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1.
 The effect of long-term waste water irrigation (up to 80 years) on soil organic matter, soil microbial biomass and its activities was studied in two agricultural soils (Vertisols and Leptosols) irrigated for 25, 65 and 80 years respectively at Irrigation District 03 in the Valley of Mezquital near Mexico City. In the Vertisols, where larger amounts of water have been applied than in the Leptosols, total organic C (TOC) contents increased 2.5-fold after 80 years of irrigation. In the Leptosols, however, the degradability of the organic matter tended to increase with irrigation time. It appears that soil organic matter accumulation was not due to pollutants nor did microbial biomass:TOC ratios and qCO2 values indicate a pollutant effect. Increases in soil microbial biomass C and activities were presumably due to the larger application of organic matter. However, changes in soil microbial communities occurred, as denitrification capacities increased greatly and adenylate energy charge (AEC) ratios were reduced after long-term irrigation. These changes were supposed to be due to the addition of surfactants, especially alkylbenzene sulfonates (effect on denitrification capacity) and the addition of sodium and salts (effect on AEC) through waste water irrigation. Heavy metals contained in the sewage do not appear to be affecting soil processes yet, due to their low availability. Detrimental effects on soil microbial communities can be expected, however, from further increases in pollutant concentrations due to prolonged application of untreated waste water or an increase in mobility due to higher mineralization rates. Received: 28 April 1999  相似文献   

2.
The effects of moisture, NO3?1 concentration and C addition on changes in denitrification capacity and total microbial biomass in a clay loam soil were investigated. Denitrification capacity was evaluated with an anaerobic slurry technique. Total microbial biomass was measured by CHC13 fumigation and by extraction of microbial ATP. The results indicate that denitrification capacity and total microbial biomass were increased only by the C addition; differences in NO3?1 concentration and moisture had no effect in this agricultural soil. The increase in denitrification capacity could be attributed solely to microbial growth, since the ratio of denitrification capacity to total microbial biomass remained constant and the increased respiration from the C amendment did not increase anaerobiosis. The results also show that denitrifiers compete as effectively for added C as do other heterotrophs.  相似文献   

3.
Analysis of manure and soil nitrogen mineralization during incubation   总被引：1，自引：0，他引：1  
Understanding the N-cycling processes that ensue after manuring soil is essential in order to estimate the value of manure as an N fertilizer. A laboratory incubation of manured soil was carried out in order to study N mineralization, gas fluxes, denitrification, and microbial N immobilization after manure application. Four different manures were enclosed in mesh bags to allow for the separate analysis of manure and soil. The soils received 0.15 mg manure N g–1 soil, and the microcosms were incubated aerobically and sampled throughout a 10-week period. Manure addition resulted in initial NH4-N concentrations of 22.1 to 36.6 mg kg–1 in the microcosms. All manured microcosms had net declines in soil mineral N. Denitrification resulted in the loss of 14.7 to 39.2% of the added manure N, and the largest N losses occurred in manures with high NH4-N content. Increased soil microbial biomass N amounted to 6.0 to 8.6% of the added manure N. While the microcosms as a whole had negative N mineralization, all microcosms had positive net nitrification within the manure bags. Gas fluxes of N2O and CO2 increased in all manured soils relative to the controls. Our results show that measurement of microbial biomass N and denitrification is important to understand the fate of manure N upon soil application.  相似文献   

4.
The study was conducted under irrigated field conditions to examine the effect of maize plants on denitrification. Both planted and unplanted field plots received 150kgNha–1 as urea. In a third treatment, which was also planted and received urea at 150kgNha–1, the soil nitrate N content was brought up to equal to that in the unplanted plots by applying additional doses of N as calcium nitrate. Soil cores were collected 24 and 72h after irrigation and the denitrification rate was measured by the acetylene inhibition method. Nitrate-N content, aerobically mineralizable C, microbial biomass carrying capacity and denitrification potential were also studied on field-moist soil. Maize plants grown under field conditions always had the potential to increase denitrification in conditions of both high and low water-filled porosity. When nitrate-N content of the planted soil decreased due to plant uptake, denitrification was reduced in the planted soils. However, when nitrate-N uptake by plants was compensated through additional doses of nitrate fertilizer, denitrification was always higher in planted than unplanted soil. The stimulatory effect of plants on denitrification was observed at both high and low soil nitrate-N concentrations, though it was more pronounced at high nitrate-N levels. The effect of plants on denitrification and related parameters was confined to the root zone. Received: 15 April 1996  相似文献   

