甘肃黄土高原旱作区土壤贮水量对春小麦水分生产力的影响

选择甘肃黄土高原旱作区5个春小麦测站2 m土层深度多年土壤贮水量与产量资料,从大气降水-土壤水-作物循环系统的理论出发,研究了土壤贮水量和农田耗水量对春小麦水分生产力的影响.结果表明:该区域是一个贮水和保水性能较好的天然土壤水库,干旱区、半干旱区、半湿润区2 m土层最大贮水量分别达470 mm、582 mm和617 m...     

The runoff characteristics under simulated rainfall on purple soil sloping cropland

Rainfall runoff is a critical hydrological process related to soil erosion and agricultural non-point pollu-tion. In this study, 25 simulation experiments on rainfall were carried out in five runoff plots. Rape (Brassica campestris) was planted on the downslope of the plots. Experiments were conducted when the vegetation coverage reached 80%. Each plot was subjected to five rainfall events differing in intensity. The results showed: (1) the runoff coefficients of overland flow and subsurface flow were less than 0.6 and 0.005, respectively; (2) the discharge of overland flow was the quadratic function of time; (3) runoff coefficient was the function of slope gradient and rain-fall intensity. When the slope gradient increased from 8.7% to 46.6%, the runoff coefficient of overland flow first increased and then decreased. The runoff coefficient reached the maximum when the slope gradient was within the range of 17.6%-36.4%; and (4) the process of subsurface flow generation included the increasing phase and reces-sion phase. Discharge was a logarithm function of time in the increasing phase, and an exponential function in the recession phase. Runoff coefficient of subsurface flow decreased first and then increased when the slope gradient varied from 8.7% to 46.6% and was not correlated with rainfall intensity.     

Mapping abandoned agricultural land in Kyzyl-Orda,Kazakhstan using satellite remote sensing

In many regions worldwide, cropland abandonment is growing, which has strong and known environmental and socio-economic consequences. Yet, spatially explicit information on the spatial pattern of abandonment is sparse, particularly in post-Soviet countries of Central Asia. When thriving reaching for key Millennium Development Goals such as food security and poverty reduction, the issue of cropland abandonment is critical and therefore must be monitored and limited, or land use transformed into an alternative one. Central Asia experienced large changes of its agricultural system after the collapse of the Soviet Union in 1991. Land degradation, which started already before independence, and cropland abandonment is growing in extent, but their spatial pattern remains ill-understood. The objective of this study was to map and analyse agricultural land use in the irrigated areas of Kyzyl-Orda, southern Kazakhstan, Central Asia. For mapping land use and identifying abandoned agricultural land, an object-based classification approach was applied. Random forest (RF) and support vector machines (SVM) algorithms permitted classifying Landsat and RapidEye data from 2009 to 2014. Overlaying these maps with information about irrigated land parcels, installed during the Soviet period, allowed indicating abandoned fields. Fusing the results of the two approaches, RF and SVM, resulted in classification accuracies of up to 97%. This was statistically significantly higher than with RF or SVM alone. Through the analysis of the land use trajectories, abandoned agricultural fields and a clear indication of abandoned land were identified on almost 50% of all fields in Kyzyl-Orda with an accuracy of approximately 80%. The outputs of this study may provide valuable information for planners, policy- and decision-makers to support better-informed decision-making like reducing possible environmental impacts of land abandonment, or identifying areas for sustainable intensification or re-cultivation.     

Reconstructing provincial cropland area in eastern China during the early Yuan Dynasty (AD1271-1294)

