A New Indicator for Global Food Security Assessment: Harvested Area Rather Than Cropland Area

Cropland area has long been used as a key indicator of food security.However,grain yield is not solely controlled by the area of the cropland.Therefore,we proposed a new indicator to assess food security.Results show that from 1992 to 2004,the global cropland area increased by 840200 km^(2)(99.4%),but the grain yield increased only by 310 million t(29.1%);and from 2004 to 2015,the cropland area decreased by 39000 km^(2)(4.64%),but the grain yield increased by 370 million t(70.84%).This result showed that grain yield was not linearly correlated with cropland area,and delimiting the threshold of cropland protection may not guarantee food security.Combined with further correlation analysis,we found that the increase in the global grain yield was more closely related to the harvested area(R^(2)=0.94),which indicated that the harvested area is a more scientific and accurate indicator than cropland area in terms of guaranteeing food security.Therefore,if governments want to ensure the food security,they should choose a new and more accurate indicator:harvested area rather than cropland area.

Reconstruction of cropland area in the European part of Tsarist Russia from 1696 to 1914 based on historical documents

To evaluate the climatic and ecological impacts of anthropogenic activities in global change research,it is essential to reconstruct historical land use and land cover change on regional and global scales.In this study,we reconstructed cropland areas for 54 provinces within the European part of Tsarist Russia(ETR)over the periods of 1696–1914 using historical data,including cropland area,population,grain consumption,and grain yield per unit area.The main results are as follows.(1)Total cropland areas and fractional cropland areas of ETR for 8 time sections during 1696–1914 were reconstructed,the former increased from 31.98×104 km2 to 147.40×104 km2,and the latter increased from 7.89%to 29.20%.The per capita cropland area decreased from 0.0246 km2 to 0.0113 km2 during 1696–1914.(2)Cropland expanded from the central and southwestern ETR to the black soil region,surrounding area of the Volga River,Ukraine region,the new Russia region,the vicinity of Ural,and north Caucasus region.(3)The expansion of territory,increase and migration of population,policies related to agricultural development and foreign trade,and the impacts of climate change were the reasons for the changes in cropland within ETR from 1696 to 1914.(4)In 1914,the cropland area and fractional cropland area of each province varied from 0.16×104 km2 and 0.76%to 5.65×104 km2 and 76.68%,respectively.(5)The comparisons show that the cropland areas of ETR in this study for 1696–1914 are higher than those in the HYDE 3.2 dataset.The main reason for this finding might be the underestimation of per capita cropland areas in the HYDE 3.2 dataset,which values remained at approximately 0.01 km2 from 1700 to 1920.

Mapping rice-fallow cropland areas for short-season grain legumes intensification in South Asia using MODIS 250 m time-series data

The goal of this study was to map rainfed and irrigated rice-fallow cropland areas across South Asia,using MODIS 250 m time-series data and identify where the farming system may be intensified by the inclusion of a short-season crop during the fallow period.Rice-fallow cropland areas are those areas where rice is grown during the kharif growing season(June–October),followed by a fallow during the rabi season(November–February).These cropland areas are not suitable for growing rabi-season rice due to their high water needs,but are suitable for a short-season(≤3 months),low water-consuming grain legumes such as chickpea(Cicer arietinum L.),black gram,green gram,and lentils.Intensification(double-cropping)in this manner can improve smallholder farmer’s incomes and soil health via rich nitrogen-fixation legume crops as well as address food security challenges of ballooning populations without having to expand croplands.Several grain legumes,primarily chickpea,are increasingly grown across Asia as a source of income for smallholder farmers and at the same time providing rich and cheap source of protein that can improve the nutritional quality of diets in the region.The suitability of rainfed and irrigated rice-fallow croplands for grain legume cultivation across South Asia were defined by these identifiers:(a)rice crop is grown during the primary(kharif)crop growing season or during the north-west monsoon season(June–October);(b)same croplands are left fallow during the second(rabi)season or during the south-east monsoon season(November–February);and(c)ability to support low water-consuming,short-growing season(≤3 months)grain legumes(chickpea,black gram,green gram,and lentils)during rabi season.Existing irrigated or rainfed crops such as rice or wheat that were grown during kharif were not considered suitable for growing during the rabi season,because the moisture/water demand of these crops is too high.The study established cropland classes based on the every 16-day 250 m normalized difference vegetation index(NDVI)time series for one year(June 2010–May 2011)of Moderate Resolution Imaging Spectroradiometer(MODIS)data,using spectral matching techniques(SMTs),and extensive field knowledge.Map accuracy was evaluated based on independent ground survey data as well as compared with available sub-national level statistics.The producers’and users’accuracies of the cropland fallow classes were between 75%and 82%.The overall accuracy and the kappa coefficient estimated for rice classes were 82%and 0.79,respectively.The analysis estimated approximately 22.3 Mha of suitable rice-fallow areas in South Asia,with 88.3%in India,0.5%in Pakistan,1.1%in Sri Lanka,8.7%in Bangladesh,1.4%in Nepal,and 0.02%in Bhutan.Decision-makers can target these areas for sustainable intensification of short-duration grain legumes.

