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1.
In temperate regions, a majority of N2O is emitted during spring soil thawing. We examined the influence of two winter field covers, snow and winter rye, on soil temperature and subsequent spring N2O emissions from a New York corn field over two years. The first season (2006-07) was a cold winter (2309 h below 0 °C at 8 cm soil depth), historically typical for the region. The snow removal treatment resulted in colder soils and higher N2O fluxes (73.3 vs. 57.9 ng N2O-N cm−2 h−1). The rye cover had no effect on N2O emissions. The second season (2007-08) was a much milder winter (1271 h below freezing at 8 cm soil depth), with lower N2O fluxes overall. The winter rye cover resulted in lower N2O fluxes (5.9 vs. 33.7 ng N2O-N cm−2 h−1), but snow removal had no effect. Climate scenarios predict warmer temperature and less snow cover in the region. Under these conditions, spring N2O emissions can be expected to decrease and could be further reduced by winter rye crops.  相似文献   

2.
A field experiment on permanent ryegrass–white clover pasture at AgResearch's Ruakura dairy farm near Hamilton, New Zealand quantified nitrous oxide (N2O) emissions from different types of dairy effluent applied to soil at three seasons and evaluated the potential of dicyandiamide (DCD) (a nitrification inhibitor) to decrease gaseous N2O emissions. Fresh or stored manure and farm dairy effluent (FDE; from dairy shed washings), with or without DCD (10 kg/ha), were applied at approximately 100 kg N/ha to plots on a well‐drained soil on volcanic parent material. A field chamber technique was used to measure N2O emissions. Application of manure or FDE, both in fresh and stored forms, to pasture generally increased N2O emissions. Overall N2O emission factors (EF) varied between 0.01% and 1.87%, depending on application season and effluent type. EFs in spring and autumn were greater than those in summer (< 0.05). Among the effluents, N2O EFs were largest from fresh FDE (1.65%) during the spring measurement period, stored manure (1.87%) during the autumn and stored FDE (0.25%) during the summer. DCD was effective in decreasing N2O EFs from fresh FDE, fresh manure, stored FDE and stored manure by 40–80%, 69–76%, 24–84% and 60–70%, respectively. DCD reduced N2O emissions during the spring and autumn seasons more effectively than in the summer season.  相似文献   

3.
Nitrogen (N) losses via nitrate (NO3) leaching, ammonia (NH3) volatilization and nitrous oxide (N2O) emissions from grazed pastures in New Zealand are one of the major contributors to environmental degradation. The use of N inhibitors (urease and nitrification inhibitors) may have a role in mitigating these N losses. A one-year field experiment was conducted on a permanent dairy-grazed pasture site at Massey University, Palmerston North, New Zealand to quantify these N losses and to assess the effect of N inhibitors in reducing such losses during May 2005-2006. Cow urine at 600 kg N ha−1 rate with or without urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) or (trade name “Agrotain”) (3 L ha−1), nitrification inhibitor dicyandiamide (DCD) (7 kg ha−1) and the use of double inhibitor (DI) containing a combination of both Agrotain and DCD (3:7) were applied to field plots in autumn, spring and summer. Pasture production, NH3 and N2O fluxes, soil mineral N concentrations, microbial biomass C and N, and soil pH were measured following the application of treatments during each season. All measured parameters, except soil microbial biomass C and N, were influenced by the added inhibitors during the three seasons. Agrotain reduced NH3 emissions over urine alone by 29%, 93% and 31% in autumn, spring and summer respectively but had little effect on N2O emission. DCD reduced N2O emission over urine alone by 52%, 39% and 16% in autumn, spring and summer respectively but increased NH3 emission by 56%, 9% and 17% over urine alone during those three seasons. The double inhibitor reduced NH3 by 14%, 78% and 9% and N2O emissions by 37%, 67% and 28% over urine alone in autumn, spring and summer respectively. The double inhibitor also increased pasture dry matter by 10%, 11% and 8% and N uptake by the 17%, 28% and 10% over urine alone during autumn, spring and summer respectively. Changes in soil mineral N and pH suggested a delay in urine-N hydrolysis with Agrotain, and reduced nitrification with DCD. The combination of Agrotain and DCD was more effective in reducing both NH3 and N2O emissions, improving pasture production, controlling urea hydrolysis and retaining N in NH4+ form. These results suggest that the combination of both urease and nitrification inhibitors may have the most potential to reduce N losses if losses are associated with urine and improve pasture production in intensively grazed systems.  相似文献   

