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[N.sub.2]O and [N.sub.2] emissions from pasture and wetland soils with and without amendments of nitrate, lime and zeolite under laboratory condition.

Introduction

Nitrous oxide, a potent greenhouse and ozone ([O.sub.3])-depleting gas, constitutes ~17.5 of New Zealand's total greenhouse gas emissions inventory (MfE 2007). Microbial processes in soil that produce [N.sub.2]O include nitrification (Inubushi et al. 1996), denitrification (Tiedje 1988; Firestone and Davidson 1989), and dissimilatory N[O.sub.3.sup.-] reduction to N[H.sub.4.sup.+] (DNRA) (Silver et al. 2001). All these processes can occur in soils and sediments across the landscape. Nitrification, strictly an aerobic process, produces [N.sub.2]O as byproduct during N[H.sub.4.sup.+]oxidation to nitrite (N[O.sub.2.sup.-]) and N[O.sub.3.sup.-] (Firestone and Davidson 1989). Denitrifieation is an anaerobic process by which oxidised N compounds, principally N[O.sub.3.sup.-] and N[O.sub.2.sup.-], are reduced to [N.sub.2]O and [N.sub.2] in a respiratory metabolism in the presence of available organic C (Firestone 1982; Tiedje 1988; Cavigelli and Robertson 2001). DNRA is also an anaerobic process that produces [N.sub.2]O as a byproduct during dissimilatory N[O.sub.3.sup.-] reduction to N[H.sub.4.sup.+] (Tiedje 1988; Silver et al. 2001). Nitrous oxide produced by various processes might form one pool before being reduced to [N.sub.2] by nitrous oxide reductase, the enzyme involved in reduction of [N.sub.2]O to [N.sub.2] (Stevens and Laughlin 1998). Emission of [N.sub.2] to the atmosphere is not associated with any environmental problems and it can be returned back to the soil through symbiotic and nonsymbiotic [N.sub.2] fixation.

New Zealand's grazed pasture systems have been identified as the major source of [N.sub.2]O emission because these receive regular inputs of N through fertilisers, biological fixation of atmospheric [N.sub.2], and recycled excretal-N deposited by grazing animals or applied through dairy farm effluents (de Klein et al. 2003). Riparian 'wetlands', natural or constructed, intercept N that enters riparian zones from adjacent pasture or uplands via surface and subsurface runoff and are regarded as one of the best farm management practices to minimise N export to water bodies (Cooper et al. 1997; Burns and Nguyen 2002; Rutherford and Nguyen 2004). Denitrification is considered to be one of the major N[O.sub.3.sup.-] removal processes in wetland zones (Hoffmann et al. 2000); therefore, [N.sub.2]O generation rates from highly organic-enriched wetlands/seepage zones are likely to be substantial.

Nitrous oxide production in soil is unavoidable as it is part of N cycling; therefore, mitigation measures should focus on ways to reduce [N.sub.2]O generation rates in soil and to lower the [N.sub.2]O : [N.sub.2] ratio in emissions. Recently, most research work has focused on reducing [N.sub.2]O emission in grazed pastures by applying nitrification inhibitor to retain N in N[H.sub.4.sup.+] form (Di and Cameron 2006); double inhibitor (urease inhibitor+nitrification inhibitor) (Dobbie and Smith 2003; Singh et al. 2006; Zaman et al. 2008); use of stand-off pads (Luo et al. 2007; Luo and Saggar 2008); zero or restricted grazing during the wet winter period to limit the development of anaerobic soil conditions that favour denitrification (Bhandral et al. 2005; Monaghan et al. 2005); and applying soil amendments (lime and zeolite) (Zaman et al. 2007). However, little is known about mitigating [N.sub.2]O emissions from riparian wetlands and shifting [N.sub.2]O: [N.sub.2]. Such lack of understanding may shift the potential environmental problem from water pollution (eutrophication) to greenhouse gas emission (Well et al. 2001; Hefting et al. 2003) as [N.sub.2]O has been found to be an important end product of denitritication in riparian soils receiving high N[O.sub.3.sup.-] pulse from adjacent pasture/ upland soils (Hefting et al. 2003).

Applying soil amendments such as zeolite and lime to pasture soils may have the potential to reduce [N.sub.2]O emission and shift the balance between [N.sub.2]O : [N.sub.2] ratio, respectively (Zaman et al. 2007). Zeolite, negatively charged natural alumino-silicates, is capable of sorbing N[H.sub.4.sup.+]-N onto the surfaces (Nguyen and Tanner 1998), while lime increases soil pH (Clough et al. 2003; Zaman et al. 2007) and may enhance the activity of nitrous oxide reductase and thus favour [N.sub.2]O reduction to [N.sub.2] (Weier and Gilliam 1986; Stevens and Laughlin 1998; Simek and Cooper 2002). Therefore, the objectives of this study were to quantify [N.sub.2]O and [N.sub.2] emissions through denitrification from pasture and wetland soils using acetylene ([C.sub.2][H.sub.2]) inhibition techniques under non-limiting N[O.sub.3.sup.-] conditions as influenced by lime or zeolite.

Materials and methods

Site and soil description

The pasture and wetland sites were situated in the dairy catchment at Toenepi (37[degrees]44'S, 175[degrees]35'E), which was located approximately 32 km from Hamilton, New Zealand. The climate is humid-temperate with mean annual temperature of 15[degrees]C and annual rainfall of 1150 mm. The pastoral soil is Topehaehae silt loam (i.e. silt loam in topsoil with blocky clay loam at 0.30-0.75m depth) derived from volcanic ash alluvium (an Orthic gley soil, NZ Soil Subgroup; Aeric Haplaquent, USDA Soil Taxonomy). Pasture vegetation consisted predominantly of ryegrass (Lolium perenne L.) and some white clover (Trifolium repens L.) grazed by dairy stock (3 cows/ha). The studied seepage wetland (6817 [m.sup.2]) was located at a footslope of the pasture site. The wetland comprises a broad, low gradient (< 1[degrees] slope) area that receives water from a spring (approximately 1 m from the wetland inlet), natural seepage, and discharges from shallow channels that intercept surface runoff and overland flow from the adjacent pasture paddocks. An artificial swale that is now filled with sediment, organic floc, and wetland plants runs through the wetland and carries most of the flow. The entire wetland complex developed due to a flow constriction at the end of the permanently wet swale that creates partially flooded condition within the area surrounding swale (with a slope of < 1[degrees] across the wetland). Wetland vegetation consists mainly of soft brome (Bromus hordaceus L.) with some floating glaucous sweet grasses (Glyceria declinata Breb.) and soft rush (Juncus effuses L.) and wiwi (Juncus edgariae L.).