5.
Summary The role of soluble organic carbon (SOC) in denitrification in four mineral soils and one organic soil was evaluated in laboratory studies. Denitrification capacities and SOC concentrations were determined by nitrate loss from air-dried flooded soil treated with a solution containing 100 g/ml N03 –-N, while the rate of consumption was measured by Warburg manometry on 20 g air-dried soils to which 10 ml water had been added. High correlation coefficients (r > 0.93) were obtained between denitrification capacities, SOC, and oxygen consumption in the five soils. A mineral soil was amended with extracts of an organic soil. After incubating for 1 week, denitrification capacity was enhanced and SOC concentrations decreased in that soil. Extracted mineral soil had a lower denitrification capacity than an unextracted one. Decreases in concentrations of SOC were related to color change. Infrared spectra of precipitates from soil extracts indicated that absorption at wave number 1420–1440 cm -1 was also related to the color changes. It was implied that low molecular weight fulvic acid like compounds represented the SOC mineralized in denitrification, and that their supply to soil solution by solubilization of organic matter influenced the denitrification rate in the soil.  相似文献   

6.
《Applied soil ecology》2006,34(3):269-277
Effluents from leather processing, a major industry that produces up to 64320 t wastewater year−1 in the town of León (Guanajuato, Mexico), are normally discharged to the river Turbio without treatment. This water is downstream used to irrigate agricultural land. Tannery wastewater contains valuable nutrients, but also contaminants, such as salts and chromium (Cr), that might affect soil processes and crop production. We investigated how almost 25 years of irrigation of agricultural land with water from the river Turbio affected soil characteristics, dynamics of carbon (C) and nitrogen (N), and microbial biomass C. Soil sampled from three adjacent fields irrigated with tannery effluent (soil A), in the vicinity irrigated with well water (soil B), and at a distance of 10 km from the irrigation canals (soil C), was characterized while dynamics of C and N were measured in an aerobic incubation experiment. Irrigation with water from the river Turbio for over 25 years had significantly increased the electrolytic conductivity from 0.64 to 2.29 dS m−1, organic C and total N content two-times, total concentration of Cr four-times, copper (Cu) two-times and sodium (Na) six-times in the clayey soils (P < 0.05). Microbial biomass was two-times larger in soil A than in soil C, while the activity of proteases and hydrolases releasing ninhydrin positive compounds and organic C appeared not to be affected. The concentrations of ammonium (NH4+) and nitrate (NO3−) were not significantly different between the soils. The concentration of nitrite (NO2−) was approximately twice larger in soil A than in soil C (P < 0.05). Although there appeared to be no adverse impact on soil characteristics and microbial biomass, oxidation of NO2− was inhibited indicating that the biological functioning of the soil might be affected. The increase in heavy metals in soil was limited, but continued irrigation with water from the river Turbio might increase sodicity and salinity that could deteriorate soil and pose a threat to future crop production.  相似文献   

7.
Under semiarid subtropical field conditions, denitrification was measured from the arable soil layer of an irrigated wheat–maize cropping system fertilized with urea at 50 or 100 kg N ha–1 year–1 (U50 and U100, respectively), each applied in combination with 8 or 16 t ha–1 year–1 of farmyard manure (FYM) (F8 and F16, respectively). Denitrification was measured by acetylene inhibition/soil core incubation method, also taking into account the N2O entrapped in soil cores. Denitrification loss ranged from 3.7 to 5.7 kg N ha–1 during the growing season of wheat (150 days) and from 14.0 to 30.3 kg N ha–1 during the maize season (60 days). Most (up to 61%) of the loss occurred in a relatively short spell, after the presowing irrigation to maize, when the soil temperature was high and a considerable NO3–-N had accumulated during the preceding 4-month fallow; during this irrigation cycle, the lowest denitrification rate was observed in the treatment receiving highest N input (U100+F16), mainly because of the lowest soil respiration rate. Data on soil respiration and denitrification potential revealed that by increasing the mineral N application rate, the organic matter decomposition was accelerated during the wheat-growing season, leaving a lower amount of available C during the following maize season. Denitrification was affected by soil moisture and by soil temperature, the influence of which was either direct, or indirect by controlling the NO3– availability and aerobic soil respiration. Results indicated a substantial denitrification loss from the irrigated wheat–maize cropping system under semiarid subtropical conditions, signifying the need of appropriate fertilizer management practices to reduce this loss.  相似文献   

