scholarly journals Modelling the genesis of equatorial podzols: age and implications on carbon fluxes

2017 ◽  
Author(s):  
Cédric Doupoux ◽  
Patricia Merdy ◽  
Célia Régina Montes ◽  
Naoise Nunan ◽  
Adolpho José Melfi ◽  
...  
Keyword(s):  
Organic Matter ◽  
Carbon Fluxes ◽  
Total Carbon ◽  
Organic C ◽  
Perched Water Table ◽  
C Dynamics ◽  
14C Age ◽  
Order Of Magnitude ◽  
Over Time ◽  
Main Carbon

Abstract. Amazonian podzols store huge amounts of carbon and play a key role in transferring organic matter to the Amazon river. In order to better understand their C dynamics, we modelled the formation of representative Amazonian podzol profiles by constraining both total carbon and radiocarbon. We determined the relationships between total carbon and radiocarbon in organic C pools numerically by setting constant C and 14C inputs over time. The model was an effective tool for determining the order of magnitude of the carbon fluxes and the time of genesis of the main carbon-containing horizons, i.e. the topsoil and deep Bh. We performed retro calculations to take in account the bomb carbon in the young topsoil horizons (14C age from 62 to 109 y). We modelled four profiles representative of Amazonian podzols, two profiles with an old Bh (14C age 6.8 × 103 and 8.4 × 103 y) and two profiles with a very old Bh (14C age 23.2 × 103 and 25.1 × 103 y). The calculated fluxes from the topsoil to the perched water-table indicates that the most waterlogged zones of the podzolized areas are the main source of dissolved organic matter found in the river network. It was necessary to consider two Bh carbon pools to accurately represent the carbon fluxes leaving the Bh as observed in previous studies. We found that the genesis time of the studied soils was necessarily longer than 15 × 103 and 130 × 103 y for the two younger and the two older Bhs, respectively, and that the genesis time calculated considering the more likely settings runs to around 15 × 103–25 × 103 and 150 × 103–250 × 103 y, respectively.

scholarly journals Modelling the genesis of equatorial podzols: age and implications for carbon fluxes

2017 ◽  
Vol 14 (9) ◽  
pp. 2429-2440 ◽  
Author(s):  
Cédric Doupoux ◽  
Patricia Merdy ◽  
Célia Régina Montes ◽  
Naoise Nunan ◽  
Adolpho José Melfi ◽  
...  
Keyword(s):  
Organic Matter ◽  
Carbon Fluxes ◽  
Total Carbon ◽  
Organic C ◽  
Perched Water Table ◽  
C Dynamics ◽  
14C Age ◽  
Order Of Magnitude ◽  
Over Time ◽  
Main Carbon

Abstract. Amazonian podzols store huge amounts of carbon and play a key role in transferring organic matter to the Amazon River. In order to better understand their C dynamics, we modelled the formation of representative Amazonian podzol profiles by constraining both total carbon and radiocarbon. We determined the relationships between total carbon and radiocarbon in organic C pools numerically by setting constant C and 14C inputs over time. The model was an effective tool for determining the order of magnitude of the carbon fluxes and the time of genesis of the main carbon-containing horizons, i.e. the topsoil and deep Bh. We performed retrocalculations to take into account the bomb carbon in the young topsoil horizons (calculated apparent 14C age from 62 to 109 years). We modelled four profiles representative of Amazonian podzols, two profiles with an old Bh (calculated apparent 14C age 6.8  ×  103 and 8.4  ×  103 years) and two profiles with a very old Bh (calculated apparent 14C age 23.2  ×  103 and 25.1  ×  103 years). The calculated fluxes from the topsoil to the perched water table indicate that the most waterlogged zones of the podzolized areas are the main source of dissolved organic matter found in the river network. It was necessary to consider two Bh carbon pools to accurately represent the carbon fluxes leaving the Bh as observed in previous studies. We found that the genesis time of the studied soils was necessarily longer than 15  ×  103 and 130  ×  103 years for the two younger and two older Bhs, respectively, and that the genesis time calculated considering the more likely settings runs to around 15  ×  103–25  ×  103 and 150  ×  103–250  ×  103 years, respectively.

scholarly journals Soil geochemistry as a driver of soil organic matter composition: insights from a soil chronosequence

