Surface Soil Organic Matter Research Articles

Spatial distribution pattern of soil organic matter in the wind erosion region of northeastern China based on the cokriging method

Soil wind erosion triggers complex particle migration from the source to downwind regions. During this process, soil organic matter (SOM), primarily adsorbed onto particle surfaces, exhibits distinct spatial differentiation across affected areas. Knowledge about the spatial distribution of SOM and its impact factors in wind erosion regions is essential for a deep understanding of global carbon cycling. In the wind erosion region of northeastern China, a crucial base for livestock and commercial grain production, profound changes in land quality driven by climate change and human activities have intricately altered SOM spatial patterns. However, detailed studies on the spatial variability of surface SOM in this region remain scarce. A total of 374 surface soil samples from this region were analyzed for SOM and soil pH. Combined with spatial data sets including particle-size distribution, soil moisture (SM), air temperature (T), and the normalized difference vegetation index (NDVI), the regional spatial distribution patterns of SOM were revealed and mapped using the ordinary kriging (OK) and cokriging (CK) approaches. The results indicated strong variations of SOM in space, with corresponding coefficients of variation exceeding 35 % across the entire region and each land use. According to the semivariogram analysis, SOM demonstrates moderate spatial dependency in the study region, exhibiting spatially positive correlations with clay content (CLAY), SM, and NDVI, and negative correlations with pH, soil sand content (SAND), and T. Among the various impact factors, incorporating SAND as an auxiliary variable in CK interpolation achieved the greatest improvement in the accuracy of SOM spatial distribution simulation compared to the OK model, increasing the explained variance from 35 % to 75 %. This simulation showed a general downward trend of SOM from the northeast to the southwest of the study region, with 65.24 % of the area displaying SOM ranging from 10-30 g·kg−1. The values of SOM greater than 30 g·kg−1, comprising 19.43 % of the total region, were primarily located in the humid and semi-humid meadow steppes and forests. In contrast, areas with SOM below 10 g·kg−1 accounted for only 15.33 %, mainly situated in the arid desert steppe and the Horqin sandy lands. These findings provide a scientific basis for understanding regional SOM loss and developing efficient measures for sand prevention and control.

Impact of Integrated Nutrient Management on Soil Micronutrients and Organic Matter Dynamics in Maize-mustard Crop Rotation in Himalayan Foothills

Aims: The purpose of this research is to investigate the effects of inorganic fertilizers and organic manures on availability of micronutrients and organic matter in soils of rainfed agriculture in foothills of Himalayas. Place and Duration of Study: Present study was conducted at Advance Centre for Rainfed Agriculture (ACRA), Rakh Dhiansar, Jammu from 2020 to 2022. Methodology: In a long-term field experiment, we investigated the effects of 10 treatments on soil micronutrients, organic matter and their correlation under rain fed agriculture. Randomized block design was used with three replications. Following are the treatments: T1 - Control, T2 - 100% RDF of N,P,K through chemicals, T3 - 50% RDF of N,P,K through chemicals, T4- 50% RD of N through crop residue, T5 - 50% RD of N through FYM, T6 -50% RDF of N,P,K through chemicals + 50% RDF of N through crop residues, T7- 50% RDF of N,P,K through chemicals + 50% RD of N through FYM, T8 - FYM @ 10 ton/ha, T9 - 100% RDF of N,P,K through chemicals + Zinc Sulphate @ 20kg/ha and T10 - Farmer practice (FYM @ 4 ton/ha + 40kg urea /ha). The micronutrients (Fe, Zn, Cu and Mn) showed maximum increase with the application of organic manures along with inorganic fertilizers over control in both surface and sub surface layers of the soil. However, in the sub-surface soil, there was less availability of these nutrients than the surface layer of the soil. The available Zn content was found maximum in the treatment T9 getting 100% NPK + ZnSO4 @ 20kg/ha over control. The treatment T8 with the application of FYM @ 10 ton/ha recorded highest content of soil organic matter in surface soil. Positive and significant correlations were observed between soil organic matter and the micronutrient content of the soil. The INM practices proved very beneficial for increasing the sustainability of soil.

