Increased N2O Fluxes Research Articles

Nitrous oxide emissions from wetland soil amended with two types of cattle manure

Purpose The implications of increased applications of high quality cattle manure to agricultural systems in Africa on N2O emissions are still only partially understood. Methods A field experiment was carried out in a wetland in central Zimbabwe to determine the effects of cattle manure quality on emissions of N2O during the growing seasons of rape and tomato crops. The static chamber and gas chromatography techniques were used to capture and measure fluxes of N2O. Results The substitution of low N by high N manure significantly increased N2O fluxes and total N lost through N2O emission. Emissions of N2O increase with increasing content of N in applied manure. Conclusions Given that N2O in agricultural soil is produced predominantly through the microbial transformations of inorganic N, the potential of a soil to emit N2O increases with the increasing availability of N and consequently the N content in applied manure. The applications of lower rate of high and low N manures were followed by lower emissions of N2O, a result that is favorable to the objective of lowering the contribution of agricultural sources to the global greenhouse gas emissions. The loss of N in emissions of N2O expressed per unit mass of harvested dry matter yield decreases with increasing manure application, dry matter yield and N uptake. Improved agronomic practices for increased crop productivity can be used as a mitigation factor for reducing the contribution of agriculture in the global emissions of N2O.

The effect of renovation of long-term temperate grassland on N2O emissions and N leaching from contrasting soils

Renovation of long-term grassland is associated with a peak in soil organic N mineralisation which, coupled with diminished plant N uptake can lead to large gaseous and leaching N losses. This study reports on the effect of ploughing and subsequent N fertilisation on the N2O emissions and DON/NO3− leaching, and evaluates the impact of ploughing technique on the magnitude and profile of N losses. This study was carried out on isolated grassland lysimeters of three Irish soils representing contrasting drainage properties (well-drained Clonakilty, moderately-drained Elton and poorly-drained Rathangan). Lysimeters were manually ploughed simulating conventional (CT) and minimum tillage (MT) as two treatments. Renovation of grassland increased N2O flux to a maximum of 0.9kgN2O–Nha−1 from poorly-drained soil over four days after treatment. Although there was no difference between CT and MT in the post-ploughing period, the treatment influenced subsequent N2O after fertiliser applications. Fertilisation remained the major driver of N losses therefore reducing fertilisation rate post-planting to account for N mineralised through grassland renovation could reduce the losses in medium to longer term. Leaching was a significant loss pathway, with the cumulative drainage volume and N leached highly influenced by soil type. Overall, the total N losses (N2O+N leached) were lowest from poorly and moderately draining soil and highest for the well draining soil, reflecting the dominance of leaching on total N losses and the paramount importance of soil properties.

Comparison of net global warming potential between continuous flooding and midseason drainage in monsoon region paddy during rice cropping

Midseason drainage is regarded as a key practice to suppress methane (CH4) emission from paddy soil during rice cultivation, but it can increase carbon dioxide (CO2) and nitrous oxide (N2O) emissions. However, the influences of midseason drainage practice on the net global warming potential (GWP) and greenhouse gas intensity (GHGI) of rice cropping systems is not well documented in the East monsoon region. In this field study, the effect of a 30-day midseason drainage practice from the 28th day after transplanting (DAT) to the 57th DAT on the three major greenhouse gas (GHG) fluxes and yield properties were compared with those of a continuous flooding system during rice cultivation in 2011 and 2012. The impact of midseason drainage on changing three GHG emissions was compared using the GWP value and GHG intensity (GHGI). Midseason drainage significantly reduced the net GWP scale by 46–50% of the continuous flooding, mainly due to 50–53% reduction of seasonal CH4 fluxes. Midseason drainage significantly increased N2O flux by 20–37% over the conventional flooding, but the influence of N2O emission increase on the net GWP scale was negligible. Midseason drainage significantly decreased soil C sequestration capacity by around 60% of continuous flooding, and then increased net GWP by 0.25–0.32Mg CO2-eq.ha−1 during rice cultivation. There was no significant difference of rice yield between two irrigation systems, and then midseason drainage can reduce GHGI by 50–56% of the continuous flooding. In conclusion, the midseason drainage practice during rice cultivation could be very useful soil management strategy to reduce GHG emission impact from lowland rice fields without impacting rice productivity.