Soil sampling and chemical analyses

Soil samples for incubation study were randomly collected (0-0.1m depth) from both pasture and wetland soils in October 2003. Collected soil samples from each pasture and wetland site were bulked and sieved (4 mm) to remove plant litters and roots. Soil bulk density was measured using 4 undisturbed soil cores. Four sieved soil samples from each site were analysed for water filled pore space (WFPS, the percent of the total soil pore space that is filled with water), pH, mineral N, total N, total C, available Olsen P, and other cations (B1akemore et al. 1987), nitrification potential Schmidt and Belser 1994), and denitrification enzyme activity (DEA) (Tiedje 1982).

Incubation procedure

The 6 treatments applied to each soil type were control (no N), control + lime, control + zeolite, N[O.sub.3.sup.-]-N applied at 200 kg N/ha, N[O.sub.3.sup.-] + lime, and N[O.sup.3.sup.-] + zeolite. Sieved soil samples providing the equivalent of 3 kg oven-dry soil for each soil type was transferred to a plastic bucket (10 L) with a lid and treated with appropriate treatments. For uniform distribution, potassium nitrate (KN[O.sub.3]) was first dissolved in 100mL water and then applied to appropriate treatments. The control treatments (no N) with or without lime and zeolite were treated with 100mL of water only. Lime was applied to each pasture and wetland softs at 15 and 20 t/ha, respectively, to raise the soil pH to 7.0 (soil pH required for optimum activity of nitrous oxide reductase). The amounts of zeolite applied to each bucket of pasture and wetland soils were 101.7 and 190g, respectively. This application rate was based on our previous findings that 1 kg of clinoptilonite can sorb 5.7 g N[H.sub.4.sup.+]-N (Nguyen and Tanner 1998). Zeolite had a density of 1.2 g/[cm.sup.3], porosity 60%, slurry pH 5-6 for 20% w/v, cation exchange capacity (CEC) 80 cmol/kg, internal surface area 32[m.sup.2]/g, and pore size/diameter ~6 A. Water-filled pore space in pasture and wetland soils after addition of N inputs and soil amendments remained unchanged and was 63% and 100%, respectively. The soil mixtures in each plastic bucket were incubated at 25[degrees]C for 28 days. To allow exchange for accumulated gases in plastic buckets, the lid from each bucket was removed twice a day for 5 min. The soil moisture losses during incubation were minimal; however, each bucket was weighed every week to correct the soil moisture content by adding de-ionised water.

Acetylene inhibition, gas sampling, and chemical analyses The [C.sub.2][H.sub.2] inhibition technique described by Tiedje et al. (1989) was used to measure [N.sub.2]O and [N.sub.2] emissions from each treatment The acetylene inhibition technique has some implications which must be considered before using this technique. This technique needs paired soil samples (with or without [C.sub.2][H.sub.2]), meaning that it is laborious and also expensive to take and analyse duplicate samples. A small amount of [C.sub.2][H.sub.2] (1%) can block nitrification, which then underestimates [N.sub.2]O emission via nitrification and further via denitrification especially if the system is N[O.sub.3.sup.-]deficient. However, in our study [C.sub.2][H.sub.2] was unlikely to underestimate [N.sub.2]O emission in the presence of abundant added N[O.sub.3.sup.-]. Denitrifiers after repeated or long exposure to [C.sub.2][H.sup.2] could adapt themselves to added [C.sub.2][H.sup.2] and use it as a source of C, which is likely to stimulate denitrification rates. We kept the [C.sub.2][H.sup.2] incubation time short (24 h) and discarded the [C.sub.2][H.sup.2]-treated soil samples after 24h to avoid this problem. Acetone, added as stabiliser to [C.sub.2][H.sup.2], was removed to minimise denitrifier stimulation by acetone. The most challenging step is the uniform distribution of desired concentration of [C.sub.2][H.sup.2] in micro-sites inhabited by relevant microorganisms; however, this may be overcome by using sieved soils.

Two sets of soil subsamples providing the equivalent of 100 g (oven-dry each) were weighed from each plastic bucket at different days (i.e. 1, 2, 3, 4, 5, 7, 10, 12, 15, 21, and 28) and transferred to a 1-L glass jar. The lid of cach jar had a rubber septum for injecting [C.sub.2][H.sup.2]/air and gas sampling. Purified [C.sub.2][H.sup.2] was injected into one set of gas jars using a 60-mL syringe to achieve the final concentration of 10% (10 kPa) in the gas phase. After injecting [C.sub.2][H.sup.2], the syringe was pushed forward and backward a few times to ensure the diffusion of [C.sub.2][H.sup.2]. Air was injected into the other set of soil samples in a similar way. The 2 sets of soil samples were then vented and then incubated at 25[degrees]C for 24 h. A 20-mL gas sample was taken from each jar after 30 min of [C.sub.2][H.sup.2]/air injection, transferred into a pre-evacuated 12-mL exetainer. After collecting the first gas sampling, 20 mL of air was injected back into each jar to maintain uniform pressure. After 24 h, another gas sample was taken from each jar in a similar way. Gas samples were analysed for [N.sub.2]O concentration on a gas chromatograph (Shimadzu GC 17A Japan) equipped with a [sup.63]Ni-electron capture detector operating at column, injector, and detector temperature of 55, 75, and 330[degrees]C, respectively. The amount of [N.sub.2] was calculated from the difference in [N.sub.2]O production between [C.sub.2][H.sup.2]-treated and non-[C.sub.2][H.sup.2]-treated soils. Both [C.sub.2][H.sup.2]- and non-[C.sub.2][H.sup.2]-treated soils were discarded after 24 h of incubation. Additional subsoil samples were also removed from each bucket at each sampling interval and analysed for mineral N (N[H.sub.4.sup.+] and N[O.sub.3.sup.-) and pH. To measure soil mineral N, a soil sample equivalent of 5 g oven-dry soil was extracted with 50 mL of 2 M KCl for 1 h on a rotary shaker followed by filtration. Soil extracts were either immediately analysed for N[H.sub.4.sup.+], N[O.sub.2.sup.-], and N[O.sub.3.sup.-] using flow injection analyser (FIA), or frozen until analyses were performed. Soil pH was determined by shaking 10g of moist soil with 20mL deionised water (soil:deionised water suspension 1:2) on a rotary shaker for 30m in and then measured with an electrode (Blakemore et al. 1987).

Statistical analyses

The 2 N (N[O.sub.3.sup.-]-N applied at 200 kg N/ha and no N) and 3 soil amendment (no amendments, zeolite, and lime) treatments were replicated 3 times in a 3 x 2 x 3 factorial experiment for each soil type. Repeated-measure analysis of variance (ANOVA) was carried out to determine the effect of time on different measured parameters. ANOVA was carried out for each individual sampling time by including N, zeolite, and lime in the ANOVA model. Least significant difference (l.s.d.) values at P = 0.05 were calculated when the interaction effects were significant. All the analyses were performed using SYSTAT (1994).

