Closed Incubation System Research Articles

Advancing Enhanced Weathering Modeling in Soils: Critical Comparison With Experimental Data

AbstractEnhanced weathering (EW) is a promising strategy to remove atmospheric by amending agricultural and forestry soils with ground silicate rocks. However, current model‐based EW assessments face large uncertainties stemming from the intricate interplay among soil processes, compounded by the absence of a detailed comparison with available observational data. Here, we address this critical gap by first advancing a dynamic, ecohydrological, and biogeochemical Soil Model for Enhanced Weathering (SMEW). We then conduct a hierarchical model‐experiment comparison with four experimental data sets of increasing complexity, from simple closed incubation systems to open mesocosm experiments. The comparison demonstrates SMEW's ability to capture the dynamics of primary variables, including soil moisture, alkalinity, and inorganic carbon. The comparison also reveals that weathering rates are consistently lower than traditionally assumed by up to two orders of magnitude. We finally discuss the implications for carbon removal scenarios and avenues for further theoretical and experimental explorations.

Effect of Phosphogypsum Amendment on Chemical Properties of Sodic Soils at Different Incubation Periods

The application of phosphogypsum (PG) on sodic soils provides nutrients to the soil, reduces the toxic effect of Na+, and improves soil properties. Laboratory experiments were performed to evaluate the effects of PG on the chemical properties of sodic soils. The treatments were arranged in a completely randomized design with five replications. The treatments included 0% GR (control), 50% GR (28.18 g·kg−1), 100% GR (56.37 g·kg−1), 150% GR (84.50 g·kg−1), and 200% GR (112.74 g·kg−1) rates that were thoroughly mixed with soil under incubation, whereas PG was mixed with topsoil before leaching at the same application rates under the leaching experiment. Soil and leachate samples from each pot were collected in 7, 14, 21, 28, and 35 days and subjected to spectrometric analysis. Results indicated that there was a highly significant ( p < 0.001 ) effect on soil pH, exchangeable sodium percentage (ESP), available P, exchangeable Na+, and Ca+2 under 35-day incubation compared with control. In a closed incubation system, most of the nutrients were released after 7 days of incubation and inconstantly released after 14 days of incubation. Furthermore, the removal of Na+ and SAR increased in initial leachate collection and decreased with the subsequent application of irrigation water (PV). Because of the high contents of Ca+2 released from PG and the residual effect of H2SO4, soil pH and ESP were rapidly reduced compared with control. Post leachate analysis also revealed that available P and extractable S-SO4−2 were significantly ( p < 0.001 ) increased in soil solutions. However, available P was decreased during incubations compared with the value of post leachate analysis. During a closed incubation, displaced Na+ replaces Ca+2 on exchange sites, resulting in increased Ca-P precipitation. Thus, the combined application of PG and irrigation water in 7 to 14 days would allow chemical reaction with the soils and reduce sodicity problems to crop planting.

Combinational system for biodegradation of olive oil mill wastewater phenolics and high yield of bio-hydrogen production

Olive oil mill wastewater (OMW) is a significant pollutant in the Mediterranean region. In the present contribution, we showed clearly that microorganisms (microalgae and OMW-microflora) activated the biodegradation of OMW-phenolics and produced a high yield of hydrogen (H2). In a closed incubation system, the appropriate adjustment of OMW-pH leads to the establishment of anoxic conditions through the oxygen consumption of microorganisms during the first incubation day. The biodegradation procedure of OMW-phenolics needs oxygen. Therefore, after the establishment of anoxic conditions, the biodegradation stopped and the activation of hydrogenases started, leading to a continuous high yield of bio-hydrogen production. If the cultivation system re-opened (oxygen enrichment), the OMW-phenolic biodegradation (oxygen dependent process) started again and therefore the detoxified OMW could be used for further biotechnological applications (production of biodiesel, bioalcohols, organic fertilizers, etc.). Apart from the environmental compatibility of the method and the sustainability of such a combinational application (OMW detoxification and high yield of hydrogen production) in the context of a green biotechnology approach, the cost/profit ratio appears to be particularly tempting and guarantees its widespread use in the near future. The present contribution proposes a solution to a major environmental problem by upgrading its solution to a high-value product.

Organic Particles: Heterogeneous Hubs for Microbial Interactions in Aquatic Ecosystems.

