内蒙古草原碳、氮储量:气候与土壤质地的关系

Understanding the spatial variability of soil carbon(C) storage and its relationship with climate and soil texture is critical for developing regional C models and for predicting the potential impact of climate change on soil C storage. On the basis of soil data from a transect across the Inner Mongolian grasslands, we determined the quantitative relationships of C and nitrogen(N) in bulk soil and particle-size fractions(sand, silt, and clay) with climate and soil texture to evaluate the major factors controlling soil C and N storage and to predict the effect of climate changes on soil C and N storage. The contents of C and N in the bulk soil and the different fractions in the 0–20 and 20–40 cm soil layers were positively correlated with the mean annual precipitation(MAP) and negatively correlated with the mean annual temperature(MAT). The responses of C storage in the soil and particle-size fractions to MAP and MAT were more sensitive in the 0–20 cm than in the 20–40 cm soil layer. Although MAP and MAT were both important factors influencing soil C storage, the models that include only MAP could well explain the variation in soil C storage in the Inner Mongolian grasslands. Because of the high correlation between MAP and MAT in the region, the models including MAT did not significantly enhance the model precision. Moreover, the contribution of the fine fraction(silt and clay) to the variation in soil C storage was rather small because of the very low fine fraction content in the Inner Mongolian grasslands.     

气候和土壤质地对中国东北地区旱地土壤有机碳影响的尺度效应

Understanding how spatial scale inffuences commonly-observed effiects of climate and soil texture on soil organic carbon (SOC) storage is important for accurately estimating the SOC pool at different scales. The relationships among climate factors, soil texture and SOC density at the regional, provincial, city, and county scales were evaluated at both the soil surface (0-20 cm) and throughout the soil profile (0-100 cm) in the Northeast China uplands. We examined 1022 profiles obtained from the Second National Soil Survey of China. The results indicated that the relationships between climate factors and SOC density generally weakened with decreasing spatial scale. The provincial scale was optimal to assess the relationship between climate factors and SOC density because regional differences among provinces were covered up at the regional scale. However, the relationship between soil texture and SOC density had no obvious trend with increasing scale and changed with temperature. There were great differences in the impacts of climate factors and soil texture on SOC density at different scales. Climate factors had a larger effect on SOC density than soil texture at the regional scale. Similar trends were seen in Heilongjiang and eastern Inner Mongolia at the provincial scale. But, soil texture had a greater effect on SOC density compared with climate factors in Jilin and Liaoning. At the city and county scales, the inffuence of soil texture on SOC density was more important than climate factors.     

Effects of Soil Texture and CaCO3 on Turnover of Organic Material in Chao Soils

Decomposition experiments of ^14C-labelled sickle alfalfa in chao soils of different texture and these soils after removal of CaCO3 were carried out under field and laboratory conditions respectively.The amount of residual ^14C in,or ^14CO2 evolved from,the soils at intervals after the beginning of devomposition were measured and the distribution of native and labelled C between particle size fractions isolated from these soils was edtermined.Results showed that contents of both labelled (^14C) and non-labelled (^12C) carbon decreased with increasing particle size.The enrichment factor for ^14C was higher than that for ^12C in the clay fraction,the reverse being true for the silt enrichment factors.The effect of soil texture on the decomposition of plant material could not be observed in chao soils when the clay content was lower than 270g kg^-1,while it became obvious once CaCO3 was removed was correlated from these soils.The decomposition rate of plant material in the soil from which the native CaCO3 Was removed was correlated significantly to both the clay content of the soil and the application rate of CaCO3.A preliminary correction equation describing the effect of clay and CaCO3 on the decomposition of organic material in chao soil was derived from the results obtained.     

Spatial Characteristics of Soil Organic Carbon Storage in China＇s Croplands

The soil organic carbon （SOC） pool is the largest component of terrestrial carbon pools. With the construction of a geographically referenced database taken from the second national general soil survey materials and based on 1546 typical cropland soil profiles, the paddy field and dryland SOC storage among six regions of China were systematically quantified to characterize the spatial pattern of cropland SOC storage in China and to examine the relationship between mean annual temperature, precipitation, soil texture features and SOC content. In all regions, paddy soils had higher SOC storage than dryland soils, and cropland SOC content was the highest in Southwest China. Climate controlled the spatial distribution of SOC in both paddy and dryland soils, with SOC storage increasing with increasing precipitation and decreasing with increasing temperature.     

