Distribution of soil organic carbon and phosphorus on an eroded hillslope of the rangeland in the northern Tibet Plateau, China

Some studies on the relationship between soil erosion and subsequent redeposition of eroded soils in the same field and soil quality have been conducted in croplands, yet few studies have revealed this relationship in rangelands. We selected a toposequence with a slope of 30% and a horizontal length of 342 m from the rangeland in the northern Tibet Autonomous Region, China (31°16′N, 92°09′E) to determine the relationship between soil erosion, soil organic carbon (SOC) content and available P patterns within a hillslope landscape. Soil samples for the determination of ¹³⁷Cs as well as SOC, available P and particle‐size fractions were collected at 20 m intervals along a transect of this hillslope. Soil redistribution was caused primarily by wind erosion at toe‐slope positions, but primarily by water erosion at the hillslope positions above the toe‐slope. In upper‐ and mid‐slope portions (0 m to 244 m horizontal length), SOC content is closely correlated to ¹³⁷Cs concentration (r = 0.74, P < 0.01, n= 15), suggesting that SOC distribution along the slope was similar to ¹³⁷Cs distribution, which itself was dependent on topographic changes. However, SOC contents in toe‐slope portions are less than those above the toe‐slope (i.e. upper‐ and mid‐slope portions), and the correlation between ¹³⁷Cs and SOC in the toe‐slope portion is weaker than that above the toe‐slope. A highly significant correlation (r = 0.72, P < 0.001, n= 20) between ¹³⁷Cs concentration and available P was found within the whole hillslope landscape, implying the distribution pattern of available P was somewhat different from that of SOC. We suggest that the distribution of SOC within the hillslope landscape is also affected by factors such as assimilation rates due to difference in grassland productivity at different points and different biological oxidation rates of carbon related to patterns of moisture distribution.     

利用燃煤飞灰作为时间标记物评价坡耕地黑土侵蚀物质和有机碳的再分配

燃煤飞灰(以下简称飞灰)作为时间标记物克服了放射性同位素137Cs示踪方法不能鉴定大气核爆炸之前的土壤再分布过程这一缺陷。本文利用土体中的飞灰研究坡耕地黑土有机碳的时空再分布特征。尝试建立飞灰在土壤中分层的方法,根据飞灰和土壤有机碳(SOC)随土壤深度的分布特征鉴定土壤堆积厚度,以及堆积土壤的相对年代。结果表明:用飞灰示踪技术鉴定的埋藏土壤表层与SOC含量随深度变化确定的埋藏表层吻合较好,景观中低洼部位在飞灰出现前就有一定的土壤堆积。各地貌部位坡肩侵蚀最为严重,有机碳含量最低;坡顶坡度较小,侵蚀微弱;坡脚和坡足发生沉积。土壤沉积速率在1.01~5.56mm a-1之间。研究结果还表明堆积部位埋藏层的SOC含量较高,说明有相当数量的有机碳被隐遁在目前的耕作层之下。因此,在评价农田土壤作为大气CO2“源”或“汇”时应该考虑景观中土壤物质迁移和埋藏作用的影响。     

137Cs tracing of the spatial patterns in soil redistribution,organic carbon and total nitrogen in the southeastern Tibetan Plateau

