Effect of soil compaction by tractor traffic on soil structure, denitrification, and yield of wheat (Triticum aestivum L.)

In a field experiment with soil compaction by tractor traffic on a loam soil, the denitrification rate (using the C₂H₂ inhibition method), the soil structure, and the wheat yield were investigated. Tractor traffic on wet soil (> – 50 mbar matric potential) reduced the pore volume, doubled the percentage of large aggregates (> 20 mm), reduced the wheat yield by about 25%, and increased the N-loss through denitrification by a factor of 3–4. Neither of these parameters were affected by tractor traffic at low soil moisture content. The weight of the tractor (1800 kg vs 4800 kg) did not significantly alter the effect of compaction on the measured parameters. There was a factor of 2–6 between the measured denitrification rate in compacted and that in uncompacted soil, and this factor showed little dependence on the average activity level on each date of measurement. Accumulated values for the measured denitrification during 75 days (May 23-August 9) were 3–5 kg N ha^–1 in uncompacted soil and 15–20 kg N ha^–1 in soil which was compacted in wet condition.     

Ammonia volatilization from Vertisols

Farmers want to minimize losses of nitrogen (N) by volatilization of ammonia when adding fertilizers and improve fertilizer recovery of N by plants. We aimed to quantify the losses of N through NH₃ volatilization as affected by soil moisture content, type of fertilizer, and placement method in Vertisols in Kenya, and conducted three experiments for the purpose under controlled conditions in the laboratory. We found that NH₃-N losses were greatest at 80% water holding capacity, which we ascribed to the ready availability of water to dissolve the fertilizer at that water content. The soil's cation exchange capacity (CEC) did not influence volatilization, whereas the soil's pH indicated the potential of the soil to volatilize ammonia. Ammonia losses from the fertilizers were in the order urea > ammonium sulphate > ammonium nitrate applied. Incorporating fertilizer within the 0–5 cm soil layer more than halved NH₃ volatilization but did not prevent it completely. These results indicate that soil pH, rather than CEC, is the main inherent characteristic influencing ammonia volatilization from Vertisols. Ammonium-based fertilizers should be incorporated within the 0–5 cm soil layer, or preferably somewhat deeper, to avoid losses via NH₃ volatilization, particularly in alkaline soils. Nitrate fertilizers are preferable to urea where the risks of NH₃ volatilization are large, provided due consideration is given to denitrification risks.     

Denitrification in drained and undrained arable clay soil

Emissions of nitrous oxide (N₂O) and nitrogen gas (N₂) from denitrification were measured using the acetylene inhibition method on drained and undrained clay soil during November 1980-June 1981. Drainage limited denitrification to about 65% of losses from undrained soil. Emissions from the undrained soil were in the range 1 to 12 g N ha^–1 h^–1 while those from the drained soil ranged from 0.5 to 6 g N ha^–1 h^–1 giving estimated total losses (N₂O + N₂) of 14 and 9 kgN ha^–1.
Drainage also changed the fraction of nitrous oxide in the total denitrification product. During December, emissions from the drained soil (1.8±0.6 gN ha^–1 h^–1) were composed entirely of nitrous oxide, but losses from the undrained soil (2.7 ± 1.1 g N ha^–1 h^–1) were almost entirely in the form of nitrogen gas (the fraction of N₂O in the total loss was 0.02). In February denitrification declined in colder conditions and the emission of nitrous oxide from drained soil declined relative to nitrogen gas so that the fraction of N₂O was 0.03 on both drainage treatments. The delayed onset of N₂O reduction in the drained soil was related to oxygen and nitrate concentrations. Fertilizer applications in the spring gave rise to maximum rates of emission (5–12g N ha^–1 h^–1) with the balance shifting towards nitrous oxide production, so that the fraction of N₂O was 0.2–0.8 in April and May.     

Mineralization of Nitrogen and N2O Production Potentials in Acid Forest Soils under Controlled Aerobic Conditions

Some acid surface mineral soils from different forest vegetations and sites in central Japan were taken during April and October in 2003 to study the net N mineralization and N₂O production potentials in the laboratory. Under the controlled aerobic conditions, 50 Pa C₂H₂ in the headspace can be used to study total gaseous-N losses during the aerobic mineralization and heterotrophic N₂O production in acid forest soils. The net N mineralization of these acid forest soils and N₂O-N production was variable with forest stands and with seasons, probably because of the quality of the litters and the variations of soil attributes. Three deciduous forest soils during two sampling reveal a higher potential for the total gaseous-N loss during the aerobic mineralization as compared with two coniferous forest soils. Heterotrophic nitrification among these acid forest soils accounted for the range from 37.0 to 76.3% of the total N₂O production under the experimental conditions, and was variable with forest stands and with seasons. Some factors regulating the net N mineralization and N₂O-N production were discussed in these acid forest soils.     

