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1.
In less populated rural areas constructed wetlands with a groundfilter made out of the local soil mixed with peat and planted
with common reed (Phragmites australis) are increasingly used to purify waste water. Particularly in the rhizosphere of the reed, nitrification and denitrification
processes take place varying locally and temporally, and the question arises to what extent this type of waste-water treatment
plant may contribute to the release of N2O. In situ N2O measurements were carried out in the two reed beds of the Friedelhausen dairy farm, Hesse, Germany, irrigated with the waste
water from a cheese dairy and 70 local inhabitants (12 m3 waste water or 6 kg BOD5 or 11 kg chemical O2 demand (CODMn) day–1). During November 1995 to March 1996, the release of N2O was measured weekly at 1 m distances using eight open chambers and molecular-sieve traps to collect and absorb the emitted
N2O. Simultanously, the N2O trapped in the soil, the soil temperature, as well as the concentrations of NH4
+-N, NO3
–-N, NO2
–-N, water-soluble C and the pH were determined at depths of 0–20, 20–40 and 40–60 cm. In the waste water from the in- and
outflow the concentrations of CODMn, BOD5, NH4
+-N, NO3
–-N, NO2
–-N, as well as the pH, were determined weekly. Highly varying amounts of N2O were emitted at all measuring dates during the winter. Even at soil temperatures of –1.5 °C in 10 cm depth of soil or 2 °C
at a depth of 50 cm, N2O was released. The highest organic matter and N transformation rates were recorded in the upper 20 cm of soil and in the
region closest to the outflow of the constructed wetland. Not until a freezing period of several weeks did the N2O emissions drop drastically. During the period of decreasing temperatures less NO3
–-N was formed in the soil, but the NH4
+-N concentrations increased. On average the constructed wetlands of Friedelhausen emitted about 15 mg N2O-N inhabitant equivalent–1 day–1 during the winter period. Nitrification-denitrification processes rather than heterotrophic denitrification are assumed to
be responsible for the N2O production.
Received: 28 October 1998 相似文献
2.
Nitrification and denitrification in the rhizosphere of rice: the detection of processes by a new multi-channel electrode 总被引:6,自引:0,他引:6
N turnover in flooded rice soils is characterized by a tight coupling between nitrification and denitrification. Nitrification
is restricted to the millimetre-thin oxic surface layer while denitrification occurs in the adjacent anoxic soil. However,
in planted rice soil O2 released from the rice roots may also support nitrification within the otherwise anoxic bulk soil. To locate root-associated
nitrification and denitrification we constructed a new multi-channel microelectrode that measures NH4
+, NO2
–, and NO3
– at the same point. Unfertilized, unplanted rice microcosms developed an oxic-anoxic interface with nitrification taking place
above and denitrification below ca. 1 mm depth. In unfertilized microcosms with rice plants, NH4
+, NO2
– and NO3
– could not be detected in the rhizosphere. Assimilation by the rice roots reduced the available N to a level where nitrification
and denitrification virtually could not occur. However, a few hours after injecting (NH4)2HPO4 or urea, a high nitrification activity could be detected in the surface layer of planted microcosms and in a depth of 20–30 mm
in the rooted soil. O2 concentrations of up to 150 μM were measured at the same depth, indicating O2 release from the rice roots. Nitrification occurred at a distance of 0–2 mm from the surface around individual roots, and
denitrification occurred at a distance of 1.5–5.0 mm. Addition of urea to the floodwater of planted rice microcosms stimulated
nitrification. Transpiration of the rice plants caused percolation of water resulting in a mass flow of NH4
+ towards the roots, thus supporting nitrification.
Received: 23 July 1999 相似文献
3.