The dynamics and activities of microbes colonizing organic particles (hereafter particles) greatly determine the efficiency of the aquatic carbon pump. Current understanding is that particle composition, structure and surface properties, determined mostly by the forming organisms and organic matter, dictate initial microbial colonization and the subsequent rapid succession events taking place as organic matter lability and nutrient content change with microbial degradation. We applied a transcriptomic approach to assess the role of stochastic events on initial microbial colonization of particles. Furthermore, we asked whether gene expression corroborates rapid changes in carbon-quality. Commonly used size fractionated filtration averages thousands of particles of different sizes, sources, and ages. To overcome this drawback, we used replicate samples consisting each of 3–4 particles of identical source and age and further evaluated the consequences of averaging 10–1000s of particles. Using flow-through rolling tanks we conducted long-term experiments at near in situ conditions minimizing the biasing effects of closed incubation approaches often referred to as “the bottle-effect.” In our open flow-through rolling tank system, however, active microbial communities were highly heterogeneous despite an identical particle source, suggesting random initial colonization. Contrasting previous reports using closed incubation systems, expression of carbon utilization genes didn’t change after 1 week of incubation. Consequently, we suggest that in nature, changes in particle-associated community related to carbon availability are much slower (days to weeks) due to constant supply of labile, easily degradable organic matter. Initial, random particle colonization seems to be subsequently altered by multiple organismic interactions shaping microbial community interactions and functional dynamics. Comparative analysis of thousands particles pooled togethers as well as pooled samples suggests that mechanistic studies of microbial dynamics should be done on single particles. The observed microbial heterogeneity and inter-organismic interactions may have important implications for evolution and biogeochemistry in aquatic systems.

CHARACTERISTICS OF PHOSPHATE ROCK MATERIALS FROM CHINA, INDONESIA AND TUNISIA AND THEIR DISSOLUTION IN INDONESIAN ACID SOILS

Dissolution of phosphate rock (PR) in soils is a primary concern for P in the PR to be available for plant. The dissolution of three PR materials, China (CPR), Ciamis (IPR) and Gafsa (GPR), in eight acid Indonesian soils (pH in water 4.1-5.7) was tested in a closed incubation system. Experiment was conducted in Soil Chemical Laboratory, Universiti Putra Malaysia and Indonesian Center for Agricultural Land Resources Research and Development from January to April 2002. The dissolution was determined from the increase in either 0.5 M NaOH extractable P (∆P) or 1 M BaCl2-triethanolamine (TEA)-extractable Ca (∆Ca) in soils amended with PR compared with control soil. Dissolution of the IPR was the highest (30-100%) followed by GPR (17-69%) and then by CPR (20-54%). The maximum dissolution followed the order: Bogor Ultisols > Bogor Oxisols > Subang Inceptisols > Bogor Inceptisols > Sukabumi Oxisols > Lebak Ultisols > Sukabumi Inceptisols > Lampung Ultisols. PR dissolution indicated a positive correlation with P retention capacity. The results implied that the extent of PR dissolution for the three PR sources (China, Indonesia and Tunisia) increased with increasing P retention capacity of the soils. PR dissolution can be based on a calibration curve of ∆Ca meaning that if ∆P is high then the amount of PR dissolution measured by ∆Ca in PR materials is also high.

CHARACTERISTICS OF PHOSPHATE ROCK MATERIALS FROM CHINA, INDONESIA AND TUNISIA AND THEIR DISSOLUTION IN INDONESIAN ACID SOILS

Dissolution of phosphate rock (PR) in soils is a primary concern for P in the PR to be available for plant. The dissolution of three PR materials, China (CPR), Ciamis (IPR) and Gafsa (GPR), in eight acid Indonesian soils (pH in water 4.1-5.7) was tested in a closed incubation system. Experiment was conducted in Soil Chemical Laboratory, Universiti Putra Malaysia and Indonesian Center for Agricultural Land Resources Research and Development from January to April 2002. The dissolution was determined from the increase in either 0.5 M NaOH extractable P (∆P) or 1 M BaCl2-triethanolamine (TEA)-extractable Ca (∆Ca) in soils amended with PR compared with control soil. Dissolution of the IPR was the highest (30-100%) followed by GPR (17-69%) and then by CPR (20-54%). The maximum dissolution followed the order: Bogor Ultisols > Bogor Oxisols > Subang Inceptisols > Bogor Inceptisols > Sukabumi Oxisols > Lebak Ultisols > Sukabumi Inceptisols > Lampung Ultisols. PR dissolution indicated a positive correlation with P retention capacity. The results implied that the extent of PR dissolution for the three PR sources (China, Indonesia and Tunisia) increased with increasing P retention capacity of the soils. PR dissolution can be based on a calibration curve of ∆Ca meaning that if ∆P is high then the amount of PR dissolution measured by ∆Ca in PR materials is also high.