The effect of ultralow-dose antibiotics exposure on soil nitrate and N2O flux.

Exposure to sub-inhibitory concentrations of antibiotics has been shown to alter the metabolic activity of micro-organisms, but the impact on soil denitrification and N2O production has rarely been reported. In this study, incubation and column transport experiments were conducted on soils exposed to as many as four antibiotics in the ng·kg−1 range (several orders of magnitude below typical exposure rates) to evaluate the impact of ultralow dose exposure on net nitrate losses and soil N2O flux over time. Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others. Sulfamethoxazole in particular had a stimulatory effect at ultralow doses, an effect also evidenced by a near 17% increase in nitrate removal during column transport. Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses. The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.

Plant-mediated methane and nitrous oxide fluxes from a carex meadow in Poyang Lake during drawdown periods

Plants have been suggested to have significant effects on methane (CH4) and nitrous oxide (N2O) fluxes from littoral wetlands, but it remains unclear in subtropical lakes. We conducted in situ measurement of CH4 and N2O fluxes for two years. To distinguish between the effects of shoots and roots, three treatments (i.e., intact plants as control, shoot clipping, and root exclusion) were used. Effects of plant biomass, temperature, and soil moisture on CH4 and N2O fluxes were analyzed. The mean ecosystem CH4 emission rate was 36 μg CH4 m−2 h−1 for drying periods, but 8219 μg CH4 m−2 h−1 for drying-wetting transition periods. CH4 fluxes were positively correlated with below-ground and total biomass, but not with above-ground biomass. Clipping did not significantly alter CH4 flux rate, but root exclusion decreased the CH4 flux by 116 % as compared to the control. N2O emissions were similar for both the drying and drying-wetting transition periods, with a mean rate of 20 μg N2O m−2 h−1. Both clipping and root exclusion significantly increased N2O fluxes as compared to the control. There was no significant correlation between CH4 and N2O fluxes. Roots dominated plant-mediated enhancement in CH4 fluxes, but played almost an equal role as shoots in plant-regulated suppression on N2O fluxes in this Carex meadow during drawdown periods.

Nitrous oxide emissions from an agro-pastoral ecotone of northern China depending on land uses

Overgrazing and intensive farming have led to severe land degradation in the past half century in the agro-pastoral ecotone of northern China. Currently, complete and periodical exclusions of grazing are commonly adopted for the restoration of these degraded grasslands. However, little is known about the effects of such land uses on nitrous oxide (N2O) emission in this region. Using static chamber technique, we quantified annual N2O emissions (from May 2012 to September 2013) from four land uses: summer-grazed grassland (SG), winter-grazed grassland (WG), ungrazed grassland since 1997 (UG) and oat cropland (OC). N2O emissions occurred mainly after farmyard manure fertilization and during spring thaw periods. Annual N2O fluxes from the SG, WG, UG and OC were 0.19, 0.15, 0.43 and 0.98kg Nha−1yr−1, respectively. The spring–thaw N2O emissions from UG and OC dominated the annual emission and accounted for 70% and 65% of the annual fluxes, respectively. In contrast, the contributions of spring thaw fluxes to total annual N2O emissions for SG and WG were only 32%. N2O fluxes during spring thaw season were positively related to soil NH4++ NO3− content accounting for 80% of N2O flux variability across all land uses. Land use conversion from the native grassland to cropland increased N2O flux both during growing and spring thaw seasons due to farmyard manure application. Instead, grazing has the potential to decrease annual N2O losses mainly through reducing spring–thaw N2O emissions.

