Measurements Of CO2 Evolution Research Articles

Development of two devices for high-throughput screening of ethanol-producing microorganisms by real-time CO2 production monitoring.

Bioethanol's importance as a renewable energy carrier led to the development of new devices for the high-throughput screening (HTS) of ethanol-producing microorganisms, monitoring ethanol production, and process optimization. This study developed two devices based on measuring CO2 evolution (an equimolar byproduct of microbial ethanol fermentation) to allow for a fast and robust HTS of ethanol-producing microorganisms for industrial purposes. First, a pH-based system for identifying ethanol producers (Ethanol-HTS) was established in a 96-well plate format where CO2 emission is captured by a 3D-printed silicone lid and transferred from the fermentation well to a reagent containing bromothymol blue as a pH indicator. Second, a self-made CO2 flow meter (CFM) was developed as a lab-scale tool for real-time quantification of ethanol production. This CFM contains four chambers to simultaneously apply different fermentation treatments while LCD and serial ports allow fast and easy data transfer. Applying ethanol-HTS with various yeast concentrations and yeast strains displayed different colors, from dark blue to dark and light green, based on the amount of carbonic acid formed. The results of the CFM device revealed a fermentation profile. The curve of CO2 production flow among six replications showed the same pattern in all batches. The comparison of final ethanol concentrations calculated based on CO2 flow by the CFM device with the GC analysis showed 3% difference which is not significant. Data validation of both devices demonstrated their applicability for screening novel bioethanol-producer strains, determining carbohydrate fermentation profiles, and monitoring ethanol production in real time.

Evaluation on maturity and stability of organic fertilisers in semi-arid Ethiopian Rift Valley

Case studies that have comprehensively examined local organic fertilisers (OFs) for their maturity and stability are rare in sub-Saharan Africa. Farmers in the semi-arid Ethiopian Rift Valley use indigenous compost (kosi) and household wastes for OFs. With the entry of fast compost that was introduced by the administration, maturity and stability of these OFs were assessed. Their maturity was assessed by: monitoring pile temperature and volume, pH, organic matter and total nitrogen contents, and carbon to nitrogen ratio; determination of NO3– to NH4+ ratio; and respirometric measurement of CO2 evolution. Their stability was assessed by weed seed germination tests and phytotoxicity bioassays. Weed seeds that were originally contained in the feedstock of the kosi and fast compost samples became inactive during the composting process. The CO2 evolution tests and phytotoxicity bioassays indicated a probable presence of some phytotoxic compounds in the kosi. Mature kosi and immature kosi in a kosi pile should be mixed before the field application. Some samples (15%) of the household wastes contained weed seeds. The combination of several assessment methods used in this study and determination methods for nitrogen components using RQ-flex is considered to be effective for on-site quality assessment of OFs in sub-Saharan Africa.

Evaluation of microbial shifts caused by a silver nanomaterial: comparison of four test systems

BackgroundBefore chemicals, pesticides and biocides are registered and approved, their effects on soil microorganisms must be tested, specifically their impact on nitrogen transformation. Following a request from the European Food Safety Authority (EFSA), the Panel on Plant Protection Products and their Residues provided an opinion document evaluating the science behind the risk assessment of plant protection products in the context of soil-dwelling organisms. The EFSA document concludes that the most relevant community-based microbial test systems should cover the widest possible range of metabolic processes without compromising test sensitivity. The EFSA document refers to the MicroResp test system, stating that although it has not been used to study the effects of pesticides on soil microbial processes, its capability should be investigated in the future. In the scope of harmonization approaches, the recommendations in the EFSA document covering pesticides could also influence the risk assessment and regulation of other kinds of chemicals, including silver nanomaterials. We therefore used the silver nanomaterial NM-300K as a model substance to evaluate the sensitivity of three functional tests covering the activities of different microbial fractions: (1) the potential ammonium oxidation (PAO) test, which considers the first step in nitrification; (2) the MicroResp test, which determines respiratory activity by measuring CO2 evolution; and (3) a colorimetric test system for exoenzyme activity. We also surveyed bacterial 16S rRNA sequence diversity by next-generation sequencing (NGS).ResultsThere was no major difference in the general sensitivity of the tests, each of which revealed significant effects at silver nanomaterial concentrations of at least 1.67 mg/kg. The PAO test was a robust and sensitive indicator of toxicity, and concentration–effect relationships were calculated for every time interval. The effects on respiration and exoenzyme activities were more variable. Among the three functional tests, the selected exoenzyme activities showed the weakest concentration–effect relationships, although silver concentrations were clearly related to two of the four activities we tested (glucosidase and arylsulfatase). We also observed a relationship between silver concentrations and respiration activity on glucose, cellobiose and alanine substrates. The bacterial orders identified by NGS differed in sensitivity to the silver nanomaterial. We found that the adverse impact on nitrifiers matched the inhibition of PAO activity. EC50 values calculated for each functional test did not identify a generally superior method.ConclusionWe found that all four test approaches were similar in sensitivity towards the model silver nanomaterial, an ion-releasing substance. We observed advantages and limitations for each test, which must be considered when selecting tests for the registration or approval of substances. It is unclear whether the sensitivity of the tests would be comparable when testing substances that do not release ions. The regulatory assessment of metabolic profiles requires further consideration in terms of substrate selection. Finally, for tests performed in multiwell plates with small quantities of soil, the quality of the concentration–effect relationships must be studied in more detail.

