Nitrous oxide emission from different fertilizers and its mitigation by nitrification inhibitors in irrigated rice

 N₂O emissions from a transplanted irrigated rice grown on a Typic Ustochrept soil at New Delhi, India, were studied to evaluate the effect of N fertilizers, i.e. urea and (NH₄)₂SO₄, alone and in combination with the nitrification inhibitors dicyandiamide (DCD) and thiosulphate. The addition of urea and (NH₄)₂SO₄ increased N₂O emissions considerably when compared to no fertilizer N application (control). N₂O measurement in the field was done by a closed-chamber method for a period of 98 days. The application of urea with DCD and thiosulphate reduced N₂O fluxes considerably. The highest total N₂O-N emission (235 g N₂O-N ha^–1) was from the (NH₄)₂SO₄ treatment, which was significantly higher than the total N₂O-N emission from the urea treatment (160 g N₂O-N ha^–1). DCD reduced N₂O-N emissions by 11% and 26% when applied with urea and(NH₄)₂SO₄, respectively, whereas thiosulphate in combination with urea reduced N₂O-N emissions by 9%. Total N₂O-N emissions were found to range from 0.08% to 0.14% of applied N. N₂O emissions were low during submergence and increased substantially during drainage of standing water. Received: 20 October 1999     

Effects of the nitrification inhibitor nitrapyrin and tillage practices on yield-scaled nitrous oxide emission from a maize field in Iran

Nitrification inhibitors can effectively decrease nitrification rates and nitrous oxide(N₂O)emission while increasing crop yield under certain conditions.However,there is no information available on the effects of nitrification inhibitors and tillage practices on N₂O emissions from maize cropping in Iran.To study how tillage practices and nitrapyrin(a nitrification inhibitor)affect N₂O emission,a split factorial experiment using a completely randomized block design with three replications was carried out in Northeast Iran,which has a cold semiarid climate.Two main plots were created with conventional tillage and minimum tillage levels,and two nitrogen(N)fertilizer(urea)management systems(with and without nitrapyrin application)were created as subplots.Tillage level did not have any significant effect on soil ammonium(NH₄⁺)and nitrate(NO₃^-)concentrations,cumulative amount and yield-scaled N₂O emission,and aboveground biomass of maize,whereas nitrapyrin application showed significant effect.Nitrapyrin application significantly reduced the cumulative amount of N₂O emission by 41%and 32%in conventional tillage and minimum tillage practices,respectively.A reduction in soil NO₃^-concentration by nitrapyrin was also observed.The average yield-scaled N₂O emission was 13.6 g N₂O-N kg^-1N uptake in both tillage systems without nitrapyrin application and was significantly reduced to 7.9 and 8.2 g N₂O-N kg^-1N uptake upon the application of nitrapyrin in minimum tillage and conventional tillage practices,respectively.Additionally,nitrapyrin application increased maize biomass yield by 4%and 13%in the minimum tillage and conventional tillage systems,respectively.Our results indicate that nitrapyrin has a potential role in reducing N₂O emission from agricultural systems where urea fertilizers are broadcasted,which is common in Iran due to the practice of traditional farming.     

Mitigation of N2O emission from an alluvial soil by application of karanjin

An incubation experiment was conducted to study N₂O emissions from a Typic Ustochrept, alluvial soil, fertilized with urea and urea combined with different levels of two nitrification inhibitors, viz karanjin and dicyandiamide (DCD). Karanjin [a furano-flavonoid, obtained from karanja (Pongamia glabra Vent.) seeds] and DCD were incorporated at rates of 5, 10, 15, 20 and 25% of applied urea-N (100 mg kg^-1 soil), to the soil adjusted to field capacity moisture content. The highest N₂O flux (366 µg N₂O-N kg^-1 soil day^-1) was obtained on day 1 after incubation from soil fertilized with urea without any inhibitor. The presence of the inhibitors appreciably reduced the mean N₂O flux from the urea-treated soils. The application of karanjin resulted in a higher mitigation of total N₂O-N emission (92-96%) compared to DCD (60-71%). Rates of N₂O flux ranged from 0.9 to 140 µg N₂O-N kg^-1 soil day^-1 from urea combined with different levels of the two inhibitors (coefficient of variation=24-272%). Karanjin (62-75%) was also more effective than DCD (9-42%) in inhibiting nitrification during the 30-day incubation period.     

