Differences In Soil Organic Carbon Content Research Articles

Response of soil water, salt, carbon and bacteria community to terrain and plant in coastal salt marsh

Terrain and plants play a crucial role in influencing or regulating the variations of water, salt, carbon, and bacteria community in the soil of coastal salt marshes. Investigating these variations and their interconnections under different conditions is essential to comprehensively understand the carbon sequestration function and reveal the underlying mechanisms of carbon sinks in coastal salt marshes. In this study, the various physicochemical properties of rhizosphere and non-rhizosphere soil under different terrain of coastal salt marsh in Jiaozhou Bay were determined. Additionally, the contents of soil carbon components including soil inorganic carbon (SIC), soil organic carbon (SOC), dissolved inorganic carbon (DIC), and dissolved organic carbon (DOC), and constituents of soil dissolved organic matter (DOM) and microbial community were analyzed. The results showed that the contents of SIC and SOC in high-terrain soil were significantly lower than those in low-terrain soil (P < 0.05). Plants could regulate the physicochemical properties, and carbon components of soil in different terrain, resulting in no significant difference in SOC contents of rhizosphere soil under different terrain. Soil DOM composition and bacterial community showed that high-terrain soil had higher bacterial diversity and activity, and plants significantly affected the bacterial community structure in soil through rhizosphere effects. The structural equation model demonstrated that terrain has an indirect impact on SOC through influencing on the fluorescence of soil DOM and bacterial diversity, and SIC through altering soil water content (SWC), electrical conductivity and DOC. Plants directly or indirectly affected SOC content, and indirectly affected SIC content by changing SWC. This study contributes to a better understanding of the complex interactions between wetland ecosystems and their soil water, salt, carbon, and bacteria community components, offering valuable information for wetland management and conservation efforts.

Influences of 13 Years New Conservation Management on Labile Soil Organic Carbon and Carbon Sequestration in Aggregates in Northeast China

New conservation management (NCM) for summer maize monocultures might cause changes in the organic carbon composition when compared with conventional tillage (CT). To investigate the difference, the soil organic carbon (SOC) under 13 years of NCM and CT was studied in Northeast China. The NCM involved the use of a 40 cm and 160 cm narrow-wide row (maize was planted in the narrow row in two lines) with straw retained, but with no tillage and change in ridge direction. SOC in different soil aggregate size classes and labile organic carbon fractions at 0–10 cm, 10–20 cm and 20–40 cm depths were evaluated. The results showed that there was no significant difference in SOC content at a 0–10 cm depth, with values ranging from 19.9 to 21.1 g·kg−1 between two management systems. The contents of microbial biomass carbon (MBC) and light fraction organic carbon (LFOC) were significantly higher in NCM than in CT in the upper 10 cm. Among the labile organic carbon fractions, the light fraction organic C (LFOC) was the most sensitive to management change. The portion of macroaggregates (&gt;0.25 mm) was higher under NCM than under CT and decreased with the increase in soil depth. NCM improved the organic carbon storage in aggregates 1–0.5 mm and reduced the organic carbon storage in microaggregates. It was concluded that NCM would be an effective and useful management choice for the enhancement of soil C sequestration in maize field systems in Northeast China.

Mesofauna as effective indicators of soil quality differences in the agricultural systems of central Cuba