The southeastern Tibetan Plateau, which profoundly affects East Asia by helping to maintain the stability of climate systems, biological diversity and clean water, is one of the regions most vulnerable to water erosion, wind erosion, tillage erosion, freeze–thaw erosion and overgrazing under global climate changes and intensive human activities. Spatial variations in soil erosion in terraced farmland (TL), sloping farmland (SL) and grassland (GL) were determined by the ¹³⁷Cs tracing method and compared with spatial variations in soil organic carbon (SOC) and total nitrogen (total N). The ¹³⁷Cs concentration in the GL was higher in the 0–0.03 m soil layer than in the other soil layers due to weak migration and diffusion under low precipitation and temperature conditions, while the ¹³⁷Cs concentration in the soil layer of the SL was generally uniform in the 0–0.18 m soil layer due to tillage-induced mixing. Low ¹³⁷Cs inventories appeared at the summit and toe slope positions in the SL due to soil loss by tillage erosion and water erosion, respectively, while the highest ¹³⁷Cs inventories appeared at the middle slope positions due to soil accumulation under relatively flat landform conditions. In the GL, the ¹³⁷Cs data showed that higher soil erosion rates appeared at the summit due to freeze–thaw erosion and steep slope gradients and at the toe slope position due to wind erosion, gully erosion, freeze–thaw erosion and overgrazing. The ¹³⁷Cs inventory generally increased from upper to lower slope positions within each terrace (except the lowest terrace). The ¹³⁷Cs data along the terrace toposequence showed abrupt changes in soil erosion rates between the lower part of the upper terrace and the upper part of the immediate terrace over a short distance and net deposition on the lower and toe terraces. Hence, tillage erosion played an important role in the soil loss at the summit slope positions of each terrace, while water erosion dominantly transported soil from the upper terrace to the lower terrace and resulted in net soil deposition on the flat lower terrace. The SOC inventories showed similar spatial patterns to the ¹³⁷Cs inventories in the SL, TL and GL, and significant correlations were found between the SOC and ¹³⁷Cs inventories in these slope landscapes. The total N inventories showed similar spatial patterns to the inventories of ¹³⁷Cs and SOC, and significant correlations were also found between the total N and ¹³⁷Cs inventories in the SL, TL and GL. Therefore, ¹³⁷Cs can successfully be used for tracing soil, SOC and total N dynamics within slope landscapes in the southeastern Tibetan Plateau.     

Soil redistribution and organic carbon accumulation under long‐term (29 years) upslope tillage systems

Few studies have demonstrated soil redistribution under upslope tillage (UT) rather than downslope tillage (DT) and its impact on soil organic carbon (SOC) redistribution in long‐term agricultural practices in hillslope landscapes. We selected two neighbouring sites from the Sichuan Basin, China, one under DT and the other under UT, to determine the pattern of soil and SOC redistribution under a long‐term UT practice. DT caused soil loss at upper slope positions and soil accumulation at lower slope positions. However, UT resulted in soil accumulation at upper slope positions and soil loss at lower slope positions. The total erosion rate decreased by 60.5% after 29 years of UT compared with DT. Having the same direction of soil movement by tillage and water exaggerated total soil loss, whereas having the two movements in the contrasting direction of soil for the two reduced it. SOC stocks at positions from summit to downslope were much larger (33.8%) and at toe‐slope positions were only slightly greater (4.5%) in the UT soils than comparable values for the DT site. The accumulation rate of SOC at the UT site increased by 0.26 Mg/ha/year compared with that at the DT site. It is suggested that soil movement by water and tillage erosion occurred in the same direction accelerates the depletion of SOC pools, whereas the opposite direction of soil movement for the two can increase SOC accumulation. Our results suggest that UT has significant impacts on soil redistribution processes and SOC accumulation on steeply sloping land.     

Erosion and deposition history derived by depth-stratigraphy of Cs and soil organic carbon

There are a number of uncertainties in the use of ¹³⁷Cs as a marker for deriving soil erosion rates. However, this should not limit other potential uses of this anthropogenic radionuclide in the study of soil landscape processes. This study outlines a sampling methodology which aids in the assessment of the history of erosion and depositional processes within a landscape unit. The depth distribution of ¹³⁷Cs and soil organic carbon (SOC) was utilized as a means of determining the erosion and depositional history of a conventionally tilled agricultural field in southern Ontario, Canada. Three transects oriented along the slope of a large field had five soil profiles excavated at the summit, sideslope, shoulder slope, footslope and toeslope landscape positions. The soils were sampled in 5 cm increments, and ¹³⁷Cs and SOC were determined on the samples. The results show that soil redistribution within landscape units of agricultural fields has been substantial both before and after fallout of ¹³⁷Cs to the soil surface. Soils in depositional areas contained significant ¹³⁷Cs and SOC at depths beyond which the plow can attain at present. This implies that a significant amount of carbon is being sequestered beneath the present plow layer, and the characterization of this pool must be considered in deriving the dynamics of SOC in agroecosystems.     

