Acetylene inhibition of nitrous oxide reduction and measurement of denitrification and nitrogen fixation in soil

Reduction of N₂O in moist soil was inhibited completely by 10^?2 atm C₂H₂ and partially by 10^?5 atm C₂H₂. The effect of C₂H₄ was 10⁴ times less than that of C₂H₂. Denitrification of NO^?₃ occurred in anaerobically or aerobically incubated waterlogged soil and in anaerobic but not in aerobic moist soil. In the absence of C₂H₂ there was transient accumulation of N₂O. In the presence of C₂H₂ there was stoichiometric conversion of NO^?₃ to N₂O. Some kinetics of the reduction of N₂O and of NO^?₃ to N₂O are presented. Denitrification of 1 μg added NO^?₃-N.g^? could be measured within 1 h. Stoichiometries of production of N₂O from NO^?₂ and NO^?₃, respectively, and production of CO₂ attributable to denitrification were consistent with reported energy yields. Reduction of C₂H₂ to C₂H₄ occurred immediately following complete denitrification of added NO^?₃. The incubation of soil in the presence and in the absence of C₂H₂ thus permits assay of both denitrification and N₂ fixation and provides information on the mole fraction of N₂O in the products of denitrification.     

Denitrification potentials: Measurement of seasonal variation using a short-term anaerobic incubation technique

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

Effects of acetylene on nitrification and denitrification in two soils during incubation with ammonium nitrate

A loam from the Frilsham and one from the Wickham Series were incubated at 50 and 90 per cent of their water contents at saturation with 100 μg NH₄NO₃-N_g^?1 soil in the presence and absence of C₂H₂ (0.5 per cent, v/v). Acetylene inhibited nitrification in both soils, but had no effect on mineralization of N. No denitrification (measured as the production of N₂O in the presence of C₂H₂) occurred during incubation at 50 per cent saturation. At 90 per cent saturation, denitrification resulted in a loss of 28.4 and 36.7 μg N_g^?1 after 48 h from the Frilsham and Wickham soils, respectively. The concurrent inhibition of nitrification had no effect on the extent of denitrification at this time. In the Wickham soil, NO₃^? was exhausted after 168 h incubation in the presence of C₂H₂ and denitrification was underestimated by 13 μg N_g^?. The data suggested that concurrent inhibition of nitrification during measurement of denitrification using the C₂H₂ inhibition technique is most likely to affect the estimate of denitrification loss when NO₃^?supply is limited by the inhibition of nitrification.     

Denitrification in waterlogged soils: In situ temperature-dependent variations

A method to measure nitrous oxide (N₂O) produced by denitrification in the field is described. The system shows a relationship between N₂O emission and the daily temperature variations of the surface soil. We compare the results with those obtained by complementary use of acetylene. A conversion factor between emitted N₂O (without C₂H₂) and reduced NO^?₃ is discussed.     

Injection of pig slurry and its effects on dynamics of nitrogen and carbon in a loamy soil unter laboratory conditions

Dynamics of nitrogen (N) and carbon (C) were investigated in a loamy soil amended or injected with pig slurry. Treatments were with or without acetylene C₂H₂ (which is assumed to inhibit reduction of nitrous oxide (N₂O) to dinitrogen (N₂), and soil cores were conditioned for 15 days at 25°C while pH, production of CO₂ and N₂O, ammonia (NH₃) emission and (nitrate) (NO₃ ^–) and (ammonium) (NH₄ ⁺) concentrations were monitored. There was no significant difference in CO₂ production between the injected and surface applied pig slurry treatments, and within 15 days ca. 5% of the C applied had been mineralized, if no priming effect was assumed. Neither the production of N₂O nor the total gaseous production of the denitrification process (N₂O plus N₂) were affected by the way the pig slurry was added to the soil. NH₃ volatilization, however, decreased by 90% when pig slurry was injected. The addition of C₂H₂ significantly increased the CO₂ production and the concentration of NH₄ ⁺, but significantly decreased the concentration of NO₃ ^–. It was concluded that the injection of pig slurry to a dry soil was an acceptable alternative to its application to the soil surface, as not only was NH₃ volatilization reduced, but the production of N₂O and N₂ through denitrification was not stimulated. It is also suggested that the composition of the organic C fraction in the pig slurry, most likely the concentration of fatty acids, had an important effect on the dynamics of N and C in the soil. Received: 12 May 1997     