Measurement of ammonia volatilization loss using a dynamic chamber technique: A case study of surface-incorporated manure and ammonium sulfate in an upland field of light-colored Andosol

The present study aimed to elucidate ammonia (NH₃) volatilization loss following surface incorporation (0–15 cm mixing depth) of nitrogen (N) fertilizer in an upland field of light-colored Andosol in central Japan. A dynamic chamber technique was used to measure the NH₃ effluxes. Poultry manure, pelleted poultry manure, cattle manure, pelleted cattle manure and ammonium sulfate were used as N fertilizers for basal fertilization to a bare soil with surface incorporation. All three experiments in summer and autumn 2007 and in summer 2008 showed negligible NH₃ volatilization losses following the application of all N fertilizers with the same application rate of 120 kg N ha⁻¹ as total N; these negligible losses were primarily ascribed to chemical properties of the soil, that is, its high cation exchange capacity (283 mmol_c kg⁻¹ dry soil) and relatively low pH(H₂O) (5.9). In addition, the surface incorporation, the very small ratio of ammoniacal N to total N for the manure, and the decrease in soil pH to ≤5.5 following applications of ammonium sulfate were also advantageous to the inhibition of NH₃ volatilization loss from the field-applied N fertilizers.     

Increasing nitrate removal at low temperatures by incorporating organic matter into paddy fields

Denitrification of paddy fields is a key process for improving water quality in fields where nitrate concentrations are high. The objective of the present study was to understand the effects of incorporating organic carbon (C) into soil on the denitrification rate of paddy fields in winter. On 11 December 2007, separate paddy field plots were prepared by incorporating 5 Mg ha⁻¹ of rice straw (RS), 11 Mg ha⁻¹ of rice straw compost (RSC) or a control. A field with a high concentration of nitrate in the water (averaging 18 mg N L⁻¹) was irrigated until 29 March. During the experiment, the daily average soil temperature at a depth of 0.05 m ranged between 3 and 15°C. The nitrate concentration in the surface water in the RS plot, where the residence time was 2 days, decreased more than the concentration in the control or RSC plots. The total estimated nitrate removal from each plot in relation to the other plots was RS > RSC = control. Measurements of the soil from each plot on 29 February 2008 showed that incorporation of RS significantly increased the denitrification potential, even at low temperatures (5–10°C). Furthermore, the RS plot contained more dissolved organic C than the control or RSC plots. This result indicates that supplying RS effectively increases denitrification under low-temperature conditions.     

Indicator of potential residual carbon in soils after exogenous organic matter application

An indicator to evaluate the proportion of exogenous organic matter (EOM) remaining in soils over the long-term after application has been developed. A database was constructed with analytical data corresponding to 83 EOMs, including sludges, composts, animal wastes, mulches, plant materials and fertilizers. The data included results of proximal analysis (soluble, SOL, hemicellulose-, HEM, cellulose-, CEL, and lignin-like, LIC, fractions, in g kg⁻¹ total organic matter) and of carbon (C) mineralization during long-term incubations under laboratory conditions (in g kg⁻¹ exogenous organic C, EOC). The potential residual organic C after EOM application to soil was assessed from the extrapolation of the incubation results. Then, partial least square regression was used to relate EOM characteristics to the proportion of potentially residual organic C previously determined from the incubations. The biochemical fractions of EOM were not predictive enough to develop the indicator. The proportion of organic C mineralized during 3 days of incubation (C_3d) was cumulated and appeared to be the most predictive variable of residual organic C. The proposed indicator of residual organic carbon in soils (expressed as g EOC kg⁻¹) was I_ROC = 445 + 0.5 SOL – 0.2 CEL + 0.7 LIC – 2.3 C_3d. The indicator was calculated for the main types of EOM applied to soils. When compared with the few field data of residual C measured in long-term field experiments, the values provided by the indicator seemed to be over-estimated (i.e. EOC degradation could be faster under field conditions than during laboratory incubations).     

