Cumulative CO2-C Emission Research Articles

Comparing theeffect of applying different types of amendments on carbon emissions and kinetics of degrading total petroleum hydrocarbons in artificial petroleum-contaminated soil.

Contamination byspent engine oil represents a significant global environmental challenge as it poses a major hazard to human health, animals, plants, microorganisms, the soil ecosystem, and aquatic ecosystems. This study assumes that some amendments differ significantly in their ability to degrade petroleum hydrocarbons. Therefore, this incubation study was conductedto investigate the effect of different types of inorganic and organic amendments (zeolite, bone char, banana leaves biochar, and wood chips biochar) on carbon emissions (CO2-C) and the kinetics of total petroleum hydrocarbons (TPHC) degradation in artificial petroleum-contaminated soil. These amendments wereadded to the soil under study at adose of 3% (w/w). At the end of the incubation period, applying zeolite, bone char, banana leaves biochar, and wood chips biochar to artificial petroleum-contaminated soil significantly reduced cumulative CO2-C emissions compared to the control. The banana leaves biochar significantly decreased TPHC concentrations in artificial petroleum-contaminated soil compared to the control treatment. At the end of the incubation period, adding banana leaves biochar to the soil showed high degradation efficiencies of TPHC which was36% higher than soil before incubation. The effectiveness of applying amendments used in this experiment on the degradation of TPHC increase was in the order of banana leaves biochar > bone char > wood chips biochar > control > zeolite. The second-order model described the kinetics of total petroleum hydrocarbons better than thefirst-order model. Banana leaves biochar added to the soil resulted in a significant increase in the degradation rate constant of total petroleum hydrocarbons (k2) compared with the control. A higher k2 value indicates that TPHC degrades more rapidly. The half-life of TPHC degradation in the soil was decreased significantly by adding banana leaves biochar. According to the second-order equation, the half-lives of control, zeolite, bone char, banana leaves biochar, and wood chips biochar were 4.0, 5.3, 2.7, 1.0, and 3.6 years, respectively. The banana leaves biochar amendment might be cheaper and more environmentally friendly than other organic amendments because it has the high potential for carbon sequestration and remediate petroleum-contaminated soil, which would increase the sustainable use of petroleum-contaminated soil leading to preserving the environment.

Carbon-scaled nitrous oxide emissions better reflect the impacts of land use changes than raw nitrous oxide emissions in the Dry Chaco region

In the Dry Chaco region, agriculture expansion has caused significant land use change hotspots. However, the post-impact of land use change on nitrous oxide (N2O) emissions and carbon (C) budgets remains unknown. This study aimed to contrast the impacts of the main land use systems on N2O emissions related to its C inputs and C budgets by comparing them with those of a native forest at two sites of the Dry Chaco region of Argentina. At Site 1, the land use system were soybean-fallow-soybean and maize-fallow-maize sequences, whereas at Site 2, it was a soybean-wheat sequence. Measurements of soil N2O and carbon dioxide (CO2) fluxes were carried out monthly using the static chamber method. The C budgets of each system were determined for the annual crop-fallow cycle by the difference between the C inputs (from annual aboveground (ABG), belowground (BG), and rhizodeposition) and C outputs (defined as cumulative CO2-C emissions). At Site 1, the native forest showed 168 and 50 % more cumulative N2O emissions than maize and soybean, respectively. However, most land use differences were based on C inputs. Thus, when the cumulative N2O emissions of each system were related to their C inputs, the N2O emissions per ton of C entered of the native forest were lower than those of soybean and similar to those of maize. The C budgets (± standard error) at Site 1 were 6.4 ± 1.3, 1.0 ± 0.3 and −0.7 ± 0.6 t C ha−1 yr−1 for native forest, maize and soybean, respectively. At Site 2, they were 3.1 ± 0.7 and −4.0 ± 0.6 t C ha−1 yr−1 for the native forest and the soybean-wheat sequence, respectively. This paper proposes a comprehensive approach that integrates C inputs and budgets when evaluating N2O emissions from different land uses as a guide to define mitigating management practices and considers a native vegetation system to unmask the real impacts of agroecosystems.

Investigating the potential of nanobonechar toward climate-smart agriculture.

