GIS空间插值模拟法与土壤类型法估算比较土壤碳储

为研究GIS空间插值模拟与土壤类型法估算土壤有机碳(soil organic carbon,SOC)储量的适用性是否一致,该文以山东省3个典型县为例,通过实地取样,采用GIS空间插值模拟和土壤类型法计算0~20 cm SOC储量以及分析土壤有机碳密度(soil organic C density,SCD)空间分布,比较GIS方法与土壤类型法计算县域尺度C储量的差异,验证GIS空间插值模拟的适用性。结果表明:1)依据GIS空间插值和土壤类型法获得的3个典型县0~20 cm土层SOC储量分别为:平邑3.88、3.93 Tg,莱阳3.54、3.57 Tg,禹城2.78、2.86 Tg;估算的平均SCD为:平邑2.2、2.23 kg/m2,莱阳2.08、2.1 kg/m2,禹城2.74、2.82 kg/m2;2)在满足一定采样量的条件下,两种方法在计算县域尺度上C储量时,结果基本一致,但GIS空间插值模拟与土壤类型法相比,更能突显SCD空间分布特征及空间递变规律,更利于分析不同因素对SCD空间分布的影响。该文可为缺失土壤类型分类或土地变更频率高区域的C储量计算提供依据。     

区域土壤有机碳密度及碳储量计算方法探讨

土体中有机碳含量在纵向和横向上都具有空间相关性。本文利用曲周县四疃乡30个土壤剖面的有机碳含量数据,采用常见的纵向拟合方法建立了基于30个土壤剖面有机碳测定数据的对数函数拟合模型,计算得到研究区的土壤有机碳密度和碳储量分别为5.60kg C m-2和4.72×108kgC;又根据研究区土壤剖面中有机碳含量分布的不规则性特点,通过对土壤剖面层次的归一化处理,利用地统计横向插值方法,计算得到该区的土壤有机碳密度和碳储量分别为3.95kg Cm-2和3.33×108kgC。由于两种算法对数据的组织方式不同,得到的土壤有机碳密度和碳储量存在较大差异。两种方法适用于土壤有机碳在剖面中分布形式不同的土壤类型。     

青藏高原土壤有机碳储量与密度分布

采用全国第二次土壤普查数据结合作者的实测数据,利用1∶100万土壤数据库对青藏高原土壤有机质层、土壤矿质层及整个剖面的土壤有机碳密度和土壤有机碳储量分别进行了估算。结果表明:青藏高原的平均土壤有机碳密度约为C 7.2 kg m-2,较前人的C 8.01~19.05 kg m-2全国平均土壤有机碳密度偏低。青藏高原总的土壤有机碳储量约为18.37 Pg,其中有机质层土壤有机碳储量约占38.14%,矿质层土壤有机碳储量则占61.86%。     

近30年安徽省耕地土壤有机碳变化及影响因素

利用安徽省第二次土壤普查和2010—2011年土壤数据,运用GIS空间分析方法,分析安徽省1980—2010年耕地土壤表层(0~20 cm)和1 m土体中有机碳密度(Soil Organic Carbon Density,SOCD)和储量时空变化特征,并探讨了农业管理措施与SOC变化的关系。结果表明:1980—2010年全省耕地剖面的表层SOCD平均值增加了0.28 kg m~(-2),1 m土体中SOCD平均值减少了0.42 kg m~(-2)。空间分布上,近30年间耕地表层SOCD在空间上呈现北增南减的趋势,增幅总体上由北向南依次减小;1 m土体中SOCD总体上中部增南部减;全省68%的耕地SOCD增加。1980—2010年全省耕地表层SOC储量增加35.30×10~9 kg,1 m土体中SOC储量增加18.12×10~9 kg;淮北平原和江淮丘陵岗地的耕地SOC储量增加,其余区域SOC储量减少。各县市SOC变化与作物根系中的有机物质含量显著正相关,表明肥料的大量使用增加了作物的秸秆和根系中的有机物质含量,增加了土壤中的有机物质的输入,促进了耕地SOC的累积。     