Low sulfide concentrations affect nitrate transformations in freshwater and saline coastal retention pond sediments

Coastal areas in the southeastern USA are prone to hurricanes and strong storms that may cause salt-water influx to freshwater aquatic sediments. These changes in environmental conditions may impact sediment processes including nitrogen (N) cycling. The relative abilities of sediment microbial communities from two freshwater golf course retention ponds that drain into the adjacent wetlands, and two proximal saline wetland ponds, to remove nitrate (NO₃⁻) were compared to assess whether low concentrations of sulfide changed N-transformation processes. Microcosms were incubated with NO₃-N (300 μg g dw⁻¹) alone, and with NO₃-N and sulfide (H₂S) (100 and 200 μg g dw⁻¹). Nitrous oxide (N₂O), nitrite (NO₂⁻), NO₃⁻, ammonium (NH₄⁺), SO₄²⁻ and acid volatile sulfides were analyzed over time. The acetylene block technique was used to measure denitrification in sediment microcosms with no added H₂S. Denitrification was measured without acetylene (C₂H₂) addition in microcosms with added H₂S. With no added H₂S, denitrification was greater in the freshwater retention ponds than in the wetland ponds. Although low H₂S concentrations generally increased NO₃-N removal rates at all sites, lag periods were increased and denitrification was inhibited by low sulfide in the freshwater sediments, as evidenced by the greater concentrations of N₂O that accumulated compared to those in the wetland sediments. In addition to the inability of the freshwater sediments to convert N₂O to N₂ in the absence of C₂H₂, anomalously high transient NO₂-N concentrations accumulated in the retention pond samples. NH₄-N formation generally decreased due to H₂S addition at the freshwater sites; NH₄-N formation increased initially at the wetland sites, but was greater when no H₂S was added. Storm events that allow influx of SO₄²⁻-containing seawater into freshwater systems may change the dominant N species produced from nitrate reduction. Even low concentrations of sulfide produced incomplete denitrification and decreased formation of NH₄⁺ in these coastal freshwater sediments.     

A gas-flow soil core method to measure field denitrification rates

A method was developed for rapid measurement of soil denitrification under conditions where natural soil structure and aeration status is maintained. Air was continuously recirculated by means of a membrane pump through a soil core and a sample loop of a gas chromatograph equipped with an electron capture detector. Addition of acetylene to the recirculating air permitted measurement of denitrification in the soil core. Because of the rapid distribution of C₂H₂ and removal of N₂O provided by the gas flow, denitrification rates could usually be determined in less than 2 h. By means of external 6-way and 8-way valves, four soil cores could be simultaneously analyzed on one gas Chromatograph equipped with dual detectors. Soil cores could also be stored at 4°C for later analysis without affecting the denitrification rate. The detection limit for denitrification rate measurements was 0.5 ngN g^?1 soil day^?1 or approximately 2.6 g N ha^?1 day^?1. Coefficients of variation for repeated measurements on the same soil core were usually less than 15%, but coefficients of variation for repacked or natural cores of the same soil were much higher (70–90%) Disruption of the natural soil structure by sieving increased the denitrification rate in an aggregated clay loam soil, but decreased the rate in a non-aggregated sandy soil. These results illustrate the importance of maintaining natural soil structure during denitrification measurements. The effect of pumping gas through soil was evaluated by comparing denitrification rates in soil cores where C₂H₂ was allowed to distribute into the soil by passive diffusion with rates obtained by pumping. Lower denitrification rates were observed in the static incubation presumably due to limited diffusion of C₂H₂ into or N₂O out of the denitrifying sites in the soil. This diffusion limitation could be overcome in the static incubations if C₂H₂ was initially distributed through the soil by pumping. This gas flow method is well suited to the study of soil denitrification rates under nearly natural conditions because the indigenous substrates and anaerobic microsites are preserved, the rapidity in which denitrification rates can be measured, and the high sensitivity and relatively low analytical variability of the method.     