Extreme climates and the unpredictability of the weather are significant obstacles to agricultural productivity. This study is the first attempt to explore the capacity of nanobonechar (NBC) for promoting climate-smart agriculture. A pot experiment was performed on maize (Zea mays L.) under a deficit irrigation system (40, 70, and 100% irrigation rates) using different soil application rates of the NBC (0, 0.5, 1, and 2% wt/wt). Additionally, the CO2-C efflux rate and cumulative CO2-C were measured in an incubation experiment. The results indicated the best performance of the 1% NBC treatment under a 70% irrigation rate in terms of the fresh and dry weights of maize plants. Total PO43- and Ca2+ were significantly higher in the plants grown in the NBC-amended soil as compared to the control, showing a gradual increase with an increase in the NBC application rate. The improved productivity of maize plants under a deficit irrigation system was associated with enhanced water-holding capacity, organic matter, and bioavailability of cations (Ca2+, K+, and Na+) and anions (PO43- and NO3-) in the soils amended with NBC. The CO2-C efflux rate and cumulative CO2-C emissions remain higher in the NBC-amended soil than in the un-amended soil, pertaining to the high contents of soil organic matter emanating from the NBC. We conclude that NBC could potentially be used as a soil amendment for promoting maize growth under a water stress condition.

Straw Inputs Improve Soil Hydrophobicity and Enhance Organic Carbon Mineralization

The mechanism of the influence of soil water repellency (SWR) and agglomeration stability on soil organic carbon (SOC) mineralization has not been thoroughly studied following different methods of returning straw to the field. The research background in this study was ordinary black soil, and the addition of straw was accomplished via straw mixing (CT), straw mulching (CM), straw deep burying (CD), and straw tripling deep burial (CE). A 120-day long-term incubation test was used to measure the contact angle between water droplets and soil, the particle size distribution of aggregates and their organic carbon (OC) content, organic carbon pool (OCP) content, OC contribution, and soil CO2-C release, the extent of SWR and the direct effect of agglomerates on SOC mineralization were assessed under different straw return methods. The results revealed that the water-droplet–soil contact angle (CA) was much greater and the rate of CA decline was significantly lower in the CD treatment compared to the CT, CM, and CE treatments, the rate of water droplet penetration on the soil surface was slower, and the SWR was improved. The CD treatment significantly increased the content of macroaggregates and their OCP content, and also significantly increased the content of microaggregates’ OC. The CO2-C emission rate and cumulative emissions were enhanced by adding the same amount of straw, with the most significant enhancement in the deep straw treatment. The cumulative CO2-C emission rate and SOC mineralization significantly increased with increases in SWR, macroaggregates content, and microaggregates OC content, but significantly decreased with increases in macroaggregates’ OC content, according to principal component analysis and Pearson’s correlation analysis. These results highlight the extent of SWR and the direct effect of agglomerate particle size distribution and OC content on SOC mineralization under different straw return methods. This will help to consolidate soil structural stability and nutrient management to support productivity and SOC sequestration in different agricultural systems.

Litter quality modifies soil organic carbon mineralization in an ecological restoration area

AbstractSoil organic carbon (SOC) mineralization impacts the loss and accumulation of carbon (C) in crucial ways. However, it is still unclear how exactly litter quality regulates the SOC mineralization process and SOC stock. We conducted a laboratory incubation experiment under different temperatures, that is 10°C, 20°C, 30°C, and 40°C, and moisture, that is 5%, 10%, and 20% regimes, as well as a control (CK), and different litter qualities, that is, Artemisia ordosica, Caragana korshinskii, and Eragrostis minor. This was conducted in soil from a revegetated area in the Tengger Desert, northern China. We investigated the impacts of litter addition on SOC mineralization by considering the chemical properties of litter, temperature, and soil moisture, as well as the cumulative CO2‐C emissions (CCE), maximum rate (MR), potential mineralizable C (C0), priming effect (PE), temperature sensitivity (Q10), moisture sensitivity (MS), and SOC stock. Litter addition increased the CCE, MR, C0, and MS but decreased the Q10, and the effects of different litter qualities on CCE, MR, C0, MS, and Q10 differed significantly. The SOC mineralization rate increased with increasing temperature and moisture and was also accelerated by the interactions between temperature and moisture. The total C and lignin contents of litter were the key factors that governed SOC mineralization. Litter addition had a positive PE on SOC mineralization, and high‐quality litter with low C:N ratio (A. ordosica and C. korshinskii) increased the PE compared with low‐quality litter with high C:N ratio (E. minor). The PE also decreased with increasing temperature and moisture. Litter addition resulted in an acceleration of the loss of SOC mineralization, and an increase in the SOC mineralization response toward moisture but reduced the SOC mineralization response toward temperature, whereas litter quality was inversely correlated with the SOC stock. Therefore, the input of low‐quality litter will decrease the loss of mineralized SOC caused by PE and diminish the accumulation of SOC in the revegetated regions. These findings may provide a reasonable litter management model to promote the stability of soil C pool in arid revegetated areas.

