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1.
Abstract. Gross N mineralization and nitrification rates were measured in soils treated with dairy shed effluent (DSE) (i.e. effluent from the dairy milking shed, comprising dung, urine and water) or ammonium fertilizer (NH4Cl) under field conditions, by injecting 15N-solution into intact soil cores. The relationships between gross mineralization rate, microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) as affected by the application of DSE and NH4Cl were also determined. During the first 16 days, gross mineralization rate in the DSE treated soil (4.3–6.1 μg N g?1 soil day?1) were significantly (P 14;< 14;0.05) higher than those in the NH4Cl treated soil (2.6–3.4 μg N g?1 soil day?1). The higher mineralization rate was probably due to the presence of readily mineralizable organic substrates in the DSE, accompanied by stimulated microbial and extracellular enzyme activities. The stable organic N compounds in the DSE were slow to mineralize and contributed little to the mineral N pool during the period of the experiment. Nitrification rates during the first 16 days were higher in the NH4Cl treated soil (1.7–1.2 μg N g?1 soil day?1) compared to the DSE treated soil (0.97–1.5 μg N g?1 soil day?1). Soil microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) increased after the application of the DSE due to the organic substrates and nutrients applied, but declined with time, probably because of the exhaustion of the readily available substrates. The NH4Cl application did not result in any significant increases in microbial biomass C, protease or urease activities due to the lack of carbonaceous materials in the ammonium fertilizer. However, it did increase microbial biomass N and deaminase activity. Significant positive correlations were found between gross N mineralization rate and soil microbial biomass, protease, deaminase and urease activities. Nitrification rate was significantly correlated to biomass N but not to the microbial biomass C or the enzyme activities. Stepwise regression analysis showed that the variations of gross N mineralization rate was best described by the microbial biomass C and N. 相似文献
2.
Nitrogen mineralization and microbial activity in permanent pastures amended with nitrogen fertilizer or dung 总被引:9,自引:0,他引:9
D. J. Hatch R. D. Lovell R. S. Antil S. C. Jarvis P. M. Owen 《Biology and Fertility of Soils》2000,30(4):288-293
Gross rates of soil processes and microbial activity were measured in two grazed permanent pasture soils which had recently
been amended with N fertilizer or dung. 15N studies of rates of soil organic matter turnover showed gross N mineralization was higher, and gross N immobilization was
lower, in a long-term fertilized soil than in a soil which had never received fertilizer N. Net mineralization was also found
to be higher in the fertilized soil: a consequence of the difference between the opposing N turnover processes of N mineralization
and immobilization. In both soils without amendments the soil microbial biomass contents were similar, but biomass activity
(specific respiration) was higher in the fertilized soil. Short-term manipulation of fertilizer N input, i.e. adding N to
unfertilized soil, or witholding N from previously fertilized soil, for one growing season, did not affect gross mineralization,
immobilization or biomass size and activity. Amendments of dung had little effect on gross mineralization, but there was an
increase in immobilization in both soils. Total biomass also increased under dung in the unfertilized soil, but specific respiration
was reduced, suggesting changes in the composition of the biomass. Dung had a direct effect on the microbial biomass by temporarily
increasing available soil C. Prolonged input of fertilizer N increases soil C indirectly as a result of enhanced plant growth,
the effect of which may not become evident within one seasonal cycle.
Received: 18 December 1998 相似文献
3.
In a cropping systems experiment in southeastern Norway, ecological (ECO), integrated (INT) and conventional (CON) forage
(FORAGE) and arable (ARABLE) model farms were compared. After 5 experimental years, topsoil was sampled in spring from spring
grain plots and incubated for 449 days at controlled temperature (15 °C) and moisture content (50% water-holding capacity).