Nitrapyrin effectiveness in reducing nitrous oxide emissions decreases at low doses of urea in an Andosol

In the tropics,frequent nitrogen(N)fertilization of grazing areas can potentially increase nitrous oxide(N₂O)emissions.The application of nitrification inhibitors has been reported as an effective management practice for potentially reducing N loss from the soil-plant system and improving N use efficiency(NUE).The aim of this study was to determine the effect of the co-application of nitrapyrin(a nitrification inhibitor,NI)and urea in a tropical Andosol on the behavior of N and the emissions of N₂O from autotrophic and heterotrophic nitrification.A greenhouse experiment was performed using a soil(pH 5.9,organic matter content 78 g kg^-1,and N 5.6 g kg^-1)sown with Cynodon nlemfuensis at 60%water-filled pore space to quantify total N₂O emissions,N₂O derived from fertilizer,soil ammonium(NH₄⁺)and nitrate(NO₃^-),and NUE.The study included treatments that received deionized water only(control,NI).No significant differences were observed in soil NH₄⁺content between the UR and UR+NI treatments,probably because of soil mineralization and NO₃^-produced by heterotrophic nitrification,which is not effectively inhibited by nitrapyrin.After 56 d,N₂O emissions in UR(0.51±0.12 mg N₂O-N concluded that the soil organic N mineralization and heterotrophic nitrification are the main processes of NH₄⁺and NO₃^-production.Additionally,it was found that N₂O emissions were partially a consequence of the direct oxidation of the soil's organic N via heterotrophic nitrification coupled to denitrification.Finally,the results suggest that nitrapyrin would likely exert significant mitigation on N₂O emissions only if a substantial N surplus exists in soils with high organic matter content.     

Gross nitrogen transformations and related N2O emissions in uncultivated and cultivated black soil

A better understanding of the nitrogen (N) cycle in agricultural soils is crucial for developing sustainable and environmentally friendly N fertilizer management and to propose effective nitrous oxide (N₂O) mitigation strategies. This laboratory study quantified gross nitrogen transformation rates in uncultivated and cultivated black soils in Northeast China. It also elucidated the contribution made by nitrification and denitrification to the emissions of N₂O. In the laboratory, soil samples adjusted to 60 % water holding capacity (WHC) were spiked with ¹⁵NH₄NO₃ and NH₄ ¹⁵NO₃ and incubated at 25 °C for 7 days. The size and ¹⁵N enrichment of the mineral N pools and the N₂O emission rates were determined between 0 and 7 days. The results showed that the average N₂O emission rate was 21.6 ng N₂O-N kg^?1 h^?1 in cultivated soil, significantly higher than in the uncultivated soil (11.6 ng N₂O-N kg^?1 h^?1). Denitrification was found to be responsible for 32.1 % of the N₂O emission in uncultivated soil, and the ratio increased significantly to 43.2 % in cultivated soil, due to the decrease in soil pH. Most of the increase in net N₂O-N emissions observed in the cultivated soil was resulting from the increased production of N₂O through denitrification. Gross nitrification rate was significantly higher in the cultivated soil than in the uncultivated soil, and the ratio of gross nitrification rate/ammonium immobilization rate was 6.87 in cultivated soil, much larger than the uncultivated soil, indicating that nitrification was the dominant NH₄ ⁺ consuming process in cultivated soil, and this will lead to the increased production of nitrate, whereas the increased contribution of denitrification to N₂O emission promoted the larger emission of N₂O. This double impact explains why the risk of N loss to the environment is increased by long-term cultivation and fertilization of native prairie sites, and controlling nitrification maybe effective to abate the negative environmental effects.     