Short Term CO2 Enrichment Increases Carbon Sequestration of Air-Exposed Intertidal Communities of a Coastal Lagoon

In-situ production responses of air-exposed intertidal communities under CO2 enrichment are reported here for the first time. We assessed the short-term effects of CO2 on the light responses of the net community production (NCP) and community respiration (CR) of intertidal Z. noltei and unvegetated sediment communities of Ria Formosa lagoon, when exposed to air. NCP and CR were measured in-situ in summer and winter, under present and CO2 enriched conditions using benthic chambers. Within chamber CO2 evolution measurements were carried out by a series of short-term incubations (30 min) using an infra-red gas analyser. Liner regression models fitted to the NCP-irradiance responses were used to estimate the seasonal budgets of air-exposed, intertidal production as determined by the daily and seasonal variation of incident photosynthetic active radiation. High CO2 resulted in higher CO2 sequestration by both communities in both summer and winter seasons. Lower respiration rates of both communities under high CO2 further contributed to a potential negative climate feedback, except in winter when the CR of sediment community was higher. The light compensation points (light intensity where production equals respiration) of Z. noltei and sediment communities also decreased under CO2 enriched conditions in both seasons. The seasonal community production of Z. noltei was 115.54 ± 7.58 g C m-2 season-1 in summer and 29.45 ± 4.04 g C m-2 season-1 in winter and of unvegetated sediment was 91.28± 6.32 g C m-2 season-1 in summer and 25.83± 4.01 g C m-2 season-1 in winter under CO2 enriched conditions. Future CO2 conditions may increase air-exposed seagrass production by about 1.5-fold and unvegetated sediments by about 1.2 fold.I

Suitability of Biodegradable Plastic Mulches for Organic and Sustainable Agricultural Production Systems

Biodegradable plastic mulch has the potential to be a sustainable technology in agricultural production systems if the mulch performs equally to polyethylene (PE) mulch and biodegrades completely into constituents that do not harm the soil ecology or environment. Reduced labor costs for removal and disposal, and reduced landfill waste add further appeal to the sustainability of biodegradable plastic mulch. Biodegradable paper mulch has been allowed in certified organic production systems in the United States for many years, while the National Organic Program (NOP) added biodegradable biobased plastic mulch to the list of allowed synthetic substances for organic crop production in Oct. 2014. Although biodegradable plastic mulch may meet the NOP biodegradability requirements (90% biodegradation within 2 years), currently no products have been approved for use in certified organic production because, so far, none meet the requirement of being completely biobased. Additionally, while the synthetic manufacturing processes that are used to make biodegradable plastic mulch are allowed by the NOP, the use of genetically modified organisms (GMOs) in the feedstocks, including their fermentation, is not allowed. Organic growers are advised always to check with their certifier before applying a product as some biodegradable mulch manufacturers and marketers erroneously advertise their product as “organic.” Looking forward, if biodegradable plastic mulch meets the NOP requirement of 90% biodegradation after 2 years, there is a possibility that 10% of plastic mulch residuals will persist (if the mulch contains nonbiodegradable ingredients); in this case, after 8 years of annual biodegradable mulch application, plastic residuals in the soil would exceed twice the amount of mulch applied per year. The current methods used by the NOP to test mulch biodegradation are laboratory based and it is uncertain if the results accurately represent field conditions. Reliable field sampling methods to measure residual mulch fragments in the soil need to be developed; however, it is unlikely such field tests will measure CO2 evolution, and thus will not be a true measure of biodegradation. Additional testing is needed under diverse field conditions to accurately quantify the rate and extent of biodegradation of mulch products that are marketed as biodegradable.