Assessing spatiotemporal heterogeneity of coastal organic nonpoint source pollution via soil erosion in Yellow River Delta, China

China has been facing severe organic pollution and the nonpoint source export from surface soil is usually overlooked in coastal areas. In this paper, from the perspective of catchment and attenuation, we have constructed a risk assessment method for coastal nonpoint source pollution (NSP) by applying the revised universal soil loss equation (RUSLE) and geostatistical analysis. Combined with the soil and water monitoring data, we have simulated regional NSP risks originating from surface soil organic matter (SOM) in the Yellow River Delta (YRD). Field surveys have verified the significant positive correlations between watershed SOM exporting risks and estuarine chemical oxygen demand (COD) fluxes during the rainy season. There present obvious logarithmic relations between the COD fluxes and the rainfall quantities, and the surface organic NSP risks. Larger NSP contributing sources are mainly located in the areas with higher soil exposure and stronger land-sea interactions. It should focus on the agricultural areas and improve relevant fertilizing and tillage methods to reduce source-exporting risks. Additionally, the summer rainfall concentrating periods need to be controlled emphatically, and vegetation-improving strategies need to be supplemented with the spatiotemporal-specific managements. This study provides a new insight for getting early terrestrial warning information for offshore organic water pollution, and presents research references for similar regional NSP issues.

Drivers of legacy soil organic matter decomposition after fire in boreal forests

AbstractBoreal forests harbor as much carbon (C) as the atmosphere and significant amounts of organic nitrogen (N), the nutrient most likely to limit plant productivity in high‐latitude ecosystems. In the boreal biome, the primary disturbance is wildfire, which consumes plant biomass and soil material, emits greenhouse gasses, and influences long‐term C and N cycling. Climate warming and drying is increasing wildfire severity and frequency and is combusting more soil organic matter (SOM). Combustion of surface SOM exposes deeper older layers of accumulated soil material that previously escaped combustion during past fires, here termed legacy SOM. Postfire SOM decomposition and nutrient availability are determined by these layers, but the drivers of legacy SOM decomposition are unknown. We collected soils from plots after the largest fire year on record in the Northwest Territories, Canada, in 2014. We used radiocarbon dating to measure Δ14C (soil age index), soil extractions to quantify N pools and microbial biomass, and a 90‐day laboratory incubation to measure the potential rate of element mineralization and understand patterns and drivers of legacy SOM C decomposition and N availability. We discovered that bulk soil C age predicted C decomposition, where cumulatively, older soil (approximately −450.0‰) produced 230% less C during the incubation than younger soil (~0.0‰). Soil age also predicted C turnover times, with old soil turnover 10 times slower than young soil. We found respired C was younger than bulk soil C, indicating most C enters and leaves relatively quickly, while the older portion remains a stable C sink. Soil age and other indices were unrelated to N availability, but microbial biomass influenced N availability, with more microbial biomass immobilizing soil N pools. Our results stress the importance of legacy SOM as a stable C sink and highlight that soil age drives the pace and magnitude of soil C contributions to the atmosphere between wildfires.

Molecular complexity and diversity of persistent soil organic matter

Managing and increasing organic matter in soil requires greater understanding of the mechanisms driving its persistence through resistance to microbial decomposition. Conflicting evidence exists for whether persistent soil organic matter (SOM) is molecularly complex and diverse. As such, this study used a novel application of graph networks with pyrolysis-gas chromatography-mass spectrometry to quantify the complexity and diversity of persistent SOM, defined as SOM that persists through time (soil radiocarbon age) and soil depth. We analyzed soils from the Cooloola giant podzol chronosequence across a large gradient of soil depths (0–15 m) and SOM radiocarbon ages (modern to 19,000 years BP). We found that the most persistent SOM on this gradient was highly aromatic and had the lowest molecular complexity and diversity. By contrast, fresh surface SOM had higher molecular complexity and diversity, with high contributions of plant-derived lignins and polysaccharides. These findings indicate that persisting SOM declines in molecular complexity and diversity over geological timescales and soil depths, with aromatic SOM compounds persisting longer with mineral association.

