Effect of differently post-treated dewatered sewage sludge on β-glucosidase activity,microbial biomass carbon,basal respiration and carbohydrates contents of soils from limestone quarries

This work has evaluated the effects of thermally dried (TDS) or composted (CDS) dewatered sewage sludge on β-glucosidase activity, total (TCH) and extractable (ECH) carbohydrate content, microbial biomass carbon and basal respiration of soils from limestone quarries under laboratory conditions. Two doses (low and high) of the dewatered sludge (DS) or of the respective TDS or CDS were applied to a clayey and a sandy soil, both coming from working quarries. The soil mixtures and the controls (soils with no added sludge) were incubated for 9 months at 25°C and 30% of field capacity. The addition of sludge increased all the studied soil parameters, and the increase depended on the amount of sludge. Except in the case of TCH and ECH, the enhancing effect decreased with time, but at the end of incubation, parameters of the treated soils were higher than those of the control. The rank order of the initial stimulating effect was soil–TDS ≥ soil–DS ≥ soil–CDS, and probably, this order depended on the proportion of stable organic matter, which was the lowest in the TDS. Values of metabolic quotient (qCO₂) were higher at the lower dose, and they did not change during incubation in the CDS-treated soils. Both TCH and ECH were the parameters with the greatest significant sludge and dose effects. Basal respiration, microbial biomass carbon and β-glucosidase activity were the best measured parameters in distinguishing the long-term effects of the three sludge types over the soils.     

Initial results from a long-term, multi-site field study of the effects on soil fertility and microbial activity of sludge cakes containing heavy metals

In a long‐term study of the effects on soil fertility and microbial activity of heavy metals contained in sewage sludges, metal‐rich sludge cakes each with high Zn, Cu or Cd concentrations were applied annually for 4 years (1994–1997) to nine sites throughout Britain. These sites were selected to represent agricultural soils with a range of physical and chemical properties, typical of those likely to be amended with sewage sludge. The aim was to establish individual total Zn (approx. 60–450 mg kg^?1), total Cu (approx. 15–200 mg kg^?1) and total Cd (approx. 0.2–4 mg kg^?1) metal dose–response treatments at each site. Sludges with low metal concentrations were added to all treatments to achieve as constant an addition of organic matter as possible. Across the nine sites, soil pH was the single most important factor controlling Zn (P < 0.001; r² = 92%) and Cd extracted with 1 m NH₄NO₃ (P < 0.001; r² = 72%), and total iron content the most important factor controlling Cu extracted with 1 m NH₄NO₃ (P < 0.001; r² = 64%). There were also positive relationships (P < 0.001) between soil organic carbon (C) concentrations and soil biomass C and respiration rates across the nine sites. Oxidation of sludge C following land application resulted in approximately 45% of the digested sludge cake C and approximately 64% of the ‘raw’ sludge cake C being lost by the end of the 4‐year application period. The sludge cake applications generally increased soil microbial biomass C and soil respiration rates, whilst most probable numbers of clover Rhizobium were generally unchanged. Overall, there was no evidence that the metal applications were damaging soil microbial activity in the short term after the cessation of sludge cake addition.     