Effects of Biochar Application on Soil Hydrothermal Environment, Carbon Emissions, and Crop Yield in Wheat Fields under Ridge–Furrow Rainwater Harvesting Planting Mode

The ridge–furrow rainwater harvesting (RFRH) planting mode is widely used in arid and semi-arid areas to solve the problems of agricultural water shortage and low productivity. However, the impact of film mulching on the stability of soil carbon pools makes this planting mode vulnerable to the risk of increased soil carbon emissions and carbon pool losses. In order to clarify the relationship between soil carbon emissions and hydrothermal factors, as well as the regulatory effect of biochar application on soil carbon sequestration and reduced emissions under this planting mode, we set up a biochar application experiment. The effects of the biochar application (at 10 Mg ha−1 biochar and 20 Mg ha−1 biochar) on the soil water dynamics, soil temperature changes, CO2-C and CH4-C flux dynamics, grain yield, carbon emission efficiency, and the net ecosystem carbon budget in wheat fields under the RFRH planting mode were investigated, with no biochar application as the control. The results showed that applying biochar increased the soil water content, soil average temperature, cumulative CH4-C uptake, wheat grain yield, and carbon emission efficiency by 3.10–12.23%, 0.98–3.53%, 59.27–106.65%, 3.51–16.42%, and 18.52–61.17%, respectively; reduced the cumulative CO2-C emissions by 7.51–31.07%; and increased the net ecosystem carbon budget by 2.91 Mg C ha−1 to 6.06 Mg C ha−1. The results obtained by equation fitting showed that in wheat fields under RFRH, the CO2-C emission fluxes had negative and positive exponential relationships with the soil water content and soil temperature, respectively, while the CH4-C uptake fluxes had no significant correlation with the soil water content and had an inverse U-shaped quadratic function relationship with soil temperature. Overall, these results suggest that the application of biochar to wheat fields under RFRH can improve grain yield, farmland carbon emission efficiency, and the net ecosystem carbon budget, and change wheat fields from a carbon source to a carbon sink. These results can provide a theoretical basis and technical support for efficient, green, and sustainable production in farmland in arid and semi-arid areas.

Revegetation enhances soil organic carbon mineralization and its temperature sensitivity in the Tengger Desert, North China

Revegetation plays a critical role in the soil organic carbon (SOC) cycle, especially in desert regions. However, the effects of this restoration practice on SOC mineralization are poorly understood, which inhibit the accurate estimation of SOC sequestration. In this study, SOC mineralization rates in revegetated sites along a chronosequence in the Tengger Desert were investigated by the incubation method, and the relationships between SOC mineralization rate and the temperature (T) and soil moisture (SM) of incubation, soil properties and vegetation characteristics were analyzed. The results showed that SOC mineralization rates and its temperature sensitivity (Q10) significantly increased after revegetation. The maximum CO2-C emission rates (MR), cumulative CO2-C emissions (CCE), potentially mineralizable SOC (C0) and Q10 increased by 0.04–5.62, 0.78–4.88, 0.94–4.04 and 0.37–0.47 times in 64 years following revegetation, respectively, while the proportion of C0 to total SOC (C0/SOC) decreased by 2.12–7.22 times. T and SM and their interaction had significant influences on MR, CCE, C0 and C0/SOC, while SM had no significant effect on Q10. The stepwise multiple linear regression analysis showed that the SOC mineralization rate had greater R2 with stand age and smaller R2 with SM, indicating that the SOC mineralization was mainly regulated by the stand age. The SEMs indicated that the soil properties were the main direct factors affecting SOC mineralization. The RDA indicated that soil AP, C:N ratio and T were the key factors controlling SOC mineralization during the revegetation process. Our findings indicated that long-term revegetation in desert regions enhanced SOC transformation and its temperature sensitivity, but decreased the percentage of CO2-C loss from soil, thus leading to SOC accumulation.

