碳排放总量, 排在前10位的地区占全国农业总排放的59.61%, 而排在后10位的地区仅占全国8.33%, 传统农业大省尤其粮食主产省区是我国农业碳排放的主要来源地;基于碳排放比重差异, 将31个地区划分为了稻田主导型、农地利用主导型、牲畜肠道发酵主导型、复合因素主导型等四种不同结构类型;农业碳排放强度, 总体呈现出西高东低的特征, 即西部>中部>东部。在此基础上, 运用Tapio脱钩模型对我国农业碳排放与农业经济发展间的脱钩关系进行了分析, 发现以弱脱钩和强脱钩为主, 说明近年来我国在农业碳减排方面取得了一定成效。

控制农业源非二氧化碳温室气体排放对中国落实温室气体减缓政策具有现实意义，对于推动农业绿色转型、实现乡村振兴具有指导价值。本文基于IPCC系数法核算了2000—2019年中国省际农业源非二氧化碳温室气体排放，刻画了农业源非二氧化碳温室气体排放强度时空演化规律；基于STRIPAT模型，解析了各地区农业源非二氧化碳温室气体的影响机理，模拟了不同情景组合下农业源非二氧化碳温室气体排放未来演变趋势。结果表明：① 动物肠道发酵甲烷排放是中国农业源非二氧化碳温室气体最主要的来源，中国农业源非二氧化碳温室气体排放逐渐由东部沿海向西部内陆地区转移。② “胡焕庸线”是单位农业增加值排放强度与单位农地面积排放强度高值区的分水岭，农牧交错带是中国单位农业增加值排放强度的高值区。③ 中国农业源非二氧化碳温室气体排放与人均GDP之间存在倒“N”型的EKC曲线关系，华北、东北和华中地区仍面临一定的减排压力，各区域农业源非二氧化碳温室气体排放影响机理存在显著差异。有效减少动物肠道发酵CH₄排放，根据区域发展特征制定因地制宜的减排政策是未来中国农业源非二氧化碳温室气体减排的关键。

The change of regional land use is the main cause for the change of carbon storage in territorial ecosystem, which affects the process of carbon emission and sink. However, previous studies on the impact of future land use change on ecosystem carbon storage considering temporal and spatial scales in the basin are still absent. This study analyzed land use change from 2005 to 2015 in the Qihe River Basin, Taihang mountainous areas, and used Markov-CLUE-S composite models to predict land use pattern of this region in 2025, under three scenarios of natural growth, farmland protection and ecological conservation. Based on the data of land use, we used carbon storage module in InVEST model to evaluate carbon storage of territorial ecosystem during the past 10 years and the future. The results showed that: (1) The carbon storage and carbon density of the ecosystem in the Qihe River Basin in 2015 were 3.16×107 t and 141.9 t/hm2, respectively, and they both had decreased by 0.07×107 t and 2.89 t/hm2 during the 10 years. (2) From 2005 to 2015, the carbon density was mainly reduced in low altitude areas, and the ratio of the increased areas was similar to that of the reduced areas in the high altitude areas. The decrease of carbon density was mainly caused by expansion of construction land in the middle and lower reaches, and degradation of forestland in the upper reach of Qihe River Basin. (3) From 2015 to 2025, the carbon storage and carbon density of ecosystem will decrease by 0.03×107 t and 1.38 t/hm2 respectively in the natural growth scenario, mainly due to the reduction of carbon sequestration capacity in low altitude areas. The farmland conservation scenario will slow down the decrease of carbon storage and carbon density (0.01×107 t and 0.44 t/hm2), mainly due to the enhancement of carbon sequestration capacity in low altitude areas. The ecological protection scenario will increase carbon storage and carbon density significantly to 3.19×107 t and 143.26 t/hm2 respectively, mainly appearing in the area above 1100 m. The ecological protection scenario can enhance carbon sequestration capacity, but it cannot effectively control the loss of farmland area. Therefore, the land use planning of the study area can comprehensively consider the ecological protection scenario and farmland conservation scenario, which not only increases carbon sink, but also ensures the farmland quality and food security.