JumpStart of soil organic matter with highly stabilized organic amendment: Implication for climate-smart agriculture

Rebuilding soil organic matter (SOM) to regionally specific targets for high quality soil that are likely maintained in the long term, here defined as “SOM JumpStart”, can unlock soil's potential for increased productivity, enhanced resilience and reduced emission as the main components for climate-smart agriculture (CSA). A field experiment was established in 2013 at Fulton County, western Illinois to use highly stabilized organic amendment (HSOA) at a rate, potentially raising surface SOM of cultivated Alfisol (low quality soil) to the level of cultivated Mollisol (high quality soil for US Midwest). Treatments included one-time application of lagoon-aged air-dried biosolids at 165 Mg ha−1, one-time application of vegetative compost at 165 Mg ha−1, chemical fertilizer at 225–50–85 kg ha−1 yr−1 (N-P-K) as control, and grass fallow as reference. In every year following the HSOA application, fertilizer (N and K) rate was reduced by 25%, and no P was applied for most years. Corn was planted annually. The HSOA JumpStart application dramatically increased SOM, leading to soil organic carbon (SOC) at 2–2.5% after biosolids and about 3% after compost for 2013–2019, as that of Mollisol, while that in chemical fertilizer control remained unchanged at 1–1.2%. For the first seven years, HSOA JumpStart increased corn grain yield by a mean of 19.8% (biosolids) and 7.1% (compost) above the control, with greater increase at precipitations-abnormal (low/high) years. The SOM JumpStart caused the shift of soil microbial physiology to high C utilization efficiency, as evident by reduced microbial metabolic quotient for CO2, leading to the decrease in CO2 emission from agricultural crop residues by 19.6% (biosolids) and 20.0% (compost). Our modeling revealed the promising soil C sequestration (excluding residual C from HSOA) over next 50 years at 10.6 Mg C ha−1 by biosolids application and 13.9 Mg C ha−1 by compost application, higher than 6.8 Mg C ha−1 anticipated by “4 per 1000″ international initiative. A simple but straightforward model suggests JumpStarted soil still contain 50% higher SOC stocks as compared to control after 50 years. Our results suggest the SOM JumpStart by HSOA such as biosolids and compost can transform conventional corn production to CSA.

Assessment of five SMAP soil moisture products using ISMN ground-based measurements over varied environmental conditions

Since the launch of Soil Moisture Active Passive (SMAP) mission in 2015, several advanced global surface soil moisture (SM) products derived from different retrieval schemes have been released. However, the factors contributing to the performance differences of these SMAP products have not been fully investigated. This study tries to fill the gap by assessing and intercomparing five SMAP products, namely, the single channel algorithm V/H-pol (SCA-V/H), dual channel algorithm (DCA), multi-temporal dual channel algorithm (MT-DCA) and the new SMAP-INRAE-BORDEAUX (SMAP-IB), using the International Soil Moisture Network (ISMN) ground measurements worldwide during 2016–2020. After reviewing the retrieval algorithms, the impact of five potential perturbing factors on the skills of all products is reported; these factors including mean surface soil temperature (MSST), surface roughness (log(SR)), vegetation density (characterized by vegetation optical depth (VOD)), mean surface soil wetness (MSSM) and soil organic matter (SOM). Results shows that the SMAP-IB product has the highest overall R value of 0.75 with ISMN ground SM, and the smallest unbiased root mean square difference (ubRMSD) values same as SCA-V and DCA (∼0.058 m3/m3). The performance of all five products in terms of R and ubRMSD rapidly degrades over the regions with high VOD, rough surface and low MSST. In contradiction with the fact that product performance degrades with increasing roughness, the ubRMSD of all five products increases with decreasing log(SR) on a relatively smooth surface (log(SR) < 6) with larger growth rates for SMAP-IB, SCA-H and MT-DCA. Regarding characterizing the temporal variations of in situ SM anomalies (Ranom), Ranom increases as the ground becomes wet for all products within a certain range (MSSM < 0.3 m3/m3). In particular, SMAP-IB and MT-DCA present higher Ranom values than the other three products under wet soil surfaces (MSSM > 0.3 m3/m3). The two metrics R and Ranom decrease significantly with increasing SOM for SMAP-IB compared to the other products, and SMAP-IB obtains the lowest values for both metrics when SOM > 20%. These findings are expected to provide useful information for appropriate product selection and improvement.