Acetylene and N-serve effects upon N2O emissions from NH4+ and NO3− treated soils under aerobic and anaerobic conditions

N₂O emissions from soils treated with NH₄⁺-N under aerobic conditions in the laboratory were 3- to 4-fold higher than those from controls (no extra N added) or when NO₃^?-N was added. Although the emission of N₂O-N in these field and laboratory experiments represented only 0.1–0.8% of the applied fertilizer NH₄⁺-N and are therefore not significant from an agronomic standpoint, these studies have conclusively demonstrated that the oxidation of applied ammoniacal fertilizers (nitrification) could contribute significantly to the stratospheric N₂O pool.Like N-serve, acetylene was shown to be a potent inhibitor of nitrification as it stopped the oxidation of NH₄⁺-N to (NO₃⁺-N + NO₂^?)-N and hence reduced the evolution of N₂O from nitrification within 60 min after its addition.Although high amounts of NO₃^?-N were present, the rate of denitrification was very low from soils with moisture up to 60% saturation. The further increase in the degree of saturation resulted in several-fold increase of denitrification which eventually became the predominant mechanism of gaseous N losses under anaerobic conditions.     

Effects of soil type and nitrate concentration on denitrification products (N2O and N2) under flooded conditions in laboratory microcosms

Abstract

Denitrification products nitrous oxide ((N₂O) and nitrogen (N₂)) were measured in three flooded soils (paddy soil from Vietnam, PV; mangrove soil from Vietnam, MV; paddy soil from Japan, PJ) with different nitrate (NO₃^–) concentrations. Closed incubation experiments were conducted in 100-mL bottles for 7 d at 25°C. Each bottle contained 2 g of air-dried soil and 25 mL solution with NO₃^– (concentration 0, 5 or 10 mg N L^?1) with or without acetylene (C₂H₂). The N₂O + N₂ emissions were estimated by the C₂H₂ inhibition method. Results showed that N₂O + N₂ emissions for 7 d were positively correlated with those of NO₃^– removal from solution with C₂H₂ (R² = 0.9872), indicating that most removed NO₃^– was transformed to N₂O and N₂ by denitrification. In PJ soil, N₂O and N₂ emissions were increased significantly (P < 0.05) by the addition of greater NO₃^– concentrations. However, N₂O and N₂ emissions from PV and MV soils were increased by the addition of 0 to 5 mg N L^?1, but not by 5 to 10 mg N L^?1. At 10 mg N L^?1, N₂ emissions for 7 d were greater in PJ soil (pH 7.0) than in PV (pH 5.8) or MV (pH 4.3) soils, while N₂O emissions were higher in PV and MV soils than in PJ soil. In MV soil, N₂O was the main product throughout the experiment. In conclusion, NO₃^– concentration and soil pH affected N₂O and N₂ emissions from three flooded soils.     

Effect of ammonium-, nitrite- and nitrate nitrogen on anaerobic nitrogenase activity in soil

Sandy loam soil, with added glucose, was incubated anaerobically under N₂ and subjected to repeated 1-h C₂H₂ reduction assays. In the presence of 1% glucose the addition of 50 μg NH₄⁺ ?N/g or of 20 μg NO^?₃ N/g (untreated soil contained 1.2 μg NH⁺₄?N and 7.10 μg NO^?₃-N/g) caused at least some suppression of nitrogenase activity. Activity developed when the KCl-extractable soil inorganic nitrogen concentration dropped below 35 μg/g. In the presence of 0.1 or 0.05% glucose the addition of 5 μg NH⁺₄?N/g caused some suppression of nitrogenase activity. However, activity developed when the soil NH₄⁺-N concentration dropped below about 4 μg/g. With 0.1% glucose and 5 μg added NO^?₂ N/g, activity did not develop until the soil NO^?₂ -N concentration dropped to zero. Added NO^?₃ N was rapidly reduced and denitrified to NO^?₂- N, N₂O-N and NH⁺₄ N and furthermore caused some inhibition of CO₂ evolution. The data from NH₄^?-addition experiments are consistent with a nitrogenase repression/ derepression threshold of 4 and 35μg NH⁺₄-N/g at 0.05 and 1% glucose concentrations, respectively. The data from NO^?₂- and NO^?₃-addition experiments suggest a combination of repression and toxicity effects in the presence of added NO^?₃ N.     