Results

Physical and chemical properties of pasture and wetland soils

Pasture and wetland soils are located in the same catchment area; however, they differed in most of their physical and chemical properties (Table 1). Pasture and wetland soils had WFPS of 63% and 100%, respectively. Wetland soil was saturated but its particle density value to calculate porosity was unknown. Therefore, a value of 100% WFPS was assumed. The total N and C and CEC of wetland soil were higher than those of the pasture soil. Wetland soil had higher denitrification enzyme activity and lower nitrification potential than those of the pasture soil; therefore, we presumed that the 2 soils would exhibit differences in processing added N[O.sub.3.sup.-] and [N.sub.2]O emissions when treated with soil amendments (zeolite and lime). Soil pH in lime-amended pasture and wetland soils during incubation remained between 7.1 and 7.2 during the incubation (data not shown).

Soil N[H.sub.4.sup.+] and N[O.sub.3.sup.-] in pasture and wetland soils

Except for the N[O.sub.3.sup.-] plus zeolite treatment, soil N[H.sub.4.sup.+] concentrations remained significantly (P<0.001) higher in N[O.sub.3.sup.-]-treated soils than in the control (Fig. 1a). Except on Day 7, soil N[H.sub.4.sup.+] concentrations in lime + N[O.sub.3.sup.-]-treated soils were significantly higher than those in control soil with or without soil amendments. Zeolite application significantly (P< 0.001) reduced soil N[H.sub.4.sup.+] concentrations in N[O.sub.3.sup.-]-treated soil and in the control soil compared with no soil amendments or soil with lime during the incubation. Soil N[H.sub.4.sup.+] concentrations in all treatments steadily decreased during incubation. In pasture soils, N[O.sub.3.sup.-] concentrations in N[O.sub.3.sup.-]-treated soils with or without soil amendments were significantly (P < 0.001) higher than those of the control soil and followed a similar trend, increased sharply on Day 1, and decreased steadily afterward (Fig. lb). Nitrate concentrations in control soil with or without soil amendments remained lower during incubation and were not affected by either lime or zeolite.

[FIGURE 1 OMITTED]

In wetland soils, soil N[H.sub.4.sup.+] concentrations in various treatments wore not significantly different soon after treatments application (Day 1) (Fig. 2a). After Day 1 onward, N[H.sub.4.sup.+] concentrations in N[O.sub.3.sup.-] alone and N[O.sub.3.sup.-] + lime treated soils showed a gradual increase and remained significantly (P < 0.001) higher than those in the N[O.sub.3.sup.-] + zeolite and control soils with or without soil amendments. Zeolite reduced N[H.sub.4.sup.+] concentrations when it was applied to soil with or without N[O.sub.3.sup.-]. Soil N[O.sub.3.sup.-] concentrations in wetland soil increased significantly (P < 0.001) in N[O.sub.3.sup.-]-treated soils with or without soil amendments compared with control soils on Day 1 (Fig. 2b) and virtually disappeared on Day 14. Soil amendments did not have any significant effect on N[O.sub.3.sup.-] concentration in either N[O.sub.3.sup.-]-treated soil or in control soils.

Pasture soil [N.sub.2]O and [N.sub.2] emissions and their ratios

Nitrous oxide emissions showed temporal variations during file 28-day incubation and were significantly (P < 0.001) higher in N[O.sub.3.sup.-]-treated soil with or without soil amendments than those of the control soils (Fig. 3a). Nitrons oxide emissions from N[O.sub.3.sup.-]-treated soils with or without soil amendments increased sharply on Day 1, decreased until Day 5, slightly increased again during Day 7 and Day 12, and decreased afterward. The estimated [N.sub.2] omissions wore always lower than those of [N.sub.2]O emission, and differed significantly with added N[O.sub.3.sup.-] and soil amendments (Fig. 3b). Lime applied to N[O.sub.3.sup.-]-treated soils and control soils significantly (P < 0.001) increased [N.sub.2] emissions compared with no lime treatments. Zeolite did not have any impact on [N.sub.2] emissions in any treatments.

[FIGURE 2 OMITTED]

Total [N.sub.2]O emissions during the 28-day incubation were significantly (P < 0.001) higher from N[O.sub.3.sup.-]-treated soils than from the control soils (Table 2). Compared with no soil amendments, lime application significantly (P < 0.001) increased total [N.sub.2]O emissions from N[O.sub.3.sup.-]-treated soil and from the control soil (no N). Such increases wore 14.2% in the control soil and 8% in N[O.sub.3.sup.-]-treated soil. Zeolite application had contrasting effects on [N.sub.2]O emission from treatments with or without added N[O.sub.3.sup.-]. Compared with no soil amendments, it decreased [N.sub.2]O emission from control soil by 2.9%, whereas it increased total [N.sub.2]O emission by 8% in N[O.sub.3.sup.-]-treated soils. The proportion of applied N emitted as [N.sub.2]O was 5.7% each for N[O.sub.3.sup.-] +zeolite and N[O.sub.3.sup.-] + lime and 5.1% for N[O.sub.3.sup.-] alone.

Total estimated [N.sub.2] emissions over a 28-day incubation period were also significantly (P < 0.001) affected by the added N[O.sub.3.sup.-] and soil amendments (Table 2). Soil treated with N[O.sub.3.sup.-] emitted significantly more [N.sub.2] than the control. Compared with the no amendment treatment, lime increased [N.sub.2] emissions by 115% in control and 62% in N[O.sub.3.sup.-]-treated soils. Zeolite application did not have consistent effects on [N.sub.2] emissions as it reduced [N.sub.2] emissions by 7% in control soil and increased [N.sub.2] emissions by 11% in N[O.sub.3.sup.-]-treated soils. In N[O.sub.3.sup.-]-treated soil, the proportion of the applied N emitted as [N.sub.2] accounted for 0.74% in the lime treatment, compared with 0.29% in the treatment with no amendment. Zeolite application decreased [N.sub.2] emissions by 7% when applied to control soil. However, when zeolite was applied to N[O.sub.3.sup.-]-treated soil, [N.sub.2] emissions increased by ~11% over the treatment with no amendment. The total percentage of the applied N[O.sub.3.sup.-]- N that was lost as gaseous emissions of both [N.sub.2]O+[N.sub.2] in pasture soils accounted for 5.3%, 5.5%, and 6.1% for N[O.sub.3.sup.-], N[O.sub.3.sup.-] + lime, and N[O.sub.3.sup.-] + zeolite treatments, respectively.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The [N.sub.2]O:[N.sub.2] ratios of different treatments varied with the applied N[O.sub.3.sup.-] and soil amendments during incubation (Table 3). Lime application significantly (P<0.001) lowered [N.sub.2]O : [N.sub.2] ratios in soil + N[O.sub.3.sup.-] and in control soil compared with no soil amendments. In the N[O.sub.3.sup.-]+ lime treatment, [N.sub.2]O:[N.sub.2] ratios ranged from 4.3 to 5.8, compared with 6.6 to 9.6 in N[O.sub.3.sup.-]-treated soil alone. Similarly, [N.sub.2]O:[N.sub.2] ratios in control + lime ranged from 1.2 to 2.1, compared with 3.4 to 5.6 in control soil alone. Nitrate application appeared to reduce the effect of lime in the combined lime + N[O.sub.3.sup.-] treatment, as evident from its higher [N.sub.2]O:[N.sub.2] ratio compared with that of control + lime. Zeolite application did not affect [N.sub.2]O : [N.sub.2] ratios in any treatments.