Reconstruction of Lu-level cropland areas in the Northern Song Dynasty （AD976-1078）

Based on data on taxed-cropland area and on the number of households in historical documents, a probabilistic model of cropland distribution and a cropland area allocation model were designed and validated. Cropland areas for the years AD976, 997, 1066, and 1078 were estimated at the level of Lu（an administrative region of the Northern Song Dynasty）. The results indicated that（1） the cropland area of the whole study region for AD976, 997, 1066, and 1078 was about 468.27 million mu（a Chinese unit of area, with1 mu=666.7m2）, 495.53 million mu, 697.65 million mu, and 731.94 million mu, respectively. The fractional cropland area（FCA） increased from 10.7% to 16.8%, and the per capita cropland area decreased from 15.7 mu to 8.4 mu.（2） With regard to the cropland spatial pattern, the FCA of the southeast, north, and southwest regions of the Northern Song territory increased by 12.0%, 5.2%, and 1.2%, respectively. The FCA of some regions in the Yangtze River Plain increased to greater than 40%, and the FCA of the North China Plain increased to greater than 20%. However, the FCA of the southwest region（except for the Chengdu Plain） in the Northern Song territory was less than 6%.（3） There were 84.2% Lus whose absolute relative error was smaller than 20% in the mid Northern Song Dynasty. The validation results indicate that our models are reasonable and that the results of reconstruction are credible.

Evaluation of global land cover maps for cropland area estimation in the conterminous United States

Global land cover data could provide continuously updated cropland acreage and distribution information,which is essential to a wide range of applications over large geographical regions.Cropland area estimates were evaluated in the conterminous USA from four recent global land cover products:MODIS land cover(MODISLC)at 500-m resolution in 2010,GlobCover at 300-m resolution in 2009,FROM-GLC and FROM-GLC-agg at 30-m resolution based on Landsat imagery circa 2010 against the US Department of Agriculture survey data.Ratio estimators derived from the 30-m resolution Cropland Data Layer were applied to MODIS and GlobCover land cover products,which greatly improved the estimation accuracy of MODISLC by enhancing the correlation and decreasing mean deviation(MDev)and RMSE,but were less effective on GlobCover product.We found that,in the USA,the CDL adjusted MODISLC was more suitable for applications that concern about the aggregated county cropland acreage,while FROM-GLC-agg gave the least deviation from the survey at the state level.Correlation between land cover map estimates and survey estimates is significant,but stronger at the state level than at the county level.In regions where most mismatches happen at the county level,MODIS tends to underestimate,whereas MERIS and Landsat images incline to overestimate.Those uncertainties should be taken into consideration in relevant applications.Excluding interannual and seasonal effects,R 2 of the FROM-GLC regression model increased from 0.1 to 0.4,and the slope is much closer to one.Our analysis shows that images acquired in growing season are most suitable for Landsat-based cropland mapping in the conterminous USA.

