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1.
Soil carbon and nitrogen dynamics as affected by long-term tillage and nitrogen fertilization 总被引:9,自引:0,他引:9
J. R. Salinas-Garcia F. M. Hons J. E. Matocha D. A. Zuberer 《Biology and Fertility of Soils》1997,25(2):182-188
Quantifying seasonal dynamics of active soil C and N pools is important for understanding how production systems can be better
managed to sustain long-term soil productivity especially in warm subhumid climates. Our objectives were to determine seasonal
dynamics of inorganic soil N, potential C and N mineralization, soil microbial biomass C (SMBC), and the metabolic quotient
of microbial biomass in continuous corn (Zea mays L.) under conventional (CT), moldboard (MB), chisel (CH), minimum tillage (MT), and no-tillage (NT) with low (45kgNha–1) and high (90kgNha–1) N fertilization. An Orelia sandy clay loam (fine-loamy, mixed, hyperthermic Typic Ochraqualf) in south Texas, United States,
was sampled before corn planting in February, during pollination in May, and following harvest in July. Soil inorganic N,
SMBC, and potential C and N mineralization were usually highest in soils under NT, whereas these characteristics were consistently
lower throughout the growing season in soils receiving MB tillage. Nitrogen fertilization had little effect on soil inorganic
N, SMBC, and potential C and N mineralization. The metabolic quotient of microbial biomass exhibited seasonal patterns inverse
to that of SMBC. Seasonal changes in SMBC, inorganic N, and mineralizable C and N indicated the dependence of seasonal C and
N dynamics on long-term substrate availability from crop residues. Long-term reduced tillage increased soil organic matter
(SOM), SMBC, inorganic N, and labile C and N pools as compared with plowed systems and may be more sustainable over the long
term. Seasonal changes in active soil C and N pools were affected more by tillage than by N fertilization in this subhumid
climate.
Received: 20 September 1996 相似文献
2.
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
3.
This study examines the effects of atrazine on both microbial biomass C and C mineralization dynamics in two contrasting agricultural
soils (organic C, texture, and atrazine application history) located at Galicia (NW Spain). Atrazine was added to soils, a
Humic Cambisol (H) and a Gleyic Cambisol (G), at a recommended agronomic dose and C mineralization (CO2 evolved), and microbial biomass measurements were made in non-treated and atrazine-treated samples at different time intervals
during a 12-week aerobic incubation. The cumulative curves of CO2–C evolved over time fit the simple first-order kinetic model [Ct = Co (1 − e
−kt
)], whose kinetic parameters were quantified. Differences in these parameters were observed between the two soils studied;
the G soil, with a higher content in organic matter and microbial biomass C and lower atrazine application history, exhibited
higher values of the total C mineralization and the potentially mineralizable labile C pool than those for the H soil. The
addition of atrazine modified the kinetic parameters and increased notably the C mineralized; by the end of the incubation
the cumulative CO2–C values were 33–41% higher than those in the corresponding non-added soils. In contrast, a variable effect or even no effect
was observed on the soil microbial biomass following atrazine addition. The data clearly showed that atrazine application
at normal agricultural rates may have important implications in the C cycling of these two contrasting acid soils. 相似文献
4.
Soil-released carbon dioxide from microbial biomass carbon in the cultivated soils of karst areas of southwest China 总被引:1,自引:0,他引:1
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
5.
Transformations and recovery of residue and fertilizer nitrogen-15 in a sandy Lixisol of West Africa
The fate of 15N-labeled plant residues from different cover-cropping systems and labeled inorganic N fertilizer in the organic, soil mineral,
microbial biomass and soil organic matter (SOM) particle-size fractions was investigated in a sandy Lixisol. Plant residues
were from mucuna (legume), lablab (legume), imperata (grass), maize (cereal) and mixtures of mucuna or lablab with imperata
or maize, applied as a surface mulch. Inorganic N fertilizer was applied as 15N-(NH4)2SO4 at two rates (21 and 42 mg N kg–1 soil). Total N release from mucuna or lablab residues was 2–3 times higher than from the other residues, whereas imperata
immobilized N throughout the study period. In contrast, 15N was mineralized from all the plant residues irrespective of the mineralization–immobilization pattern observed for total
N. After 168 days, 69% of soil mineral N in mucuna- or lablab-mulched soils was derived from the added residues, representing
4–8% of residue N, whereas 9–30% of inorganic N was derived from imperata, maize and the mixed residues. At the end of the
study, 4–19% of microbial biomass N was derived from the added residue/fertilizer-N, accounting for 1–3% of added residue-N.