基于随机森林的县域土壤有机碳密度及储量估算

采用2009年云南省玉龙县土壤调查数据,基于土壤类型法将所测样点的土壤有机质含量转换为有机碳密度,经克里金插值进行空间化,再以2009年landsat7-Level2影像及SRTM 90 m数字高程模型数据为基础,提取归一化植被指数、亮度、绿度、湿度、坡度、坡向、曲率等与土壤有机碳形成密切相关的解释变量;通过随机森林模型模拟土壤有机碳密度及其空间分布,基于有机碳密度估算出0～20 cm表层土壤的有机碳总储量,并对两种模拟结果进行误差分析。结果显示:克里金和随机森林的估算结果分别为2.4×10~8和1.7×10~8 t,均方根误差分别为20.77和14.11,普通克里金插值误差较大,且对采样点数量及空间分布有较强的依赖性;随机森林模型不仅能处理高维数据,还能给出多个变量的重要性,估算结果精度更高,也更接近区域实际情况,对小尺度的细节表现更佳,适于地形复杂且样点有限的县域土壤有机碳密度及其储量的估算。     

江苏表层土壤有机碳密度和储量估算和空间分布分析

基于1:50万的江苏土壤图和江苏土壤的数据,运用地理信息系统技术,对江苏表层土壤有机碳密度及储量做出估算,并且分析了土壤有机碳密度的空间分布差异。结果表明:土壤有机碳密度介于4.2kgm-2到20.32kgm-2之间,土壤有机碳储量为673892.8×106kg;土壤有机碳密度具有高度的空间变异性,兴化、南通和无锡的有机碳密度最高,沿海地区的有机碳密度比较高,最低的为淮阴及其附近地区。     

青藏高原色季拉山流石滩表层土壤有机碳的空间变化特征及影响因素

[目的] 分析青藏高原不同海拔下表层土壤可溶性有机碳(DOC),易氧化有机碳(ROC)、碳库稳定性及碳储量变化特征研究及土壤有机碳(SOC),DOC的影响因素,为后续复杂地形寒区SOC的稳定性研究提供科学依据。[方法] 以色季拉山流石滩为研究区,以单因素方差分析法分析了4 300～4 700 m之间不同海拔土壤物理性质,DOC,ROC以及SOC的含量特征,结合Pearson相关分析与冗余分析探讨了DOC,ROC与各因子之间的相互关系。[结果] ①土壤容重、密度与海拔呈负相关,其最大值分别为1.56,1.12 g/cm³,土壤含水率和孔隙度与海拔呈正相关,其最大值分别为74.22%,58.70%; ②SOC含量随海拔升高呈现先升高后降低趋势,DOC,ROC随海拔升高而呈现出波动变化趋势; ③海拔4 400 m时DOC/SOC,ROC/SOC达到最大值,可溶性有机碳储量(DOCS)和有机碳储量(SOCS)均值分别为40.779 g/m²,8.105 kg/m²,流石滩土壤碳库稳定性较好; ④DOC与土壤物理性质不相关,但与SOCS有一定相关性;ROC则与物理性质和SOC及其相关因子均有一定的相关性;各因子对色季拉山流石滩土壤DOC和ROC变化的解释贡献率排序大小为：DOCS＞土壤孔隙度＞ROC/SOC＞土壤含水率＞SOC＞SOCS＞DOC/SOC＞土壤密度。[结论] 不同海拔流石滩表层土壤DOC,ROC与海拔有一定相关性,且DOCS、土壤孔隙度与ROC/SOC均是影响DOC,ROC含量的重要因子,同时各因子间存在密切的关系。     

