Improved Wetland Soil Organic Carbon Stocks of the Conterminous U.S. Through Data Harmonization

Wetland soil stocks are important global repositories of carbon (C) but are difficult to quantify and model due to varying sampling protocols, and geomorphic/spatio-temporal discontinuity. Merging scales of soil-survey spatial extents with wetland-specific point-based data offers an explicit, empirical and updatable improvement for regional and continental scale soil C stock assessments. Agency-collected and community-contributed soil datasets were compared for representativeness and bias, with the goal of producing a harmonized national map of wetland soil C stocks with error quantification for wetland areas of the conterminous United States (CONUS) identified by the USGS National Landcover Change Dataset. This allowed an empirical predictive model of SOC density to be applied across the entire CONUS using relational %OC distribution alone. A broken-stick quantile-regression model identified %OC with its relatively high analytical confidence as a key predictor of SOC density in soil segments; soils <6% OC (hereafter, mineral wetland soils, 85% of the dataset) had a strong linear relationship of %OC to SOC density (RMSE = 0.0059, ~4% mean RMSE) and soils >6% OC (organic wetland soils, 15% of the dataset) had virtually no predictive relationship of %OC to SOC density (RMSE = 0.0348 g C cm−3, ~56% mean RMSE). Disaggregation by vegetation type or region did not alter the breakpoint significantly (6% OC) and did not improve model accuracies for inland and tidal wetlands. Similarly, SOC stocks in tidal wetlands were related to %OC, but without a mappable product for disaggregation to improve accuracy by soil class, region or depth. Our layered harmonized CONUS wetland soil maps revised wetland SOC stock estimates downward by 24% (9.5 vs. 12.5Pg C) with the overestimation being entirely an issue of inland organic wetland soils (35% lower than SSURGO-derived SOC stocks). Further, SSURGO underestimated soil carbon stocks at depth, as modeled wetland SOC stocks for organic-rich soils showed significant preservation downcore in the NWCA dataset (<3% loss between 0 and 30 cm and 30 and 100 cm depths) in contrast to mineral-rich soils (37% downcore stock loss). Future CONUS wetland soil C assessments will benefit from focused attention on improved organic wetland soil measurements, land history, and spatial representativeness.

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Biochar Effects on Carbon Stocks in the Coffee Agroforestry Systems of the Himalayas

Sustainable Agriculture Research ◽

10.5539/sar.v7n4p103 ◽

2018 ◽

Vol 7 (4) ◽

pp. 103 ◽

Cited By ~ 1

Author(s):

Ngamindra Dahal ◽

Roshan Man Bajracharya ◽

Lal Mani Wagle

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Low Income ◽

Smallholder Farmers ◽

Carbon Stocks ◽

Agricultural Practice ◽

Coffee Agroforestry ◽

Incremental Change ◽

C Stocks ◽

Soc Stocks

Coffee agroforestry is an emerging agricultural practice in the mid hills of Nepal. Smallholder farmers of low-income strata have progressively adopted coffee as a perennial crop over seasonal crops. A multi-year study was conducted to test effects of locally produced biochar derived from coffee wastes, e.g., pulp and husks, on carbon stocks of: i) coffee trees, and, ii) soil organic carbon (SOC) in selected coffee growing pockets. We conducted on-farm experimental trials in three different physiographical locations of the Nepal mid-hills, namely, Chandanpur (Site I at 1475masl), Panchkhal (Site II at 1075masl), and Talamarang (Site III at 821masl) where smallholders grow coffee together with other cereal crops and vegetables. We applied biochar to the soil at a rate of 5 Mgha-1, then, monitored the SOC and biomass growth of the coffee trees in the three treatment plots at sites I, II and III over two years beginning in 2013. The average stocks of aboveground carbon in coffee trees increased from 6.2±4.3 Mgha-1 to 9.1±5.2 Mgha-1 over the trial period of two years in biochar treated plots. The same in control plots increased from 5.6±2.8 Mgha-1 to 6.7±4.7 Mgha-1. In the biochar plots, the average increments of ABG carbon was 0.73 Mgh-1 while in the control it was 0.29 Mgh-1. Analysis of soil organic carbon of the plots indicated overall incremental change in carbon stocks in the coffee farms. During the base year, the average SOC stocks in the top 0-15cm layer of the soil at sites I, II, and III were estimated 74.88 ± 15.93; 63.96 ±16.71 and 33.05 ±4.42 Mgha-1 respectively. Although both the biochar treated and control plot registered incremental change in SOC stocks, the volumes were remarkably higher in the former than the latter. Compared to the baseline data, the changes in SOC stocks in the three biochar treated plots were 19.8, 49.8 and 45.3 Mgha-1, respectively, whereas in the control plots these were 8.3, 29.3 and 11.3 Mgha-1, respectively. The higher incremental rates of C-stocks in all the biochar treated plots in comparison to the corresponding control plots of the coffee agroforestry implies that application of biochar can enhance accumulation of carbon in the form of aboveground biomass and soil organic carbon.