Short-term drought response of N2O and CO2 emissions from mesic agricultural soils in the US Midwest

Climate change is causing the intensification of both rainfall and droughts in temperate climatic zones, which will affect soil drying and rewetting cycles and associated processes such as soil greenhouse gas (GHG) fluxes. We investigated the effect of soil rewetting following a prolonged natural drought on soil emissions of nitrous oxide (N2O) and carbon dioxide (CO2) in an agricultural field recently converted from 22 years in the USDA Conservation Reserve Program (CRP). We compared responses to those in a similarly managed field with no CRP history and to a CRP reference field. We additionally compared soil GHG emissions measured by static flux chambers with off-site laboratory analysis versus in situ analysis using a portable quantum cascade laser and infrared gas analyzer. Under growing season drought conditions, average soil N2O fluxes ranged between 0.2 and 0.8μgNm−2min−1 and were higher in former CRP soils and unaffected by nitrogen (N) fertilization. After 18 days of drought, a 50mm rewetting event increased N2O fluxes by 34 and 24 fold respectively in the former CRP and non-CRP soils. Average soil CO2 emissions during drought ranged from 1.1 to 3.1mgCm−2min−1 for the three systems. CO2 emissions increased ∼2 fold after the rewetting and were higher from soils with higher C contents. Observations are consistent with the hypothesis that during drought soil N2O emissions are controlled by available C and following rewetting additionally influenced by N availability, whereas soil CO2 emissions are independent of short-term N availability. Finally, soil GHG emissions estimated by off-site and in situ methods were statistically identical.

Short-term effects of biogas digestate and cattle slurry application on greenhouse gas emissions affected by N availability from grasslands on drained fen peatlands and associated organic soils

Abstract. A change in German energy policy has resulted in a strong increase in the number of biogas plants in Germany. As a consequence, huge amounts of nutrient-rich residues, the by-products of the fermentative process, are used as organic fertilizers. Drained peatlands are increasingly used to satisfy the huge demand for fermentative substrates (e.g., energy crops, grass silage) and the digestate is returned to the peatlands. However, drained organic soils are considered as hot spots for nitrous oxide (N2O) emissions and organic fertilization is additionally known to increase N2O emissions from managed grasslands. Our study addressed the questions (a) to what extent biogas digestate and cattle slurry application increase N2O and methane (CH4) fluxes as well as the mineral nitrogen use efficiency (NUEmin) and grass yield, and (b) how different soil organic matter contents (SOMs) and nitrogen contents promote the production of N2O. In addition NH3 volatilization was determined at one application event to obtain first clues with respect to the effects of soil and fertilizer types. The study was conducted at two sites within a grassland parcel, which differed in their soil organic carbon (SOC) and N contents. At each site (named Corg-medium and Corg-high) three plots were established: one was fertilized five times with biogas digestate, one with cattle slurry, and the third served as control plot. On each plot, fluxes of N2O and CH4 were measured on three replicates over 2 years using the closed chamber method. For NH3 measurements we used the calibrated dynamic chamber method. On an annual basis, the application of biogas digestate significantly enhanced the N2O fluxes compared to the application of cattle slurry and additionally increased the plant N-uptake and NUEmin. Furthermore, N2O fluxes from the Corg-high treatments significantly exceeded N2O fluxes from the Corg-medium treatments. Annual cumulative emissions ranged from 0.91 ± 0.49 to 3.14 ± 0.91 kg N ha−1 yr−1. Significantly different CH4 fluxes between the investigated treatments or the different soil types were not observed. Cumulative annual CH4 exchange rates varied between −0.21 ± 0.19 and −1.06 ± 0.46 kg C ha−1 yr−1. Significantly higher NH3 losses, NUEmin and grass yields from treatments fertilized with biogas digestate compared to those fertilized with cattle slurry were observed. The total NH3 losses following the splash plate application were 18.17 kg N ha−1 for the digestate treatments and 3.48 kg N ha−1 for the slurry treatments (36 and 15% of applied NH4+–N). The observed linear increase of 16 days' cumulative N2O–N exchange or annual N2O emissions, with mean groundwater level and ammonium application rate, reveals the importance of site-adapted N fertilization and the avoidance of N surpluses in Corg-rich grasslands.

Methane, carbon dioxide and nitrous oxide fluxes in soil profile under a winter wheat-summer maize rotation in the North China Plain.