2021 ◽  
Author(s):  
Moritz Mainka ◽  
Laura Summerauer ◽  
Daniel Wasner ◽  
Gina Garland ◽  
Marco Griepentrog ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Development ◽  
Total Carbon ◽  
Soil Geochemistry ◽  
Change Over Time ◽  
Δ13c And Δ15n ◽  
Soil Chronosequence ◽  
Peak Areas ◽  
Over Time

Abstract. A central question in carbon research is how stabilization mechanisms in soil change over time with soil development and how this is reflected in qualitative changes of soil organic matter (SOM). To address this matter, we assessed the influence of soil geochemistry on bulk SOM composition along a soil chronosequence in California, USA spanning 3 million years. This was done by combining data on soil mineralogy and texture from previous studies with additional measurements on total carbon (C), stable isotope values (δ13C and δ15N), and spectral information derived from Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS). To assess qualitative shifts in bulk SOM, we analysed the peak areas of simple plant-derived (S-POM), complex plant-derived (C-POM), and predominantly microbially derived OM (MOM) and their changes in abundance across soils varying several millennia to millions of years in weathering and soil development. We observed that SOM became increasingly stabilized and microbially-derived (lower C : N ratio, increasing δ13C and δ15N) as soil weathering progresses. Peak areas of S-POM (i.e. aliphatic root exudates) did not change over time, while peak areas of C-POM (lignin) and MOM (components of microbial cell walls (amides, quinones, and ketones)) increased over time and depth and were closely related to clay content and pedogenic iron oxides. Hence, our study suggests that with progressing soil development, SOM composition co-varies with changes in the mineral matrix. Our study indicates that a discrimination in favour of structurally more complex OM compounds (C-POM, MOM) gains importance as the mineral soil matrix becomes increasingly weathered.

scholarly journals An improved estimate of microbially mediated carbon fluxes from the Greenland ice sheet

2012 ◽  
Vol 58 (212) ◽  
pp. 1098-1108 ◽  
Author(s):  
J.M. Cook ◽  
A.J. Hodson ◽  
A.M. Anesio ◽  
E. Hanna ◽  
M. Yallop ◽  
...  
Keyword(s):  
Carbon Fixation ◽  
Ice Sheet ◽  
Stable State ◽  
Greenland Ice Sheet ◽  
Carbon Fluxes ◽  
Total Carbon ◽  
Biological Production ◽  
Spatial Uniformity ◽  
Annual Carbon ◽  
Order Of Magnitude

AbstractMicrobially mediated carbon fluxes on the surface of the Greenland ice sheet (GrIS) were recently quantified by Hodson and others (2010) using measurements of the surface coverage of debris (cryoconite) and rates of biological production associated with debris near the ice-sheet margin. We present updated models that do not assume the same spatial uniformity in key parameters employed by Hodson and others (2010) because they make use of biomass distribution and biological production data from a 79 km transect of the GrIS. Further, the models presented here also include for the first time biomass associated with both cryoconite holes and surficial algae. The predicted annual carbon flux for a small (1600 km2) section of ice surrounding the field transect is about four times that estimated using spatially uniform biomass and production in this area. When surficial algae are included, the model predicts about 11 times more carbon fixation via photosynthesis per year than the cryoconite-only models. We therefore suggest that supraglacial carbon fluxes from the GrIS have previously been underestimated by more than an order of magnitude and that the hitherto overlooked surficial algal ecosystem can be the most crucial contributor. The GrIS is shown to be in a relatively stable state of net autotrophy according to our model and so a strong link between bare-ice area and total carbon fluxes is evident. The implication is a biomass feedback to surface albedo and enhanced ablation as a result. Climate predictions for the year 2100 show that greater carbon fixation could also result from climate warming.

Organic matter investigation in agricultural Apennine topsoils (Emilia-Romagna Region): carbon pools and isotopic C signature

2020 ◽  
Author(s):  
Enrico Mistri ◽  
Gianluca Bianchini ◽  
Claudio Natali ◽  
Livia Vittori Antisari ◽  
Gloria Falsone ◽  
...  
Keyword(s):  
Organic Matter ◽  
Humic Acids ◽  
Crop Yields ◽  
Agricultural Soils ◽  
Total Carbon ◽  
Organic C ◽  
Soil C ◽  
Rural Development Programme ◽  
Isotopic Analyses ◽  
Emilia Romagna Region