Influence of N and non-N salts on atmospheric methane oxidation by upland boreal forest and tundra soils 总被引:10,自引:0,他引:10
S. C. Whalen 《Biology and Fertility of Soils》2000,31(3-4):279-287
The short-term (24 h) and medium-term (30 day) influence of N salts (NH4Cl, NaNO3 and NaNO2) and a non-N salt (NaCl) on first-order rate constants, k (h–1) and thresholds (CTh) for atmospheric CH4 oxidation by homogenized composites of upland boreal forest and tundra soils was assessed at salt additions ranging to 20 μmol
g–1 dry weight (dw) soil. Additions of NH4Cl, NaNO3 and NaCl to 0.5 μmol g–1 dw soil did not significantly decrease k relative to watered controls in the short term. Higher concentrations significantly reduced k, with the degree of inhibition increasing with increasing dose. Similar doses of NH4Cl and NaCl gave comparable decreases in k relative to controls and both soils showed low native concentrations of NH4
+-N (≤1 μmol g–1dw soil), suggesting that the reduction in k was due primarily to a salt influence rather than competitive inhibition of CH4 oxidation by exogenous NH4
+-N or NH4
+-N released through cation exchange. The decrease in k was consistently less for NaNO3 than for NH4Cl and NaCl at similar doses, pointing to a strong inhibitory effect of the Cl– counter-anion. Thresholds for CH4 oxidation were less sensitive to salt addition than k for these three salts, as significant increases in CTh relative to controls were only observed at concentrations ≥1.0 μmol g–1 dw soil. Both soils were more sensitive to NaNO2 than to other salts in the short term, showing a significant decrease in k at an addition of 0.25 μmol NaNO2 g–1 dw soil that was clearly attributable to NO2
–. Soils showed no recovery from NaCl, NH4
+-N or NaNO3 addition with respect to atmospheric CH4 oxidation after 30 days. However, soils amended with NaNO2 to 1.0 μmol NaNO2 g–1 dw showed values of k that were not significantly different from controls. Recovery of CH4-oxidizing ability was due to complete oxidation of NO2
–-N to NO3
–-N. Analysis of soil concentrations of N salts necessary to inhibit atmospheric CH4 oxidation and regional rates of N deposition suggest that N deposition will not decrease the future sink strength of upland
high-latitude soils in the atmospheric CH4 budget.
Received: 30 April 1999 相似文献
4.
Incubation of soil under low partial pressures of acetylene (10 Pa) is a widely used method to specifically inhibit nitrification
due to the suicide inhibition of ammonium monooxygenase (AMO), the first enzyme in NH4
+ oxidation by nitrifying bacteria. Although the inhibition of AMO is irreversible, recovery of activity is possible if new
enzyme is synthesized. In experiments with three different soils, NH4
+ concentrations decreased and NO3
– concentrations increased soon after acetylene was removed from the atmosphere. Recovery of NO production started immediately
after the removal of acetylene. The release rates of NO and N2O were higher in soil samples which were only preincubated with 10 Pa acetylene than in those which were kept in the presence
of 10 Pa acetylene. In the permanent presence of 10 Pa acetylene, NH4
+ and NO3
– concentrations stayed constant, and the release rates of NO and N2O were low. These low release rates were apparently due to processes other than nitrification. Our experiments showed that
the blockage of nitrification by low (10 Pa) acetylene partial pressures is only reliable when the soil is kept in permanent
contact with acetylene.
Received: 17 July 1996 相似文献
5.
《Applied soil ecology》2010,46(3):225-231
There are plans to vegetate soil of the former lake Texcoco and use wastewater sludge to provide nutrients. However, the Texcoco soil is N depleted, so the amount of N available to the vegetation might be limited and the dynamics of C and N affected. We investigated how emissions of CO2, N2O and N2, and dynamics of mineral N were affected when different types of N fertilizer, i.e. NH4+, NO3−, or unsterilized or sterilized wastewater sludge, were added to the Texcoco soil. An agricultural soil served as control. Sewage sludge added to an alkaline saline soil (Texcoco soil) induced a decrease in concentrations of NH4+ and NO3−. Addition of sewage sludge increased the CO2 emission rate > two times compared to soil amended with sterilized sludge. The NH4+ concentration was lower when sludge was added to an agricultural soil for the first 28 days and in the Texcoco soil for 56 days compared to soil amended with sterilized sludge. Production of N2O in the agricultural soil was mainly due to nitrification, even when sludge was added, but denitrification was the main source of N2O in the Texcoco soil. Microorganisms in the sludge reduced N2O to N2, but not the soil microorganisms. It was found that microorganisms added with the sludge accelerated organic material decomposition, increased NH4+ immobilization, and induced immobilization of NO3− (in Texcoco soil). These results suggest that wastewater sludge improves soil fertility at Otumba (an agricultural soil) and would favour the vegetation of the Texcoco soil (alkaline saline). 相似文献
6.
