Easily Oxidizable Carbon Research Articles

Comparing the Effects of Biochar and Straw Amendment on Soil Carbon Pools and Bacterial Community Structure in Degraded Soil

The degradation of soil often occurs due to the depletion of organic matter. Both biochar and straw have value as two primary means of remediating soil. In this study, we compared the effects of biochar and straw on soil organic carbon pools and on microbial communities in degraded soil. We added straw (maize) and biochar (maize-derived) to the degraded soil at the ratios of total soil weight (0, 1, 2, or 4%), respectively. Soil samples were collected after 180 days. We determined that upon straw addition, there was an increase in microbial biomass carbon (MBC), dissolved organic carbon (DOC), and easily oxidizable carbon (EOC). Upon biochar addition, there was an increase in soil total organic carbon and recalcitrant organic carbon. Analysis of bacterial community was conducted via 16SrDNA sequencing with an Illumina MiSeq platform and revealed that the relative abundance of Actinobacteria increased, but the Bacteroidetes and Chloroflexi decreased with straw addition. We further found that the addition of straw altered the Shannon and Simpson diversity index values, whereas biochar did not impact soil bacterial diversity. Nonmetric multidimensional scaling and canonical correspondence analyses revealed that bacterial community structure was influenced by both biochar and straw addition. Mantel testing further revealed that this community structure was associated with soil EOC (r = 0.286, P = 0.001), DOC (r = 0.174, P = 0.002), and MBC (r = 0.299, P = 0.002) upon straw treatments. These results suggested that straw can improve soil labile organic carbon pools and soil bacterial communities better than biochar, whereas biochar (via pyrolysis at 550 °C, for 2 h) can improve carbon sequestration better than straw in degraded soil.

Long-term tillage and straw returning effects on organic C fractions and chemical composition of SOC in rice-rape cropping system

ABSTRACTUnderstanding the different C pools and chemical composition of soil organic carbon (SOC) in cropping system is imperative for sustaining soil quality. This study examined the effects of tillage and straw returning practices on organic C fractions and chemical composition of SOC under a rice-rape system in central China. The field experiment consisted of conventional tillage (CT); conventional tillage with straw returning (CTS); no-tillage (NT); and no-tillage with straw returning (NTS) treatments. Compared to CT, NT significantly increased SOC stocks, SCMI and C fractions of 0–20 cm depth by 6–50%. The SOC, particulate organic carbon (POC), microbial biomass carbon (MBC), easily oxidizable carbon (EOC), dissolved organic carbon (DOC) contents of 0–20 cm depth were 16, 80, 24, 22 and 13%, respectively, higher under NTS treatment. Straw returning enhanced the relative contents of O-alkyl C, carbonyl C, alkyl C, A/O-A ratio, and aromaticity. The correlations of SOC with C fractions and SCMI were significant. O-alkyl C was positively correlated with C fractions and negatively correlated with carbonyl C and alkyl C. In conclusion, long-term tillage and straw returning significantly affected the fractions and chemical compositions of SOC, could be viable option for improving the soil quality in the rice-rape rotation system.

Labile organic carbon fractions and carbon pool management index in a 3-year field study with biochar amendment

The aims of this research were to (i) systematically investigate the soil organic carbon (SOC) and labile SOC fraction dynamics over a period of 3 years under biochar amendment, (ii) reveal the relations of labile SOC fractions to SOC, and (iii) evaluate the sensitivity of SOC to biochar added at different rates by determining C pool management index (CPMI). The SOC, labile SOC fractions, and the CPMI in the 0–20-cm layer were analyzed via a 3-year field experiment of maize. Four biochar treatments were studied, with application rates of 0, 15.75, 31.5, and 47.25 t ha−1 (CK, BC1, BC2, and BC3, respectively). Biochar was applied manually before sowing only in the first year of this experiment; an equal mineral NPK fertilizer was applied to each treatment annually. The average data of this 3-year field study demonstrated that biochar incorporation significantly increased SOC, particulate organic carbon (POC), easily oxidizable carbon (EOC), light fraction organic carbon (LFOC), and microbial biomass carbon (MBC) by 31.75–83.62, 92.72–323.30, 29.90–51.55, 194.30–437.37, and 31.13–93.12%, respectively, compared to the control; their concentrations increased with increasing biochar addition rates, except for MBC. In addition, EOC, POC, and LFOC were significantly positively related with SOC. Compared to the control, the DOC contents were reduced after biochar addition, but the specific reasons for this finding need to be further studied. Biochar incorporation could not only significantly improve the soil quality via increasing the soil organic C fractions, but also increase C sequestration rates in the long term by increasing the non-labile C pool (NLC). The CPMI could be used as a representative index in evaluating the impacts of biochar on SOC content and soil quality.