<p>The exploitation of soils due to farming has produced a progressive loss of soil organic matter (SOM) over the years. At the same time, the degradation of SOM has led to a decline of several ecosystem services provided by soil, especially in mountain. Against this background, the partnership between Department of Physics and Earth Sciences of University of Ferrara and Department of Agricultural and Food Sciences of University of Bologna led to the creation of the SaveSOC2 project (Save Soil Organic Carbon), funded by Rural Development Programme of Emilia-Romagna Region. This project primarily seeks to investigate and promote carbon storage processes in agricultural soils of Emilia-Romagna Region (NE Italy). The present study outlines an overview about the SOM dynamics of “I Rodi” organic farm, located in the Modena Apennine. “I Rodi” produces and processes small organic fruits, especially raspberries. Three different sites (grassland -G, very low productive raspberries -LR, and good productive raspberries -GR) have been selected and the topsoils (0-15 cm and 15-30 cm) have been investigated. Elemental and isotopic analyses of soil C were performed using an EA-IRMS. In particular, the application of the Thermally Based Separation protocol [1] allowed the determination of both inorganic (IC) and organic (OC) carbon contents in each soil sample. OC accounted for 93.50% of the total carbon (1.72-4.84 wt.%). The negative δ<sup>13</sup>C values of the total carbon (from -27.8 to -19.7 ‰) confirmed the predominance of OC over IC in the investigated soils. The average values of OC isotopic C signature showed a decreasing trend among the three sites (-28.2, -27.2 and -25.8‰ for GR, G and LR, respectively), with the low productivity site having the highest δ<sup>13</sup>C value. The isotopic C signature of separated organic C fractions (0-15 cm topsoils) showed that humin (832-879 g/kg), which is the SOM fraction mostly interacting with the soil mineral phase and the largest pool, confirmed the observed trend (-27.5, -27.0, -26.4‰, GR, G and LR). The humic acids (6-17 g/kg) showed similar trend but lower δ<sup>13</sup>C values in all sites (-28.5, -28.0, -26.8 ‰, GR, G and LR). Finally, fulvic acids (5-10 g/kg) differed, having dissimilar trend and values of δ<sup>13</sup>C (-27.1, -26.8, -26.0 ‰ for G, GR and LR). Comparing to G, the GR data suggested that organic management i) did not decrease quantity and quality of organic matter, and ii) it was more efficient in OC stabilisation, increasing the amount of less transformed OC in both humin and humic acids (more negative δ<sup>13</sup>C values). In the LR site, instead, the observed trend can be due to low suitability of this soil to raspberries production, negatively affecting both crop yields and organic C dynamics. In our opinion, in order to combine agricultural productivity and its sustainability, more attention should be paid both to soil management and suitability in the area.</p><p>[1] Natali C., Bianchini G., Vittori Antisari L. 2018. Thermal separation coupled with elemental and isotopic analysis: A method for soil carbon characterisation. Catena 164, 150-157.</p>

scholarly journals Changes in the stocks of C and N in organic matter fractions in soil cropped with coffee and fertilized with sunn hemp and ammonium sulfate

2018 ◽  
Vol 39 (3) ◽  
pp. 999
Author(s):  
Wander Douglas Pereira ◽  
Fábio Lúcio Martins Neto ◽  
Ricardo Henrique Silva Santos ◽  
Teógenes Senna de Oliveira ◽  
Segundo Sacramento Urquiaga Caballero
Keyword(s):  
Organic Matter ◽  
Ammonium Sulfate ◽  
Soil Samples ◽  
Total N ◽  
Organic C ◽  
Green Manuring ◽  
Time Zero ◽  
Sunn Hemp ◽  
C And N ◽  
Over Time