Effects of aromatic crops based cropping systems and residue returning on soil CO2 emission compared to fallow soil

Two years field experiment was done to investigate the impact of aromatic crops based cropping systems and crop residue returning on soil CO2 efflux and its relationship with soil temperature and moisture. Eight diversified cropping systems were compared to fallow soil as control, total nine treatments: T1-(B-W-C) (basil-wheat-cowpea), T2-(B-W-M) (basil-wheat-menthol mint), T3-(B-P-C) (basil-potato-cowpea), T4-(B-P-M) (basil-potato-menthol mint), T5-(B-L-C) (basil-lentil-cowpea), T6 -(B-L-M) (basil-lentil-menthol mint), T7-(B-Pe-C) (basil-pea-cowpea), T8-(B-Pe-M) (basil-pea-menthol mint) and T9-(F-F-F) (fallow soil). Surface soil CO2 efflux, temperature and moisture of each crop were measured in each season at 15 days interval. Cumulative soil CO2-C emission was calculated on basis of soil CO2 efflux values obtained. T9-(F-F-F) emitted maximum CO2-C in both cropping years, 21.57 Mg C ha−1 and 24.28 Mg C ha−1 in first and second year, respectively. Within cropping systems, maximum was emitted by T1-(B-W-C) and T7-(B-Pe-C). T1 (13.64 Mg C ha−1) and T7 (13.48 Mg C ha−1) in first cropping year while in second cropping year both these cropping systems (T1 and T7) emitted 15.82 Mg C ha−1. Minimum soil CO2-C in both the cropping years was emitted from cropping system T4-(B-P-M) (10.66 Mg C ha−1 and 12.74 Mg C ha−1). Crop residue of the previous crop returned back to soil had significant effect on soil CO2 efflux. Soil CO2-C emission of all treatments (T1-T9) was found to increase with subsequent cropping year. Simple linear regression analysis was performed to elucidate the correlation between soil CO2 efflux, temperature and moisture in all the seasons (rainy, winter and summer). In each season, the soil CO2 efflux was positively correlated to soil temperature and negatively correlated with soil moisture in both the cropping years. Aromatic crops based diversified cropping systems along with residue retention did not decrease the soil CO2-C emission but showed less emission compared to fallow soil.

Biochar–manure changes soil carbon mineralization in a Gray Luvisol used for agricultural production

Biochar is a source of stable organic matter being explored as a manure additive. A 64 d incubation experiment was conducted to quantify the short-term effect of manure (RM), biochar–manure (BM), raw biochar (BC), RM + BC, and BM + BC amendment on soil carbon (C) and nitrogen (N) mineralization. Manure increased CO2-C emission rates, with the highest cumulative CO2-C emissions being observed for RM + BC. Treatments with BM halted soil C mineralization, indicating manure-C stabilization. By contrast, neither RM nor BM affected soil N mineralization. Applying BM might benefit soil C sequestration by lowering CO2-C emissions over the long term.

Nutrient retention, availability and greenhouse gas emissions from biochar-fertilized Chernozems

Amending soil with pyrogenic-C (biochar) has emerged as a potential best management practice to accumulate organic matter (OM), reduce greenhouse gas (GHG) emissions and increase nutrient retention among degraded, marginally-productive croplands. Nevertheless, the impact of biochar application on intensively cropped prairie eco-regions is not well documented, particularly when co-applied with chemical fertilizer. Our objective was to determine the effect of biochar on cumulative CO2-C, N2O-N and CH4-C emissions, water-extractable OM, and available N (AN; NH4-N + NO3-N) and P (AP; PO4-P) in the presence or absence of NP-fertilizer. Biochar was applied to two surface Chernozems (0–15 cm) of contrasting texture [i.e., sandy clay loam (Raymond) and clayey (Lethbridge)] at six rates (0, 0.15, 0.5, 3, 10 and 20 Mg ha−1) in combination with (+NP) or without (−NP) urea-N (150 kg N ha−1) and KH2PO4 (50 kg P ha−1). A total of 72 soil columns were incubated at 21 °C for 86 d. Biochar addition increased soil total C up to 24.9 g kg−1 and 28.7 g kg−1 in Raymond and Lethbridge, respectively, but did not affect water-extractable OM. Cumulative N2O-N and CH4-C emissions were not influenced by biochar, regardless of whether or not NP-fertilizer was added (p > 0.05). Cumulative CO2-C emissions varied between soil textures and were increased or decreased non-linearly by biochar addition under –NP only. Available P increased within +NP soil with increasing biochar rates reaching 43.9 mg kg−1 in Raymond and 79.5 mg kg−1 in Lethbridge when biochar was applied at 20 Mg ha−1. A similar but less pronounced response was observed for AN. Our results indicate that biochar-only application is not a practical management approach for improving soil fertility and nutrient cycling in surface Chernozems. Nevertheless, co-applying biochar with NP-fertilizer appears to improve soil P availability in the short-term.