There were no detectable differences between model farms in terms of total soil C or N. For INT and CON, however, values of
microbial biomass C and N, microbial quotient (Cmic/Corg), and C and N mineralization were, or tended to be, higher for FORAGE than for ARABLE. For the ECO treatment, values were
similar for FORAGE and ARABLE and did not differ significantly from that of CON-FORAGE. For INT and CON, the metabolic quotient
(qCO2) was lower for FORAGE than for ARABLE. Again, for the ECO treatment, values were similar for FORAGE and ARABLE and did not
differ significantly from that of CON-FORAGE. We estimated the sizes of conceptual soil organic matter pools by fitting a
decomposition model to biomass and mineralization data. This resulted in a 48% larger estimate for CON-FORAGE than for CON-ARABLE
of physically protected biomass C. For physically protected organic C the difference was 42%. Moreover, the stability of soil
aggregates against artificial rainfall was substantially greater for CON-FORAGE than for CON-ARABLE. On this basis, we hypothesized
that the lower qCO2 values in the FORAGE soils were mainly caused by a smaller proportion of active biomass due to enclosure of microorganisms
within aggregates. Altogether, our results indicated a poorer inherent soil fertility in ARABLE than in FORAGE rotations,
but the difference was small or absent in the ECO system, probably owing to the use of animal and green manures and reduced
tillage intensity in the ECO-ARABLE rotation.
Received: 28 October 1998 相似文献
4.
Phosphorus mineralization and microbial biomass in a Florida Spodosol: effects of water potential, temperature and fertilizer application 总被引:1,自引:0,他引:1
Phosphorus mineralization and microbial biomass were measured in the surface 5 cm of a Spodosol (sandy, siliceous hyperthermic
Ultic Alaquod) from north-central Florida. Soils from fertilized and unfertilized plantations of loblolly pine (Pinus taeda L.) were incubated at a range of water potentials (∼0, –3, –8, –10 and –1500 kPa) and temperatures (15 °C, 25 °C and 38 °C)
for 14 days and 42 days. Increasing water potential and temperature increased specific P mineralization (mineralization expressed
as a percentage of total P) regardless of fertilizer treatment. An increase in water potential from –10 kPa to –0.1 kPa resulted
in an increase of between 38% and 239% in the concentration of KCl-extractable inorganic P, depending on incubation temperature
and time. An increase in incubation temperature from 15 °C to 38 °C resulted in an increase of between 13% and 53% in KCl-extractable
inorganic P. Changes in specific P mineralization with change in water potential or temperature were not affected by fertilizer
application. This suggests that, although specific P mineralization was greater in the fertilized soils, environmental control
of P mineralization was the same for both treatments. Specific P mineralization was most sensitive when soils were at higher
water potentials, and decreased logarithmically to water potentials of between –3 kPa and –8 kPa. Specific P mineralization
was relatively insensitive to changes in water potential when water potential was lower than –8 kPa. Microbial biomass C showed
no consistent responses to changes of temperature or water potential and was not significantly correlated with specific P
mineralization. Our results suggest that field estimates of P mineralization in these Spodosols may be improved by accounting
for changes in soil water potential and temperature.
Received: 30 October 1997 相似文献
5.
We manipulated Collembola Folsomia candida Willem density and observed the density effect on carbon and nitrogen mineralization and on nematodes in microcosms filled
with mineral soil. Collembolan densities were 0 (control), 25 (low), 100 (medium), and 400 (high) individuals per microcosm.
The Collembola enhanced soil respiration and nitrogen mineralization rate in a density-dependent manner (P < 0.05). The correlation between collembolan density and the metabolic quotient of microbes, qCO2, was weakly positive (r = 0.44, P < 0.05). Collembola did not affect microbial biomass. These results suggested that enhanced carbon and nitrogen mineralization
was an indirect effect of Collembola mediated by increased microbial activity. Collembola changed the Cnema/Cmic ratio, but only when present at the low density. Thus, Collembola had both positive and negative effects on the nematode
population. The positive impact probably depends on the enhancement of microbial activity due to Collembola grazing behavior,
while the negative effect appears to result from predation of nematodes. 相似文献
6.