2000—2020年中国湿地变化趋势及其与农田之间的面积转化

为探究湿地和农田转化对全国湿地面积的影响,本研究利用2000年、2010年和2020年3期土地利用数据,采用土地利用动态度和土地利用转移矩阵方法,分析了过去20年中国湿地面积的变化、分布状况。结果表明:1)2020年中国湿地面积为34.17万km^(2),其中沼泽湿地面积最大。中国56%~57%的湿地分布在西藏、青海、黑龙江和内蒙古;2)2000—2020年,中国湿地面积净增加5600 km^(2),其中,湿地和农田之间的转化使湿地面积净增加1 500 km^(2),贡献了全国湿地面积增加的27.48%。20年间人工/库塘湿地增加最多,达7800 km^(2),其中,由农田退耕为湿地占人工/库塘湿地面积增加的54.78%;沼泽湿地减少最多,为3300 km^(2),沼泽湿地开垦为农田占沼泽湿地面积减少的89.99%;3)湿地围垦以沼泽湿地转化为农田为主,2000—2020年中国42.57%的沼泽湿地转化为农田,集中在东北地区;农田退耕以农田转化为人工/库塘湿地为主。湿地恢复使中国湿地面积整体增加,但沼泽等具有较高生态功能的天然湿地大面积丧失。

淮河流域典型农田区气溶胶散射特性的日变化和季节变化研究

利用2019年寿县国家气候观象台气溶胶散射系数、气溶胶质量浓度及相关气象观测数据,统计分析了淮河流域农田区域的气溶胶散射特征及其成因,为该区域气溶胶污染辐射强迫及其对农业生产影响方面的研究提供了定量观测证据。研究表明:该地区气溶胶散射系数具有显著的季节变化规律,冬季最高,夏季最低;三个波长(450、525、635 nm)气溶胶日平均散射系数分别为329.8±180.0、270.2±153.7、214.4±128.4 Mm^(-1),并且散射系数日变化与天气要素和大气层结日变化规律具有很好的相关性,且冬季日振幅远小于其他三季;?ngstr?m指数年平均值为1.32,后向散射比年平均值为0.15,气溶胶质量散射系数年平均值为4.83 m^(2)/g,表明淮河流域农田区域的气溶胶以细颗粒为主;气溶胶散射系数大小主要受偏西风调控,散射系数与能见度具有高度的负相关幂函数关系;污染日的气溶胶散射系数远大于清洁日,污染物很大程度上影响了光辐射在大气中的传输能力,污染程度高,大气的散射作用就越强。

黑河中游耕地变化与节水灌溉对地表耗水与地下水的影响

为探究黑河中游耕地面积变化与节水灌溉影响下地表水耗水及地下水动态演变特征,基于1985—2022年黑河莺落峡、正义峡水文站实测径流量月数据和中游地区49眼地下水观测井埋深月数据,结合对节水灌溉的实地调研结果,利用统计分析等方法,分析了地表水耗水和地下水埋深对耕地面积变化与节水灌溉的响应。结果表明:耕地面积变化、节水灌溉和水量统一调度多重影响下,黑河中游地表水耗水量略有下降;黑河中游地下水埋深总体呈增大趋势,扩耕较大的大满灌区东南部与东北部及友联灌区中部地下水埋深明显增大;不同灌溉方式对地下水埋深也有较大影响,河灌区地下水埋深随地表水入渗补给量变化,井灌区和混灌区地下水埋深随地下水开采量变化。

基于多源数据融合产品的黄河中游多沙粗沙区耕地时空动态变化

[目的]黄河中游多沙粗沙区是我国典型的生态脆弱区,准确量化该区耕地时空动态变化对评估区域粮食安全、生态修复效益、水土流失状况及黄河下游安澜等都具有重要意义。[方法]基于5种30 m高分辨率土地利用/覆被数据集产品(CNLUCC、GLC_FCS30、CLCD、AGLC-2000-2015、GlobeLand30),运用耕地利用动态度、偏差系数、转移矩阵、空间一致性分析等方法对比分析多源产品耕地在多沙粗沙区的时空特征,形成30 m分辨率高精度融合数据集产品,并对其进行验证,在此基础上基于融合产品分析1990-2020年黄河中游多沙粗沙区耕地的数量、分布、结构特征。[结果]现有多源数据集产品之间耕地特征存在较大差异,而融合产品精度均优于单独使用5种现有产品。基于融合产品分析发现,1990-2020年耕地面积呈先增加后波动式降低的趋势,退耕还林(草)工程实施为分界线;1990-2020年耕地面积净减少3170.59 km^(2),减少17.63%,且>15°的坡耕地面积占比逐年减少;耕地的动态转移类型主要为草地,其次为人工地表。退耕还林(草)等生态工程的实施和城镇化建设是导致耕地减少的主要原因。[结论]综合分析多源产品的优劣,基于目标地类融合和解释多源数据探究的有效方法,以深入研究某区域的地类特征,从而获得更为精确的研究结论。