Erosional impacts on soil properties and corn yield on Alfisols in central Ohio

Accelerated soil erosion can impact upon agronomic productivity by reducing topsoil depth (TSD), decreasing plant available water capacity and creating nutrient imbalance in soil and within plant. Research information on soil‐specific cause – effect relationship is needed to develop management strategies for restoring productivity of eroded soils. Therefore, two field experiments were established on Alfisols in central Ohio to quantify erosion‐induced changes in soil properties and assess their effects on corn growth and yield. Experiment 1 involved studying the effects of past erosion on soil properties and corn yield on field runoff plots where soil was severely eroded and comparing it with that on adjacent slightly eroded soil. In addition, soil properties and corn grain yield in runoff plots were compared on side‐slopes with that on toe‐slopes or depositional sites. Experiment 2 involved relating corn growth and yield to topsoil depth on a sloping land. With recommended rates of fertilizer application, corn grain yield did not differ among erosional phases. Fertilizer application masked the adverse effects of erosion on corn yield. Corn grain yield on depositional sites was about 50 per cent more than that on side‐slope position. Corn plants on the side‐slope positions exhibited symptoms of nutrient deficiency, and the ear leaves contained significantly lower concentrations of P and Mg and higher concentrations of Mn and K than those grown on depositional sites. Corn grain yield in experiment 2 was positively correlated with the TSD. Soil in the depositional site contained significantly more sand and silt and less clay than that on the side‐slope position. There were also differences in soil properties among erosional phases. The soil organic carbon (SOC) content was 19\7 g kg⁻¹ in slightly eroded compared with 15\1 g kg⁻¹ in severely eroded sites. Aggregate stability and the mean weight diameter (MWD) were also significantly more in slightly eroded than severely eroded soils. Adverse effects of severe erosion on soil quality were related to reduction in soil water retention, and decrease in soil concentration of N and P, and increase in those of K, Ca and Mg. Severe erosion increased leaf nutrient contents of K, Mn and Fe and decreased those of Ca and Mg. Corn grain yield was positively correlated with aggregation, silt and soil N contents. It was also negatively correlated with leaf content of Fe. Copyright © 2000 John Wiley & Sons, Ltd.     

Simulation and 137Cs tracer show tillage erosion translocating soil organic carbon,phosphorus, and potassium

Research on how tillage‐induced soil redistribution affects soil properties is limited for complex slopes in nonmechanized agricultural areas. The objectives of this study are (1) to examine the vertical redistribution of soil organic C (SOC), extractable P and K induced by tillage on a complex slope, (2) to assess the effects of tillage erosion on soil profile properties, and (3) to elucidate the variations in soil properties induced by both vertical mixture and downslope transport of soil within the landscape. Simulated tillage was conducted in the Yangtze Three Gorges Reservoir Area, China. The ¹³⁷Cs data showed that intense tillage caused the soil vertical mixture and downslope transport. The redistribution of ¹³⁷Cs and soil constituents varied with the number of tillage passes and location in relation to curvature. SOC was completely depleted with the disappearance of soil profiles at the summit position, while SOC concentrations decreased by 26% for the till layer and increased by 29% for the sublayer at the toeslope position for the 15‐tillage operation, as compared with those of pretillage. The vertical redistribution of extractable P and K followed a similar pattern to that of SOC. The gap and variation in soil constituents between the till layer and sublayer declined after tillage, suggesting that the mixing effect of tillage attenuates the variability of soil properties in the vertical direction. Net loss and gain of soil constituents occurred at the summit and toeslope positions, respectively, suggesting that the downslope transport of soil induced by tillage accentuates the variability of soil properties in the lateral direction.     

Impacts of soil erosion on organic carbon and nutrient dynamics in an alpine grassland soil

The impact of soil erosion on the nutrient dynamics in alpine grassland soils is still an essential problem. Selecting a grass-covered hillslope in eastern Tibet Plateau, the cesium-137 (¹³⁷Cs) technique was used to determine the impacts of soil erosion on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK). The ¹³⁷Cs data revealed that there were distinct soil redistribution patterns in different hillslope positions because of the influences of slope runoff, plant coverage and grazing activity. For the upper slope, soil erosion first decreased downward, followed by soil deposition in its lower part. In contrast, for middle and toe slopes, there was an increasing soil erosion along a downslope transect. Across the lower slope, soil erosion showed an irregular variation. Influenced by the selective transport of water erosion, SOC, TN and TP storage decreased with increasing soil erosion in upper, middle and toe slopes. In contrast, SOC, TN and TP storage varied little with soil erosion in the lower slope. On the whole hillslope, TK storage also varied little with soil erosion due to the large amount of potassium elements derived from soil parent materials. Particularly noteworthy was the greatest storage of SOC, TN and TP in the lower slope where most obvious net soil erosion occurred, which is closely related to the humus accumulation combined with gravel separation as well as weathering and pedogenesis of parent rocks induced by soil freeze-thaw.     