4.
Nitrous oxide (N2O) is a greenhouse gas and agricultural soils are major sources of atmospheric N2O. Its emissions from soils make up the largest part in the global N2O budget. Research was carried out at the experimental fields of the Leibniz-Institute of Agricultural Engineering Potsdam-Bornim (ATB). Different types (mineral and wood ash) and levels (0, 75 and 150 kg N ha−1) of fertilization were applied to annual (rape, rye, triticale and hemp) and perennial (poplar and willow) plants every year. N2O flux measurements were performed 4 times a week by means of gas flux chambers and an automated gas chromatograph between 2003 and 2005. Soil samples were also taken close to the corresponding measuring rings. Soil nitrate and ammonium were measured in soil extracts.N2O emissions had a peak after N fertilization in spring, after plant harvest in summer and during the freezing–thawing periods in winter. Both fertilization and plant types significantly altered N2O emission. The maximum N2O emission rate detected was 1081 μg N2O m−2 h−1 in 2004. The mean annual N2O emissions from the annual plants were more than twofold greater than those of perennial plants (4.3 kg ha−1 vs. 1.9 kg ha−1). During January, N2O fluxes considerably increased in all treatments due to freezing–thawing cycles. Fertilization together with annual cropping doubled the N2O emissions compared to perennial crops indicating that N use efficiency was greater for perennial plants. Fertilizer-derived N2O fluxes constituted about 32% (willow) to 67% (rape/rye) of total soil N2O flux. Concurrent measurements of soil water content, NO3 and NH4 support the conclusion that nitrification is main source of N2O loss from the study soils. The mean soil NO3-N values of soils during the study for fertilized soils were 1.6 and 0.9 mg NO3-N kg−1 for 150 and 75 kg N ha−1 fertilization, respectively. This value reduced to 0.5 mg NO3-N kg−1 for non-fertilized soils.  相似文献   

5.
Conservation tillage practices are widely used to protect against soil erosion and soil C losses, whereas winter cover crops are used mainly to protect against N losses during autumn and winter. For the greenhouse gas balance of a cropping system the effect of reduced tillage and cover crops on N2O emissions may be more important than the effect on soil C. This study monitored emissions of N2O between September 2008 and May 2009 in three tillage treatments, i.e., conventional tillage (CT), reduced tillage (RT) and direct drilling (DD), all with (+CC) or without (−CC) fodder radish as a winter cover crop. Cover crop growth, soil mineral N dynamics, and other soil characteristics were recorded. Furthermore, soil concentrations of N2O were determined eight times during the monitoring period using permanently installed needles. There was little evidence for effects of the cover crop on soil mineral N. Following spring tillage and slurry application soil mineral N was dominated by the input from slurry. Nitrous oxide emissions during autumn, winter and early spring remained low, although higher emissions from +CC treatments were indicated after freezing events. Following spring tillage and slurry application by direct injection N2O emissions were stimulated in all tillage treatments, reaching 250-400 μg N m−2 h−1 except in the CT + CC treatment, where emissions peaked at 900 μg N m−2 h−1. Accumulated emissions ranged from 1.6 to 3.9 kg N2O ha−1. A strong positive interaction between cover crop and tillage was observed. Soil concentration profiles of N2O showed a significant accumulation of N2O in CT relative to RT and DD treatments after spring tillage and slurry application, and a positive interaction between slurry and cover crop residues. A comparison in early May of N2O emissions with flux estimates based on soil concentration profiles indicated that much of the N2O emitted was produced near the soil surface.  相似文献   