Effects of phosphorus addition with and without ammonium, nitrate, or glucose on N2O and NO emissions from soil sampled under Acacia mangium plantation and incubated at 100 % of the water-filled pore space

An incubation experiment was conducted to examine the effects of phosphorus (P) addition with and without ammonium, nitrate, or glucose on N₂O and NO emissions from soil taken under Acacia mangium plantation and incubated at 100 % water-filled pore space (WFPS). Additions of NO ₃ ^? stimulated the N₂O and NO emissions while NH ₄ ⁺ did not, showing that denitrification was the main process of N₂O and NO production in the study condition. When NO ₃ ^? was added with P significantly (P?<?0.05) increased N₂O emissions regardless of the ratio of the added nitrogen and carbon, suggesting that P addition stimulated denitrification activity. The activation of denitrification by P addition is possibly attributed to two mechanisms: (1) the added-P stimulated denitrification by relieving P shortage for denitrifying bacteria and (2) the added-P stimulated activity of heterotrophic soil microflora with increased O₂ consumption promoting the development of anaerobic conditions with stimulation of denitrification.     

The effect of some carbon substrates on denitrification rates and carbon utilization in soil

Summary Soil was amended with a variety of carbon sources, including four soluble compounds (glucose, sucrose, glycerol and mannitol) and two plant residues (straw and alfalfa).. Potential denitrification rates, measured both as N₂O accumulation and NO₃ ^– disappearance, were compared, and the predicted values of available C, measured as CO₂ production and water-extractable C, were assessed.The two measures of denitrification agreed well although N₂O accumulation was, found to be most sensitive. Soil treated with the four soluble C compounds resulted in the same rate of denitrification although glycerol was not as rapidly oxidized. Alfalfa-amended soil produced a significantly higher rate of denitrification than the same amount of added straw. CO₂ evolution was found to be a good predictor of denitrification over the first 2 days of sampling, but neither measure of available substrate C correlated well with denitrification rate beyond 4 days, when NO₃ ^– was depleted in most treatments. The data with alfalfa-amended soil suggested that denitrifiers used water-extractable C. materials produced by other organisms under anaerobic conditions.     

Estimation of the total gaseous nitrogen losses from clay soils under laboratory and field conditions

Acetylene blockage was evaluated as a method for measuring losses of N₂O + N₂ from two Denchworth series clay soils. The denitrification potential in anaerobic, dark incubations at 20°C with nitrate (equivalent to 100 kg N ha^?1 0–20 cm depth), maximum water holding capacity, and acetylene (1%), was equivalent to 32 ± 11 and 39 ± 6 kg N ha^?1 per day for the two 0–20 cm soils and was positively correlated with carbon content (r= 0.98). After 4 days N₂O was reduced to N₂ in the presence of C₂H₂. In April 1980 following irrigation (24 mm) and applications of ammonium nitrate (70 kg N ha^?1) and acetylene, the mean nitrous oxide flux from soil under permanent grass was 0.05 ± 0.01 kg N₂O-N ha^?1 per day for 8 days. In June 1980, the losses of nitrogen from cultivated soils under winter wheat after irrigation (36 mm) and acetylene treatment were 0.006 ± 0.002 and 0.04–0.07 ± 0.01 kg N ha^?1 per day respectively before and after fertilizer application (70 kg N ha^?1). The nitrous oxide flux in the presence of acetylene decreased briefly, indicating that nitrification was rate determining in drying soil.     

Nitrous oxide production at different soil moisture contents in an arable soil in China

Abstract

Laboratory incubations were conducted to investigate nitrous oxide (N₂O) production from a subtropical arable soil (Typic Plinthodults) incubated at different soil moisture contents (SMC) and with different nitrogen sources using a 10% (v/v) acetylene (C₂H₂) inhibitory technique at 25°C. The production of N₂O and CO₂ was monitored during the incubations and changes in the contents of KCl-extractable NO^? ₃-N and NH⁺ ₄-N were determined. The production of N₂O increased slightly with an increase in SMC from 40% water-holding capacity (WHC) to 70% WHC, but increased dramatically at 100% WHC. After incubation the NO^? ₃-N content increased even at a SMC of 100% WHC. At a SMC of 100% WHC, the addition of NH⁺ ₄-N promoted the production of N₂O and CO₂, whereas the addition of NO^? ₃-N decreased N₂O production. Compared with the incubation without C₂H₂, the presence of C₂H₂ increased NH⁺ ₄-N content, but decreased NO^? ₃-N content, and there was no significant difference in N₂O production. These results indicate that heterotrophic nitrification contributes to N₂O production in the soil.     