N2O, NH3 and NOx Emissions as a Function of Urea Granule Size and Soil Type Under Aerobic Conditions

We examined the influence of various urea granule sizes (< 2, 7.0, 9.9 and 12.7 mm) applied into a silt loam soil (experiment 1) and soil types (sandy, silt and clay loam) treated with the largest granule (experiment 2) on gaseous N loss (except N₂) at field capacity. The prilled urea (PU) was mixed into the soil whereas the urea granules were point-placed at a 5.0-cm depth. For experiment 1, N₂O emission was enhanced with increasing granule size, ranging from 0.17–0.50% of the added N during the 45-day incubation period. In the case of experiment 2, the sandy loam soil (0.59%) behaved similarly with the silt loam (0.53%) but both showed remarkably lower emissions than were found for the clay loam soil (2.61%). Both nitrification and N₂O emissions were delayed by several days with increasing granule size, and the latter was influenced by mineral N, soil water and pH. By contrast, the NH₃ volatilization decreased with increasing granule size, implying the inhibition of urease activity by urea concentration gradients. Considering both experimental results, the NH₃ loss was highest for the PU-treated (1.73%) and the larger granules regardless of soil type did not emit more than 0.27% of the added N over 22 days, possibly because the high concentrations of either mineral N or NH₄ ⁺ in the soil surface layer (0–2.5 cm) and the high H₊ buffering capacity might regulate the NH₃ emission. Similar to the pattern of NH₃ loss, NO_x emission was noticeably higher for the PU-treated soil (0.97%) than for the larger granule sizes (0.09–0.29%), which were the highest for the sandy and clay loam soils. Positional differences in the concentration of mineral N and nitrification also influenced the NO_x emission. As such, total NH₃ loss was proportional to total NO_x emission, indicating similar influence of soil and environmental conditions on both. Pooled total N₂O, NH₃ and NO_x emission data suggest that the PU-treated soil could induce greater gaseous N loss over larger urea granules, largely in the form of NH₃ and NO_x emissions, whereas a similar increase with the largest granule size was mainly due to the total N₂O flux.     

Enhanced-efficiency nitrogen fertilizers reduce winter losses of nitrous oxide,but not of ammonia,from no-till soil in a subtropical agroecosystem

Nitrogen (N) gas losses can be reduced by using enhanced-efficiency N (EEN) fertilizers such as urease inhibitors and coating technologies. In this work, we assessed the potential of EEN fertilizers to reduce winter losses of nitrous oxide (N₂O-N) and ammonia (NH₃-N) from a subtropical field experiment on a clayey Inceptisol under no-till in Southern Brazil. The EEN sources used included urea containing N-(n-butyl) thiophosphoric triamide (UR+NBPT), polymer-coated urea (P-CU) and copper-and-boron-coated urea (CuB-CU) in addition to common urea (UR) and a control treatment without N fertilizer application. N₂O-N and NH₃-N losses were assessed by using the static chamber method and semi-open static collectors, respectively. Both N₂O-N and NH₃-N exhibited two large peaks with an intervening period of low soil moisture and air temperature. Although the short-term effect was limited to the first few days after application, UR + NBPT urea decreased soil N₂O-N emissions by 38% relative to UR. In contrast, urease inhibitor technology had no effect on NH₃-N volatilization. Both coating technologies (CuB-CU and P-CU) were ineffective in reducing N losses via N₂O production or NH₃ volatilization. The N₂O emission factor (% N applied released as N₂O) was unaffected by all N sources and amounted to only 0.48% of N applied—roughly one-half the default factor of IPCC Tier 1 (1%). Based on our findings, using NBPT-treated urea in the cold winter season in subtropical agroecosystems provides environmental benefits in the form of reduced soil N₂O emissions; however, fertilizer coating technologies provide no agronomic (NH₃) or environmental (N₂O) advantages.     