6.
After implementation of legislative measures for the reduction of environmental hazards from nitrate leaching and ammonia volatilisation when using organic manures and fertilizers in Europe, much attention is now paid to the specific effects of these fertilizers on the dynamics of global warming-relevant trace gases in soil. Particularly nitrogen fertilizers and slurry from animal husbandry are known to play a key role for the CH4 and N2O fluxes from soils. Here we report on a short-term evaluation of trace gas fluxes in grassland as affected by single or combined application of mineral fertilizer and organic manure in early spring. Methane fluxes were characterised by a short methane emission event immediately after application of cattle slurry. Within the same day methane fluxes returned to negative, and on average over the 4-day period after slurry application, only a small but insignificant trend to reduced methane oxidation was found. Nitrous oxide emissions showed a pronounced effect of combined slurry and mineral fertilizer application. In particular fresh cattle slurry combined with calcium ammonium nitrate (CAN) mineral fertilizer induced an increase in mean N2O flux during the first 4 days after application from 10 to 300 μg N2O-N m−2 h−1. 15N analysis of emitted N2O from 15N-labelled fertilizer or manure indicated that easily decomposable slurry C compounds induced a pronounced promotion of N2O-N emission derived from mineral CAN fertilizer. Fluxes after application of either mineral fertilizer or slurry alone showed an increase of less than 5-fold. The NOx sink strength of the soil was in the range of −6 to −10 μg NOx-N m−2 h−1 and after fertilization it showed a tendency to be reduced by no more than 2 μg NOx-N m−2 h−1, which was a result of both, increased NO emission and slightly increased NO2 deposition. Associated determination of the N2O:N2 emission ratio revealed that after mineral N application (CAN) a large proportion (c. 50%) was emitted as N2O, while after application of slurry with easily decomposable C and predominantly -N serving as N-source, the N2O:N2 emission ratio was 1:14, i.e. was changed in favour of N2. Our work provides evidence that particularly the combination of slurry and nitrate-containing N fertilizers gives rise to considerable N2O emissions from mineral fertilizer N pool.  相似文献   

7.
Mixed responses of soil nitrous oxide (N2O) fluxes to reduced tillage/no-till are widely reported across soil types and regions. In a field experiment on a Danish sandy loam soil we compared N2O emissions during winter barley growth following five years of direct drilling (DD), reduced tillage (RT) or conventional tillage (CT). Each of these tillage treatments further varied in respect to whether the resulting plot crop residues were retained (+Res) or removed (−Res). Sampling took place from autumn 2007 to the end of spring 2008. Overall N2O emissions were 27 and 26% lower in DD and RT, respectively, relative to N2O emissions from CT plots (P < 0.05). We observed that in residue removal scenarios N2O emissions were similar for all tillage treatments, but in residue retention scenarios N2O emissions were significantly higher in CT than in either DD or RT (P < 0.05). Irrespective of residue management, N2O emissions from DD and RT plots never exceeded emissions from CT plots. Retention of residue was estimated to reduce emissions from DD plots by 39% and in RT plots by 9%, but to increase N2O emissions from the CT plots by 35%. Relative soil gas diffusivity (Rdiff), soil NO3-N, soil temperature, tillage and residue were important driving factors for N2O emission (P < 0.05). A multiple linear regression model using Rdiff to represent the water factor explained N2O emissions better than a water-filled pore space (WFPS) based model, suggesting a need for review of the current use of WFPS in N2O prediction models. We conclude that on light textured soils, no-till has the potential for reducing N2O emissions when crop residues are returned to the soil.  相似文献   