连续施用无害化污泥对沙质潮土土壤肥力和微生物学性质的影响

以小麦-玉米轮作体系下的沙质潮土为研究对象,选用经无害化处理后的城市污泥产物,通过2013~2015年田间定位试验,研究了不同城市污泥施用量对土壤肥力的影响,以期为城市污泥资源化利用提供理论基础和技术依据。设置单施化肥(CK)、CK+污泥15 t·hm~(-2)(CS1)、CK+污泥30 t·hm~(-2)(CS2)和CK+污泥45 t·hm~(-2)(CS3)共4个处理。主要研究结果如下:(1)连续定位试验结果表明,同一施用量污泥处理的土壤p H值随施用时间的增加呈下降趋势;土壤有机质(SOM)和养分含量如全氮(TN)、有效磷(AP)和速效钾(AK)随施用时间的增长呈上升趋势;(2)与CK比较,在2015年玉米季施用污泥各处理的土壤p H值显著降低了0.34~0.83个单位(P0.05),且与污泥施用量呈反比,以高施量污泥45 t·hm~(-2)下降最多;土壤SOM、TN、AP和AK分别显著提高了52.1%~166.9%、77.3%~177.8%、215.7%~486.3%和167.2%~379.0%(P0.05),且与污泥施用量呈正比,以高施量污泥45 t·hm~(-2)效果最显著;(3)试验所用污泥施用量范围内不会造成土壤和植物籽粒重金属污染,能够保持土壤环境健康;(4)与CK比较,施用污泥各处理土壤微生物量碳(MBC)、氮(MBN)含量均显著提高(P0.05),且与污泥施用量呈正比,并且季节不同也显著影响土壤MBC、MBN含量(P0.05);施用污泥能够显著提高土壤MBC/MBN(P0.05),说明施用污泥能够改变土壤微生物群落组成;(5)施用污泥,尤其是高施量污泥45 t·hm~(-2),在保证土壤和植物籽粒质量安全下,其土壤培肥效果最优。     

Effect of a fly ash and gypsum mixture on rice cultivation

Abstract

The salt titration (ST) method was evaluated as a method to determine ZPC in comparison with the potentiometric titration (PT) method for 26 soils with variable charge clays, i.e., Oxisols and Ultisols from Thailand and Andisols from Japan. In addition to the determination of ST-pH₀ as the zero point of charge, a calculation procedure (STPT method) was adopted here in order to acquire more information from the titration curve. Furthermore, for the purpose of cross-checking of ZPC determined by the PT method, the ST procedure was successively applied to the samples analyzed by the PT method (PTST method).

The soil to solution ratios of 1: 10 to 1: 5 gave almost an identical ST-pH₀ value for every soil. The values of both ST-pH₀ and PT-ZPC ranged from 4.7 to 6.3 for the Andisols, while for the Oxisols and Ultisols, they were always below 4.2. The difference between the values of ST-pH₀ and PT-ZPC was only slight for the Andisols, whereas it was sometimes large (0.4 pH unit) for the Oxisols and Ultisols. Nevertheless, it was concluded that the ST method with its modification (STPT) was comparable to or even better than the PT method for the soil characterization work due to its convenience and simplicity.     

Effect of freezing and thawing processes on some physical properties of saline–sodic soils mixed with sewage sludge or fly ash

Dispersion of saline–sodic soils was rather difficult to leach. Therefore, negative effects of freeze–thaw on soil physical properties should be reduced by inexpensive and practical methods. This study investigates the effect of freeze–thaw cycles (3, 6, and 9) on wet aggregate stability, bulk density, and permeability coefficient in three soils with different electrical conductivity and exchangeable sodium percentage levels (soil I: 5.30 dS m⁻¹, 47.51%; soil II: 42.80 dS m⁻¹, 55.45%; soil III: 36.30 dS m⁻¹, 59.34%) which consist of different proportions of sewage sludge and fly ash by volume (10%, 20%, and 30%). The experiment was conducted under laboratory conditions using disturbed and non-cropped soil samples mixed with sewage sludge and fly ash. Soils mixed with sewage sludge produced higher aggregate stability and permeability coefficients and lower bulk density values as compared to the soils mixed with fly ash. Sewage sludge added with a rate of 30% eliminated the negative effects of freeze–thaw processes on wet aggregate stability. Freeze–thaw processes did not affect the bulk density of the soils II and III, which were mixed with sewage sludge. However, fly ash addition decreased the bulk density of these soils very significantly after nine freeze–thaw cycles. Addition of sewage sludge or fly ash with rates of 20% and 30% significantly increased the permeability coefficients in soil I after nine freeze–thaw cycles. Results indicated that addition of sewage sludge and/or fly ash to saline–sodic soils could be alternative way for reducing negative effects of freezing–thawing on soil wet aggregate stability, bulk density, and permeability coefficient.     