The production and consumption of the greenhouse gases (GHGs) methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) in soil profile are poorly understood. This work sought to quantify the GHG production and consumption at seven depths (0–30, 30–60, 60–90, 90–150, 150–200, 200–250 and 250–300 cm) in a long-term field experiment with a winter wheat-summer maize rotation system, and four N application rates (0; 200; 400 and 600 kg N ha−1 year−1) in the North China Plain.The gas samples were taken twice a week and analyzed by gas chromatography. GHG production and consumption in soil layers were inferred using Fick’s law. Results showed nitrogen application significantly increased N2O fluxes in soil down to 90 cm but did not affect CH4 and CO2 fluxes. Soil moisture played an important role in soil profile GHG fluxes; both CH4 consumption and CO2 fluxes in and from soil tended to decrease with increasing soil water filled pore space (WFPS). The top 0–60 cm of soil was a sink of atmospheric CH4, and a source of both CO2 and N2O, more than 90% of the annual cumulative GHG fluxes originated at depths shallower than 90 cm; the subsoil (>90 cm) was not a major source or sink of GHG, rather it acted as a ‘reservoir’. This study provides quantitative evidence for the production and consumption of CH4, CO2 and N2O in the soil profile.

Nitrous oxide emissions from soil due to urine deposition by grazing cattle in Brazil

Urine deposition to the soil can result in nitrous oxide emissions through the microbial processes of nitrification and denitrification. The objective of this experiment was to estimate N2O emissions from urine depositions to grassland during summer in Southeast Brazil. A field experiment was conducted in which N2O emissions were measured from known volumes of urine applied to the soil, using the static chamber method. Measurements continued for one month after application. Application of urine to soil increased N2O fluxes compared to those from the control site. There were two significant N2O emission peaks for the urine treatment at around the 3rd and 13th days after application, the first in response to the urine application and the second most likely in response to a rainfall event. The N2O emissions accounted for 0.2% of the applied urine N. These represent the first data relating to emissions from urine depositions by grazing cattle in Brazil. Further measurements across a range of soil and weather conditions in Brazil are required to develop national and regional specific emission factors for inventory development.

Effects of invasion of Spartina alterniflora and exogenous N deposition on N2O emissions in a coastal salt marsh

Vegetation alteration and nitrogen inputs (via run-off, atmospheric deposition, and wastewater) as a result of anthropogenic activities strongly affected the emission of N2O from coastal marshes. To gain insight into impacts of the invasion of Spartina alterniflora and N deposition on N2O fluxes, mesocosms experiments were conducted to measure N2O emissions from marshes vegetated with S. alterniflora and a native Phragmites australis, with or without exogenous N at the rates of 2.7gNm−2, respectively. Mean N2O fluxes during the growing season in S. alterniflora mesocosms without N addition was 9.36μgm−2h−1, significantly higher than 6.79μgm−2h−1 in P. australis mesocosms. The stimulatory effects could be attributed to higher plant biomass of S. alterniflora providing more labile organic C to the rhizosphere for nitrobacteria and denitrifying bacteria, and to more oxygen transported to the rhizosphere facilitating coupled nitrification and denitrification. N deposition increased N2O fluxes in S. alterniflora and P. australis mesocosms by 13.5% and 48.2%, respectively, suggesting that exogenous N significantly promoted N2O emissions from coastal marshes. Compared to mesocosms without N fertilization, the increase rate of total N accumulation and above-ground biomass under N addition were 63.1% and 28.0% in the S. alterniflora mesocosms, whereas 26.7% and 15.3% in the P. australis mesocosms, respectively. This meant stronger competition of S. alterniflora with soil microorganisms for the available N, leading to lower increment of N2O fluxes in the S. alterniflora mesocosms under N addition. Thus, it could be concluded that both the invasion of S. alterniflora and atmospheric N deposition dramatically stimulated N2O emissions from coastal marshes, and that N2O fluxes in the S. alterniflora marshes weakly responded to N addition.