Soil mesofauna play an essential role in soil functioning. However, in studies on the impact of agricultural management on soil quality, the overall abundance of soil mesofauna and specific groups thereof has not been widely used as an indicator in developing countries. Here, we used soil mesofauna as a soil quality indicator compared to more traditional soil chemical, physical, and microbial indicators, in a comparison of the impact of three diverse agricultural management systems in Central Cuba: state (CSt), conventional private (CPr), and organic private (OPr) farms. We sampled the top 20 cm of soil of 30 fields from 12 farms and 1 natural reference site (NR) and analysed a number of soil chemical, physical, and microbial soil parameters as well as mesofauna (Acari and Collembola, further subdivided into Mesostigmata–Prostigmata–Oribatida–Astigmata and Isotomidae–Entomobryidae, respectively). Differences in soil properties between agricultural fields and natural soil were observed (especially in the multivariate analysis), but no significant differences were observed between agricultural systems, probably due to a lack of differences in soil organic carbon (SOC) content. The mesofauna differed strongly between the NR and the two conventional management practices (CSt and CPr), both in total numbers and in group numbers for most groups and in both rainy and dry seasons, whereas there were almost no significant differences between NR and OPr. Principal component analysis based on mesofauna clearly distinguished NR from all farming systems and OPr from CSt and CPr. Differences in soil mesofauna were mainly attributed to the use of synthetic pesticides. We conclude that in this context, without clear differences in SOC content between agricultural fields, mesofauna is a superior soil quality indicator. Our results indicate that simple counts of total abundance are as useful as counts of specific mesofauna groups irrespective of the sampling period (dry or wet season).

Effects of Biochar on Soil Organic Carbon of Eroded Cultivated Layer of Slope Farmland in Purple Hilly Area

Soil organic carbon (SOC) is the largest carbon pool in the terrestrial ecosystem. It is not only the core index of cultivated land soil quality evaluation but also an important part of the global carbon cycle. In order to understand the response characteristics of SOC in the cultivated layer to the interaction of soil erosion and management measures, the eroded cultivated layer of typical purple soil slope farmland in the Three Gorges Reservoir area was the research object. The in-situ tests of five erosion degrees on sloping farmland were established using the shovel erosion simulation test method; taking no fertilizer (CK) as a control measure, two types of restorative management measures were set up, namely chemical fertilizer (F) and biochar+chemical fertilizer (BF), to clarify the differences in SOC content under different erosion degrees and management measures and to analyze the variation characteristics and interannual variation trend of SOC along the cultivated-layer profile. The results showed that:① BF significantly increased the soil organic carbon content in the cultivated layer of purple soil slope farmland; the SOC of BF was 90.25% and 23.84% higher than that of CK and F on average, respectively. Soil erosion significantly reduced the content of SOC (12.25%-27.74%) under CK measures, but there was no significant difference in the profile distribution of SOC under different erosion degrees. ② The SOC content in the surface layer (0-10 cm) of slope farmland was the highest, and the two measures had the most obvious effect on improving the SOC contents, which were 120.59% and 66.90%, respectively. ③ After three consecutive years of experiments, the SOC content in the cultivated-layer of slope farmland changed significantly. Under CK, the average annual loss of SOC was 12.52%, whereas under BF, the average annual increase in SOC content was 9.31%. ④ The correlation between SOC and soil physical and chemical properties was different in the various soil layers; the deeper the soil layer was, the weaker the correlation was. Therefore, biochar combined with chemical fertilizer (BF) was an important management measure to improve the erosive cultivated layer and enhance soil fertility for slope farmland in the purple hilly area. The results of this study can provide basic parameters for the rational regulation of cultivated layers and the improvement of soil fertility.

Eight years organic amendment application alters N2O emission potential by increasing soil O2 consumption rate

Organic amendments are efficient measures that can be employed to increase both nitrogen use efficiency and soil organic carbon (SOC) content. However, the long-term effects of such measures on soil N2O emission and the associated underlying mechanisms are still unclear. Here, we sampled soils that were part of two long-term trials after eight years of different amounts and types of organic amendment addition, and investigated the response of soil N2O emissions to different types of mineral N addition under oxic condition. Further, we selected two soil samples with a large difference in SOC content and investigated the responses of soil CO2, N2O, NO, and N2 emissions as well as O2 consumption to NH4+, NO3−, and nitrification inhibitor addition under limited O2 diffusion condition and anoxic condition. Results showed that long-term organic amendments significantly increased SOC content, while the stimulated effect on N2O and N2 emissions owing to increased SOC contents was more pronounced with NH4+ addition under limited O2 diffusion condition than under oxic or anoxic conditions. Further, in all treatments under limited O2 diffusion condition, soil O2 concentration and N2O production showed significant inverse relationships, suggesting that O2 directly regulates N2O production. We speculated that the decrease in O2 availability with higher SOC contents owing to enhanced soil respiration, instead of the increased supply of electron donors, is primarily responsible for the stimulated N2O emissions. This implied that practices which reduce limited O2 diffusion conditions might help to minimize the stimulated N2O emissions from increased SOC content.