陕西省土壤有机碳密度空间分布及储量估算

土壤有机碳是反映土壤质量以及土壤缓冲能力的一个重要指标,对于温室效应与全球气候变化具有重要的控制作用。研究以陕西省第二次土壤普查数据为主要资料,结合多年的相关研究数据,对陕西省土壤碳密度及储量进行估算,并分析了陕西省土壤有机碳密度的空间分布特征。结果表明:榆林、延安地区北部以及商洛等地区分布的风沙土、黄绵土、石质土等土壤有机碳密度最小,小于4 kg m-2;陕西南部地区的土壤有机碳密度主要在4~9 kg m-2之间;咸阳地区及渭南地区土壤有机碳密度也较高,主要在9~12 kg m-2之间;关中地区渭河及其两岸、秦岭部分山区土壤有机碳密度最大,最高达30 kg m-2以上;陕西省平均土壤有机碳密度为6.87 kg m-2,在全省的22个土壤类型中,有13个土壤有机碳密度低于全国平均水平,占全省土壤总面积的77.42%,全省土壤有机碳储量约为1.41×1012kg。本研究为我国土壤碳库和碳平衡的研究提供基础数据。     

基于1:5万数据库的福建省土壤全氮密度及储量估算研究

土壤全氮对于全球温室效应和水体富营养化具有重要的调控作用。基于福建省第二次土壤普查3 082个剖面数据和最新建立的1:5万大比例尺矢量土壤图,对全省土壤全氮储量进行了估算。结果表明：福建省土壤总面积为12.08×106 hm2,表层（0~20 cm）和剖面（0~100 cm）土壤的全氮密度分别为0.35 kg?m-2 和0.97 kg?m-2,储量为42.06 Tg和116.83 Tg。全省土壤全氮密度整体呈自北向南逐渐递减的趋势,且沿海低而内陆高。从不同土壤类型来看,山地草甸土的表层和剖面全氮密度最高,分别为0.85 kg?m-2和2.09 kg?m-2;而风沙土的表层和剖面全氮密度最低,分别为0.11 kg?m-2和0.27 kg?m-2。从不同行政区来看,南平市和龙岩市的表层土壤全氮密度最高,分别为0.40 kg?m-2 和 0.39 kg?m-2,而南平市和三明市的剖面土壤全氮密度最高,分别为1.19 kg?m-2 和 1.11 kg?m-2。总体而言,福建省土壤全氮密度和储量空间分布差异很大,今后可依据不同行政区和土壤类型的全氮分布制定合理的施肥管理措施。     

喀斯特小流域土壤有机碳密度及碳储量空间分布异质性

为阐明喀斯特小流域土壤有机碳密度分布特征及有机碳储量空间分布格局,采用野外布点采样、实验室测定和地统计学分析相结合的方法,利用2 755个详细调查的剖面样地和23 536个土壤样品,定量研究了喀斯特小流域土壤有机碳密度、碳储量的空间异质性及分布特征。结果表明:后寨河小流域表层(0—20cm)土壤有机碳含量和密度的平均值为分别为25.07g/kg和5.23kg/m~2,剖面土壤(0—100cm)土壤有机碳含量和有机碳密度分别为20.71g/kg和10.21kg/m~2,两层土壤有机碳含量和密度均属于中等变异强度。10cm土层深度有机碳储量为1.48×10~8 kg,20cm土层深度有机碳储量为2.65×10~8 kg,30cm土层深度土壤有机碳储量3.43×10~8 kg,100cm土层深度有机碳储量5.39×10~8 kg。各层土壤有机碳储量的块金值C_0随着土层深度的增加而增加,而0—100cm的块金值C_0最大。4种土层深度土壤有机碳储量呈现为中部低,四周高,南部最低的趋势。海拔、坡度、岩石裸露率和石砾含量是影响喀斯特小流域土壤有机碳储量空间异质性的主导因子。     