8.
Nitric oxide (NO) and nitrous oxide (N2O) emissions were measured from experimental dung and urine patches placed on boreal pasture soil during two growing seasons and one autumn period until soil freezing. N2O emissions in situ were studied by a static chamber method. NO was measured with a dynamic chamber method using a NO analyser in situ. Mean emissions from the control plots were 47.6±4.5 μg N2ON m−2 h−1 and 12.6±1.6 μg NON m−2 h−1. N2O and NO emissions from urine plots (132±21.2 μg N2ON m−2 h−1 and 51.9±7.6 μg NON m−2 h−1) were higher than those from dung plots (110.0±20.1 μg N2ON m−2 h−1 and 14.7±2.1 μg NON m−2 h−1). There was a large temporal variation in N2O and NO emissions. Maximum N2O emissions were measured a few weeks after dung or urine application, whereas the maximum NO emissions were detected the following year. NO was responsible on average 14% (autumn) and 34% (summer) of total (NO+N2O)N emissions from the pasture soil. NO emissions increased with increasing soil temperature and with decreasing soil moisture. N2O emissions increased with increasing soil moisture, but did not correlate with soil temperature. Therefore we propose that N2O and NO were produced mainly during different microbial processes, i.e., nitrification and denitrification, respectively. The results show that the overall conditions and mechanism especially for emissions of NO are still poorly understood but that there are differences in the mechanisms regulating N2O and NO production.  相似文献   

9.
有机无机肥配施对酸性菜地土壤硝化作用的影响   总被引:5,自引:0,他引:5  
通过室内培养和田间试验, 研究了有机无机肥配施对酸性菜地土硝化作用的影响。培养试验条件为60%土壤最大持水量和25 ℃。 结果表明,土壤硝化作用模式为指数方程,延滞期10天。与纯化肥处理(NPK)相比,鲜猪粪配施无机肥(FPM+NPK)和猪粪堆肥配施无机肥(CPM+NPK)均能降低土壤硝化势和氨氧化潜势,猪粪堆肥配施无机肥还能增加土壤微生物量碳、 氮。鲜猪粪配施无机肥和猪粪堆肥配施无机肥处理在硝化培养和田间试验期间N2O释放量均没有差异,但硝化培养期间鲜猪粪配施无机肥的N2O释放量显著低于纯化肥处理,田间试验期间猪粪堆肥配施无机肥的N2O释放量显著低于纯化肥处理。培养试验结束后的土壤pH值与土壤硝化势间,以及硝化培养期间N2O累积释放量与土壤硝化势间均存在显著正相关关系。本研究表明, 有机无机肥配施显著影响土壤硝化作用以及硝化培养期间和田间N2O释放。  相似文献   

10.
We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak (Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO2, CH4 and N2O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH4 uptake rates (<1 kg C ha−1 yr−1) and, coinciding with WFPS values >70%, episodes of CH4 emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH4 (4.7 kg C ha−1 yr−1). The N2O releases at the cropland and pasture sites (2.7 and 4.8 kg N2O-N ha−1 yr−1) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N2O-N ha−1 yr−1). The highest N2O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH4 and N2O. On the contrary, afforestation resulted in increases in SOM content and CH4 uptake, as well as decreases in N2O emissions.  相似文献   

11.
The effect of reduced tillage (RT) on nitrous oxide (N2O) emissions of soils from fields with root crops under a temperate climate was studied. Three silt loam fields under RT agriculture were compared with their respective conventional tillage (CT) field with comparable crop rotation and manure application. Undisturbed soil samples taken in September 2005 and February 2006 were incubated under laboratory conditions for 10 days. The N2O emission of soils taken in September 2005 varied from 50 to 1,095 μg N kg−1 dry soil. The N2O emissions of soils from the RT fields taken in September 2005 were statistically (P < 0.05) higher or comparable than the N2O emissions from their respective CT soil. The N2O emission of soils taken in February 2006 varied from 0 to 233 μg N kg−1 dry soil. The N2O emissions of soils from the RT fields taken in February 2006 tended to be higher than the N2O emissions from their respective CT soil. A positive and significant Pearson correlation of the N2O–N emissions with nitrate nitrogen (NO3 –N) content in the soil was found (P < 0.01). Leaving the straw on the field, a typical feature of RT, decreased NO3 –N content of the soil and reduced N2O emissions from RT soils.  相似文献   