Impacts of continuous biochar application on major carbon fractions in soil profile of North China Plain’s cropland: In comparison with straw incorporation

Although the increase of soil organic carbon (SOC) in biochar-amended soil has been well documented, there is a lack of understating on the responses of soil inorganic carbon (SIC) to biochar application in soil profile. Here, we conducted a field study to investigate the effects of 10-year application of biochar at 4.5 Mg ha−1 yr−1 (B4.5) and 9.0 Mg ha−1 yr−1 (B9.0), and straw return (SR) of 15 Mg ha−1 yr−1 on SOC and SIC and their dissolved fractions. Our results showed significant difference in SOC content over 0–20 cm, with an order of B9.0 (8.46 g kg−1) > B4.5 (7.58 g kg−1) > SR (6.81 g kg−1) > control (5.26 g kg−1). However, SIC content was significantly lower under biochar (1.0–2.0 g kg−1) and control (1.0–2.0 g kg−1) than straw incorporation (3.2–3.7 g kg−1) over 0–40 cm. On average, DOC:SOC ratio (an index of SOC desorption) was significantly lower under biochar (~2.0%) and SR (2.6%) treatments than under control (3.1%), implying that both biochar and straw amendments can enhance SOC stability. Over the ten years, 62–81% of biochar-C was converted to SOC in the 0–100 cm layer, which was significantly higher than that (21%) of straw-C. Our estimation suggested that total carbon loss rate was 51–53% under biochar amendment and 70% with straw incorporation. This study highlights that biochar application has great potential for carbon sequestration in cropland of north China.

Phenolic acid-degrading Paraburkholderia prime decomposition in forest soil

Plant-derived phenolic acids are catabolized by soil microorganisms whose activity may enhance the decomposition of soil organic carbon (SOC). We characterized whether phenolic acid-degrading bacteria enhance SOC mineralization in forest soils when primed with 13C-labeled p-hydroxybenzoic acid (pHB). We further tested whether pHB-induced priming could explain differences in SOC content among mono-specific tree plantations in a 70-year-old common garden experiment. pHB addition primed significant losses of SOC (3–13 µmols C g−1 dry wt soil over 7 days) compared to glucose, which reduced mineralization (-3 to -8 µmols C g−1 dry wt soil over 7 days). The principal degraders of pHB were Paraburkholderia and Caballeronia in all plantations regardless of tree species or soil type, with one predominant phylotype (RP11ASV) enriched 23-fold following peak pHB respiration. We isolated and confirmed the phenolic degrading activity of a strain matching this phylotype (RP11T), which encoded numerous oxidative enzymes, including secretion signal-bearing laccase, Dyp-type peroxidase and aryl-alcohol oxidase. Increased relative abundance of RP11ASV corresponded with higher pHB respiration and expression of pHB monooxygenase (pobA), which was inversely proportional to SOC content among plantations. pobA expression proved a responsive measure of priming activity. We found that stimulating phenolic-acid degrading bacteria can prime decomposition and that this activity, corresponding with differences in tree species, is a potential mechanism in SOC cycling in forests. Overall, this study highlights the ecology and function of Paraburkholderia whose associations with plant roots and capacity to degrade phenolics suggest a role for specialized bacteria in the priming effect.