Nitrous oxide emission as affected by changes in soil water content and nitrogen fertilization

Nitrous oxide emission was measured in laboratory incubations of an alluvial soil (58% clay, pH 7.4). The soil was amended with 40 mg N kg⁻¹ as NaNO₃ or NH₄Cl, or with NaCl as a control. Each fertilization treatment was adjusted to three different water contents: constant 60% WHC (water-holding capacity), constant 120% WHC, and water content alternating between 60 and 120% WHC. During an 8-day incubation period N₂O emission rates and inorganic nitrogen concentrations in soil (NH₄⁺, NO₂⁻, NO₃⁻) were determined at regular intervals. In the control and after nitrate application small N₂O emission rates occurred with only minor variations over time, and no differences between the water treatments. In contrast, with ammonium application N₂O emission rates were much higher during the first two days of incubation, with peaks in the constant 60% WHC and 120% WHC at day 1 and in the changing-water treatment at day 2, when the first wet period (120% WHC) was completed. This N₂O peak in the changing-water treatment was 4 to 9 times higher than with constant WHC and occurred when both, NH₄⁺ and NO₂⁻ concentrations declined sharply. Thus, this N₂O emission flush can be attributed to nitrifier denitrification. After the second rewetting of the NH₄⁺-amended soil no further N₂O emission peak was observed, being in accordance with small NH₄⁺ and NO₂⁻ concentrations in soil at that time. The unexpectedly small N₂O fluxes in the constant 120% WHC treatment after nitrate application were probably caused by the reduction of N₂O to N₂ under the prevailing conditions. It can be concluded that continuous wetting or flooding of a soil is an effective measure to reduce N₂O emissions immediately after the application of NH₄⁺ fertilizers.     

The influence of nitrate and ammonium fertilization on N2O release and CH4 uptake of a well-drained topsoil demonstrated by a soil microcosm experiment

The effects of the application of KNO₃ and NH₄Cl (100 kg N ha^?1) on N₂O release and CH₄ uptake by a well-aerated topsoil (porosity: 55%, water-filled pore space: 67% of the total pore space) were studied in a laboratory incubation experiment over 50 days using a soil microcosm system with an automated registration of N₂O and CH₄ fluxes. The total N₂O-N losses over 50 days were low for all treatments and amounted to 0.9 mg m^?2 for the control, 1.2 mg m^?2 for the soil columns fertilized with KNO3, and 7.3 mg m^?2 for the soil columns fertilized with NH₄Cl. The slightly elevated N₂O release after the application Of NH₄Cl was associated with the nitrification of NH₄⁺ added. Only ?0.06% of the fertilized NH₄?N was lost as N₂O. This nitrogen fertilization reduced the CH₄ uptake of the soil columns by 43% (NH₄Cl) and 21% (KNO₃), respectively.     

NH3 Volatilization,N2O Emission and Microbial Biomass Turnover from 15N-Labeled Manure Under Laboratory Conditions

On irrigated agricultural soils from semi-arid and arid regions, ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission can be a considerable source of N losses. This study was designed to test the capture of ¹⁵N loss as NH₃ and N₂O from previous and recent manure application using a sandy, calcareous soil from Oman amended one or two times with ¹⁵N labeled manure to elucidate microbial turnover processes under laboratory conditions. The system allowed to detect ¹⁵N enrichments in evolved N₂O-N and NH₃-N of up to 17% and 9%, respectively, and total N, K₂SO₄ extractable N and microbial N pools from previous and recent ¹⁵N labeled manure applications of up to 7%, 8%, and 15%. One time manured soil had higher cumulative N₂O-N emissions (141 µg kg^?1) than repeatedly manured soil with 43 µg kg^?1 of which only 22% derived from recent manure application indicating a priming effect.     