How do soil organic carbon stocks change after cropland abandonment in Mediterranean humid mountain areas?

The effects of land use changes on soil carbon stocks are a matter of concern stated in international policy agendas on the mitigation of greenhouse emissions. Afforestation is increasingly viewed as an environmental restorative land use change prescription and is considered one of the most efficient carbon sequestration strategies currently available. Given the large quantity of CO2 that soils release annually, it is important to understand disturbances in vegetation and soil resulting from land use changes. The main objective of this study is to assess the effects of land abandonment, land use change and afforestation practices on soil organic carbon (SOC) dynamics. For this aim, five different land covers (bare soil, permanent pastureland, secondary succession, Pinus sylvestris (PS) and Pinus nigra (PN) afforestation), in the Central Spanish Pyrenees, were analysed. SOC dynamics have been studied in the bulk soil, and in the fractions separated according to two methodologies: (i) aggregate size distribution, and (ii) density fractionation, and rates of carbon mineralization have been determined by measuring CO2 evolution using an automated respirometer. The results showed that: (i) SOC contents were higher in the PN sites in the topsoil (10cm), (ii) when all the profiles were considered no significant differences were observed between pastureland and PN, (iii) SOC accumulation under secondary succession is a slow process, and (iv) pastureland should also be considered due to the relative importance in SOC stocks. The first step of SOC stabilization after afforestation is the formation of macro-aggregates promoted by large inputs of SOC, with a high contribution of labile organic matter. However, our respiration experiments did not show evidence of SOC stabilization. SOC mineralization was higher in the top layers and values decreased with depth. These results gain insights into which type of land management is most appropriate after land abandonment for SOC.

Effect of pyrolysis temperatures on stability and priming effects of C3 and C4 biochars applied to two different soils

Biochar (BC) is a recalcitrant soil amendment that is being used for long-term carbon sequestration while also enhancing soil fertility. In an effort to better understand the interaction of soil type and biochar type, Mollisol (Minnesota) and Ultisol (Georgia) were incubated with biochars prepared from C3 (rice hull and wheat straw) and C4 (maize stover and switch grass) crop residues at 400°C and 600°C and the stability of biochar was studied by CO2 evolution measurements for 60 days. The C3 and C4 biochars were applied to the Ultisol and Mollisol samples which had a long term history of cropping with C4 and C3 crops, respectively. Overall the total and fixed C content of biochar increased, while the N content decreased with increase in pyrolysis temperature from 400°C to 600°C, thus increasing the C:N of the biochar. The volatile matter component of biochar decreased significantly at the higher pyrolysis temperature. In the Mollisol, the wheat straw biochar prepared (WSBC) at 600°C was more stable than the rice hull biochar (RHBC). However, in the Ultisol, RHBC was more stable than the WSBC. Corn stover biochar (CSBC) prepared at 600°C showed greater stability in both the Mollisol and Ultisol. The WSBC and CSBC prepared at 600°C which showed negative priming of native soil organic matter (SOM) had greater potential for long term carbon sequestration in soil. The δ13C signatures of the CO2 evolved on the 2nd day matched δ13C signatures of biochar confirming the contribution of biochar. On days 9 and 20 the δ13C signatures matched that of control soil indicating very little or no contribution of biochar to CO2 evolution. In spite of significant changes in pH and EC of soil biochar mixtures, these parameters had no effect on C mineralization. Nonlinear regression model confirms that the decomposition rate constant was higher in the 400°C biochar than in the 600°C biochar. Corn biochar prepared at 600°C could be useful for enhancing carbon storage in both the Mollisol and Ultisol. Soil organic matter level might have controlled the direction and magnitude of priming effect.