Nitrous oxide and carbon dioxide emissions from grassland amended with sewage sludge

Abstract. Land disposal of sewage sludge in the UK is set to increase markedly in the next few years and much of this will be applied to grassland. Here we applied high rates of digested sludge cake (1–1.5×10³ kg total N ha⁻¹) to grassland and incorporated it prior to reseeding. Using automated chambers, nitrous oxide (N₂O) and carbon dioxide (CO₂) fluxes from the soil were monitored 2–4 times per day, for 6 months after sludge incorporation. Peaks of N₂O emission were up to 1.4 kg N ha⁻¹ d⁻¹ soon after incorporation, and thereafter were regularly detected following significant rainfalls. Gas emissions reflected diurnal temperature variations, though N₂O emissions were also strongly affected by rainfall. Although emissions decreased in the winter, temperatures below 4 °C stimulated short, sharp fluxes of both CO₂ and N₂O as temperature increased. The aggregate loss of nitrogen and carbon over the measurement period was up to 23 kg N ha⁻¹ and 5.1 t C ha⁻¹. Losses of N₂O in the sludge-amended soil were associated with good microbial conditions for N mineralization, and with high carbon and water contents. Since grassland is an important source of greenhouse gases, application of sewage sludge can be at least as significant as fertilizer in enhancing these emissions.     

Automated sampling system for long-term monitoring of nitrous oxide and methane fluxes from soils

We describe an automated gas sampling system for monitoring trace gas fluxes from soils. The sampling system allows automated collection of gas samples in glass vials using a syringe pump connected to an automated static chamber installed in the field. The gas samples are transferred to a laboratory and then analyzed using a gas chromatography system. Comparisons between manual and automated sampling of standard gases showed good agreement ( r ² = 0.99996 for N₂O, r ² = 0.999 for CH₄ and r ² = 0.998 for CO₂). In a field test, replicated flux measurements using two chambers generally showed good agreement. The sampling system allows frequent and long-term monitoring of fluxes under a wide range of weather conditions (tested temperatures ranged from –6.5 to 40°C; 127 mm day⁻¹ max precipitation). The major advantages of the system are its increased portability, ease of operation and cost effectiveness compared with on-line automated sampling/analytical systems.     

Respiration of nitrous oxide in suboxic soil

Reduction of nitrous oxide (N₂O) is an autonomous respiratory pathway. Nitrous oxide is an alternative electron acceptor to O₂ when intensive biological activity and reduced diffusivity result in an O₂ deficit. Hypoxic or anoxic micro sites may form even in well-aerated soils, and provide a sink for N₂O diffusing through the gas-filled pore space. We reproduced similar in vitro conditions in suboxic (0.15% O₂) flow-through incubation experiments with samples from a Stagnosol and from a Histosol. Apparent half-saturation constants ( k _m) for N₂O reduction were similar for both soils and were, on average, 3.8 μmol mol⁻¹ at 5°C, 5.1 μmol mol⁻¹ at 10°C, and 6.9 μmol mol⁻¹ at 20°C. Respiration of N₂O was estimated to contribute a maximum proportion of 1.7% to total respiration in the Stagnosol (pH 7.0) and 0.9% in the Histosol (pH 2.9).     

Carbon and nitrogen mineralization of sewage sludge compost in soils with a different initial pH

Soil properties may affect the decomposition of added organic materials and inorganic nitrogen (N) production in agricultural soils. Three soils, Potu (Pu), Sankengtzu (Sk) and Erhlin (Eh) soils, mixed with sewage sludge compost (SSC) at application rates of 0 (control), 25, 75 and 150 Mg ha⁻¹ were selected from Taiwan for incubation for 112 days. The aim of the present study was to examine the effects of SSC application rates on the carbon decomposition rate, N transformation and pH changes in three soils with different initial soil pH values (4.8–7.7). The results indicated that the highest peaks of the CO₂ evolution rate occurred after 3 days of incubation, for all treatments. The Pu soil (pH 4.8) had a relatively low rate of CO₂ evolution, total amounts of CO₂ evolution and percentage of added organic C loss, all of which resulted from inhibition of microbial activity under low pH. For the Pu and Sk soils, the concentration of NH₄⁺-N reached its peak after 7–14 days of incubation, which indicated that ammonification might have occurred in the two soils with low initial pH values. NO₃⁻-N rapidly accumulated in the first 7 days of incubation in the Eh soil (pH 7.7). The direction and extent of the soil pH changes were influenced by the N in the SSC and the initial soil pH. Ammonification of organic N in the SSC caused the soil pH to increase, whereas nitrification of mineralized N caused the soil pH to decline. Consequently, the initial soil pH greatly affected the rate of carbon decomposition, ammonification and nitrification of SSC.     