Influence of sewage sludge and heavy metals on nematodes in an arable soil

Summary The abundance of nematodes was investigated in agricultural plots treated in three different ways, the first with no treatment, the second with 300 m³ ha^-1 a^-1 raw sewage sludge and the third with 300 m³ ha^-1 a^-1 sewage sludge with the addition of heavy metals. The nematodes were determined down to the genus and were assigned to five feeding groups. Total nematode numbers were highest in the site treated with sewage sludge and heavy metals. The smallest total numbers were found in the control site. The plant-feeding nematode genera showed different patterns of abundance depending on the sludge treatment and heavy metal content. For the mycophagic and bacteriophagic nematodes, numbers increased with the amount of sludge, especially in the sites with a higher heavy metal content. The family Rhabditidae was the most numerous group in the sludge plus heavy metals treatment. In contrast to these findings, the omnivorous nematodes were very rare in the sludgetreated plots and were completely absent in plots treated with sludge plus heavy metals, whereas predatory nematodes were numerous only after the application of sludge alone.     

Microbial activity in grassland soil amended with sewage sludge containing varying rates and combinations of Cu, Ni and Zn

 Cu, Ni and Zn were added at different rates (low and±25% of current limits) and combinations to sewage sludges and the effects on soil microorganisms were monitored in laboratory incubations. Respiration was measured frequently during weeks 1–7, whilst extractable metals (with EDTA and CaCl₂), microbial biomass C and metabolic quotient were recorded at 3 and 7 weeks. Inputs of one metal affected extractable concentrations of that metal and of the second metal tested in each experiment. Cu behaved differently from Ni and Zn, with little extractable by CaCl₂. Whereas CaCl₂-Ni and -Zn increased markedly between weeks 3 and 7, Cu concentrations did not change. Respiration was reduced at 1 week by Ni inputs and by Cu in combination with Ni. Zinc inputs at 1 week, and all metal inputs after 3 weeks, increased respiration. Biomass C was lower at higher metal inputs and with Zn the exception occurred at 3 weeks when biomass C was higher. Metal inputs generally increased metabolic quotient, although responses to Zn were often non-significant. Not all metal responses were additive, with effects of one metal frequently more pronounced with high levels of another. For Cu, the organic bound fraction was a better predictor of microbial response than the exchangeable fraction. For Ni the reverse was the case in one experiment, whilst extractable Zn was not closely correlated with microbial indices. Metal inputs close to permitted levels, in particular Cu, affected microbial processes but responses varied with time after sludge application. Received 26 August 1998     

Effects of N-enriched sewage sludge on soil enzyme activities

Sewage sludge is increasingly used as an organic amendment to soil, especially to soil containing little organic matter. However, little is known about utility of this organic amendment with N-enriched or adjusted C:N ratios in soil. We studied the effects of adding of different doses (0, 100, 200 and 300 t ha⁻¹) and C:N ratios (3:1, 6:1 and 9:1) of sewage sludge on enzyme activities (β-glucosidase, alkaline phosphatase, arylsulphatase and urease) in a clay loam soil at 25 °C and 60% soil water holding capacity. Nitrogen was added in the form of (NH₄)₂ SO₄ solution to the sludge to reduce the C:N ratio from 9:1 to 6:1 and 3:1. The addition of different doses and C:N ratios of the sludge caused a rapid and significant in the enzymatic activities in soils, this increase was specially noticeable in soil treated with high doses of the sludge. In general, enzymatic activities in sludge-amended soils tended to decrease with the incubation time. All activities reached peak values at 30 days incubation and then gradually decreased up to 90 days of incubation. Sewage sludges also the increased available metal (Cu, Ni, Pb and Zn) contents in the soils. However, the presence of available soil metals due to the addition of the sludge at all doses and C:N ratios did negatively affect all enzymatic activities in the soils. This experiment indicated that all doses and C:N ratios of sewage sludge applied to soil would have harmful effects on enzymatic activity. Some heavy metals found in sewage sludge may negatively influence soil enzyme activities during the decomposition of the sludge.     