基于氮磷养分管理的畜禽场粪便匹配农田面积

该文基于种养平衡的生态模式,根据上海地区单位饲养规模畜禽场粪便产生量及其氮磷含量和各类农作物氮磷需求量,研究分析了基于氮磷养分管理的单位养殖规模畜禽场产生的粪便还田利用需匹配的三大类农作物种植面积。结果表明:在畜禽粪便作为农作物氮磷养分的来源和满足农作物氮养分需求的前提下,根据农作物对氮磷养分需求的木桶效应,各类畜禽粪便提供的磷养分总体上超过各类农作物对磷养分的需求量,具有流失污染环境的隐患。因此,提出了畜禽场粪便还田利用农田面积匹配应基于农作物磷养分需求,不足的氮养分可通过化肥氮给予补充,从而达到种养结合、环境友好的畜禽生态养殖。

近10年来甘肃省粮食生产现状及增产途径分析

明确甘肃省粮食生产能力及其进一步提高的途径,对未来保障区域粮食安全具有重要意义。通过调查近10年来甘肃省耕地面积、粮食播种面积、粮食总产量、粮食单产等数据资料,探讨耕地面积、粮食播种面积、粮食总产量和粮食单产之间的相互关系,以阐明甘肃省粮食生产的潜力及其主要影响因素。结果表明,甘肃省耕地面积和粮食播种面积在近10年间呈先下降后上升的趋势,二者呈显著线性相关(P<0.01);粮食总产量和单产波动上升,但粮食播种面积的变化对粮食总产量无显著影响,单产提高是引起粮食总产量增加的主要因素。分析认为提高单位面积的粮食生产能力是保障甘肃省粮食安全的主要出路,而提高旱地粮食单产则是实现甘肃省新增25亿kg粮食的主要突破口。

西藏主要农区农田土壤肥力状况研究

西藏由于其特殊的地理位置、气候类型和地质历史以及耕作习惯,使其具有特殊的土壤特征.在2002～2004年间,我们对西藏主要农业区的林芝、拉萨、日喀则、山南等4地(市)的农田土壤进行了采样分析,分析结果显示:4地(市)农田土壤酸碱性由弱酸性至弱碱性(pH 6.5～9.0);养分的基本状况是有机质含量在5～50 g/kg之间,变幅较大,N素少(全N 0.2～2 g/kg,速效N 20～80 mg/kg),P素缺(全P 0.22～1.42 g/kg,速效P1～133 mg/kg),K素(全K 1.9～12.2 g/kg,速效K 80～1290 mg/kg)和微量元素比较丰富(Cu10～443mg/kg,Zn47～266mg/kg,Fe 1880～7550mg/kg,Mo0.2～6.6mg/kg,Mn 196～736mg/kg,B 0.5～138mg/kg).

广西耕地资源变化与粮食安全分析

在详细分析2000—2008年广西耕地变化趋势及造成耕地减少原因的基础上,采用最小人均耕地面积及耕地压力指数等方法,对粮食安全状况进行了研究,同时详细分析了工业化发展所处阶段及经济发展与耕地资源变化之间的关系,并结合广西新一轮土地利用总体规划预测的社会经济发展目标,运用统计分析方法预测了2020年耕地保有量。结果表明,广西2000-2008年粮食生产处于供不足需的状态,且处于工业化初期阶段,其工业化发展及城镇化的提高是建立在耕地资源的占用之上。