Wetland soil [N.sub.2]O and [N.sub.2] emissions and their ratios

Nitrous oxide emissions in wetland soils also showed temporal variations during the 28-day incubation and were significantly (P<0.001) higher in N[O.sub.3.sup.-]-treated soil with or without soil amendments than control soils with or without soil amendments (Fig. 4a). Nitrous oxide emissions in N[O.sub.3.sup.-]-treated soils with or without soil amendments steadily increased after Day 2, exhibited their highest peak at Day 10, and decreased sharply afterward. After Day 15, [N.sub.2]O emissions in N[O.sub.3.sup.-]-treated soils fell back to the level of the control. Lime applied to N[O.sub.3.sup.-]-treated soils significantly increased [N.sub.2]O emissions compared with treatments with no lime only during Day 7 and Day 12. Zeolite application did not have any effect on [N.sub.2]O emissions either in control soil or in N[O.sub.3.sup.-]-treated soils. The estimated [N.sub.2] emissions were significantly higher from N[O.sub.3.sup.-] treated soils than those of the control treatments (Fig. 4b). Lime applied to N[O.sub.3.sup.-]-treated soils significantly (P < 0.001 ) increased [N.sub.2] emissions compared with no lime treatments. Zeolite did not show any effect on [N.sub.2] emissions in any treatments.

Total [N.sub.2]O emissions from wetland soft significantly (P < 0.1001) varied with the added N[O.sub.3.sup.-] and soil amendments during the 28-day incubation and were higher from N[O.sub.3.sup.-]-treated soils than from the control soils (Table 4). Lime did not have a consistent effect on [N.sub.2]O emission when applied to soil with or without N[O.sub.3.sup.-]. Compared with no soil amendments, lime application increased total [N.sub.2]O emissions from N[O.sub.3.sup.-]-treated soil by 5%, whereas it reduced [N.sub.2]O emission in control soil by 28%. Compared with no soil amendments, zeolite decreased [N.sub.2]O emission from control and N[O.sub.3.sup.-]-treated soils by 300,4 and 4%, respectively. The proportion of applied N emitted as [N.sub.2]O from wetland soils was 25% for N[O.sub.3.sup.-] + lime, 23% for N[O.sub.3.sup.-] + zeolite, and 24% for N[O.sub.3.sup.-] only.

Total estimated [N.sub.2] emission in wetland soil over a 28-day incubation period also varied significantly (P<0.001) among N[O.sub.3.sup.-]-treated soils and the control (Table 4). Soil treated with N[O.sub.3.sup.-] emitted significantly more [N.sub.2] than control soils. Compared with the no amendment treatment, lime increased [N.sub.2] emissions by 11% in the control and 61% in N[O.sub.3.sup.-]-treated soils. Zeolite application decreased [N.sub.2] emissions by 27% and 4% when applied to control and N[O.sub.3.sup.-]-treated soils, respectively. In N[O.sub.3.sup.-]-treated soil, the proportion of the applied N emitted as [N.sub.2] was 9% for lime, 5.3% for zeolite, and 5.5% for no amendment treatments. The total percentage of the applied N[O.sub.3.sup.-]-N lost as gaseous emissions of both [N.sub.2]O and [N.sub.2] in wetland soils accounted for 29%, 34%, and 28% for N[O.sub.3.sup.-], N[O.sub.3.sup.-] +lime, and N[O.sub.3.sup.-] + zeolite treatments, respectively.

The [N.sub.2]O:[N.sub.2] ratios in wetland soil varied with the application of N[O.sub.3.sup.-] and soil amendments during incubation (Table 5). [N.sub.2]O : [N.sub.2] ratios were relatively higher during the first 2 weeks of incubation compared with the later stage of incubation. [N.sub.2]O:[N.sub.2] ratios were significantly (P<0.001) lower in lime-treated soils in the control soft as well as in N[O.sub.3.sup.-] treated soils compared with no soil amendments. In the N[O.sub.3.sup.-] + lime treatment, [N.sub.2]O: [N.sub.2] ratios were in the range 0.6-2.7 compared with 1.1-4.1 in N[O.sub.3.sup.-] treatment alone. Similarly, [N.sub.2]O:[N.sub.2] ratios in control+lime ranged from 0.6 to 1.2 compared with 0.9 to 2.3 in control soil alone. [N.sub.2]O :[N.sub.2] ratios were not affected when zeolite was applied to control or N[O.sub.3.sup.-]-treated soils.

Discussion

The pasture and wetland soils were collected firm adjacent locations but differed in their physical and chemical properties ====== and exhibited different trends of N[O.sub.3.sup.-] processing and gaseous N emissions. In the absence of zeolite, soil N[H.sub.4.sup.+] concentration in both pasture and wetland soils receiving N[O.sub.3.sup.-] increased initially. This increase could partly be attributed to anaerobic mineralisation of soil organic N and partly to the immobilisation of added N[O.sub.3.sup.-] by soil microbes (Smith et al. 1994), assuming that both mineralisation and immobilisation occur simultaneously. The steady increase in soil N[H.sub.4.sup.+] concentration in wetland soil without added zeolite during the incubation further suggests DNRA (Silver et al. 2001; Hefting et al. 2003) and other unknown mechanisms of N[H.sub.4.sup.+] production. Soil N[H.sub.4.sup.+] concentration in pasture soil receiving N[O.sub.3.sup.-] decreased subsequently with concomitant increase in N[O.sub.3.sup.-] concentration, while in wetland soil, soil N[H.sub.4.sup.+] was retained, probably due to the lack of nitrification by anaerobic condition (100% WFPS). Nitrification is optimum at around 60% of WFPS, which is very close to the soil moisture content of our pasture soil and does not proceed when soil moisture content exceeds 80% of its WFPS (Lima and Doran 1984; Zaman and Chang 2004). Zeolite application reduced soil N[H.sub.4.sup.+] concentrations in both pasture and wetland soils due to the sorption of N[H.sub.4.sup.+] (Nguyen and Tanner 1998). Nitrate in wetland soils disappeared at faster rate than in pasture soils because of the greater ability to process N[O.sub.3.sup.-] by wetland soil in the presence of excessive organic C and anaerobic conditions (Hoffmann et al. 2000). Nitrate moving through riparian and seepage areas is subject to denitrification, plant uptake, DNRA, and microbial immobilisation; however, denitrification is considered to be the major N[O.sub.3.sup.-] removal process, in which N[O.sub.3.sup.-] is enzymatically reduced to [N.sub.2]O and [N.sub.2] (Hoffmann et al. 2000; Groffman et al. 2002; Matheson et al. 2003; Smith et al. 2003).