区域土地利用变化是导致生态系统碳储量变化的主要原因,影响其碳源、碳汇效应,但以往结合时空尺度探讨流域未来土地利用变化对生态系统碳储量影响的研究尚不多见。以太行山淇河流域为例,分析2005-2015年土地利用变化,采用Markov-CLUE-S复合模型预测2025年自然增长、耕地保护及生态保护情景下的土地利用格局,并基于土地利用数据,运用InVEST模型的碳储量模块评估2005-2015年及未来不同情景下的生态系统碳储量。结果表明：① 2015年淇河流域生态系统碳储量和平均碳密度分别为3.16×10⁷ t和141.9 t/hm²,自2005年以来分别下降0.07×10⁷ t和2.89 t/hm²。② 2005-2015年碳密度在低海拔区域以减少为主,在高海拔区域增加区与减少区比例相当,淇河中下游地区建设用地的大肆扩张以及上游林地的退化是导致碳密度下降的主要原因。③ 2015-2025年自然增长情景下碳储量和碳密度下降仍较明显,主要是低海拔区域固碳能力的减弱;耕地保护情景减缓了碳储量和碳密度的下降幅度,主要是由于低海拔区固碳能力的增强;生态保护情景下,碳储量和碳密度显著增加,分别达到3.19×10⁷ t和143.26 t/hm²,主要发生在海拔高于1100 m的区域。生态保护情景能够增强固碳能力,但不能有效控制耕地面积的减小。因此,研究区土地利用规划可统筹考虑生态保护和耕地保护情景,既能增加碳汇,又能保障耕地质量和粮食安全。

Based on registered population data, this paper examined a variety of population density models to explore the spatio-temporal pattern of the registered population of Nanjing during the past century. The results showed that: (1) The number of registered residents in Nanjing from 1928 to 2017 showed a flat "S"-shaped growth trend, forming an extensive dispersion with localized concentration types. The population density was the greatest in the Qinhuai River area, which has been the main registered population center. (2) The spatial structure of the registered population included: point-single center, axis-double center, enclave compound-multi center, and radiation-circle polycentric center. (3) The polycentric model, which is based on the central place theory, provided the best explanation for the features of the spatial structure of the registered population. The registered population distribution pattern in Nanjing was attributed to the joint action of four spatial location rules: the distance-decay law, allometric growth effect, spatial polarization characteristic, and regional-edge structure. (4) The transitions in the city during the past century were not a de-urbanization but a temporary fluctuation because of social transformation. Notable differences remained between traditional-Chinese residential center and the central business district.

以户籍人口数据为基础,运用多种人口密度模型,探究1928—2017年南京城市户籍人口时空格局演变特征,探讨了单中心与多中心城市人口密度模型的适用性,归纳总结了南京城市户籍人口空间结构的演化过程与响应机制。研究表明：① 1928—2017年南京城市户籍人口数量呈扁“S”型阶梯式增长态势与向心式“大分散、小集中”的户籍人口分布格局,以秦淮河为核心的人口集聚区一直是南京城市户籍人口分布的主中心;② 百年尺度南京城市户籍人口空间结构特征呈现点状单中心、轴式双中心、飞地式复合多中心与放射圈层式多中心等4个发展阶段;③ 南京城市户籍人口分布格局可归因成距离衰减规律、异速增长效应、空间极化特性、区域边缘结构等4种空间区位法则的共同作用结果。基于中心地理论的多中心模型假设验核效果最优,符合城市户籍人口分布格局的识别特征;④ 近百年来南京城市户籍人口时空格局演变历程是中国近现代城市转型的缩影。南京历经百年制度变迁,城市户籍人口的“强中心”空间格局一直保持稳定,未见逆城市化端倪。中国传统城市人口居住中心与西方以城市规划用地功能为基础的中心商务区有本质区别。

：Research on the spatiotemporal evolution of urban air pollution and its driving forces has great theoretical and practical significance because it helps to deeply understand the mutual feedback mechanism between urban environment and socio-economic system and improve the efficiency of environmental governance. This paper illustrated the regional evolution characteristics of six urban ambient air pollutants, namely, CO, NO2, O3_8h, PM10, PM2.5, and SO2, in 286 sample cities at the prefecture level in China from 2014 to 2019, starting from the year when the "Air Pollution Prevention and Control Action Plan" was fully implemented in China. The interactions between the concentrations of each pollutant were then analyzed on the basis of panel regression models. Furthermore, random forest model was employed to explore the correlations between concentrations of these six pollutants and thirteen natural and socio-economic impact factors so as to sort out crucial ones. The results are shown in three aspects. First, the average annual concentration of O3_8h increased while that of the other urban ambient air pollutants decreased year by year, among which SO2 concentration decreased the most. Although the typical heavy pollution areas had shrunk, cities in the Beijing-Tianjin-Hebei region, Shandong Peninsula region, Shanxi Province, and Henan Province still have witnessed relatively high concentrations of air pollutants. Second, there was a significant interaction between concentrations of these six pollutants, indicating that comprehensive measures for urban air pollution prevention are necessary. Third, the impact of natural factors and socio-economic factors on urban air quality varied greatly towards different air pollutants, together with a nonlinear response relationship with the pollutant concentrations. Within the selected five natural factors of temperature, precipitation, wind speed, humidity and NDVI, the urban annual average temperature had the strongest correlation with air pollutant concentrations, followed by NDVI. Among the eight selected socio-economic factors, the level of land urbanization and the proportion of secondary production were the two leading drivers of the urban air pollution, followed by the total power consumption and traffic factors. Besides, partial dependence model was used to further analyze the response threshold of different pollutant concentrations to the dominant influencing factors. In consideration of the limited ability of human to control the physical environment and meteorological conditions, it is recommended that urban air quality should be further effectively improved by means of the optimization of urban density, the control of man-made emission sources, and the implementation of strict air pollution prevention and control measures.