Impact of biochar water extract addition on soil organic carbon mineralization and C fractions in different tillage systems

The role of biochar has been identified in soil organic carbon (SOC) mineralization, but the role of dissolved organic carbon (DOC) derived from biochar water extract (BE) is not well recognized. Therefore, rotary tillage (RT) and no-tillage (NT) with two moisturizers treatments; BE and distilled water (WA) were used to study the influence of DOC (through BE) on SOC mineralization and C fractions. Four soil sampling depths (0–10, 10–20, 20–30, 30–50 cm) were used for laboratory incubation. The results showed a significant increase in cumulative CO2-C emissions in upper soil that decreased with increase in soil depth. BE increased cumulative CO2-C emissions about 50% and 46% (0–10 cm), 45% and 26% (10–20 cm), 42% and 55% (20–30 cm), 16% and 43% (30–50 cm) than WA in NT and RT, respectively. Moreover, NT had 13% more cumulative CO2-C emissions than RT at 0–10 cm, but RT had 10% and 38% higher cumulative CO2-C emissions than NT at 10–20 and 20–30 cm soil depths, respectively. BE increased microbial quotient (Mq) almost 47%, 70%, 24% and 167% at 0–10, 10–20, 20–30 and 30–50 cm soil depths, respectively. Increase in Mq significantly decreased SOC and some carbon fractions. Notably, BE did not modify DOC in whole soil profile under both tillage systems. BE had significant higher MBC at 30–50 cm soil depth than WA in both tillage systems. RT had significant higher (4%) MBC than NT at 20–30 cm soil depth. Overall, addition of DOC from BE in soil enhances C mineralization by modifying Mq.

Regulation of soil aggregate size under different fertilizations on dissolved organic matter, cellobiose hydrolyzing microbial community and their roles in organic matter mineralization

The mineralization of soil organic matter is closely related to climate change. Labile organic matter and microbial community are vital intrinsic factors in controlling the mineralization of soil organic matter. Regulation of soil aggregate size on dissolved organic matter (DOM), the cellobiose hydrolyzing microbial community, and their roles in organic matter mineralization remains unclear. The mineralization of organic matter in large macroaggregates (LMA, >2 mm), small macroaggregates (SMA, 0.25–2 mm), and microaggregates (MI, <0.25 mm) from an Ultisol treated with long-term non-fertilizers (Ck), chemical fertilizers (NPK) and animal manure (AM) was observed in this study. The concentration and structure of DOM, activity of β-glucosidase, and the abundance, diversity, and community composition of GH1 (glycoside hydrolase family 1) microbial β-glucosidase encoding genes were investigated. The cumulative CO2-C emissions occurred in the order LMA < SMA < MI in each fertilization treatment and followed the sequence Ck < NPK < AM in each size of aggregate. The concentration of DOM in the soil aggregates increased as the aggregate size decreased, while the structural complexity of DOM followed the opposite trend. The activity of β-glucosidase in the smaller aggregates was higher than that in the larger aggregates, and the abundance and diversity of the GH1 microbial β-glucosidase genes generally echoed the same trend. The dominant microbial classes harboring GH1 β-glucosidase genes in the soil aggregates were Actinobacteria, Alphaproteobacteria, Gammaproteobacteria, Flavobacteria, Eurotiomycetes, and Sordariomycetes. The relative abundance of Actinobacteria, Sordariomycetes, and Eurotiomycetes revealed significant differences among the aggregates. Redundancy analysis confirmed that microbial GH1 β-glucosidase community in the soil aggregates was primarily regulated by DOM concentration and pH. Structural equation modelling revealed that soil aggregates mainly regulated the β-glucosidase activity and DOM concentration and then the abundance and diversity of the GH1 microbial β-glucosidase genes in controlling organic matter mineralization.