Relating the biological stability of soil organic matter to energy availability in deep tropical soil profiles

Tropical subsoils contain large reservoirs of carbon (C), most of which is stored in soil organic matter (SOM). Subsoil OM is thought to be particularly stable against microbial decomposition due to various mechanisms and its position in the soil profile, potentially representing a long-term C sink. However, few experiments have explicitly investigated SOM stability and microbial activity across several orders of magnitude of soil C concentrations as a function of soil depth. The objective of this study was to evaluate the biological stability of SOM in the upper 1.4 m of tropical forest soil profiles. We did so by measuring CO2 evolution during a 90-day laboratory incubation experiment on a sample set that was previously characterized for C and nutrient concentrations and microbial biomass. We concurrently measured the energy content of SOM using differential scanning calorimetry (DSC) as an index of the energy available for microbial metabolism, with the hypothesis that the biological stability of SOM would be inversely related to the energy contained within it. Cumulative CO2 evolution, mean respiration rates, and the energy density of SOM (energy released during combustion normalized to soil C) all declined with soil depth (P < 0.01). Biological indices of C stability were well correlated with measures of SOM energy. There was no change in the mean respiration rate as a function of depth when normalized to soil C, and a trend toward increased respiration per-unit microbial biomass (P = 0.07). While reduced microbial respiration in subsoils suggests an increase in the biological stability of SOM, we suggest this is driven principally by concurrent declines in energy availability as measured by DSC and the size of the microbial biomass pool. On a per-unit biomass basis, subsoil OM may be as prone to decomposition and destabilization as surface SOM.

Mineralization of Eroded Organic Carbon Transported from a Loess Soil into Water

The fate of soil-derived organic C (SOC) transported during erosion is a large uncertainty in assessing the impact of soil erosion on aquatic environments and in balancing C budgets. In our study, we determined C mineralization from solid soil organic C and dissolved organic C (DOC) translocated from a loess soil into surface water. We used runoff generated during rainfall simulation experiments. Both total runoff C and DOC were incubated to measure CO2 evolution during 28-d experiments. Cumulative CO2 emissions from runoff accounted for 3.9 to 4.8% of initial runoff C. It was estimated that 3.3 to 3.7% of initial solid SOC was mineralized contributing to 69 to 80% of total C mineralization from runoff. Mineralization of DOC was larger (7.3–30.2% of initial DOC) and showed a much larger variability than mineralization from solid SOC. However, DOC mineralization contributed to 20 to 31% of total C mineralization from runoff only because of the much smaller amounts of DOC than solid SOC. We could confirm a preferential removal of labile C from soils by water erosion. Nevertheless, the majority of this C will contribute to an aquatic C sink with less than 5% being potentially mineralizable. Our results indicated that the base level of C mineralization from translocated C was derived from the solid phase whereas the variability depends largely on DOC.

Characterization of hydrocarbon-degrading bacteria isolated from oil-contaminated sediments in the Sultanate of Oman and evaluation of bioaugmentation and biostimulation approaches in microcosm experiments

Two oil-polluted sediments (PD and KH) were sampled from a coastal region in Oman for the isolation of hydrocarbon-degrading bacteria and for testing different bioremediation approaches. Fourty strains were isolated, eighteen were affiliated to Marinobacter whereas the rest belonged to Pseudomonas, Halomonas, Hahella and Alcanivorax. All strains grew well at 2–7% salinity and between 20 and 60 °C. The strains exhibited a better growth on long chain than on short chain alkanes. Biostimulation and bioaugmentation were compared in both sediments and oil biodegradation was followed by measuring CO2 evolution and by gas chromatography (GC). The evolved CO2 reached 0.45 ± 0.02 and 2.23 ± 0.07 mg CO2 g−1 sediment after 88 days in the untreated PD and KH sediments, respectively. While the addition of inorganic nutrients resulted in 1.2–3.7 fold increase in CO2 evolution in both sediments, the addition of the bacterial consortium was only effective in the PD sediment. The maximum CO2 evolution was measured when both nutrients and bacteria were added and this corresponded to a total oil mineralization of 2.6 ± 0.12 and 1.49 ± 0.04% of the initial oil after 88 days in the PD and KH sediments, respectively. GC analysis confirmed the CO2 data and showed that most of the degraded compounds belonged to alkanes. We conclude that the Omani polluted sediments contain halotolerant and thermotolerant bacteria and biostimulation is more efficient than bioaugmentation for their cleanup.