Pollution of carbonate soils in a Mediterranean climate due to a tailings spill

The retention walls in a pond containing the residues from the pyrite mine of Aznalcóllar (southern Spain) broke open on 25 April 1998, spilling approximately 6 × 10⁶ m³ of polluted water and toxic tailings, which affected some 55 km². Drying and aeration of the tailings resulted in oxidation, forming an acidic solution with high pollutant contents, the effects of which were studied in a calcareous soil. The infiltration of this solution markedly affected only the first 12 mm of the soil, where strong acidification caused the weathering of the carbonates, and where the fine mineral particles were hydrolysed. The SO₄²⁻ ions in the acidic solution precipitated almost entirely at this depth, forming gypsum, hydroxysulphates and complex sulphates. The Fe³⁺ ions also precipitated there, mainly in amorphous or poorly crystallized forms, adsorbing to As, Sb, Tl and Pb dissolved in the acidic solution. The Al³⁺ ions, though partly precipitating in the acidic layer, accumulated mostly where the soil pH exceeded 5.5 (12–14 mm in depth). They did so primarily as amorphous or poorly crystallized forms, adsorbing to Cu dissolved in the acidic solution. The Zn²⁺ and Cd²⁺ ions accumulated mainly at pH > 7.0 (19–21 mm in depth), being adsorbed chiefly by clay mineral. After 15 months, only the first 20 mm of the soil were acidified by the oxidation of the tailings and most of the pollutants did not penetrate deeper than 100 mm. Consequently, the speed of the cleanup of the toxic spill is not as important as a thorough removal of tailings together with the upper 10 cm of the soil.     

Sequential extraction methods for soil organic nitrogen

(pp. 825–831)
This study was carried out to clarify the effects of soil nitrate before cultivation and amounts of basal-dressed nitrogen on additional N application rate and yields of semi-forced tomato for three years from 1998 to 2000. The amounts and timing of additional N dressing were determined based on diagnosis of petiole sap nitrate. The top-dressing was carried out with a liquid fertilizer when the nitrate concentration of a leaflet's petiole sap of leaf beneath fruit which is 2–4 cm declined below 2000 mg L⁻¹.
For standard yield by the method of fertilizer application based on this condition, no basal-dressed nitrogen was required when soil nitrate before cultivation was 150 mg kg⁻¹ dry soil or higher in the 0–30 cm layer; 38 kg ha⁻¹ of basal-dressed nitrogen, which corresponds to 25% of the standard rate of fertilizer application of Chiba Prefecture, was optimum when soil nitrate before cultivation was 100150 mg kg⁻¹ dry soil; 75 kg ha⁻¹ of basal-dressed nitrogen, which corresponds to 50% of the standard, was optimum when soil nitrate before cultivation was under 100 mg kg⁻¹ dry soil. A standard yield was secured and the rate of nitrogen fertilizer application decreased by 49–76% of the standard by keeping the nitrate concentration of tomato petiole sap between 1000–2000 mg L⁻¹ from early harvest time to topping time under these conditions.     

Impact of water percolation on nutrient leaching from an irrigated paddy field in Japan

Abstract. We examined the effect on soil nutrient status and sustainability of water percolation through an irrigated paddy field in Japan, to the depth of drainage (40 cm). The difference between amounts of nutrients leached by percolation and those supplied by irrigation indicated that 25–130 kg ha⁻¹ Ca, 8–24 kg ha⁻¹ Mg, from −1 to 9 kg ha⁻¹ K, and 8–17 kg ha⁻¹ Fe, respectively, were lost each year from the 0–40 cm soil layer during rice cultivation, when the supply from fertilization and rainfall and the loss in grain harvest were not accounted for. When the supply of K from rainfall and the loss in grain harvest were taken into account, a total K loss of about 10 kg ha⁻¹ was estimated. The electrical neutrality of inorganic ions in the percolating water was always maintained. From these results we estimate that the amounts of exchangeable Ca and Mg in the soil to a depth of 40 cm would decrease by 50% within 50–260 and 30–100 years, respectively, if similar management were continued without fertilization. The total amount of carbon dioxide (ΣCO₂) leached in percolating water during the period of rice cultivation was 120–325 kg C ha⁻¹, which corresponded to 0.47–0.94% of the soil organic carbon to 40 cm depth.     