土壤润湿性受土壤特性及土地使用的影响

Depth distribution of soil wettability and its correlations with vegetation type, soil texture, and pH were investigated under various land use (cropland, grassland, and forestland) and soil management systems. Wettability was evaluated by contact angle with the Wilhelmy plate method. Water repellency was likely to be present under permanently vegetated land, but less common on tilled agricultural land. It was mostly prevalent in the topsoil, especially in coarse-textured soils, and decreased in the subsoil. However, the depth dependency of wettability could not be derived from the investigated wide range of soils. The correlation and multiple regression analysis revealed that the wettability in repellent soils was affected more by soil organic carbon (SOC) than by soil texture and pH, whereas in wettable soils, soil texture and pH were more effective than SOC. Furthermore, the quality of SOC seemed to be more important in determining wettability than its quantity, as proofed by stronger hydrophobicity under coniferous than under deciduous forestland. Soil management had a minor effect on wettability if conventional and conservation tillage or different grazing intensities were considered.     

土壤矿物吸附和土壤团聚体对土壤有机碳含量的影响研究

Soil organic carbon (SOC) can act as a sink or source of atmospheric carbon dioxide; therefore, it is important to understand the amount and composition of SOC in terrestrial ecosystems, the spatial variation in SOC, and the underlying mechanisms that stabilize SOC. In this study, density fractionation and acid hydrolysis were used to assess the spatial variation in SOC, the heavy fraction of organic carbon (HFOC), and the resistant organic carbon (ROC) in soils of the southern Hulunbeier region, northeastern China, and to identify the major factors that contribute to this variation. The results showed that as the contents of clay and silt particles (0--50 μm) increased, both methylene blue (MB) adsorption by soil minerals and microaggregate contents increased in the 0--20 and 20--40 cm soil layers (P < 0.05). Although varying with vegetation types, SOC, HFOC, and ROC contents increased significantly with the content of clay and silt particles, MB adsorption by soil minerals, and microaggregate content (P < 0.05), suggesting that soil texture, the MB adsorption by soil minerals and microaggregate abundance might be important factors influencing the spatial heterogeneity of carbon contents in soils of the southern Hulunbeier region.     

不同耕作方式对中国东北黑土有机碳的短期影响

A tillage experiment, consisting of moldboard plow （MP）, ridge tillage （RT）, and no-tillage （NT）, was performed in a randomized complete block design with four replicates to study the effect of 3-year tillage management on SOC content and its distribution in surface layer （30 cm） of a clay loam soil in northeast China. NT did not lead to significant increase of SOC in topsoil （0-5 cm） compared with MP and RT; however, the SOC content in NT soil was remarkably reduced at a depth of 5-20 cm. Accordingly, short-term （3-year） NT management tended to stratify SOC concentration, but not necessarily increase its storage in the plow layer for the soil.     

蔬菜连作对铜尾矿土壤中有机碳、腐殖质碳以及可溶性有机碳的影响

Carbon of humus acids （HSAC） and dissolved organic carbon （DOC） are the most active forms of soil organic carbon （SOC） and play an important role in global carbon recycling. We investigated the concentrations of HSAC, water-soluble organic carbon （WSOC）, hot water-extractable organic carbon （HWOC） and SOC in soils under different vegetation types of four copper mine tailings sites with differing vegetation succession time periods in Tongling, China. The concentrations of HSAC, WSOC, HWOC and SOC increased with vegetation succession. WSOC concentration increased with the accumulation of SOC in the tailings, and a linearly positive correlation existed between the concentrations of HSAC and SOC in the tailings. However, the percentages of HSAC and DOC in the SOC decreased during vegetation succession. The rate of SOC accumulation was higher when the succession time was longer than 20 years, whereas the speeds of soil organic matter （SOM） decomposition and humification were slow, and the concentrations of HSAC and DOC increased slowly in the tailings. The percentage of carbon of humic acid （HAC） in HSAC increased with vegetation succession, and the values of humification index （HI）, HAC/carbon of fulvic acid, also increased with the accumulation of HSAC and SOC in soils of the tailings sites. However, the HI value in the each of the tailings was less than 0.50. The humification rate of SOM was lower than the accumulation rate of SOM, and the level of soil fertility was still very low in the tailings even after 40 years of natural restoration.     