Influence of former lynchets on soil cover structure and soil organic carbon storage in agricultural land,Central Czechia

Lynchets represent a traditional landscape element in agricultural landscapes having multiple functions in soil material redistribution, water retention, biodiversity and landscape character. They act as a barrier to translocated soil matter, and they can store a significant amount of soil material and soil organic carbon. Lynchets developed in many regions during formation of agriculture landscape as field boundaries or path networks. Further management led to unleveling of the fields and development of lynchets. During the 20th century, a large number of lynchets disappeared in Central and Western Europe due to land consolidation, intensification and industrialization of agriculture. This study was performed at a large agricultural study plot with dissected relief (Central Czechia) with the aim of assessing the influence of former but now completely levelled lynchets on actual soil stratigraphy, depth, soil organic carbon stocks and structure of soil units. The soil profiles in 20‐m‐long transects perpendicular to former lynchets were analysed, and statistical relationships between the positions above, in and below the former lynchets were assessed. The results showed high variability of studied soil characteristics in the areas of former lynchets. Statistically significant greater A horizon thickness (50–100 cm) and SOC stock (12.7 kg/m²) were observed in the location of a former lynchet, where colluvial soils were identified. Other areas of accumulation were identified below a lynchet, at the former break‐in‐slope. The strip above a lynchet was identified as a sediment delivery area, having a partly truncated soil profile. SOC concentration and SOC stock in A horizon did not differ significantly in the positions in, above or below a lynchet.     

Slope gradient and shape effects on soil profiles in the northern mountainous forests of Iran

In order to evaluate the variability of the soil profiles at two shapes (concave and convex) and five positions (summit, shoulder, back slope, footslope and toeslope) of a slope, a study of a virgin area was made in a Beech stand of mountain forests, northern Iran. Across the slope positions, the soil profiles demonstrated significant changes due to topography for two shape slopes. The solum depth of the convex slope was higher than the concave one in all five positions, and it decreased from the summit to shoulder and increased from the mid to lower slope positions for both convex and concave slopes. The thin solum at the upper positions and concave slope demonstrated that pedogenetic development is least at upper slope positions and concave slope where leaching and biomass productivity are less than at lower slopes and concave slope. A large decrease in the thickness of O and A horizons from the summit to back slope was noted for both concave and convex slopes, but it increased from back slope toward down slope for both of them. The average thickness of B horizons increased from summit to down slopes in the case of the concave slope, but in the case of convex slope it decreased from summit to shoulder and afterwards it increased to the down slope. The thicknesses of the different horizons varied in part in the different positions and shape slopes because they had different plant species cover and soil features, which were related to topography.     

Long‐term cropping systems and tillage management effects on soil organic carbon stock and steady state level of C sequestration rates in a semiarid environment

A calcareous and clayey xeric Chromic Haploxerept of a long‐term experimental site in Sicily (Italy) was sampled (0–15 cm depth) under different land use management and cropping systems (CSs) to study their effect on soil aggregate stability and organic carbon (SOC). The experimental site had three tillage managements (no till [NT], dual‐layer [DL] and conventional tillage [CT]) and two CSs (durum wheat monocropping [W] and durum wheat/faba bean rotation [WB]). The annually sequestered SOC with W was 2·75‐times higher than with WB. SOC concentrations were also higher. Both NT and CT management systems were the most effective in SOC sequestration whereas with DL system no C was sequestered. The differences in SOC concentrations between NT and CT were surprisingly small. Cumulative C input of all cropping and tillage systems and the annually sequestered SOC indicated that a steady state occurred at a sequestration rate of 7·4 Mg C ha⁻¹ y⁻¹. Independent of the CSs, most of the SOC was stored in the silt and clay fraction. This fraction had a high N content which is typical for organic matter interacting with minerals. Macroaggregates (>250 µm) and large microaggregates (75–250 µm) were influenced by the treatments whereas the finest fractions were not. DL reduced the SOC in macroaggregates while NT and CT gave rise to higher SOC contents. In Mediterranean areas with Vertisols, agricultural strategies aimed at increasing the SOC contents should probably consider enhancing the proportion of coarser soil fractions so that, in the short‐term, organic C can be accumulated. Copyright © 2010 John Wiley & Sons, Ltd.     