High night temperature stimulates photosynthesis, biomass production and growth during the vegetative stage of rice plants

The effects of night temperature on biomass accumulation and plant morphology were examined in rice ( Oryza sativa L.) during vegetative growth. Plants were grown under three different night temperatures (17, 22 and 27°C) for 63 days. The day temperature was maintained at 27°C in all treatments. The final biomass of the plants was greatest in the plants grown at the highest night temperature. Total leaf area and tiller number were also the greatest in this treatment. Growth analysis indicated that the relative growth rate in the 27°C night-temperature treatment was maximal between days 21–42 and this was caused by increases in leaf area ratio, leaf weight ratio and specific leaf area. Plant total nitrogen contents did not differ among treatments. However, nitrogen allocation to the leaf blades was highest and the accumulation of sucrose and starch in the leaf blades and sheaths was the lowest in the 27°C night-temperature treatment by day 42. Despite this, dark respiration was also highest, and both the gross and net rates of CO₂ uptake at the level of the whole plant at day 63 were the highest in the 27°C night-temperature treatment. Thus, high night temperature strongly stimulated the growth of leaf blades during the early stage of rice plant growth, leading to increased biomass during the vegetative stage of the rice plants. As the CO₂ uptake rate per total leaf area was higher, photosynthesis at the level of the whole plant was also stimulated by a high night temperature.     

Net nitrogen mineralization and nitrification rates in forest soil in northeastern Taiwan

We used a laboratory incubation approach to measure rates of net N mineralization and nitrification in forest soils from Fu-shan Experimental Forest WS1 in northern Taiwan. Net mineralization rates in the O horizon ranged from 4.0 to 13.8 mg N kg⁻¹ day⁻¹, and net nitrification rates ranged from 2.2 to 11.6 mg N kg⁻¹ day⁻¹. For mineral (10–20 cm depth) soil, net mineralization ranged from 0.06 to 2.8 mg N kg⁻¹ day⁻¹ and net nitrification rates ranged from 0.02 to 2.8 mg N kg⁻¹ day⁻¹. We did not find any consistent differences in N mineralization or nitrification rates in soils from the upper and lower part of the watershed. We compared the rates of these processes in three soil horizons (to a soil depth of 30 cm) on a single sampling date and found a large decrease in both net N mineralization and nitrification with depth. We estimated that the soil total N pool was 6,909 kg N ha⁻¹. The present study demonstrates the importance of the stock of mineral soil N in WS1, mostly organic N, which can be transformed to inorganic N and potentially exported to surface and ground water from this watershed. Additional studies quantifying the rates of soil N cycling, particularly multi-site comparisons within Taiwan and the East Asia–Pacific region, will greatly improve our understanding of regional patterns in nitrogen cycling.     

Interpreting pH and nitrate concentration in solutions drained from acid soils. Possible artefacts of lysimeters

Abstract. Solutions collected from lysimeters of acid soils can show pH values close to or even above neutral. Laboratory experiments on an acid soil from Burundi were planned to test if denitrification or CO₂ degassing might explain such a paradox. In the first experiment, soil profiles were reconstituted in columns and leached with 55 μ m Ca(NO₃)₂ solutions at 30 °C and 4 °C. Two drainage regimes were applied: intermittent suction or no suction at the bottom of the columns. In the second experiment, pH values were measured in solutions drained from different horizons at 30 °C, before and after equilibration with ambient air. Sterilized soil was also tested in the same way. Results from experiment 1 showed that despite the accumulation of water in the bottom of soil profiles when no suction was applied, aeration still existed so that reduction reactions, namely denitrification, are not expected to affect greatly the percolate composition. Indeed nitrate concentration was similar in both drainage regimes and was close to the input value. The pH values in percolates were close to 7 at 30 °C and they dropped to about 5.5 when the columns were at 4 °C. In experiment 2, equilibration of percolates with ambient air resulted in pH increase which was greater for the top horizon (C-rich) but negligible when the soil was first sterilized. These convergent results illustrate the very important effect of CO₂ degassing on pH of drained solutions when microbial activity is stimulated at high temperatures, in C-rich soil. This is of prime importance when interpreting results from lysimeter experiments. By chance, this study also showed that large quantities of nitrate can be produced in soil at low temperatures.     