Reconstructing historical land use and land cover change (LUCC) at the regional scale is an important component of global environmental change studies and of improving global historical land use datasets. By analyzing data in historical documents, including military-oriented cropland (hereafter M-cropland) area, the number of households engaged in M-cropland (hereafter M-household) reclamation, cropland area, and the number of households, we propose a conversion relationship between M-cropland area and cropland area reclaimed by each household. A provincial cropland area estimation method for the Yuan Dynasty is described and used to reconstruct the provincial cropland area for AD1290. Major findings are as follows. (1) Both the M-cropland and cropland areas of each household were high in the north and low in the south during the Yuan Dynasty, which resulted from different natural conditions and planting practices. Based on this observation, the government-allocated M-cropland reclamation area to each household was based on the cropland area reclaimed by each household. (2) The conversion relationship between M-cropland and cropland areas per household showed conversion coefficients of 1.23 and 0.65 for the south and north, respectively. (3) The cropland area in the entire study area in AD1290 was 535.4×10⁶ mu (Chinese area unit, 1 mu=666.7 m²), 57.8% in the north and 42.2% in the south. The fractional cropland areas for the entire study area, north, and south were 6.8%, 6.6%, and 7.1%, respectively and the per capita cropland areas for the whole study area, north, and south were 6.7, 15.6, and 4.1 mu, respectively. (4) Cropland was mainly distributed in the middle and lower reaches of the Yellow River (including the Fuli area), Huaihe River Basin (including Henan Province), and middle and lower reaches of the Yangtze River (including Jiangzhe, Jiangxi, and Huguang provinces).     

北宋中期路域耕地面积的再估算

基于历史文献研究的方法,利用北宋中期垦田数据及宋代人口粮食需求量、粮食亩产量等史料,考察了北宋中期南北方的垦田隐匿特点、北宋户均垦田数的合理范围及西南五路的户均基本垦田需求,并据此对北宋中期路域耕地面积进行了再估算。主要结论：北宋垦田隐匿比例不具有北高南低的区域分异特征;北宋户均垦田数的合理范围为20~100亩;西南五路的户均基本垦田需求数约为20~30亩;北宋中期境内耕地面积约为731.9×10⁶今亩,土地垦殖率为16.9%,其中,北方耕地面积约占29.7%,南方约占70.3%;黄淮海平原、长江中下游平原、两湖平原和成都平原等是北宋耕地的主要分布区,而西南地区垦殖率较低。合理订正北宋中期路域耕地面积,对重建中国过去千年LUCC数据集具有重要意义。     

基于能值分析的江苏省耕地生态足迹区域差异

以江苏省耕地生态足迹为研究对象,在考虑不同地区的土地利用效率的基础上,把太阳辐射、降水量、土壤 肥力、土地利用效率、耕地面积等作为构成承载力的实质因素,计算了江苏省不同地区的耕地生态承载力。研究结 果表明：就人均耕地生态承载力而言,苏北地区普遍大于苏中和苏南地区,盐城市、淮安市和宿迁市最大,无锡市、 南京市和苏州市最小。就人均耕地生态足迹而言,苏南地区普遍小于苏北和苏中地区,盐城市、南通市和淮安市最 大,而无锡市、苏州市和常州市最小。江苏省13 个地市的生态差额指数都小于0.5,即耕地都处于不可持续性状态, 其区域差异是：南北两端好于中部,南端的苏州市、无锡市最好;而江苏中部,又是中间好于东西两侧,东侧的南通 市、盐城市最差。     

皖江自然湿地土壤碳密度及其开垦为农田后的变化

于2005年分别采集了安徽沿江4个淡水湖泊的自然湿地及其周边围垦农田的代表性土壤剖面样品,测定了总有机碳含量,讨论了天然淡水湿地有机碳密度与深度分布特征及其开垦为农田后的变化。结果显示,湿地表层（0～30cm）和全剖面（0～100cm）中的碳密度分别为42．5～57．4t／hm^2和81．5～91．6t／hm^2;而农田则分别为22．4～48．4t／hm^2和41．4～76．5t／hm^2。湿地开垦为农田后,土壤表层和全剖面的土壤有机碳含量明显降低,且有机碳含量的变异性增大。表明湿地开垦为农田后,其碳库失去稳定性。但是,开垦的旱地土壤的有机碳含量和碳密度显著低于开垦的稻田,故湿地开垦为旱地更不利于湿地碳库保护。因而,将湿地垦殖为水田是相对较有利于湿地碳库保护的人为土地利用方式。湿地开垦的碳库损失可能是土壤的大气CO2源效应的主要途径。     