Long-term effects of farmyard manure and sewage sludge on some soil biochemical characteristics

 Changes in some soil biochemical properties were investigated following repeated applications of aerobically digested sewage sludge (SS) under field conditions over 12 years, and compared with those of an adjacent soil cultivated and amended with 5 t ha^–1 year^–1 (dry weight) farmyard manure (FYM) for at least 40 years, as well as with those of an adjacent uncultivated soil, in order to ascertain changes in soil quality. A short-term aerobic incubation was used to determine the potential of the samples to mineralize the organic C supplied. Results indicated that cultivation caused a reduction in total, humified and potentially mineralizable organic C, total N, light-fraction (LF) C, total and water-soluble carbohydrates, phenolic compounds, cation-exchange capacity (CEC), microbial biomass C, specific respiration, hydrolytic and urease activities, and an increase in the heavy metal content. Total and water-soluble carbohydrates and phenolic compounds expressed as a percentage of total organic C (TOC) were similar in the differently managed plots. Of the two amendments, FYM treatments showed higher amounts of TOC and N, LF-C, total and water-soluble carbohydrates, phenolic substances, CEC, specific respiration of biomass, hydrolytic and urease activities, similar amounts and characteristics of humified organic matter and lower concentrations of Cu, Zn and Cr. Both FYM and SS were inadequate treatments for the restoration of soil organic matter lost as a consequence of cultivation. Received: 20 October 1998     

Impact of landspread sewage sludge and earthworm introduction on established earthworms and soil structure

Summary Sewage sludge was applied to twelve 4-m² plots in two forest (mixed hardwood, Norway spruce plantation) site and one old field site. The earthworm Eisenia fetida was introduced to half the control and half the treated plots. Earthworm populations were sampled by formalin extraction and hand-sorting five times in the year following treatment. One year after treatment, soil samples were wet-sieved and water-stable aggregate size-class arrays were determined.The dominant earthworm in the study site, Lumbricus terrestris, increased in density and mean individual biomass in response to sludge treatment in mixed hardwood and old field plots. In the Norway spruce plots, L. terrestris increased in individual biomass but decreased in density following sludge application. The density of the introduced E. fetida rapidly declined in all control plots. One year after introduction, E. fetida was found only in the sludge-treated Norway spruce plot. The introduction of E. fetida with sludge decreased the density and biomass of L. terrestris in the hardwood plots.Sludge treatment increased the percentages of 4-mm diameter water-stable aggregates in old field and hardwood plots. The addition of E. fetida with sludge in the hardwood plots generated no increase in 4-mm water-stable aggregates. In the old field, sludge + E. fetida increased the 4-mm water-stable aggregates. Little change in water-stable aggregates in response to either treatment combination was seen in the Norway spruce site.     

Speciation of Zn,Cu, and Pb in the soil depending on soil texture and fertilization with sewage sludge compost