Rate and mode of application of the urease inhibitor N-(n-butyl) thiophosphoric triamide on ammonia volatilization from surface-applied urea

A laboratory study evaluated the effect of rate (0, 100, 250, 500, 750 or 1000 mg/kg) and mode of application of the urease inhibitor N -( n -butyl) thiophosphoric triamide (nBTPT) (coating the urea granule, adding to the urea melt or adding to urea ammonium nitrate (UAN) solutions) on NH₃ volatilization from urea, at three temperatures (5, 15 and 25 °C), with four contrasting soil types. Daily ammonia loss was measured for up to 21 days after surface N application, using ventilated soil enclosures. Ammonia loss from unamended urea varied with soil type and temperature and ranged from 8.2 to 31.9% of the N applied. nBTPT was highly effective in lowering NH₃ volatilization from urea and in delaying the time of maximum rate of loss. The average % inhibition over all soils, temperatures and formulations was 61.2, 69.9, 74.2, 79.2 and 79.8% for the 100, 250, 500, 750 or 1000 mg/kg nBTPT concentration, respectively. The % inhibition with nBTPT was lower at 15 °C compared with at 5 or 25 °C and was lower in UAN solutions than in granular products. There was little difference between the melted and coated granular products in lowering NH₃ loss or in soil N transformations. The stability of nBTPT in urea products was dependent on its mode of application and on the storage temperature. Incorporating nBTPT in the urea melt produced a more homogeneous product with superior stability than coating the urea granule.     

Assessment of N2O, NOx and NH3 emissions from a typical rural catchment in Eastern China

To evaluate the atmospheric load of reactive gaseous nitrogen in the fast-developing Eastern China region, we compiled inventories of nitrous oxide (N₂O), nitrogen oxide (NO_x) and ammonia (NH₃) emissions from a typical rural catchment in Jiangsu province, China, situated at the lower reach of the Yangtze River. We considered emissions from synthetic N fertilizer, human and livestock excreta, decomposition of crop residue returned to cropland and residue burning, soil background and household energy consumption. The results showed that, for the 45.5 km² catchment, the annual reactive gaseous emission was 279 ton N, of which 7% was N₂O, 16% was NO_x and 77% was NH₃. Synthetic N fertilizer application was the dominant source of N₂O and NH₃ emissions and crop residue burning was the dominant source of NO_x emission. Sixty-seven percent of the total reactive gaseous N was emitted from croplands, but on a per unit area basis, NO_x and NH₃ emissions in residential areas were higher than in croplands, probably as a result of household crop residue burning and extensive human and livestock excreta management systems. Emission per capita was estimated to be 18.2 kg N year⁻¹ in the rural catchment, and emission per unit area was 56.9 kg N ha⁻¹year⁻¹ for NH₃ + NO_x, which supports the observed high atmospheric N deposition in the catchment. Apparently, efficient use of N fertilizer and biological utilization of crop straw are important measures to reduce reactive gases emissions in this rural catchment.     

Relationship between N2O and NO emission potentials and soil properties in Japanese forest soils

To determine the relationship between nitrous oxide (N₂O) and nitric oxide (NO) emission rates and soil properties in forest soils, N₂O and NO emission rates in soils were measured in incubation experiments under standardized temperature and water conditions (water content at a water-holding capacity of 60%) using soils packed into a cylindrical core, and variations in the soil properties were also determined. The N₂O emission rates from nitrification and from denitrification were determined separately using a nitrification inhibitor (10 Pa acetylene). Soil samples were taken from 25 forest stands in a central temperate area of Japan. The N₂O and NO emission rates were highly variable, even under the standardized temperature and water-holding capacity (60%) conditions. According to a partial least squared regression model analysis, the C:N ratio and pH strongly affected the N₂O emission rate, whereas     , water-soluble Al and the C:N ratio strongly affected the NO emission rate. The C:N ratio negatively affected the emission rate of both N oxide gases, suggesting that N mineralization is an important factor in the rates of N oxide gas emission. The acetylene inhibition experiment showed that N₂O emission from denitrification was positively affected by pH, water-filled pore space and filling density, and negatively affected by the C:N ratio, total carbon and total nitrogen.