13C/12C Ratios of soil organic matter as indicators of vegetation changes in the congo

The ¹³C/¹²C ratios were determined for the organic matter of all horizons of a podzol profile and of the A₁ horizons of some ferrallitic soils, in some grass shoots and in a fossil root fragment from the B_2h horizon of the podzol. The isotope ratio in the organic matter of the A₁ horizon of the podzol matches those in grass shoots from the present savanna vegetation. The ratios in the lower horizons match those of organic matter in the A₁ horizons of soils under forest and that of the fossil root fragment in the B_2h horizon. The ratios thus demonstrate that the humus enrichment of the B_2h horizon of the podzol occurred while it was under forest vegetation and that the present grass vegetation did not take part in the podzolization process. The differences also indicate that savanna replaced forest vegetation after the profile had been formed.     

Carbon input from 13C-labeled crops in four soil organic matter fractions

This study quantified the fate of new carbon (C) in four crop sequences (lentil–wheat, canola–wheat, pea–wheat, and continuous wheat). Lentil–wheat and continuous wheat were grown in intact soil cores from a Brown Chernozem (BCz) and canola–wheat, pea–wheat, and continuous wheat in cores from a Dark Brown Chernozem (DBCz). In the first growing cycle, plants were pulse-labeled with ¹³C-CO₂. Soil ¹³C pools were measured once after the labeled growing cycle to quantify root biomass contribution to soil organic matter (SOM) in a single cycle and again after a second growing cycle to quantify the fate of labeled root and shoot residues. ¹³C was quantified in four SOM fractions: very light (VLF), light (LF), heavy (HF), and water extractable organic matter (WEOM). For BCz lentil, BCz wheat, DBCz canola, DBCz pea, and DBCz wheat in the labeling year, root-derived C estimates were 838, 572, 512, 397, and 418 mg of C per kg soil, respectively. At the end of the second growing cycle, decreases in root-derived C were greater in the VLF, which lost 62 to 95 % of its labeled ¹³C, than the LF (lost 21 to 56 %) or HF (lost 20 to 47 %). Root-derived C in WEOM increased 38 to 319 %. On DBCz, even though wheat and pea produced less aboveground biomass than canola, they generated similar amounts of SOC by fraction indicating that their residues were more efficiently stabilized into the soil than canola residues. Combining ¹³C repeat-pulse labeling and SOM fractionation methods allowed new insights into C dynamics under different crop sequences and soil types. This combination of methods has great potential to improve our understanding of soil fertility and SOM stabilization.     

Seasonal and age-related changes in the stable isotope composition (15N/14N and 13C/12C) of millipedes and collembolans in a temperate forest soil

Seasonal changes in environmental conditions and biotic interactions are often ignored when using stable isotope analysis for reconstructing the trophic structure of soil communities in temperate ecosystems. In this study, we estimated seasonal and age-related changes in δ¹³C and δ¹⁵N values in three epigeic species of collembolans (Pogonognathellus longicornis, Orchesella flavescens and Isotoma viridis) and two litter-dwelling species of millipedes (Polydesmus denticulatus and Leptoiulus proximus) in deciduous and coniferous forest stands in central Russia. Age-related changes in δ¹³C or δ¹⁵N values were either absent or negligible (within 1‰) in L. proximus, but adult and subadult specimens of P. denticulatus were enriched in ¹⁵N compared to early larval stages. Since the adults of P. denticulatus were generally more enriched in ¹⁵N than adults of L. proximus, they presumably occupy more distinct trophic niches than juveniles do. Age-related changes in isotopic composition were small or absent in collembolans studied. Neither δ¹³C nor δ¹⁵N values of millipedes changed significantly during the vegetation season. In contrast, consistent seasonal changes in δ¹³C and δ¹⁵N values were found in collembolans. Increased δ¹³C values coincided with the period of minimum soil moisture and correlated with a decreased C/N ratio in collembolan tissues. These changes can largely be attributed to the depletion of lipid-rich storage tissues. Seasonal changes in δ¹⁵N values were similar among collembolan species, yet slightly varied between habitats. A general trend of increasing δ¹⁵N values from June to September–October may indicate either a reduced importance of non-vascular plants (algae and lichen) in collembolan diet or variation in the isotopic composition of these plants. Overall, our data show that seasonal variations should be taken into account when estimating the isotopic composition of epigeic collembolans in forest soils.     