Precipitation reconstruction since the last deglacial based on the stable carbon isotopic composition of a loess section in western Central Asia

The topography of the Tianshan Mountains and the Pamir Plateau strongly shapes the seasonality of precipitation in Central Asia (CA): cold-season (October-April) precipitation dominates western CA and warm-season (May-September) precipitation dominates eastern CA. The precipitation/moisture patterns between western and eastern CA are completely opposite at seasonal, decadal and centennial scale. However, the pattern contrasts for millennial or longer time scales remain unknown. In this study, we investigated the precipitation variations in western CA, as recorded in a 6.5-m loess section in southern Kazakhstan, which has accumulated since ~14.4 ka. According to the robust relationship between the surface soil organic matter δ13C and the climatic parameters, the δ13C signature is here considered as a precipitation proxy. The record reveals an overall decreasing precipitation before ~6.0 ka followed by an increasing trend afterward, being consistent with the previously reported precipitation records in western CA. The late-deglaciation precipitation in western CA is in phase with that in eastern CA at millennial scales, which are both driven by the North Atlantic Oscillation (NAO) and the Siberian High.

Changes in particulate and mineral-associated organic carbon with land use in contrasting soils

Soil organic carbon (SOC) is the largest terrestrial carbon (C) stock, and the capacity of soils to preserve organic C (OC) varies with many factors, including land use, soil type, and soil depth. We investigated the effect of land use change on soil particulate organic matter (POM) and mineral-associated organic matter (MOM). Surface (0−10 cm) and subsurface (60−70 cm) samples were collected from paired sites (native and cropped) of four contrasting soils. Bulk soils were separated into POM and MOM fractions, which were analyzed for mineralogy, OC, nitrogen, isotopic signatures, and 14C. The POM fractions of surface soils were relatively unaffected by land use change, possibly because of the continuous input of crop residues, whereas the POM fractions in corresponding subsurface soils lost more OC. In surface soils, MOM fractions dominated by the oxides of iron and aluminum (oxide-OM) lost more OC than those dominated by phyllosilicates and quartz, which was attributed to diverse organic matter (OM) input and the extent of OC saturation limit of soils. In contrast, oxide-OM fractions were less affected than the other two MOM fractions in the subsurface soils, possibly due to OC protection via organo-mineral associations. The deviations in isotopic signature (linked with vegetation) across the fractions suggested that fresh crop residues constituted the bulk of OM in surface soils (supported by greater 14C). Increased isotopic signatures and lower 14C in subsurface MOM fractions suggested the association of more microbially processed, aged OC with oxide-OM fractions than with the other MOM fractions. The results reveal that the quantity and quality of OC after land use change is influenced by the nature of C input in surface soils and by mineral-organic association in subsurface soils.

Inversion Estimation of Soil Organic Matter in Songnen Plain Based on Multispectral Analysis

Sentinel-2A multi-spectral remote sensing image data underwent high-efficiency differential processing to extract spectral information, which was then matched to soil organic matter (SOM) laboratory test values from field samples. From this, multiple-linear stepwise regression (MLSR) and partial least square (PLSR) models were established based on a differential algorithm for surface SOM modeling. The original spectra were subjected to basic transformations with first- and second-derivative processing. MLSR and PLSR models were established based on these methods and the measured values, respectively. The results show that Sentinel-2A remote sensing imagery and SOM content correlated in some bands. The correlation between the spectral value and SOM content was significantly improved after mathematical transformation, especially square-root transformation. After differential processing, the multi-band model had better predictive ability (based on fitting accuracy) than single-band and unprocessed multi-band models. The MLSR and PLSR models of SOM had good prediction functionality. The reciprocal logarithm first-order differential MLSR regression model had the best prediction and inversion results (i.e., most consistent with the real-world data). The MLSR model is more stable and reliable for monitoring SOM content, and provides a feasible method and reference for SOM content-mapping of the study area.

Wildfires can increase regulated nitrate, arsenic, and disinfection byproduct violations and concentrations in public drinking water supplies