Different effectiveness of closed embryo culture system with time-lapse imaging (EmbryoScopeTM) in comparison to standard manual embryology in good and poor prognosis patients: a prospectively randomized pilot study

BackgroundPreviously manual human embryology in many in vitro fertilization (IVF) centers is rapidly being replaced by closed embryo incubation systems with time-lapse imaging. Whether such systems perform comparably to manual embryology in different IVF patient populations has, however, never before been investigated.We, therefore, prospectively compared embryo quality following closed system culture with time-lapse photography (EmbryoScope™) and standard embryology.We performed a two-part prospectively randomized study in IVF (clinical trial # NCT92256309). Part A involved 31 infertile poor prognosis patients prospectively randomized to EmbryoScope™ and standard embryology. Part B involved embryos from 17 egg donor-recipient cycles resulting in large egg/embryo numbers, thus permitting prospectively alternative embryo assignments to EmbryoScope™ and standard embryology.We then compared pregnancy rates and embryo quality on day-3 after fertilization and embryologist time utilized per processed embryo.ResultsPart A revealed in poor prognosis patients no differences in day-3 embryo scores, implantation and clinical pregnancy rates between EmbryoScope™ and standard embryology. The EmbryoScope™, however, more than doubled embryology staff time (P < 0.0001). In Part B, embryos grown in the EmbyoScope™ demonstrated significantly poorer day-3 quality (depending on embryo parameter between P = 0.005 and P = 0.01). Suspicion that conical culture dishes of the EmbryoScope™ (EmbryoSlide™) may be the cause was disproven when standard culture dishes demonstrated no outcome difference in standard incubation.ConclusionsThough due to small patient numbers preliminary, this study raises concerns about the mostly uncontrolled introduction of closed incubation systems with time lapse imaging into routine clinical embryology. Appropriately designed and powered prospectively randomized studies appear urgently needed in well-defined patient populations before the uncontrolled utilization of these instruments further expands.Trial registrationNCT02246309 Registered September 18, 2014.

Oocyte Scoring Enhances Embryo-Scoring in Predicting Pregnancy Chances with IVF Where It Counts Most.

ContextOur center’s quality improvement optimization process on many occasions anecdotally suggested that oocyte assessments might enhance embryo assessment in predicting pregnancy chances with in vitro fertilization (IVF).ObjectiveTo prospectively compare a morphologic oocyte grading system to standard day-3 morphologic embryo assessment.Design, Setting, PatientsWe prospectively investigated in a private academically-affiliated infertility center 94 consecutive IVF cycles based on 6 criteria for oocyte quality: morphology, cytoplasm, perivitelline space (PVS), zona pellucida (ZP), polar body (PB) and oocyte size, each assigned a value of -1 (worst), 0 (average) or +1 (best), so establishing an average total oocyte score (TOS). Embryo assessment utilized grade and cell numbers of each embryo on day-3 after oocyte retrieval. Clinical pregnancy was defined by presence of at least one intrauterine gestational sac.InterventionsStandard IVF cycles in infertile women.Main Outcome MeasuresPredictability of pregnancy based on oocyte and embryo-grading systems.ResultsAverage age for all patients was 36.5 ± 7.3 years; mean oocyte yield was 7.97± 5.76; Patient specific total oocyte score (PTOS) was -1.05 ± 2.24. PTOS, adjusted for patient age, was directly related to odds of increased embryo cell numbers (OR 1.12, P = 0.025), embryo grade (OR 1.19, P < 0.001) and clinical pregnancy [OR 1.58 (95%CI 1.23 to 2.02), P < 0.001]. Restricting the analysis to day three embryos of high quality (8-cell/ good grades), TOS was still predictive of clinical pregnancy (OR 2.08 (95%CI 1.26 to 3.44, P = 0.004). Among the 69 patients with embryos of Grade 4 or better available for transfer 23 achieved Clinical Pregnancy. When the analysis was restricted to the 69 transfers with good quality embryos (≥ Grade 4) the Oocyte Scoring System (TOS) (AUC±SE 0.863±0.044, oocyte score) provided significantly greater predictive value for clinical pregnancy compared to the embryo grade alone (AUC 0.646 ± 0.072, embryo grade) p = 0.015.ConclusionsOocyte-scoring, thus, provides useful clinical information especially in good prognosis patients with large numbers of high quality embryos. This finding appears of particular importance at a time when many IVF centers are committing sizable investments to closed incubation systems with time-lapse photography, which are exclusively meant to define embryo morphology.