8.
We investigated Cd, Zn, and Cd + Zn toxicity to soil microbial biomass and activity, and indigenous Rhizobium leguminosarum biovar trifolii, in two near neutral pH clay loam soils, under long-term arable and grassland management, in a 6-month laboratory incubation, with a view to determining the causative metal. Both soils were amended with Cd- or Zn-enriched sewage sludge, to produce soils with total Cd concentrations at four times (12 mg Cd g−1 soil), and total Zn concentrations (300 mg Zn kg−1 soil) at the EU upper permitted limit. The additive effects of Cd plus Zn at these soil concentrations were also investigated. There were no significant differences in microbial biomass C (B C), biomass ninhydrin N (B N), ATP, or microbial respiration between the different treatments. Microbial metabolic quotient (defined as qCO2 = units of CO2–C evolved unit−1 biomass C unit−1 time) also did not differ significantly between treatments. However, the microbial maintenance energy (in this study defined as qCO2-to-μ ratio value, where μ is the growth rate) indicated that more energy was required for microbial synthesis in metal-rich sludge-treated soils (especially Zn) than in control sludge-treated soils. Indigenous R. leguminosarum bv. trifolii numbers were not significantly different between untreated and sludge-treated grassland soils after 24 weeks regardless of metal or metal concentrations. However, rhizobial numbers in the arable soils treated with metal-contaminated sludges decreased significantly (P < 0.05) compared to the untreated control and uncontaminated sludge-treated soils after 24 weeks. The order of decreasing toxicity to rhizobia in the arable soils was Zn > Cd > Cd + Zn.  相似文献   

9.
Nitrogen dynamics in different types of pasture in the Austrian Alps   总被引：7，自引：0，他引：7  
 Soil N dynamics were compared in Alpine pastures on two mountains. N-pool sizes and N fluxes were measured relative to N losses via leaching and denitrification in summer. On each mountain, four types of pasture were studied: (1) forest pastures, (2) recently developed pastures formed by forest clearance ("new pastures"), (3) older established pastures, and (4) pastures planted with clover. At both study sites (Scheuchegg and Teufelstein) we obtained similar results. Compared with forest pasture soils, open pasture soils were found to have greater microbial biomass and faster mineralisation potentials, but net field mineralisation rates were slower. In the forest pastures, highest N losses via denitrification were found. Higher potential leaching of NO3 –, estimated by accumulation of NO3 – on ion-exchange resins, in the forest pasture soils suggests lower N uptake by microbes and herbaceous plants compared with open pastures. N2O-production rates of the forest pasture soils at the Scheuchegg site (11.54 μg N2O-N m–2 h–1) were of similar magnitude to those reported for spruce forests without pastures, but at Teufelstein (53.75 μg N2O-N m–2 h–1) they were higher. However, if forest pastures are not overgrazed, no elevated N loss through N2O production and leaching of NO3 – is expected. Denitrification rates in the open pastures (0.83–7.50 μg N2O-N m–2 h–1) were low compared with reports on lowland pastures. In soils of the new pastures, rates of microbial N processes were similar to those in the established pastures, indicating a high capacity of soils to restore their internal N cycle after forest clearance. Received: 19 August 1999  相似文献   

10.
 This study examines the effect of soil P status and N addition on the decomposition of 14C-labelled glucose to assess the consequences of reduced fertilizer inputs on the functioning of pastoral systems. A contrast in soil P fertility was obtained by selecting two hill pasture soils with different fertilizer history. At the two selected sites, representing low (LF) and high (HF) fertility status, total P concentrations were 640 and 820 mg kg–1 and annual pasture production was 4,868 and 14,120 kg DM ha–1 respectively. Soils were amended with 14C-labelled glucose (2,076 mg C kg–1 soil), with and without the addition of N (207 mg kg–1 soil), and incubated for 168 days. During incubation, the amounts of 14CO2 respired, microbial biomass C and 14C, microbial biomass P, extractable inorganic P (Pi) and net N mineralization were determined periodically. Carbon turnover was greatly influenced by nutrient P availability. The amount of glucose-derived 14CO2 production was high (72%) in the HF and low (67%) in the LF soil, as were microbial biomass C and P concentrations. The 14C that remained in the microbial biomass at the end of the 6-month incubation was higher in the LF soil (15%) than in the HF soil (11%). Fluctuations in Pi in the LF soil during incubation were small compared with those in HF soil, suggesting that P was cycling through microbial biomass. The concentrations of Pi were significantly greater in the HF samples throughout the incubation than in the LF samples. Net N mineralization and nitrification rates were also low in the LF soils, indicating a slow turnover of microorganisms under limited nutrient supply. Addition of N had little effect on biomass 14C and glucose utilization. This suggests that, at limiting P fertility, C turnover is retarded because microbial biomass becomes less efficient in the utilization of substrates. Received: 18 October 1999  相似文献   

11.