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Uncertainties in the land-use flux resulting from land-use change reconstructions and gross land transitions

Earth System Dynamics ◽

10.5194/esd-8-91-2017 ◽

2017 ◽

Vol 8 (1) ◽

pp. 91-111 ◽

Cited By ~ 17

Author(s):

Anita D. Bayer ◽

Mats Lindeskog ◽

Thomas A. M. Pugh ◽

Peter M. Anthoni ◽

Richard Fuchs ◽

...

Keyword(s):

Land Use ◽

Agricultural Land ◽

Land Use Changes ◽

Terrestrial Ecosystem ◽

Grid Cell ◽

Carbon Stocks ◽

Dynamic Global Vegetation Model ◽

Soil C ◽

Tropical Regions ◽

C Stocks

Abstract. Land-use and land-cover (LUC) changes are a key uncertainty when attributing changes in measured atmospheric CO2 concentration to its sinks and sources and must also be much better understood to determine the possibilities for land-based climate change mitigation, especially in the light of human demand on other land-based resources. On the spatial scale typically used in terrestrial ecosystem models (0.5 or 1°) changes in LUC over time periods of a few years or more can include bidirectional changes on the sub-grid level, such as the parallel expansion and abandonment of agricultural land (e.g. in shifting cultivation) or cropland–grassland conversion (and vice versa). These complex changes between classes within a grid cell have often been neglected in previous studies, and only net changes of land between natural vegetation cover, cropland and pastures accounted for, mainly because of a lack of reliable high-resolution historical information on gross land transitions, in combination with technical limitations within the models themselves. In the present study we applied a state-of-the-art dynamic global vegetation model with a detailed representation of croplands and carbon–nitrogen dynamics to quantify the uncertainty in terrestrial ecosystem carbon stocks and fluxes arising from the choice between net and gross representations of LUC. We used three frequently applied global, one recent global and one recent European LUC datasets, two of which resolve gross land transitions, either in Europe or in certain tropical regions. When considering only net changes, land-use-transition uncertainties (expressed as 1 standard deviation around decadal means of four models) in global carbon emissions from LUC (ELUC) are ±0.19, ±0.66 and ±0.47 Pg C a−1 in the 1980s, 1990s and 2000s, respectively, or between 14 and 39 % of mean ELUC. Carbon stocks at the end of the 20th century vary by ±11 Pg C for vegetation and ±37 Pg C for soil C due to the choice of LUC reconstruction, i.e. around 3 % of the respective C pools. Accounting for sub-grid (gross) land conversions significantly increased the effect of LUC on global and European carbon stocks and fluxes, most noticeably enhancing global cumulative ELUC by 33 Pg C (1750–2014) and entailing a significant reduction in carbon stored in vegetation, although the effect on soil C stocks was limited. Simulations demonstrated that assessments of historical carbon stocks and fluxes are highly uncertain due to the choice of LUC reconstruction and that the consideration of different contrasting LUC reconstructions is needed to account for this uncertainty. The analysis of gross, in addition to net, land-use changes showed that the full complexity of gross land-use changes is required in order to accurately predict the magnitude of LUC change emissions. This introduces technical challenges to process-based models and relies on extensive information regarding historical land-use transitions.