土壤持水特性参数与土壤质地尺度关系的联合多重分形分析

Soil water-retention characteristics at measurement scales are generally different from those at application scales, and there is scale disparity between them and soil physical properties. The relationships between two water-retention parameters, the scaling parameter related to the inverse of the air-entry pressure (αvG, cm-1) and the curve shape factor related to soil pore-size distribution (n) of the van Genuchten water-retention equation, and soil texture (sand, silt, and clay contents) were examined at multiple scales. One hundred twenty-eight undisturbed soil samples were collected from a 640-m transect located in Fuxin, China. Soil water-retention curves were measured and the van Genuchten parameters were obtained by curve fitting. The relationships between the two parameters and soil texture at the observed scale and at multiple scales were evaluated using Pearson correlation and joint multifractal analyses, respectively. The results of Pearson correlation analysis showed that the parameter αvG was significantly correlated with sand, silt, and clay contents at the observed scale. Joint multifractal analyses, however, indicated that the parameter αvG was not correlated with silt and sand contents at multiple scales. The parameter n was positively correlated with clay content at multiple scales. Sand content was significantly correlated with the parameter n at the observed scale but not at multiple scales. Clay contents were strongly correlated to both water-retention parameters because clay content was relatively low in the soil studied, indicating that water retention was dominated by clay content in the field of this study at all scales. These suggested that multiple-scale analyses were necessary to fully grasp the spatial variability of soil water-retention characteristics.     

湿润速率和粘粒含量对红壤沟间侵蚀的影响

An aggregate stability test and a simulated rainfall test were conducted on four representative Ultisols from southeastern China. The soils selected, with clay contents ranging between 117 and 580 g kg-1 , were derived from shale and Quaternary red clay. The stability of aggregates (2–5 mm in diameter) obtained from the soil samples were determined by the Le Bissonnais method. For determination of infiltration, runoff, and erosion, the soil samples were packed in 30 cm × 60 cm trays, wetted at rates of 2, 10, and 60 mm h-1 , and then exposed to simulated rainfall at 60 mm h-1 for 1 h. The results indicated that both aggregate stability and slaking caused by fast wetting increased with increasing clay content. The effect of wetting rate (WR) on infiltration and seal formation varied with clay contents. In the soil with low clay content (sandy loam), the infiltration rate was affected slightly by WR due to low aggregate stability and slaking. In the soils with medium clay content (silt clay loam and clay), WR affected infiltration significantly due to the high aggregate slaking force. In the soil with high clay content, the effect of WR on infiltration was significant, but not as evident as in the soils with medium clay content, which may be related to high aggregate stability by wetting partially compensating for slaking force. The effect of WR on soil loss was similar to that of runoff, but more pronounced. The findings from this study indicated that the relationship between wetting rate and clay content should be considered when predicting interrill erosion in Ultisols.     

The soil organic carbon: Clay ratio in North Devon,UK: Implications for marketing soil carbon as an asset class

Building up stocks of agricultural soil organic carbon (SOC) can improve soil conditions as well as contribute to climate change mitigation. As a metric, the ratio of SOC to clay offers a better predictor of soil condition than SOC alone, potentially providing a benchmark for ecosystem service payments. We determined SOC:clay ratios for 50 fields in the North Devon UNESCO World Biosphere Reserve using 30 cm soil cores (divided into 0–10 cm and 10–30 cm depth samples), with soil bulk density, soil moisture and land-use history recorded for each field. All the arable soils exceeded the minimum desirable SOC:clay ratio threshold, and the ley grassland soils generally exceeded it but were inconsistent at 10–30 cm. Land use was the primary factor driving SOC:clay ratios at 0–10 cm, with permanent pasture fields having the highest ratios followed by ley grass and then arable fields. Approximately half of the fields sampled had potential for building up SOC stock at 10–30 cm. However, at this depth, the effect of land use is significantly reduced. Within-field variability in SOC and clay was low (coefficient of variation was ~10%) at both 0–10 cm and 10–30 cm, suggesting that SOC:clay ratios precisely characterized the fields. Due to the high SOC:clay ratios found, we conclude that there is limited opportunity to market additional carbon sequestration as an asset class in the North Devon Biosphere or similar areas. Instead, preserving existing SOC stocks would be a more suitable ecosystem service payment basis.     