Seasonal variation of N2O emissions in France inferred from atmospheric N2O and 222Rn measurements

Nitrous oxide (N2O) concentrations and 222Rn activities are measured semi‐continuously at three stations in France: Gif‐sur‐Yvette (a semi‐urban station near Paris), Trainou tower (a rural station) and Puy‐de‐Dôme (a mountain site). From 2002 to 2011, we have found a mean rate of N2O increase of 0.7 pbb a−1. The analysis of the mean diurnal N2O and 222Rn cycles shows maximum variabilities at the semi‐urban site of Gif‐sur‐Yvette (0.96 ppb for N2O and 2 Bq m−3 for 222Rn) compared to the rural site of Trainou tower (0.32 ppb for N2O and 1.3 Bq m−3 for 222Rn). The use of 222Rn as a tracer for vertical mixing and atmospheric transport, combined with the semi‐continuous N2O measurements, allows estimation of N2O emissions by applying the Radon‐Tracer‐Method. Mean N2O emissions values between 0.34 ± 0.12 and 0.51 ± 0.18 g(N2O) m−2 a−1 and 0.52 ± 0.18 g(N2O) m−2 a−1were estimated in the catchment area of Gif‐sur‐Yvette and Trainou, respectively. The mean annual N2O fluxes at Gif‐sur‐Yvette station correlate well with annual precipitation. A 25% increase in precipitation corresponds to a 32% increase in N2O flux. The N2O fluxes calculated with the Radon‐Tracer‐Method show a seasonal cycle, which indicates a strong contribution from the agricultural source, with the application of fertilizers in the early spring inducing a strong increase in N2O emissions. Finally, the results of the Radon‐Tracer‐Method agree well with the national and global emission inventories, accounting for the uncertainties of both methods.

Biochar and Earthworm Effects on Soil Nitrous Oxide and Carbon Dioxide Emissions

Biochar is the product of pyrolysis produced from feedstock of biological origin. Due to its aromatic structure and long residence time, biochar may enable long-term carbon sequestration. At the same time, biochar has the potential to improve soil fertility and reduce greenhouse gas (GHG) emissions from soils. However, the effect of biochar application on GHG fluxes from soil must be investigated before recommendations for field-scale biochar application can be made. A laboratory experiment was designed to measure carbon dioxide (CO) and nitrous oxide (NO) emissions from two Irish soils with the addition of two different biochars, along with endogeic (soil-feeding) earthworms and ammonium sulfate, to assist in the overall evaluation of biochar as a GHG-mitigation tool. A significant reduction in NO emissions was observed from both low and high organic matter soils when biochars were applied at rates of 4% (w/w). Earthworms significantly increased NO fluxes in low and high organic matter soils more than 12.6-fold and 7.8-fold, respectively. The large increase in soil NO emissions in the presence of earthworms was significantly reduced by the addition of both biochars. biochar reduced the large earthworm emissions by 91 and 95% in the low organic matter soil and by 56 and 61% in the high organic matter soil (with and without N fertilization), respectively. With peanut hull biochar, the earthworm emissions reduction was 80 and 70% in the low organic matter soil, and only 20 and 10% in the high organic matter soil (with and without N fertilization), respectively. In high organic matter soil, both biochars reduced CO efflux in the absence of earthworms. However, soil CO efflux increased when peanut hull biochar was applied in the presence of earthworms. This study demonstrated that biochar can potentially reduce earthworm-enhanced soil NO and CO emissions. Hence, biochar application combined with endogeic earthworm activity did not reveal unknown risks for GHG emissions at the pot scale, but field-scale experiments are required to confirm this.

What are the impacts of grazing and cutting events on the N2O dynamics in humid temperate grassland?