Wildfires are a concern for water quality in the United States, particularly in the wildland-urban interface of populous areas. Wildfires combust vegetation and surface soil organic matter, reduce plant nutrient uptake, and can alter the composition of runoff and receiving waters. At the wildland-urban interface, fires can also introduce contaminants from the combustion of man-made structures. We examine post-wildfire effects on drinking water quality by evaluating concentrations and maximum contaminant level (MCL) violations of selected contaminants regulated in the U.S. at public drinking water systems (PWSs) located downstream from wildfire events. Among contaminants regulated under the U.S. Safe Drinking Water Act, nitrate, arsenic, disinfection byproducts, and volatile organic compounds (VOCs) were analyzed in watersheds that experienced major wildfires. Surface water sourced drinking water (SWDW) nitrate violations increased by an average of 0.56 violations per PWS and concentrations increased by 0.044 mg-N/L post-wildfire. Groundwater sourced drinking water (GWDW) nitrate violations increased by 0.069 violations per PWS and concentrations increased by 0.12 mg-N/L post-wildfire. SWDW total trihalomethane (TTHM) violations increased by 0.58 violations per PWS and concentrations increased by 10.4 μg/L. SWDW total haloacetic acid (HAA5) violations increased by 0.82 violations per PWS and concentrations increased by 8.5 μg/L. Arsenic violations increased by 1.08 violations per PWS and concentrations increased by 0.92 μg/L. There was no significant effect of wildfires on average VOC violations. Nitrate violations increased in 75% of SWDW sites and 34% of GWDW sites post-wildfire, while about 71% and 50% of SWDW sites showed an increase in TTHM and HAA5 violations. Violations also increased for 35% of arsenic and 44% of VOC sites post-wildfire. These findings support the need for increased awareness about the impact of wildfires on drinking water treatment to help PWS operators adapt to the consequences of wildfires on source water quality, particularly in wildfire-prone regions.

Influence of organic matter on soil hydrothermal processes in the Tibetan Plateau: Observation and parameterization

AbstractIn the central-eastern Tibetan Plateau (TP) there is abundant organic matter in topsoils, which plays a crucial role in determining soil hydraulic properties that need to be properly described in land surface models. Limited soil parameterizations consider the impacts of soil organic matter (SOM), but they still show poor performance in the TP. A dedicated field campaign is therefore conducted by taking undisturbed soil samples in the central TP to obtain in-situ soil hydraulic parameters and to advance SOM parameterizations. The observed findings are twofold. 1) The SOM pore-size distribution parameter, derived from measured soil water retention curves, has been demonstrated to be much underestimated in previous studies. 2) SOM saturated hydraulic conductivity is overestimated. Accordingly, a new soil hydraulic parameterization is established by modifying a commonly used one based on observations, which is then evaluated by incorporating it into Noah-MP. Compared with the original ones, the new parameterization significantly improves surface soil liquid water simulations at stations with high surface SOM content, especially in the warm season. A further application with the revised Noah-MP indicates that SOM can enhance sensible heat flux but decrease evaporation and subsurface soil temperature in the warm season, and tends to have a much weak effect in the cold season. This study provides insights into the role of SOM in modulating soil state and surface energy budget. Note that, however, there are many other factors at play and the new parameterization is not necessarily applicable beyond the TP.

Sediment source apportionment following wildfire in an upland commercial forest catchment

Wildfires can have major impacts on water scarcity and water quality linked to off-site transfer of polluting ash and nutrients. Understanding sediment sources in burnt landscapes can help to develop mitigation strategies, especially in catchments planted with introduced species that are prone to fire. We investigated sediment sources activated by post-fire rainfall in a small-forested catchment that was impacted by a severe wildfire. The aim was to use environmental radionuclides and elemental geochemistry as tracers to apportion sediment sources within burnt plantation systems. Surficial (0–2 cm) topsoil (n = 9), sub-surficial (2–4 cm) topsoil (i.e. below the burnt layer; n = 8) samples from burnt hillslopes and forest roads (n = 5) and stream banks (n = 5) soil samples were taken in the Quivolgo catchment, El Maule region, Chile. Sediment samples (n = 9) were collected from behind a v-notched weir on three dates after the fire: May 2017, July 2017 and October 2017. Soil and sediment samples were analysed by gamma spectrometry and wavelength-dispersive X-ray fluorescence (WD-XRF) used to obtain tracer properties. These were evaluated visually and statistically to identify potential non-conservative tracers. Sediment apportionment was undertaken using the MixSIAR mixing model. The tracer selection procedure resulted in ten tracers being used for sediment apportionment. Tracer suitability was based on (i) weak and non-significant linear relationship between tracer concentrations and specific surface area (SSA) and soil organic matter (SOM), and (ii) conservative behaviour supported by the inclusion of sediment samples within source convex hull. Sediments from sub-surface layer (2–4 cm) were the dominant source during the first two periods contributing 55 ± 11 and 78 ± 10% respectively, whereas road contribution was only important in the last period (71 ± 14%). Apportionment showed a shift in sediment source (i.e. from forest roads to hillslopes) compared to a previous study in the same catchment before wildfire. The main driver of erosion was attributed to overland flow convergence and consequent rill erosion across burnt hillslopes. The study demonstrated combined use of environmental radionuclides with elemental geochemistry for sediment apportionment within burnt forest plantations and highlighted a switch in predominant source (e.g. sub-surface burnt soil) activated by post-fire rainfall events. The findings in this research will help forest companies to develop strategies to reduce off-site impacts of sediment release after wildfire in forest plantations.