Despite the potential to provide N to crops, the rapid incorporation of green manure nutrients into stable fractions of organic matter in the soil (SOM) may reduce the efficiency of green manuring. Thus, the objective of this work was to characterize the changes of C and N stocks in fractions of SOM cultivated with coffee (Coffea arabica L.) and fertilized with sunn hemp (Crotalaria juncea) and ammonium sulfate. To study the changes in organic C (OC) and total N (TN) in soil and fractions of SOM over time, soil samples were collected in the 0–5 and 5–10 cm layers, with the initial sampling done prior to the application of sunn hemp residues and ammonium sulfate. Five samples were collected every 2 months after the application of the legume and ammonium sulfate. The soil samples were submitted to densimetric and granulometric fractionation, obtaining the free light organic matter (F-LOM), particulate organic matter (POM), and organic matter associated with minerals (MAM). OC and TN stocks were then determined in soil and the SOM fractions. The changes in the stocks of OC (?StcC) in the soil in relation to time zero were positive in the evaluations carried out in the two layers. The fractions of SOM showed positive ?StcC at almost all of the evaluated times. The N supplied to the soil in the form of mineral and organic fertilizer promoted an increase of 0.24 Mg ha-1 of N in the 0–5 cm layer until after 60 days. Of this total, 0.03 Mg ha-1 was associated with F-LOM, 0.07 Mg ha-1 with POM, and the remainder was associated with MAM. Nearly 60% of the N that was supplied to the soil was drawn to the stable fractions of the SOM, indicating a rapid stabilization of this nutrient in the most recalcitrant organic compartments. Despite that, the variations in N stocks of MAM became smaller over time, and eventually became negative, in relation to time zero. This indicates the mineralization of N of this compartment. In the 5–10 cm layer, no effect of time was observed in the soil TN, N-POM, or N-MAM stocks. Additionally, under the conditions of this experiment, the majority of the N supplied to the soil was rapidly incorporated into the most stable fraction of SOM, and this might can reduced the efficiency of the green manuring.

Development of a Swiss National Soil Spectral Model Library using data-driven modeling

2020 ◽  
Author(s):  
Philipp Baumann ◽  
Anatol Helfenstein ◽  
Andreas Gubler ◽  
Reto Meuli ◽  
Armin Keller ◽  
...  
Keyword(s):  
Soil Properties ◽  
Near Infrared ◽  
Diffuse Reflectance Spectroscopy ◽  
Monitoring Network ◽  
Total Carbon ◽  
Data Driven ◽  
Local Approach ◽  
Organic C ◽  
Soil C ◽  
Over Time

<p>Soil data at different scales are needed for assessments and monitoring of soil functions. Soil diffuse reflectance spectroscopy using visible–Near Infrared and mid-Infrared energies can be used to estimate a range of soil properties, rapidly and inexpensively. However the spectroscopic modeling is challenging because of the large soil diversity and its complex composition. We developed a National Soil Spectral library (SSL) (n = 4339) using samples from (i) the Swiss Soil Monitoring Network (NABO; 7 sampling campaigns at 71 agricultural locations since 1985, n = 592) and (ii) the National Biodiversity Monitoring (BDM) Program (n = 4295, 1094 locations across a 5x5 km grid). The SSL will provide spectroscopic models for estimation of functional soil properties at different scales (e.g. total carbon (C) and nitrogen, organic C, texture, pH and cation exchange capacity). We used a rule-based algorithm, Cubist, for the modelling. The models were tuned across full combinations of {5, 10, 20, 50, 100} committees and {2, 5, 7, 9} neighbors, using 5 times repeated 10-fold cross-validation grouped by location. Further, transfer learning with RS-LOCAL tuning was performed for each of the 71 monitoring sites separately by a hold out approach in order to select optimal instances from the remaining SSL. Total soil C in the reference data ranged from 0.1% to 58.3% C and the best Cubist model had a cross-validated RMSE of 0.82% C. The RS-LOCAL approach (RMSE<sub>mean</sub> = 0.14 %) was on average 2.5 times more accurate for the estimation of C over time at each of the 71 NABO sites compared to the general Cubist approach. Our results suggest that data-driven selection of SSL instances targeted to closely related soils produces less biased estimation of soil properties over time at smaller geographic extents. The general Cubist calibration models are useful when reference analyses in a new study area are scarce. In conclusion, the Swiss SSL models can be used to cost-efficiently estimate a range of soil properties for a diverse applications and purposes in Switzerland.</p>

Organic matter characteristics under native forest, long-term pasture, and recent conversion to Eucalyptus plantations in Western Australia: microbial biomass, soil respiration, and permanganate oxidation

Soil Research ◽  
2002 ◽  
Vol 40 (5) ◽  
pp. 859 ◽  
Author(s):  
D. S. Mendham ◽  
A. M. O'Connell ◽  
T. S. Grove
Keyword(s):  
Land Use ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Microbial Biomass ◽  
Soil Respiration ◽  
Western Australia ◽  
Soil Texture ◽  
Total Carbon ◽  
Organic C ◽  
Highly Correlated