Atmospheric concentrations of nitrous oxide (N2O) have been increasing over the last century with much of this increase from agricultural soils, fertilized with nitrogen. To understand the N2O emissions from terrestrial ecosystems (e.g. grassland soils) it is necessary to understand the processes leading to N2O production. From February to August in 2010, we conducted a field study to measure the N2O fluxes using the chamber technique, at a grazed and cut grassland site in South West Ireland. The objectives of the study were: 1) to understand the temporal variation of the N2O fluxes during the spring and summer periods; 2) to examine the separate effects of grazing and cutting events on N2O fluxes; and 3) to examine the relationship of soil ammonium (NH4+−N) and soil nitrate (NO3--N) with N2O fluxes. We found the highest peak of daily N2O flux occurred at the start of spring; however the total of summer fluxes (June, July and August) of 1.81±0.7kg N2O–Nha−1 were higher than those of the spring (March, April and May) fluxes of 1.51±0.6kg N2O–Nha−1. The soil NH4+−N concentration was higher than the soil NO3–N concentration over the study period and elevated N2O fluxes coincided with elevated soil NH4–N concentrations. There were two short (2day duration) cattle grazing events; one on April 26/27 and the second on June 27/28. There were two grass cutting (for silage) events: on May 30 and on August 4. After the two grazing and two cutting events, the N2O fluxes increased markedly. After both grazing events, there was an immediate step increase of ~200μg N2O–Nm−2h−1, after which the fluxes decreased over the next few weeks. After both cutting events, there was a gradual increase in N2O fluxes over the next several weeks. We found that the N2O flux increases post grazing, were due to grazing only, since the other variables (soil temperature, WFPS, N application) did not change. However, the flux increases post cutting could not ascribed to cutting only, as other flux favouring variables of: changes in soil temperature and WFPS also occurred at this time. The N2O fluxes correlated better with soil NH4–N concentration (r2=0.73 (p=<0.05)) than with NO3--N (r2=0.25 (p=not significant)). The occurrence of elevated NH4–N in conjunction with elevated WFPS, frequently in the range of 50–60% suggests that nitrification rather than denitrification was likely the dominant process involved in the production of N2O at this site.

Spatial and seasonal variations of atmospheric N2O and CO2 fluxes from a subtropical mangrove swamp and their relationships with soil characteristics

Marine ecosystems are a known net source of greenhouse gases emissions but the atmospheric gas fluxes, particularly from the mangrove swamps occupying inter-tidal zones, are characterized poorly. Spatial and seasonal fluxes of nitrous oxide (N2O) and carbon dioxide (CO2) from soil in Mai Po mangrove swamp in Hong Kong, South China and their relationships with soil characteristics were investigated. The N2O fluxes averaged from 32.1 to 533.7μgm−2h−1 and the CO2 fluxes were between 10.6 and 1374.1mgm−2h−1. Both N2O and CO2 fluxes in this swamp showed large spatial and seasonal variations. The fluxes were higher at the landward site than the foreshore bare mudflat, and higher fluxes were recorded in warm, rather than cold, seasons. The landward site had the highest content of soil organic carbon (OC), total Kjeldahl nitrogen (TKN), nitrate (NO3−–N) and total phosphorus (TP), while the bare mudflat had the highest ammonium nitrogen (NH4+–N) concentration and soil denitrification potential activity. The N2O flux was related, positively, to CO2 flux. Soil NO3−–N and TP increased N2O flux, while soil OC and TP concentrations contributed to the CO2 flux. The results indicated that the Mai Po mangrove swamp emitted significant amounts of greenhouse gases, and the N2O emission was probably due to soil denitrifcation.

Nitrous oxide emission from highland winter wheat field after long-term fertilization