Soil restorative effects of mulching on aggregation and carbon sequestration in a Miamian soil in central Ohio

Soils play a key role in the global carbon cycle, and can be a source or a sink of atmospheric carbon (C). Thus, the effect of land use and management on soil C dynamics needs to be quantified. This study was conducted to assess: (1) the role of aggregation in enhancing soil organic carbon (SOC) and total soil nitrogen (TSN) concentrations for different mulch rates, (2) the association of SOC and TSN with different particle size fractions, and (3) the temporal changes in the SOC concentration within aggregate and particle size fractions with duration of mulching. Two experiments were initiated, one each in 1989 and 1996, on a Crosby silt loam (Aeric Ochraqualf or Stagnic Luvisol) in central Ohio. Mulch treatments were 0, 8, and 16 Mg ha⁻¹ yr⁻¹ without crop cultivation. Soil samples from 0–5 cm and 5–10 cm depths were obtained in November 2000; 4 and 11 years after initiating the experiments. Mulch rate significantly increased SOC and TSN concentrations in the 0–5 cm soil layer only. The variation in the SOC concentration attributed to the mulch rate was 41 per cent after 4 years of mulching and 52 per cent after 11 years of mulching. There were also differences in SOC and TSN concentrations among large aggregate size fractions, up to 2 mm size after 4 years and up to 0ċ5 mm after 11 years of mulching. There were also differences in SOC and TSN concentrations among particle size fractions. Variation in the SOC concentration in relation to particle size was attributed to clay by 45–51 per cent, silt by 34–36 per cent, and to sand fraction by 15–19 per cent. Bulk of the TSN (62–67 per cent) was associated with clay fraction and the rest was equally distributed between silt and sand fractions. The enrichment of SOC and TSN concentrations in the clay fraction increased with depth. The C:N ratio was not affected by the mulch rate, but differed significantly among particle size fractions; being in the order of sand >silt >clay. Copyright © 2003 John Wiley & Sons, Ltd.     

Soil organic carbon content and soil structure quality of clayey cropland soils: A large-scale study in the Swiss Jura region

Soil organic carbon (SOC) fashions soil structure, which is a key factor of soil fertility. Existing SOC content recommendations are based on SOC:clay ratio thresholds of >1:10. However, the corresponding SOC content might be considered hard to reach in clayey soils, whose structure degradation risk is assumed to be high. Here, we analysed the SOC content and soil structure quality of soils under similar cropping practices with clay contents ranging from 16% to 52%. Five undisturbed soil cores (5–10 cm layer) were collected from 96 fields at 58 farms in the Swiss Jura region. We assessed the soil structure quality visually using the CoreVESS method. Gravimetric air content and water content, and bulk density at −100 hPa were also measured, and the soil structure degradation index was calculated. We found that the relationship between SOC and clay content held over the clay content range, suggesting that reaching an acceptable SOC:clay ratio is not limited by large clay contents. This suggests that the 1:10 SOC:clay ratio may remain useful for clayey soils. In contrast to what was expected, it is not more challenging to reach this ratio in clayey soils even if it implies reaching very large SOC contents. SOC content explained the considered physical properties better than clay content. From a soil management point of view, these findings suggest that the soil texture determines a potential SOC content, while the SOC:clay ratio is determined by farming practices regardless of the clay content.     

冲积平原区土壤碳密度估算及其空间分布

冲积平原区通常具有复杂的剖面质地层次排列,为了准确估算冲积平原区土壤碳密度的空间分布特征,该文在华北冲积平原区的河北曲周县选取了121个土壤剖面,测定了各土层有机碳含量,构建了基于负指数函数的土壤有机碳垂向分布模型,结合地统计学方法绘制了该县土壤碳密度的空间分布图。结果表明,土壤有机碳含量随深度增加呈逐渐递减的趋势,各土层有机碳含量均属于中等变异程度。0~20和20~40 cm土壤有机碳空间连续性较好,它们的空间相关距离分别为14和3 km,而下层(40 cm)土壤有机碳均表现为纯块金效应结构。土壤有机碳垂向分布模型可以很好地描述剖面土壤有机碳含量的变化特征,且预测与实测的土壤有机碳含量的均方根误差仅为0.70 kg/m3,决定系数达到了0.95。曲周县土壤有机碳密度的空间分布总体表现为西北高东南低的趋势。其空间分布主要受土壤类型和质地的影响,其中潮土和盐化潮土的碳密度明显高于褐土化潮土,质地较细的土壤(轻壤、中壤和粘土)碳密度明显高于质地较粗的土壤(砂土和砂壤)。该研究为冲积平原区土壤碳密度的估算提供了一种新的方法。     