Dynamics of soil microbial biomass and nitrogen availability in a flooded rice soil amended with different C and N sources 总被引:4,自引:0,他引:4
A greenhouse experiment was conducted to compare effects of different C and N sources applied to a flooded soil on soil microbial
biomass (SMB) C and N, extractable soil organic N (NORG), and NH4
+-N in relation to plant N accumulation of rice (Oryza sativa L.). In addition to a control without inputs (CON), four treatments were imposed receiving: prilled urea (PU), rice straw
(RS), RS and PU (RS+PU), or Sesbania rostrata as green manure (SES). Treatments were arranged according to a completely randomized design with four replicates and further
consisted of pots with and without transplanted rice. While plant effects on the SMB were relatively small, the application
of organic N sources resulted in a rapid increase in SMB until 10 days after transplanting (DAT) followed by a gradual decline
until 73 DAT. Plant N accumulation data in these treatments clearly indicated that the SMB underwent a transition from a sink
to a source of plant-available soil N during the period of crop growth. Seasonal variation of the SMB was small in treatments
without amendment of organic material (CON, PU) presumably due to a lack of available C as energy source. Extractable NORG was significantly affected by soil planting status and organic N source amendment, but represented only a small N pool with
little temporal variation despite an assumed rapid turnover. Among the three treatments receiving the same amount of N from
different sources, the recovery efficiency of applied N was 58% for PU and 28% for both RS+PU and SES treatments at 73 DAT.
The N uptake of rice, however, was not driven by N availability alone, as most evident in the RS+PU treatment. We assume that
root physiological functions were impeded after application of organic N sources.
Received: 1 June 1999 相似文献
7.
Exchangeable ammonium and nitrate from different nitrogen fertilizer preparations in polyacrylamide-treated and untreated agricultural soils 总被引:3,自引:0,他引:3
J. L. Kay-Shoemake M. E. Watwood L. Kilpatrick K. Harris 《Biology and Fertility of Soils》2000,31(3-4):245-248
High molecular weight, anionic polyacrylamide (PAM) is currently being used as an irrigation water additive to significantly
reduce soil erosion associated with furrow irrigation. PAM contains amide-N, and PAM application to soils has been correlated
with increased activity of soil enzymes, such as urease and amidase, involved in N cycling. Therefore we investigated potential
impacts of PAM treatment on the rate at which fertilizer N is transformed into NH4
+ and NO3
– in soil. PAM-treated and untreated soil microcosms were amended with a variety of fertilizers, ranging from common rapid-release
forms, such as ammonium sulfate [(NH4)2SO4] and urea, to a variety of slow-release formulations, including polymerized urea and polymer-encapsulated urea. Ammonium
sulfate was also tested together with the nitrification inhibitor dicyandiamide (DCD). The fertilizers were applied at a concentration
of 1.0 mg g–1, which is comparable to 100 lb acre–l, or 112 kg ha–1. Potassium chloride-extractable NH4
+-N and NO3
–-N were quantified periodically during 2–4 week incubations. PAM treatment had no significant effect on NH4
+ release rates for any of the fertilizers tested and did not alter the efficacy of DCD as a nitrification inhibitor. However,
the nitrification rate of urea and encapsulated urea-derived NH4
+-N was slightly accelerated in the PAM-treated soil.
Received: 16 January 1998 相似文献
8.
A rapid chloroform-fumigation extraction method for measuring soil microbial biomass carbon and nitrogen in flooded rice soils 总被引:2,自引:0,他引:2
C. Witt J. L. Gaunt C. C. Galicia J. C. G. Ottow H.-U. Neue 《Biology and Fertility of Soils》2000,30(5-6):510-519
A chloroform-fumigation extraction method with fumigation at atmospheric pressure (CFAP, without vacuum) was developed for
measuring microbial biomass C (CBIO) and N (NBIO) in water-saturated rice soils. The method was tested in a series of laboratory experiments and compared with the standard
chloroform-fumigation extraction (CFE, with vacuum). For both methods, there was little interference from living rice roots
or changing soil water content (0.44–0.55 kg kg–1 wet soil). A comparison of the two techniques showed a highly significant correlation for both CBIO and NBIO (P<0.001) suggesting that the simple and rapid CFAP is a reliable alternative to the CFE. It appeared, however, that a small
and relatively constant fraction of well-protected microbial biomass may only be lysed during fumigation under vacuum. Determinations
of microbial C and N were highly reproducible for both methods, but neither fumigation technique generated NBIO values which were positively correlated with CBIO. The range of observed microbial C:N ratios of 4–15 was unexpectedly wide for anaerobic soil conditions. Evidence that this
was related to inconsistencies in the release, degradation, and extractability of NBIO rather than CBIO came from the observation that increasing the fumigation time from 4 h to 48 h significantly increased NBIO but not CBIO. The release pattern of CBIO indicated that the standard fumigation time of 24 h is applicable to water-saturated rice soils. To correct for the incomplete
recovery of CBIO, we suggest applying the k
C factor of 2.64, commonly used for aerobic soils (Vance et al. 1987), but caution is required when correcting NBIO data. Until differences in fumigation efficiencies among CFE and CFAP are confirmed for a wider range of rice soils, we suggest
applying the same correction factor for both methods.
