Annual N2O Emissions Research Articles

Temporal Patterns of N2O Fluxes From a Rainfed Maize Field in Northeast China

Rainfed agriculture is one of the most common farming practices in the world and is vulnerable to global climate change. However, only limited studies have been conducted on rainfed agriculture, mainly using low-frequency manual techniques, which caused large uncertainties in estimating annual N2O emissions. In this study, we used a fully automated system to continuously measure soil N2O emissions for two years (April 2017 to March 2019) in a typical rainfed maize field in Northeast China. The annual N2O emissions were 2.8 kg N ha−1 in year 1 (April 2017 to March 2018) and 1.8 kg N ha−1 in year 2 (April 2018 to March 2019), accounting for 1.9 and 1.2% of the nitrogen fertilizer applied, respectively. The inter-annual variability was mainly due to different weather conditions encountered in years 1 and 2. A severe drought in year 1 reduced plant N uptake, leaving high mineral N in the soil, and the following moderate rainfalls promoted a large amount of N2O emissions. The seasonal pattern of N2O fluxes was mainly controlled by soil temperature and soil nitrate concentration. Both soil moisture and the molar ratio of NO/N2O indicate that N2O and NO were mainly derived from nitrification, resulting in a significant positive correlation between N2O and NO flux in the intra-rows (where nitrogen fertilizer was applied). Moreover, we observed that the N2O emissions during the freeze–thaw periods were negligible in this region for rainfed agriculture. Our long-term and high-resolution measurements of soil N2O emissions suggest that sampling between LST 9:00 and 10:00 is the best empirical sampling time for the intermittent manual measurements.

Spatial Evaluation of Greenhouse Gas Fluxes in a Sasa (Dwarf Bamboo) Invaded Wetland Ecosystem in Central Hokkaido, Japan

To evaluate the effect of vegetation change on greenhouse gas (GHG) budget from a wetland ecosystem, the CO2, CH4 and N2O budgets from whole area (21.5 ha) of the Bibai Wetland, where dwarf bamboo (Sasa) or Ilex has invaded into original Sphagnum dominated vegetation, located in Hokkaido, Japan were estimated. The original Sphagnum-dominated vegetation was changed from a sink to a source of CO2 by invasion of short-Sasa (50 cm > height), while the invasion of tall-Sasa (50 cm < height < 150 cm) or Ilex increased CO2 uptake. Annual CH4 emission was decreased by the invasion of Sasa or Ilex. The annual N2O emission was slightly increased by invasion of Ilex only. These GHG budgets were correlated with the environmental factors related to the water table depth. The distribution of vegetation and environmental factors was estimated from satellite image bands, and the GHG budget of the entire wetland was estimated. The whole wetland area was considered to be a sink for GHG (−113 Mg CO2-eq y−1) and CO2 uptake by tall-Sasa occupied 71% of the GHG budget. The vegetation change due to the lowering of the water table depth currently increases the rate of carbon accumulation in the ecosystem by about 5 times.

Model comparison and quantification of nitrous oxide emission and mitigation potential from maize and wheat fields at a global scale

Maize and wheat are major cereals that contribute two-thirds of the food energy intake globally. The two crops consume about 35% of the nitrogen (N) fertilizer used in agriculture and thereby contribute to fertilizer-induced nitrous oxide (N2O) emissions. Thus, estimation of spatially disaggregated N2O emissions from maize and wheat fields on a global scale could be useful for identifying emission and mitigation hotspots. It could also be needed for prioritizing mitigation options consistent with location-specific production and environmental goals. N2O emission from four models (CCAFS-MOT, IPCC Tier-I, IPCC Tier-II and Tropical N2O) using a standard gridded dataset from global maize and wheat fields were compared and their performance evaluated using measured N2O emission data points (777 globally distributed datapoints). The models were used to quantify spatially disaggregated N2O emission and mitigation potential from maize and wheat fields globally and the values were compared. Although the models differed in their performance of capturing the level of measured N2O emissions, they produced similar spatial patterns of annual N2O emissions from maize and wheat fields. Irrespective of the models, predicted N2O emissions per hectare were higher in some countries in East and South Asia, North America, and Western Europe, driven mainly by higher N application rates. The study indicated a substantial N2O abatement potential if application of excess N in the maize and wheat systems is reduced without compromising the yield of the crops through technological and crop management innovations. N2O mitigation potential is higher in those countries and regions where N application rates and current N2O emissions are already high. The estimated mitigation potentials are useful for hotspot countries to target fertilizer and crop management as one of the mitigation options in their Nationally Determined Contributions (NDCs) to the United Nations Framework Convention on Climate Change (UNFCCC).