The influence of land-use management on Walkley-Black soil carbon (C) concentration, 3 concentrations of permanganate oxidisable C (33, 167, and 333 mm), microbial biomass, and soil respiration in a laboratory incubation was tested in surface soil from 10 sites in south-western Australia. The sites ranged in total C concentration from 1.9 to 8.3%, and represented a broad climatic and soil-type distribution across south-western Australia. At each of the sites, 0-10 cm soil was collected from plots in pasture (20-71 years old), Eucalyptus globulus plantation (7-10 years old, established on ex-pasture), and native vegetation. Soil profiles and position in the landscape for each of the land-use types were matched as closely as possible at each site to minimise influences other than land use. Total C was highly correlated with clay content. Land use caused no significant change in the relationship between total C and soil texture, and land use had little effect on total C concentration. Permanganate-oxidisable C was highly correlated with Walkley-Black organic C (R2�>�0.90) for all 3 concentrations that were investigated. Only the most dilute concentration of permanganate-oxidisable C (33 mm) was sensitive enough to detect small changes in soil organic matter with land use (P = 0.045). Microbial biomass and respiration at 25 kPa matric potential moisture content and 35°C temperature were used as biological indicators of soil organic matter lability. Cumulative respired C was more sensitive to land use than Walkley-Black organic C, with lower respiration in native soils compared with managed soils with low C concentrations, but higher than the managed soils at sites with high C concentrations. Microbial biomass was not significantly affected by land use. Microbial biomass and cumulative respired C were strongly influenced by soil texture, with the microbial quotient (proportion of microbial biomass in total carbon) and the proportion of total C respired significantly lower in soils with higher silt and clay contents. Land use had no significant effect on these relationships. Overall, land use caused only minor differences in the biological and chemical indicators of organic matter quality across a broad range of sites in south-western Australia.

Effect of crop management on C and N in long-term crop rotations after adopting no-tillage management: Comparison of soil sampling strategies

1998 ◽  
Vol 78 (1) ◽  
pp. 155-162 ◽  
Author(s):  
C. A. Campbell ◽  
F. Selles ◽  
G. P. Lafond ◽  
B. G. McConkey ◽  
D. Hahn
Keyword(s):  
Organic Matter ◽  
Crop Rotations ◽  
No Tillage ◽  
Negative Consequences ◽  
Total N ◽  
Organic C ◽  
Soil C ◽  
Soil C And N ◽  
C And N ◽  
Over Time

Society is interested in increasing C storage in soil to reduce CO2 concentration in the atmosphere, because the latter may contribute to global warming. Further, there is considerable interest in the use of straw for industrial purposes. Using soil samples taken from the 0- to 7.5-cm and 7.5- to 15-cm depths in May 1987 and September 1996, we determined organic C and total N in five crop rotations (nine treatments) using automated Carlo Erba combustion analyzer. The experiment was managed using conventional mechanical tillage from 1957 to 1989; it was changed to no-tillage management in 1990. Our objective was to determine: (a) if change to no-tillage management had changed soil C and N storage, and (b) if method of calculating organic C and N change would influence interpretation of the results. All three methods of calculation confirmed the efficacy of employing best management practices (e.g., fertilization based on soil tests, reducing summerfallow, including legumes in rotations) for increasing or maintaining soil organic matter, and showed that the latter was directly associated with the amount of crop residues returned to the soil. Where bulk density was significantly different between sampling times, the often used mass per fixed depth (MFD) (i.e., volume basis) calculation can lead to erroneous conclusions. When the recently recommended mass per equal depth (MED) method of calculation was used, it showed that 6 yr of no-tillage did not increase soil organic C or total N. However, in unfertilized systems, where crop yields are gradually decreasing since the change, there is an accompanying decrease in organic matter, while fertilized, or high-fertility systems that include legume hay crops, in which wheat yields have been maintained have tended to maintain the organic matter level over time. When the MFD calculation was used, there was no change in C over time when straw was harvested in the F–W–W system; however, the MED calculation and concentrations tend to show a decrease in soil C and N. This suggests that in time, industrial use of straw may have negative consequences for soil conservation. We concluded that concentrations may be as effective as MED for assessing changes in organic matter, provided "amounts" are not required. Key words: Straw removal, fertilizers, legumes, cropping frequency, C mass calculation

Microbial and biochemical changes induced by rotation and tillage in a soil under barley production

1993 ◽  
Vol 73 (1) ◽  
pp. 39-50 ◽  
Author(s):  
D. A. Angers ◽  
N. Bissonnette ◽  
A. Légère ◽  
N. Samson
Keyword(s):  
Alkaline Phosphatase ◽  
Organic Matter ◽  
Microbial Biomass ◽  
Phosphatase Activity ◽  
Alkaline Phosphatase Activity ◽  
Soil Layer ◽  
Red Clover ◽  
Organic C ◽  
Top Soil ◽  
Total Organic C