The turnover of organic matter determines the availability of plant nutrients in unfertilized soils, and this applies particularly to the alkaline saline soil of the former Lake Texcoco in Mexico. We investigated the effects of alkalinity and salinity on dynamics of organic material and inorganic N added to the soil. Glucose labelled with 14C was added to soil of the former Lake Texcoco drained for different lengths of time, and dynamics of 14C, C and N were investigated with the Detran model. Soil was sampled from an undrained plot and from three drained for 1, 5 and 8 years, amended with 1000 mg 14C‐labelled glucose kg?1 and 200 mg NH4+‐N kg?1, and incubated aerobically. Production of 14CO2 and CO2, dynamics of NH4+, NO2– and NO3–, and microbial biomass 14C, C and N were monitored and simulated with the Detran model. A third stable microbial biomass fraction had to be introduced in the model to simulate the dynamics of glucose, because > 90 mg 14C kg?1 soil persisted in the soil microbial biomass after 97 days. The observed priming effect was mostly due to an increased decay of soil organic matter, but an increased turnover of the microbial biomass C contributed somewhat to the phenomenon. The dynamics of NH4+ and NO3– in the NH4+‐amended soil could not be simulated unless an immobilization of NH4+ into the microbial biomass occurred in the first day of the incubation without an immediate incorporation of it into microbial organic material. The dynamics of C and a priming effect could be simulated satisfactorily, but the model had to be adjusted to simulate the dynamics of N when NH4+ was added to alkaline saline soils. 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.
Soils are a major source of atmospheric NO and N2O. Since the soil properties that regulate the production and consumption of NO and N2O are still largely unknown, we studied N trace gas turnover by nitrification and denitrification in 20 soils as a function
of various soil variables. Since fertilizer treatment, temperature and moisture are already known to affect N trace gas turnover,
we avoided the masking effect of these soil variables by conducting the experiments in non-fertilized soils at constant temperature
and moisture. In all soils nitrification was the dominant process of NO production, and in 50% of the soils nitrification
was also the dominant process of N2O production. Factor analysis extracted three factors which together explained 71% of the variance and identified three different
soil groups. Group I contained acidic soils, which showed only low rates of microbial respiration and low contents of total
and inorganic nitrogen. Group II mainly contained acidic forest soils, which showed relatively high respiration rates and
high contents of total N and NH4
+. Group III mainly contained neutral agricultural soils with high potential rates of nitrification. The soils of group I produced
the lowest amounts of NO and N2O. The results of linear multiple regression conducted separately for each soil group explained between 44–100% of the variance.
The soil variables that regulated consumption of NO, total production of NO and N2O, and production of NO and N2O by either nitrification or denitrification differed among the different soil groups. The soil pH, the contents of NH4
+, NO2
– and NO3
–, the texture, and the rates of microbial respiration and nitrification were among the important variables.
Received: 28 October 1999 相似文献
9.