Averaged across treatments, particulate SOM fractions accounted for less than 1% of the total soil by weight but contained
20% of total soil C and 8% of soil N. Soils amended with mucuna or lablab incorporated more N in the 250–2000 μm SOM pool,
whereas soil amended with imperata or the mixed residues incorporated similar proportions of labeled N in the 250–2000 μm
and 53–250 μm fractions. In contrast, in soils receiving the maize or inorganic fertilizer-N treatments, higher proportions
of labeled N were incorporated into the 53–250 μm than the 250–2000 μm fractions. The relationship between these differences
in residue/fertilizer-N partitioning into different SOM particle-size fractions and soil productivity is discussed.
Received: 12 March 1999 相似文献
6.
Organic matter, microbial biomass and enzyme activity of soils under different crop rotations in the tropics 总被引:8,自引:0,他引:8
Soil organic matter level, soil microbial biomass C, ninhydrin-N, C mineralization, and dehydrogenase and alkaline phosphatase
activity were studied in soils under different crop rotations for 6 years. Inclusion of a green manure crop of Sesbania aculeata in the rotation improved soil organic matter status and led to an increase in soil microbial biomass, soil enzyme activity
and soil respiratory activity. Microbial biomass C increased from 192 mg kg–1 soil in a pearl millet-wheat-fallow rotation to 256 mg kg–1 soil in a pearl millet-wheat-green manure rotation. Inclusion of an oilseed crop such as sunflower or mustard led to a decrease
in soil microbial biomass, C mineralization and soil enzyme activity. There was a good correlation between microbial biomass
C, ninhydrin-N and dehydrogenase activity. The alkaline phosphatase activity of the soil under different crop rotations was
little affected. The results indicate the green manuring improved the organic matter status of the soil and soil microbial
activity vital for the nutrient turnover and long-term productivity of the soil.
Received: 7 January 1996 相似文献
7.
保护性耕作对黑土微生物群落的影响 总被引:9,自引:2,他引:7
耕作方式通过影响土壤微生物群落而影响土壤生态系统过程。本研究以传统耕作玉米连作处理为对照,通过测定土壤微生物量碳及磷脂脂肪酸含量,分析了保护性耕作(包括免耕玉米连作和免耕大豆-玉米轮作)对黑土微生物群落的影响。结果表明,保护性耕作可显著增加土壤表层(0~5cm)全碳、全氮、水溶性有机碳、碱解氮和微生物量碳(P0.05),为微生物代谢提供了丰富的资源。同时,保护性耕作显著提高了土壤表层(0~5cm)总脂肪酸量、真菌和细菌生物量(P0.05),提高了土壤的真菌/细菌值,有利于农田土壤生态系统的稳定性。研究结果对于探讨保护性耕作的内在机制具有重要意义。 相似文献
8.
The critical S concentration and S requirement of the soil microbial biomass of a granitic regosol was examined. S was applied
at the rate of 0, 5, 10, 20, 30 and 50 μg S as MgSO4·7H2O, together with either 3000 μg glucose-C or 3333 μg cellulose-C, 400 μg N, and 200 μg P g –1 soil and 200 μg K g–1 soil. Microbial biomass, inorganic SO4
2–-S, and CO2 emission were monitored over 30 days during incubation at 25 °C. Both glucose and cellulose decomposition rates responded
positively to the S made available for microbial cell synthesis. The amounts of microbial biomass C and S increased with the
level of applied S up to 10 μg S g–1 soil and 30 μg S g–1 soil in the glucose- and cellulose-amended soil, respectively, and then declined. Incorporated S was found to be concentrated
within the microbial biomass or partially transformed into soil organic matter. The concentration of S in the microbial biomass
was higher in the cellulose- (4.8–14.2 mg g–1) than in the glucose-amended soil (3.7–10.9 mg g–1). The microbial biomass C:S ratio was higher in the glucose- (46–142 : 1) than in the cellulose-amended soil (36–115 : 1).