Effect of the nitrification inhibitor nitrapyrin on the fate of nitrogen applied to a soil incubated under laboratory conditions

The aim of this study was to examine the effect of the nitrification inhibitor nitrapyrin on the fate and recovery of fertilizer nitrogen (N) and on N mineralization from soil organic sources. Intact soil cores were collected from a grassland field. Diammonium phosphate (DAP) and urea were applied as N sources. Cores were equilibrated at –5 kPa matric potential and incubated at 20 °C for 42 to 56 days. Changes in NH₄⁺‐N, accumulation of NO₃^–‐N, apparent recovery of applied N, and emission of N₂O (acetylene was used to block N₂O reductase) were examined during the study. A significant increase in NH₄⁺‐N released through mineralization was recorded when nitrapyrin was added to the control soil without N fertilizer application. In the soils to which N was added either as urea or DAP, 50–90 % of the applied N disappeared from the NH₄⁺‐N pool. Some of this N (8–16 %) accumulated as NO₃^–‐N, while a small proportion of N (1 %) escaped as N₂O. Addition of nitrapyrin resulted in a decrease and delay of NH₄⁺‐N disappearance, accumulation of much lower soil NO₃^–‐N contents, a substantial reduction in N₂O emissions, and a 30–40 % increase in the apparent recovery of added N. The study indicates that N recovery can be increased by using the nitrification inhibitor nitrapyrin in grassland soils at moisture condition close to field capacity.     

Nitrogen fertilizers promote denitrification

A laboratory study was conducted to compare the effects of different N fertilizers on emission of N₂ and N₂O during denitrification of NO₃ ^– in waterlogged soil. Field-moist samples of Drummer silty clay loam soil (fine-silty, mixed, mesic Typic Haplaquoll) were incubated under aerobic conditions for 0, 2, 4, 7, 14, 21, or 42 days with or without addition of unlabelled (NH₄)₂SO₄, urea, NH₄H₂PO₄, (NH₄)₂HPO₄, NH₄NO₃ (200 or 1000 mg N kg^–1 soil), or liquid anhydrous NH₃ (1000 mg N kg^–1 soil). The incubated soil samples were then treated with ¹⁵N-labelled KNO₃ (250 mg N kg^–1 soil, 73.7 atom% ¹⁵N), and incubation was carried out under waterlogged conditions for 5 days, followed by collection of atmospheric samples for ¹⁵N analyses to determine labelled N₂ and N₂O. Compared to samples incubated without addition of unlabelled N, all of the fertilizers promoted denitrification of ¹⁵NO₃ ^–. Emission of labelled N₂ and N₂O decreased in the order: Anhydrous NH₃>urea<$>\gg<$> (NH₄)₂HPO₄>(NH₄)₂SO₄≃NH₄NO₃≃NH₄H₂PO₄. The highest emissions observed with anhydrous NH₃ or urea coincided with the presence of NO₂ ^–, and ¹⁵N analyses indicated that these emissions originated from NO₂ ^– rather than NO₃ ^–. Emissions of labelled N₂ and N₂O were significantly correlated with fertilizer effects on soil pH and water-soluble organic C. Received: 17 January 1996     

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.     

Nitrous oxide emission from wetland rice soil as affected by the application of controlled-availability fertilizers and mid-season aeration

 N₂O emission from a wetland rice soil as affected by the application of three controlled-availability fertilizers (CAFs) and urea was investigated through a pot experiment. N₂O fluxes from the N fertilized paddy soil averaged 44.8–69.3 μg N m^–2 h^–1 during the rice growing season, accounting for 0.28–0.51% of the applied N. The emission primarily occurred during the mid-season aeration (MSA) and the subsequent re-flooding period. Fluxes were highly correlated with the NO₃ ^– and N₂O concentrations in the soil water. As there were relatively large amounts of NH₄ ⁺-N present in the soil of the CAF treatments at the beginning of MSA, leading to large amounts of NO₃ ^–-N during the MSA and the subsequent re-flooding period, the tested CAFs were not effective in reducing N₂O emission from this paddy soil. The potential of applied CAFs to reduce N₂O emissions from paddy soil is discussed. Received: 25 May 1999     

Nitrate Transformation and N2O Emission in a Typical Intensively Managed Calcareous Fluvaquent Soil: A 15-Nitrogen Tracer Incubation Study

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO₃-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N₂O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO₃-N decreased. When ¹⁵NO₃-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg^?1 only 1.1 ± 0.4 mg kg^?1 NO₃-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N₂O-N emissions were at levels of only micrograms kg^?1 soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N₂O.     