Net global warming potential, greenhouse gas intensity and carbon footprint as affected by different tillage systems from Chinese double-cropping paddy fields

Conservation tillage may be an alternative system for rice production in China, yet differences in net global warming potential (NGWP), greenhouse gas intensity (GHGI) and carbon footprint (CF) among different tillage methods are poorly documented. Accordingly, a 3-year field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions and changes in soil organic carbon (SOC) under conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) methods in Chinese double-rice cropping systems. There was no difference in SOC content among the tillage treatments, but SOC sequestration under NT reduced obviously with the increase of soil depth at 0∼20 cm. CH4 emissions were conspicuously correlated with SOC content at soil depth below 5 cm. Tillage methods had no significant effect on N2O emission, except for the substantial N2O emission under NT during non-rice season. Compared with the NT plots, the annual CH4 emission and NGWP were significantly increased in the CT and RT plots over the three years. There were no significant differences among the tillage methods with respect to GHGI and CF, whereas the grain yields were greatly increased in the RT plot. We conclude that RT practice are promising in rice production for higher grain yield with similar GHGI and CF, while increasing productivity of the NT system is a high priority since the CH4 emission and NGWP can be dramatically reduced.

Fencing facility affects plant species and soil organic carbon in temperate steppes

Fencing facility has been widely employed in steppes. However, the effects of fencing facility on plant species and soil organic carbon (SOC) have been rarely understood in steppes. Using soil sampling and plant quadrat clipping methods, in this study, we investigated the effects of fencing facility on the distributions of plant species and SOC in the temperate steppes of the Inner Mongolia. Plant biomass significantly increased with approaching fencing facility and was obviously higher in the leeward (south) than windward (north) sides. Perennial grasses accounted for approximately 68%–76% of the total aboveground biomass in both sides of fencing facility. SOC content also significantly increased with approaching fencing facility in the 0–10 soil layer but slightly increased in the 10–30 cm soil layer. Wind erosion and dust storm did markedly neither change the fractions of soil texture nor cause the difference in SOC content between the windward and leeward sides. Fencing facility increased SOC storage by 16.5% and 9.1% at 0.1 and 0.5 m locations relative to at 3 m location in the 0–10 cm soil layer, respectively. Edge effect is suggested as a potential mechanism driving the variations of plant species and SOC in both sides of fencing facility.

Difference in soil organic carbon content in various land uses and soil depths of lateritic belt of West Bengal

Soil organic carbon (SOC) is the key indicator of soil quality and overall sustainability of the environment. Information of OC in soil is very important as it influences chemical, physical and biological soil properties. In order to assess the difference in SOC content along depth and land uses and relationship of SOC with soil properties, a total of 54 soil samples were collected from 3 soil depths and 6 land uses of lateritic soil of Birbhum district of West Bengal. The soil physical properties like bulk density, particle density, sand, silt and clay content; chemical properties like pH, EC, OC, available N, P2O5, K2O, S were estimated following standard procedure. Results exhibited significant variation of SOC with soil depths and land uses. There was decrease in SOC value with increase in soil depth for all studied land uses. The SOC value was highest and lowest forest and fallow land respectively for all the soil depths. Unrelatedly of soil depths, forest land and fallow land recorded highest and lowest SOC respectively. But, unrelatedly of land uses, 0-20 cm and 40-60 cm soil depth noted highest and lowest SOC respectively. The value of SOC due to combined effect of depth and land uses was noted highest and lowest in 0-20 cm depth of forest and 40-60 cm depth of orchard land respectively. The soil pH, BD, sand and silt content exhibited significant negative correlation with SOC and available K2O and S and clay disclosed significantly positive correlation with SOC.