Background, aim, and scope  Heavy metal (HM) mobility in soil depends on the HM species in it. Therefore, knowledge of the HM speciation in soil allows the prediction of HM impact on the environment. HM speciation in soil depends on the metal chemical origin, soil texture, and other factors such as the origin and level of soil contamination. Recently, the problem of organic waste utilization is of great importance as the amount of this recyclable material is continually increasing. One of the possible ways of recycling is the use of processed organic wastes for agricultural needs. In this research, aerobically composted sewage sludge was used, the utilization of which is of essential importance. But one of the most serious restrictions is HM transfer from such material to the soil. Therefore, a prediction of HM mobility in soil and its migration in the environment is an important issue when using sewage sludge compost (SSC) in agriculture. Zn, Cu, and Pb speciation was performed according to the modified methodology of Tessier et al. (Anal Chem 51:844–851, 1979) in two different (sandy and clay) soils with background HM amounts and in soil samples amended with aerobically digested SSC to find out the predominant species of the investigated HM and to predict their potential availability. Materials and methods  The modified method of sequential extraction initially proposed by Tessier et al. (Anal Chem 51:844–851, 1979) is designed for HM speciation into five species where HM mobility decreases in the order: F1—exchangeable HM (extracted with 1 M MgCl₂ at an initial pH of 7 and room temperature), F2—carbonate-bound HM (extracted with 1 M CH₃COONa buffered to pH 5 at room temperature), F3—Fe/Mn oxide-bound HM (extracted with 0.04 M NH₂OH·HCl at an initial pH of 2 at 96°C), F4—organic matter-complexed or sulfide-bound HM (extracted with 0.02 M HNO₃ and 30% (v/v) H₂O₂ at a ratio of 1:1 and an initial pH of 2 at 85°C), and F5—the residual HM (digested with HNO₃, HF, and HCl mixture). After digestion, HM amounts in solution were determined by atomic absorption spectrometry (AAS ‘Hitachi’). Mixtures of uncontaminated soils of different textures (clay and sandy) with SSC in ratios 20:1, 10:1, and 5:1 were used to simulate the land application with SSC. During a period of 7 weeks, changes in Zn, Cu, and Pb content within species were investigated and compared weekly in soil–SSC mixtures with their speciation in pure soil and in the SSC. Results  Results in the SSC showed that more HM were found as mobile species compared to the soils, and in sandy soil, more were found in the mobile species than in clay soil. But the HM speciation strongly depended on the metal chemical origin. According to the potential availability, HM ranked in the following order: Zn>Pb>Cu. Zinc generally occurred in the mobile species (F1 and F3), especially in sandy soils amended with SSC, and changes of the Zn speciation were insignificant at the end of the experiment. Pb transfer to insoluble compounds (F5) was evident in the SSC–soil mixtures. This confirms that Pb is extremely immobile in the soil. However, the observed increase of Pb amounts in the mobile species (F1 and F2) during the course of experiment shows a critical trend of Pb mobilization under anthropogenic influence. Copper in the soil–SSC mixtures had a trend to form compounds of low mobility, such as organic complexes and sulfides (F4) and nonsoluble compounds (residual fraction F5). Initially, the amounts of mobile Cu species (F1 and F2) increased in the soils amended with SSC, probably due to the influence of SSC of anthropogenic origin with lower pH and high organic matter content, but Cu mobility decreased nearly to the initial level again after 3–4 weeks. Hence, the soil has a great specific adsorption capacity to immobilize Cu of anthropogenic origin. Discussion  Zn mobility and environmental impact was greater than that seen for Cu and Pb, while mobility of both Cu and Pb was similar, but variable depending on soil texture and contamination level. The effect on the shift of HM mobility and potential availability was greater in sandy SSC-amended soils than in clay soils and increased with an increasing amount of SSC. Conclusions  Usage of SSC for land fertilization should be strictly regulated, especially regarding Pb amounts. Recommendations and perspectives  The influence of SSC on Cu and Zn mobility and potential availability was more significant only in the case of sandy soil with a higher SSC ratio. Nevertheless, this waste product of anthropogenic origin increased Pb mobility in all cases in spite of only moderate Pb mobility in SSC itself. Therefore, aerobic processing of sewage sludge must be strictly regulated, especially regarding Pb amounts, and SSC ratios must be in control regarding HM amounts when using it for on-land application.     

