退耕还林对农业生产结构影响的实证研究——以陕北吴起县为例

首先运用描述性统计方法从种植业、畜牧业和林业、渔业等几方面对退耕还林前后农业生产结构的变化进行分析;然后借助洛伦兹曲线和基尼系数,分别计算了吴起县退耕还林前后的农业生产结构合理化指数,得出退耕还林后吴起县农业生产结构合理化综合指数有所提高(由0.8270提高到0.8596),但仍有进一步调整的空间;特别是退耕还林前后劳动力合理化指数都偏低(分别仅为0.7426和0.7762),说明吴起县劳动力结构调整力度还有待加强。     

Labor‐saving technologies and structural transformation in northern Ghana

Labor‐saving technologies played a fundamental role historically in the structural transformation of agrarian economies. We focus on an emerging labor‐saving trend in Ghana, use of motorized tricycles (MTs), which provide an affordable alternative to manually transferring crops from plots to homestead. A household survey collected in 2017 in northern Ghana is used to shed light on how the time savings made available by using MTs may be converted into activities that enhance agricultural productivity and/or diversify the household away from agriculture. Detailed information collected on the agricultural production and agro‐processing behavior of 1,400 households allows us to examine the above transformative channels. Ordinary least squares and instrumental variable regressions are applied to quantify the effect of MTs on related outcomes. We find households are able to diversify their farming activities into selling processed agricultural goods with the time savings provided through MT adoption. Policies aimed to foster the diffusion of MTs elsewhere in Ghana may expedite structural change and, hence, economic growth.     

近10年长江经济带多尺度耕地利用变化特征

[目的]研究长江经济带耕地利用特征及其变化规律,辅助跨区域耕地保护与管理、促进农业可持续发展。[方法]基于合作博弈赋权法的多指标综合评价法,利用耕地规模、投入和产出指数,分析长江经济带近10年多空间尺度变化特征。[结果](1)2005~2015年期间长江经济带耕地规模指数、投入强度、产出能力均呈现增长态势,增长比例分别为8.98%、124.27%、18.81%。(2)长江经济带不同尺度耕地利用变化特征存在显著差异。上游耕地规模指数增长20.26%,中游地区耕地投入强度增长明显,下游地区耕地规模指数下降3.86%,但耕地产出能力提升显著。从省域尺度上来看,"云南—贵州—湖南—湖北"一带耕地规模指数增加明显,云南、安徽、贵州和四川4省耕地投入强度的涨幅超20%,四川、安徽、江西、江苏省耕地产出能力增长明显。地级及以上城市尺度耕地规模指数、投入强度和产出能力呈"大范围增长,局部小幅降低"格局。(3)地级及以上尺度耕地规模指数、投入强度和产出能力变动关系错位明显。[结论]大区域多尺度耕地利用变化特征对比分析,有助于进一步理解区域耕地利用变化的深层次动力机制,是有效推进跨区域耕地利用与保护、统筹安排农业发展布局和助力流域乡村振兴的重要参考。     

河北粮食生产可持续发展策略研究

河北粮食生产主要受到社会重大变革、政策调整、农业生产条件、农资投入、科技进步、价格变动等因素的综合影响,单产比播种面积对总产的影响更大。分析了河北省粮食生产发展的制约因素:耕地减少、水资源短缺和成本、效益限制。分析粮食增产潜力,文章认为应以农用水资源为主的农业生产条件合理确定河北省粮食生产品种结构与布局以及粮食产量目标。提出应在基本粮田保护区设立、中低产田、水利建设与节水、优良品种及农业科技等方面着力加强。同时在耕地流转、政府投入、种粮补贴等方面也应配套政策措施。     

四川省耕地压力时空变化特征分析

文章以四川省21个市(州)为研究对象,基于最小人均耕地面积和压力指数模型,对1990～2008年四川省及其21个市(州)的耕地压力进行了测算,并对压力等级进行了评价。研究结果显示,四川省的耕地压力时空变化情况大致可以分为3个阶段:1990～1994年耕地压力指数缓慢上升,1995～1999年耕地压力指数持续下降,2000～2008年耕地压力指数波浪式上升;各市(州)间差异显著,除宜宾市和凉山州外,压力指数都在增加;多数市(州)压力等级处于明显区,耕地压力较大;耕地压力较大的区域主要分布在人口密度大、经济发展较快、农业基础设施薄弱和耕地综合生产能力低的地区。在以上基础上提出了相应的建议以保障四川省粮食安全。     

