喀斯特峰丛洼地次生林土壤有机碳的剖面分布特征

采用样方法研究了喀斯特峰丛洼地八角枫(Alangium chinensis)、盐肤木(Rhus chinensis)、黄荆(Vitex negundo) 3种典型次生林群落土壤有机碳（SOC）含量、密度的剖面分布特征。结果表明,土壤有机碳含量与土壤根系生物量呈极显著正相关;不同次生林群落060 cm土壤有机碳平均含量和密度不同,依次为黄荆八角枫盐肤木,盐肤木的碳含量显著低于黄荆和八角枫群落,碳密度显著低于黄荆;3种次生林群落土壤碳含量和密度都与土壤深度有较好的线性关系,随土壤深度的增加而降低,2060 cm各层次的差异不显著,但均显著低于010 cm土层;不同次生林群落土壤各层次碳含量和密度均表现为为黄荆八角枫盐肤木,其中盐肤木群落1040 cm 3个层次的碳含量及2030 cm的碳密度显著低于另外2个群落。由此可见,喀斯特峰丛洼地退化生态系统合理的植被恢复方式是促进该区域生态重建和碳贮存的关键。     

Cassava, Manihot esculenta Crantz and wild relatives: Their relationships and evolution

About ninety eight species of Manihot arerecognized. All of them are native to the New world and areconcentrated in four regions of diversity in Brazil and CentralAmerica. All the Manihot species so far examinedhave 2n = 36 chromosomes. Interspecific hybrids betweencassava and its wild relatives show relatively regular meiosis, andfurther generations can be obtained. Electrophoresis shows affinityamong species of different sections, and between some of them andcassava. Both polyploidy and apomixis may have contributed tospeciation in this genus. Polyploidy offered genetic variabilitywhile apomixis is responsible for perpetuating new hybrid typesadapted to different environments. Cassava may have originated byhybridization between two wild Manihot speciesfollowed by vegetative reproduction of the hybrid.     

黄土丘陵区坡沟系统不同侵蚀方式的水力特性初步研究

 采用多坡段组合模型,通过室内人工模拟降雨实验,初步研究坡沟系统中片蚀、细沟侵蚀、浅沟及切沟侵蚀的水力、泥沙参数变化及其相互间的关系,以雷诺数、弗劳德数及过水断面单位能量为不同侵蚀方式发生的动力临界指标,初步得出不同侵蚀方式发生的水动力临界值,对揭示坡沟系统土壤侵蚀规律和产沙预报具有重要意义。     

The role of Quaternary environmental change in the evolution of landscapes: case studies from southern Africa

The paper begins by examining the importance of southern African Quaternary environmental change. The Quaternary is characterised by repeated climatic changes of considerable amplitude; analysis of these fluctuations reveals the ubiquity of change and the fundamental dynamism of earth systems. Change is normal and, despite the fact that southern Africa was not subject to Quaternary glaciation per se, the influence of variations in, say, amount and seasonality of rainfall, has been very marked indeed. The Quaternary also represents the time period during which people have become a dominant environmental agent in the subcontinent; southern Africa has played a crucial role in the evolution of hominids and their development has been influenced strongly by accompanying environmental change. The relationship between geomorphology and climate in southern Africa is explored, revealing the degree and extent to which its landscapes are determined by changing environmental conditions, especially during the Tertiary and Quaternary; how apparent is the legacy of the past? This leads to a consideration of the types of geomorphological evidence, some more reliable than others, that can be utilised in order to reveal the details of Quaternary environmental change. Arid and semiarid landscapes appear to preserve more evidence of former environmental conditions, although high contemporary erosion rates and the paucity of long terrestrial-sedimentary sequences hinder their complete elucidation. Two case studies of Quaternary change in the subcontinent are presented, from the southwestern Cape and Namibia. These examples document the increasing intensity of human impact on landscapes to the extent that people now play the dominant geomorphological role, especially in semiarid and coastal areas. The conclusion offers pointers as to how geomorphological evidence of Quaternary change can be used to assist in the better management of contemporary and future environmental conditions.     