Nitrogen excretion rates of 15N-labeled earthworms and contributions of 15N excretion products to organic (dissolved organic N) and inorganic (NH4-N, NO3-N) soil N pools were determined at 10 °C and 18 °C under laboratory conditions. Juvenile and adult Lumbricus terrestris L., pre-clitellate and adult Aporrectodea tuberculata (Eisen), and adult Lumbricus rubellus (Hoffmeister) were labeled with 15N by providing earthworms with 15N-labeled organic substrates for 5–6 weeks. The quantity of 15N excreted in unlabeled soil was measured after 48 h, and daily N excretion rates were calculated. N excretion rates ranged
from 274.4 to 744 μg N g–1 earthworm fresh weight day–1, with a daily turnover of 0.3–0.9% of earthworm tissue N. The N excretion rates of juvenile L. terrestris were significantly lower than adult L. terrestris, and there was no difference in the N excretion rates of pre-clitellate and adult A. tuberculata. Extractable N pools, particularly NH4-N, were greater in soils incubated with earthworms for 48 h than soils incubated without earthworms. Between 13 and 40% of
excreted 15N was found in the 15N-mineral N (NH4-N+NO3-N) pool, and 13–23% was in the 15N-DON pool. Other fates of excreted 15N may have been incorporation in microbial biomass, chemical or physical protection in non-extractable N forms, or gaseous
N losses. Earthworm excretion rates were combined with earthworm biomass measurements to estimate N flux from earthworm populations
through excretion. Annual earthworm excretion was estimated at 41.5 kg N ha–1 in an inorganically-fertilized corn agroecosystem, and was equivalent to 22% of crop N uptake. Our results suggest that the
earthworms could contribute significantly to N cycling in corn agroecosystems through excretion processes.
Received: 12 April 1999 相似文献
10.
Influence of nitrogen on cellulose and lignin mineralization in blackwater and redwater forested wetland soils 总被引:2,自引:0,他引:2
J. A. Entry 《Biology and Fertility of Soils》2000,31(5):436-440
Microcosms were used to determine the influence of N additions on active bacterial and active fungal biomass, cellulose degradation
and lignin degradation at 5, 10 and 15 weeks in soils from blackwater and redwater wetlands in the northern Florida panhandle.
Blackwater streams contain a high dissolved organic C concentration which imparts a dark color to the water and contain low
concentrations of nutrients. Redwater streams contain high concentrations of suspended clays and inorganic nutrients, such
as N and P, compared to blackwater streams. Active bacterial and fungal biomass was determined by direct microscopy; cellulose
and lignin degradation were measured radiometrically. The experimental design was a randomized block. Treatments were: soil
type (blackwater or redwater forested wetlands) and N additions (soils amended with the equivalent of 0, 200 or 400 kg N ha–1 as NH4NO3). Redwater soils contained higher concentrations of C, total N, P, K, Ca, Mn, Fe, B and Zn than blackwater soils. After N
addition and 15 weeks of incubation, the active bacterial biomass in redwater soils was lower than in blackwater soils; the
active bacterial biomass in blackwater soils was lower when 400 kg N ha–1, but not when 200 kg N ha–1, was added. The active fungal biomass in blackwater soils was higher when 400 kg N ha–1, but not when 200 kg N ha–1, was added. The active fungal biomass in redwater wetland soils was lower when 200 kg N ha–1, but not when 400 kg N ha–1, was added. Cellulose and lignin degradation was higher in redwater than in blackwater soils. After 10 and 15 weeks of incubation,
the addition of 200 or 400 kg N as NH4NO3 ha–1 decreased cellulose and lignin degradation in both wetland soils to similar levels. This study indicated that the addition
of N may slow organic matter degradation and nutrient mineralization, thereby creating deficiencies of other plant-essential
nutrients in wetland forest soils.
Received: 7 April 1999 相似文献
11.