成都典型区水稻土有机碳组分构成及其影响因素研究

农田生态系统土壤有机碳对农业生产、生态平衡和全球气候变化至关重要,有机碳组分构成及平均驻留时间对深入了解土壤有机碳特征及演变规律意义重大。通过土壤呼吸培养实验和三库一级动力学方程,模拟分析了成都典型区水稻土有机碳组分构成特征;利用土壤定量化属性与有机碳各组分相关及回归分析,建立研究区土壤有机碳各组分预测模型。结果表明,有机碳组分的活性碳、慢性碳和惰性碳含量在表层(0~20 cm)分别为0.42、6.13、11.43 g kg-1,均高于亚表层(20~40 cm)的0.23、4.09、7.50 g kg-1,两土层间有机碳组分含量具有显著性差异,但有机碳组分比例没有显著性差异。剖面(0~100 cm)有机碳组分含量随着深度增加而减小,活性碳和慢性碳比例随着深度增加而降低,惰性碳比例则随着深度增加显著升高。容重、全氮和全磷对有机碳各组分含量,质地对活性碳组分含量、比例及平均驻留时间,p H对慢性碳和惰性碳组分比例均具有显著影响;活性碳和惰性碳组分含量与土壤全氮、碳氮比、p H以及土壤细粉粒(0.02~0.002 mm)含量间存在显著线性关系,可用来预测水稻土有机碳各组分含量,研究结果对其他地区土壤有机碳各组分研究及预测具有积极启示作用。     

气候因子对森林土壤有机碳影响的幅度效应研究

揭示不同幅度上气候因子对土壤有机碳(Soil organic carbon,SOC)影响的主控性变化,是预测未来气候变化对SOC演变趋势影响的基础。本文利用中国西南地区363个森林土壤剖面数据,基于大区、省和地级市3个幅度,研究了气候因子对森林SOC密度的影响随幅度变化的规律及不同幅度下的主控气候因子。结果表明,年均降水量与SOC密度的相关性均随着幅度的减小而减弱,而年均气温与SOC密度的相关性随幅度变化的规律不明显,有较强的区域差异。大区幅度上,SOC密度主要受年均降水量和年均气温的综合作用。省级幅度上,西藏自治区东部主控因子为年均降水量,而四川和云南两省为年均气温。地级市幅度上,各市的主控因子基本与其所属的省一致。气候因子对SOC密度变异的解释能力在大区幅度上约20%,且随着幅度的减小解释能力也逐渐减小。     

长期施肥下红壤有机碳及其颗粒组分对不同施肥模式的响应

采集不同施肥24年的红壤,采用物理分组的方法,观测了长期不同施肥下红壤有机碳及其组分变化,并结合历史资料分析了不同施肥模式对红壤有机碳及其颗粒组分的影响。结果表明,化肥配施有机肥（NPKM）处理下红壤总有机碳含量（10.33 g/kg）,砂粒（2000～53 m）、细粉粒（5～2 m）和粘粒（2 m）组分中的有机碳含量显著高于其他处理。与不施肥（CK）相比,施用化肥（NPK、2NPK）和有机肥（NPKM、M）显著地提高了红壤有机碳在砂粒和粘粒中的分配比例,而降低了其在粗粉粒和细粉粒的分配比例。施化肥（NPK、2NPK）、单施有机肥（M）、化肥配施有机肥（NPKM）处理,土壤有机碳的平均固定速率分别为0.05 t/(hm2?a)、0.18 t/(hm2?a)、0.26 t/(hm2?a)。相关分析表明,不同施肥模式下红壤有机碳的固定量与碳投入量之间存在着极显著的线性相关关系（R2=0.909, P0.01）,土壤的固碳效率为8.1%;随着碳投入的增加,粗粉粒和细粉粒有机碳储量逐渐下降,而砂粒和粘粒中碳储量逐渐增加,并且粘粒增加速率要远远高于砂粒。以上结果说明,红壤中有机碳还没有达到饱和,还具有一定的固碳潜力,增加的有机碳主要固持在粘粒中,粘粒是红壤有机碳的主要固持组分。