土地整治对平原区及丘陵区田块利用的影响

土地整治中各类工程措施的实施,会对土地整治区域中田块的利用产生影响,量化评估土地整治对田块利用产生的影响,不仅可以完善土地整治的理论,而且能为土地整治项目规划设计方案的优化提供依据。该文将土地整治对田块利用的影响归纳为对田块规模、田块形状、田块空间特征和田块耕作效率影响4个方面,选择湖北省监利县毛市镇联盟土地整治项目与湖北省老河口市洪山咀办事处兰家岗村低丘岗地土地整治项目作为平原区项目和丘陵区项目的典型代表,量化评估了2个项目区土地整治对田块利用产生的影响,并对其进行了比较分析。研究结果表明在平原区项目和丘陵区项目中,土地整治对田块利用的影响表现出极强的相似性,综合表现为:1)田块的规模被扩大,小规模的田块并合并,田块的规模变得相对均匀;2)田块的外形被分割的更加规整,田块几何形状的相似性增强,人类对土地的干扰程度增加;3)整治区域中的田块由整治前的许多离散小田块的组合方式转变成整治后由少数大田块高度连接的组合方式,田块在分布上趋于集中;4)田块耕作的效率提高,二者平均耕作时间分别由整治前的57、62min/hm2减少到整治后的45和48min/hm2。同时,在平原区项目和丘陵区项目中,土地整治对田块规模、田块外形、田块空间分布特征和田块耕作效率影响的幅度上存差异,丘陵区项目在田块规模、田块破碎度、田块密度以及耕作时间的变化幅度上要大于平原区项目,这主要是由于地貌类型和区域本底条件的不同引起的。     

Effects of land consolidation in plains and hills on plots use

土地整治中各类工程措施的实施,会对土地整治区域中田块的利用产生影响,量化评估土地整治对田块利用产生的影响,不仅可以完善土地整治的理论,而且能为土地整治项目规划设计方案的优化提供依据。该文将土地整治对田块利用的影响归纳为对田块规模、田块形状、田块空间特征和田块耕作效率影响4个方面,选择湖北省监利县毛市镇联盟土地整治项目与湖北省老河口市洪山咀办事处兰家岗村低丘岗地土地整治项目作为平原区项目和丘陵区项目的典型代表,量化评估了2个项目区土地整治对田块利用产生的影响,并对其进行了比较分析。研究结果表明在平原区项目和丘陵区项目中,土地整治对田块利用的影响表现出极强的相似性,综合表现为：1）田块的规模被扩大,小规模的田块并合并,田块的规模变得相对均匀;2）田块的外形被分割的更加规整,田块几何形状的相似性增强,人类对土地的干扰程度增加;3）整治区域中的田块由整治前的许多离散小田块的组合方式转变成整治后由少数大田块高度连接的组合方式,田块在分布上趋于集中;4）田块耕作的效率提高,二者平均耕作时间分别由整治前的57、62 min/hm2减少到整治后的45和48 min/hm2。同时,在平原区项目和丘陵区项目中,土地整治对田块规模、田块外形、田块空间分布特征和田块耕作效率影响的幅度上存差异,丘陵区项目在田块规模、田块破碎度、田块密度以及耕作时间的变化幅度上要大于平原区项目,这主要是由于地貌类型和区域本底条件的不同引起的。     