Denitrification rate determined by nitrate disappearance is higher than determined by nitrous oxide production with acetylene blockage

A mixed beech and spruce forest soil was incubated under potential denitrification assay (PDA) condition with 10% acetylene (C 2H 2) in the headspace of soil slurry bottles. Nitrous oxide (N 2O) concentration in the headspace, as well as nitrate, nitrite and ammonium concentrations in the soil slurries were monitored during the incubation. Results show that nitrate disappearance rate was higher than N 2O production rate with C 2H 2 blockage during the incubation. Sum of nitrate, nitrite, and N 2O with C 2H 2 blockage could not recover the original soil nitrate content, showing an N imbalance in such a closed incubation system. Changes in nitrite and ammonium concentration during the incubation could not account for the observed faster nitrate disappearance rate and the N imbalance. Non-determined nitric oxide (NO) and N 2 production could be the major cause, and the associated mechanisms could vary for different treatments. Commonly applied PDA measurement likely underestimates the nitrate removal capacity of a system. Incubation time and organic matter/nitrate ratio are the most critical factors to consider using C 2H 2 inhibition technique to quantify denitrification. By comparing the treatments with and without an antibiotic, the results suggest that microbial N uptake probably played a minor role in N balance, and other denitrifying enzymes but nitrate reductase could be substantially synthesized during the incubation.

Characteristics of phosphate rock materials and their dissolution in some acidic Indonesian soils

Dissolution of phosphate rock (PR) materials in soil is a primary concern for phosphorus (P) in the PR to become plant available. The dissolution of three PR materials, China PR (CPR), Ciamis PR (CiamisPR) and Gafsa PR (GPR), in eight acid Indonesian soils was evaluated in a closed incubation system. Dissolution of PR was measured from the increase in either 0.5M NaOH extractable P (ΔP) or 1M BaCl2-triethanolamine (TEA)-extractable Ca (ΔCa) in soils amended with PR compared with control soil. Dissolution of the CiamisPR was the highest (30 – 100%) followed by GPR (17 – 69%) and then by CPR (20 – 54%). The maximum dissolution of PR in soil followed the order: Bogor Ultisols ≥ Bogor Oxisols ≥ Subang Inceptisols > Bogor Inceptisols > Sukabumi Oxisols > Lebak Ultisols > Sukabumi Inceptisols ≥ Lampung Ultisols. A curvilinear relationship was obtained between PR dissolution and P retention capacity and between ΔP and ΔCa.

Transformation of sulfate and organic S in rice straw in flooded paddy soils and its availability to plants using sulfur-35 labeling