The critical S concentration in the microbial biomass (defined as that required to achieve 80% of the maximum synthesis of
microbial biomass C) was estimated to be 5.1 mg g–1 in the glucose- and 10.9 mg g–1 in the cellulose-amended soil. The minimum requirement of SO4
2–-S for microbial biomass formation was estimated to be 11 μg S g–1 soil and 21 μg S g–1 soil for glucose- and cellulose-amended soil, respectively. The highest levels of activity of the microbial biomass were
observed at the SO4
2–-S concentrations of 14 μg S g–1 soil and 17 μg S g–1 soil, for the glucose and cellulose amendments, respectively, and were approximately 31–54% higher during glucose than cellulose
decomposition.
Received: 20 October 1999 相似文献
9.
Giancarlo Renella Amar M. Chaudri Céline M. Falloon Loretta Landi Paolo Nannipieri Philip C. Brookes 《Biology and Fertility of Soils》2007,43(6):751-758
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
10.
We compared the dynamics of net mineralization of nitrogen (N) derived from white clover material (Ndfc) as measured by the
difference and the 15N methods in a pot experiment with a sandy loam (15°C and pF 2.4) planted with Italian ryegrass. On day 22, mineralized Ndfc
(soil mineral N plus plant N uptake) was 5.8% and 1.3% of added N for the 15N and the difference methods, respectively. The discrepancy was reduced on day 43. On day 64, the relationship was reversed,
and on day 98 the values given by the two methods were 22.8% and 29.5%, respectively. The results obtained by the two methods
were linearly correlated (r = 0.987) and, on average, did not differ significantly. Nevertheless, the different temporal patterns led to appreciably
different parameter values as estimated by fitting of a reparameterized Richards model. On day 22, clover amendment reduced
mineralized N derived from soil (Ndfs) by 3.4 mg N pot–1. The reason for this was that the clover amendment led to a reduction in plant growth and uptake of Ndfs, most likely because
of allelopathy, while mineral Ndfs did not increase correspondingly. Clover-induced Ndfs in the microbial biomass of 5.1 mg
N pot–1 suggested that the mineral Ndfs not taken up by plants had been reimmobilized. Towards the end of the experiment, clover-induced
Ndfs in the biomass declined to 1.5 mg N pot–1, while mineralized Ndfs due to clover amendment increased to 5.1 mg N pot–1. The results strongly suggested that this increase was caused by a real stimulation of humus N mineralization by clover amendment
rather than by isotope displacement or pool substitution.
Received: 5 May 1997 相似文献
11.
Microwave irradiation was evaluated as a non-toxic alternate to chloroform fumigation for routine measurement of soil microbial
biomass C. Microwave energy was applied to moist soil to disrupt microbial cells. The flush of C released was then measured
after extraction or incubation. Microwave irradiation at 800 J g–1 soil was optimal because this level resulted in an almost instantaneous rise in soil temperature (≥80 °C), an abrupt reduction
in microbial activity, maximal release of biomass C, and minimal solubilization of humic substances. Both incubation-CO2 titration and extraction-colorimetry methods were used on separate 20-g subsamples to compare the labile C in the microwave-treated
and untreated soil samples. The incubation-titration method was also used to measure C in chloroform-fumigated soil samples.
Averaged across soils, the chloroform fumigation yielded 123.3±5.1 mg CO2-C kg–1. Microwave irradiation yielded 93.6±3.9 mg CO2-C kg–1 soil determined by incubation and 52.4±2.4 mg C kg–1 soil determined by extraction, accounting for 76% and 42% of the net flush of C measured by the chloroform fumigation. Microwave-stimulated
net flushes of C were correlated closely (r
2=0.974 for incubation or 0.908 for extraction) with microbial biomass C measured by the chloroform fumigation. Little correlation
was found with the total soil organic C (r
2=0.241 for incubation or for 0.166 extraction). Mean efficiency factors for incubation (K
MI) or extraction (K
ME) were used to calculate microbial biomass C from net flushes of C between microwaved and unmicrowaved soils. Values of K
MI and K
ME were not affected by soil pH, bulk density or clay contents. Extraction of microwaved soil by 0.5M K2SO4 proved to be a simple, fast, precise, reliable, and safe method to measure soil microbial biomass C.
Received: 12 September 1997 相似文献
12.