Applications of reduced tillage in hills of central Nepal

Conventional tillage practices on steep and fragile landscape of Himalayan hills result in significant loss of topsoil during rainy season. Soil erosion in Nepal mid-hills is the most critical during pre-monsoon season. Many reviews argue that reduced tillage could be an option to tackle this problem. However, very few field experiments to evaluate reduced tillage systems have to date been conducted in this region. Thus, a field experiment was initiated in factorial randomized complete block design on acidic sandy loam soil (Lithic Dystochrept) during the summer season of 2001 at Kathmandu University (1500 masl) to assess the effects of tillage and cropping patterns on soil and nutrient losses, crop yield and soil fertility. Two main treatments viz. conventional and reduced till, and two sub-treatments viz. sole maize (Zea mays) and maize + soybean (Glycine max) were considered. Soil organic carbon (OC), total nitrogen (N), plant available phosphorus (P) and exchangeable potassium (K) were determined for the original soil and eroded sediment using standard methods. Two years of data indicated annual soil and nutrient losses to be significantly lowered by reduced till as compared to conventional till. Total annual soil loss from conventional and reduced till was 16.6 and 11.1 Mg/ha, respectively. Similarly, annual nutrient losses associated with the eroded sediment were 188 kg OC/ha, 18.8 kg N/ha, <1 kg P/ha and 3.8 kg K/ha for conventional till and 126 kg OC/ha, 11.8 kg N/ha, <1 kg P/ha and 2.4 kg K/ha for reduced till. Soil OC and N losses were significantly higher in conventional till and this may be one of the major causes of fertility depletion in the Nepalese hills. Soil chemical properties did not differ due to tillage and cropping systems; however, over years pH, N and P were increased irrespective of treatments. Although treatments were at par for maize grain yield, conventional till + soybean produced highest grain yield (4.0 Mg/ha) followed by reduced till + soybean (3.9 Mg/ha) and conventional till sole maize (3.8 Mg/ha). Mixed cropping of legumes and maize do not help conserve soil and nutrient loss in hills of central Nepal. Thus, reduced till could be a viable option for minimizing soil and nutrient losses without sacrificing economic yields in central hills of Nepal.     

河南省农业生产碳汇的演变趋势及其集聚特征分析

农业生产具有碳排放和碳吸收的双重属性,针对当前农业生产碳汇研究系统边界模糊不清、中观尺度研究成果少、核算项目缺失统一性和完整性等问题,本文在全面核算2000—2015年河南省传统农业碳排放和碳吸收的基础上,分析了该省农业生产碳汇的演变趋势,并利用基尼系数和洛伦兹曲线研究其空间集聚特征。研究结果表明,河南省农业生产系统表现碳汇特征,其碳汇量整体呈现逐渐增长趋势,至2015年全省农业生产碳汇量为3 235.11万t,相当于当年能源消费碳排放量的22.53%,因此农业生产对于减缓温室效应等方面具有一定的作用。河南省农业生产碳汇量增长的主要原因在于随着农业现代化的不断推进和农业生产能力的不断提高,其农业生产碳吸收能力快于碳排放增长速度。自然因素是河南省农业碳排放的主要方面,至2015年自然因素产生的碳排放占河南省农业生产碳排放总量的70.15%;而人工农资投入碳排放增长率相对较快,是全省碳排放量增长的主要原因,2000—2015年全省人工农资投入碳排放量年均增长率为3.27%,是其自然因素碳排放年均增长率的3.85倍。河南省各地农业生产碳汇在地域空间上表现增长的普遍性、相对稳定性和较显著集聚性特征,呈现显著的南北和东西差异,东部和北部农业地区碳汇数值相对较高,而南部和西部农业碳汇数值对较低。     

The soils of a typical slope in the Himalayas (Nepal): Their main characteristics and distribution

This study is based on a sequence of soils on a typical slope of the Himalayas in central Nepal from 2300 m to 4000 m. Above 2300 m the land is forested and at 4000 m forest gives way to alpine meadows.The soils have developed in silty loam materials derived from weathering of micaschists. They are humic, acid and strongly desaturated. Their spatial distribution is related to the bioclimatic zonation: acid brown soils and deep humic acid soils occur in the mountain zone and podzols and brown podzolic soils in the subalpine and alpine ones.Biological activity and “maturation” of humus decrease with increasing elevation. The podzolization process dominates. There is intense weathering of ferruginous phyllosilicates in eluvial horizons and accumulation of amorphous products in B horizons.     