The higher [N.sub.2]O emissions from N[O.sub.3.sup.-]-treated soils of pasture and wetland compared with the control (Figs 3a and 4a) axe attributed to the substantial amounts of added N[O.sub.3.sup.-] (Figs lb and 2b). Total [N.sub.2]O emitted by wetland soils were 3 times higher than those of pasture soils, probably due to the conducive conditions for denitrilication in wetland soil (low WFPS (100%), and highly enriched organic matter sediment; Table 1). Higher rates of [N.sub.2]O emissions from wetland soils were also observed by other researchers (Fennessy and Crank 1997; Hoffmann et al. 2000; Smith et al. 2003).

Zeolite application only reduced total [N.sub.2]O emissions from wetland soils. Such reductions were due to the sorption of N[H.sub.4.sup.+] by zeolite (Nguyen and Tanner 1998; Zaman et al. 2007) and possibly the zeolite's high CEC (80 cmol/kg), as shown by the lower N[H.sub.4.sup.+] concentrations in Figs la and 2a. Such sorption lowers the opportunity for nitrification of N[H.sub.4.sup.+] to N[O.sub.3.sup.-], and hence the N[O.sub.3.sup.-] concentrations in these treatments decreased (as shown in Figs lb and 2b), which in turn could have decreased [N.sub.2]O emission via nitrification and denitrification (Table 4). Denitrification did not account for the total observed N[O.sub.3.sup.-] disappearance in wetland soils, suggesting that other transformation processes, which were not measured in this study, were responsible for most of the N[O.sub.3.sup.-] removal and require further investigation.

The amount of [N.sub.2]O emitted as a percentage of the applied N in our incubation study is higher than those of the Intergovernmental Panel on Climate Change (IPCC), which uses a default global emission factor of 1.25% (0.25-2.25%) for fertiliser-induced emission (FIE) (Bouwman et al. 2002). Such higher [N.sub.2]O losses could be due to the incubation procedure at optimum temperature and moisture, disruption of soil (sieved) which provides additional sources of C and nutrients for denitrifying bacteria, abundant availability of N[O.sub.3.sup.-] in the absence of other N removal processes such as plant N uptake, and N[O.sub.3.sup.-] leaching losses. However, several studies have shown that the amount of N lost as [N.sub.2]O varies with soil type, N fertiliser type, and other soil and crop managements, and is often greater than the default value of IPCC (Barton et al. 1999; Corre et al. 1999; Walker et al. 2002).

Lime applied to both pasture and wetland soils significantly increased [N.sub.2]O emissions; however, it lowered [N.sub.2]O: [N.sub.2] ratios compared with all other treatments with no lime application. Wetland soils with lime emitted 9 times more [N.sub.2] and exhibited lower [N.sub.2]O: [N.sub.2] ratios than pasture soils. High soil pH is reported to stimulate the activity of nitrous oxide reductase, the enzyme that reduces [N.sub.2]O to [N.sub.2] (Arab and Smith 1991; Weier et al. 1993; Stevens and Laughlin 1998). For example, soil pH values from 4.5 to 6.5 have been reported to inhibit nitrous oxide reductase (Weier and Gilliam 1986; Flessa et al. 1998). In addition, low soil pH limits organic C and mineral N availability to denitrifying bacteria (Simek and Cooper 2002); thereby, the increased [N.sub.2] emission from lime-treated soils, compared with other soil treatments with soil pH of 6 in pasture and 5.8 in wetland soil, was attributed to the high soil pH (>7.1) in limed soils. Stevens and Laughlin (1998) also observed a big increase in [N.sub.2] emission when soil pH increased from 6.5 to 8. Daum and Schenk (1998) also reported that neutral pH enhances [N.sub.2] emissions while acidic conditions favour [N.sub.2]O emission via denitrification. The higher [N.sub.2] emission by wetland soil compared with pasture soils is attributed to the low [O.sub.2], greater C availability, and low WFPS of wetland soil, which increase [N.sub.2] emission by stimulating nitrous oxide reductase.

In N[O.sub.3.sup.-]-treated soils of pasture and wetland, [N.sub.2]O : [N.sub.2] ratios during the first 2 weeks of incubation were higher probably due to the lower activity of nitrous oxide reduetase in the presence of high soil N[O.sub.3.sup.-] concentration (Tables 4 and 5). This is also supported by Sabrawat and Keeney (1986) and Cho et aL (1997), who also reported high [N.sub.2]O:[N.sub.2] ratios in an increased N[O.sub.3.sup.-] environment. A range of [N.sub.2]O : [N.sub.2] ratios (0-16) is reported in the literature because they depend on soil water content, amount of soluble organic C, and N[O.sub.3.sup.-] concentration (Weier et al. 1993; Maag and Vinther 1996; Cho et al. 1997). Reducing [N.sub.2]O emission and lowering the [N.sub.2]O :[N.sub.2] ratios are critical for mitigation of gaseous N emissions, as more [N.sub.2] rather than harmful [N.sub.2]O is emitted to the atmosphere. Our study agrees with others which suggest that wetland soil could offer the best option to be used to intercept N lost from adjacent farmlands through surface runoff or leaching before entering water bodies. Similarly, liming pasture and wetland soils can shift the balance between harmful [N.sub.2]O and non-greenhouse [N.sub.2] and may be considered as one of the potential mitigation tools for [N.sub.2]O emission. This laboratory or controlled environment study has raised some questions about whether or not the reduction in [N.sub.2]O from wetland with liming is sustainable. Continued liming of wetland over a period of time may enhance vegetation and C deposition into rhizosphere in wetland and this in turn may affect N dynamics by changing N mineralisation/immobilisation (Tiedje 1988). Carbon deposition into the rhizosphere may also affect the production of [N.sub.2]O and [N.sub.2] and their ratio (Aulakh et al. 2001), as organic C is known to affect the activity of denitrifiers and nitrous oxide reductase. Similarly, liming may also accelerate C decomposition, causing the release of C[O.sub.2] from wetland into the atmosphere. Therefore, studies addressing these issues should be the focus of future research.