Changes in Soil Organic Carbon Dynamics in a Native C4 Plant-Dominated Tidal Marsh Following Spartina alterniflora Invasion

AbstractInvasion of an exotic C4 plant Spartina alterniflora has been shown to increase soil organic carbon (SOC) concentrations in native C3 plant-dominated coastal wetlands of China. However, little is known about the effects of S. alterniflora invasion on SOC concentrations and fractions in tidal marshes dominated by native C4 plants. In this study, a field experiment was conducted in a tidal marsh dominated by the native C4 plant Cyperus malaccensis in the Minjiang River estuary, China. Concentrations of SOC and liable SOC fractions, dissolved organic carbon (DOC), microbial biomass carbon (MBC), and easily oxidizable carbon (EOC), were measured in the top 50-cm soils of the C. malaccensis community, as well as those of three S. alterniflora communities with an invasion duration of 0–4 years (SA-4), 4–8 years (SA-8), and 8–12 years (SA-12), respectively. Results showed that both SOC stocks in the 50-cm soils and mean SOC concentrations in the surface soils (0–10 cm) of the C. malaccensis community increased with the duration of S. alterniflora invasion, whereas SOC concentrations in the 10–50-cm soils decreased slightly during the initial period of S. alterniflora invasion, before increasing again. The pattern of changes in labile SOC fractions (DOC, MBC, and EOC) with invasion duration was generally similar to that of SOC, while the ratios of labile SOC fractions to total SOC (DOC:SOC, MBC:SOC, and EOC:SOC) decreased significantly with the duration of S. alterniflora invasion. The findings of this study suggest that invasion of the exotic C4 plant S. alterniflora into a marsh dominated by the native C4 plant C. malaccensis would enhance SOC sequestration owing to the greater amount of biomass and lower proportion of labile SOC fractions present in the S. alterniflora communities.

Effects of maize stover and its biochar on soil CO2 emissions and labile organic carbon fractions in Northeast China

Soil labile organic carbon pools are sensitive indicators of soil quality, early changes in soil organic carbon (SOC) stocks, and effects of different soil tillage practices. Impacts of atmospheric greenhouse gas (GHG) emissions on the global climate have encouraged the search for effective alternative methods to promote sustainable agriculture and mitigate climate change. We measured soil CO2 emissions and dissolved organic carbon (DOC), easily oxidizable carbon (EOC), light fraction organic carbon (LFOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) in maize (Zea mays L.) fields treated with maize stover and a maize stover-derived biochar amendment during three consecutive maize growing seasons in a brown earth in Shenyang, China. We considered the following three treatments: CK (application of mineral NPK fertilizer; 120kgNha−1, 60kgP2O5ha−1, and 60kgK2Oha−1), ST (maize stover application; 7.5tha−1), and BC (7.5tha−1 of maize stover was charred, with a yield of 35% of the original biomass; 2.63tha−1). Both ST and BC treatments received the same fertilization as CK. Mean data of the three-year experiment indicated that the CO2 emissions of ST and BC were significantly higher than CK by 129.7% and 24.4%, respectively. In both ST and BC treatments, SOC and labile organic C fractions were increased. The sensitivities of each labile organic C fraction varied with different treatments. Soil CO2 emissions under biochar addition were significantly lower than that of stover incorporation. Overall, biochar application was a more effective practice based on the comprehensive consideration of improving soil quality and with regard to CO2 mitigation in the experiment.

Labile Organic Carbon Fractions, Regulator of CO2 Emission: Effect of Plant Residues and Water Regimes

The soil organic carbon (C) pool is the largest among the terrestrial C pools, and plays a vital role in the exchange of CO2. The increase in CO2 emission from soil to atmosphere has raised concerns about potential global warming. The current study was conducted with the objectives to investigate the relationship between labile organic C fractions and CO2 fluxes in an Alfisol soil treated with green manure (GM) and wheat straw (WS), and moisture regimes namely, W1 (50%) and W2 (100%). The incorporation of GM and WS increased (p < 0.05) the CO2 emission and labile C fractions under both water regimes. The CO2 fluxes showed positive correlation with all measured soil labile organic C fractions, i.e., total organic carbon (TOC), light fraction of organic carbon (LFOC), particulate organic carbon (POC), easily oxidizable carbon (EOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), reducing sugar carbon (RSC), and readily mineralizable carbon (RMC). The overall effect of labile C fractions on the CO2 emission was in the order LFOC > POC > EOC > DOC > MBC > RSC > RMC > TOC. The results demonstrated that LFOC, POC, EOC, DOC, MBC, RSC, and RMC had higher effects on CO2 fluxes as compared to TOC. The LFOC was more suitable and sensitive indicator than POC, EOC, DOC, MBC, WSC, RMC, and RSC for CO2 emissions and change in the soil organic C status.