江苏省乡村聚落演化的多尺度特征与空间关联性分析

乡村聚落演化与发展是农村社会特定人地关系的集中体现,其空间关联性是乡村聚落规划与重构的基础。该研究以江苏省为例,综合运用核密度分析、景观分维指数与空间热点探测方法,分析2009－2018年江苏省乡村聚落演化的多尺度特征与地域分异性规律,定量测度乡村聚落演化与不同地理要素的空间关联性及其增减变化的空间自相关特征。研究结果表明：江苏乡村聚落变化呈现出\     

珠江三角洲小流域地下水化学特征及演化规律

珠江三角洲地下水环境日益恶化,已成为制约经济社会发展的重要因素。以珠海市具有典型特征的闭合小流域作为研究对象,分旱、雨两季采集地下水分析主要离子及D、18O同位素,全面系统地研究了地下水水化学的时空变异特征与演变规律。结果表明：研究区内地下水主要受大气降水及附近地表水体渗透补给,以蒸发及地下水径流排泄,季节变化对区域内水化学空间变异性影响较小。沿地下水流方向（补给区-径流区-排泄区）,地下水化学类型主要从Ca-Na（Mg）-HCO3型向Na-Cl和Na-K-HCO3-CO3型演化,风化-溶滤、离子交换、海陆交互作用是控制当地地下水质演变的主要水文化学过程。     

浙江庆元香菇文化系统景观特征及演变

浙江省庆元县是世界人工栽培香菇的发源地, 2014年庆元香菇文化系统入选中国重要农业文化遗产。农业遗产景观是农业文化遗产在现代生活中最直观的表现,研究遗产地的景观特征和演变状况,有助于深入理解区域景观的状况及影响因素,实现遗产的有效保护和发展。本文运用Landsat 1991年、2001年、2010年和2018年的卫星影像结合实地调研,研究庆元香菇文化系统遗产地的景观现状、特征及结构,分析1991—2018年各景观类型演变规律及可能驱动要素。结果表明:1)遗产地景观类型主要包括森林、耕地、居民地和水体4类,其中森林面积达到1 643.23km~2(86.61%),是优势景观类型。2)区内山高、林密、溪流和菌菇资源丰富,形成了"河流-村落-梯田-森林"的垂直景观结构,并拥有西洋殿、菇寮等独特的香菇文化景观,人类与自然环境和谐共生。3)1991—2018年,遗产地森林面积增加139.28km~2(7.34%),耕地面积减少154.53km~2(8.15%),居民地面积增加11.86km~2(0.63%),水体面积增加3.48km~2(0.18%)。4)景观变化与相关政策密切相关, 20世纪后半期,遗产地森林砍伐严重,森林覆盖率由79.27%降低到77.97%; 21世纪以来,封山育林和生态林业建设使森林覆盖率从77.97%上升至86.61%,退耕还林和城镇化政策则分别促使了耕地面积减少和居民地面积的微弱扩张。总之,浙江庆元香菇文化系统遗产地景观结构独特,得益于当地居民林-菇共育的传统理念、香菇栽培技术的进步和当地森林保护等政策的施行,遗产地森林面积经历轻微的下降后又迅速增加,为遗产保护和传承提供了保障。     