开展城市空气质量时空格局演变特征及其影响因素的研究,对于深入认识城市环境与社会经济系统的互馈机理、制定高效的环境治理措施、提升城市发展质量具有重要的理论与实践意义。本文以中国全面实施《大气污染防治行动计划》的2014年为起点,刻画了2014—2019年286个地级以上城市6种空气污染物浓度（CO、NO₂、O₃、PM₁₀、PM_2.5、SO₂）的时空演变特征,并基于面板回归模型分析各污染物浓度之间的相互作用关系;进而利用随机森林模型对城市6种空气污染物浓度与13个自然和社会经济影响因子的关联强度进行探究,从中梳理出关键影响因子。结果显示：① 研究期内,O₃污染加剧,其余污染物年均浓度逐年下降,其中SO₂浓度降幅最大。虽然典型的重污染区范围有所减小,但京津冀、山东半岛、山西、河南等地区的城市空气污染物浓度仍相对较高。② 城市6种空气污染物浓度之间存在显著的相互影响关系,城市空气复合污染特征明显。③ 自然因素和社会经济因素对不同种类空气污染物浓度的影响差异较大,且与污染物浓度之间呈非线性响应关系。自然因素中,城市年均气温与空气污染物浓度的关联强度最大,其次是植被指数。社会经济影响因素中,土地城市化水平和二产比重是主导影响因子,其次是电力消耗总量和交通因子。偏依赖分析进一步刻画了不同污染物浓度对主导影响因子的响应突变阈值。鉴于人类对于自然环境和气象条件的控制能力有限,建议继续通过优化城市密度、控制人为排放源及严格的空气污染防控措施以进一步有效提高城市空气质量。

Elhorst  provides Matlab routines to estimate spatial panel data models at his website. This article extends these routines to include the bias correction procedure proposed by Lee and Yu if the spatial panel data model contains spatial and/or time-period fixed effects, the direct and indirect effects estimates of the explanatory variables proposed by LeSage and Pace, and a selection framework to determine which spatial panel data model best describes the data. To demonstrate these routines in an empirical setting, a demand model for cigarettes is estimated based on panel data from forty-six US states over the period 1963–1992.

Agriculture consolidates the process of natural reproduction and economic reproduction. Spatial pattern of agricultural region is comprehensively influenced by factors such as natural geography, economic and social development and advances in technology. Along with the changes of these influencing factors over a long period, agricultural pattern and agricultural function present regional differentiation and spatio-temporal evolution. This lays a scientific foundation for comprehensive agricultural regionalization. China is currently experiencing a new period of coordinated development of industrialization, urbanization, informatization and agricultural modernization. This paper firstly investigates spatio-temporal changes and dynamic characteristics of modern agriculture development conditions in China. Then, it puts forward the coupling measure index system of agricultural natural factors and regional function, zoning principles and scientific method of modern agricultural regionalization under the new development background. Using cluster analysis and qualitative analysis, it carries out a comprehensive research and puts forward China's modern agriculture regionalization scheme in the new era, which divides China into 15 agricultural first-grade regions and 53 agricultural sub-regions. After doing a comparative analysis with the new scheme and the previous one, which was published in 1981, the paper makes a systematic interpretation on current producing situation, regional function, spatial pattern changes and agricultural development trend of each agricultural region and the whole country at last. The results of this research provide scientific basis for strategic structural adjustment and development of modern agriculture in each region. At the theoretical level, this paper provides a research reference for the development of modern agriculture and rural geography. At the application level, it promotes integrated geography research to serve the rural revitalization and national development strategic needs in the transition period in China. The regional agriculture is a natural, economic and technological complex system, with the characteristics of complexity, dynamics and high risk. As such, based on the congnition of spatial differentiation of modern agriculture development patterns, it is necessary to deeply analyze the regional differentiation of agricultural endogenous power, agriculture and rural territorial types, to improve observational research of agricultural geographical engineering and technology, and the economic, ecological, climatic integrated effects of regional agriculture transformation, to summarize systematically regional agricultural models and regional transformation patterns, to explore the early warning mechanism of modern agricultural complex system, and to study continuously the theories and strategic decision-making for promoting agricultural modernization and rural revitalization.