Soil Properties Control Microbial Carbon Assimilation and Its Mean Residence Time

Microbial assimilation and stabilization of soil organic carbon (SOC) is an important process in global carbon cycling. For an improved understanding of climate-induced changes in ecosystem C dynamics, it is important to know the group-specific turnover of microbial C. Consequently, we wanted to answer the questions if fungi store newly assimilated C longer than bacteria and if climatic and edaphic properties of different regions affect microbial C assimilation and its subsequent release. This study presents results from a 112-day long field experiment where endogenous soil microorganisms were labelled with 13C labelled glucose to follow the dynamics of newly assimilated C in two study regions (Kraichgau and Swabian Alb). Whereas microbial assimilation of newly added C was higher in Kraichgau than in Swabian Alb, the opposite result was obtained for the mean residence time (MRT) of microbial biomass C (76 days in Kraichgau and 93 days in Swabian Alb). The accelerated turnover rates of microbial C in the warmer soils of Kraichgau with lower clay content might be an important mechanism explaining the differences in SOC content between both regions. Gram-positive bacteria assimilated more 13C-glucose into their biomass than fungi and the MRT of C was higher in bacteria as compared to fungi in both regions. Beside these dynamic substrate utilization strategies, we could proof cross feeding by gram-negative bacteria. Carbon MRT in fungi was region specific and was best represented by a two-pool model; the initial MRT ranged between 5 to 39 days and was, in the end, higher than 4 years. This provides evidence of a possible shift in fungal community composition; fast growing fungi dominant in the early phase and internal redistribution of C in the second phase of decomposition. Our study identified microbial group and region specific MRT of freshly assimilated C as an important parameter, which might help to explain the commonly found variation in soil respiration and SOC stabilization.

Effects of Plum Plantation Ages on Soil Organic Carbon Mineralization in the Karst Rocky Desertification Ecosystem of Southwest China

Soil organic carbon (SOC) mineralization is closely related to carbon source or sink of terrestrial ecosystem. Understanding SOC mineralization under plum plantation is essential for improving our understanding of SOC responses to land-use change in karst rocky desertification ecosystem. In this study, 2-year, 5-year, and 20-year plum plantations and adjacent abandoned land dominated by herbs were sampled, and a 90-day incubation experiment was conducted to investigate the effect of plum plantations with different ages on SOC mineralization in subtropical China. Results showed that: (1) Plum plantation significantly decreased SOC content compared with abandoned land, but there was no significant difference in SOC content among plum plantations with different ages. Oppositely, the accumulative SOC mineralization (Ct) and potential SOC mineralization (C0) showed different responses to plum plantation ages. (2) The dynamics of the SOC mineralization were a good fit to a first-order kinetic model. Both C0 and Ct in calcareous soil of this study was several- to 10-folds lower than other soils in non-karst regions, indicating that SOC in karst regions has higher stability. (3) Correlation analysis revealed that both Ct and C0 was significantly correlated with soil calcium (Ca), suggesting an important role of Ca in SOC mineralization in karst rocky desertification areas. In conclusion, a Ca-rich geological background controls SOC mineralization in karst rocky desertification areas.

Substitution of mineral fertilizers with biogas digestate plus biochar increases physically stabilized soil carbon but not crop biomass in a field trial

Various organic amendments are scrutinized as potential agricultural management strategies to ensure soil productivity while mitigating climate change due to the accumulation of soil organic matter (OM). The objectives of this experiment were to study the effects of biochar and biogas digestate versus mineral fertilizer on crop aboveground biomass as well as fractions and mineralization of soil organic carbon (SOC). Samples of a sandy Cambisol were taken 14 months after establishment of a field experiment in Germany. Treatments included application of equal nitrogen in the form of mineral fertilizer or liquid biogas digestate without biochar (B0), with 1 Mg biochar ha−1season−1 for two growing seasons (B2), or with 40 Mg biochar ha−1 application (B40). Soil fractionation in water separated water-extractable and free particulate (fPOM) OM, followed by sonification and sieving to isolate occluded particulate (oPOM) and < 20 μm aggregate-occluded and mineral-associated OM. CO2 emissions were measured during 92-day laboratory incubations at 10 and 20 °C. Analysis of variance found digestate lowered (p < 0.05) rye aboveground biomass compared to mineral fertilizer (9.3 vs. 10.6 Mg ha−1), while biochar had no effect. B40 treatments increased C mineralization during incubation by 16% and contained 3.8 times more SOC than B0 treatments. This additional SOC was allocated to fPOM (52%), oPOM (22%), and the <20 μm fraction (26%). Digestate application increased SOC content of oPOM by 11% compared to mineral fertilizer. Furthermore, combined application of 40 Mg biochar ha−1 with digestate resulted in 20% more SOC in the <20 μm fraction than biochar with mineral fertilizer. The lack of a significant fertilizer or biochar-fertilizer interaction effect on C mineralization during incubation demonstrates the stability of SOC from digestate alone or in combination with biochar. The absence of significant differences in SOC content between B0 and B2 treatments demonstrates the difficulty of documenting SOC sequestration in the field at low biochar application rates.