1980－2015年云南坡耕地资源时空分布及演变特征分析

坡耕地资源作为山丘区耕地的重要组成部分,分析坡耕地时空分布及演变特征对合理规划利用坡耕地资源、开展区域坡耕地水土生态环境治理具有重要意义。该文利用1980－2015年7个时相土地利用数据,采用土地利用转移矩阵、动态度模型、核密度分析和景观指数模型对云南坡耕地时空分布及演变特征进行分析。结果表明：1）云南坡耕地面积为472.55万hm2,占耕地面积的比例为69.79%,平均坡度为15.62°,不同分区坡耕地空间分布差异显著。2）近35年坡耕地与林地、草地、水田等土地利用类型发生了显著的动态转移过程,但转出与转入总体均衡,转移过程中坡耕地面积呈小幅增加趋势。3）大部分坡耕地坡度大于8°,其中＞15°坡耕地比例高达78.54%,近35年来各坡度分级坡耕地均处于动态演变过程,坡度＜15°的坡耕地面积呈增加趋势,而坡度＞15°的坡耕地面积呈减小趋势,不同坡度分级坡耕地面积存在"减小→增大→减小"或"减小→增大→减小→增大"的动态变化过程,＞25°坡耕地动态变化的波动幅度最大。4）近35年坡耕地核密度分布呈小幅度变化趋势,大部分区域坡耕地分布处于低密度区,高密度区面积占比最小,坡耕地分布呈现出4个显著的聚集分布带。5）坡耕地景观优势度在8种土地利用类型中处于中间位置,而破碎化特征则在8种土地利用类型中最为显著,近35年坡耕地景观破碎化程度减小,坡耕地集中连片程度得到加强。     

京津冀地区县域农产品生产功能的时空格局及耦合特征

为了揭示京津冀地区县域农产品生产功能的空间格局、演化趋势及耦合特征,该研究构建包括县域种植业生产、林果生产、畜禽产品生产和水产品生产的农产品生产功能评价模型,并借助空间探索性数据分析技术进行系统分析。研究结果表明:12000-2013年,京津冀地区县域农产品生产功能呈现规律性分布,平原区种植业生产功能较强;市辖区周边县域的畜禽产品生产功能较强;低山丘陵区林果生产功能较强;水产品生产强功能区则分布于东部沿海一带。研究期间,京津冀地区县域农产品生产功能整体提升。22000-2013年间,县域种植业生产功能和畜禽产品生产功能集聚效应略有减弱,水产品生产功能的集聚效应基本不变,林果生产功能的集聚效应增强,农产品综合生产功能同质集聚特征显著。3种植业生产功能呈现明显的正向时空相关性,且二元化结构显著;畜禽产品生产功能与种植业生产、林果生产功能呈现显著的正向耦合性,且耦合性在增强。建议各县域结合农产品生产功能现状及功能间的耦合性差异,合理调整农业生产结构及布局,促进京津冀地区农产品生产功能的协同发展。     

黄河三角洲国土空间演变的时空分异特征与驱动力分析

科学有效掌握国土空间时空演变特征及其驱动机制是优化与构建国土空间保护开发格局的基本前提.该研究以黄河三角洲为例,围绕"过程-格局-驱动"的逻辑主线,基于2000、2010和2020年遥感数据构建国土空间分类体系,利用弦图可视化模型和地学信息图谱刻画国土空间演变过程,借助重心偏移模型和空间自相关分析法明晰国土空间演变的时...     

中国主要粮食作物磷肥偏生产力时空演变特征及驱动因素

[目的]中国旱地及水旱轮作区经过长久以来多种施肥模式的调整,各区域土壤磷素状况变异较大,探讨各区域土壤磷肥盈亏量和作物磷肥偏生产力的时空演变及主要驱动因素,为维持土壤磷素表观平衡和磷肥的科学管理提供理论指导.[方法]以农业农村部1988—2019年在全国旱地及水旱轮作区开展的长期监测数据库为基础,分析东北、华北、长江中...     