Microbial biomass and mineralizable nitrogen distributions in no-tillage and plowed soils 总被引:8,自引:0,他引:8
J. W. Doran 《Biology and Fertility of Soils》1987,5(1):68-75
Summary Distribution of soil microbial biomass and potentially mineralizable nitrogen (PMN) in long-term tillage comparisons at seven sites in the United States varied with tillage management and depth in soil. Microbial biomass and PMN levels of no-tillage soils averaged 54% and 37% higher, respectively, than those in the surface layer of plowed soil. Biomass and PMN levels were greatest in the surface 0 to 7.5-cm layer of no-tillage soil and decreased with depth in soil to 30 cm. Biomass and PMN levels of plowed soil, however, were generally greatest at the 7.5 –15 cm depth. Microbial biomass levels were closely associated with soil distributions of total C and N, water content, and water-soluble C as influenced by tillage management. Potentially mineralizable N levels in soil were primarily associated with distributions of microbial biomass and total N. Absolute levels of PMN and microbial biomass and the relative differences with tillage management were dependent on climatic, cropping, and soil conditions across locations. The additional N contained in soil biomass and PMN in the surface 0–7.5 cm of no-tillage compared with plowed soils ranged from 13 to 45 and 12 to 122 kg N/ha, respectively, for 6 of 7 locations. Fertilizer placement below the biologically rich surface soil layer and/or rotational tillage may improve short-term nitrogen use efficiency and crop growth on reduced-tillage soils.Contribution from USDA-ARS in cooperation with the Nebraska Agricultural Experimental Station, published as paper no. 8086, Journal Series, Nebraska Agricultural Experimental Station 相似文献
13.
R. M. Palma N. M. Arrigo M. I. Saubidet M. E. Conti 《Biology and Fertility of Soils》2000,32(5):381-384
The response of a series of soil microbial, chemical, and enzymatic chacacteristics to two different tillage systems (conventional
and no-tillage) and two crop rotations (continuous corn and soybean–corn) was evaluated in a long-term field experiment in
the Rolling Pampas Region, Marcos Juárez, Córdoba, Argentina. The parameters studied included: oxidizable, soluble and respiration
C, total and hydrolyzable N, microbial activity, ammonifiers, nitrifiers, cellulolytic and total microflora, protease and
urease activities. After 15 years, oxidizable C, total N and hydrolyzable N showed no differences regarding no-tillage systems.
However, differences were found regarding control soil. While soluble C did not exhibit any significant differences, respiration
C and microbial activity were indicators sensitive to different treatments. Enzymatic activities, protease in particular,
did reflect changes due to management. Fluctuation in microbial population counts were more related to plant residues than
to tillage systems.
Received: 29 May 1999 相似文献
14.
Estimating the active and total soil microbial biomass by kinetic respiration analysis 总被引:1,自引:0,他引:1
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
15.
Effects of increasing periods under intensive arable vegetable production on biological, chemical and physical indices of soil quality 总被引:6,自引:0,他引:6
The effects on soil condition of increasing periods under intensive cultivation for vegetable production on a Typic Haplohumult
were compared with those of pastoral management using soil biological, physical and chemical indices of soil quality. The
majority of the soils studied had reasonably high pH, exchangeable cation and extractable P levels reflecting the high fertilizer
rates applied to dairy pasture and more particularly vegetable-producing soils. Soil organic C (Corg) content under long-term pasture (>60 years) was in the range of 55 g C kg–1 to 65 g C kg–1. With increasing periods under vegetable production soil organic matter declined until a new equilibrium level was attained
at about 15–20 g C kg–1 after 60–80 years. The loss of soil organic matter resulted in a linear decline in microbial biomass C (Cmic) and basal respiratory rate. The microbial quotient (Cmic/Corg) decreased from 2.3% to 1.1% as soil organic matter content declined from 65 g C kg–1 to 15 g C kg–1 but the microbial metabolic quotient (basal respiration/Cmic ratio) remained unaffected. With decreasing soil organic matter content, the decline in arginine ammonification rate, fluorescein
diacetate hydrolytic activity, earthworm numbers, soil aggregate stability and total clod porosity was curvilinear and little
affected until soil organic C content fell below about 45 g C kg–1. Soils with an organic C content above 45 g C kg–1 had been under pasture for at least 30 years. At the same Corg content, soil biological activity and soil physical conditions were markedly improved when soils were under grass rather
than vegetables. It was concluded that for soils under continuous vegetable production, practices that add organic residues
to the soil should be promoted and that extending routine soil testing procedures to include key physical and biological properties
will be an important future step in promoting sustainable management practices in the area.
Received: 18 November 1997 相似文献
16.