Variation in Tree Growth along Soil Formation and Microtopographic Gradients in Riparian Forests

Policy makers are interested in managing forests to store carbon. Optimizing this strategy requires understanding how carbon storage varies across environmental gradients. We explored variation in tree growth rate, tree longevity, and surface soil organic matter across 135 Connecticut River riparian forest plots. Tree growth rate did not vary significantly with climate but rather increased with sediment accretion rate, soil pH and decreased with plot elevation, where elevation was measured relative to the stage of the 2-year flood. By contrast, surface soil organic matter was negatively related to pH and tree growth rate. Tree species longevities were greater at higher elevations with coarser soils. The faster growth rates at lower elevations allow for restoring forest structure rapidly, whereas flood intolerant but longer-lived tree species allow more durable carbon sequestration at higher elevations. The close associations of growth rate, sediment accretion, and pH suggest that riverine nutrient inputs are important to maintaining the exceptionally high productivity of floodplains. Environmental assessments of river dams should consider impacts of intercepting sediments and reducing flooding on downstream floodplain fertility and productivity. Restoration of riparian locations with high deposition of sediments and associated nutrients may be an opportunity to maximize both nutrient and carbon sequestration.

Remote sensing inversion of surface soil organic matter at jointing stage of winter wheat based on unmanned aerial vehicle multispectral

The rapid monitoring of soil organic matter (SOM) content in large-scale salinized wheat fields can provide data for promoting research in saline soils and carbon cycle. Based on field sampling and remote sensing images of unmanned aerial vehicle, we established remote sensing prediction models of regional SOM using three methods, i.e., multiple linear regression (MLR), partial least squares (PLSR), and support vector machine regression (SVR) for bare land and wheat field, respectively. The models were validated and compared to identify the optimal inversion model of SOM. Moreover, the SOM in the area was inverted using the optimal model, with the inversion results being compared with the data by interpolation. The results showed that the spectrum after the filtering of 5×5 median was best related to surface SOM. Among the three models, the SVR model had the highest prediction accuracy, followed by the PLSR, while the MLR lowest. The SVR model was the best one for estimating wheat field, with coefficient of determination (R2) and root mean square error (RMSE) of 0.89 and 0.20, respectively, and the validated R2 and RMSE were 0.82 and 0.24, respectively. The bare land SOM was also best fitted by the SVR model, with R2 and RMSE were 0.63, 0.26, respectively, and the verified R2 and RMSE were 0.61, 0.25, respectively, but without statistical significance. The inversion of the optimal model revealed that SOM content in this region ranged from 17.51 to 22.53 g·kg-1, with an average of 19.51 g·kg-1, which was generally consistent with the field measurement. Compared with the inversion results, the interpolation data were limited in accuracy. Overall, our study suggested that the unmanned aerial vehicle-based multi-spectral analysis could be applied to quick and accurate estimation of SOM content in saline soil at the jointing stage of winter wheat.

Effect of Different Tillage Options and Residue Retention for Sustainable Crop Production in Wheatmungbean- Rice Cropping Pattern in Dry Areas

The study was conducted to know the productivity and soil fertility status of intensified rice-wheat (RW) systems by adding a third pre-rice crop mungbeani.ewheat-mungbeanrice cropping pattern. The trial comprises five packages of practices including crop residue retention, seeding methods with tillage options imposed on the component crops in the same cropping pattern. The results indicated that keeping standing 30% crop residue in the field with minimum disturbance of soil had significant contribution on grain yield of wheat-mungbean-rice sequence compare to conventional practice of well-till without crop residue retention. System productivity and fertility were evaluated under five levels of tillage options (zero, strip, raised bed, minimum tillage by power tiller operated system (PTOS) and conventional tillage practice (CTP) in a RWM cropping pattern. Both permanent raised bed and strip till with 30% straw retention produced the highest productivity in all years and the lowest yield was also found from conventional practice with 30% straw retention.Soil organic matter in surface soil had increased by 0.12% after 3years crop cycles with 30% SR from rice and wheat and full residue retention from mungbean crop. Straw retention is an important component of soil management and may have long term positive impacts on soil quality. The combination of raised bedsystems and strip tillage with 30% residues retained appears to be a very promising technology for sustainable intensification of wheat-mungbean-rice croppingpattern in dry zone areas.&#x0D; Bangladesh Agron. J. 2019, 22(2): 67-75