12.
 Land use changes in semiarid grasslands have long-lasting effects. Reversion to near-original conditions with respect to plant populations and productivity requires more than 50 years following plowing. The impact of more subtle management changes like small, annual applications of N fertilizer or changing cattle stocking rates, which alters N redistribution caused by grazing and cattle urine deposition, is not known. To investigate the long-term effects of N addition to the Colorado shortgrass steppe we made weekly, year-round measurements of N2O and CH4 from the spring of 1990 through June 1996. Fluxes of NOx (NO plus NO2) were measured from October 1995 through June 1996. These measurements illustrated that large N applications, either in a single dose (45 g N m–2), simulating cattle urine deposition, or in small annual applications over a 15-year period (30 g N m–2) continued to stimulate N2O emissions from both sandy loam and clay loam soils 6–15 years after N application. In sandy loam soils last fertilized 6 years earlier, average NOx emissions were 60% greater than those from a comparable, unfertilized site. The long-term impact of these N additions on CH4 uptake was soil-dependent, with CH4 uptake decreased by N addition only in the coarser textured soils. The short-term impact of small N additions (0.5–2 g N m–2) on N2O, NOx emissions and CH4 uptake was observed in field studies made during the summer of 1996. There was little short-term effect of N addition on CH4 uptake in either sandy loam or clay loam soils. Small N additions did not result in an immediate increase in N2O emissions from the sandy loam soil, but did significantly increase N2O flux from the clay loam soil. The reverse soil type, N addition interaction occurred for NOx emissions where N addition increased NOx emissions in the coarser textured soil 10–20 times those of N2O. Received: 31 October 1997  相似文献   

13.
Agricultural soils contribute significantly to atmospheric nitrous oxide (N2O). A considerable part of the annual N2O emission may occur during the cold season, possibly supported by high product ratios in denitrification (N2O/(N2+N2O)) and nitrification (N2O-N/(NO3-N+NO2-N)) at low temperatures and/or in response to freeze-thaw perturbation. Water-soluble organic materials released from frost-sensitive catch crops and green manure may further increase winter emissions. We conducted short-term laboratory incubations under standardized moisture and oxygen (O2) conditions, using nitrogen (N) tracers (15N) to determine process rates and sources of emitted N2O after freeze-thaw treatment of soil or after addition of freeze-thaw extract from clover. Soil respiration and N2O production was stimulated by freeze-thaw or addition of plant extract. The N2O emission response was inversely related to O2 concentration, indicating denitrification as the quantitatively prevailing process. Denitrification product ratios in the two studied soils (pH 4.5 and 7.0) remained largely unaltered by freeze-thaw or freeze-thaw-released plant material, refuting the hypothesis that high winter emissions are due to frost damage of N2O reductase activity. Nitrification rates estimated by nitrate (NO3) pool enrichment were 1.5-1.8 μg NO3-N g−1 dw soil d−1 in freeze-thaw-treated soil when incubated at O2 concentrations above 2.3 vol% and one order of magnitude lower at 0.8 vol% O2. Thus, the experiments captured a situation with severely O2-limited nitrification. As expected, the O2 stress at 0.8 vol% resulted in a high nitrification product ratio (0.3 g g−1). Despite this high product ratio, only 4.4% of the measured N2O accumulation originated from nitrification, reaffirming that denitrification was the main N2O source at the various tested O2 concentrations in freeze-thaw-affected soil. N2O emission response to both freeze-thaw and plant extract addition appeared strongly linked to stimulation of carbon (C) respiration, suggesting that freeze-thaw-induced release of decomposable organic C was the major driving force for N2O emissions in our soils, both by fuelling denitrifiers and by depleting O2. The soluble C (applied as plant extract) necessary to induce a CO2 and N2O production rate comparable with that of freeze-thaw was 20-30 μg C g−1 soil dw. This is in the range of estimates for over-winter soluble C loss from catch crops and green manure plots reported in the literature. Thus, freeze-thaw-released organic C from plants may play a significant role in freeze-thaw-related N2O emissions.  相似文献   