黑土区典型小流域土壤侵蚀空间格局模拟研究

利用校正后的基于GIS的USLE模型预测了黑土区域土壤侵蚀量的空间分布格局。研究结果表明,研究区小流域年侵蚀量值范围在0~60t/(hm² a),无侵蚀、轻度侵蚀、中度侵蚀和强度侵蚀面积分别占研究区总面积的28.7%,56.2%,18.6%和0.1%。研究区坡顶土壤侵蚀量较少〔0~5t/(hm² a)〕,坡肩和坡背侵蚀量较大〔3~15t/(hm² a)〕。基于GIS的USLE不能够很好地模拟黑土区坡麓和坡足区域土壤沉积和侵蚀沟的空间分布格局,但可以较好地模拟坡顶、坡肩和坡背处的土壤流失状况。     

Modeling soil carbon transported by water erosion processes

Long‐term monitoring is needed for direct assessment of soil organic carbon (SOC), soil, and nutrient loss by water erosion on a watershed scale. However, labor and capital requirements preclude implementation of such monitoring at many locations representing principal soils and ecoregions. These considerations warrant the development of diagnostic models to assess erosional SOC loss from more readily obtained data. The same factors affect transport of SOC and mineral soil fraction, suggesting that given the gain or loss of soil minerals, it may be possible to estimate the SOC flux from the data on erosion and deposition. One possible approach to parameterization is the use of the revised universal soil loss equation (RUSLE) to predict soil loss and this multiplied by the per cent of SOC in the near‐surface soil and an enrichment factor to obtain SOC loss. The data obtained from two watersheds in Ohio indicate that a power law relationship between soil loss and SOC loss may be more appropriate. When measured SOC loss from individual events over a 12‐year period was plotted against measured soil loss the data were logarithmically linear (R²=0·75) with a slope (or exponent in the power law) slightly less than would be expected for a RUSLE type model. The stable aggregate size distribution in runoff from a plot scale may be used to estimate the fate of size pools of SOC by comparing size distributions in the runoff plot scale and river watershed scales. Based upon this comparison, a minimum of 73 per cent of material from runoff plots is deposited on the landscape and the most stable carbon pool is lost from watershed soils to aquatic ecosystems and atmospheric carbon dioxide. Implicit in these models is the supposition that water stable soil aggregates and primary particles can be viewed as a tracer for SOC. Copyright © 2000 John Wiley & Sons, Ltd.     

Short-range variation in a Wisconsin soilscape (USA)

Here we report on the variation of a soilscape in south central Wisconsin, USA. The variation in soil properties and soil features results in four soil order (Entisols, Inceptisols, Alfisols and Mollisols). Observations were made along a 200 m transect in a field that was cultivated since 1870. Slopes ranged from 7.5% on the back slope to 0% in the lower part. The soilscape had a total relief difference of 7.0 m. The soils were studied by 41 soil pits (60 cm), 6 soil pits (125 cm), 15 soil augers (100 cm), and ground-penetrating radar imagery. The summit and shoulder consist of coarse glacial outwash (loamy sands) over limestone whereas the lower part is lacustrine sediments over coarse outwash (loams, silty loams). The A-horizon thickness ranged from 14 to 52 cm with thick A horizons at the toeslope that also had the lowest soil pH. The soil organic carbon (SOC) contents of the A horizons ranged from 11.6 to 46.9 g C kg^–1, and the higher contents are in the lower part of the soilscape. SOC stocks (0–20 cm depth) ranged from 50 to 70 Mg C ha^–1 on the summit and backslope, but were 80 to 95 Mg C ha^–1 in the flat part of the soilscape. The lowest soybean yields (1.6 Mg ha^–1) were found at the summit and the highest yield (6.3 Mg ha^–1) at the lower end of the backslope. Soybean yields were correlated to the thickness of the A horizon, and every 10 cm increase in A horizon thickness yielded an extra 0.6 Mg soybeans ha^–1. Analysis of spherical magnetic particles was used to estimate soil erosion rates that were highest on the backslope (16.2 Mg ha^–1 yr^–1) and rates of soil deposition in the lowest part of the soilscape was 18.8 Mg ha^P1 yr^–1. It seems that there is no net soil and SOC loss within this soilscape. All in all, we found 4 soil taxonomic orders within 200 m. The variation in this soilscape was substantial and probably enhanced by 140 years of cultivation.     