Initial results from long-term field studies at three sites on the effects of heavy metal-amended liquid sludges on soil microbial activity

In a long‐term study of the effects on soil fertility and microbial activity of heavy metals contained in sewage sludges, metal‐amended liquid sludges each with elevated Zn, Cu or Cd concentrations were applied over a 3‐year period (1995–1997) to three sites in England. The experiments were sited adjacent to experimental plots receiving metal‐rich sludge cakes enabling comparisons to be made between the effects of heavy metal additions in metal‐amended liquid sludges and sludge cakes. The liquid sludge additions were regarded as ‘worst case’ treatments in terms of likely metal availability, akin to a long‐term situation following sewage sludge additions where organic matter levels had declined and stabilised. The aim was to establish individual Zn (50–425 mg kg^?1), Cu (15–195 mg kg^?1) and Cd (0.3–4.0 mg kg^?1) metal dose–response treatments at each site, but with significantly smaller levels of organic matter addition than the corresponding sludge cake experiments. There were no differences (P > 0.05) in soil respiration rates, biomass carbon concentrations or most probable numbers of clover Rhizobium between the treatments at any of the sites at the end of the liquid sludge application programme. Soil heavy metal extractability differed between the metal‐amended liquid sludge and metal‐rich sludge cake treatments; Zn and Cd extractabilities were higher from the liquid sludge additions, whereas Cu extractability was higher from the sludge cake application. These differences in metal extractability in the treated soil samples reflected the contrasting NH₄NO₃ extractable metal contents of the metal‐amended liquid sludges and sludge cakes that were originally applied.     

Uncoupling of microbial CO2 production and release in frozen soil and its implications for field studies of arctic C cycling

Knowledge of seasonal trends and controls of soil CO₂ emissions to the atmosphere is important for simulating atmospheric CO₂ concentrations and for understanding and predicting the global carbon cycle. This is particularly the case for high arctic soils subject to extreme fluctuating environmental conditions. Based on field measurements of soil CO₂ efflux, temperature, water content, pore gas composition in soil and frozen cores as well as detailed temperature experiments performed in the laboratory, we evaluated seasonal controls of CO₂ effluxes from a well-drained tundra heath site in NE-Greenland. During the growing season, near-surface temperatures correlated well with observed CO₂ effluxes (r²>0.9). However, during intensive thawing of near-surface layers we observed up to 1.5-fold higher effluxes than expected due to temperature alone. These high rates were consistent with high CO₂ concentrations in frozen soil (>10% CO₂) and suggested a spring burst event during soil thawing and a corresponding trapping of produced CO₂ during winter. Laboratory experiments revealed that microbial soil respiration continued down to a least −18 °C and that up to 80% of the produced CO₂ was trapped in soil at temperatures between 0 and −9 °C. The trapping of CO₂ in frozen soil was positively correlated with soil moisture (r²=0.85) and led to an abrupt change of the temperature sensitivity (Q₁₀) observed for soil CO₂ release at 0 °C with Q₁₀ values below 0 °C being up to 100-fold higher than above 0 °C. The results of sub-zero CO₂ production allowed us to predict the microbial soil respiration throughout the year and to evaluate to what extent burst events during thawing can be explained by the release of CO₂ being produced and trapped during winter. Taking only the upper 20 cm of the soil into account, winter soil respiration accounted for about 40% of the annual soil respiration. At least 14% of the winter CO₂ production was trapped during the winter 2000-2001 and observed to be released upon thawing. Thus, the site-specific winter soil respiration is an important part of the annual C cycle and CO₂ trapping should be accounted for in future field and modelling studies of soil respiration dynamics in arctic ecosystems. In conclusion, we have discovered a soil moisture dependent uncoupling of CO₂ production and release in frozen soils with important implications for future field studies of Arctic C cycling.     