14.
The availability of labile organic C for microbial metabolic processes could be an important factor regulating N2O emissions from tropical soils. We explored the effects of labile C on the emissions of N2O from a forest soil in the State of Rondônia in the southwestern quadrant of the Brazilian Amazon. We measured emissions of N2O from a forest soil after amendments with solutions containing glucose, water only or NO3. Addition of glucose to the forest soil resulted in very large increases in N2O emissions whereas the water only and NO3 additions did not. These results suggest a strong C limitation on N2O production in this forest soil in the southwestern Amazon.  相似文献   

15.
Applications of dairy farm effluents to land may lead to ammonia (NH3) volatilization and nitrous oxide (N2O) emissions. Nitrogen (N) transformation process inhibitors, such as urease inhibitors (UIs) and nitrification inhibitors (NIs), have been used to reduce NH3 and N2O losses derived from agricultural N sources. The objective of this study was to examine the effects of amending dairy effluents with UI (N-(n-butyl) thiophosphoric triamide (NBTPT)) and NI (dicyandiamide (DCD)) on NH3 and N2O emissions. Treatments included either fresh or stored manure and either fresh or stored farm dairy effluent (FDE), with and without NBTPT (0.25 g kg?1 N) or DCD (10 kg ha?1), applied to a pasture on a free-draining volcanic parent material soil. The nutrient loading rate of FDE and manure, which had different dry matter contents (about 2 and 11 %, respectively) was 100 kg N ha?1. Application of manure and FDE led to NH3 volatilization (15, 1, 17 and 0.4 % of applied N in fresh manure, fresh FDE, stored manure and stored FDE, respectively). With UI (NBTPT), NH3 volatilization from fresh manure was significantly (P?<?0.05) decreased to 8 % from 15 % of applied N, but the UI did not significantly reduce NH3 volatilization from fresh FDE. The N2O emission factors (amount of N2O–N emitted as a percentage of applied N) for fresh manure, fresh FDE and stored FDE were 0.13?±?0.02, 0.14?±?0.03 and 0.03?±?0.01 %, respectively. The NI (DCD) was effective in decreasing N2O emissions from stored FDE, fresh FDE and fresh manure by 90, 51 and 46 % (P?<?0.05), respectively. All types of effluent increased pasture production over the first 21 days after application (P?<?0.05). The addition of DCD resulted in an increase in pasture production at first harvest on day 21 (P?<?0.05). This study illustrates that UIs and NIs can be effective in mitigating NH3 and N2O emissions from land-applied dairy effluents.  相似文献   

16.
Nitrous oxide emissions were studied with a static chamber technique during 2 years from a drained organic soil in eastern Finland. After drainage, the soil was forested with birch (Betula pendula Roth) and 22 years later, part of the forest was felled and then used for cultivation of barley (Hordeum vulgare L.) and grass. The annual N2O emissions from the cultivated soil (from 8.3 to 11.0 kg N2O-N ha−1 year−1) were ca. twice the annual emission from the adjacent forest site (4.2 kg N2O-N ha−1 year−1). The N2O emissions from the soils without plants (kept bare by regular cutting or tilling) were also lower (from 6.5 to 7.1 kg N2O-N ha−1 year−1) than those from the cultivated soil. There was a high seasonal variation in the fluxes with a maximum in spring and early summer. The N2O fluxes during the winter period accounted for 15-60% of the total annual emissions. N2O fluxes during the snow-free periods were related to the water table (WT) level, water-filled pore space, carbon mineralisation and the soil temperature. A linear regression model with CO2 production, WT and soil temperature at the depth of 5 cm as independent variables explained 54% of the variation in the weekly mean N2O fluxes during the snow-free periods. N2O fluxes were associated with in situ net nitrification, which alone explained 58% of the variation in the mean N2O fluxes during the snow-free period. The N2O-N emissions were from 1.5 to 5% of net nitrification. The acetylene blockage technique indicated that most of the N2O emitted in the snow-free period originated from denitrification.  相似文献   