M. D. Serna J. Bañuls A. Quiñones E. Primo-Millo F. Legaz 《Biology and Fertility of Soils》2000,32(1):41-46
The objectives of this work were to evaluate the inhibitory action on nitrification of 3,4-dimethylpyrazole phosphate (DMPP)
added to ammonium sulphate nitrate [(NH4)2SO4 plus NH4NO3; ASN] in a Citrus-cultivated soil, and to study its effect on N uptake. In a greenhouse experiment, 2 g N as ASN either with or without 0.015 g
DMPP (1% DMPP relative to NH4
+-N) was applied 6 times at 20-day intervals to plants grown in 14-l pots filled with soil. Addition of DMPP to ASN resulted
in higher levels of NH4
+-N and lower levels of NO3
–-N in the soil during the whole experimental period. The NO3
–-N concentration in drainage water was lower in the ASN plus DMPP (ASN+DMPP)-treated pots. Also, DMPP supplementation resulted
in greater uptake of the fertilizer-N by citrus plants. In another experiment, 100 g N as ASN, either with or without 0.75 g
DMPP (1% DMPP relative to NH4
+-N) was applied to 6-year-old citrus plants grown individually outdoors in containers. Concentrations of NH4
+-N and NO3
–-N at different soil depths and N distribution in the soil profile after consecutive flood irrigations were monitored. In
the ASN-amended soil, nitrification was faster, whereas the addition of the inhibitor led to the maintenance of relatively
high levels of NH4
+-N and NO3
–-N in soil for longer than when ASN was added alone. At the end of the experiment (120 days) 68.5% and 53.1% of the applied
N was leached below 0.60 m in the ASN and ASN+DMPP treatments, respectively. Also, leaf N levels were higher in plants fertilized
with ASN+DMPP. Collectively, these results indicate that the DMPP nitrification inhibitor improved N fertilizer efficiency
and reduced NO3
– leaching losses by retaining the applied N in the ammoniacal form.
Received: 31 May 1999 相似文献
12.
M. V. Cheshire C. N. Bedrock B. L. Williams B. T. Christensen I. Thomsen P. Alpendre 《Biology and Fertility of Soils》1999,28(3):306-312
Wheat straw enclosed in mesh bags was buried for periods up to 1 year over two seasons in Scottish, Danish and Portuguese
soils treated with 15NH4NO3 or NH4
15NO3. Scottish soils were: Terryvale, a poorly drained sandy loam; and Tipperty, an imperfectly drained brown forest soil with
a higher clay content. The Danish soil (Foulum) was a freely drained sandy loam and the Portuguese soils were a sandy soil
(Evora) and a clay soil (Beja). During the first month, 15N was being incorporated into the straw in the Tipperty, Terryvale and Foulum soils simultaneously as the total N content
was decreasing. Subsequently, the straws began to show net immobilization and the total N content of the original straw was
exceeded in Tipperty and Foulum soils after 4 months and 8 months, respectively. Net immobilization in Terryvale was detected
only in the second season and did not occur in the first because of high soil moisture content. The rates of 15N incorporation were similar in the two Portuguese soils, and a loss of N was only detected after 8 months. After 1 month,
in the two clay soils, Beja and Tipperty, 15NO3
– was incorporated into straw to a greater extent than 15NH4
+ and this was attributed to 15NH4
+ fixation by clay minerals. In contrast, 15NH4
+ was more efficiently incorporated than 15NO3
– under waterlogged conditions (Terryvale) and NO3
– loss could be attributed to denitrification. The proportion of added 15N in the straw residue after 1 month varied between 6% and 18% for 15NH4
+ and 2% and 23% for 15NO3
– and immobilization of N in the longer term tended to be greater in soils from northern Europe than from Portugal.
Received: 19 January 1998 相似文献
13.
Effects of salts and moisture content on N2O emission and nitrogen dynamics in Yellow soil and Andosol in model experiments 总被引:2,自引:0,他引:2
The effects of salt type and its concentration on nitrification, N mineralization and N2O emission were examined under two levels of moisture content in Yellow soil and Andosol samples as simulated to agriculture
under arid/semi-arid conditions and under heavy application of fertilizer in a glass-house, respectively. The salt mixtures
were composed of chlorides (NaCl and NH4Cl) or sulphates [Na2SO4 and (NH4)2SO4] and were added at various concentrations (0, 0.1, 0.2, 0.4 and 0.6 M as in the soil solution). These salts were added to
non-saline Yellow soil at different moisture contents (45 or 40 and 65% of maximum water-holding capacity; WHC) and their
effects on the changes in mineral N (NH4
+-N and NO3
–-N) concentration as well as N2O emission were examined periodically during laboratory incubation. We also measured urease activities to know the effect
of salts on N mineralization. Furthermore, Ca(NO3)2 solution was added at various concentrations (0, 0.1, 0.3, 0.5 and 0.8 M as in the soil solution) to a non-saline Andosol
taken from the subsurface layer in a glass-house and incubated at different moisture contents (50% and 70% of WHC) to examine
their effects on changes in mineral N. Nitrification was inhibited by high, but remained unaffected by low, salt concentrations.