Crop rotations and tillage practices can modify not only the total amount of organic matter (OM) in soils but also its composition. The objective of this study was to determine the changes in total organic C, microbial biomass C (MBC), carbohydrates and alkaline phosphatase activity induced by 4 yr of different rotation and tillage combinations on a Kamouraska clay in La Pocatière, Quebec. Two rotations (continuous barley (Hordeum vulgare L.) versus a 2-yr barley–red clover (Trifolium pratense L.) rotation) and three tillage treatments (moldboard plowing (MP), chisel plowing (CP) and no-tillage (NT)) were compared in a split-plot design. Total organic C was affected by the tillage treatments but not by the rotations. In the top soil layer (0–7.5 cm), NT and CP treatments had C contents 20% higher than the MP treatment. In the same soil layer, MBC averaged 300 mg C kg−1 in the MP treatment and up to 600 mg C kg−1 in the NT soil. Hot-water-extractable and acid-hydrolyzable carbohydrates were on average 40% greater under reduced tillage than under MP. Both carbohydrate fractions were also slightly larger in the rotation than in the soil under continuous barley. The ratios of MBC and carbohydrate C to total organic C suggested that there was a significant enrichment of the OM in labile forms as tillage intensity was reduced. Alkaline phosphatase activity was 50% higher under NT and 20% higher under CP treatments than under MP treatment and, on average, 15% larger in the rotation than in the continuous barley treatment. Overall, the management-induced differences were slightly greater in the top layer (0–7.5 cm) than in the lower layer of the Ap horizon (7.5–15 cm). All the properties measured were highly correlated with one another. They also showed significant temporal variations that were, in most cases, independent of the treatments. Four years of conservation tillage and, to a lesser extent, rotation with red clover resulted in greater OM in the top soil layer compared with the more intensive systems. This organic matter was enriched in labile forms. Key words: Soil management, soil quality, organic matter, carbohydrates, microbial biomass, phosphatase

Soil stripping and replacement for the rehabilitation of bauxite-mined land at Weipa. I. Initial changes to soil organic matter and related parameters

Soil Research ◽  
2000 ◽  
Vol 38 (2) ◽  
pp. 345 ◽  
Author(s):  
G. D. Schwenke ◽  
D. R. Mulligan ◽  
L. C. Bell
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Field Experiments ◽  
Surface Soil ◽  
Soil Disturbance ◽  
Microbial Biomass C ◽  
Low Grade ◽  
Double Pass ◽  
Organic C ◽  
The Difference

At Weipa, in Queensland, Australia, sown tree and shrub species sometimes fail to establish on bauxite-mined land, possibly because surface-soil organic matter declines during soil stripping and replacement. We devised 2 field experiments to investigate the links between soil rehabilitation operations, organic matter decline, and revegetation failure. Experiment 1 compared two routinely practiced operations, dual-strip (DS) and stockpile soil, with double-pass (DP), an alternative method, and subsoil only, an occasional result of the DS operation. Other treatments included variations in stripping-time, ripping-time, fertiliser rate, and cultivation. Dilution of topsoil with subsoil, low-grade bauxite, and ironstone accounted for the 46% decline of surface-soil (0–10 cm) organic C in DS compared with pre-strip soil. In contrast, organic C in the surface-soil (0–10 cm) of DP plots (25.0 t/ha) closely resembled the pre-strip area (28.6 t/ha). However, profile (0–60 cm) organic C did not differ between DS (91.5 t/ha), DP (107 t/ha), and pre-strip soil (89.9 t/ha). Eighteen months after plots were sown with native vegetation, surface-soil (0–10 cm) organic C had declined by an average of 9% across all plots. In Experiment 2, we measured the potential for post-rehabilitation decline of organic matter in hand-stripped and replaced soil columns that simulated the DS operation. Soils were incubated in situ without organic inputs. After 1 year’s incubation, organic C had declined by up to 26% and microbial biomass C by up to 61%. The difference in organic C decline between vegetated replaced soils (Expt 1) and bare replaced soils (Expt 2) showed that organic inputs affect levels of organic matter more than soil disturbance. Where topsoil was replaced at the top of the profile (DP) and not ploughed, inputs from volunteer native grasses balanced oxidation losses and organic C levels did not decline.

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