Soil labile organic carbon and carbon-cycle enzyme activities under different thinning intensities in Chinese fir plantations

Thinning is a silvicultural tool that is used to facilitate the growth of timber plantations worldwide. Plantations are important CO2 sinks, but the mechanism by which thinning affects the quantity and stability of soil organic carbon (SOC) is poorly understood. In this study, we examined the effects of different thinning intensities (low-intensity thinning treatment with 30% of the trees removed; high-intensity thinning treatment with 70% of the trees removed; control treatment without tree removal) on the quantity and stability of SOC in Chinese fir (Cunninghamia lanceolata [Lamb.] Hook) plantations in southeastern China. The amounts of SOC, microbial biomass carbon (MBC), easily oxidizable carbon (EOC), cold-water- soluble organic carbon (CWSOC) and hot-water- extractable organic carbon (HWEOC) and the carbon-cycle-related enzyme activities (β-glucosidase, invertase and cellulose) were quantified. We found that thinning significantly decreased the amount of SOC compared with the control treatment, but the effect differed by sampling date. The MBC and EOC were significantly higher in the high-intensity thinning treatment than in the control and low-intensity thinning treatments, whereas the invertase and β-glucosidase activities were significantly higher in the control treatment. However, the amounts of CWSOC, HWEOC and cellulose activity did not differ among the treatments, which indicates that the MBC, EOC and the activities of invertase and β-glucosidase were better indicators of changes in SOC to thinning. In addition, the MBC, EOC, CWSOC and the β-glucosidase and cellulase activities peaked in the warmer months. Our results indicate that thinning treatments in Chinese fir plantations decreased the SOC quantity and enzyme activities and that high-intensity thinning may lead to an increase of labile SOC.

Organic carbon and its fractions in paddy soil as affected by different nutrient and water regimes

As an essential indicator of soil quality, soil organic carbon (SOC) and its fractions play an important role in many soil chemical, physical, and biological properties. A 4-year field experiment was conducted to determine the effects of different nutrient and water regimes on paddy soil organic carbon quality by measuring the major SOC fractions. Four nutrient regimes were compared: (i) control; (ii) chemical fertilizers only (CF), (iii) combined application of chemical fertilizers with farmyard manure (FYM) (CM), and (iv) combined application of chemical fertilizers and wheat straw (CS). Two soil water regimes included continuous waterlogging (CWL) and alternate wetting and drying (AWD). The total organic carbon (TOC) and total nitrogen (TN) in paddy soil were 40–60% and 37–67% higher in the combined organic sources and chemical fertilizers treatment against the sole chemical fertilizers treatment (CF), especially under continuous waterlogging (CWL). By fractionalizing SOC, it was observed that, under the water regimes of CWL, easily oxidizable carbon (EOC), particulate organic carbon (POC), light fraction organic carbon (LFOC), microbial biomass carbon (MBC), and mineralizable organic carbon (MNC) in the organically treated paddy soil were significantly ( P<0.05) lower, as compared with alternate wetting and drying (AWD). Especially for CM treatment, EOC, POC, LFOC, MBC, and MNC in the paddy soils under the regime of CWL were 23.5%, 32.7%, 16.3%, 56.8% and 25.1% lower than those by AWD, respectively. The proportions of EOC, POC, LFOC, MBC and MNC as a percent of TOC in the CWL were lower than those in the AWD, especially for the CM treatment. In the water regime of CWL, no significant differences were seen in the corresponding proportion of all the investigated organic fractions to soil total organic carbon (TOC) among the three fertilization treatments, whereas in the AWD, the corresponding proportions of different carbon fractions to TOC in the organic fertilizer treatments were significantly ( P<0.05) higher than those in the chemical fertilizer treatment. Under continuous waterlogging, the proportion of soil water stable aggregate >250 μm (WSA) decreased by 42–45% and clay dispersion ratio ( R CD) increased by 12–38%, as compared to the water regimes of AWD, when FYM or wheat straw was incorporated into paddy soil. Correlation analysis showed that, under the water regimes of AWD, WSA was significantly and positively related to EOC, LFOC and POC with the coefficients ( r) of 0.822, 0.889, 0.912 ( P<0.01), respectively. R CD was negatively correlated to EOC, LFOC and POC with the r=−0.796, −0.854, and −0.897 ( P<0.01), respectively, under AWD. Under the water regimes of CWL, there were no significant ( P<0.05) correlations between WSA as well as R CD and any organic carbon fraction except POC.