Sulfur transformation and its availability to plants in two flooded paddy soils, derived from Black soil in Heilongjiang (soil 1) and from Red earth in Jiangxi (soil 2), were investigated in a closed incubation system using carrier-free 35S–SO 4 2− and 35S-labeled rice straw. After incubation for 120 days, 51.1% and 60.3% of the 35S added in the Na 2 35SO 4 treatment were found in the sulfate–S fraction, 14.0% and 11.1% as sulfide–S, 5.2% and 5.3% as other non-sulfate inorganic S fraction (OI-S), 9.5% and 6.0% as C–O–S, 8.1% and 7.3% as C-bonded S, and 12.1% and 10.0% as non-reducible organic S fraction (NRO-S) for soil 1 and soil 2, respectively. Since soil Eh increased greatly after planting the rice, sulfide–S and OI-S could be transformed into sulfate as plant-available S. Most of the 35S uptake by plants came from sulfate– 35S, sulfide– 35S and OI– 35S, with little contribution from C–O– 35S, C-bonded 35S or NRO– 35S. In the treatment with 35S-labeled rice straw, 23.3% and 26.4% of the 35S applied was found in the sulfate–S fraction, 25.3% and 26.3% as sulfide–S, 6.0% and 6.1% as OI-S, 16.4% and 14.0% as C–O–S, 10.1% and 8.3% as C-bonded S, and 18.9% and 18.9% as NRO-S at 120th day of incubation in these two soils, respectively. Higher availability of C–O– 35S, C-bonded 35S and NRO– 35S from 35S-labeled straw was observed in the 35S-labeled straw treatment, compared to the carrier-free Na 2 35SO 4 treatment.

Assay system for measurement of denitrification-N loss from ornamental plants potted in peat substrate

An assay system was evaluated for denitrification measurement with potted ornamental plants cultivated in peat substrate (Pelargonium zonale, Euphorbia pulcherrima). Flow-through chambers only enclosing the pot of the plants were considered best for denitrification measurement. Loss of N2O from the chambers by transport through the plant shoot was negligible with both species. To determine (N2O + N2)-N loss, C2H2 was applied to inhibit reduction of N2O. Experiments were conducted with unplanted substrate in closed incubation systems to determine optimum C2H2 concentration and pre-treatment duration. Complete inhibition of N2O reduction in peat substrate was achieved using 1 vol% C2H2. However, a concentration of 5 vol% C2H2 was chosen for further experiments because C2H2 concentrations in flow-through chambers varied. The duration of C2H2 pre-treatment (0, 2, 12, 24 h) showed no clear effect on (N2O + N2)-N accumulation. However, a pre-treatment duration of 2 h was chosen to guarantee immediate inhibition of N2O reductase at the start of experiments. Exposure to C2H2 gas proved to affect plants of both species. During C2H2 exposition in flow-through chambers, the leaves of P. zonale became chlorotic (48 h) and necrotic (72 h). E. pulcherrima showed no chlorosis but did exhibit leaf epinasty (24 h) and wilting (96 h). Transpiration of P. zonale and C availability in the growing medium of both species were not affected by 52 h and 24 h treatments with C2H2, respectively. As N emissions usually ended within 38 h of C2H2 treatment, it was concluded that side effects of C2H2 did not affect denitrification measurements.

Dissolution of phosphate rock fertilisers in some soils of Okinawa, Japan

The ability of phosphate rock (PR) to dissolve rapidly in soil is a primary concern in its direct application as P fertiliser. The dissolution of 4 PR materials (Togo, South Africa, Florida, Morocco PRs) in 15 soil samples in Okinawa was investigated in a closed-incubation system for 7 days. The fertilisers were mixed with the soils at rates of addition of 600–1200 µg Ca/g soil. The extent and rate of dissolution of the PRs were determined by measuring the increase in extractable Ca of the fertilised soils compared with unfertilised soils, i.e. the delta Ca (ΔCa) technique. Generally, the amounts of dissolution of 3 of the PRs were very low (mean 6·7% for Togo PR, 13·6% for South Africa PR, and 20·8% for Florida PR). However, Morocco PR dissolved to an appreciable extent (mean 60·8%), suggesting that it can be an alternative P source, especially in the red and yellow soils of Okinawa. Soil properties identified as affecting dissolution were different for the different PRs. In order to predict the suitability of Morocco PR for Okinawan soils, the extent of its dissolution was related to soil properties in a multiple regression analysis. Results indicated that the best regression model for predicting the amount of dissolution was the combination of pH, Ca saturation, and Truog P (r2 = 0·55**). Measured values of percentage dissolution of Morocco PR were significantly correlated with calculated percentages (r = 0·844***), indicating that the equation obtained could offer a rapid estimation of amount of dissolution of Morocco PR in Okinawan soils.