These phenomena were shown in both the model experiments. It was considered that the salinity level for inhibition of nitrification
was an electric conductivity (1 : 5) of 1 dS m–1. This level was independent of the type of salts or soil, and was not affected by soil moisture content. The critical level
of salts for urease activities was about 2 dS m–1. The emission rate of N2O was maximum at the beginning of the incubation period and stabilized at a low level after an initial peak. There was no
significant difference in N2O emission among the treatments at different salt concentrations, while higher moisture level enhanced N2O emission remarkably.
Received: 29 July 1998 相似文献
14.
Nitrogen fertilizers promote denitrification 总被引:8,自引:0,他引:8
A laboratory study was conducted to compare the effects of different N fertilizers on emission of N2 and N2O during denitrification of NO3
– in waterlogged soil. Field-moist samples of Drummer silty clay loam soil (fine-silty, mixed, mesic Typic Haplaquoll) were
incubated under aerobic conditions for 0, 2, 4, 7, 14, 21, or 42 days with or without addition of unlabelled (NH4)2SO4, urea, NH4H2PO4, (NH4)2HPO4, NH4NO3 (200 or 1000 mg N kg–1 soil), or liquid anhydrous NH3 (1000 mg N kg–1 soil). The incubated soil samples were then treated with 15N-labelled KNO3 (250 mg N kg–1 soil, 73.7 atom% 15N), and incubation was carried out under waterlogged conditions for 5 days, followed by collection of atmospheric samples
for 15N analyses to determine labelled N2 and N2O. Compared to samples incubated without addition of unlabelled N, all of the fertilizers promoted denitrification of 15NO3
–. Emission of labelled N2 and N2O decreased in the order: Anhydrous NH3>urea<$>\gg<$> (NH4)2HPO4>(NH4)2SO4≃NH4NO3≃NH4H2PO4. The highest emissions observed with anhydrous NH3 or urea coincided with the presence of NO2
–, and 15N analyses indicated that these emissions originated from NO2
– rather than NO3
–. Emissions of labelled N2 and N2O were significantly correlated with fertilizer effects on soil pH and water-soluble organic C.
Received: 17 January 1996 相似文献
15.
The short-term cover crops increase soil labile organic carbon in southeastern Australia 总被引:1,自引:0,他引:1
Xiaoqi Zhou Chengrong Chen Shunbao Lu Yichao Rui Hanwen Wu Zhihong Xu 《Biology and Fertility of Soils》2012,48(2):239-244
Little information is available about the effects of cover crops on soil labile organic carbon (C), especially in Australia.
In this study, two cover crop species, i.e., wheat and Saia oat, were broadcast-seeded in May 2009 and then crop biomass was
crimp-rolled onto the soil surface at anthesis in October 2009 in southeastern Australia. Soil and crop residue samples were
taken in December 2009 to investigate the short-term effects of cover crops on soil pH, moisture, NH4+–N, NO3−–N, soluble organic C and nitrogen (N), total organic C and N, and C mineralization in comparison with a nil-crop control
(CK). The soil is a Chromic Luvisol according to the FAO classification with 48.4 ± 2.2% sand, 19.5 ± 2.1% silt, and 32.1 ± 2.1%
clay. An exponential model fitting was employed to assess soil potentially labile organic C (C
0) and easily decomposable organic C for all treatments based on 46-day incubations. The results showed that crop residue biomass
significantly decreased over the course of 2-month decomposition. The cover crop treatments had significantly higher soil
pH, soluble organic C and N, cumulative CO2–C, C
0, and easily decomposable organic C, but significantly lower NO3−–N than the CK. However, no significant differences were found in soil moisture, NH4+–N, and total organic C and N contents among the treatments. Our results indicated that the short-term cover crops increased
soil labile organic C pools, which might have implications for local agricultural ecosystem managements in this region. 相似文献
16.