Effectiveness of acetylene inhibition of N2O reduction for measuring denitrification in soils of varying wetness

Abstract

The use of acetylene (C₂H₂) in the inhibition of N₂O to N₂ is widely used for measuring denitrification. The objective of this study was to determine the effectiveness of acetylene inhibition of N₂O reduction for short‐term and prolonged incubation studies in soils of varying water saturation, and to find out the possible reasons for lower N₂O recovery in continuously sealed incubations. Two experiments carried out in the laboratory reconfirmed that acetylene was very effective in inhibiting the reduction of N₂O in denitrification even for the prolonged incubation period (up to 96 h) under moist to saturated soil water contents. With 90 and 120% water‐filled pore space (WFPS), the accumulated N₂O in containers kept sealed throughout the study period, was 28 to 41% less than total headspace N₂O produced in containers that were opened, flushed and fresh C₂H₂ added every 24 h. Interpretation of our results suggest the lower N₂O amount recovered from continuously sealed containers at high WFPS, as compared to short‐term incubations (flushed containers), resulted primarily from delayed N₂O release from soil and not greater N₂O dissolved in soil solution, lower rates of denitrification, or decomposition/loss of C₂H₂ during prolonged incubation. Reduction of N₂O diffusion from soil cores showed direct relationship with head space concentration‐of N₂O and soil WFPS. From these results it is concluded that to obtain quantitative recovery of N₂O produced via denitrification, especially from soil with high WFPS soil cores should be vigorously shaken before head‐space N₂O analysis.     

Effectiveness of acetylene inhibition of N2O reduction for measuring denitrification in soils of varying wetness

Abstract

The use of acetylene (C₂H₂) in the inhibition of N₂O to N₂ is widely used for measuring denitrification. The objective of this study was to determine the effectiveness of acetylene inhibition of N₂O reduction for short‐term and prolonged incubation studies in soils of varying water saturation, and to find out the possible reasons for lower N₂O recovery in continuously sealed incubations. Two experiments carried out in the laboratory reconfirmed that acetylene was very effective in inhibiting the reduction of N₂O in denitrification even for the prolonged incubation period (up to 96 h) under moist to saturated soil water contents. With 90 and 120% water‐filled pore space (WFPS), the accumulated N₂O in containers kept sealed throughout the study period, was 28 to 41% less than total headspace N₂O produced in containers that were opened, flushed and fresh C₂H₂ added every 24 h. Interpretation of our results suggest the lower N₂O amount recovered from continuously sealed containers at high WFPS, as compared to short‐term incubations (flushed containers), resulted primarily from delayed N₂O release from soil and not greater N₂O dissolved in soil solution, lower rates of denitrification, or decomposition/loss of C₂H₂ during prolonged incubation. Reduction of N₂O diffusion from soil cores showed direct relationship with headspace concentration of N₂O and soil WFPS. From these results it is concluded that to obtain quantitative recovery of N₂O produced via denitrification, especially from soil with high WFPS soil cores should be vigorously shaken before head‐space N₂O analysis.     

N dynamics and sources of N2O production following pig slurry application to a loamy soil

Carbon (C) and Nitrogen dynamics and sources of nitrous oxide (N₂O) production were investigated in a loamy soil amended with pig slurry. Pig slurry (40000kgha^–1) or distilled H₂O was applied to intact soil cores of the upper 5cm of a loamy soil which were incubated under aerobic conditions for 28 days at 25°C. Treatments were with or without acetylene (C₂H₂), which is assumed to inhibit the reduction of N₂O to dinitrogen (N₂), and with or without dicyandiamide (DCD), which is thought to inhibit nitrification. Volatilization of ammonia (NH₃), pH, carbon dioxide (CO₂) and N₂O production, and ammonium (NH₄ ⁺) and nitrate NO₃ ^–) concentrations were monitored. The pH of the pig slurry amended soil increased from an initial value of 7.1 to pH 8.3 within 3 days; it then decreased slowly but was still at a value of 7.4 after 28 days. Twenty percent of the NH₄ ⁺ applied volatilized within 28 days. Sixty percent of the C applied in the pig slurry evolved as CO₂, if no priming effect was assumed, but only 38% evolved when the soil was amended with DCD. Pig slurry significantly increased denitrification and the ratio between its gaseous products, N₂O and N₂, was 0.21. No significant increases in NO₃ ^– concentration occurred, and N₂O produced through nitrification was 0.07mg N₂O-N kg^–1 day^–1 or 33% of the total N₂O produced. C₂H₂ was used as a C substrate by microorganisms and increased the production of N₂O. Received: 12 May 1997     