Received: 1 June 1999 相似文献
9.
Effects of long-term waste water irrigation on soil organic matter, soil microbial biomass and its activities in central Mexico 总被引:4,自引:0,他引:4
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
10.
Soil microbial biomass and nitrogen supply in an irrigated lowland rice soil as affected by crop rotation and residue management 总被引:5,自引:0,他引:5
C. Witt Kenneth G. Cassman Johannes C. G. Ottow Ulrich Biker 《Biology and Fertility of Soils》1998,28(1):71-80
Processes that govern the soil nitrogen (N) supply in irrigated lowland rice systems are poorly understood. The objectives
of this paper were to investigate the effects of crop rotation and management on soil N dynamics, microbial biomass C (CBIO) and microbial biomass N (NBIO) in relation to rice N uptake and yield. A maize-rice (M-R) rotation was compared with a rice-rice (R-R) double-cropping
system over a 2-year period with four cropping seasons. In the M-R system, maize (Zea mays L.) was grown in aerated soil during the dry season (DS) followed by rice (Oryza sativa L.) grown in flooded soil during the wet season (WS). In the R-R system, rice was grown in flooded soil in both the DS and
WS. Three fertilizer N rates (0, 50 or 100 kg urea-N ha–1 in WS) were assigned to subplots within the cropping system main plots. Early versus late crop residue incorporation following
DS maize or rice were established as additional treatments in sub-subplots in the second year. In the R-R system, the time
of residue incorporation had a large effect on NO3
–-N accumulation during the fallow period and also on extractable NH4
+-N, rice N uptake and yield in the subsequent cropping period. In contrast, time of residue incorporation had little influence
on extractable N in both the fallow and rice-cropping periods of the M-R system, and no detectable effects on rice N uptake
or yield. In both cropping systems, CBIO and NBIO were not sensitive to residue incorporation despite differences of 2- to 3-fold increase in the amount of incorporated residue
C and N, and were relatively insensitive to N fertilizer application. Extractable organic N was consistently greater after
mid-tillering in M-R compared to the R-R system across N rate and residue incorporation treatments, and much of this organic
N was α-amino N. We conclude that N mineralization-immobilization dynamics in lowland rice systems are sensitive to soil aeration
as influenced by residue management in the fallow period and crop rotation, and that these factors have agronomically significant
effects on rice N uptake and yield. Microbial biomass measurements, however, were a poor indicator of these dynamics.
Received: 31 October 1997 相似文献
11.
Mineralization of N from organic materials added to soil depends on the quality of the substrate as a carbon, energy and
nutrient source for the saprophytic microflora. Quality reflects a combination of biochemical and physical attributes. We
investigated how biochemical composition interacts with particle size to affect the soil microflora and N dynamics following
incorporation of crop residues into soil. Four fresh shoot and root crop residues were cut into coarse and fine particle sizes,
and incorporated into sandy-loam soil which was incubated under controlled environment conditions for 6 months. In the case
of the highest biochemical quality material, potato shoot (C/N ratio of 10 : 1), particle size had no effect on microbial
respiration or net N mineralization. For lower biochemical quality Brussels sprout shoot (C/N ratio of 15 : 1), reducing particle
size caused microbial respiration to peak earlier and increased net mineralization of N during the early stages of decomposition,
but reduced net N mineralization at later stages. However, for the lowest biochemical quality residues, rye grass roots (C/N
ratio of 38 : 1) and straw (C/N ratio of 91 : 1) reducing particle size caused microbial respiration to peak later and increased
net immobilization of N. For Brussels sprout shoot, reducing particle size decreased the C content and the C/N ratio of residue-derived
light fraction organic matter (LFOM) 2 months following incorporation. However C and N content of LFOM derived from the other
materials was not affected by particle size. For materials of all qualities, particle size had little effect on biomass N.