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Assessing the response of soil carbon in Australia to changing inputs and climate using a consistent modelling framework

Biogeosciences ◽

10.5194/bg-18-5185-2021 ◽

2021 ◽

Vol 18 (18) ◽

pp. 5185-5202

Author(s):

Juhwan Lee ◽

Raphael A. Viscarra Rossel ◽

Mingxi Zhang ◽

Zhongkui Luo ◽

Ying-Ping Wang

Keyword(s):

Global Change ◽

Future Climate Change ◽

Natural Environments ◽

Soil Organic C ◽

Total N ◽

Organic C ◽

Soil C ◽

Continental Scale ◽

Modelling Framework ◽

C Stocks

Abstract. Land use and management practices affect the response of soil organic carbon (C) to global change. Process-based models of soil C are useful tools to simulate C dynamics, but it is important to bridge any disconnect that exists between the data used to inform the models and the processes that they depict. To minimise that disconnect, we developed a consistent modelling framework that integrates new spatially explicit soil measurements and data with the Rothamsted carbon model (Roth C) and simulates the response of soil organic C to future climate change across Australia. We compiled publicly available continental-scale datasets and pre-processed, standardised and configured them to the required spatial and temporal resolutions. We then calibrated Roth C and ran simulations to estimate the baseline soil organic C stocks and composition in the 0–0.3 m layer at 4043 sites in cropping, modified grazing, native grazing and natural environments across Australia. We used data on the C fractions, the particulate, mineral-associated and resistant organic C (POC, MAOC and ROC, respectively) to represent the three main C pools in the Roth C model's structure. The model explained 97 %–98 % of the variation in measured total organic C in soils under cropping and grazing and 65 % in soils under natural environments. We optimised the model at each site and experimented with different amounts of C inputs to simulate the potential for C accumulation under constant climate in a 100-year simulation. With an annual increase of 1 Mg C ha−1 in C inputs, the model simulated a potential soil C increase of 13.58 (interquartile range 12.19–15.80), 14.21 (12.38–16.03) and 15.57 (12.07–17.82) Mg C ha−1 under cropping, modified grazing and native grazing and 3.52 (3.15–4.09) Mg C ha−1 under natural environments. With projected future changes in climate (+1.5, 2 and 5.0 ∘C) over 100 years, the simulations showed that soils under natural environments lost the most C, between 3.1 and 4.5 Mg C ha−1, while soils under native grazing lost the least, between 0.4 and 0.7 Mg C ha−1. Soil under cropping lost between 1 and 2.7 Mg C ha−1, while those under modified grazing showed a slight increase with temperature increases of 1.5 ∘C, but with further increases of 2 and 5 ∘C the median loss of TOC was 0.28 and 3.4 Mg C ha−1, respectively. For the different land uses, the changes in the C fractions varied with changes in climate. An empirical assessment of the controls on the C change showed that climate, pH, total N, the C : N ratio and cropping were the most important controls on POC change. Clay content and climate were dominant controls on MAOC change. Consistent and explicit soil organic C simulations improve confidence in the model's estimations, facilitating the development of sustainable soil management under global change.

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Historical and future carbon stocks in forests of northern Ontario, Canada

Carbon Balance and Management ◽

10.1186/s13021-021-00184-5 ◽

2021 ◽

Vol 16 (1) ◽

Author(s):

Michael T. Ter-Mikaelian ◽

Alemu Gonsamo ◽

Jing M. Chen ◽

Gang Mo ◽

Jiaxin Chen

Keyword(s):