干旱半干旱区农田土壤碳垂直剖面分布特征研究

以中国干旱半干旱区农田土壤为研究对象,通过收集自然农田和长期定位站点（178个剖面,0~100 cm土层）农田土壤碳的数据并对其进行整合,分析了农田土壤有机碳和无机碳含量的垂直剖面分布特征及其影响因素。结果表明,随土层深度增加,农田土壤有机碳呈下降趋势,表层含量高于底层;不同地区农田土壤无机碳含量变化趋势不一,随土壤深度增加整体呈现升高的趋势,但是也有一些地区呈现下降趋势。土壤剖面深度为100 cm的农田土壤有机碳和无机碳密度平均值分别为8.33和15.83 kg m-2,农田土壤无机碳储量大约是土壤有机碳的2倍。土壤深度为0~30 cm的有机碳占100 cm总有机碳含量的45%,无机碳仅占100 cm总无机碳含量的29%;土壤无机碳主要集中在30~100 cm土层,占100 cm总无机碳含量的71%,远高于有机碳在此土层占100 cm总有机碳含量的百分比（55%）。综合自然农田和长期定位站点农田土壤碳的数据,土壤容重与土壤p H是影响农田土壤有机碳和无机碳分布特征的重要因素：自然农田土壤有机碳与土壤p H（R2=0.61,p〈0.01）和土壤容重（R2=0.64,p〈0.01）呈显著负相关;长期定位站点土壤无机碳与土壤p H（R2=0.56,p〈0.01）和土壤容重（R2=0.63,p〈0.01）呈显著正相关。中国干旱半干旱区农田土壤有机碳和无机碳的分布特征与影响因素,将为陆地生态系统碳储量估算提供数据基础与理论支撑。

陕西省采矿业污染农田土壤中Cd、Pb的释放特征

【目的】研究陕西省采矿业污染农田土壤中Cd、Pb的分布及其释放特征。【方法】以采自陕西凤县、潼关、洛南某铅锌矿区污染农田土壤（FX、TG、LN）为研究对象，测定不同粒径土壤中Cd、Pb的总量和有效态量，并对不同农田土壤中Cd、Pb的化学形态进行了探讨，采用批处理法对FX、TG、LN土壤中Cd和Pb的释放动力学特征进行了分析。【结果】3个矿区污染农田土壤Cd总量均严重超标，TG和LN土壤Pb总量也达超标水平，FX、TG和LN土壤中Cd、Pb总量分别达到了107．84，218．62，179．29mg／kg及208．93，2216．61，1046．24mg／kg。3种土壤不同粒径土样中Cd、Pb总量均随着土壤粒径减小而增加，3种土壤Cd、Pb有效态量从大到小依次为TG〉LN〉FX。FX、TG、LN土壤中Cd有效态量分别为11．59～16．73，21．10～23．07，16．01～16．73mg／kg；Pb有效态量分别为18．30～25．05，140．22～210．59，25．81～44．06mg／kg。化学形态分析表明，在3种土壤中Cd、Pb均以碳酸盐结合态和硫化物态为主，水溶态所占比例较小；在FX土壤中未检测到水溶态Cd和Pb，在LN土壤中未检测到水溶态Pb。在污染土壤中水溶态cd、Pb的释放基本在12h以后达到平衡，其释放过程分为快速释放、慢速释放和动态平衡3个阶段，其释放规律符合准二级动力学过程。【结论】陕西省采矿业已经造成严重的农田土壤重金属污染，FX、TG和LN3种污染土壤中Cd、Pb的释放与土壤粒径以及重金属污染物的来源密切相关，水溶态Cd、Pb的释放过程是复杂的非均相扩散过程。

我国粮食主产区耕地复种指数变化特征与潜力分析

为了解粮食主产区耕地复种指数变化特征与潜力,进一步挖掘粮食主产区的生产能力,稳定全国粮食安全大局,利用1979-2008年统计资料,对我国粮食主产区耕地面积、农作物总播种面积、粮食播种面积进行分析,并采用最大复种指数与热量、水资源之间的定量化关系模型,分析粮食主产区的复种指数理论潜力和可挖掘潜力。结果表明:1979-2008年期间我国粮食主产区耕地面积减少,农作物播种面积增加,粮食总产量与单产攀升,粮食总产量占全国比重升高,耕地复种指数东北区、黄淮海区上升,长江中下游地区下降。以2008年的耕地复种指数为参照,东北区、黄淮海区、长江中下游区理论可挖掘潜力分别为28%、48%、94%。