Calibration of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Trapping in Alkaline Solutions during Soil Incubation at Varying Temperatures Using a Respicond VI

Measurements of carbon dioxide (CO2)-evolution from soils are important in evaluating biomass and activity of soil microorganisms, as well as decomposition of soil organic matter. The Respi- cond VI is a fully computerized system allowing continuous measurement of CO2 evolution in short- and long-term soil incubation experiments in up to 96 incubation vessels. The measure- ment of CO2 evolution is based on the absorption of CO2 by an electrolyte (KOH solution) produc- ing a change in the cell conductance measured using two electrodes. In this study, the Respicond VI was recalibrated yielding 174.5 mg CO2 as constant A expressing the theoretical maximum amount of CO2 absorbed in 10 ml 0.5 M KOH. This value of A corresponds to 34.9 mg CO2 ml −1 1 M KOH. The constant A does neither depend on the investigated incubation temperatures (5˚C - 25˚C) nor on the concentrations of the KOH solutions (0.5, 0.1, 0.05 M KOH). To eliminate any influence of changing incubation temperatures, either induced by uncertainties in temperature control or as a part of the experimental setup, on the conductance of KOH solution, a correction procedure was developed using a factor calculated from changing conductance of KOH solutions in incubation vessels without soil.

What's the flux? Unraveling how CO2 fluxes from trees reflect underlying physiological processes

What's the flux? Unraveling how <scp>CO</scp>₂ fluxes from trees reflect underlying physiological processes

Salinity reduces the ability of soil microbes to utilise cellulose

An incubation experiment was conducted to determine the response of soil microbial biomass and activity to salinity when supplied with two different carbon forms. One nonsaline and three saline soils of similar texture (sandy clay loam) with electrical conductivities of the saturation extract (ECe) of 1, 11, 24 and 43 dS m−1 were used. Carbon was added at 2.5 and 5 g C kg−1 (2.5C, 5C) as glucose or cellulose; soluble N and P were added to achieve a C/N ratio of 20 and C/P ratio of 200. Soil microbial activity was assessed by measuring CO2 evolution continuously for 3 weeks; microbial biomass C and available N and P were determined on days 2, 7, 14 and 21. In all soils, cumulative respiration was higher with 5C than with 2.5C and higher with glucose than with cellulose. Cumulative respiration was highest in the nonsaline soil and decreased with increasing EC, whereas the decrease was gradual with glucose, there was a sharp drop in cumulative respiration with cellulose from the nonsaline soil to soil with EC11 with little further decrease at higher ECs. Microbial biomass C and available N and P concentrations were highest in the nonsaline soil but did not differ among the saline soils. Microbial biomass C was higher and available N was lower with 5C than with 2.5C. The C form affected the temporal changes of microbial biomass and available nutrients differentially. With glucose, microbial biomass was highest on day 2 and then decreased, whereas available N showed the opposite pattern, being lowest on day 2 and then increasing. With cellulose, microbial biomass C increased gradually over time, and available N decreased gradually. It is concluded that salinity reduced the ability of microbes to decompose cellulose more than that of glucose.

Influence of the microporous layer on carbon corrosion in the catalyst layer of a polymer electrolyte membrane fuel cell

Corrosion of the catalyst support reduces PEM fuel cell performance via catalyst layer (CL) degradation (loss of porosity, catalyst connectivity, and active catalyst surface area). Carbon corrosion was investigated in a segmented cell for cathode gas diffusion layers (GDLs) with and without a microporous layer (MPL) to investigate the spatial aspects of GDL effect on corrosion. The cells were aged in situ using an accelerated stress test (AST) for carbon-support corrosion consisting of consecutive holds at 1.3 V. Carbon corrosion was quantified by measuring CO2 evolution during the AST.Performance degradation was substantial both with and without cathode MPL, but the degradation of the CL after prolonged corrosion was lower in the presence of an MPL. This was corroborated by better cell performance, higher remaining Pt active area, lower kinetic losses and smaller Pt particle size. The cell with an MPL showed increasingly nonuniform current distribution with corrosion time, which is correlated to the distribution of the Pt particle growth across the active area. This cell also showed an increase in mass-transport resistance due to MPL degradation. Without an MPL, GDL carbon fibers caused localized thinning in the cathode CL, originating from the combined effects of compression and corrosion.