We conclude that the impact of particle size on soil microbial activities, and the protection of senescent microbial tissues
from microbial attack, is dependant on the biochemical quality of the substrate.
Received: 3 July 1998 相似文献
12.
Long-term monitoring of microbial biomass, N mineralisation and enzyme activities of a Chernozem under different tillage management 总被引:13,自引:0,他引:13
We investigated the influence of tillage (conventional, minimum and reduced) on selected soil microbial properties of a fine-sandy
loamy Haplic Chernozem over a period of 8 years. The microbial biomass and soil microbial processes were affected mostly by
type of tillage and to a lesser extent by the date of soil sampling. Whereas xylanase activity was significantly higher in
the 0 to 10-cm soil layer of the reduced and minimum tillage systems within the first year of the experiment (protease and
phosphatase activities were significantly higher in the second year), significant treatment effects on microbial biomass,
N mineralisation and potential nitrification were observed after a 4-year period. The slow response of substrate-induced respiration
to the change in type of tillage may have been due to the differences in the biomass C turnover rates. After a 4-year period,
the stratification of the soil microbial biomass within the profile of reduced and minimum tillage systems was probably responsible
for the more intensive soil microbial processes near the soil surface compared with conventional tillage. In the 20 to 30-cm
layer, N mineralisation, potential nitrification and xylanase activity in the conventional treatment were significantly higher
than in the minimum and reduced tillage plots due to buried organic materials. Discriminant analysis underlined the similarity
of the enzyme activity patterns in the top layer of the reduced and minimum tillage treatments, and in both layers of the
conventional tillage system. The trend towards a significant increase in functional diversity caused by reduced tillage became
obvious within the first year of the experiment, and this effect was still manifest after 8 years. All relationships suggested
that there were differences in available resources (e.g. organic matter) along the sequence of different tillage systems;
this was reflected in part by enhanced enzymatic and microbial activities in the soil layers. In conclusion, this study showed
that soils affected by tillage may be classified on the basis of their functional diversity. Therefore, the soil microbial
properties chosen for microbiological soil monitoring (microbial biomass, N mineralisation and enzyme activities involved
in C, N and P cycling) provide a reliable tool with which to estimate early changes in the dynamics and distribution of soil
microbial processes within soil profiles.
Received: 3 February 1998 相似文献
13.
Water and N availability are the major limiting factors of primary production in desert ecosystems, and the response of soil
biota to these two factors is of great importance. We examined the immediate response of soil nematodes and the microbial
biomass to a single pulse of water amendment in N-treated plots in the Israeli Negev desert. Plots were treated with 0, 50
and 100 kg NH4NO3 ha–1 in December 1992, and at the end of the summer period (August 1993) the plots were exposed to a 15 mm water. Soil samples
from the 0–10 cm layer were collected daily and analysed soil moisture, total soluble N, nematode populations and microbial
biomass. Soil moisture increased to 8.5%, then gradually decreased to 2% during the 11 days of the study. Microbial biomass,
soil respiration and metabolic quotient values did not exhibit any significant correlation with soil N levels. Free-living
nematode population levels in the different plots were found to increase from a mean level of 45 500 to a mean level of 92 300
individuals m–2. N treatment was found to affect the patterns of free-living nematode population dynamics. The results of this study demonstrated
the importance of moisture availability levels and the ability to mobilize previous N inputs into available N which, occurring
in pulses, can affect the microbial ecophysiological status, nematode population dynamics and the interrelationship between
these two important components in the desert soil milieu.
Received: 5 November 1998 相似文献
14.