Inhibitory effect of nitrate on reduction of N2O to N2 by soil microorganisms

The ability of soils to reduce N₂O to N₂ depends very largely on their NO₃^? content. Low concentrations of NO₃^? delay reduction of N₂O to N₂ by soil microorganisms, and high concentrations of NO₃^? almost completely inhibit this process. The inhibitory effect of NO₃^? on N₂O reduction increases markedly with decrease in soil pH. These observations account for the finding in previous work that accumulation of N₂O during denitrification of NO₃^? in soils incubated in closed systems is favored by high NO₃^? concentration and by low pH. They also indicate that, even if increased N fertilization of soils does not lead to a significant increase in the amount of N volatilized from soils as N₂ and N₂O through denitrification of NO₃^?, it may cause a substantial increase in the ratio of N₂O to N₂ and thereby pose a threat to the stratospheric ozone layer.     

Denitrification characteristics of subtropical soils in China affected by soil parent material and land use

Forty‐five soil samples were collected from rice paddy land (R), tea garden land (T), forestland (F), brush land (B), and upland (U) in Jiangxi province, a subtropical region of China. These soils were derived from Quaternary red earth (Q), Tertiary red sandstone (S), and granite (G). Their denitrification capacities were determined after treatment with 200 mg NO₃⁻‐N kg⁻¹ soil by measuring changes in NO₃⁻‐N content during a 28‐day anaerobic incubation under N₂ gas in the headspace, at 30°C. The subtropical soils studied here were characterized by generally small denitrification capacities, ranging from no denitrification capacity to complete disappearance of added NO₃⁻‐N within 11 days of incubation. With few exceptions, NO₃⁻‐N reduction with incubation time followed a first‐order relationship with reaction constants of 0 – 0.271 day⁻¹, but the data could be simulated better by a logarithmic relationship. Thus, denitrification capacity was determined by the reaction constant of the first‐order reaction, the slope of the logarithmic relationship, and the averaged NO₃⁻‐N reduction rate in the first 7 days of anaerobic incubation (ranging from 0 to 28.5 mg kg⁻¹day⁻¹), and was significantly larger in the soils derived from G than from Q and S for all land uses except for rice paddy land. Soil organic carbon and nitrogen availability are the key factors that determine differences in denitrification capacity among the three soil parent materials. Rice cultivation significantly promoted denitrification capacity compared with the other four land uses and masked the effect of soil parent materials on denitrification capacity. This is most likely due to increases in organic carbon and total N content in the soil, which promoted the population and biological activities of microorganisms which are able to respire anaerobically when the rice soil is flooded. Neither the increased pH of upland soil caused by the addition of lime for upland crop production, nor the decreased pH of the tea garden soil by the acidification effect of tea plants altered soil denitrification capacity. Our results suggest that land use and management practices favour soil carbon and/or nitrogen accumulation and anaerobic microorganism activities enhance soil denitrification capacity.     

Gaseous nitrogen losses from fertilized soil during nitrification and denitrification using the acetylene blockage technique

Summary A sandy soil amended with different forms and amounts of fertilizer nitrogen (urea, ammonium sulphate and potassium nitrate) was investigated in model experiments for N₂O emission, which may be evolved during both oxidation of ammonia to nitrate and anaerobic respiration of nitrate. Since C₂H₂ inhibits both nitrification and the reduction of N₂O to N₂ during denitrification, the amount of N₂O evolved in the presence and absence of C₂H₂ represents the nitrogen released through nitrification and denitrification.Results show that amounts of N₂O-N lost from soils incubated anaerobically with 0.1% C₂H₂ and treated with potassium nitrate (23.1 µg N-NO ₃ ^– /g dry soil) exceeded those from soils incubated in the presence of 20% oxygen and treated with even larger amounts of nitrogen as urea and ammonium sulphate. This indicates that nitrogen losses by denitrification may potentially be higher than those occurring through nitrification.