Climate Change ◽

Natural Resources ◽

Forest Ecosystem ◽

Carbon Stocks ◽

First Century ◽

Historical Simulation ◽

C Stocks ◽

C Stock ◽

Forest C ◽

Soc Stocks

Abstract Background Forests in the Far North of Ontario (FNO), Canada, are likely the least studied in North America, and quantifying their current and future carbon (C) stocks is the first step in assessing their potential role in climate change mitigation. Although the FNO forests are unmanaged, the latter task is made more important by growing interest in developing the region’s natural resources, primarily for timber harvesting. In this study, we used a combination of field and remotely sensed observations with a land surface model to estimate forest C stocks in the FNO forests and to project their future dynamics. The specific objective was to simulate historical C stocks for 1901–2014 and future C stocks for 2015–2100 for five shared socioeconomic pathway (SSP) scenarios selected as high priority scenarios for the 6th Assessment Report on Climate Change. Results Carbon stocks in live vegetation in the FNO forests remained relatively stable between 1901 and 2014 while soil organic carbon (SOC) stocks steadily declined, losing about 16% of their initial value. At the end of the historical simulation (in 2014), the stocks were estimated at 19.8, 46.4, and 66.2 tCha−1 in live vegetation, SOC, and total ecosystem pools, respectively. Projections for 2015–2100 indicated effectively no substantial change in SOC stocks, while live vegetation C stocks increased, accelerating their growth in the second half of the twenty-first century. These results were consistent among all simulated SSP scenarios. Consequently, increase in total forest ecosystem C stocks by 2100 ranged from 16.7 to 20.7% of their value in 2015. Simulations with and without wildfires showed the strong effect of fire on forest C stock dynamics during 2015–2100: inclusion of wildfires reduced the live vegetation increase by half while increasing the SOC pool due to higher turnover of vegetation C to SOC. Conclusions Forest ecosystem C stock estimates at the end of historical simulation period were at the lower end but within the range of values reported in the literature for northern boreal forests. These estimates may be treated as conservatively low since the area included in the estimates is poorly studied and some of the forests may be on peat deposits rather than mineral soils. Future C stocks were projected to increase in all simulated SSP scenarios, especially in the second half of the twenty-first century. Thus, during the projected period forest ecosystems of the FNO are likely to act as a C sink. In light of growing interest in developing natural resources in the FNO, collecting more data on the status and dynamics of its forests is needed to verify the above-presented estimates and design management activities that would maintain their projected C sink status.

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Soil carbon stocks and their variability across the woodlands of peninsular Spain

Biogeosciences Discussions ◽

10.5194/bgd-10-10913-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 10913-10936

Author(s):

E. Doblas-Miranda ◽

P. Rovira ◽

L. Brotons ◽

J. Martínez-Vilalta ◽

J. Retana ◽

...

Keyword(s):

Global Change ◽

Vegetation Cover ◽

Carbon Stocks ◽

Annual Precipitation ◽

Future Climate Change ◽

Mean Annual Temperature ◽

Soil C ◽

C Stocks ◽

The Impact ◽

Peninsular Spain

Abstract. Global warming effects in our ecosystems could be offset by reducing carbon emissions and protecting and increasing carbon stocks. Accurate estimates of carbon stocks and fluxes of soil organic carbon (SOC) are thus needed to asses the impact of climate and land-use change on soil C uptake and soil C emissions to the atmosphere. Here, we present an assessment of SOC stocks in woodlands (forest, shrublands and grasslands) of peninsular Spain based on field measurements in more than 900 soil profiles. Estimations of soil C stocks for the 7 796 306 plots of the Spanish Forest Map (24.3 × 106 ha.) were carried out using a statistical model that included, as explanatory variables, vegetation cover, parent material, soil consistency, mean annual temperature, total annual precipitation and elevation, and the influence of spatial correlation. We present what we believe is the most reliable estimation of current SOC in woodlands of peninsular Spain thus far, based on the considered predictors, the high number of profiles and the validity and refinement of the data layers employed. Mean concentration of SOC was 8.8 kg m−2, which is slightly higher than that presented in previous studies. This value corresponds to a total stock of 2574 Tg SOC, which is four times the amount of carbon estimated to be stored in the biomass of Spanish forests. Climate and vegetation cover were the main variables influencing SOC, with important ecological implications for peninsular Spanish ecosystems in the face of global change. The fact that SOC was positively related to annual precipitation and negatively related to mean annual temperature suggests that future climate change may strongly reduce the potential of Spanish soils as carbon sinks. However, this may be mediated by changes in vegetation cover (e.g., by favouring the development of forests associated to higher SOC values) and threatened by perturbations such as fire. The estimations presented here should improve our capacity to respond to global change by carbon stocks conservation and management.

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Simulation of soil carbon dynamics in Australia under a framework that better connects spatially explicit data with Rᴏᴛʜ C

10.5194/bg-2020-150 ◽

2020 ◽

Author(s):

Juhwan Lee ◽

Raphael A. Viscarra Rossel ◽

Zhongkui Luo ◽

Ying Ping Wang

Keyword(s):