Conclusions

Both pasture and wetland soils exhibited different trends of N[O.sub.3.sup.-] processing and [N.sub.2]O and [N.sub.2] emissions after treating with N[O.sub.3.sup.-] and soil amendments. The conducive environment of wetland soil for denitrification facilitated the disappearance of added N[O.sub.3.sup.-] faster than ill pasture soil. Wetland soils emitted 3 times more [N.sub.2]O than pasture soils when amended with N[O.sub.3.sup.-]. This study has highlighted the importance of liming to stimulate [N.sub.2]O emissions and shift the balance between [N.sub.2]O and [N.sub.2] and this may be considered as a potential management tool to reduce the amount of fertiliser N moving from pasture and wetland into waterways by stimulating its conversion to gases. Since the experiment was conducted under laboratory conditions, field trials would be necessary to test the importance of these soil amendments in the presence of plants, because plant roots introduce oxygen and soluble organic C which may affect the production of [N.sub.2]O and [N.sub.2] and their ratio.

Acknowledgment

We thank Summit Quinphos (NZ) Ltd and NIWA for funding rids project. We also thank our NIWA Hamilton staff members Kerry Costley and James Sukius for their technical assistance in the feld and laboratory work. We also thank Professor Art Gold, Department of Natural Resources Sciences, Coastal Institute in Kingston, University of Rhode Island, Kingston, RI, for his help in designing the experiment and positive comments in preparing this manuscript.

Manuscript received 21 November 2007, accepted 10 April 2008

References

Arah JRM, Smith KA (1991) Nitrous oxide production and denitrification in Scottish arable soils. Journal of Soil Science 42, 351-367. doi: 10.1111/ j.1365-2389.1991.tb00414.x

Aulakh MS, Khera TS, Doran JW, Bronson KF (2001) Denitrification, [N.sub.2]O and C[O.sub.2] fluxes in rice-wheat cropping system as affected by crop residues, fertilizer N and legume green manure. Biology and Fertility of Soils 34, 375-389. doi: 10.1007/s003740100420

Barton L, McLay CDA, Schipper LA, Smith CT (1999) Annual denitrification rates in agricultural and forest soils: a review. Australian Journal of Soil Research 37, 1073-1093. doi: 10.1071/ SR99009

Bhandral R, Bolan NS, Sagger S, Hedlcy MJ (2005) Effect of compaction and nitrogen sources on nitrous oxide emissions. In 'Proceedings of the 18th Annual Workshop on Developments in Fertilisor Application Technologies and Nutrient Management'. (Eds LD Currie, JA Hanly) pp. 201-208. (Fertiliser and Lime Research Centre, Massey University: Palmerston North, New Zealand)

Blakemore LC, Searle BK, Daly BK (1987) Methods for chemical analysis of soils. New Zealand Soil Bureau of Science Report 80, Department of Science and Industrial Research Lower Hutt, New Zealand.

Bouwman AF, Boumas LJM, Batjes NH (2002) Emissions of [N.sub.2]O and NO from fertilized fields: Summary of available measurement data. Global Biogeochemical Cycles 16, 1-13.

Burns DA, Nguyen ML (2002) Nitrate movement and removal along a shallow groundwater flow path in a riparian wetland within a sheep-grazed pastoral catchment, Results of a tracer study. New Zealand Journal Marine and Freshwater Research 36, 371-385.

Cavigelli MA, Robertson GP (2001) Role of denitrifier diversity in rates of nitrous oxide consumption in a terrestrial ecosystem. Soil Biology and Biochemistry 33, 297-310.

Cho CM, Burton DL, Chang C (1997) Denitrification and fluxes of nitrogenous gases from soil under steady oxygen distribution. Canadian Journal of Soil Science 77, 261-269.

Clough TJ, Sherlock RR, Kelliher FM (2003) Can liming mitigate [N.sub.2]O fluxes from a urine-amended soil? Australian Journal of Soil Research 41, 439-457. doi: 10.1071/SR02079

Cooper AB, Ngapo NI, Parminter TG, Strond MJ (1997) Encouraging implementation of riparian buffer schemes--the New Zealand experience. In 'Buffer zones: Their processes and potential in water protection'. (Eds NE Haycock, TP Bort, KWT Goulding, G Pinay) pp. 255-264. (Quest Environmental: UK)

Corre MD, Pennock DJ, Van Kissel C, Kirk Elliott D (1999) Estimation of annual nitrous oxide emissions from a transitional grassland-forest region in Saskatchewan, Canada. Biogeochemistry 44, 29-49. doi: 10.1007/BF00992997

Daum D, Schenk MK (1998) Influence of nutrient solution pH on [N.sub.2]O and [N.sub.2] emissions from a soilless culture system. Plant and Soil 203, 279-287. doi: 10.1023/A:1004350628266

de Klein CAM, Barton L, Sherlock RR, Li Z, Littlejohn RP (2003) Estimating a nitrous oxide emission factor for animal urine from some New Zealand pastural soils. Australian Journal of Soil Research 41, 381-399. doi: 10.1071/SR02128

Di HJ, Cameron KC (2006) Nitrous oxide emissions from two dairy pasture soils as affected by different rates of fine particle suspension nitrification inhibitor, dicyandiamide. Biology and Fertility of Soils 42, 472-480. doi: 10.1007/s00374-005-0038-5

Dobbie KE, Smith KA (2003) Impact of different forms of N fertilizers on [N.sub.2]O emission from intensive grassland. Nutrient Cycling in Agroecosystems 67, 37-46. doi: 10.1023/A:1025119512447

Fennessy MS, Cronk JK (1997) The effectiveness and restoration potential of riparian ecotones for the management of no point source pollution, particularly nitrate. Critical Reviews in Environmental Science and Technology 27, 285-317.

Firestone MK (1982) Biological denitrification. In 'Nitrogen in agricultural soils'. Number 22 in the series agronomy. (Ed. FJ Stevenson) pp. 289-326. (American Society of Agronomy Inc., Crop Science Society of America Inc., Soil Science Society of America Inc.: Madison, WI)

Firestone MK, Davidson EA (1989) Microbiological basis of NO and [N.sub.2]O production and consumption in soil. In 'Exchange of the trace gases between terrestrial ecosystems and the atmosphere'. Report for the Dahlem Workshop on exchange of gases between Terrestrial Ecosystems and the Atmosphere, Berlin 1989. (Eds MO Andreae, DS Schimel) pp. 7-22. (John Wiley: New York)

Fiessa H, Wild U, Klemisch M, Pfadenhauer J (1998) Nitrous oxide and methane fluxes from organic soils under agriculture. European Journal of Soil Science 49, 327-335. doi: 10.1046/j.1365-2389.1998.00156.x

Groffman PM, Gold AJ, Kellog DQ, Addy K (2002) Mechanisms, rates and assessment of [N.sub.2]O in groundwater, riparian zones and rivers. In 'Proceedings of the 3rd International Symposium on Non-C[O.sub.2] Greenhouse Oases, Scientific Understanding, Control Options and Policy Aspects'. 21-23 January 2002, Maastricht, Netherlands. (Eds J Van Ham, APM Baede, R Guicherit, JGFM Williams-Jacobse) pp. 159-166. (Millpress: Rotterdam, The Netherlands)

Hefting Mid, Bobbink R, de Caluwe H (2003) Nitrous oxide emission and denitrification in chronically nitrate-loaded riparian buffer zones. Journal of Environmental Quality 32, 1194-1203.