Land-use related organic matter dynamics in North Cameroon soils assessed by 13C analysis of soil organic matter fractions

Topsoil samples from cultivated and adjacent non‐cultivated fields on three major agricultural soils in North Cameroon were fractionated into particle‐size fractions that were analysed subsequently for their C and ¹³C contents. The aim was to obtain further insight into the dynamics of soil organic matter (SOM) in relation to land use in Cameroon. Since organic carbon contents of the fractions were often very small, samples and analyses were extensively replicated to obtain robust statistical estimates of observed differences. For each soil type, differences in δ¹³C values between fields could be related to changes in the input and decomposition of organic matter arising from soil type, land management and, for example, the nature and abundance of weeds. Turnover of organic matter appeared to be fastest in the sand fraction, which is in line with results from earlier studies. In the finer fractions, clear differences in reaction to changes in input and decomposition were observed, that seem to be linked to differences in clay mineralogy. The results illustrate that SOM in the various fractions is much less stable and more strongly affected by changes in land use than might be assumed on the basis of changes in total SOM contents alone. At the same time, they demonstrate the relevance of ¹³C isotope analyses of SOM for studies on the impact of land use on these savannah soils with little SOM that are highly susceptible to degradation.     

Input related microbial carbon dynamic of soil organic matter in particle size fractions

This paper investigated the flow of carbon into different groups of soil microorganisms isolated from different particle size fractions. Two agricultural sites of contrasting organic matter input were compared. Both soils had been submitted to vegetation change from C3 (Rye/Wheat) to C4 (Maize) plants, 25 and 45 years ago. Soil carbon was separated into one fast-degrading particulate organic matter fraction (POM) and one slow-degrading organo-mineral fraction (OMF). The structure of the soil microbial community were investigated using phospholipid fatty acids (PLFA), and turnover of single PLFAs was calculated from the changes in their ¹³C content. Soil enzyme activities involved in the degradation of carbohydrates was determined using fluorogenic MUF (methyl-umbelliferryl phosphate) substrates.We found that fresh organic matter input drives soil organic matter dynamic. Higher annual input of fresh organic matter resulted in a higher amount of fungal biomass in the POM-fraction and shorter mean residence times. Fungal activity therefore seems essential for the decomposition and incorporation of organic matter input into the soil. As a consequence, limited litter input changed especially the fungal community favoring arbuscular mycorrhizal fungi. Altogether, supply and availability of fresh plant carbon changed the distribution of microbial biomass, the microbial community structure and enzyme activities and resulted in different priming of soil organic matter.Most interestingly we found that only at low input the OMF fraction had significantly higher calculated MRT for Gram-positive and Gram-negative bacteria suggesting high recycling of soil carbon or the use of other carbon sources. But on average all microbial groups had nearly similar carbon uptake rates in all fractions and both soils, which contrasted the turnover times of bulk carbon. Hereby the microbial carbon turnover was always faster than the soil organic carbon turnover and higher carbon input reduced the carbon storage efficiency from 51% in the low input to 20%. These findings suggest that microbial community preferentially assimilated fresh carbon sources but also used recycled existing soil carbon. However, the priming rate was drastically reduced under carbon limitation. In consequence at high carbon availability more carbon was respired to activate the existing soil carbon (priming) whereas at low carbon availability new soil carbon was formed at higher efficiencies.     

The quality of exogenous organic matter: short-term effects on soil physical properties and soil organic matter fractions

We examined the short-term effect of five organic amendments and compared them to plots fertilized with inorganic fertilizer and unfertilized plots on aggregate stability and hydraulic conductivity, and on the OC and ON distribution in physically separated SOM fractions. After less than 1 year, the addition of organic amendments significantly increased ( P  <   0.01) the aggregate stability and hydraulic conductivity. The stability index ranged between 0.97 and 1.76 and the hydraulic conductivity between 1.23 and 2.80 × 10⁻³ m/s for the plots receiving organic amendments, compared with 0.34–0.43, and 0.42–0.64 × 10⁻³ m/s, respectively, for the unamended plots. There were significant differences between the organic amendments (P <  0.01), although these results were not unequivocal for both soil physical parameters. The total OC and ON content were significantly increased ( P  <   0.05) by only two applications of organic fertilizers: between 1.10 and 1.51% OC for the amended plots versus 0.98–1.08% for the unamended and between 0.092 and 0.131% ON versus 0.092–0.098% respectively. The amount of OC and ON in the free particulate organic matter fraction was also significantly increased ( P  <   0.05), but there were no significant differences ( P  <   0.05) in the OC and ON content in the POM occluded in micro-aggregates and in the silt + clay-sized organic matter fraction. The results showed that even in less than 1 year pronounced effects on soil physical properties and on the distribution of OC and ON in the SOM fractions occurred.     