Effect of long-term fertilization on decomposition of crop residues and their incorporation into microbial communities of 6-year stored soils

To investigate the effects of long-term fertilization on microbial decomposition of residues and priming effect (PE), 13C-labeled maize (Zea mays L.) residues were supplied to arable soils with a 20-year application of compost (COM), mineral NPK fertilizer (NPK), or without any treatments, the no-fertilizer control (NF). The soils that had been stored for 6 years were used in the present incubation experiment. The release of CO2–C and the microbial incorporation of residue-derived C determined by phospholipid fatty acids (PLFAs) analysis were monitored over a 90-day incubation period. Residue additions significantly increased cumulative CO2–C emission and induced positive PE. Cumulative residue-derived CO2-C emission and PE mainly occurred within the first 15 days. The COM soil had significantly higher cumulative residue-derived CO2–C emission but lower PE than the NF and NPK soils. Residue additions significantly increased microbial abundance and changed the composition of main microbial groups. The COM soil showed a significantly lower relative fungal abundance (mol%) but a higher relative actinomycetes abundance than the NF and NPK soils. The incorporation of residue-derived C within fungi was the highest among all the main microbial groups and decreased from 15 to 45 days, while the incorporation of residue-derived C within actinomycetes increased with time in three soils. The incorporation of residue-derived C within fungi was the highest in the COM soil over the course of incubation. The long-term compost input promoted fungal use of residue C and stimulated residue decomposition.

Dynamics of soil organic carbon mineralization and C fractions in paddy soil on application of rice husk biochar

Biochar plays a pivotal role in carbon storage-fractionation-mineralization process in soil. However, uncertainty still remains about the influence of biochar on these inter-related processes that links to C cycling in soil. A three years field experiment was initiated in 2013 at ICAR-National Rice Research Institute, Cuttack, India, to study the deviation in C mineralization and C fractions caused by the application of six doses of rice husk derived biochar (RHB), ranging from 0.5 t ha−1 to 10.0 t ha−1. The results showed an increase in cumulative CO2-C emission with increasing RHB rates. However, the model-fitted mineralization rates (dC/dt) did not show significant difference between treated and control soils at the end of incubation period in a laboratory study. In addition, microbial quotient and % C from RHB utilized showed a decreasing trend with increasing rates of RHB application, establishing the carbon sequestration potential of RHB. The highest rate (10.0 t ha−1) of RHB application accumulated maximum total organic C (3.26%) and a larger share of non-labile C (63.8%) among the treatments. An increase in rice grain yield (1–24%, depending on rate of RHB application) was observed with increasing rates of RHB which further established that RHB application not only enhanced C storage but also enhanced the productivity of rice by enhancing the soil fertility.

Impacts of earthworm activity on the fate of straw carbon in soil: a microcosm experiment.

Earthworms not only facilitate carbon (C) stabilization, but also accelerate organic matter mineralization by enhancing microbial respiration. However, the fate (mineralization vs stabilization) of newly added C by straw returning in arable lands with earthworm activity is still unclear. In the present 40days incubation study, we incorporated artificially 13C-labeled straw into soil with and without presence of earthworms (Metaphire guillelmi). Flux measurements of CO2 from soil (mineralization) were taken regularly, while straw-derived C remaining in the soil (stabilization) was measured at the end of the incubation. There was no significant difference of the cumulative CO2 emission between earthworm presence and absence treatment. However, earthworm presence significantly decreased straw-derived cumulative CO2-C emission when compared with the treatment without earthworm. Besides, earthworm incubation led to a significantly low light fraction organic carbon (LFOC) content and straw-derived LFOC proportion. Relative to the non-earthworm treatment, straw-derived C content significantly decreased in micro-aggregates (< 0.25mm), but increased in large macro-aggregates (> 2mm) in the earthworm treatment. In total, only 3.8% of added straw C was assimilated by earthworm within 40days, while most of the straw C remained in the soil. Earthworms decreased straw-derived CO2-C emission from 10.0 to 8.1% when compared with the non-earthworm treatment. In the present short period incubation experiment, compared with the soil without earthworms, the presence of Metaphire guillelmi (1) resulted a higher soil CO2 emissions, which may mainly evolved from the older SOC, and (2) stabilized more residue-derived C in the soil aggregates. We therefore propose that Metaphire guillelmi may increase soil organic carbon pool turnover rates in the short term after straw returning by replacement of older SOC with newly added straw C.

In Situ Persistence and Migration of Biochar Carbon and Its Impact on Native Carbon Emission in Contrasting Soils under Managed Temperate Pastures.