长江三角洲耕地数量变化趋势及总量动态平衡前景分析

论文利用长江三角洲地区近50年长序列耕地统计、近10多年土地利用调查数据及相关社会经济资料,重点从长江三角洲耕地数量变化的阶段性及与经济发展水平之间关系宏观分析的角度,探讨该区未来10～15年耕地变化趋势及实施区域耕地总量动态平衡的可能性。分析表明,长江三角洲耕地面积随人均GDP的增长呈良好的指数减少关系,人均GDP低于12000元/人,经济增长占用耕地的压力较大;人均GDP超过30000元/人时,这种压力将开始显著减缓。现阶段长江三角洲仍处于经济发展对耕地的压力较大的发展阶段,但已较1995年前明显减轻,估计至2004年前后,该区经济增长对耕地的压力将开始得到缓解。按现有的土地复垦整理补充耕地的投资力度,至2010年耕地面积仍将比1998年减少5.5×104hm2左右,若加大复垦整理的投资力度至现状水平的2倍,则保持耕地数量不减少也是可能实现的。

典型区域果园土壤有机质变化特征研究

在黄土高原、胶东半岛和北京郊区果园选择11个采样区,按照5～10年、10～15年和15年以上3个园龄段,利用GPS定位系统,共采集0～20cm表层土壤样品99份,并在取样果园附近选择普通农田作为对照采集土壤样品33份,测定了果园与普通农田土壤的有机质含量,并从果园土壤有机质数量特征、果园与农田差异特征以及有机质随园龄段变化特征3个方面进行统计分析。研究结果表明:胶东半岛栖霞和北京郊区果园土壤有机质含量较高,黄土高原宝塔较低。与农田相比,60%多的果园土壤有机质未发生显著变化,明显提高的果园不到30%,明显降低的果园不到10%;土壤有机质发生变化的果园,平均提高0.62%,平均降低0.20%;随园龄增加,两个样点果园土壤有机质明显提高,其他果园变化不显著。在优质高产果园区,果园土壤有机质提高归因于施用有机肥、果园种草、青草或秸秆还田。总体上看,典型区域果园土壤有机质高低值差异较大,土壤有机质含量普遍不高,果业持续发展能力较低。

褐土区农田土壤氮磷淋溶特征及其管理措施

自20世纪90年代以来,持续过量氮磷化肥投入导致农业面源污染日益严重,了解农田土壤氮磷淋溶特征是降低地下水污染的基础。基于田间调查、长期定位肥料试验和田间试验,分析褐土区氮磷的盈余状况,阐明该区农田土壤氮磷的盈余变化、淋溶特征;评价田间管理措施对农田土壤氮磷淋溶的影响。结果表明,典型褐土区关中平原过量施氮的土壤达到83%以上,大量土壤硝态氮已经迁移到100 cm土层以下,15%的水井地下水的硝态氮含量超过10 mg·L−1(WHO饮用水标准);80%耕层土壤有效磷(Olsen-P)含量已超过20 mg·kg−1,富磷土壤已出现可溶性磷素向耕层以下迁移的现象。氮肥和磷肥的投入量、氮磷吸收量和土壤氮磷残留量之间存在着3个发展阶段:环境友好-资源高效阶段、环境低风险-资源低效阶段和环境有害-资源无效阶段。与当地常规水肥投入量相比,在保证产量的前提下,化肥减量、降低灌溉量、施用生物炭或秸秆还田都可以降低氮磷淋失量;其中化肥减量、降低灌溉可显著降低氮磷的淋失,其次是施用生物炭和秸秆。施用秸秆条件下,阻控硝态氮淋失与微生物生物量碳氮的提高、土壤硝化势降低或反硝化势升高有关。此外,需要关注褐土区粮果复合系统中土壤氮磷淋溶的环境效应、地下水硝酸盐污染的溯源等问题。

中国粮食主产区农田生态健康问题与技术对策探讨

粮食问题是关系我国国民经济发展和全面建设小康社会的重大战略问题,我国人多地少的国情决定了必须走持续提高粮食单产的道路,但是高产再高产过程带来了农田生态系统的压力不断增加,农田生态系统结构破坏、功能退化甚至破坏的态势日益严峻,严重制约了作物生产力的持续提高。如何构建健康型高产农田生产系统是我国粮食安全战略实施急需解决的重大保障技术。本文在对分析中国农业生态健康研究动态及进展的基础上,针对我国农田生态健康存在的问题,从作物-土壤-环境的系统角度出发,构建我国健康型农田生态系统的技术支撑体系,并提出了技术对策与研究重点。