Movement and turnover of soil organic matter as indicated by carbon isotope measurements

The distribution in a New Zealand pasture soil of total organic carbon, of ¹³C/¹²C and ¹⁴C/¹²C ratios, up to a depth of l m and over a period of 15 yr, has been analysed to provide models for radiocarbon enrichment and organic matter turnover. For the enrichment model, the parameters of C input, rates of decomposition and diffusion down the soil profile, and turnover rates have been determined. Input rates are compatible with herbage productivity measurements; the turnover period is estimated as 63 yr, and the downward diffusivity of C is estimated at 13cm² yr^?1. The steady state model indicates that a small fraction of the soil organic C, about 16%, is relatively very old and uniformly distributed throughout the soil profile. Most of the remaining fraction of modern C, other than “bomb” C, is less than 100 yr old and decreases exponentially with increasing depth. The models provide a rational integration of empirical measurements of C input, rates of organic matter decomposition, diffusivity and turnover, enabling an unknown to be calculated from measured parameters. They also provide a rational and precise method for determining the age of soil organic matter from radiocarbon measurements and have been used to examine alternative hypotheses for the distribution of UC with depth.     

Predicting soil organic matter stability in agricultural fields through carbon and nitrogen stable isotopes

In order to evaluate the sustainability and efficiency of soil carbon sequestration measures and the impact of different management and environmental factors, information on soil organic matter (SOM) stability and mean residence time (MRT) is required. However, this information on SOM stability and MRT is expensive to determine via radiocarbon dating, precluding a wide spread use of stability measurements in soil science. In this paper, we test an alternative method, first developed by Conen et al. (2008) for undisturbed Alpine grassland systems, using C and N stable isotope ratios in more frequently disturbed agricultural soils. Since only information on carbon and nitrogen concentrations and their stable isotope ratios is required, it is possible to estimate the SOM stability at greatly reduced costs compared to radiocarbon dating. Using four different experimental sites located in various climates and soil types, this research proved the effectiveness of using the C/N ratio and δ¹⁵N signature to determine the stability of mOM (mineral associated organic matter) relative to POM (particulate organic matter) in an intensively managed agro-ecological setting. Combining this approach with δ¹³C measurements allowed discriminating between different management (grassland vs cropland) and land use (till vs no till) systems. With increasing depth the stability of mOM relative to POM increases, but less so under tillage compared to no-till practises. Applying this approach to investigate SOM stability in different soil aggregate fractions, it corroborates the aggregate hierarchy theory as proposed by Six et al. (2004) and Segoli et al. (2013). The organic matter in the occluded micro-aggregate and silt & clay fractions is less degraded than the SOM in the free micro-aggregate and silt & clay fractions. The stable isotope approach can be particularly useful for soils with a history of burning and thus containing old charcoal particles, preventing the use of ¹⁴C to determine the SOM stability.     

不同封育年限草地土壤有机质组分及其碳库管理指数

土壤有机质对草地封育的生态效应具有重要指示作用,本文结合野外调查和室内分析,研究了半干旱区不同封育年限草地土壤有机质组分及其碳库管理指数变化,以分析土壤有机质对草地封育的响应特征,从而为该区土壤质量的改善和植被建设的生态效应评价提供依据。研究结果表明,土壤有机质及不同活性有机质含量均随土层加深而降低,且在各土层基本表现出封育18年、封育23年封育13年未封育封育3年的趋势。除封育3年土壤的3种活性有机质碳库管理指数在090cm土壤剖面均低于100外,封育13年草地060cm土层、封育18和23年草地090cm土层的3种活性有机质碳库管理指数均高于100,表明随年限的延长,封育对土壤有机质的改善深度也在加深。土壤3种活性有机质与有机质及多数土壤性质呈极显著正相关,能更为灵敏和直观地表征土壤管理的长期效应和土壤质量变化。     