农业是自然再生产与经济再生产过程的统一,农业地域格局取决于自然、经济、社会和技术等要素的综合影响,而且伴随着这些要素的长期变化而产生时空演化和区域分异,由此奠定了综合农业区划的科学基础。本文探讨了中国工业化、城镇化、信息化和农业现代化协调发展新战略,剖析了现代农业发展环境的时空转变及其动态特征,建立了农业自然要素与农业地域功能耦合测度指标体系,应用聚类分析和定性评判综合手段提出了新时期中国现代农业区划原则和方法,制定了全国现代农业区划方案。该方案包括15个农业一级区、53个农业二级区,并与1981年农业综合区划方案进行比较分析,深入揭示了快速工业化、城镇化、信息化进程中中国农业生产结构、地域功能、格局动态和发展趋向,为新时期加快各地区现代农业战略性结构调整,促进农业现代化发展奠定了重要基础,为创新发展现代农业与乡村地理学,促进地理学综合研究服务国家战略需求提供了重要参考。

China puts forward the national strategy of fallow plan so as to improve the sustainable grain production capacity of arable land and alleviate the continuous decline of the groundwater level in the Huang-Huai-Hai Plain. Aiming at estimation of sustainable grain productivity for ensuring the implementation of this strategy, this paper learns management experience and experimental production from agricultural experiment station and adopts step-by-step correction method in twelve agricultural ecological zones, which are relatively uniform in social and economic conditions based on the sustainable theory and water balance. The results showed that: (1) The total sustainable grain production capacity of arable land under water balance in the Huang-Huai-Hai Plain was 116 million t/year. (2) The yield gap of sustainable grain productivity was -0.67 million t/year, the wheat yield gap was -3.31 million t/year due to limited-water irrigation and the maize yield gap was positive. (3) The loss area of wheat production is mainly distributed in Heilonggang area, Luxi Plain, the Beijing-Tianjin-Tangshan Plain and the eastern Henan Plain, and the potential area is mainly in Xuhuai Plain, the Northern Anhui Plain and Jiaoxi Yellow River Flood Plain. The research was valuable for understanding the sustainable productivity of cultivated land and implementing the reliable spatial pattern of agricultural production in the Huang-Huai-Hai Plain.

为缓解黄淮海平原区地下水水位的持续下降,国家提出耕地资源休养生息的战略,而实施耕地资源休养生息的关键,是确保水平衡下的耕地资源可持续生产能力。本文从可持续理论和水平衡的条件出发,将黄淮海划分成12个自然条件、社会经济条件相对均一的农业生态区,采用不同农业生态区代表实验站限水高产的产量和管理经验,以水定产并逐步修正,得到了黄淮海平原区耕地可持续生产能力,并与现实产量对比得到产量差。结果表明：① 水平衡条件下黄淮海平原区耕地的可持续粮食生产能力为1.16亿t/年;② 可持续总产产量差为-67.85万t/年,由于限水灌溉造成的粮食产能损失为小麦331.84万t/年,玉米不存在产能损失;③ 小麦主要压产地区为黑龙港地区、鲁西平原、豫东平原以及京津唐平原,而徐淮低平原、豫东平原以及胶西黄泛平原具有一定的提产潜力。通过测算,进一步认识了黄淮海平原区耕地可持续产能状况,为区域粮食生产的合理布局以及农业限水限产提供可靠依据。

China's agricultural sector is dominated by smallholder farms, which mostly exhibit relatively low nutrient use efficiency, low agricultural income and substantial non-point-source pollution. Here we assess the spatial feasibility and cost-effectiveness of agricultural land consolidation in China by integrating data from over 40,000 rural surveys, ecological modelling and geostatistical analysis. We found that 86% of Chinese croplands could be consolidated to establish a large-scale farming regime with an average field size greater than 16 ha. This would result in a 59% and 91% increase in knowledge exchange and machinery use, respectively, contributing to a 24% reduction in total nitrogen input, an 18% increase in nitrogen use efficiency and a 39% reduction in labour requirement, while doubling labour income. Despite requiring a one-time investment of approximate US$370 billion for land consolidation, total agricultural profits would double due to agricultural production costs being halved.© 2021. The Author(s), under exclusive licence to Springer Nature Limited.