长期施肥下红壤旱地的固碳效率

红壤旱地的有机碳含量普遍较低,通过外源添加有机肥是增加土壤有机碳含量的重要手段。本研究以红壤旱地长期肥料试验为基础,研究了不同施肥处理的土壤有机碳含量和储量的变化规律,并进一步探讨碳投入与玉米产量及土壤碳储量的量化关系。结果表明:施用有机肥可以大幅提升红壤旱地的有机碳含量,氮磷钾+有机肥(NPKM)和有机肥(OM)处理在27年间的增加速率分别为0.08 g/(kg·a)和0.06 g/(kg·a),有机碳储量的增加速率分别为0.24t/(hm~2·a)和0.16 t/(hm~2·a);与不施肥(CK)处理相比,NPKM和OM处理的土壤有机碳含量分别增加了51.5%和42.0%,有机碳储量则分别增加57.1%和45.7%。进一步分析表明,有机碳投入量与土壤有机碳储量变化速率之间存在显著的正相关关系(R~2=0.971 5,P0.001),且线性拟合方程(y=–0.158+0.086x)表明,双季玉米种植下红壤旱地的固碳效率为8.6%,当有机碳投入量为1.84 t/(hm~2·a)时,红壤旱地的有机碳储量保持平衡。因此,施用有机肥是提高红壤旱地有机碳储量的有效途径,固碳效率和土壤有机碳平衡点则可以有效指导红壤旱地有机肥的管理措施。     

县域尺度土壤有机碳储量估算的样点密度优化

县域是我国国家尺度土壤碳库估算的基本地域单元,合理的土壤样品采集密度是保证估算精度要求的基础。以桃源县为例,设置4.70、0.90、0.60、0.40、0.25、0.15、0.10和0.05个km-2共8个样点密度梯度,利用经典统计学和地统计学方法,研究样点密度对县域尺度土壤有机碳库估算精度的影响。经典统计表明,随着样点密度的降低,重复抽样下土壤有机碳均值及其变异系数的波动逐渐增大,标准误差呈幂函数增加(Y=0.025X-0.47,R2=0.97,p0.01)。地统计学分析表明,随着样点密度的降低,块金值和基底效应逐渐增加,偏基台、变程和决定系数的波动幅度逐渐增大,拟合残差呈幂函数增加(Y=0.001 4X-1.66,R2=0.56,p0.05);土壤有机碳空间分布的局部差异逐渐被弱化,重复抽样下县域土壤有机碳库储量及其平均误差的波动逐渐增强,均方根误差呈幂函数增加(Y=0.77X-0.05,R2=0.59,p0.05)。从整体上看,样点密度小于0.15个km-2时,以上变化均急剧增强,土壤碳储量估算的精度快速降低。因此,综合科学、高效和经济方面的考虑,估算县域农田表层土壤有机碳储量的最佳样点密度为0.15个km-2。本研究结果可为开展区域尺度土壤有机碳野外调查提供辅助支持。     

Soil organic carbon stock and fractional distribution across central-south China

The stock and stability of soil organic carbon (SOC) are critical to soil functions and global carbon cycle, but little quantitative information is available on the precise location and chemical components of SOC for soils across a wide range of climatic gradients. Here, a broad range of zonal soils were collected in forest land at topsoil (0–15 cm) and subsoil (15–30 cm) from temperate to tropical climatic gradient in central to south China. The stock and stability of SOC were determined in terms of aggregate and humic fractionation. SOC in bulk soils with a less significant geographic variation was comparably higher at Haplic Luvisoils in temperate regions (3637.61 g m⁻²) and Rhodi-Humic Ferrosols in tropical regions (3446.12 g m⁻²) than in the other experimental soils, but a consistent decreasing trend was observed along the soil profiles with the SOC stock was 1.11–1.97 times higher in the topsoil than in the subsoils. In addition, insoluble humin residue (HMr) as the dominant components of SOC ranged from 643.95 to 2696.90 g m⁻² and decreased from temperate to tropical regions, which was consistent with the zonal variation of humic acids (HAs), but contrary to the zonal variation of fulvic acids (FAs) that fluctuated in a range of 39.67–389.55 g m⁻² across the experimental sites. According to the results of partial correlation analysis, the variation of FAs stock was significantly attributed to soil pH, bulk density, iron and aluminum oxides, clay, and clay mineral content (|r|>0.61, p < 0.05), while these soil physical properties showed a contradictory effects on HAs, iron-linked humin (HMi), clay-combined humin (HMc), and HMr. Moreover, the aggregate-associated carbon stock was mainly stored in macroaggregates (36.34–76.09%) for both SOC and its chemical components, especially in topsoils, and its zonal variation was associated with that of bulk soils. In general, the redundancy analysis (RDA) revealed that mean annual precipitation (MAP) accounted for 81.8% and 13.8% of the variance in SOC chemical and physical fractionation, respectively, while the corresponding contribution of mean annual temperature (MAT) was 1.5% and 34.7%. With the increase of MAT and MAP, the chemical stability of SOC decreased in the molecular structure, and the physical protection of SOC by aggregate exhibited a unimodal trend. The obtained results would facilitate the development of regional soil carbon prediction and land management against global warming.     