Evidence of peptides in low-molecular-weight fractions of soil organic matter

Summary Organic matter was extracted from three soils, a Berwick sandy loam, a Franklin loamy sand, and a Cumberland silty loam. The extracts were separated into high (>8000 daltons) and low-molecular-weight (<8000 daltons) fractions using gel filtration. Reverse-phase high performance liquid chromatography at 214 nm was used to separate the peptides into low-molecular-weight fractions. Peptide samples were collected with an integrated fraction collector and hydolyzed with an immobilized protease column reactor. High performance liquid chromatography with fluorescence detection was used to determine the amino-acid contents of the collected samples. The results indicated that peptide intermediates are present in soil size fractions. Greater quantities of several amino acids were released from the peptide hydrolyzates of the Berwick sandy loam and Franklin loamy sand, compared with the Cumberland silty loam, an uncultivated soil. These findings indicate that organic intermediates (e.g., peptides) are more prevalent in biologically active soils than in relatively inert soils.     

Using soil organic matter fractions as indicators of soil physical quality

The objective of this study was to evaluate the use of chemical and physical fractions of soil organic matter (SOM ), rather than SOM per se , as indicators of soil physical quality (SPQ ) based on their effect on aggregate stability (AS ). Chemically extracted humic and fulvic acids (HA and FA ) were used as chemical fractions, and heavy and light fractions (HF and LF ) obtained by density separation as physical fractions. The analyses were conducted on medium‐textured soils from tropical and temperate regions under cropland and pasture. Results show that soil organic carbon (SOC ), SOM fractions and AS appear to be affected by land use regardless of the origin of the soils. A general separation of structurally stable and unstable soils between samples of large and small SOC content, respectively, was observed. SOM fractions did not show a better relationship with AS than SOC per se . In both geographical regions, soils under cropland showed the smallest content of SOC , HA and carbon concentration in LF and HF , and the largest HF /LF ratio (proportion of the HF and LF in percent by mass of bulk soil). With significant associations between AS and SOC content (0.79**), FA /SOC (r  = −0.83*^*), HA /FA (r  = 0.58*^*), carbon concentration of LF (r  = 0.69*^*) and HF (r  = 0.70*^*) and HF /LF ratio (r  = 0.80*^*), cropland showed lowest AS . These associations indicate that SOM fractions provide information about differences in SOM quality in relation to AS and SPQ of soils from tropical and temperate regions under cropland and pasture.     

Climatic influences on active fractions of soil organic matter

Biologically active fractions of soil organic matter are important in understanding decomposition potential of organic materials, nutrient cycling dynamics, and biophysical manipulation of soil structure. We evaluated the quantitative relationships among potential C and net N mineralization, soil microbial biomass C (SMBC), and soil organic C (SOC) under four contrasting climatic conditions. Mean SOC values were 28±11 mg g⁻¹ (n=24) in a frigid–dry region (Alberta/British Columbia), 25±5 mg g⁻¹ (n=12) in a frigid–wet region (Maine), 11±4 mg g⁻¹ (n=117) in a thermic–dry region (Texas), and 12±5 mg g⁻¹ (n=131) in a thermic–wet region (Georgia). Higher mean annual temperature resulted in consistently greater basal soil respiration (1.7 vs 0.8 mg CO₂–C g⁻¹ SOC d⁻¹ in the thermic compared with the frigid regions, P<0.001), greater net N mineralization (2.8 vs 1.3 mg inorganic N g⁻¹ SOC 24 d⁻¹, P<0.001), and greater SMBC (53 vs 21 mg SMBC g⁻¹ SOC, P<0.001). Specific respiratory activity of SMBC was, however, consistently lower in the thermic than in the frigid regions (29 vs 34 mg CO₂–C g⁻¹ SMBC d⁻¹, P<0.01). Higher mean annual precipitation resulted in consistently lower basal soil respiration (1.1 vs 1.3 mg CO₂–C g⁻¹ SOC d⁻¹ in the wet compared with the dry regions, P<0.01) and lower SMBC (31 vs 43 mg SMBC g⁻¹ SOC, P<0.001), but had inconsistent effects on net N mineralization that depended upon temperature regime. Specific respiratory activity of SMBC was consistently greater in the wet than the dry regions (≈33 vs 29 mg CO₂–C g⁻¹ SMBC d⁻¹, P<0.01). Although the thermic regions were not able to retain as high a level of SOC as the frigid regions, due likely to high annual decomposition rates, biologically active soil fractions were as high per mass of soil and even 2–3-times greater per unit of SOC in the thermic compared with the frigid regions. These results suggest that macroclimate has a large impact on the portion of soil organic matter that is potentially active, but a relatively small impact on the specific respiratory activity of SMBC.     