Impact of atmospheric CO2 and plant life forms on soil microbial activities

From the global change perspective, increase of atmospheric CO₂ and land cover transformation are among the major impacts caused by human activities. In this study, we are addressing the combined issues of the effect of CO₂ concentration increase and plant type on soil microbial activities by asking how annual and perennial plant groups affect soil microbial processes under elevated CO₂. The experimental design used a mix of species of different growth forms for both annuals and perennials. Our objective was: (1) to determine how two years of annual or perennial plant cover and CO₂ enrichment could affect Mediterranean soil microbial processes; (2) to test the resistance and the resilience of these soil functional processes after a natural perturbation. We determined the effects of 2 years atmospheric CO₂ enrichment on soil potential respiration (SIR), denitrification (DEA) and nitrification (NEA) activities. We could not find any significant effect of CO₂ increase on SIR, DEA and NEA. However, we found a strong effect of the plant cover type, i.e. annuals versus perennials, on the potential microbial activity related to N cycling. DEA and NEA were significantly higher in soil under annual plants while SIR was not significantly different. To determine whether these changes would survive a natural perturbation, we carried out a rain event experiment once the experimental treatments (i.e. different plant cover and atmospheric CO₂ concentration) were stopped. The soil potential respiration, as expressed by the SIR, was not affected and remained stable. DEA rates converged rapidly under annuals and perennials after the rain event. Under both annuals and perennials NEA increased significantly after the rain event but remained significantly higher in the soil with annual plants. The relative change of the soil microbial processes induced by annual and perennial plants was inversely related to the density and the diversity of the corresponding microbial functional groups.     

Influence of polychlorinated biphenyls on microbial biomass and its activity in grassland soil

Microbial biomass content, soil respiration and biomass specific respiration rate were measured in two parts of an area polluted by a municipal waste incinerator [polychlorinated biphenyls (PCBs) from combustion processes]. The soils in the studied parts differed significantly only in their levels of PCBs. The concentration of PCBs found in a control plot (4.4 ng g^-1 soil) can be regarded as a background value while the polluted plot contained an increased amount of PCBs (14.0 ng g^-1 soil). A significantly lower microbial biomass (decreased by 23%, based on the chloroform-fumigation extraction technique) and a lower specific respiration rate (decreased by 14%) were observed in the polluted plot in comparison with the control plot at the end of experimental period (1992–1994). Furthermore, a lower ability of microorganisms in the polluted plot to convert available C_org into new biomass was found in laboratory incubations with glucose-amended samples.     

Flow-microcalorimetry measurements of aerobic and anaerobic soil microbial activity

Heat output can be used as an indicator of microbial activity and is usually measured in a microcalorimeter with closed ampoules. In long-term experiments particularly, interpretation of the data is hindered by the changing environment in the closed ampoules because of O₂ consumption and CO₂ enrichment. We used a combination of a flow-microcalorimeter and a gas chromatograph to measure the heat flux and CO₂ and N₂O production rates under controlled conditions. Simultaneous detection of the heat output and CO₂ emission allowed calculation of the calorimetric: CO₂ (Cal/CO₂) ratio. A mean ratio of-435 kJ mol^-1 CO₂ was detected in six different soils amended with glucose and incubated under aerobic conditions. This ratio indicated that CO₂ was the end-product of catabolism. In wet 10–12 mm soil aggregates of a gleyic vertisol amended with glucose, values of-285 kJ mol^-1 CO₂ under an aerobic and-141 kJ mol^-1 CO₂ under a N₂ atmosphere was determined. These findings indicated that fermentative metabolism occurred. The Cal/CO₂ ratio was not affected when enough NO _inf3 ^sup- was available and denitrification processes (N₂O production) were possible.     

Long-term impact of fertilization on activity and composition of bacterial communities and metabolic guilds in agricultural soil