Abstract. Nitrous oxide (N2O) is an important greenhouse gas. N2O emissions from soils vary with fertilization and cropping practices. The response of N2O emission to fertilization of agricultural soils plays an important role in global N2O emission. The objective of this study was to assess the seasonal pattern of N2O fluxes and the annual N2O emissions from a rain-fed winter wheat (Triticum aestivum L.) field in the Loess Plateau of China. A static flux chamber method was used to measure soil N2O fluxes from 2006 to 2008. The study included 5 treatments with 3 replications in a randomized complete block design. Prior to initiating N2O measurements the treatments had received the same fertilization for 22 years. The fertilizer treatments were unfertilized control (CK), manure (M), nitrogen (N), nitrogen + phosphorus (NP), and nitrogen + phosphorus + manure (NPM). Soil N2O fluxes in the highland winter wheat field were highly variable temporally and thus were fertilization dependent. The highest fluxes occurred in the warmer and wetter seasons. Relative to CK, m slightly increased N2O flux while N, NP and NPM treatments significantly increased N2O fluxes. The fertilizer induced increase in N2O flux occurred mainly in the first 30 days after fertilization. The increases were smaller in the relatively warm and dry year than in the cold and wet year. Combining phosphorous and/or manure with mineral N fertilizer partly offset the nitrogen fertilizer induced increase in N2O flux. N2O fluxes at the seedling stage were mainly controlled by nitrogen fertilization, while fluxes at other plant growth stages were influenced by plant and environmental conditions. The cumulative N2O emissions were always higher in the fertilized treatments than in the non-fertilized treatment (CK). Mineral and manure nitrogen fertilizer enhanced N2O emissions in wetter years compared to dryer years. Phosphorous fertilizer offset 0.50 and 1.26 kg N2O-N ha−1 increases, while manure + phosphorous offset 0.43 and 1.04 kg N2O-N ha−1 increases by N fertilizer for the two observation years. Our results suggested that the contribution of single N fertilizer on N2O emission was larger than that of NP and NPM and that manure and phosphorous had important roles in offsetting mineral N fertilizer induced N2O emissions. Relative to agricultural production and N2O emission, manure fertilization (M) should be recommended while single N fertilization (N) should be avoided for the highland winter wheat due to the higher biomass and grain yield and lower N2O flux and annual emission in m than in N.

Do plant species influence soil CO2 and N2O fluxes in a diverse tropical forest?

To test whether plant species influence greenhouse gas production in diverse ecosystems, we measured wet season soil CO2 and N2O fluxes close to ∼300 large (&gt;35 cm in diameter at breast height (DBH)) trees of 15 species at three clay‐rich forest sites in central Amazonia. We found that soil CO2 fluxes were 38% higher near large trees than at control sites &gt;10 m away from any tree (P &lt; 0.0001). After adjusting for large tree presence, a multiple linear regression of soil temperature, bulk density, and liana DBH explained 19% of remaining CO2 flux variability. Soil N2O fluxes adjacent to Caryocar villosum, Lecythis lurida, Schefflera morototoni, and Manilkara huberi were 84%−196% greater than Erisma uncinatum and Vochysia maxima, both Vochysiaceae. Tree species identity was the most important explanatory factor for N2O fluxes, accounting for more than twice the N2O flux variability as all other factors combined. Two observations suggest a mechanism for this finding: (1) sugar addition increased N2O fluxes near C. villosum twice as much (P &lt; 0.05) as near Vochysiaceae and (2) species mean N2O fluxes were strongly negatively correlated with tree growth rate (P = 0.002). These observations imply that through enhanced belowground carbon allocation liana and tree species can stimulate soil CO2 and N2O fluxes (by enhancing denitrification when carbon limits microbial metabolism). Alternatively, low N2O fluxes potentially result from strong competition of tree species with microbes for nutrients. Species‐specific patterns in CO2 and N2O fluxes demonstrate that plant species can influence soil biogeochemical processes in a diverse tropical forest.

Greenhouse Gas Emissions Measured 24 Hours after Surface and Subsurface Application of Different Manure Types

Greenhouse gas (GHG) emissions from agricultural activities such as land application of livestock manure cannot be ignored when assessing overall emissions from anthropogenic sources. The magnitude of these emissions is influenced by management practices such as manure placement during land application. The objective of this work was to compare GHG fluxes resulting from the surface and subsurface application of liquid and solid manure. For this comparison, all measurements were made 24 h after application using a static chamber method. The results showed that subsurface application significantly increased carbon dioxide equivalent (CO2-e) fluxes for both solid and liquid manure. The overall CO2-e fluxes from injected treatments were 3.2 times greater than CO2-e fluxes from the surface-applied plots, mainly due to a pronounced increase in N2O fluxes, which was likely caused by increased denitrification rates. The CO2-e fluxes from liquid manure applications were also greater than the CO2-e fluxes from solid manure applications, probably due to greater levels of ammonium available for nitrification and subsequent denitrification. Methane (CH4) fluxes were negligible for all manure types and application methods 24 h after application. For this particular study, measured specific fluxes (total flux per kg N applied) remained relatively constant with application rate, indicating that GHG emissions from manure applications were approximately proportional to the amount of manure applied.