Temporal changes in distribution and composition of N from labeled fertilizer in soil organic matter fractions

Variations in the amount and composition of immobilized nitrogen (N) in major soil organic matter fractions were investigated in a 730-day soil incubation experiment using ¹⁵N-labeled urea and ¹⁵N nuclear magnetic resonance spectroscopy with the cross polarization/magic angle spinning (¹⁵N CPMAS NMR) method. After 730 days, 24.7% of the applied N was recovered from the soil as organic N. The urea-derived N recovered from humic acids and humin decreased from 11.2 and 33.8% of the applied amount after 14 days to 1.6 and 20.4% after 730 days, respectively. When these values were corrected for the microbial biomass (MB) N, they ranged from 9.0 to 1.2% and 28 to 18%, respectively. The proportion of urea-derived N recovered from fulvic acids was low, ranging between 0.4 and 5.8% (with MB N) or 5.6% (without MB N) of the applied amount, whereas that from water-soluble nonhumic substances (WS-NHS; NHS in the fulvic acid fraction) remained high, 28–33% of the applied amount after correction for the contribution of MB N up to day 365, and decreased to 0.9% thereafter. The ¹⁵N CPMAS NMR spectra of humic acids, fulvic acids, and humin showed the largest signal at −254 to −264 ppm, corresponding to peptide/amide N. The proportions of heterocyclic, peptide/amide, guanidine/aniline, and free amino N in the urea-derived humic acid N were 3–7, 83–90, 5–7, and 2–4%, respectively. More than 80% loss of the urea-derived humic acid N did not markedly alter their composition. No time-dependent variations were also observed for the proportions of respective N functional groups in humin N, which were 3–5, 71–78, 12–17, and 6–10% in the same order as above. These results suggest the greater importance of physical stability than structural variation for the initial accumulation of organic N in soil.     

Decomposition temperature sensitivity of isolated soil organic matter fractions

The general consensus is that a warming climate will result in the acceleration of soil organic matter (SOM) decomposition, thus acting as a potential positive feedback mechanism. However, the debate over the relative temperature sensitivity of labile versus recalcitrant SOM has not been fully resolved. We isolated acid hydrolysis residues to represent a recalcitrant pool of SOM and particulate organic matter (POM) to represent a labile pool of SOM, and incubated each at different temperatures to determine temperature sensitivity of decomposition. Short-term incubations of POM generated results consistent with published experiments (i.e., greater proportion of C respired and lower Q₁₀ than whole soil), while incubations of acid hydrolysis residues did not. The contrasting results illustrate the difficulty in assessing temperature sensitivity of labile versus stable SOM decomposition, partly because of the inability to quantitatively isolate labile versus stable SOM pools and to be sufficiently certain that respiration responses to temperature are not masked by processes such as enhanced stabilization or microbial inhibition/adaptation. Further study on the temperature sensitivity of decomposition of isolated SOM fractions is necessary to better explain and predict temperature responses of bulk SOM decomposition.     

Buffer capacity and Cu affinity of soil particulate organic matter (POM) size fractions

Particulate organic matter fractions (POM), defined as sand‐sized organic separates in soils, are known to be labile organic components with a rapid turnover. Recently, POM fractions were identified to be metal‐enriched in both metal‐contaminated and uncontaminated soils. However, mechanisms for such metal‐enrichment are poorly understood, because of the paucity of information on the chemical properties of POM. The aim of this study was to quantify the reactivity of POM towards Cu and to show a POM‐size effect on this reactivity. POM was isolated from soils with different organic amendment managements: straw (S), conifer compost (CC), and non‐amended (NA). Two POM size fractions were isolated by density‐fractionation in water: 50–200 μm and 200–2000 μm. These fractions were studied for their metal contents, acid‐base properties and affinity toward Cu. The buffer capacity and Cu affinity were modeled by FITEQL 4.0 software and compared between the two POM size fractions. Each POM size fraction provided a buffer capacity due to the presence of reactive sites, the greatest being for the 50–200 μm POM fractions. A signature of organic inputs as seen by the buffer capacities was observed for the 50–200 μm but not for the 200–2000 μm POM fractions. But Cu affinity was comparable between the coarse and fine POM fractions and no significant differences were found between NA, S and CC samples. We checked the hypothesis that decreasing POM size due to degradation processes generates more reactive surface sites. Results confirmed that soil POM plays a key role as a metal sink, due to its chemical properties.     