Hoffmann CC, Rysgaard S, Berg P (2000) Denitrification rates predicted by nitrogen-15 labeled nitrate microcosm studies, in-situ measurements, and modelling. Journal of Environmental Quality 29, 2020-2028.

Inubushi K, Naganuma H, Kitahara S (1996) Contribution of denitrification and autotrophic and heterotrophic nitrification to nitrous oxide production in Andosols. Biology and Fertility of Soils 23, 292-298. doi: 10.1007/BF00335957

Linn DM, Doran JW (1984) Effect of water-filled pore space on carbon dioxide and nitrous oxide production in tilled and nontilled soils. Soil Science Society of America Journal 48, 1267-1272.

Luo J, Saggar S (2008) Nitrous oxide and methane emissions from a dairy farm stand-off pad. Australian Journal of Experimental Agriculture 48, 179-182. doi: 10.1071/EA07242

Lun J, Saggar S, Bhandral R, Lindsey S, Bolan N, Qiu W, Kear M, Sun W (2007) Nitrous oxide emissions from a livestock stand-off pad and farm dairy effluent applied to pastoral soils. In 'Nutrient removal and water quality issues. Proceedings of the Annual New Zealand Land Treatment Collective Conference'. Technical Session 28. (Eds H Wang, M Quintern) pp. 139-149.

Maag M, Vinther FP 0996) Nitrous oxide emission by nitrification and denitrification in different soil types end at different soil moisture contents and temperature. Applied Soil Ecology 4, 5-14. doi: 10.1016/0929-1393(96)00106-0

Matheson FE, Nguyen ML, Cooper AB, Burt TP (2003) Short-term nitrogen transformation rates in riparian wetland soil determined with nitrogen-15. Biology and Fertility of Soils 38, 129-136. doi: 10.1007/ s00374-003-0640-3

MfE (2007) New Zealand Greenhouse Gas Inventory 1990-2005. The National Inventory Report and common reporting format, Ministry for the Environment, Wellington, New Zealand.

Monaghan RM, de Klein CAM, Wilcock RJ, Smith LC, Thorrold BS (2005) Managing nutrient losses and greenhouse gas emissions from dairy farm within the Bog Bum catchment, Southland. In 'Proceedings of the 18th Annual Workshop on Developments in Fertiliser Application Technologies end Nutrient Management'. (Eds LD Currie, JA Hanly) pp. 151-161. (Fertiliser and Lime Research Centre, Massey University: Palmerston North, New Zealand)

Nguyen ML, Tanner CC (1998) Ammonium removal from wastewaters using natural New Zealand zeolites. New Zealand Journal of Agriculture Research 41, 427-446.

Rutherford JC, Nguyen ML (2004) Nitrate removal in riparian wetlands, interactions between surface flow and soils. Journal of Environmental Quality 33, 1133-1143.

Sahrawat KL, Keeney DR (1986) Nitrous oxide emission from soils. In 'Advances in soil science, Vol. 4'. (Ed. BA Stewart) pp. 103-148. (Springer-Verlag: New York)

Schmidt EL, Belser LW (1994) Autotrophic nitrifying bacteria. In 'Methods of soil analysis. Part 2, Microbiological and biochemical properties'. (Eds RW Weaver, S Angle, P Bottomley, D Bezdicek, S Smith, A Tabatabai, A Wollum) pp. 159-177. (Soil Science Society of America Inc.: Madison, WI)

Silver WL, Herman DJ, Firestone MK (2001) Dissimilatory nitrate reduction to ammonium in upland tropical forest soils. Ecology 82, 2410-2416.

Simek M, Cooper JE (2002) The influence of soil pH on denitrification: progress towards the understanding of this interaction over the last 50 years. European Journal of Soil Science 53, 345-354. doi: 10.1046/j.1365-2389.2002.00461.x

Singh J, Saggar S, Bolen N, Zaman M (2006) Influence of urease and nitrification inhibitors on ammonia and nitrous oxide emissions under field conditions. In 'Proceedings of the 19th Annual Workshop on Implementing Sustainable Nutrient Management Strategies in Agriculture'. (Eds LD Currie, JA Hanly) pp. 162-170. (Fertiliser and Lime Research Centre, Massey University: Palmerston North, New Zealand)

Smith CJ, Chalk PM, Crawford DM, Wood T (1994) Estimating gross nitrogen mineralization and immobilization rates in anaerobic and aerobic soil suspensions. Soil Science Society of America Journal 58, 1652-1660.

Smith KA, Ball T, Conen F, Dobbie KE, Rey A (2003) Exchange of greenhouse gases between soil and atmosphere, interactions of soil physical factors and biological processes. European Journal of Soil Science 54, 779-791. doi: 10.1046/j.1351-0754.2003.0567.x

Stevens RJ, Laughlin RJ (1998) Measurements of nitrous oxide and di-nitrogen emissions from agricultural soils. Nutrient Cycling in Agroecosystems 52, 131-139. doi: 10.1023/A:1009715807023

SYSTAT (1994) 'Systat for Windows, Version 5 edition.' (Systat Inc.: Evanston, IL)

Tiedje JM (1982) Denitrification. In 'Methods of soil analysis. Part 2'. 2nd edn, Agronomy Monograph No. 9. (Ed. AL Page) pp. 1011-1026. (American Society of Agronomy, Soil Science Society of America: Madison, WI)

Tiedje JM (1988) Ecology of denitrification and dissimilatory nitrate reduction to ammonium. In 'Biology of anaerobic microorganisms'. (Ed. JB Zehnder) pp. 179-244. (John Wiley: New York)

Tiedje JM, Simkins S, Groffman PM 0989) Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods. Plant and Soil 115, 261-284. doi: 10.1007/ BF02202594

Walker JT, Geron CD, Vose JM, Swank WT (2002) Nitrogen trace gas emissions from a riparian ecosystem in southern Appalachia_ Chemosphere 49, 1389-1398. doi: 10.1016/S0045-6535(02)00320-X

Weier KL, Doran JW, Power JF, Walters DT (1993) Denitrification and the dinitrogen/nitrous oxide ratio as affected by soil water, available carbon, and nitrate. Soil Science Society of America Journal 57, 66-72.

Weier KL, Gilliam JW (1986) Effect of acidity on denitrification and nitrous oxide evolution from Atlantic Coastal Plain soils. Soil Science Society of America Journal 50, 1202-1205.