植被重建下露天煤矿排土场边坡土壤碳储量变化

植被重建是治理排土场边坡水土流失最直接也是最有效的生物措施,研究不同植被重建模式下土壤有机碳(SOC)和全氮(TN)含量的空间分布规律是筛选适宜排土场边坡生长的植被模式的重要条件。选取内蒙古黑岱沟露天煤矿治理15年的排土场边坡中4种植被重建模式(自然恢复地、草地、灌木林、乔木林),采集270个土壤剖面(0~100 cm)样品,研究不同重建模式下SOC储量的变化。结果表明:(1)植被重建模式显著影响剖面SOC、TN含量及分布(p0.05),0~10 cm和10~20 cm SOC、TN均呈草地灌木乔木自然恢复地,20 cm以下各土层SOC、TN虽然也表现相似的特征,但差异随土层深度增加越来越小。(2)剖面SOC密度和储量表现为原地貌区治理排土场新建排土场。经15年植被重建后,排土场边坡表现出巨大的固碳能力,1 m深度的林地和草地碳储量分别增加了5.38、11.85 t hm-2,但仅原地貌水平的1/2和3/5。(3)林地和草地的固碳速率分别为35.87、79.01 g m-2a-1,草地的固碳速率是林地的2.2倍,从土壤固碳及水土流失防治的角度考虑,建议矿区排土场边坡植被重建优先选择草地,其次灌木。     

Spatial variability of soil organic carbon in a catchment of the Loess Plateau

Abstract

The issue of soil organic carbon (SOC) is of increasing concern. Because SOC, as an important soil component in farming systems, is essential for improving soil quality, sustaining food production and quality, and maintaining water quality and as a major part of the terrestrial carbon reservoir, it plays an important role in the global carbon cycle. In this paper, a total of 665 soil samples from different depths were collected randomly in the autumn of 2007, and the spatial variability of SOC content at a small catchment of the Loess Plateau was analysed using classical statistics and geo-statistical analysis. In nonsampled areas classical kriging was utilized for interpolation of SOC estimation. The classic statistical analysis revealed moderate spatial variability with all five layers of SOC-content. In addition, the average SOC content decreased with soil depth and the relationship can be modelled by an exponential equation (y=3.1795x ^?1.2015, R ²=0.9866) and all of the SOC-content data in the different depth were normally distributed. The geo-statistical analysis indicated a moderate spatial dependence in 0–60 cm, while in the 60–80 cm depth spatial dependence was strong. The semi-variogram could be fitted by an exponential model for 0–10 cm depth; by a spherical model for 10–20 cm depth and 60–80 cm depth; and by a Gaussian model for 20–60 cm depth. The range increases with increasing depth. In addition, classical kriging could successfully interpolate SOC content in the catchment. In general, the geo-statistics method on a watershed scale could be accurately used to evaluate spatial variability of the SOC content in the Loess Plateau, China.     