17.
The contribution of nitrification to the emission of nitrous oxide (N2O) from soils may be large, but its regulation is not well understood. The soil pH appears to play a central role for controlling N2O emissions from soil, partly by affecting the N2O product ratios of both denitrification (N2O/(N2+N2O)) and nitrification (N2O/(NO2+NO3). Mechanisms responsible for apparently high N2O product ratios of nitrification in acid soils are uncertain. We have investigated the pH regulation of the N2O product ratio of nitrification in a series of experiments with slurries of soils from long-term liming experiments, spanning a pH range from 4.1 to 7.8. 15N labelled nitrate (NO3) was added to assess nitrification rates by pool dilution and to distinguish between N2O from NO3 reduction and NH3 oxidation. Sterilized soil slurries were used to determine the rates of chemodenitrification (i.e. the production of nitric oxide (NO) and N2O from the chemical decomposition of nitrite (NO2)) as a function of NO2 concentrations. Additions of NO2 to aerobic soil slurries (with 15N labelled NO3 added) were used to assess its potential for inducing denitrification at aerobic conditions. For soils with pH?5, we found that the N2O product ratios for nitrification were low (0.2-0.9‰) and comparable to values found in pure cultures of ammonia-oxidizing bacteria. In mineral soils we found only a minor increase in the N2O product ratio with increasing soil pH, but the effect was so weak that it justifies a constant N2O product ratio of nitrification for N2O emission models. For the soils with pH 4.1 and 4.2, the apparent N2O product ratio of nitrification was 2 orders of magnitude higher than above pH 5 (76‰ and 14‰). This could partly be accounted for by the rates of chemodenitrification of NO2. We further found convincing evidence for NO2-induction of aerobic denitrification in acid soils. The study underlines the role of NO2, both for regulating denitrification and for the apparent nitrifier-derived N2O emission.  相似文献   

18.
The application of biochar produced from wood and crop residues, such as sawdust, straw, sugar bagasse and rice hulls, to highly weathered soils under tropical conditions has been shown to influence soil greenhouse gas (GHG) emissions. However, there is a lack of data concerning GHG emissions from soils amended with biochar derived from manure, and from soils outside tropical and subtropical regions. The objective of this study was to quantify the effect on emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) following the addition, at a rate of 18 t ha−1, of two different types of biochar to an Irish tillage soil. A soil column experiment was designed to compare three treatments (n = 8): (1) non-amended soil (2) soil mixed with biochar derived from the separated solid fraction of anaerobically digested pig manure and (3) soil mixed with biochar derived from Sitka Spruce (Picea sitchensis). The soil columns were incubated at 10 °C and 75% relative humidity, and leached with 80 mL distilled water, twice per week. Following 10 weeks of incubation, pig manure, equivalent to 170 kg nitrogen ha−1 and 36 kg phosphorus ha−1, was applied to half of the columns in each treatment (n = 4). Gaseous emissions were analysed for 28 days following manure application. Biochar addition to the soil increased N2O emissions in the pig manure-amended column, most likely as a result of increased denitrification caused by higher water filled pore space and organic carbon (C) contents. Biochar addition to soil also increased CO2 emissions. This was caused by increased rates of C mineralisation in these columns, either due to mineralisation of the labile C added with the biochar, or through increased mineralisation of the soil organic matter.  相似文献   