Background

Little is known about the effects of gypsum application to remediate saline–sodic soils in the tropics and the role of microbial indicators in soil reclamation.

Aims

Our study aimed at (1) remediating a highly weathered, irrigated sodic Lixisol under prolonged urban crop production by clean water and gypsum application and (2) to determine the remediation effects on soil microbial indices.

Methods

A three-factorial on-farm experiment with maize (Zea mays L.) was used to study effects on soil microbial biomass of (1) soil degradation at two levels of salinity, (2) irrigation with clean water and wastewater, and (3) the impact of added gypsum during a typical growing season.

Results

At the high-degradation site, the 0.5 M K2SO4 extractable carbon (C) content was 40% higher than at the low-degradation site. In addition, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were 20% lower than at the low-degradation site, while fungal ergosterol was even 40% lower, leading to a 33% lower ergosterol/MBC ratio. Wastewater irrigation increased MBN but decreased ergosterol content at the low-degradation site while having no effect at the high-degradation site. Gypsum amendment led to higher MBN at the low-degradation site but to lower MBN at the high-degradation site. Gypsum amendment always increased the ergosterol content whereby this increase was stronger at the low-degradation site, especially in combination with wastewater irrigation.

Conclusions

From a microbial perspective, high soil degradation levels should be avoided by treatment of a saline–sodic wastewater prior to its use for irrigation rather than relying on future remediation strategies of affected field sites.  相似文献   

12.
Predicting the impact of irrigation practices on soil N mineralization and N balance is an important issue to optimize N fertilization and reduce the N losses towards the environment. The effect of summer irrigation on N dynamics was investigated in two arable fields in Southern France. Net N mineralization was assessed by combining frequent measurements of water and mineral N contents in soil and the use of a calculation model (LIXIM). It was first calculated assuming that denitrification was negligible. This hypothesis led to inconsistent results, apparent net N mineralized being smaller under irrigated than non-irrigated conditions and net mineralization kinetics being erratic. The occurrence of denitrification was confirmed by the use of 15NO3 tracing in an experiment carried out in summer, including three irrigated treatments. The average 15N recovery varied from 45% to 85% and was smallest in the most frequently irrigated treatment. Over the 8-week experiment, the N losses varied from 30 to 38 kg ha−1 in the irrigated treatments. They were satisfactorily simulated by a simple denitrification model (NEMIS). Combining the LIXIM model and the simulated or calculated denitrification allowed to predict satisfactorily the evolution of soil mineral N accounting for the effects of temperature and moisture. The net N mineralized for 8 weeks varied from 34 kg N ha−1 in the un-irrigated to 46 kg N ha−1 in the irrigated treatments. The drying–rewetting cycles did not induce a flush of N mineralization. Our results suggest that denitrification has to be accounted for in irrigated systems, particularly in warm conditions and when the topsoil contains high nitrate contents.  相似文献   

13.
 Soil microbial biomass and the emission of CO2 from the soil surface were measured in yellow soils (Ultisols) of the karst areas of southwest China. The soils are relatively weathered, leached and impoverished, and have a low input of plant residues. The measurements were made for a 1-year period and show a reciprocal relationship between microbial biomass and surface CO2 efflux. The highest (42.6±2.8 mg CO2-C m–2 h–1) and lowest (15.6±0.6 mg CO2-C m–2 h–1) CO2 effluxes are found in the summer and winter, respectively. The cumulative CO2 efflux is 0.24 kg CO2-C m–2 year–1. There is also a marked seasonal variation in the amount of soil microbial biomass carbon, but with the highest (644±71 μg C g–1 soil) and lowest (270±24 μg C g–1 soil) values occurring in the winter and summer, respectively. The cumulative loss of soil microbial biomass carbon in the top 10 cm of the soil was 608 μg C g–1 year–1 soil over 17 sampling times. The mean residence time of microbial biomass is estimated at 105 days, suggesting that the carbon in soil microbial biomass may act as a source of the CO2 released from soils. Received: 13 July 1999  相似文献   