黑土坡耕地横坡垄作对减少径流及土壤有机碳流失的作用

东北黑土坡耕地受土壤侵蚀和习惯顺坡耕作措施的影响,水土流失严重,土壤有机碳含量呈逐年下降趋势.针对东北黑土坡耕地不同垄作措施水土流失及土壤有机碳变化特征不明确的问题,采用田间定位试验的方法,探究了顺坡垄作和横坡垄作对坡耕地水土流失及土壤有机碳变化的影响.结果表明:(1)横坡垄作相对于顺坡垄作能显著减少径流总量97.1％...     

A mass balance approach to assess carbon dioxide evolution during erosional events

The accelerated greenhouse effect and the degradation of land resources by water and wind erosion are two major, yet interrelated global environmental challenges. Accelerated decomposition of soil organic carbon (SOC) in cultivated soils results in decline in SOC stocks over time and also contributes to increased levels of CO₂ in the atmosphere. Off‐site transport of SOC in runoff waters during erosional events also contributes to SOC depletion, but there is a paucity of data in the literature documenting erosional SOC losses and the fate of eroded SOC. In this paper, we present a mass balance approach to compute CO₂ evolved from mineralization of SOC during transport and deposition of eroded soils. Erosion‐induced CO₂ emission rates ranging between 6 and 52 g C m⁻² yr⁻¹ were computed using data on SOC stocks and dynamics from a series of long‐term experiments conducted across a range of ecological regions. For the cropland of the world, we estimated an annual flux of 0.37 Pg CO₂‐C to the atmosphere due to water erosion. This flux is significant and suggests that water erosion must be taken into consideration when constructing global and regional C budgets. Through its contribution to atmospheric CO₂ increase, water erosion can have a positive feedback on the accelerated greenhouse effect. Copyright © 2001 John Wiley & Sons, Ltd.     

科尔沁沙地半固定沙丘不同坡位土壤C,N特征

[目的]研究沙丘不同坡位土壤碳氮的分布特征,旨在探索沙丘不同坡位植被演替机制。[方法]选取高于5m的半固定沙丘,沿主要风向于坡底、坡中、坡顶和背风坡设置样点,对土壤容重、土壤总有机碳含量和土壤总氮含量进行测定,并计算碳氮比、碳氮密度和碳氮储量。[结果](1)不同坡位土壤碳含量均随深度增加显著降低,主要变异层发生在0—40cm层。不同坡位土壤碳含量在30—40cm层和60—100cm层存在差异。(2)氮含量与容重在不同坡位和不同深度均不存在显著差异性,碳氮比在坡底和坡顶存在显著的垂直差异性,背风坡60—100cm层土壤碳氮比显著高于其它坡位。(3)各坡位土壤碳密度随深度增加显著下降。30—40cm层土壤碳密度存在显著的坡位差异,而土壤氮密度的垂直差异和坡位间差异均不显著。(4)半固定沙丘土壤碳氮储量分别为716.89和94.14kg/m2,不同坡位差异性不显著;碳储量的构成在4种坡位差异较大,而各坡位不同深度土壤氮储量对总储量的贡献差异较小。[结论]科尔沁沙地半固定沙丘土壤碳氮含量与密度不同坡位的差异较小,同时各坡位的碳氮均存在显著的垂直差异性,尤其在30—40cm层,变异程度较大,这可能与该层植物根系分布有关。     

Soil greenhouse gas emissions,organic carbon and crop yield following pinewood biochar and biochar–manure applications at eroded and depositional landscape positions: A field trial in South Dakota,USA