C:N Ratio ◽

Clay Content ◽

Spatially Explicit ◽

Natural Environments ◽

Soil Organic C ◽

Total N ◽

Organic C ◽

Soil C ◽

Continental Scale ◽

C Stocks

Abstract. We simulated soil organic carbon (C) dynamics across Australia with the Rothamsted carbon model (Rᴏᴛʜ C) under a framework that connects new spatially-explicit soil measurements and data with the model. Doing so helped to bridge the disconnection that exists between datasets used to inform the model and the processes that it depicts. Under this framework, we compiled continental-scale datasets and pre-processed, standardised and configured them to the required spatial and temporal resolutions. We then calibrated Rᴏᴛʜ C and run simulations to predict the baseline soil organic C stocks and composition in the 0–0.3 m layer at 4,043 sites in cropping, modified grazing, native grazing, and natural environments across Australia. The Rᴏᴛʜ C model uses measured C fractions, the particulate, humus, and resistant organic C (POC, HOC and ROC, respectively) to represent the three main C pools in its structure. The model explained 97–98 % of the variation in measured total organic C in soils under cropping and grazing, and 65 % in soils under natural environments. We optimised the model at each site and experimented with different amounts of C inputs to predict the potential for C accumulation in a 100-year simulation. With an annual increase of 1 Mg C ha−1 in C inputs, the model predicted a potential soil C increase of 13.58 (interquartile range 12.19–15.80), 14.21 (12.38–16.03), and 15.57 (12.07–17.82) Mg C ha−1 under cropping, modified grazing and native grazing, and 3.52 (3.15–4.09) Mg C ha−1 under natural environments. Soils under native grazing were the most potentially vulnerable to C decomposition and loss, while soils under natural environments were the least vulnerable. An empirical assessment of the controls on the C change showed that climate, pH, total N, the C:N ratio, and cropping were the most important controls on POC change. Clay content and climate were dominant controls on HOC change. Consistent and explicit soil organic C simulations improve confidence in the model's predictions, contributing to the development of sustainable soil management under global change.

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Uncertainties in the land use flux resulting from land use change reconstructions and gross land transitions

10.5194/esd-2016-24 ◽

2016 ◽

Cited By ~ 1

Author(s):

Anita D. Bayer ◽

Mats Lindeskog ◽

Thomas A. M. Pugh ◽

Richard Fuchs ◽

Almut Arneth

Keyword(s):

Land Use ◽

Agricultural Land ◽

Land Use Changes ◽

Terrestrial Ecosystem ◽

Co2 Concentration ◽

Carbon Stocks ◽

Dynamic Global Vegetation Model ◽

Soil C ◽

Tropical Regions ◽

C Stocks

Abstract. Land-use and land-cover (LUC) changes are a key uncertainty when attributing changes in measured atmospheric CO2 concentration to its sinks and sources, and must also be much better understood to determine possibilities for land-based climate change mitigation, especially in the light of human demand on other land-based resources. On the spatial scale typically used in terrestrial ecosystem models (0.5 or 1 degrees) changes in LUC over time periods of a few years or more can include bi-directional changes on the sub-grid level, such as the parallel expansion and abandonment of agricultural land (e.g. in shifting cultivation), or cropland-grassland conversion (and vice versa). These complex changes between classes within a gridcell have often been neglected in previous studies, and only net changes of land between natural vegetation cover, cropland and pastures accounted for, mainly because of a lack of reliable high-resolution historical information on gross land transitions. In the present study we applied a state-of-the-art dynamic global vegetation model with a detailed representation of croplands and carbon-nitrogen dynamics to quantify the uncertainty in terrestrial ecosystem carbon stocks and fluxes arising from the choice between net and gross representations of LUC. We used three frequently applied global and one recent European LUC datasets, two of which resolve gross land transitions, either in Europe or in tropical regions. When considering only net changes, land-use-transition uncertainties (expressed as one standard deviation around decadal means) in global carbon emissions from LUC (ELUC) are &pm;0.23, &pm;0.76 and &pm;0.49 Pg C a−1 in the 1980s, 1990s and 2000s, respectively, or between 17 % and 42 % of mean ELUC. Carbon stocks at the end of the 20th century vary by &pm;13 Pg C for vegetation and &pm;41 Pg C for soil C due to the choice of LUC reconstruction, i.e. around 3 % of the respective C pools. Accounting for sub-grid (gross) land conversions significantly increased the effect of LUC on global and European carbon stocks and fluxes, most noticeably enhancing global cumulative ELUC by 33 Pg C (1750–2014) and entailing a significant reduction in carbon stored in vegetation, although the effect on soil C stocks was limited. Simulations demonstrated that assessments of historical carbon stocks and fluxes are highly uncertain due to the choice of LUC reconstruction and that the consideration of different contrasting LUC reconstructions is needed to account for this uncertainty. The analysis of gross in addition to net land changes showed that the full complexity of gross land-use changes is required in order to accurately predict the magnitude of LUC change emissions. This introduces technical challenges to the process-based models and relies on extensive information on historical land use transitions.