14.
 Soils from the former Lake Texcoco are alkaline saline and were artificially drained and irrigated with sewage effluents since the late 1980s. Undrained soil and soil drained for 1, 5 and 8 years were sampled, characterized and incubated aerobically for 90 days at 22±1  °C while production of CO2, available P and concentrations of NH4 +, NO2 – and NO3 – were monitored. Artificial drainage decreased pHH2O, water holding capacity, organic C, total N, and Na+, K+, Mg2+, B, Cl– and SO4 2– concentrations, increased inorganic C and Ca2+ concentrations more than 5-fold while total P was not affected. Microbial biomass C decreased with increased length of drainage but bacteria, actinomycetes, denitrifiers and cellulose-utilizing bacteria tended to show opposite trends. CO2 production was less in soils drained ≥5 years compared to undrained soil but more than in soils drained for 1 year. Emission of NH3 was negligible and concentrations of NH4 + remained constant over time in each soil. Nitrification, as witnessed by increases in NO3 – concentrations, occurred in soil drained for 8 years. NO2 – concentrations decreased in soils drained ≤1 year in the first 7 days of the incubation and remained constant thereafter. It was found that artificial drainage of soils from the former Lake Texcoco profoundly affected soil characteristics. Decreases in pH and Na+, K+, Cl– and SO4 2– concentrations made conditions more favourable for plant growth, although low concentrations of inorganic N and available P might be limiting factors. Received: 1 December 1999  相似文献   

15.
Most important, yet least understood, question, how microbial activity in soil under saline water irrigation responds to carbon (C) varying qualitatively (most labile form to extreme recalcitrant form) with or without maintaining C/N ratio was investigated in an incubation experiment. Soil samples from a long-term saline-water (electrical conductivity, EC ≈ 0, 6, and 12 dS m?1)- irrigated field were incorporated with three different C substrates, viz., glucose, rice straw (RS), and biochar with or without nitrogen (N as ammonium sulfate, NH4SO4) and were incubated at 25 °C for 56 days. Cumulative respiration (CR), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and dehydrogenase activity (DEA) concentrations decreased with increasing EC (P < 0.05), but less so in soils amended with glucose followed by RS and biochar. The addition of N to soils amended with different C substrates significantly decreased CR, MBC, DEA, and available phosphorus (P) concentrations at a given EC level.  相似文献   

16.
We examined the impact of long-term cattle grazing on soil processes and microbial activity in a temperate salt marsh. Soil conditions, microbial biomass and respiration, mineralization and denitrification rates were measured in upper salt marsh that had been ungrazed or cattle grazed for several decades. Increased microbial biomass and soil respiration were observed in grazed marsh, most likely stimulated by enhanced rates of root turnover and root exudation. We found a significant positive effect of grazing on potential N mineralization rates measured in the laboratory, but this difference did not translate to in situ net mineralization measured monthly from May to September. Rates of denitrification were lowest in the grazed marsh and appeared to be limited by nitrate availability, possibly due to more anoxic conditions and lower rates of nitrification. The major effect of grazing on N cycling therefore appeared to be in limiting losses of N through denitrification, which may lead to enhanced nutrient availability to saltmarsh plants, but a reduced ability of the marsh to act as a buffer for land-derived nutrients to adjacent coastal areas. Additionally, we investigated if grazing influences the rates of turnover of labile and refractory C in saltmarsh soils by adding 14C-labelled leaf litter or root exudates to soil samples and monitoring the evolution of 14CO2. Grazing had little effect on the rates of mineralization of 14C used as a respiratory substrate, but a larger proportion of 14C was partitioned into microbial biomass and immobilized in long- and medium-term storage pools in the grazed treatment. Grazing slowed down the turnover of the microbial biomass, which resulted in longer turnover times for both leaf litter and root exudates. Grazing may therefore affect the longevity of C in the soil and alter C storage and utilization pathways in the microbial community.  相似文献   