Soil amendments can help reduce greenhouse gas (GHG) emissions and increase soil organic carbon (SOC) and crop yield. However, most biochar studies have been conducted on single soil type under controlled conditions. To address this limitation, the aim of this research was to investigate how field biochar and manure applications affect soil quality, plant productivity, and GHG emissions at eroded (sandy loam) and depositional (clay loam) positions in a climate transition zone (udic to ustic and mesic to frigid temperature). A field study was established in 2013 in South Dakota, USA, under a corn–soya bean rotation. Soil treatments included biochar, manure, a manure and biochar mixture, and a control (untreated soil). Soil properties (pH, electrical conductivity (EC), SOC, available nitrogen, available phosphorus and available potassium) were measured in 2017. Plant productivity parameters in 2016 and 2017 and GHG fluxes were measured during the 2016 and 2017 growing seasons. Compared with the control, SOC increased under all treatments at the eroded position (biochar 26%, manure 24%, and manure–biochar mixture 15%) and increased under biochar (25%) and the manure–biochar mixture (25%) at the depositional position. Plant parameters were similar under all treatments at both positions. Area-scaled CO₂ fluxes were lower in soils treated with biochar compared with the control at the eroded landscape position but not at the depositional landscape position. Area-scaled N₂O fluxes were lower in soils treated with biochar at both positions. Furthermore, the biochar–manure mixture treatment emitted lower area-scaled N₂O fluxes compared with manure alone at both positions. This study suggests that for eroded and depositional landscape positions, biochar can improve soil organic carbon and the effects of the biochar and biochar–manure mixture on GHG emissions vary based on the soil texture.     

Potential of mine land reclamation for soil organic carbon sequestration in Ohio

Soils are an effective sink for carbon storage and immobilization through biomass productivity and enhancement of soil organic carbon (SOC) pool. The SOC sink capacity depends on land use and management. Degraded lands lose large amounts of C through SOC decomposition, erosion, and leaching. Thus, restoration of disturbed and degraded mine lands can lead to increase in biomass productivity, improved soil quality and SOC enhancement and sequestration. Reclamation of mined lands is an aggrading process and offers significant potential to sequester C. A chronosequence study consisting of 0‐, 5‐, 10‐, 15‐, 20‐ and 25‐year‐old reclaimed mine soils in Ohio was initiated to assess the rate of C sequestration by pasture and forest establishment. Undisturbed pasture and forest were used as controls. The SOC pool of reclaimed pasture sites increased from 15·3 Mg ha⁻¹ to 44·4 Mg ha⁻¹ for 0–15 cm depth and from 10·8 Mg ha⁻¹ to 18·3 Mg ha⁻¹ for 15–30 cm depth over the period of 25 years. The SOC pool of reclaimed forest sites increased from 12·7 Mg ha⁻¹ to 45·3 Mg ha⁻¹ for 0–15 cm depth and from 9·1 Mg ha⁻¹ to 13·6 Mg ha⁻¹ for 15–30 cm depth over the same time period. The SOC pool of the pasture site stabilized earlier than that of the forest site which had not yet attained equilibrium. The SOC sequestered in 0–30 cm depth over 25 years was 36·7 Mg ha⁻¹ for pasture and 37·1 Mg ha⁻¹ for forest. Copyright © 2000 John Wiley & Sons, Ltd.     

黑土坡耕地侵蚀和沉积对物理性组分有机碳积累与损耗的影响

以侵蚀和沉积过程明显的黑土坡耕地为研究对象,通过测定不同地形部位表层和典型剖面土壤不同粒级的水稳性团聚体、颗粒态有机碳（POC）以及团聚体结合态有机碳含量,探讨土壤侵蚀和沉积对土壤有机碳（SOC）损失、迁移和累积过程的影响。研究结果表明：上坡三个侵蚀部位表层土壤大团聚体、矿质结合态有机碳（MOC）以及团聚体结合态有机碳含量随侵蚀速率增加而减小;沉积部位（尤其是坡脚）POC含量和POC/SOC较低,而MOC含量和MOC/SOC较高。始终处于沉积状态的坡脚部位,各粒级有机碳组分的深度分布均表现出土壤累积和埋藏特征,并随着粒级的减小累积现象趋于明显。上述结果反映了土壤侵蚀优先使与细颗粒和微团聚体结合的SOC迁移流失,并在低洼的沉积区累积;埋藏层中的侵蚀物质（如微团聚体、颗粒态有机质）通过深埋作用和重新团聚作用形成稳定的大团聚体,最终促进SOC的固定。