Land‐use change trajectories up to 2050: insights from a global agro‐economic model comparison

Changes in agricultural land use have important implications for environmental services. Previous studies of agricultural land‐use futures have been published indicating large uncertainty due to different model assumptions and methodologies. In this article we present a first comprehensive comparison of global agro‐economic models that have harmonized drivers of population, GDP, and biophysical yields. The comparison allows us to ask two research questions: (1) How much cropland will be used under different socioeconomic and climate change scenarios? (2) How can differences in model results be explained? The comparison includes four partial and six general equilibrium models that differ in how they model land supply and amount of potentially available land. We analyze results of two different socioeconomic scenarios and three climate scenarios (one with constant climate). Most models (7 out of 10) project an increase of cropland of 10–25% by 2050 compared to 2005 (under constant climate), but one model projects a decrease. Pasture land expands in some models, which increase the treat on natural vegetation further. Across all models most of the cropland expansion takes place in South America and sub‐Saharan Africa. In general, the strongest differences in model results are related to differences in the costs of land expansion, the endogenous productivity responses, and the assumptions about potential cropland.     

A Note: Reducing Cropland Abandonment in China – Do Agricultural Cooperatives Play a Role?

Cropland abandonment occurring both nationally and globally threatens food security and environmental sustainability. We explore whether agricultural cooperatives help reduce cropland abandonment, using data collected from 5,593 households in 229 villages in China. By estimating a two-stage residual inclusion approach, we provide evidence that the existence of agricultural cooperatives in rural villages reduces the probability of cropland abandonment and the abandonment ratio. Further analysis shows that cooperative effects on cropland abandonment and the abandonment ratio are heterogeneous across geographic locations.     

Links between economic liberalization and rural resource degradation in the developing regions

This paper examines evidence of the effects of economic liberalization and globalization on rural resource degradation in developing countries. The principal resource effects of concern are processes of land use change leading to forestland conversion, degradation and deforestation. The main trends in globalization of interest are trade liberalization and economy-wide reforms in developing countries that have 'opened up' the agroindustrial sectors, thus increasing their export-orientation. Such reforms have clearly spurred agroindustrialization, rural development and economic growth, but there is also concern that there may be direct and indirect impacts on rural resource degradation. The direct impacts may occur as increased agricultural activity leads to conversion of forests and increased land degradation from 'unsustainable' production methods. However, there may also be indirect effects if agroindustrial development displaces landless, near-landless and rural poor generally, who then migrate to marginal agricultural lands and forest frontier regions. This paper explores these direct and indirect effects of globalization and agroindustrialization on rural resource degradation both generally, plus through examining case study evidence. The paper focuses in particular on the examples of structural adjustment, trade liberalization and agricultural development in Ghana, and maize sector liberalization in Mexico under North American Free Trade Agreement (NAFTA).     

Agricultural land use change in Karamoja Region,Uganda

We examine dramatic cropland expansion in Karamoja, Uganda by investigating the links between biophysical and political historical events leading to the current state of agricultural land use. Our objective was to quantify agricultural expansion, uncover the dominant drivers leading to the current state of agricultural land use and its impacts on livelihoods. Region wide analysis of remotely sensed data, land use policy and history as well as farmer interviews were undertaken. We posit that government programs instituting sedentary agriculture are the most significant drivers of cropland expansion in Karamoja. We show a 299% increase in cropland area between 2000 and 2011 with most expansion occurring in Moroto District (from 706 ha to 23,328 ha). We found no evidence of an increase in overall crop production or food security and food aid continues to be essential due to recurrent crop failures. Due to lack of resources for inputs (e.g., seeds and labor) cultivated fields remain very small in size and over 55% of once cultivated land is left fallow. Our findings bring into question whether continued promotion of rain-fed agriculture in Karamoja serves the best interests of the people. Current cropland expansion is directly competing and compromising pasture areas critical for livestock-based livelihoods. Without strong agricultural extension programs and major investments in climate-smart options, cropland expansion will continue to have a net negative impact, especially in the context of current climate projections which indicate a future decrease in rainfall, increase in temperature and an increase in the frequency and magnitude of extreme events.     