Concentration and stock of carbon in the soils affected by land uses and climates in the western Himalaya,India

Soils are the third biggest sink of carbon on the earth. Hence, suitable land uses for a climatic condition are expected to sequester optimum atmospheric carbon in soils. But, information on how climatic conditions and land uses influence carbon accumulation in the soils on the Himalayan Mountains is not known. This study reports the impact of four climatic conditions (sub-tropical, altitude: 500–1200 m; temperate 1200–2000 m; lower alpine 2000–3000 m; upper alpine, 3000–3500 m) and four land uses (forest, grassland, horticulture, agriculture) on the concentrations and stocks of soil organic carbon (SOC) in upper (0–30 cm) and deeper (30–100 cm) soil depths on the western Himalayan Mountains of India. The study also explored the drivers which influenced the SOC stock build up on the mountains. Rainfall and soil moisture showed quadratic relations, whereas temperature declined linearly with the altitude. SOC stock as well as concentration was the highest (101.8 Mg ha^− 1 in 0–30 cm, 227.97 Mg ha^− 1 in 0–100 cm) in temperate and the lowest in sub-tropical climate (37 Mg ha^− 1 in 0–30 cm, 107.04 Mg ha^− 1 in 0–100 cm). Pattern of SOC stock build up across the altitude was: temperate > lower alpine > upper alpine > sub-tropical. SOC stocks in all land uses across the climatic conditions, except agriculture in lower alpine, was higher (0.7 to 41.6%) in the deeper than upper soil depth. SOC stocks in both the depths showed quadratic relations with soil temperature and soil moisture. Other factors like fine soil particles, land-use factor and altitude influenced positively whereas slope and pH, negatively to the SOC stocks. In all climatic conditions, other than temperate, SOC stocks were greater in natural ecosystems like forests and pastures (112.5 to 247.5 Mg ha^− 1) than agriculture (63 to 120.4 Mg ha^− 1). In temperate climate, SOC stock in agriculture (253.6 Mg ha^− 1) on well formed terraces was a little higher than forest (231.3 Mg ha^− 1) on natural slope. These observations, suggest that land uses on temperate climate may be treated as potential sinks for sequestration of the atmospheric carbon. However, agriculture in subtropical climate need to be pursued with due SOC protection measures like the temperate climate for greater sequestration of the atmospheric carbon.     

Long-term fertilization effects on carbon pools and carbon management index of loamy soil under grass–forage legumes mixture in semi-arid environment

ABSTRACT

Soil organic carbon (SOC) is a key component for sustaining crop production. A field experiment was conducted during 2004–2018 to assess the changes in soil carbon fractions under different fertilization practices in grass-legumes mixture. The result indicates that application of farmyard manure (FYM) at 80 Mg ha^–1 has increased SOC concentration leading to carbon sequestration rate of 4.2 Mg ha^–1 year^–1. Further, it has increased the proportion of labile carbon in the total SOC and have accumulated 126, 60, 83 and 95% higher very labile, labile, less labile and non-labile C stock than that of control plot, respectively, in top 30 cm soil layer. Inorganic fertilization and FYM 20 Mg ha^–1 influenced SOC concentration, SOC stock and C sequestration rate similarly. The highest carbon management index (264) was found in the treatment receiving FYM 80 Mg ha^–1 and it was positively correlated with SOC (r = 0.84**). The sensitivity index of the SOC varied from 26 to 152% and the differences were greatest in FYM treatments. The result indicates that grass-legumes mixture build-up the SOC in long term and the addition of FYM further increases it.     