Effects of soil moisture, temperature, and nitrogen fertilization on soil respiration and nitrous oxide emission during maize growth period in northeast China

To evaluate the response of soil respiration and nitrous oxide (N2O) emission to soil moisture, temperature and nitrogen fertilization, and to estimate the contribution of soil and rhizosphere to total soil carbon dioxide (CO2) and N2O emissions, a field experiment was conducted in the Sanjiang Mire Wetland Experimental Station, Chinese Academy of Sciences, in the northeast of China. The experiment included four treatments: bare soil fertilized with 150 kg N ha−1 yr−1 (CK), and maize-cropped soils amended with 0 (N0), 150 (N150), and 250 (N250) kg N ha−1 yr−1. The cumulative soil CO2 emission in the CK, N0, N150, and N250 treatments was estimated to be 698, 863, 962, and 854 g CO 2 C m−2, respectively. The seasonal soil CO2 fluxes were significantly affected by soil temperature, with a Q 10 value between 1.99 and 2.47. Analysis of the stepwise regression indicated that the CO2 flux can be quantitatively described by a linear combination of soil moisture content and soil temperature 5 cm below ground. Approximately 70, 58, 60, and 44% of the variability in CO2 flux can be explained by these two parameters, in CK, N0, N150, and N250, respectively. Nitrogen fertilization with 150 kg N ha−1 yr−1 increased CO2 fluxes by 14.5% compared with soils fertilized with 0 kg N ha−1 yr−1. However, in the soil fertilized with 250 kg N ha−1 yr−1, high N fertilization suppressed soil respiration. There was an exponential relationship between soil temperature 5 cm below ground and N2O flux, with a Q 10 value of 1.30–2.91. Mean cumulative soil N2O emissions during the maize-growing season in the CK, N0, N150, and N250 treatments were estimated to be 86, 44, 200, and 484 mg N2O-N m−2, respectively. In contrast to the maize planting, soil fertilized with 150 kg N ha−1 yr−1 and with 250 kg N ha−1 yr−1 increased N2O fluxes by 354 and 1000%, compared with soils fertilized with 0 kg N ha−1 yr−1, respectively. Soil respiration and N2O fluxes measurement using the root-exclusion technique indicated that the rhizosphere of the maize could be the dominant habitat of soil respiration and N2O formation.

Nitrous oxide emissions from an Uruguayan argiudoll under different tillage and rotation treatments

Lack of local data limits estimation of nitrous oxide (N2O) emissions from different land uses of Uruguay. As a first step towards obtaining local information, we measured from August 2003 to September 2004 N2O fluxes from a rotation-by-tillage experiment established in 1993 and from a nearby natural pasture (NP). Nitrous oxide emission rates were measured on an event-driven basis by using the closed chamber technique with six replicates per treatment. Fluxes varied considerably with time and the higher rates (more than 30 g N ha−1 day−1) were generally associated with periods of high soil water content, high temperature, and/or decreasing soil nitrate. We could not identify, however, any statistically significant correlation between flux and these variables. Throughout the evaluation period, fluxes from crops or cultivated pastures tended to be higher than those from NP, but the effects of tillage (no-till and conventional tillage) or rotation (continuous tillage and rotation with pasture) were not consistent. The application of 112 kg N ha−1 to barley did not increase N2O fluxes probably due to a high fertilizer use efficiency caused by the recommended three-split application and by the lack of rain during this period. The annual cumulative flows of different treatments compared well with those estimated using IPCC methodology, but the high spatial and temporal variability observed in this one-year study indicate that further research is needed to obtain reliable data on N2O fluxes from agricultural soils of Uruguay.