稳定性同位素技术在土壤重要有机组分循环转化研究中的应用

土壤有机质包含多种不同结构的有机物质,如碳水化合物(中性糖、氨基糖)、蛋白质(氨基酸)、木质素等,这些组分在土壤中的保留时间从几天到几百万年,在有机质循环过程中的积累和转化动态各有特征,其作用和贡献也有所不同.由于有机质各组分本身在土壤中稳定存在,只有利用同位素示踪技术才能定量研究有机质及其组分的循环动态.本文概述了利用稳定同位素示踪技术研究有机质中的一些重要组分的来源、可利用性和转化动态及其生物标识作用的进展情况,从而深入了解土壤有机质循环转化动态及调控机制.     

不同有机物料对苏打盐化土有机碳和活性碳组分的影响

【目的】在大同盆地苏打盐化土上,研究不同有机物料对春玉米产量、土壤有机碳及活性碳组分的影响,明确土壤有机碳及活性碳组分与主要盐碱指标的相关关系,为苏打盐化土改良及有机物料资源化利用提供理论支撑。【方法】2016-2017年在山西省北部怀仁县开展田间定位试验,设对照(CK)、风化煤、生物炭、牛粪和秸秆5个处理,各处理有机物料施用量按照每年9000 kg/hm^2等有机碳投入量折算,收获时对春玉米进行测产。2017年春玉米收获后,采集土壤样品测定土壤有机碳总量(SOC)和水溶性有机碳(WSOC)、易氧化有机碳(EOC)、轻组有机碳(LFOC)含量,分析土壤活性碳组分占有机碳的比例、土壤有机碳及活性碳组分与盐碱指标之间的关系。【结果】与CK相比,生物炭和秸秆处理春玉米产量无明显差异,而风化煤和牛粪处理春玉米产量则分别显著提高30.2%和30.3%。添加有机物料促进了0-20 cm土层SOC累积,其中以风化煤和牛粪处理效果最佳,较CK分别提高47.6%和36.1%。在有机碳组分方面,风化煤和牛粪处理提高WSOC、EOC含量的效果显著高于生物炭、秸秆处理;风化煤、牛粪和秸秆处理的LFOC含量显著高于生物炭处理。四类有机物料处理的WSOC占总有机碳的比例差异不显著,牛粪处理的占比显著高于CK。EOC占总有机碳的比例以牛粪处理最高,风化煤次之,且二者均显著高于CK处理;LFOC占总有机碳的比例则表现为秸秆、牛粪>风化煤、生物炭> CK。此外,添加有机物料能有效降低0-20 cm土层土壤pH、电导率(EC)和碱化度(ESP),其中以风化煤和牛粪处理降幅最大。相关分析表明,土壤SOC与pH、EC和ESP呈显著负相关。【结论】通过有机物料改良效果比较,发现牛粪和风化煤处理能促进苏打盐化土有机碳累积,提高可溶性、易氧化态及轻组有机碳组分在总有机碳中的占比,降低土壤pH、EC和ESP,明显提高春玉米产量。因此,风化煤和牛粪是山西北部苏打盐化土良好的改良剂。     

13C NMR spectra of soil organic fractions extracted with organic solvents

Soil organic fractions extracted in sequence with ethyl ether, acetone, benzene and dioxane have been investigated with ¹³C NMR spectroscopy. The spectra of ethyl ether and acetone fractions are identical and show the presence of signals assigned to normal long chain (C_23±2) fatty acids. A very similar spectral pattern is displayed by the benzene fraction which appears to consist of a mixture (50 ± 10)% of normal fatty acids and normal alkanes (C_21±3). A comparison with data in the literature indicates that the well developed signals at 14, 23, 30 (very intense) and 32 ppm are a common feature of the lipid fraction extracted from different soils.A completely different spectrum has been obtained from the dioxane fraction. Most signals appearing in the range 55–75 ppm can be attributed to oxygen bonded sp³ carbon atoms. The lack of aromatic signals seems to exclude the possibility that this fraction was derived from lignin residues.The comparison with ¹H NMR spectra and the occurrence of distinct and sharp signals indicate that ¹³C NMR is a valuable tool in the study of soil organic fractions extracted with organic solvents.