Effects of various nitrogen fertilizers on emission of nitrous oxide from soils

Summary Field studies of the effects of different N fertilizers on emission of nitrous oxide (N20) from three Iowa soils showed that the N₂O emissions induced by application of 180 kg ha^–1 fertilizer N as anhydrous ammonia greatly exceeded those induced by application of the same amount of fertilizer N as aqueous ammonia or urea. On average, the emission of N₂O-N induced by anhydrous ammonia was more than 13 times that induced by aqueous ammonia or urea and represented 1.2% of the anhydrous ammonia N applied. Experiments with one soil showed that the N₂O emission induced by anhydrous ammonia was more than 17 times that induced by the same amount of N as calcium nitrate. These findings confirm indications from previous work that anhydrous ammonia has a much greater effect on emission of N₂O from soils than do other commonly used N fertilizers and merits special attention in research relating to the potential adverse climatic effect of N fertilization of soils.Laboratory studies of the effect of different amounts of NH₄OH on emission of N₂O from Webster soil showed that the emission of N₂O-N induced by addition of 100 g NH₄OH-N g^–1 soil represented only 0.18% of the N applied, whereas the emissions induced by additions of 500 and 1 000 g NH4OH-N g^–1 soil represented 1.15% and 1.19%, respectively, of the N applied. This suggests that the exceptionally large emissions of N₂O induced by anhydrous ammonia fertilization are due, at least in part, to the fact that the customary method of applying this fertilizer by injection into soil produces highly alkaline soil zones of high ammonium-N concentration that do not occur when urea or aqueous ammonia fertilizers are broadcast and incorporated into soil.     

Effect of Inorganic N Composition of Fertilizers on Nitrous Oxide Emission Associated with Nitrification and Denitrification

We studied the effect of repeated application (once every 2 d) of a fertilizer solution with different ratios of NH₄ ⁺ - and NO₃ ^?-N on N₂O emission from soil. After the excess fertilizer solution was drained from soil, the water content of soil was adjusted to 50% of the maximum water-holding capacity by suction at 6 × 10³ Pa. Repeated application of NH₄ ⁺- rich fertilizer solution stimulated nitrification in soil more than NO₃ ^?-rich fertilizer. Although the evolution of N₂O through nitrifier denitrification tended to increase with the repeated addition of a fertilizer solution rich in NH₄ ⁺ rather than in NO₃ ^?, the contribution of nitrifier denitrification remained at levels of 20 to 36% of the total emission regardless of the inorganic N composition. The total emission of N₂O also tended to increase with the application of NH₄ ⁺- rather than NO₃ ^?-rich fertilizer. It was suggested that the coupled process of nitrification and denitrification at micro-aerobic sites became important when fertilizer rich in NH₄ ⁺ was applied to soil under relatively aerobic conditions.     

不同碳源添加对钙质土高累积硝态氮向土壤有机氮库转化的研究

Excessive amounts of nitrate have accumulated in many soils on the North China Plain due to the large amounts of chemical N fertilizers or manures used in combination with low carbon inputs. We investigated the potential of different carbon substrates added to transform soil nitrate into soil organic N (SON). A 56-d laboratory incubation experiment using the 15 N tracer (K15 NO3 ) technique was carried out to elucidate the proportion of SON derived from accumulated soil nitrate following amendment with glucose or maize straw at controlled soil temperature and moisture. The dynamics and isotopic abundance of mineral N (NO3 and NH+4 ) and SON and greenhouse gas (N2O and CO2 ) emissions during the incubation were investigated. Although carbon amendments markedly stimulated transformation of nitrate to newly formed SON, this was only a substitution effect of the newly formed SON with native SON because SON at the end of the incubation period was not significantly different (P > 0.05) from that in control soil without added C. At the end of the incubation period, amendment with glucose, a readily available C source, increased nitrate immobilization by 2.65 times and total N2O-N emission by 33.7 times, as compared with maize straw amendment. Moreover, the differences in SON and total N2O-N emission between the treatments with glucose and maize straw were significant (P < 0.05). However, the total N2O-N emission in the straw treatment was not significantly (P > 0.05) greater than that in the control. Straw amendment may be a potential option in agricultural practice for transformation of nitrate N to SON and minimization of N2O emitted as well as restriction of NO3-N leaching.     