Spatial distribution characteristics of soil organic carbon in subtropical forests of mountain Lushan, China.

The study on the spatial distribution of forest soil organic carbon (SOC) is of great significance for accurate assessment of carbon storage in forest ecosystems. In the present study, by taking eight kinds of forest soils of Mountain Lushan in the subtropical area as the research object, we studied the spatial distribution characteristics of SOC in this mountainous area. The results showed that the SOC content and SOC density (SOCD) of main forest types in the Mountain Lushan were lower than the national and the world average. The soil layer of Lushan forest was thinner, and the SOC and active SOC (ASOC) contents of different forest types and SOCDs are the highest in the surface soil. SOCD of the topsoil accounts for 32.64-54.03% of the total SOCD in the whole soil profile. Surface litter is an important source of SOC, and the different vegetation types are the important reason for the different spatial distribution of SOC in this area. Soil SOC contents in the high-altitude forest (bamboo forest, deciduous broadleaf forest, Pinus taiwanensis forest, evergreen-deciduous forest, and coniferous-broadleaved mixed forest) were higher than those in the low-altitude forest (evergreen broadleaf forest, shrub, and Pinus massoniana forest). However, the difference in SOC content exhibited at the altitude gradient is significantly lower than that in SOC in the soil profile. This indicates that both soil depth and elevation are the important factors that affected SOC distribution. However, the influence of soil depth on spatial distribution of SOC may be more complex than that of altitude. Vegetation types and soil properties are the main reasons for the large differences of reduction rate in the contents of SOC and ASOC.

Effects of environmental factors on soil organic carbon under natural or managed vegetation restoration

AbstractTo expand the scientific understanding of soil organic carbon (SOC) accumulation in restored ecosystems, we used 246 soil samples from a rocky catchment (10.24 km2) in an ecologically fragile karst area of southwest China and measured the effects of environmental factors under different vegetation restoration types (managed, including forage grassland and plantation forest, or natural, including grassland, shrubland, and secondary forest) on soil organic carbon content (SOCC) and soil organic carbon density (SOCD). Significantly higher SOCC and SOCD were found in natural vegetation than in managed vegetation and tillage land but no differences in SOCC or SOCD were detected between managed vegetation and tillage land. The environmental factors include rock outcrop ratio (ROR), bulk density, altitude, soil depth, slope gradient, and pH, all showing significant effect on SOC. The proportion of variations in SOCC and SOCD explained by environmental factors was higher in natural vegetation restoration than in managed vegetation restoration, and this proportion increased along the successional gradient. However, the environmental factors driving variations in SOCC and SOCD differed according to vegetation type. Soil bulk density had the strongest effect on SOCC variation in all vegetation types, except for forage grassland, in which the variation was instead controlled by ROR. The variation of SOCD was mainly driven by ROR in most vegetation types, except for tillage land and forage grassland, in which the driving factor was altitude. This results indicated that natural vegetation restoration is more beneficial to SOC sequestration than managed vegetation restoration and thus for mitigating global climate change. Accordingly, future studies should take these different environmental drivers under different vegetation restoration types into consideration when modeling SOC and guiding restoration management.

Long-term Effects of Organic Waste Fertilizers on Soil Structure, Tracer Transport, and Leaching of Colloids.