Phases of soil erosion-derived colluviation in the loess hills of South Germany

In South Germany, soil erosion is as old as farming and dates back to Early Neolithic times. Its sedimentary products form thick colluvial and alluvial sediment bodies in all drainage basins. Numerous local studies exist but the extrapolation of findings from local case studies to a regional scale has been problematic. Here, a graphical approach is used for frequency analysis of existing data. A frequency distribution for optical dates on colluvial sediments from the beginning of agriculture until 1200 AD was constructed by: (1) representing the optical ages by Gaussian-distributions and (2) summing all the single curves. The resulting graph clearly shows phases of increased colluviation during periods of stronger human impact. A first significant increase occurred during the Bronze Age. During the Iron Age/Roman period and at around 800 AD, distinct maxima appear in the distribution, and highest frequencies are present towards the end of the analysed period at around 1100 AD. Conclusions that can be drawn from such an approach are limited by sampling bias and other factors, but for the analysed period, and on a regional and long-term scale, colluviation seems to have been mainly triggered by intensity of land use. Climatic fluctuations are of only secondary importance. Rainfall events that were sufficiently erosive to produce colluvial sediments occurred throughout the agricultural periods. The limiting factor for colluvium production was sensitivity of the landscape to erosion, and this is a result of land use.     

Watershed-scale assessment of soil quality in the loess hills of southwest Iowa

Soil quality is a concept that integrates soil biological, chemical and physical factors into a framework for soil resource evaluation. Conventional tillage practices can result in a loss of soil organic matter and decreased soil quality. The potential for soil quality degradation with tillage may vary depending upon landscape position and the spatial distribution of critical soil properties. Information on how to accurately integrate soil spatial information across fields, landscapes and watersheds is lacking in the literature. The primary objective of this study was to evaluate the long-term effect of conventional and ridge-tillage on soil quality in three small watersheds at the Deep Loess Research Station near the town of Treynor in southwest Iowa. Soil types included Monona silt loams in summit positions, Ida or Dow silt loams in backslope positions, and Napier or Kennebec silt loams in footslope positions. We removed surface soil cores from transects placed along topographic gradients in each watershed and quantified total soil organic C (SOC), total soil N (TN), particulate organic matter C (POM-C) and N (POM-N), microbial biomass C (MB-C), N mineralization potential (PMIN-N), nitrate N, extractable P and K, pH, water-stable macroaggregates (WSA), and bulk density (BD). We used terrain analysis methods to group the data into landform element classes to evaluate the effect of topographic position on soil quality. Results indicate that soil quality is higher under long-term ridge-tillage compared with conventional tillage. Soil quality differences were consistently documented among the three watersheds by: (1) quantification of soil indicator variables, (2) calculation of soil quality index values, and (3) comparison of indicator variable and index results with independent assessments of soil function endpoints (i.e. sediment loss, water partitioning at the soil surface, and crop yield). Soil quality differences under ridge-till were found specifically for the backslope and shoulder landform elements, suggesting that soil quality increases on these landform elements are responsible for higher watershed-scale soil quality in the ridge-tilled watershed.     

喀斯特峰丛洼地退耕还林还草的土壤生态效应

石漠化生态重建的关键是恢复植被,本质是提高土地生产力。本文以典型喀斯特峰丛洼地的坡耕地为对照,对退耕种植任豆、香椿、板栗、柑橘、任豆+桂牧1号、桂牧1号和撂荒7种主要模式固定标准地的21个土壤指标进行调查分析,探讨了退耕还林还草的土壤综合生态效应,筛选了优化模式。结果表明,与同纬度地区的红壤相比,喀斯特峰丛洼地的土壤质量除全钾和速效磷含量稍低外均较高;退耕还林还草显著或极显著提高了大部分土壤主要养分、水分和矿质养分含量,降低了SiO2含量,除任豆模式外均恢复到了石漠化以下水平,同时提高了土壤微生物种群数量、BC、BC/SOM和BC/TN,但BN和BN/TN略有降低;聚类分析直观地将坡耕地和7种模式分为土壤显著改良型、改良型、缓慢改良型和改良迟滞型4种类型,其中香椿和板栗的土壤生态效应最好。