Characterization of Carbon Corrosion in a Segmented PEM Fuel Cell

Corrosion of the catalyst support is an important degradation mechanism in PEM fuel cells because it reduces the overall cell performance by decreasing the active catalyst surface area, catalyst connectivity, and the porosity and hydrophobicity of the catalyst layer. Carbon corrosion rates were investigated in a segmented cell with and without a microporous layer (MPL) on the cathode. The cells were aged in-situ using a protocol for accelerated stress testing (AST) for carbon-support corrosion consisting of consecutive holds at 1.3 V. Carbon corrosion was quantified by measuring CO2 evolution during the potential holds. Although more carbon was corroded in the cell with the MPL on the cathode, corrosion in the catalyst layer was lower than in the cell without the MPL because a portion of the evolved CO2 originated from the MPL rather than from the catalyst layer. This was corroborated by the higher remaining ECSA and lower kinetic losses after prolonged corrosion for the MPL case. Both GDL cases exhibited substantial performance degradation and ECSA loss. Cell with the MPL was more resistant to prolonged carbon corrosion.

English

&nbsp; Decomposition of maize straw incorporated into soil with various nitrogen amended carbon to nitrogen (C/N) ratios under a range of moisture was studied through a laboratory incubation trial.&nbsp;The experiment was set up to simulate the most suitable C/N ratio for straw carbon (C) decomposition and sequestering in the soil.&nbsp;The purpose of this study was to determine organic C decomposition by measuring CO2&nbsp;evolution using alkali traps. Maize straw mixed with clay loam topsoil was supplied with four initial nitrogen rates (40, 80, 160, 320 mg N/0.5 g C) using (NH4)2SO4,&nbsp;to adjust its C/N ratio to 80, 40, 18 and 9. The soil moisture content was maintained at four moisture levels to achieve 60, 70, 80 and 90% of field capacity.&nbsp;Each of the four nitrogen rates were tested against four moisture levels, arranged in complete randomized design&nbsp;and incubated at 20&deg;C for 52 days. Results reveal that decomposition rates and cumulative CO2-C was increased by about 40% in straw amended treatments as compared to the controls. On average, about 34.56% of the added straw C was mineralized to CO2-C. Also, there was highly significant relationship between CO2-C emission and incubation period (R2&nbsp;= 0.98). Further, straw addition with interactive effect of nitrogen and moisture had significant relationships (p&nbsp;&lt; 0.05) with cumulative amounts of CO2-C, soil organic C and microbial biomass nitrogen. In conclusion, straw returning with appropriate N doses and optimum moisture can sequester and restore organic C in soil, thereby improving soil quality. &nbsp; Key words:&nbsp;CO2&nbsp;evolution, C/N ratio, microbial biomass, moisture, straw decomposition.

Effect of decomposition intensity of incorporated chickpea manure on stability and saturated hydraulic conductivity of a clay loam and clay soil

The role of organic matter (OM) in soil aggregation and saturated hydraulic conductivity (Ksat) has long been recognised but their depedence on the intensity of decay is less studied. The objective of this study was to determine the effect of decomposition intensity of incorporated chickpea manure on soil aggregate stability and Ksat. Samples of a clay loam and clay soil were collected from the top 15 cm layer and amended with chickpea green or mature dry manure and incubated at 30°C and ~60% water holding capacity. Decomposition intensity was determined by measuring CO2 evolution using NaOH traps, aggregate stability by wet sieving and Ksat by the constant head method. All determinations were made 3, 7 and 30 days after incubation and the data analysed following the general linear model for a 2 × 3 × 3 factorial in randomised complete block design. Evolution of CO2 in both soils and manure was highest on day 7 compared to day 3 and 30. In both soils >60% of the soil aggregates were macroaggregates >0.5 mm but the relative proportion of microaggregates <0.5 mm increased from ~10 to ~20% in the control and to ~15% in the amended cay loam soil in the day 30 treatments.Decomposition intensity was increased by incorporating chickpea manure which resulted in improved soil aggregate stability and Ksat especially in soil with low clay content. CO2which is a simple product of decomposition may be used as a rapid indicator of soil aggregate stability and water movement in agricultural soils. Key words: Green manure, organic matter, aggregate stability, chickpea, incubation, soil texture.