Understanding the effects of early degradation on isotopic tracers: implications for sediment source attribution using compound-specific isotope analysis (CSIA)

Abstract. Application of compound-specific isotope analysis (CSIA) in sediment fingerprinting source apportionment studies is becoming more frequent, as it can potentially provide robust land-use-based source attribution of suspended sediments in freshwater and marine systems. Isotopic tracers such as δ13C values of vegetation-derived organic compounds are considered to be suitable for the CSIA-based fingerprinting method. However, a rigorous evaluation of tracer conservativeness in terms of the stability of isotopic signature during detachment and transport of soil during erosion is essential for the suitability of the method. With the aim to identify potential fractionation and shifts in tracer signature during early degradation of organic matter in surface soils, we measured concentrations and δ13C values of long-chain fatty acids and n-alkanes from fresh plant biomass (as vegetation is a direct source of these compounds to the soils), degraded organic horizon (O horizon), and mineral soil (A horizon) from various forest types with different humus forms (five sites). The bulk δ13C values showed continuous 13C enrichment through the degradation stages from fresh plant material to the O and A horizons, ranging between 3.5 ‰ and 5.6 ‰. Compound-specific δ13C values showed a general 13C enrichment for both long-chain fatty acids (up to 5 ‰) and n-alkanes (up to 3.9 ‰) from fresh plant biomass to the O horizon overlying the A horizon. However, only slight or no further changes occurred from the O to the A horizon. We also compared compound-specific δ13C values between two soil particle size classes (&lt;2 mm and &lt;63 µm) from four sites and found no significant differences of tracer values between them, with even less fractionation for the long-chain n-alkanes within the soil particle fractions. This points to the conclusion that sampling and analysing bulk soil material might be valid for the isotopic tracer applications. We further conclude that our results support the suitability of studied isotopic tracers as a representative source soil signature in the CSIA-based sediment source attribution, as they demonstrated necessary stability in the plant–soil system during organic matter degradation.

A 15,400-year record of natural and anthropogenic input of mercury (Hg) in a sub-alpine lacustrine sediment succession from the western Nanling Mountains, South China.

A 15400-year mercury (Hg) accumulation history was reconstructed from a lake sediment core collected from Daping Swamp in western Nanling Mountains, South China. Our results show that the natural input of Hg was deeply influenced by varying climatic conditions. Under wet and warm conditions, increased surface soil organic matter induced by improved vegetation conditions favor an increased input of surface soil-bound Hg to the lake, thus leading to higher Hg accumulation rate, and on the other hand, the direct atmospheric wet deposition of Hg into the lake would also be enhanced. In contrast, under relatively cold and dry conditions, it would display an inverse picture. The signal of anthropogenic influence possibly derived from regional Hg pollution likely started at ~ 3400cal. years BP, roughly corresponding to the early stage of the Shang Dynasty in Chinese history. Four periods of increased anthropogenic Hg inputs appeared in ~ 3358-2170, ~ 2170-1730, ~ 1369-1043, and especially ~ 600-250cal. years BP, corresponded to the Shang and Zhou, the Qin and Han, the Sui and Tang, and the Ming and Qing dynasties in China, respectively. A clearly weakened anthropogenic input occurred between~1750 and 1400cal. years BP, coinciding with the Three Kingdoms to the Southern and Northern Dynasties. Our results revealed the history of the natural Hg accumulation since the Last Deglacial period, and the existence of regional atmospheric Hg induced from anthropogenic activity spanning the last ~ 3400years.