基于GIS技术的新疆绿洲农用土地分等研究——以和田皮山县为例

农用土地等级划分是土地管理的基础性工作;以新疆维吾尔自治区和田地区的皮山县农业用地等级划分为例,就GIS技术在新疆绿洲农用土地等级划分的应用进行探讨,着重论述了在GIS技术支持和绿洲特殊地理环境背景下,农用土地数据的处理过程,建立相应的数据图库,对比实际情况,分析分等结果。     

Addressing climate change cause and effect on land cover and land use in South Asia

This paper evaluates the role of trade liberalization and agricultural intensification in mitigating climate change cause and effects on land use and emissions using a computable general equilibrium model. Our results indicate that cropland expansion triggered by climate-induced crop productivity changes results in deforestation and increases emissions in South Asia and globally. Global full trade liberalization on all goods is the optimum policy for South Asia despite significant global deforestation, but for the world, unilateral partial trade liberalization on all goods is a more appropriate policy while ensuring a considerable emissions reduction for South Asia. These results indicate that mitigation responses to climate change are location specific and no one trade policy is suitable at the regional and global levels. Lastly, agricultural intensification by improving productivity growth is the best strategy in land-based emissions mitigation, thereby avoiding the transformation of forest and pasture lands for agricultural cultivation both at regional and global levels.     

Agricultural Payments and Land Concentration: A Semiparametric Spatial Regression Analysis

Over the last twenty years, both crop production and agricultural payments have shifted toward larger operations. This study examines whether payments from federal farm programs contributed to increased concentration of cropland and farmland. Using zip code–level data constructed from the microfiles of the 1987–2002 agriculture censuses we examine the association between government payments per acre and subsequent growth in land concentration. A semiparametric generalized additive model (GAM) controls for location and historical concentration, sales per acre, and ratio of cropland area to zip code area. Findings indicate, both with and without nonparametric controls, government payments are strongly associated with subsequent concentration growth.     

The research cost of adapting agriculture to climate change: A global analysis to 2050

Investments in agricultural research and development (R&D) made over the next few decades will likely prove critical in offsetting adverse climate change impacts on the global food system. In this study, we offer cost estimates of public R&D-led adaptation to climate change grounded in an explicit framework relating the flow of annual R&D expenditures to building knowledge capital and thereby raising productivity in agriculture. Our research uses a comprehensive collection of historical public agricultural R&D expenditure and a literature review of elasticity estimates linking knowledge stocks to agricultural productivity growth for key world regions. Given climate-driven crop yield projections generated from extreme combinations of crop and global circulation models, we find that offsetting crop yield losses projected by climate and crop models over 2006–2050 would require increased R&D adaptation investments of between $187 billion and $1,384 billion (in 2005 $PPP) if we invest between 2020 and 2040. This is 16–118% higher than global R&D investment if present spending trends continue. Although these costs are significant, worldwide R&D-led climate adaptation could offer favorable economic returns. Moreover, R&D-led adaptation could deliver gains in food security and environmental sustainability by mitigating food price increases and slowing cropland expansion.     