The spatial in situ variability of soil N2O emissions (measured by micro-chambers, radius 0.033 m), N2O content, water content, NO3
–, NH4
+, inorganic carbon and organic carbon concentrations was investigated on a silt loam by means of geostatistical methods and
nonparametric statistics. The sampling grid consisted of different spacings between sampling points which ranged from 0.1 m
to 50 m. There were no significant correlations between N2O emissions and soil parameters (P>0.1) when all the sampling points were considered. In the centre of the grid a "hot area" was localized with significantly
higher N2O emissions, and NO3
– and NH4
+ concentrations (P≤0.05). Within this hot area the N2O soil content significantly correlated with N2O emissions (P≤0.05). When semiovariograms were computed without data of the hot area samples, N2O emissions showed a weak spatial correlation (range: 4.3 m). The calculations including all data led to pure nugget effects
for all parameters except for soil water content (range >40 m) and N2O soil content (range 16.4 m).
Received: 19 December 1997 相似文献
17.
Gross N mineralization and nitrification rates and their relationships to microbial biomass C and N and enzyme (protease,
deaminase and urease) activities were determined in soils treated with dairy shed effluent (DSE) or NH4
+ fertilizer (NH4Cl) at a rate equivalent to 200 kg N ha–1 at three water potentials (0, –10 and –80 kPa) at 20 °C using a closed incubation technique. After 8, 16, 30, 45, 60 and
90 days of incubation, sub-samples of soil were removed to determine gross N mineralization and nitrification rates, enzyme
activities, microbial biomass C and N, and NH4
+ and NO3
– concentrations. The addition of DSE to the soil resulted in significantly higher gross N mineralization rates (7.0–1.7 μg
N g–1 soil day–1) than in the control (3.8–1.2 μg N g–1 soil day–1), particularly during the first 16 days of incubation. This increase in gross mineralization rate occurred because of the
presence of readily mineralizable organic substrates with low C : N ratios, and stimulated soil microbial and enzymatic activities
by the organic C and nutrients in the DSE. The addition of NH4Cl did not increase the gross N mineralization rate, probably because of the lack of readily available organic C and/or a
possible adverse effect of the high NH4
+ concentration on microbial activity. However, nitrification rates were highest in the NH4Cl-treated soil, followed by DSE-treated soil and then the control. Soil microbial biomass, protease, deaminase and urease
activities were significantly increased immediately after the addition of DSE and then declined gradually with time. The increased
soil microbial biomass was probably due to the increased available C substrate and nutrients stimulating soil microbial growth,
and this in turn resulted in higher enzyme activities. NH4Cl had a minimal impact on the soil microbial biomass and enzyme activities, possibly because of the lack of readily available
C substrates. The optimum soil water potential for gross N mineralization and nitrification rates, microbial and enzyme activities
was –10 kPa compared with –80 kPa and 0 kPa. Gross N mineralization rates were positively correlated with soil microbial biomass
N and protease and urease activities in the DSE-treated soil, but no such correlations were found in the NH4Cl-treated soil. The enzyme activities were also positively correlated with each other and with soil microbial biomass C and
N. The forms of N and the different water potentials had a significant effect on the correlation coefficients. Stepwise regression
analysis showed that protease was the variable that most frequently accounted for the variations of gross N mineralization
rate when included in the equation, and has the potential to be used as one of the predictors for N mineralization.
Received: 10 March 1998 相似文献
18.