Groundwater as a major source of dissolved organic matter to Arctic coastal waters

Groundwater is projected to become an increasing source of freshwater and nutrients to the Arctic Ocean as permafrost thaws, yet few studies have quantified groundwater inputs to Arctic coastal waters under contemporary conditions. New measurements along the Alaska Beaufort Sea coast show that dissolved organic carbon and nitrogen (DOC and DON) concentrations in supra-permafrost groundwater (SPGW) near the land-sea interface are up to two orders of magnitude higher than in rivers. This dissolved organic matter (DOM) is sourced from readily leachable organic matter in surface soils and deeper centuries-to millennia-old soils that extend into thawing permafrost. SPGW delivers approximately 400–2100 m3 of freshwater, 14–71 kg of DOC, and 1–4 kg of DON to the coastal ocean per km of shoreline per day during late summer. These substantial fluxes are expected to increase as massive stocks of frozen organic matter in permafrost are liberated in a warming Arctic.

武夷山不同海拔森林表层土壤轻组有机质特征

土壤轻组有机质是土壤有机质的重要组分，研究轻组有机质在不同森林生态系统土壤中的变化规律对理解土壤有机质形成与转换具有重要意义。以福建省武夷山国家级自然保护区不同海拔的常绿阔叶林（海拔600 m）、针阔混交林（海拔1000 m）和针叶林（海拔1400 m）为研究对象，利用密度分组方法分离了表层（0-5 cm和5-10 cm）土壤轻组有机质，研究了不同海拔森林土壤轻组有机质特征及其影响因素。结果表明：针阔混交林表层土壤的轻组有机质含量大于针叶林和常绿阔叶林（P < 0.05），并且轻组有机碳的含量变化亦是如此（P < 0.05），而轻组有机氮的含量无显著差异（P > 0.05）。表层土壤对应土层的轻组C：N大于土壤C：N，针阔混交林轻组C：N和土壤C：N均大于其他林分类型。0-5 cm与5-10 cm土层针阔混交林的轻组有机碳、氮储量均大于针叶林和常绿阔叶林（P < 0.05），并且针阔混交林的轻组有机碳、氮储量所占土壤有机碳与总氮的比重均大于其余两种林分。0-10 cm土层针叶林土壤有机碳与总氮含量与储量最高，并随海拔降低而减小，但差异不显著（P > 0.05）。相关分析结果表明，轻组有机碳、氮储量与SOC、DOC、MBC和细根生物量具有显著相关关系（P < 0.05），而与年凋落物量无关（P > 0.05），说明地下细根可能是土壤轻组有机质的重要来源。因此，在未来气候和植被变化共同作用下，地下细根对土壤轻组有机质的形成可能具有不可忽视的作用。;Soil light fraction organic matter is an important component of soil organic matter. It is crucial to understand the relationship between soil organic matter and climate change by studying the variation of light fraction organic matter along an elevation gradient in subtropical China. Taking evergreen broad-leaved forest (EBF), mixed coniferous and broad-leaved forest (BCF), and coniferous forest (CF) at different altitudes (from low to high elevation) in Wuyishan National Park in Fujian Province as research objects, the light fraction organic matter in surface soil (0-5 cm and 5-10 cm) was separated by density fractionation analyses, as well as the characteristics of light fraction organic matter and its influencing factors in different forest ecosystems were studied. The results showed that the content of light fraction organic matter in BCF was higher than that in CF and EBF in 0-5 cm and 5-10 cm soil layers (P < 0.05). The pattern of the content of light fraction organic carbon was similar to the light fraction organic matter, but there was no significant difference in light organic nitrogen content (P > 0.05). The light fraction C/N was greater than soil C/N, and the light fraction C/N and soil C/N in BCF were greater than those of other forest types in the same soil layer. In 0-5 cm and 5-10 cm soil layer, the storage of light fraction organic carbon and nitrogen in BCF were higher than those in CF and EBF (P < 0.05), and the contribution of light fraction organic carbon and nitrogen to soil organic matter in BCF was higher than that of the other two forests. The contents and storage of soil organic carbon and total nitrogen in CF was the highest in 0-10 cm, and decreased with the decrease of altitude, but the difference was not significant (P > 0.05). The correlation analysis showed that the storage of light fraction organic carbon and nitrogen was significantly correlated with soil organic carbon, dissolved organic carbon, microbial biomass carbon and fine root biomass (P < 0.05), but not annual litterfall (P > 0.05), suggesting that root derived organic matter might be an important source of light fraction organic matter in soil. Therefore, we concluded that belowground sources may play an important role in regulation of the formation of light fraction organic matter in soil under future climate change.