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Linking Vegetation, Soil Carbon Stocks, and Earthworms in Upland Coniferous–Broadleaf Forests

Forests ◽

10.3390/f12091179 ◽

2021 ◽

Vol 12 (9) ◽

pp. 1179

Author(s):

Anastasiia I. Kuznetsova ◽

Anna P. Geraskina ◽

Natalia V. Lukina ◽

Vadim E. Smirnov ◽

Elena V. Tikhonova ◽

...

Keyword(s):

Soil Carbon ◽

Carbon Stocks ◽

Mineral Layer ◽

Forest Zone ◽

Soil C ◽

C Stocks ◽

European Part Of Russia ◽

Organic Horizons ◽

Soil Carbon Stocks ◽

The Impact

Linking vegetation, soil biota, and soil carbon stocks in forests has a high predictive value. The specific aim of this study was to identify the relationships between vegetation, earthworms, and soil carbon stocks in nine types of forests dominating autonomous landscape positions in a coniferous–broadleaf forest zone of the European part of Russia. Mountain forests were selected in the Northwest Caucasus, while plain forests were selected in Bryansk Polesie and on the Moskva-Oka plain. One-way analysis of variance (ANOVA) and v-tests were used to assess the impact of different factors on soil C stocks. To assess the contribution of vegetation, litter quality, and earthworms to variation of carbon stocks in organic (FH-layer) and mineral layer (0–50 cm), the method of hierarchical partitioning was performed. The highest C stocks in the organic horizons were associated with the low-quality litter, i.e., with a low base saturation, high acidity, and wide C/N ratio. The highest soil C stocks in the mineral layers were found in mixed forests with the highest richness of plant species, producing litterfall of different quality. The С stock in the organic horizon was negatively related to the biomass of worms that process the litter, while the carbon stock in the mineral layers was positively related to the biomass of worms whose life activity is related to the mineral layers. These findings demonstrated the substantial influence of plants producing a litter of different quality, and of earthworms, belonging to different functional groups, on soil С stocks in coniferous–broadleaf forests.

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Potential contribution by cotton roots to soil carbon stocks in irrigated Vertosols

Soil Research ◽

10.1071/sr08180 ◽

2009 ◽

Vol 47 (3) ◽

pp. 243 ◽

Cited By ~ 11

Author(s):

N. R. Hulugalle ◽

T. B. Weaver ◽

L. A. Finlay ◽

N. W. Luelf ◽

D. K. Y. Tan

Keyword(s):