Organic waste fertilizers have previously been observed to significantly affect soil organic carbon (SOC) content and soil structure. However, the effect of organic waste fertilizers on colloid dispersibility and leaching of colloids from topsoil has not yet been studied extensively. We investigated how the repeated application of different types of agricultural (liquid cattle slurry and solid cattle manure) and urban waste fertilizers (sewage sludge and composted organic household waste) affected soil physical properties, colloid dispersion from aggregates, tracer transport, and colloid leaching from intact soil cores. Total porosity was positively correlated with SOC content. Yearly applications of sewage sludge increased absolute microporosity (pores <30 μm) and decreased relative macroporosity (pores >30 μm) compared with the unfertilized control, whereas organic household waste compost fertilization increased both total porosity and the absolute porosity in all pore size classes (though not significant for 100-600 μm). Treatments receiving large amounts of organic fertilizers exhibited significantly lower levels of dispersible colloids compared with an unfertilized control and a treatment that had received moderate applications of cattle slurry. The content of water-dispersible colloids could not be explained by a single factor, but differences in SOC content, electrical conductivity, and sodium adsorption ratio were important factors. Moreover, we found that the fertilizer treatments did not significantly affect the solute transport properties of the topsoil. Finally, we found that the leaching of soil colloids was significantly decreased in treatments that had received large amounts of organic waste fertilizers, and we ascribe this primarily to treatment-induced differences in effluent electrical conductivity during leaching.

Impact of landslides on soil characteristics: Implications for estimating their age

The slopes of Mount Elgon, a complex volcano at the border between Uganda and Kenya, are frequently affected by landslides with disastrous effects on the livelihood of its population. Since local people greatly depend on the land for crop production, this paper examines if and how fast physico-chemical characteristics in landslide scars recover. A chronosequence of 18 landslides covering a period of 103years was sampled in order to explore differences between topsoil inside and outside landslide scars. For each landslide, two topsoil samples were taken within the landslide and two in nearby undisturbed soils to compare their physico-chemical characteristics. Samples inside the landslides were located at the transition zone between the depletion and accumulation zone, which is situated at the contact line between the plan concave and plan convex section of the landslide. No differences were found for available phosphorus, Ca2+, Mg2+ content or for the fine earth texture. Recent landslides had however lower content of soil organic carbon (OC) and K+, and higher content of rock fragments and Na+ than the adjacent soils. Soil OC content increased significantly with age and reached levels of the corresponding undisturbed soils after ca. 60years. Older landslides had even higher OC contents than soils adjacent to the landslide. Hence landslide scars act as local carbon sink. We suggest that the occurrence of rock fragments in the topsoil is a useful indicator for mapping past landslides. Moreover, the difference in soil OC content between landslide scars and adjacent soil could be used for estimating the age of landslides in data-poor regions.

Differences in fertilization impacts on organic carbon content and stability in a paddy and an upland soil in subtropical China

The stability of soil organic carbon (SOC) is of great importance in controlling long-term carbon (C) sequestration and feedbacks of soil C pools to climate change. It has been well documented that rice cropping and organic amendments could enhance SOC stocks, while the stability of the sequestered C has not been well understood yet. The objective of this study was to examine the difference in SOC content and stability between a paddy and an upland field under long-term fertilization and to explore the potential link between SOC chemical and biological stability. Soils were collected from two adjacent long-term paddy (annually double-rice cropping) and upland (annually double-corn cropping) experiments with the same soil parent material, where different fertilization regimes were initiated in 1981 and 1986, respectively. The chemical and biological stability of SOC were measured by acid hydrolysis and aerobic incubations, respectively. The C concentration was significantly higher in the paddy soil than in the upland soil, regardless of fertilization regimes. As compared to the initial level, long-term rice cropping without any fertilization (CK) significantly enhanced SOC concentration, whereas corn cropping led to a slight decline. Manure amendments combined with inorganic NPK fertilizers (NPKM) significantly increased SOC content relative to the inorganic NPK application alone treatment (NPK) in both the upland and paddy fields. The paddy soil had significantly greater cumulative C released per gram of soil C (i.e., the biological stability of SOC) than the upland soil. Cumulative C released per gram of soil C was significantly higher in NPKM than in NPK in both the paddy and upland soils, whereas no significant difference was observed between the CK and NPK treatments. Acid hydrolysis could reveal the difference in C stability between the paddy and upland soils, but could not characterize the effect of fertilization. Rice cropping facilitates SOC accumulation relative to upland cropping, whereas the inherent SOC stability is lower under the former than the latter in the site. The lower SOC turnover in the paddy than in the upland is mainly due to anaerobic conditions. Organic amendments significantly enhance SOC, but reduce its stability in both the paddy and upland fields. The sensitivity of acid hydrolysis is relatively low in determining SOC stability.