Pyrogenic carbon (PyC) is an important component of the global soil carbon (C) pool, but its fate, persistence, and loss dynamics in contrasting soils and environments under planted field conditions are poorly understood. To fill this knowledge gap, a 13C-labelled biochar, as a surrogate material for PyC, produced from Eucalyptus saligna by slow pyrolysis (450°C; δ13C -36.7‰) was surface (0−10 cm) applied in C3 dominated temperate pasture systems across Arenosol, Cambisol and Ferralsol. The results show a low proportion of the applied biochar-C mineralised over 12 months in a relatively clay- and C-poor Arenosol (i.e., 2.0% loss via mineralisation), followed by a clay- and C-rich Cambisol (4.6%), and clay-, C- and earthworm-rich Ferralsol (7.0%). The biochar-C mean residence time (MRT), estimated by different models, varied between 44−1079 (Arenosol), 18−172 (Cambisol), and 11−29 (Ferralsol) years, with the shorter MRT estimated by a one-pool exponential and the longer MRT by an infinite-pool power or a two-pool exponential model. The two-pool model was best fitted to biochar-C mineralisation. The biochar-C recovery in the 12−30 cm soil layer varied from between 1.2% (Arenosol), 2.5−2.7% (Cambisol) and 13.8−15.7% (Ferralsol) of the applied biochar-C after 8−12 months. There was a further migration of biochar-C below the 50-cm depth in the Arenosol, as the combined biochar-C recovery in the mineralised pool and soil profile (up to 30 or 50 cm) was 82%, in contrast to 101% in the Cambisol and 104% in the Ferralsol after 12 months. These results indicate that the downward migration of biochar-C was greatest in the Arenosol (cf. Cambisol and Ferralsol). Cumulative CO2-C emission from native soil-plant sources was lower (p <0.10) in the biochar-amended vs. non-amended Ferralsol. This field-based study shows that the downward migration of biochar-C exceeded its loss via mineralisation in the Arenosol and Ferralsol, but not in the Cambisol. It is thus important to understand biochar-soil interactions to maximise long-term biochar C sequestration potential in planted soil systems.

Effects of soluble organic carbon addition on CH4 and CO2 emissions from paddy soils regulated by iron reduction processes

An incubation experiment with the addition of glucose was conducted to evaluate the effects of carbon and iron (Fe(III)) reduction on methane (CH4) and carbon dioxide (CO2) emissions from paddy soils. Soils of a rice–rapeseed (Brassica napus) rotation and rice–fallow/flooded rotation were collected from Qianjiang (QR and QF, respectively) and Xianning (XR and XF). Incubation was conducted under flooding at 25°C ± 1°C with or without (CK) glucose over 40 days. With glucose addition, cumulative CH4-C emissions from QR, QF, XR and XF soils were 5.31, 35.26, 13.92 and 27.58 mg kg–1, respectively, and cumulative CO2-C emissions were 594.33, 620.49, 549.42 and 792.46 mg kg–1. Compared with CK, glucose addition significantly (P &lt; 0.05) increased cumulative CH4 fluxes in QR and QF soils 11.07-fold and 1.39-fold, respectively, and cumulative CO2 fluxes 0.41-fold and 0.44-fold, whereas the effects of glucose addition on CH4 and CO2 fluxes in XR and XF soils were negligible. In addition, the soil Fe(II)/(Fe(II) + Fe(III)) fraction correlated positively with CH4 fluxes during the major emission period (P &lt; 0.05), and the Fe(II) production rate was positively correlated with the CO2 flux during the whole incubation period. Furthermore, Fe(III) reduction strongly competed with CH4 emission, especially in XR and XF soils, which derived from quaternary red clay. The results suggest that Fe(III) reduction plays a key role in mediating the carbon cycle of paddy soils.

Dynamics of CO2 Emission and Biochemical Properties of a Sandy Calcareous Soil Amended with Conocarpus Waste and Biochar