基于Landsat遥感影像和1∶50 000土壤数据库的福州市耕地有机碳动态变化研究

耕地土壤碳库是全球碳库中最为活跃的部分,其变化对全球气候变化产生重要影响。目前对耕地土壤有机碳估算多采用中、小系列比例尺的土壤数据库,较少结合遥感影像与大比例尺土壤数据库进行估算。基于此,本研究采用Landsat遥感影像和1∶50 000高精度土壤数据库,以福建省福州市为例,基于遥感与碳循环过程模型对1987年和2016年耕地土壤有机碳动态变化进行研究。结果表明,利用Landsat影像反演得到的耕地土壤基础呼吸与土壤有机碳相关性强,建立的1987年和2016年模型R²分别为0.637和0.752。研究期间,全市耕地土壤有机碳密度从东部沿海向西部内陆地区递增,整体发挥着“碳汇”作用,有机碳密度和储量分别增加0.20 kg·m^-2和2.946×10⁵ t。从不同土壤类型比较得出,黄壤、红壤和水稻土是“碳汇”,有机碳密度分别增加0.70 kg·m^-2、0.40 kg·m^-2和0.19 kg·m^-2;其他土类为“碳源”,其中,水稻土碳储量最大,两期在全市总碳储量中占比均超过90%。从不同行政区比较得出,仓山区、长乐区、马尾区和连江县为“碳源区”,其他地区为“碳汇区”,其中,仓山区碳储量一直为全市最低,两期占比均不足0.5%,而福清市则一直居于全市首位,占比均高于20%。总体而言,福州市耕地土壤有机碳30年间空间动态变化显著,在不同土类和行政区间存在差异,今后应根据不同耕地土壤类型和行政区的有机碳情况有针对性进行耕地管理。     

How do hedgerows influence soil organic carbon stock in livestock‐grazed pasture?

Hedgerows have the potential to influence ecosystem function in livestock‐grazed pasture. Despite this, they are often ignored when quantifying farmland ecosystem service delivery. In this study, we assess the contribution of hedgerows to the ecosystem function of carbon (C) storage, with a particular emphasis on soil organic carbon (SOC). We measured SOC stock (kg C m^?2), on an equivalent soil mass basis, at 0–0.15 m depth in pasture adjacent to 38 hedgerows (biotic) and 16 stone walls or fences (abiotic controls) across ten farms in the county of Conwy, Wales, UK. Pasture SOC stock (~7 kg C m^?2) was similar adjacent to biotic and abiotic field boundaries, positively associated with soil moisture and negatively with soil bulk density (BD). For biotic boundaries, two further variables were significantly associated with SOC stock, distance from hedgerow (decrease in SOC stock) and slope orientation (upslope SOC stock greater than downslope). For pasture adjacent to hedgerows, a model combining the aforementioned variables (BD, soil moisture, distance from hedgerow, slope orientation) explained 78% of variation in SOC stock. This study demonstrates that whilst hedgerows do have subtle positive effects on SOC stock in adjacent pasture, SOC storage adjacent to field boundaries is influenced more by soil moisture content and BD than field boundary type.     

Assessing and mapping topsoil organic carbon stock at regional scale: A scorpan kriging approach conditional on soil map delineations and land use

In order to assess the potential of soils as C reservoir at regional scale, accurate estimates of soil organic carbon (SOC) are required, and different approaches can be used. This study presents a method to assess and map topsoil organic carbon stock (Mg ha⁻¹) at regional scale for the whole Emilia Romagna plain in Northern Italy (about 12 000 km²). A Scorpan Kriging approach is proposed, which combines the trend component of soil properties as derived from the 1:50 000 soil map with geostatistical modeling of the stochastic, locally varying but spatially correlated component. The trend component is described in terms of varying local means, calculated taking into account soil type and dominant land use. The resulting values of SOC, sand, silt, and clay contents are retained for calculating topsoil SOC stocks, using a set of locally calibrated pedotransfer functions (PTFs) to estimate bulk density. The maps of each soil attribute are validated over a subset of 2000 independent and randomly selected observations. As compared to the standard approach based on the mean values for delineation, results show lower standard errors for all the variables used for SOC stock assessment, with a relative improvement (RI) ranging from 4 per cent for SOC per cent to 24 per cent for silt. The total C stock (0–30 cm) in the study area is assessed as 73·24 ± 6·67 M t, with an average stock of 62·30 ± 5·55 Mg ha⁻¹. The SOC stock estimates are used to infer possible SOC stock changes in terms of carbon sequestration potential and potential carbon loss (PCL). Copyright © 2010 John Wiley & Sons, Ltd.