Root Growth ◽

Soil Carbon ◽

Crop Residues ◽

Climatic Factors ◽

Carbon Stocks ◽

Potential Contribution ◽

Soil C ◽

C Stocks ◽

Root Death ◽

Soil Carbon Stocks

The well-documented decline in soil organic carbon (SOC) stocks in Australian cotton (Gossypium hirsutum L.) growing Vertosols has been primarily analysed in terms of inputs from above-ground crop residues, with addition to soil C by root materials being little studied. Potential contribution by cotton roots to soil carbon stocks was evaluated between 2002 and 2008 in 2 ongoing long-term experiments near Narrabri, north-western New South Wales. Experiment 1 consisted of cotton monoculture sown either after conventional tillage or on permanent beds, and a cotton–wheat (Triticum aestivum L.) rotation on permanent beds; Experiment 2 consisted of 4 cotton-based rotation systems sown on permanent beds: cotton monoculture, cotton–vetch (Vicia villosa Roth.), cotton–wheat, and cotton–wheat–vetch. Roundup-Ready™ (genetically modified) cotton varieties were sown until 2005, and Bollgard™ II-Roundup Ready™-Flex™ varieties thereafter. Root growth in the surface 0.10 m was measured with the core-break method using 0.10-m-diameter cores. A subsample of these cores was used to evaluate relative root length and root C concentrations. Root growth in the 0.10–1.0 m depth was measured at 0.10-m depth intervals with a ‘Bartz’ BTC-2 minirhizotron video microscope and I-CAP image capture system (‘minirhizotron’). The video camera was inserted into clear, plastic acrylic minirhizotron tubes (50-mm-diameter) installed within each plot, 30° from the vertical. Root images were captured 4–5 times each season in 2 orientations, left and right side of each tube, adjacent to a furrow, at each time of measurement and the images analysed to estimate selected root growth indices. The indices evaluated were the length and number of live roots at each time of measurement, number of roots which changed length, number and length of roots which died (i.e. disappeared between times of measurement), new roots initiated between times of measurement, and net change in root numbers and length. These measurements were used to derive root C turnover between times of measurements, root C added to soil through intra-seasonal root death, C in roots remaining at end of season, and the sum of the last 2 indices: root C potentially available for addition to soil C stocks. Total seasonal cotton root C potentially available for addition to soil C stocks ranged between ~50 and 400 g/m2 (0.5 and 4 t/ha), with intra-seasonal root death contributing 25–70%. These values are ~10–60% of that contributed by above-ground crop residues. As soil organic carbon in irrigated Vertosols can range between 40 and 60 t/ha, it is unlikely that cotton roots will contribute significantly to soil carbon stocks in irrigated cotton farming systems. Seasonal root C was reduced by cotton monoculture, stress caused by high insect numbers, and sowing Bollgard II varieties; and increased by sowing non-Bollgard II varieties and wheat rotation crops. Permanent beds increased root C but leguminous rotation crops did not. Climatic factors such as cumulative day-degrees and seasonal rainfall were positively related to seasonal root C. Root C turnover was, in general, highest during later vegetative/early reproductive growth. Large variations in root C turnover and seasonal C indices occurred due to a combination of environmental, management and climatic factors.

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Soil organic carbon stocks in tropical soil systems under rainforests controlled by geochemistry

10.5194/egusphere-egu2020-12993 ◽

2020 ◽

Author(s):

Mario Reichenbach ◽

Peter Fiener ◽

Florian Wilken ◽

Johan Six ◽

Laurent Kidinda ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Tropical Forest ◽

Carbon Stocks ◽

Parent Material ◽

Temperate Climate ◽

Soil C ◽

Geochemical Properties ◽

The Relationship ◽

Soc Stocks

Soil mineralogy plays an important role in stabilizing soil organic carbon (SOC) against decomposition by forming organo-mineral complexes with reactive mineral surfaces. However, few studies take the influence of parent material geochemistry on the development of C stabilization mechanisms into account. In addition, studies evaluating C stabilization in soil are often limited to temperate climate zones with young to intermediate aged soils. This is not representative for older, deeply weathered and leached tropical systems and limits our understanding of the relationship between geology, soil formation and their effect on C stabilization.Here, we study the relationship between soil carbon stabilization and the geochemical properties of soils developed on different parent material along geomorphic transects in pristine tropical forest systems under comparable climate. Our study is located in the eastern part of the Congo basin along the East African Rift Mountain System where we sampled 36 one meter soil cores along nine geomorphic transects on geologies ranging from mafic to felsic geochemistry.Carbon stocks ranged between 2.67 tC ha-1 to 85.75 tC ha-1 and were on average composed of 4.5% (&#177;5.3% SD) coarse particulate organic matter, 46.0% (&#177;10.3% SD) (micro)aggregates associated C and 49.6% (&#177;11.2% SD) free silt and clay associated C. Our analysis shows that the topographic position of the investigated soils had no effect on SOC stocks and the distribution of soil C fractions. Regression models and partial correlation analysis reveal that strong correlations of SOC stocks exists to geochemical properties of the solid phase of soil but not to the distribution of soil C fractions. SOC decreased strongly with soil depth on soils developed on felsic parent material, but less so on mafic or intermediate parent material. In addition, mafic geochemistry shows significantly higher SOC stocks compared to their felsic counterparts.We conclude that despite long-lasting weathering, the contrasting geochemistry of the underlying parent material leaves a footprint in soil geochemistry that affects C stocks but less so on stabilization mechanisms. We hypothesis that carbon dynamics in these undisturbed tropical forest systems are more driven by C input and nutrient recycling than by variation in C stabilization potential.&#160;&#160;

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