Enhanced dissolution of phosphate rocks in the rhizosphere

Dissolution of two phosphate rocks (PRS) which vary in their chemical reactivity was examined using two soils in the absence (closed-incubation and open-leaching) and presence (thin-layer) of plants. Greater dissolution was obtained in the presence than in the absence of plants. In the absence of plants, open-leaching resulted in higher dissolution than the closed-incubation system. Removal of the dissolved Ca from the zone of PR dissolution is considered to be the main reason for the increased dissolution in the open-leaching columns. In the case of the thin-layer experiment, removal of Ca and P through plant uptake and the supply of protons (H+) through the release of organic acids are considered to be the main reasons for the enhanced dissolution of PRs in the rhizosphere.

Assessing nitrogen mineralization from soil organic matter using anion exchange membranes

A simple method to assess differences in potential contribution of organic nitrogen mineralization to plant available N among soils may be useful in fertility research as well as routine soil testing. We deployed a method to assess mineralizable soil organic N using anion exchange membrane (AEM) burial. The method is based on a simple closed incubation system in which strips of AEM are buried directly in soil to adsorb NO 3 - released from organic matter. An index of mineralization was obtained using the amount of NO 3 - adsorbed on an AEM strip removed at the end of each incubation. The same incubation system but using 0.001M CaCl2 solution to extract NO3-N was used as the reference method. The mineralization indices obtained from both methods were compared with each other and with plant uptake. A total of 74 soils from across Saskatchewan were used in the study to provide a range of soil properties. Correlations between test values and N uptake by plants in two separate experiments showed the 2 week AEM incubation to be more closely correlated with plant N uptake (r2 = 0.86**** and 0.57****, respectively) than the reference method (r2 = 0.60**** and 0.48****, respectively). With this method, we were able to determine the influence of different tillage systems and landscape positions on mineralizable N. The results showed that the NO 3 - released from soil organic matter and accumulated on the AEM reflected the expected effect of three different tillage systems and two landscape positions on mineralizable N. Cropping systems with continuous alfalfa (Medicago sativa) showed higher N release from soil organic matter than a canola (Brassica napus)-lentil (Lens culinaris)-barley (Hordeum vulgare) rotation did. Higher N mineralization was found in the lower slope positions of the landscape where organic matter contents are highest. Direct burial of AEM appears to be a simple and effective method of including a measure of N mineralization in a soil test.

Comparison of sulfur mineralisation in open and closed incubation systems and from field moist and conditioned soils

Abstract The amounts of sulfur (S) mineralised in three soils incubated in both open (i.e. leached) and closed systems increased with time over the period of the incubation. However, the rates and patterns of S release differed with the soil type and incubation technique used. The pattern of S mineralisation during the open incubation was a rapid release of S in the first two weeks, followed by a slightly slower almost linear rate of release for the remainder of the incubation. The pattern of S release during the closed incubation was slightly curvilinear. In the short term, the closed system released similar or greater amounts of S than the open system. However, in the long term, more S would be mineralised in the open than that in the closed system. Conditioning (i.e. pre‐incubation of air‐dried samples) did not significantly affect the amounts of S mineralised in the soils incubated in the open system, but did in two soils incubated in the closed system.

Practical Simulation Of Composting In The Laboratory

A closed incubation system was developed for laboratory simulation of composting conditions at the interior of a large compost pile. A conductive heat flux control system (CHFC) was used to adjust the temperature of the internal wall to that of the compost center and compensate for heat loss. Insulated small vessels (400 cm 3) controlled by the CHFC system were compared with similar vessels maintained at 30°C (mesophilic) and 55°C (thermophilic), and with large vessels (10 000 cm 3) with and without the CHFC. Compost temperature rose rapidly to a maximum within 2-4 days, then gradually decreased. In mesophilic treatments (no CHFC), temperature at the matrix center increased to a maximum of 36°C in the small vessel and 50°C in the large vessel, while temperature in both vessels reached 50°C with the CHFC. Microbial activity was maintained by allowing compost to self-heat and controlling temperature externally with the CHFC. Higher temperatures were sustained for longer periods in CHFC vessels than in vessels without the CHFC. Periodic mixing of the compost matrix increased temperature and CO 2 evolution. Small vessels were successfully used in laboratory simulation of field-scale composting of a soil/organic matrix containing TNT and RDX munitions. The small vessel system reduced subsample error in compost monitoring from that of the large vessels. The CHFC has particular utility in research requiring expensive chemicals or hazardous substances.