2001—2020年鄱阳湖平原耕地复种时空变化研究

目的 区域特点背景下,利用遥感手段实时获取局部区域耕地复种信息并分析其时空变化特征,可有效反映区域农业集约化变化趋势。方法 文章以鄱阳湖平原为研究区域,利用MODIS09Q1数据建立二波段增强型植被指数（Two-band Enhanced Vegetation Index,EVI2）;基于时序EVI2,利用二次差分法提取研究区2001—2020年耕地复种频率逐年结果;基于Mann-Kendall检验方法、最小二乘法、转移矩阵等方法分析20年复种时空变化特征。结果 基于EVI2提取复种频率的总体精度为90.70%,Kappa系数0.81,满足应用要求。研究区复种以一年二熟为主,耕地整体复种水平以2013年为突变年份呈波动上升趋势,2001—2013年研究区复种降低,2013—2020年则表现为上升趋势,其中2020年复种较2018年和2019年都有所上升,表明恢复早稻政策作用明显。空间上看,20年间研究区82.14%的耕地复种并未表现出明显的变化,保持稳定状态;复种显著降低区域主要分布在余江县、鹰潭市、抚州市、南昌市等县市区部分区域,显著上升区域则主要分布在新建县、余干县北部、鄱阳县北部等。从转移类型上来看,主要发生一年一熟和一年二熟间的相互转换。2001—2013年一年二熟转为一年一熟现象严重,2013—2020年则一年一熟转为一年二熟现象明显。结论 基于EVI2提取复种频率取得了良好的效果。长时序复种频率时空变化特征反映了研究区耕地集约化程度加强的趋势,可为区域“藏粮于地”战略布局提供数据支撑和理论依据。未来研究可进一步从种植制度的视角去理解多年的不同种植制度和休耕策略是如何结合的,从而丰富耕地集约化评价理论体系。     

吉林省耕地利用碳排放测度及其与粮食生产脱钩分析

[目的]通过分析吉林省县域耕地利用碳排放时空变化、碳排放结构、碳排放空间分布、脱钩效应以及碳排放驱动因素,以期从耕地低碳利用角度,为吉林省农业高质量发展和制定减排政策提供科学参考。[方法]文章运用系数法,计算2000—2020年吉林省47个县域单元的耕地利用碳排放量;采用Tapio脱钩模型,分析耕地利用碳排放与粮食产量之间的脱钩特征;利用空间回归模型,分析耕地利用碳排放的驱动因素。[结果]（1）吉林省县域耕地利用碳排放时空变化特征：2000—2016年吉林省耕地利用碳排放量增长,2016—2020年开始缓慢下降;碳排放结构方面,碳排放量从大到小分别是化肥、翻耕、灌溉、农用柴油、农膜和农药;碳排放空间分布呈现西高东低的格局。（2）耕地利用碳排放与粮食生产脱钩特征：呈现强脱钩和弱脱钩特征的县域数量增多,呈现强负脱钩和扩张性负脱钩特征的县域数量减少;吉林省东部地区的县域脱钩特征逐渐优于西部地区,吉林省整体县域的脱钩特征朝着理想状态发展。（3）耕地利用碳排放量驱动因素分析结果表明：人均农业GDP、农村用电量、农业机械化程度和化肥施用强度因素对耕地利用碳排放量为正向驱动,城镇化率对耕地利用碳排放...     

基于NDVI时序数据的华北地区耕地物候参数时空变化特征

[目的]耕地物候作为农业生态系统的重要特征之一,是进行农作物长势监测与估产、田间管理、农作物合理布局等的重要依据。利用遥感方法提取大区域尺度耕地物候参数和种植制度的时空变化特征,有助于从整体上掌握农业资源的空间分布情况,为农业生产决策和区域粮食安全评价提供服务。[方法]文章基于1999年和2013年的SPOT/VGT NDVI逐旬时间序列数据,采用TIMESAT软件集成的非对称高斯函数拟合法对数据进行平滑重构,通过比例阈值法提取了华北地区耕地物候参数(生长季开始期和结束期),分析其时空分布特征,并依据年内NDVI变化曲线峰值数目来确定耕地的生长季个数,识别耕地种植制度。[结果]华北地区作物生长开始期和结束期都存在明显的空间差异,15年来河北北部、北京、天津等地区,第一季作物返青/出苗期变化不大。而河南南部和中部地区,2013年第二季作物出苗期明显提前,由1999年6月下旬7月上旬,提前至6月上旬。我国华北地区种植制度仍以一年两熟制为主,华北地区北部受热量资源制约,仍旧保持一年一熟制不变。与1999年相比,华北地区2013年两熟制种植面积下降了21.1%,而一熟制种植面积增加了38.7%。[结论]华北地区耕地物候的时空变化与种植制度密切相关,同时也受到自然资源和人类活动的共同影响。     