Site of nitrous oxide production in field soils

Summary Nitrous oxide (N₂O) fluxes at the soil surface and concentrations at 0.1, 0.2, and 0.3 m were determined in a 40-year-old planted tallgrass (XXX) prairie, a 40-year-old white pine (Pinus strobus) plantation, and field plots treated annually for 18 years either with 33 metric tons of manure ha^–1 (330 kg N ha^–1) and NH₄NO₃ (80 kg N ha^–1) or with only NH₄NO₃ (control). Nitrous oxide fluxes from the prairie, forest, manure-amended, and control sites from 13 May to 10 November 1980 ranged from 0.2 to 1.3, 3.5 to 19.5, 3.7 to 79.0, and 1.7 to 24.8 ng N₂O-N m^–2s^–1, respectively. We observed periods when there was no apparent relationship between the N₂O flux from the surface and N₂O concentrations in the soil profile. This was generally the case in the prairie and in the field sites following the application of N fertilizer. The N₂O concentrations in the soil profile increased markedly and coincided with increased soil water content following periods of heavy rainfall for all sites except the prairie. Nitrous oxide concentration gradients indicate that following heavy rainfalls the site of N₂O production was moved from the surface deeper into the soil profile. We suggest that the source of N₂O production near the surface is nitrification and that N₂O is produced by denitrification of NO₃ leached into the soil following heavy rainfall.     

No significant difference in N2O emission,fertilizer-induced N2O emission factor and CH4 absorption between anaerobically digested cattle slurry and chemical fertilizer applied timothy (Phleum pratense L.) sward in central Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) and methane (CH₄) fluxes from a fertilized timothy (Phleum pratense L.) sward on the northern island of Japan were measured over 2?years using a randomized block design in the field. The objectives of the present study were to obtain annual N₂O and CH₄ emission rates and to elucidate the effect of the applied material (control [no nitrogen], anaerobically digested cattle slurry [ADCS] or chemical fertilizer [CF]) and the application season (autumn or spring) on the annual N₂O emission, fertilizer-induced N₂O emission factor (EF) and the annual CH₄ absorption. Ammonium sulfate was applied to the CF plots at the same application rate of NH₄-N to the ADCS plots. A three-way ANOVA was used to examine the significance of the factors (the applied material, the application season and the year). The ANOVA for the annual N₂O emission rates showed a significant effect with regard to the applied material (P?=?0.042). The annual N₂O emission rate from the control plots (0.398?kg N₂O-N ha^?1?year^?1) was significantly lower than that from the ADCS plots (0.708?kg N₂O-N ha^?1?year^?1) and the CF plots (0.636?kg N₂O-N ha^?1?year^?1). There was no significant difference in the annual N₂O emission rate between the ADCS and CF plots. The ANOVA for the EFs showed insignificance of all factors (P?>?0.05). The total mean?±?standard error of the EFs (fertilizer-induced N₂O-N emission/total applied N) was 0.0024?±?0.0007 (kg N₂O-N [kg N]^?1), which is similar to the reported EF (0.0032?±?0.0013) for well-drained uplands in Japan. The CH₄ absorption rates differed significantly between years (P?=?0.014). The CH₄ absorption rate in the first year (3.28?kg CH₄?ha^?1?year^?1) was higher than that in the second year (2.31?kg CH₄?ha^?1?year^?1), probably as a result of lower precipitation in the first year. In conclusion, under the same application rate of NH₄-N, differences in the applied materials (ADCS or CF) and the application season (autumn or spring) led to no significant differences in N₂O emission, fertilizer-induced N₂O EF and CH₄ absorption.