Practical Simulation of Composting in the Laboratory

A closed incubation system was developed for laboratory simulation of composting conditions at the interior of a large compost pile. A conductive heat flux control system (CHFC) was used to adjust the temperature of the internal wall to that of the compost center and compensate for heat loss. Insulated small vessels (400 cm 3) controlled by the CHFC system were compared with similar vessels maintained at 30°C (mesophilic) and 55°C (thermophilic), and with large vessels (10 000 cm3) with and without the CHFC. Compost temperature rose rapidly to a maximum within 2-4 days, then gradually decreased. In mesophilic treatments (no CHFC), temperature at the matrix center increased to a maximum of 36°C in the small vessel and 50°C in the large vessel, while temperature in both vessels reached 50°C with the CHFC. Microbial activity was maintained by allowing compost to self-heat and controlling temperature externally with the CHFC. Higher temperatures were sustained for longer periods in CHFC vessels than in vessels without the CHFC. Periodic mixing of the compost matrix increased temperature and CO2 evolution. Small vessels were successfully used in laboratory simulation of field-scale composting of a soil/organic matrix containing TNT and RDX munitions. The small vessel system reduced subsample error in compost monitoring from that of the large vessels. The CHFC has particular utility in research requiring expensive chemicals or hazardous substances.

The incorporation and transformations of 35S in soil: Effects of soil conditioning and glucose or sulphate additions

Sulphur transformations in soil maintained in a closed incubation system were monitored by means of labelling with radioactive 35S-SO 4. The distribution of 35S between phosphate-extraetable S, biomass-S, hydriodic acid (HI)-reducible S and carbon-bonded S was determined at intervals of between 1 and 120 days of incubation. In studies were carrier free 35S-SO 4 was added to soil, the amount and rate of 35S incorporation into the soil depended on the treatment of the soil prior to incubation. When soil was conditioned (maintained at 20°C and 75% field moisture capacity for 2 weeks) prior to the addition of 35S, there was a comparatively slow rate of incorporation. An average of 8–19% 35S incorporation occurred within 1–5 days and a maximum of 48% incorporation between 90 and 120 days. Air-dried soil incubated without conditioning, showed a faster incorporation in the short to medium term, 14–28% 35S incorporated within 1–5 days, and a maximum of 43% incorporation after c 60 days. A third treatment, using air-dried soil to which 1% glucose C had been added, showed a very high and rapid rate of incorporation of 35S into soil organic fractions within 5 days of incubation. A maximum of 84% incorporation was reached within 16 days. The incorporation of 35S into HI-reducible and C-bonded forms of S showed considerable differences between treatments. In the short-term, most of the incorporation in the conditioned soil was into HI-reducible forms. The two treatments which received no conditioning showed a much higher proportion of 35S incorporation into C-bonded S. In the longer term, in the air-dried and glucose-treated samples, some of the 35S originally incorporated into C-bonded forms of S appeared to be transformed to HI-reducible S or remobilized to extractable forms of S. Microbial biomass in the conditioned soil showed no significant labelling until the 24th day of incubation. The other two treatments showed significant amounts of 35S incorporation into the biomass within 3 days, and could account for the higher level of 35S in C-bonded forms in these treatments. In the glucose-treated soil, in the short-term, up to 90% of the incorporated 35S was found in the biomass-S pool. Addition of carrier sulphate together with 35S-SO 4 appeared to have a retarding effect on the incorporation of the 35S into the soil. In the presence of added sulphate, most of the incorporated 35S was present as HI-reducible S and there was no significant labelling of the soil biomass-S during 32 days of incubation.

Sulfur mineralization in sphagnum peat

Abstract Open and closed incubation systems were studied as means of quantifying sulfate fractions in sphagnum peat moss. Sulfate was extracted in the closed system with a 0.15% CaCl2‐H2O or a 500 mg P/L extractant. Sulfate was extracted in the open system with 10 mM KC1, 0.15% , CaCl2‐H2O, or 500 mg P/L extractant. Extractants were quantified by ion chromatography. Phosphate extractant released more sulfate than CaCl2, in the closed system. There was a significant increase over time of sulfate released by the CaCl2 extractant. In the open system, there was no significant difference in release and total amounts leached of sulfate‐S between extractants. The closed system released more sulfate‐S than the open system. Phosphate extractants in both systems mineralized 43% of initial sulfur content