Well RJ, Augustin J, Davis SM, Griffith K, Myrold DD (2001) Production and transport of denitrification gases in shallow ground water. Nutrient Cycling in Agroecosystems 60, 65-75. doi: 10.1023/ A:1012659131811

Zaman M, Chang SX (2004) Substrate type, temperature, and moisture content affect gross and net soil N mineralization and nitrification rates in agroforestry systems. Biology and Fertility of Soils 39, 269-279. doi: 10.1007/s00374-003-0716-0

Zaman M, Nguyen ML, Blennerhassett JD, Quin BF (2008) Reducing N[H.sub.3], [N.sub.2]O end N[O.sub.3.sup.-]-N losses from a pasture soil with urease or nitrification inhibitors and elemental S-amended nitrogenous fertilizers. Biology and Fertility of Soils 44, 693-705. doi: 10.1007/ s00374-007-0252-4

Zaman M, Nguyen ML, Matheson FE, Blennerhassett JD, Quin BF (2007) Can soil amendments (zeolite or lime) shift the balance between nitrous oxide and dinitrogen emissions from pasture and wetland soils receiving urine or urea-N? Australian Journal of Soil Research 45, 543-553. doi: 10.1071/SR07034

M. Zaman(A'D), M. L. Nguyen (B), and S. Saggar (C)

(A) Summit-Quinphos (NZ) Ltd, Private Bag 3029, Waikato mail Centre 3240, Hamilton, New Zealand.

(B) Soil and Water Management & Crop Nutrition, Joint FAO/IAEA Division of Nuclear Techniques in Food & Agriculture, PC) Box 100, A-1400 Vienna, Austria.

(C) Landcare Research, Private Bag 11052, Palmerston North, New Zealand.

(D) Corresponding author. Email: zamanm_99@yahoo.com
Table 1. Some soil physical and chemical properties of wetland and
pasture soils
Mean values from 4 replicates are shown

Analyses type Pasture Wetland
 soil soil

pH 6 5.8
N[H.sub.4.sup.+] (mg N/kg soil) 3.20 37
N[O.sub.3] (mg N/kg soil) 26 0.45
Total N (%) 0.44 0.5
Total C (%) 4.5 6.1
CEC (cmol/kg) 12 16
Base saturation (%) 63 53
Soil bulk density (g/[cm.sup.3]) 1.04 0.55
Soil water content (volume basis, %) 38 136
Porosity (%) 61 79
Water filled pore space (%) 63 100
DEA (mg [N.sub.2]O-N/kg soil.day) 18.7 225
Nitrification potential (mg N[O.sub.3]-N/kg 12 0.7
 soil.day)

Table 2. Total [N.sub.2]O or [N.sub.2] emissions and their relative
changes in pasture soil as affected by N[O.sub.3.sup.-]-N and soil
amendments during the 28 days of incubation
Mean values from 3 replicates are shown. n.a., Not applicable

Treatments Total [N.sub.2]O or Changes in [N.sub.2]O
 [N.sub.2] or [N.sub.2] emission
 emission (kg N/ha) relative to no soil
 amendments (%)

 [N.sub.2]O [N.sub.2] [N.sub.2]O [N.sub.2]

Control (no N) 4.8 0.86 n.a. n.a.
Control + zeolite 4.7 0.80 -2.9 -7
Control + lime 5.5 1.84 14.2 115
N[0.sub.3] only 14.9 1.44 n.a. n.a.
N[0.sub.3] + zeolite 16.1 1.59 8 11
N[0.sub.3] + lime 16.1 2.33 8 62
l.s.d. (P = 0.05) 0.20 0.12 n.a. n.a.

Table 3. [N.sub.2]O: [N.sub.2] ratios as affected by addition of
lime and zeolite to pasture soil treated with N[O.sub.3.sup.-]-N

Mean values from 3 replicates are shown

Treatments Days after treatment application

 1 3 5 7 10

Control (no N) 5.5 5.6 4.6 4.8 5.3
Control + lime 1.4 1.9 2.0 1.9 2.0
Control + zeolite 5.1 5.2 4.0 5.3 5.5
N[O.sub.3] only 8.3 8.1 8.0 7.8 9.6
N[O.sub.3] + lime 4.6 5.1 5.3 5.1 5.8
N[O.sub.3] + zeolite 8.0 7.7 7.3 7.4 9.0
l.s.d. (P = 0.05) 1.14 1.27 0.77 0.78 1.04

Treatments Days after treatment
 application

 12 15 21 28

Control (no N) 5.1 3.4 4.3 4.8
Control + lime 2.1 1.5 1.2 1.2
Control + zeolite 4.8 3.4 4.1 5.1
N[O.sub.3] only 8.5 7.2 6.6 6.9
N[O.sub.3] + lime 5.2 5.8 4.3 4.3
N[O.sub.3] + zeolite 7.3 7.9 6.8 7.6
l.s.d. (P = 0.05) 0.77 0.59 0.58 1.04

Table 4. Total [N.sub.2]O or [N.sub.2] emissions and their relative
changes in wetland soil as affected by N[O.sub.3.sup.-]-N and soil
amendments daring the 28 days of incubation
Mean values from 3 replicates are shown. n.a, Not applicable

Treatments Total [N.sub.2]O or Changes in [N.sub.2]O
 [N.sub.2] emission or [N.sub.2] emission
 (kg N/ha) relative to no soil
 amendments (%)

 [N.sub.2]O [N.sub.2] [N.sub.2]O [N.sub.2]

Control (no N) 0.10 0.035 na. n.a.
Control + zeolite 0.07 0.026 -30 -27
Control + lime 0.07 0.04 -28 11
N[O.sub.3] only 47.8 11.05 n.a. n.a.
N[O.sub.3] + zeolite 46 10.63 -4 -4
N[O.sub.3] + lime 50.4 17.83 5 61
l.s.d. (P = 0.05) 0.57 0.32 n.a. n.a.

Table 5. [N.sub.2]O: [N.sub.2] ratios as affected by addition of Time
and zeolite to wetland soil treated with N[O.sub.3.sup.-]-N
Mean values from 3 replicates are shown

Treatments Days after treatment application

 1 3 5 7 10

Control (no N) 2.1 1.9 1.8 2.3 1.7
Control + How 0.7 1.0 0.8 1.2 0.7
Control + zeolite 2.6 2.0 1.3 2.4 1.8
N[O.sub.3] only 3.4 3.0 3.0 3.3 4.1
N[O.sub.3] + lime 2.7 1.6 1.2 1.9 2.7
N[O.sub.3] + zeolite 3.5 2.5 2.9 3.1 4.2
l.s.d (P = 0.05) 0.41 0.30 0.23 0.38 0.19

Treatments Days after treatment
 application

 12 15 21 28

Control (no N) 1.7 1.8 1.2 0.9
Control + How 0.8 0.8 0.6 0.6
Control + zeolite 1.9 1.7 1.0 1.0
N[O.sub.3] only 3.4 1.1 1.1 1.1
N[O.sub.3] + lime 1.2 0.8 0.6 0.8
N[O.sub.3] + zeolite 3.5 1.3 1.0 1.0
l.s.d (P = 0.05) 0.28 0.32 -- --
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