Differences in chemical composition of soil organic carbon resulting from long-term fertilization strategies.

Chemical composition of soil organic carbon (SOC) is central to soil fertility. We hypothesize that change in SOC content resulting from various long-term fertilization strategies accompanies the shift in SOC chemical structure. This study examined the effect of fertilization strategies along with the time of fertilizer application on the SOC composition by 13C nuclear magnetic resonance (NMR) spectroscopy. The soils (Aquic Inceptisol) subjected to seven fertilizer treatments were collected in 1989, 1999 and 2009, representing 0, 10 and 20 years of fertilization, respectively. The seven fertilizer treatments were (1–3) balanced fertilization with application of nitrogen (N), phosphorus (P) and potassium (K) including organic compost (OM), half organic compost plus half chemical fertilizer (1/2OM), and pure chemical NPK fertilizer (NPK); (4–6) unbalanced chemical fertilization without application of one of the major elements including NP fertilizer (NP), PK fertilizer (PK), and NK fertilizer (NK); and (7) an unamended control (CK). The SOC content in the balanced fertilization treatments were 2.3–52.6% and 9.4–64.6% higher than in the unbalanced fertilization/CK treatments in 1999 and 2009, respectively, indicating significant differences in SOC content with time of fertilizer application between the two treatment groups. There was a significantly greater proportion of O-alkyl C and a lower proportion of aromatic C in the balanced fertilization than in unbalanced fertilization/CK treatments in 1999, but not in 2009, because their proportions in the former treatments approached the latter in 2009. Principal component analysis further showed that the C functional groups from various fertilization strategies tended to become compositionally similar with time. The results suggest that a shift in SOC chemical composition may be firstly dominated by fertilization strategies, followed by fertilization duration.

Effect of Reclamation on the Vertical Distribution of SOC in Three Types of Wetland Soils

To investigate how reclamation of wetlands in three different soil types impacts the vertical distribution of soil organic carbon (SOC) content in soil profiles, contents and density of soil organic carbon (SOC) in soil profiles of three types of wetland soils in wetland, soybean and paddy field in Sanjiang Plain were determined. Both soybean and paddy field were reclaimed from wetland. We observed that reclamation significantly reduced SOC content in 0-10,10-20 and 20-30 cm soil layers in meadow albic soil and meadow marsh soil, and 0-10,10-20,20-30 and 30-40 cm soil layers in peat bog soil, there were no significant difference in SOC contents in soil layers under 0-30 or 0-40 cm before and after reclamation. After reclamation, SOC density in three types of wetland soils decreased, and SOC density in soybean field were higher than that in paddy field. Either in wetlands or farm lands in the three types of wetland soils, most of the SOC storage in 0-100 cm soil layer was stored in 0-50 cm soil layer. Though wetland reclamation reduced the SOC content, it hasn’t changed the regularity of SOC vertical distribution. The relationships between SOC content and soil depth in wetlands and farm lands all could be described by exponential functions in three types of soils. The specific functions are useful to estimate and predict the regional SOC pool by models.