19.
Earthworm activity may have an effect on nitrous oxide (N2O) emissions from crop residue. However, the importance of this effect and its main controlling variables are largely unknown. The main objective of this study was to determine under which conditions and to what extent earthworm activity impacts N2O emissions from grass residue. For this purpose we initiated a 90-day (experiment I) and a 50-day (experiment II) laboratory mesocosm experiment using a Typic Fluvaquent pasture soil with silt loam texture. In all treatments, residue was applied, and emissions of N2O and carbon dioxide (CO2) were measured. In experiment I the residue was applied on top of the soil surface and we tested (a) the effects of the anecic earthworm species Aporrectodea longa (Ude) vs. the epigeic species Lumbricus rubellus (Hoffmeister) and (b) interactions between earthworm activity and bulk density (1.06 vs. 1.61 g cm−3). In experiment II we tested the effect of L. rubellus after residue was artificially incorporated in the soil. In experiment I, N2O emissions in the presence of earthworms significantly increased from 55.7 to 789.1 μg N2O-N kg−1 soil (L. rubellus; p<0.001) or to 227.2 μg N2O-N kg−1 soil (A. longa; p<0.05). This effect was not dependent on bulk density. However, if the residue was incorporated into the soil (experiment II) the earthworm effect disappeared and emissions were higher (1064.2 μg N2O-N kg−1 soil). At the end of the experiment and after removal of earthworms, a drying/wetting and freezing/thawing cycle resulted in significantly higher emissions of N2O and CO2 from soil with prior presence of L. rubellus. Soil with prior presence of L. rubellus also had higher potential denitrification. We conclude that the main effect of earthworm activity on N2O emissions is through mixing residue into the soil, switching residue decomposition from an aerobic and low denitrification pathway to one with significant denitrification and N2O production. Furthermore, A. longa activity resulted in more stable soil organic matter than L. rubellus.  相似文献   

20.
Previous laboratory studies using epigeic and anecic earthworms have shown that earthworm activity can considerably increase nitrous oxide (N2O) emissions from crop residues in soils. However, the universality of this effect across earthworm functional groups and its underlying mechanisms remain unclear. The aims of this study were (i) to determine whether earthworms with an endogeic strategy also affect N2O emissions; (ii) to quantify possible interactions with epigeic earthworms; and (iii) to link these effects to earthworm-induced differences in selected soil properties. We initiated a 90-day 15N-tracer mesocosm study with the endogeic earthworm species Aporrectodea caliginosa (Savigny) and the epigeic species Lumbricus rubellus (Hoffmeister). 15N-labeled radish (Raphanus sativus cv. Adagio L.) residue was placed on top or incorporated into the loamy (Fluvaquent) soil. When residue was incorporated, only A. caliginosa significantly (p < 0.01) increased cumulative N2O emissions from 1350 to 2223 μg N2O-N kg−1 soil, with a corresponding increase in the turnover rate of macroaggregates. When residue was applied on top, L. rubellus significantly (p < 0.001) increased emissions from 524 to 929 μg N2O-N kg−1, and a significant (p < 0.05) interaction between the two earthworm species increased emissions to 1397 μg N2O-N kg−1. These effects coincided with an 84% increase in incorporation of residue 15N into the microaggregate fraction by A. caliginosa (p = 0.003) and an 85% increase in incorporation into the macroaggregate fraction by L. rubellus (p = 0.018). Cumulative CO2 fluxes were only significantly increased by earthworm activity (from 473.9 to 593.6 mg CO2-C kg−1 soil; p = 0.037) in the presence of L. rubellus when residue was applied on top. We conclude that earthworm-induced N2O emissions reflect earthworm feeding strategies: epigeic earthworms can increase N2O emissions when residue is applied on top; endogeic earthworms when residue is incorporated into the soil by humans (tillage) or by other earthworm species. The effects of residue placement and earthworm addition are accompanied by changes in aggregate and SOM turnover, possibly controlling carbon, nitrogen and oxygen availability and therefore denitrification. Our results contribute to understanding the important but intricate relations between (functional) soil biodiversity and the soil greenhouse gas balance. Further research should focus on elucidating the links between the observed changes in soil aggregation and controls on denitrification, including the microbial community.  相似文献   

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