中国传统农区1820年耕地数据网格化方法

Recent studies have demonstrated the importance of LUCC change with climate and ecosystem simulation, but the result could only be determined precisely if a high-resolution underlying land cover map is used. While the efforts based satellites have provided a good baseline for present land cover, what the next advancement in the research about LUCC change required is the development of reconstruction of historical LUCC change, especially spatially-explicit historical dataset. Being different from other similar studies, this study is based on the analysis of historical land use patterns in the traditional cultivated region of China. Taking no account of the less important factors, altitude, slope and population patterns are selected as the major drivers of reclamation in ancient China, and used to design the HCGM (Historical Cropland Gridding Model, at a 60 km×60 km resolution), which is an empirical model for allocating the historical cropland inventory data spatially to grid cells in each political unit. Then we use this model to reconstruct cropland distribution of the study area in 1820, and verify the result by prefectural cropland data of 1820, which is from the historical documents. The statistical analyzing result shows that the model can simulate the patterns of the cropland distribution in the historical period in the traditional cultivated region efficiently. Foundation: National Natural Science Foundation of China, No.40471007; Innovation Knowledge Project of CAS, No.KZCX2-YW-315 Author: Lin Shanshan (1982–), Master, specialized in historical environmental change.     

近300年中国耕地数据集重建与耕地变化分析

针对中国历史时期不同政体耕地记录的特点,分别采用因素修正、引用替换、线性内插、衔接对比、人地关系检验、垦殖趋势检验、行政面积比例调整等方法对历史耕地数据进行修正,重建了基于现代省界的近300年中国分省耕地数据集,从数量角度对中国耕地总量和分省耕地变动特点进行分析,得到以下主要结论：① 在耕地总量上,SAGE和周荣的数据明显高估,本文结果与HYDE、CHCD和章有义数据的平均差异率在15%以下;但在省域尺度上,与SAGE、HYDE数据库存在明显差异,相对差异率>30%的省份比重分别为94%和61%,与CHCD数据较为接近,相对差异率>30%的省份比重为22%,但部分省份差异明显,仍需进一步分析研究;② 伴随清中期后的人口爆炸,近300年中国耕地增长近3.2倍,由清朝初年的42.4×10⁶ hm²增加至1985年的136.9×10⁶ hm²,根据增长速率变化可分为五个阶段,即清前中期快速增长阶段、清后期低速增长阶段、民国时期波动阶段、建国初期剧烈增长阶段和建国后耕地流失阶段,影响耕地变化主要是国家政策、战乱、经济发展等驱动因素。③ 从省域尺度看,近300年中国各区域耕地变化差异显著。清初,中国耕地主要集中于长江中下游平原、黄淮海平原、关中盆地及银川平原等地,此后,内地的垦殖活动不断增强,外围农区呈由南向北的趋势不断开荒。建国后,耕地开垦逐步向西北和东北方向发展。     

重庆市武隆县农地流转下农业劳动力对耕地撂荒的不同尺度影响

在农地流转市场日趋完善的背景下,农户间的耕地流转无疑会缓解因部分农户劳动力不足造成的耕地撂荒现象,但仅从农户尺度上分析难以揭示农业劳动力数量与耕地撂荒间的关系。运用重庆市武隆县17 个乡镇40个自然村的308 份农户调查数据,通过二分类Logistic 回归模型、简单相关和偏相关分析,从农户和村庄两个层次上探讨农业劳动力对耕地撂荒的影响程度及农地流转对两者关系的影响。结果显示：① 农户尺度上亩均农业劳动力对耕地是否撂荒的影响不显著,而在村庄尺度上显著。② 亩均务农劳动力与耕地撂荒规模的偏相关回归分析中,控制耕地流转和不控制流转条件下,农户尺度上两者的偏相关系数和简单相关系数分别为-0.138 和-0.027,前者在1%水平上显著,而后者不显著;村庄尺度上,控制流转和不控制流转的相关系数分别为-0.273 和-0.294,均在5%水平上显著。③ 在农地流转市场较为完善的地区,选择在村庄尺度上进行农业劳动力对耕地撂荒影响分析研究是比较合理的。