V. Acosta-Martínez Z. Reicher M. Bischoff R. F. Turco 《Biology and Fertility of Soils》1999,29(1):55-61
The influence of tree leaf amendment and N fertilization on soil quality in turfgrass environments was evaluated. Our objective
was to assess changes in soil quality after additions of leaf materials and N fertilization by monitoring soil chemical and
physical parameters, microbial biomass and soil enzymes. Established perennial ryegrass (Lolium perenne) plots were amended annually with maple (Acer spp.) leaves at three different rates (0, 2240, and 4480 kg ha–1 year–1) and treated with three nitrogen rates (0, 63, and 126 kg N ha–1 year–1). Tree leaf mulching did not significantly affect water infiltration or bulk density. However, trends in the data suggest
increased infiltration with increasing leaf application rate. Tree leaf mulching increased total soil C and N at 0–1.3 cm
depth but not at 1.3–9.0 cm. Extracted microbial phospholipid, an indicator of microbial biomass size, ranged from 28 to 68
nmol phospholipid g–1 soil at the 1.3–9.0 cm depth. The activity of β-glucosidase estimated on samples from 0–1.3 cm and 1.3–9.0 cm depths, and
dehydrogenase activity estimated on samples from 1.3–9.0 cm were significantly increased by leaf mulching and N fertilizer
application. Changes in microbial community composition, as indicated by phospholipid fatty acid methyl ester analysis, appear
to be due to seasonal variations and did not reflect changes due to N or leaf amendment treatments. There were no negative
effects of tree leaf mulching into turfgrass and early data suggest this practice will improve soil chemical, physical, and
biological structure.
Received: 10 December 1997 相似文献
17.
Tillage practice influences on the physical protection, bioavailability and composition of particulate organic matter 总被引:7,自引:0,他引:7
This study was conducted to determine whether separation of particulate organic matter (POM) that is biologically labile
from aggregate entrapped material improves the usefulness of POM as an index of soil C and N dynamics. The effects of conventional
(CT) and no-tillage (NT) practices on POM were assessed using soils from three 10-year trials in Illinois. Loose and occluded
POM in the 0–5 cm depth were separated from 1994 samples. Use of NT practices increased C and N contents at 0–5 cm relative
to CT practices and those increases were most apparent in the occluded POM fraction. The correlation between total POM-N and
potentially mineralizable N (PMN) was stronger than that between PMN and either the loose or occluded-POM fractions. In 1995,
both the microbial biomass, estimated as chloroform-labile C (CFEC), and PMN were correlated with POM-C and N, but the relationship
was weak when data (from different tillage and depth combinations) were not treated in aggregate. POM-C and CFEC were most
strongly correlated in surface depths and in CT treatments. In NT 0–5 cm samples, PMN contents were similar (≈27 mg N kg–1 soil) at all sites despite notable differences in POM-N concentrations; PMN was not related to POM-N in CT samples. There
was no consistent relationship between PMN and POM-N contents in 5–30 cm samples. DRFTIR spectra indicated that carbohydrates
were most abundant in POM at 0–5 cm. Relatively low PMN rates and enrichment of polysaccharides in POM in the sicl soil suggest
that physical protection of labile organic substrates was more important at that site than at sites with lighter textured
soils. Improved fractionation and incubation techniques and alleviation of laboratory artifacts will improve our ability to
relate POM quantity, distribution and composition to biologically mediated C and N dynamics occurring in the field.
Received: 2 December 1999 相似文献
18.
水旱轮作后免耕水稻土微生物数量和生物量的变化特征研究 总被引:4,自引:1,他引:3
土壤微生物数量和生物量能迅速反映土壤肥力和土壤质量的演变趋势。通过野外调查和室内分析,研究了水旱轮作后,不同免耕年限土壤微生物数量和生物量的变化特点。结果表明:水旱轮作后,免耕耕层(0~20cm)土壤微生物数量、生物量P和生物多样性显著低于常规耕作,而微生物生物量C和N显著高于常规耕作;随着免耕年限延长,生物多样性、微生物生物量C和N在免耕7~8年时最低;免耕0~5cm土壤微生物数量和生物量显著高于5~10cm,而常规耕作0~5cm和5~10cm土壤微生物数量和生物量无显著差异。 相似文献
19.