近20年我国县域耕地物候变化空间格局研究

[目的]耕地物候的时空格局研究可以为生态环境建设、农业生产管理等提供依据。[方法]文章基于2001—2017年全国范围内MODIS EVI时间序列数据,使用Savitzky-Golay滤波函数对EVI时间序列曲线进行重建,然后利用动态阈值法提取出了耕地的生长季始期、生长季末期和生长季长度,通过Sen氏斜率计算出了3项物候参数在2001—2017年的变化趋势。[结果](1)从像素单元来看,全国耕地物候生长季始期变化中有53.07%的像元表现为提前趋势;生长季末期物候变化中有76.78%的像元表现为推迟趋势;生长季长度变化中有70.03%的像元表现为延长趋势。(2)从县域单元来看,我国耕地物候的变化趋势以生长季长度延长为主,这类县域在全国县域单元中的占比为64.2%。(3)从空间格局来看,表现为生长季长度延长趋势的县域主要集中在我国东部三大平原、四川盆地以及东部平原向中部地区的过渡带中。[结论]近20年来我国县域耕地物候生长季长度的延长趋势明显且空间差异显著,这是自然地理要素与人类活动等因素综合作用的结果。     

CROPLAND DIVERSION (SET-ASIDE) IN THE US AND UK

Lessons from a variety of past and present US cropland diversion programmes are important for evaluating UK set-aside proposals. The structure and operation of current US programmes and the major UK proposals are described. A comparative economic welfare analysis of generic cropland diversion in the US and UK reveals the different types of potential impacts due principally to their different agricultural support programmes. Government cost savings and land rental payments can be misleading benefit and cost indicators for set-aside. Major problems with US programmes include slippage of production control, lack of targeting, inadequate overall efficiency evaluations, and goal conflict. The most appropriate role for cropland diversion may be as a compensatory mechanism to aid the agricultural adjustment process in the face of price restraint, while securing the most valuable non-market conservation and environmental services from idled farm land.     

中国耕地集约化与规模化利用耦合特征分析

[目的]集约化与规模化利用是提高我国耕地资源利用效率的两个重要途径。已有研究多针对单一的耕地集约化或规模化利用,考虑两者相互关系的研究缺乏,使得两化的耦合特征尚不明确。[方法]文章选择表征耕地集约化与规模化利用的重要指标,在县级尺度上分析我国耕地集约化和规模化利用特征,引入耦合模型揭示耕地集约化和规模化利用的耦合特征,并对两化的耦合发展模式进行划分。[结果]我国县级尺度耕地集约化和规模化利用耦合度较高,两化之间密切关联;但耦合协调性存在明显的区域差异:东部沿海地区两者的耦合性较好,而西北、西南、东北等区域的耦合协调度偏低,部分县域甚至失衡。从耦合相对发展度看,南方耕地的规模化利用程度较低,集约化利用水平较高,北方耕地呈现相反态势。在耕地集约化和规模化利用耦合模式中,"初级协调—集约化发展滞后型"和"中级协调—规模化发展滞后型"两种模式占主导地位。[结论]研究结果可为我国农业土地利用总体规划、空间布局、结构优化与调整等提供科学支撑,促进农业土地资源的高效利用。     

Evidence of climate change impacts on crop comparative advantage and land use

Relative agricultural productivity shocks emerging from climate change will alter regional cropland use. Land allocations are sensitive to crop profits that in turn depend on yield effects induced by changes in climate and technology. We develop and apply an integrated framework to assess the impact of climate change on agricultural productivity and land use for the U.S. Northern Great Plains. Crop-specific yield–weather models reveal crop comparative advantage due to differential yield impacts of weather across the region's major crops, that is, alfalfa, wheat, soybeans, and maize. We define crop profits as a function of the weather-driven yields, which are then used to model land use allocation decisions. This ultimately allows us to simulate the impact of climate change under the RCP4.5 emissions scenario on land allocated to the region's major crops as well as to grass/pasture. Upon removing the trends effects in yields, climate change is projected to lower yields by 33–64% over 2031–2055 relative to 1981–2005, with soybean being the least and alfalfa the most affected crops. Yield projections applied to the land use model at present-day input costs and output prices reveals that Dakotas’ grass acreage will increase by up to 23%, displacing croplands. Wheat acreage is expected to increase by up to 54% in select southeastern counties of North Dakota and South Dakota, where maize/soy acreage had increased by up to 58% during 1995–2016.