Progress of organic matter degradation and maturity of compost produced in a large-scale composting facility

To monitor the progress of organic matter degradation in a large-scale composting facility, the percentage of organic matter degradation was determined by measuring CO(2) evolution during recomposting of compost samples withdrawn from the facility. The percentage of organic matter degradation was calculated as the ratio of the amount of CO(2) evolved from compost raw material to that evolved from each sample during recomposting in the laboratory composting apparatus. It was assumed that the difference in the cumulative emission of CO(2) between the compost raw material and a sample corresponds to the amount of CO( 2) evolved from the sample in the composting facility. Using this method, the changes in organic matter degradation during composting in practical large-scale composting facilities were estimated and it was found that the percentage of organic matter degradation increased more vigorously in the earlier stages than in the later stages of composting. The percentage of organic matter degradation finally reached 78 and 55% for the compost produced from garbage-animal manure mixture and distillery waste (shochu residue), respectively. It was thus ascertained that organic matter degradation progressed well in both composting facilities. Furthermore, by performing a plant growth assay, it was observed that the compost products of both the facilities did not inhibit seed germination and thus were useful in promoting plant growth.

Carbon dioxide emissions from Ultisol under different land uses in mid–subtropical China

Soil organic carbon (SOC) pools and turnover time are highly sensitive to site variables and land-use change. In order to ascertain mass distributions of different SOC pools influenced by land use and evaluate their relationships with carbon mineralization and different soil properties, a 62-day laboratory incubation under a range of moisture (20 to 100% of water-holding capacity) and temperature conditions (5–45 °C) was conducted to measure CO 2 evolution from four land-use types, and data from the incubation study were fitted to a three-pool first-order model that separated mineralizable soil organic carbon into active, slow and resistant carbon pools. The results indicate that: (1) The active carbon pool comprised 1.2–3.5% of SOC with a mean residence time of 49–65 days, (2) The slow carbon pool comprised 25.3–60% of SOC with a mean residence time of 2–27 yr, (3) The resistant pool accounted for 36.5–73.9% of SOC in four land-use types. The woodland had the highest resistant carbon pool and lowest active carbon pool, which indicates it to be more stable than other land-use types. Soil carbon derived respiration was well correlated with all the organic carbon pools as well as C:N ratio and soil derived respiration. SOC was positively correlated with slow and resistant carbon pool, and soil derived respiration. CO 2 emissions increased ( r 2 = 0.273–0.544, P < 0.0001) with increasing temperature (up to 40 °C), with emissions reduced at the lowest and highest soil moisture contents. The Q 10 values (the factor by which respiration rate increase for a 10 °C increase in temperature) (from 5 °C to 45 °C, at 60% of water-holding capacity) of 1.9 ± 0.2, 2.2 ± 0.3, 2.3 ± 0.3, and 3.2 ± 0.5 were observed for paddy, orchard, woodland and upland, respectively, and decreased with decreasing moisture content when soil water content was less than its optimum value, but an opposite trend was shown when soil retained water at contents higher than the optimum water content. Inclusion of both moisture and temperature in our multiple polynomial models resulted in much better predictions of CO 2 ( r 2 = 0.70–0.78, P < 0.0001) emissions than predictions obtained using temperature ( r 2 = 0.27–0.54, P < 0.01) or moisture ( r 2 = 0.29–0.45, P < 0.01) alone. Our study indicates that vegetation type and/or management practices which control soil biological and biochemical properties, were important predictors of C fluxes in this short-term experiment.

Evaluation of Fiber Content Relative to Other Measures of Compost Stability

Improved methods for assessing compost stability are needed. We collected thirteen separate compost samples from a single windrow over a 91 d period. Initial assessment of compost stability used standard analyses, including total C and N concentration, C:N ratio, and inorganic N concentration. Compost C and N lability were assessed by measuring CO2 evolution during a 24 hr period, and also using a commercially available compost evaluation kit which includes both CO2 and NH3 release to establish a Maturity Index. We also estimated slowly degradable C fractions in the composts using neutral detergent fiber (NDF) and lignin methods developed for ruminant feed analysis. The relationship between stability and each compost constituent was evaluated using simple linear regression. Some widely-used parameters, like compost C:N ratio, changed very little during compost aging. Compost CO evolution showed a strong linear relationship with the compost age, with a coefficient of determination (r2) of 0.82. Likewise, fiber and lignin concentration increased during compost maturation as more easily available C was used by microbes (r2 = 0.70 to 0.80). The Solvita Maturity Index was related to the compost age (r2=0.59), but fluctuated due to temporary changes in windrow conditions. These results indicate that microbial respiration and fiber analysis can be used to establish relative differences in compost stability.