ABSTRACT Biochar is a carbon-rich product obtained by biomass pyrolysis and considered a mean of carbon sequestration. In this research, a sandy calcareous soil from the Farm of the College of Food & Agriculture Sciences, King Saud University, Saudi Arabia, was amended with either woody waste of Conocarpus erectus L. (CW) or the biochar (BC) produced from CW at rates of 0 (control), 10, 30 and 50 g kg−1. The effects of the amendments on soil pH, dissolved organic carbon (DOC), microbial biomass carbon (MBC), CO2 emission and metabolic quotient (qCO2) of the sandy calcareous soil were studied in a 60-d incubation experiment. The results showed that the addition of CW led to a significant decrease in soil pH compared to the control and the addition of BC. The CO2-C emission rate was higher in the first few days of incubation than when the incubation time progressed. The cumulative CO2-C emission from the soil amended with CW, especially at higher rates, was higher (approximately 3- to 6-fold) than that from the control and the soil amended with BC. The BC-amended soil showed significant increases in CO2-C emission rate during the first days of incubation as compared to the non-amended soil, but the increase in cumulative CO2-C emission was not significant after 60 d of incubation. On the other hand, CW applications resulted in considerably higher cumulative CO2-C emission, MBC and DOC than the control and BC applications. With the exception of 0 day (after 1 h of incubation), both CW and BC applications led to lower values of qCO2 as compared to the control. The power function kinetic model satisfactorily described the cumulative CO2-C emission. Generally, the lowest values of CO2 emission were observed in the soil with BC, suggesting that the contribution of BC to CO2 emission was very small as compared to that of CW.

Long Term Effect of Land Reclamation from Lake on Chemical Composition of Soil Organic Matter and Its Mineralization

Since the late 1950s, land reclamation from lakes has been a common human disturbance to ecosystems in China. It has greatly diminished the lake area, and altered natural ecological succession. However, little is known about its impact on the carbon (C) cycle. We conducted an experiment to examine the variations of chemical properties of dissolved organic matter (DOM) and C mineralization under four land uses, i.e. coniferous forest (CF), evergreen broadleaf forest (EBF), bamboo forest (BF) and cropland (CL) in a reclaimed land area from Taihu Lake. Soils and lake sediments (LS) were incubated for 360 days in the laboratory and the CO2 evolution from each soil during the incubation was fit to a double exponential model. The DOM was analyzed at the beginning and end of the incubation using UV and fluorescence spectroscopy to understand the relationships between DOM chemistry and C mineralization. The C mineralization in our study was influenced by the land use with different vegetation and management. The greatest cumulative CO2-C emission was observed in BF soil at 0–10 cm depth. The active C pool in EBF at 10–25 cm had longer (62 days) mean residence time (MRT). LS showed the highest cumulative CO2-C and shortest MRT comparing with the terrestrial soils. The carbohydrates in DOM were positively correlated with CO2-C evolution and negatively correlated to phenols in the forest soils. Cropland was consistently an outlier in relationships between DOM chemistry and CO2-evolution, highlighting the unique effects that this land use on soil C cycling, which may be attributed the tillage practices. Our results suggest that C mineralization is closely related to the chemical composition of DOM and sensitive to its variation. Conversion of an aquatic ecosystem into a terrestrial ecosystem may alter the chemical structure of DOM, and then influences soil C mineralization.

Effect of mono- and divalent cations on sorption of water-extractable organic carbon and microbial activity

Sorption is an important process for retention of organic carbon (C) in soils. The effect of Na+ and Ca2+ on sorption of organic C has been studied in salt-affected soils, but little is known about the effect of K+ and Mg2+ ions on sorption of water-extractable organic C (WEOC). The effect of Na+, K+, Ca2+ and Mg2+ ions on sorption of WEOC and its decomposition were investigated in a loamy sand (7.5 % clay) and a sandy clay loam (34.4 % clay). Salinity was developed with NaCl, KCl, MgCl2 or CaCl2 to obtain different concentrations of exchangeable Na+, K+, Ca2+ and Mg2+ at an electrical conductivity in a 1:5 soil/water extract (EC1:5) of 1 dS m−1. Water-extractable organic C was derived from wheat straw, and microbial activity after sorption was quantified by measuring CO2 emission from the soils for 27 days. The concentration of sorbed C was higher in the sandy clay loam than in the loamy sand and decreased in the treatment order Ca2+ > Mg2+ > K+ > Na+, but cumulative CO2-C emission after sorption was highest from the Na+ and lowest from the Ca2+ treatments. The strong binding in the Ca2+ and Mg2+ treatments can be explained by the low zeta potential and the high covalency index of cation binding with C, whereas zeta potential was high and the covalency index was low in the Na+ treatments. Although K+ is also monovalent, WEOC was more strongly bound in the K+ than in the Na+ treatment. The weak binding with Na increased the accessibility of the sorbed C to soil microbes and, thus, microbial activity. Our results suggest that monovalent cations may enhance decomposition and leaching of WEOC in saline soils with Na+ having a greater effect than K+. Divalent cations, particularly Ca2+, enhance the binding of organic matter and thus organic C stabilization, whereas Mg2+ ions have a smaller effect.