Carbon and nitrogen dynamics in ageing earthworm casts in grasslands of the eastern plains of Colombia 总被引:5,自引:0,他引:5
The effects of a large species of anecic earthworm, Martiodrilus carimaguensis Jiménez and Moreno, on soil C and N dynamics were investigated in a native savanna and a man-made pasture of the eastern
plains of Colombia. We compared, across time (11 months), the total C, total N, NH+
4 and NO–
3 contents in the earthworm casts, the underlying soil and the adjacent soil. Additional sampling of root biomass and macrofauna
was performed. In the two management systems, the total C and N contents were higher in casts (4.33–7.50%) than in the bulk
soil (2.81–4.08%), showing that the earthworms selected food substrates with high organic contents. In general, C contents
significantly increased during cast ageing (+100%), possibly because of CO2 fixation processes, dead root accumulation and/or macrofaunal activities in casts. In fresh casts, NH+
4 levels were very high (294.20–233.98 μg g–1 dry cast) when compared to the soil (26.96–73.95 μg g–1 dry soil), due to the intense mineralisation processes that occurred during the transit of soil and organic matter through
the earthworm gut. During the first week of cast ageing, NH+
4 levels sharply decreased, while NH–
3 levels showed successive peaks in the casts, the underlying soil and the adjacent soil. These results suggested the rapid
production of NO–
3 by nitrification processes in the fresh casts, followed by diffusion to the nearby soil, first vertically, then horizontally.
After 2 weeks of cast ageing, NH+
4 and NO–
3 levels only showed slight variations, likely because of organic matter protection in stable dry casts. The root biomass was
higher (1.6–4.7 times) below the old earthworm casts. The ecological significance of these results is discussed.
Received: 22 October 1998 相似文献
19.
Girma Abera Endalkachew Wolde-meskel Lars R. Bakken 《Biology and Fertility of Soils》2012,48(1):51-66
Seasonal drought in tropical agroecosystems may affect C and N mineralization of organic residues. To understand this effect,
C and N mineralization dynamics in three tropical soils (Af, An1, and An2) amended with haricot bean (HB; Phaseolus vulgaris L.) and pigeon pea (PP; Cajanus cajan L.) residues (each at 5 mg g−1 dry soil) at two contrasting soil moisture contents (pF2.5 and pF3.9) were investigated under laboratory incubation for 100–135 days.
The legume residues markedly enhanced the net cumulative CO2–C flux and its rate throughout the incubation period. The cumulative CO2–C fluxes and their rates were lower at pF3.9 than at pF2.5 with control soils and also relatively lower with HB-treated than
PP-treated soil samples. After 100 days of incubation, 32–42% of the amended C of residues was recovered as CO2–C. In one of the three soils (An1), the results revealed that the decomposition of the recalcitrant fraction was more inhibited by drought stress than easily
degradable fraction, suggesting further studies of moisture stress and litter quality interactions. Significantly (p < 0.05) greater NH4+–N and NO3−–N were produced with PP-treated (C/N ratio, 20.4) than HB-treated (C/N ratio, 40.6) soil samples. Greater net N mineralization
or lower immobilization was displayed at pF2.5 than at pF3.9 with all soil samples. Strikingly, N was immobilized equivocally
in both NH4+–N and NO3−–N forms, challenging the paradigm that ammonium is the preferred N source for microorganisms. The results strongly exhibited
altered C/N stoichiometry due to drought stress substantially affecting the active microbial functional groups, fungi being
dominant over bacteria. Interestingly, the results showed that legume residues can be potential fertilizer sources for nutrient-depleted
tropical soils. In addition, application of plant residue can help to counter the N loss caused by leaching. It can also synchronize
crop N uptake and N release from soil by utilizing microbes as an ephemeral nutrient pool during the early crop growth period. 相似文献
20.
Laboratory incubation study showed that iron pyrites retarded nitrification of urea-derived ammonium (NH4
+), the effect being greatest at the highest level (10000 mg kg–1 soil). Nitrification inhibition with 10000 mg pyrite kg–1 soil, at the end of 30 days, was 40.3% compared to 55.9% for dicyandiamide (DCD). The inhibitory effect with lower rates
of pyrite (100–500 mg kg–1) lasted only up to 9 days. Urea+pyrite treatment was also found to have higher exchangeable NH4
+-N compared to urea alone. DCD-amended soils had the highest NH4
+-N content throughout. Pyrite-treated soils had about 7–86% lower ammonia volatilization losses than urea alone. Total NH3 loss was the most with urea+DCD (7.9% of applied N), about 9% more than with urea alone.
Received: 11 November 1995 相似文献