R. Roscoe C. A. Vasconcellos A. E. Furtini-Neto G. A. A. Guedes L. A. Fernandes 《Biology and Fertility of Soils》2000,32(1):52-59
We studied the relationship between urease activity (UA) and soil organic matter (SOM), microbial biomass N (Nbiom) content, and urea-N fertilizer assimilation by maize in a Dark Red Latosol (Typic Haplustox) cultivated for 9 years under
no-tillage (NT), tillage with a disc plough (DP), and tillage with a moldboard plough (MP). Two soil depths were sampled (0–7.5 cm
and 7.5–15 cm) at 4 different times during the crop cycle. Urea was applied at four different rates, ranging from 0 to 240 kg
N ha–1. The levels of fertilizer N did not affect the UA, SOM content, and Nbiom content. No significant difference between the treatments (NT, DP, and MP) was observed for SOM during the experiment, probably
because the major part of the SOM was in recalcitrant pools, since the area was previously cultivated (conventional tillage)
for 20 years. The Nbiom content explained 97% and 69% of the variation in UA in the upper and deeper soil layer, respectively. UA and biomass N were
significantly higher in the NT system compared to the DP and MP systems. The highest maize productivity and urea-N recovery
was also observed for the NT system. We observed that the increase in urea-N losses under NT, possibly as a consequence of
a higher UA, was compensated for by the increase in N immobilized in the biomass.
Received: 2 July 1999 相似文献
15.
Within different land‐use systems such as agriculture, forestry, and fallow, the different morphology and physiology of the plants, together with their specific management, lead to a system‐typical set of ecological conditions in the soil. The response of total, mobile, and easily available C and N fractions, microbial biomass, and enzyme activities involved in C and N cycling to different soil management was investigated in a sandy soil at a field study at Riesa, Northeastern Germany. The management systems included agricultural management (AM), succession fallow (SF), and forest management (FM). Samples of the mineral soil (0—5, 5—10, and 10—30 cm) were taken in spring 1999 and analyzed for their contents on organic C, total N, NH4+‐N and NO3—‐N, KCl‐extractable organic C and N fractions (Corg(KCl) and Norg(KCl)), microbial biomass C and N, and activities of β‐glucosidase and L‐asparaginase. With the exception of Norg(KCl), all investigated C and N pools showed a clear relationship to the land‐use system that was most pronounced in the 0—5 cm profile increment. SF resulted in greater contents of readily available C (Corg(KCl)), NH4+‐N, microbial biomass C and N, and enzyme activities in the uppermost 5 cm of the soil compared to all other systems studied. These differences were significant at P ≤ 0.05 to P ≤ 0.001. Comparably high Cmic:Corg ratios of 2.4 to 3.9 % in the SF plot imply a faster C and N turnover than in AM and FM plots. Forest management led to 1.5‐ to 2‐fold larger organic C contents compared to SF and AM plots, respectively. High organic C contents were coupled with low microbial biomass C (78 μg g—1) and N contents (10.7 μg g—1), extremely low Cmic : Corg ratios (0.2—0.6 %) and low β‐glucosidase (81 μg PN g—1 h—1) and L‐asparaginase (7.3 μg NH4‐N g—1 2 h—1) activities. These results indicate a severe inhibition of mineralization processes in soils under locust stands. Under agricultural management, chemical and biological parameters expressed medium values with exception for NO3—‐N contents which were significantly higher than in SF and FM plots (P ≤ 0.005) and increased with increasing soil depth. Nevertheless, the depth gradient found for all studied parameters was most pronounced in soils under SF. Microbial biomass C and N were correlated to β‐glucosidase and L‐asparaginase activity (r ≥ 0.63; P ≤ 0.001). Furthermore, microbial biomass and enzyme activities were related to the amounts of readily mineralizable organic C (i.e. Corg(KCl)) with r ≥ 0.41 (P ≤ 0.01), suggesting that (1) KCl‐extractable organic C compounds from field‐fresh prepared soils represent an important C source for soil microbial populations, and (2) that microbial biomass is an important source for enzymes in soil. The Norg(KCl) pool is not necessarily related to the size of microbial biomass C and N and enzyme activities in soil.<?show $6#> 相似文献