17.
The application of mineral N fertilizers may influence biologically mediated processes that are important in nutrient transformations and availability. This study was conducted to assess the effect of N application on microbial activities in irrigated and non-irrigated winter wheat systems. Carbon decomposition and microbial biomass C in soils with three N application rates (0, 150, and 300 kg N ha–1 as urea) were measured over 40 days in a laboratory incubation experiment. Carbon, N, and P contents in the soil under the irrigated wheat were higher than those in the soil under the non-irrigated wheat. The reverse trend was observed for soil pH and Ca and Mg contents. However, soils from the two systems had similar C/N ratios. Carbon decomposition and microbial biomass C in the soil under the irrigated wheat increased significantly (p <0.05). Increasing rates of N fertilizer resulted in higher C decomposition and microbial biomass C levels in both soil systems. Results indicate that different wheat cropping systems affect soil properties that will then have an impact on C turnover in the soil. Moreover, the irrigated wheat system favors soil conditions required for a faster C turnover. In conclusion, it is likely that due to positive effects on microbial activity, N fertilization will increase nutrient cycling and, subsequently, crop productivity will improve in N-poor soils.  相似文献   

18.
Microbial activity levels of two soil materials, excavated from a wetland and irrigated with municipal wastewater effluent or Missouri River water, were compared. The wastewater had twice the electrical conductivity and four times the sodium concentration as river water. We performed activity assays on the soils before leaching, immediately after leaching, and after harvesting plants. Gas chromatography was used to measure carbon dioxide (CO2) evolved in soil samples incubated for 7 d. Activity was significantly reduced in preleached wastewater–irrigated soils compared with river water–irrigated soils. Immediately after leaching, activity significantly increased and was similar to river water–irrigated soils. Activity decreased slightly after plant harvest in postleached treatments. Increased activity after leaching may be related to decreased salinity and sodicity, which probably lowered osmotic pressure in the soil. Our study demonstrated that soil salinity and sodicity induced by wastewater irrigation decreased microbial activity, which may impact nutrient cycling and glycophytic vegetation communities in wetlands.  相似文献   

19.
A short-term anaerobic incubation technique using the C2H2 inhibition of N2O-reductase for comparing denitrification potentials of soils is described. Twenty grams of soil with added NO?13 are incubated in the presence of He and 0.1 atm C2H2 at 25°C and 0 soil matric potential for 8 h. N2O evolution is linear within 60 to 120 min. The denitrification potential of soils stored at 4°C decreased markedly over 21 days of storage in accordance with changes in the available C. Denitrification under an anaerobic atmosphere was observed at 4 C. Denitrification potentials were independent of NO?33 concentrations above 25 μg NO?3-N g?1 soil. Biphasic linear rates of N2O evolution were observed in one soil. Incubation of this soil with chloramphenicol suggested the first linear phase is attributable to the in situ enzyme activity at the time of sampling. The second linear phase is indicative of the dentrification potential and is attributed to the full induction of denitrifying enzymes. The denitrification potential of a soil was maintained at or close to the maximum for 8 months of the year. During midsummer months the denitrification potential decreased markedly and the soil demonstrated a biphasic rate of denitrification suggesting an in situ denitrification activity less than the maximum potential. Results indicate that the maximum denitrification potential of this soil may often be limited not by NO?3 but by available C.  相似文献   

20.
 A model describing the respiration curves of glucose-amended soils was applied to the characterization of microbial biomass. Both lag and exponential growth phases were simulated. Fitted parameters were used for the determination of the growing and sustaining fractions of the microbial biomass as well as its specific growth rate (μ max). These microbial biomass characteristics were measured periodically in a loamy silt and a sandy loam soil incubated under laboratory conditions. Less than 1% of the biomass oxidizing glucose was able to grow immediately due to the chronic starvation of the microbial populations in situ. Glucose applied at a rate of 0.5 mg C g–1 increased that portion to 4–10%. Both soils showed similar dynamics with a peak in the growing biomass at day 3 after initial glucose amendment, while the total (sustaining plus growing) biomass was maximum at day 7. The microorganisms in the loamy silt soil showed a larger growth potential, with the growing biomass increasing 16-fold after glucose application compared to a sevenfold increase in the sandy loam soil. The results gained by the applied kinetic approach were compared to those obtained by the substrate-induced respiration (SIR) technique for soil microbial biomass estimation, and with results from a simple exponential model used to describe the growth response. SIR proved to be only suitable for soils that contain a sustaining microbial biomass and no growing microbial biomass. The exponential model was unsuitable for situations where a growing microbial biomass was associated with a sustaining biomass. The kinetic model tested in this study (Panikov and Sizova 1996) proved to describe all situations in a meaningful, quantitative and statistically reliable way. Received: 19 July 1999  相似文献   

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