To explore long-term impact of organic and inorganic fertilizers on microbial communities, we targeted both the total bacterial community and the autotrophic ammonia oxidizing bacteria (AOB) in soil from six treatments at an experimental field site established in 1956: cattle manure, sewage sludge, Ca(NO₃)₂, (NH₄)₂SO₄, unfertilized and unfertilized without crops. All plots, except the bare fallows, were cropped with maize. Effects on activity were assessed by measuring the basal respiration and substrate induced respiration (SIR) rates, and the potential activity of the AOB. To determine the bacterial community composition, 16S rRNA genes were used to fingerprint total soil communities by terminal restriction fragment length polymorphism analysis and AOB communities by denaturing gradient gel electrophoresis. The fertilization regimes had clear effects on both activity and composition of the soil communities. Basal respiration and r, which was kinetically derived as the exponentially growing fraction of the SIR-response, correlated well with the soil organic C content (r=0.93 and 0.66, respectively). Soil pH ranged from 3.97 to 6.26 in the treatments and was found to be an important factor influencing all microbial activities. pH correlated negatively with the ratio between basal respiration and SIR (r=0.90), indicating a decreased efficiency of heterotrophic microorganisms to convert organic carbon into microbial biomass in the most acid soils with pH 3.97 and 4.68 ((NH₄)₂SO₄ and sewage sludge fertilized plots, respectively). The lowest SIR and ammonia oxidation rates were also found in these treatments. In addition, these treatments exhibited individually different community fingerprints, showing that pH affected the composition of AOB and total bacterial communities. The manure fertilized plots harbored the most diverse AOB community and the pattern was linked to a high potential ammonia oxidation activity. Thus, the AOB community composition appeared to be more strongly linked to the activity than the total bacterial communities were, likely explained by physiological differences in the populations present.     

Effects of cow manure and sewage sludge on the activity and kinetics of <Emphasis Type="SmallCaps">l</Emphasis>-glutaminase in soil

A study was conducted to investigate the effects of cow manure and sewage sludge application on the activity and kinetics of soil l-glutaminase. Soil samples were collected from a farm experiment in which 0, 25, and 100 Mg ha⁻¹ of either cow manure or sewage sludge had been applied annually for 4 consecutive years to a clay loam soil (Typic Haplargid). A chemical fertilizer treatment had also been applied. Results indicated that the effects of chemical fertilizer and the solid waste application on pH in the 18 surface soil (0–15 cm) samples were not significant. The organic C content, however, was affected significantly by the different treatments, being the greatest in soils treated with 100 Mg ha⁻¹ cow manure, and the least in the control treatment. l-Glutaminase activity was generally greater in solid-waste applied soils and was significantly correlated (r = 0.939, P < 0.001) with organic C content of soils. The values of l-glutaminase maximum velocity (Vmax) ranged from 331 to 1,389 mg NH₄ ⁺–N kg⁻¹ 2 h⁻¹. Values of the Michaelis constant (K _m) ranged from 35.1 to 71.7 mM. Organic C content of the soils were significantly correlated with V _max (r = 0.919, P < 0.001) and K _m (r = 0.763, P < 0.001) values. These results demonstrate the considerable influence that solid waste application has on this enzymatic reaction involved in N mineralization in soil.     

煤粉尘添加量与温度对山西省两种土壤碳释放规律的影响

采用室内培养试验, 观测不同温度和不同煤粉尘用量条件下山西省电厂土和焦化厂土两种土壤的碳释放规律。结果表明, 室温(16~23 ℃)和25 ℃恒温下, 培养前期(4~9 d)土壤CO₂ 的释放量均为最大, 且25 ℃ 恒温培养土壤CO₂ 的释放量是室温条件下的2 倍左右。随煤粉尘添加量的增加, 土壤CO₂ 的释放量显著增加,且土壤活性有机质相应增加, 添加高量煤粉尘土壤CO₂ 的释放量最高达57.5 mg·kg^-1·d^-1, 两种土壤活性有机碳的增幅为0.3~3.8 g·kg^-1。不同温度和不同煤粉尘用量条件下电厂土释放的CO₂ 均高于焦化厂土, 可能是电厂土含有较高的有机碳和较低的黏粒所致。由此可知, 温度是影响土壤有机碳分解的主要因素, 其次是添加煤粉尘的量, 土壤理化性质也是原因之一。本研究表明, 煤粉尘的降落一方面增加了土壤CO₂ 的释放, 另一方面增加了土壤碳库。