Dwipendra Thakuria Narayan C. Talukdar Chandan Goswami Samarendra Hazarika Mohan C. Kalita Gary D. Bending 《Biology and Fertility of Soils》2009,45(3):237-251
To achieve higher yields and better soil quality under rice–legume–rice (RLR) rotation in a rainfed production system, we
formulated integrated nutrient management (INM) comprised of Azospirillum (Azo), Rhizobium (Rh), and phosphate-solubilizing bacteria (PSB) with phosphate rock (PR), compost, and muriate of potash (MOP). Performance
of bacterial bioinoculants was evaluated by determining grain yield, nitrogenase activity, uptake and balance of N, P, and
Zn, changes in water stability and distribution of soil aggregates, soil organic C and pH, fungal/bacterial biomass C ratio,
casting activities of earthworms, and bacterial community composition using denaturing gradient gel electrophoresis (DGGE)
fingerprinting. The performance comparison was made against the prevailing farmers’ nutrient management practices [N/P2O5/K2O at 40:20:20 kg ha−1 for rice and 20:30:20 kg ha−1 for legume as urea/single super-phosphate/MOP (urea/SSP/MOP)]. Cumulative grain yields of crops increased by 7–16% per RLR
rotation and removal of N and P by six crops of 2 years rotation increased significantly (P < 0.05) in bacterial bioinoculants-based INM plots over that in compost alone or urea/SSP/MOP plots. Apparent loss of soil
total N and P at 0–15 cm soil depth was minimum and apparent N gain at 15–30 cm depth was maximum in Azo/Rh plus PSB dual
INM plots. Zinc uptake by rice crop and diethylenetriaminepentaacetate-extractable Zn content in soil increased significantly
(P < 0.05) in bacterial bioinoculants-based INM plots compared to other nutrient management plots. Total organic C content in
soil declined at 0–15 cm depth and increased at 15–30 cm depth in all nutrient management plots after a 2-year crop cycle;
however, bacterial bioinoculants-based INM plots showed minimum loss and maximum gain of total organic C content in the corresponding
soil depths. Water-stable aggregation and distribution of soil aggregates in 53–250- and 250–2,000 μm classes increased significantly
(P < 0.05) in bacterial bioinoculants-based INM plots compared to other nutrient management plots. Fungal/bacterial biomass
C ratio seems to be a more reliable indicator of C and N dynamics in acidic soils than total microbial biomass C. Compost
alone or Azo/Rh plus PSB dual INM plots showed significantly (P < 0.05) higher numbers of earthworms’ casts compared to urea/SSP/MOP alone and bacterial bioinoculants with urea or SSP-applied
plots. Hierarchical cluster analysis based on similarity matrix of DGGE profiles revealed changes in bacterial community composition
in soils due to differences in nutrient management, and these changes were seen to occur according to the states of C and
N dynamics in acidic soil under RLR rotation. 相似文献
20.
M. R. Carter 《Biology and Fertility of Soils》1991,11(2):135-139
Summary Microbial biomass C and N respond rapidly to changes in tillage and soil management. The ratio of biomass C to total organic C and the ratio of mineral N flush to total N were determined in the surface layer (0–5 cm) of low-clay (8–10%), fine sandy loam, Podzolic soils subjected to a range of reduced tillage (direct drilling, chisel ploughing, shallow tillage) experiments of 3–5 years' duration. Organic matter dynamics in the tillage experiments were compared to long-term conditions in several grassland sites established on the same soil type for 10–40 years. Microbial biomass C levels in the grassland soils, reduced tillage, and mouldboard ploughing treatments were 561, 250, and 155 g g-1 soil, respectively. In all the systems, microbial biomass C was related to organic C (r=0.86), while the mineral N flush was related to total N (r=0.84). The average proportion of organic C in the biomass of the reduced tillage soils (1.2) was higher than in the ploughed soils (0.8) but similar to that in the grassland soils (1.3). Reduced tillage increased the average ratio of mineral N flush to total soil N to 1.9, compared to 1.3 in the ploughed soils. The same ratio was 1.8 in the grassland soils. Regression analysis of microbial biomass C and percent organic C in the microbial biomass showed a steeper slope for the tillage soils than the grassland sites, indicating that reduced tillage increased the microbial biomass level per unit soil organic C. The proportion of organic matter in the microbial biomass suggests a shift in organic matter equilibrium in the reduced tillage soils towards a rapid, tillage-induced, accumulation of organic matter in the surface layer. 相似文献