Nitrification inhibitors reduce N2O emissions induced by application of biogas digestate to oilseed rape

Winter oilseed rape (WOSR) is the major oil crop cultivated in Europe and the most important feedstock for biodiesel. Up to 90% of the greenhouse gas (GHG) emissions from biodiesel production can occur during oilseed rape cultivation. Therefore, mitigation strategies are required and need to focus on direct nitrous oxide (N2O) emission as one of the largest GHG contributors in biodiesel production. Earlier studies show that nitrification inhibitors (NIs) can reduce N2O emissions derived from N-fertilization. Since information on the effect of biogas digestates with or without NIs on N2O emissions from WOSR fields is scarce, the aim of this study was to evaluate their effects on N2O emissions, mineral N dynamics, and oil yield in WOSR production fertilized with digestate. The study was conducted at five sites across Germany over three years resulting in 15 full site-years data sets. Across all sites and years, N2O emission from WOSR fertilized with biogas digestate (180 kg NH4+-N ha−1yr−1) ranged between 0.2 and 3.5 kg N2O–N ha−1 yr−1. Due to the reduction of the nitrate concentrations following digestate application, application of NI significantly reduced annual N2O emission by 36%. Our results demonstrate that NI can be an effective measure for reducing N2O emissions from digestate application, but its effectiveness depends on soil and weather conditions, and ultimately on the site-specific potential for N2O production and release. There was no effect of NI application on grain and oil yield.

Impact of climate change on greenhouse gas emissions and water balance in a dryland-cropping region with variable precipitation

Wheat covers a significant fraction of the US Pacific Northwest (PNW) dryland agriculture. Past studies have suggested that management practices can differentially affect productivity and emission of greenhouse gases (GHGs) across the different agro-ecological Zones (AEZs) in PNW. In this study we used CropSyst, a biophysically-based cropping systems model that simulates crop processes and water and nitrogen cycles, with the purpose of evaluating relevant scenarios and contributing analyses to inform adaptation and mitigation strategies aimed at reducing and managing the risks of climate change. We compared the baseline historical period of 1980–2010 with three future periods: 2015–2045 (2030s), 2035–2065 (2050s), and 2055–2085 (2070s). The uncertainty of the future climate was captured using 12 general circulation models (GCMs) forced with two representative carbon dioxide concentration pathways (RCP 4.5 and 8.5). The study region was divided into three AEZs: crop-fallow (CF), continuous cropping to fallow transition (CCF), and continuous cropping (CC). The results indicated that areas with higher precipitation, N fertilization, and mineralization produced more N2O emissions during both baseline and future periods. The average annual N2O emission during the baseline period was between 1.8 and 4.1 kg ha−1 depending on AEZ. The overall N2O emission showed decreasing future trends from 2030s to 2070s which resulted from a higher proportion of N used by crops. From 2015 to 2085 under RCP 4.5, the average N2O emission was between 1.8 and 4.4 kg ha−1 year−1. They are slightly higher under RCP 8.5 since it is a warmer scenario. The soil organic carbon (SOC) content decreased during the baseline period while SOC did not reach equilibrium with the cropping systems considered in the study. SOC decreased during the future periods as well, with rate of change ranging from −146 to −352 kg ha−1year−1 depending on AEZ and RCP. Warming increased SOC oxidation in future scenarios, but after an initial increase of SOC losses during the 2030s period, the rate of SOC losses decreased in the 2050s, and more so in the 2070s as SOC and carbon input reached equilibrium with losses. Higher carbon input resulted from higher biomass production under elevated CO2 scenarios. The total GHG emissions were 1.95, 3.16 and 4.84 Mg CO2-equivalent ha−1year−1 under RCP 4.5, and 1.99, 3.43 and 5.49 Mg CO2-equivalent ha−1year−1 under RCP 8.5 during 2070s in CF, CCF and CC respectively, with N2O accounting for about 81% of total GHG emissions.

Contribution of crop residue, soil, and fertilizer nitrogen to nitrous oxide emissions varies with long-term crop rotation and tillage

Agriculture is an important contributor to N2O emissions – a potent greenhouse gas – with high peaks occurring when soil mineral nitrogen (N) is high (e.g., after mineralization of organic N and N fertilizer application). Nitrogen dynamics in soil and consequently N2O emissions are affected by crop and soil management practices (e.g., crop rotation and tillage), an effect mostly assessed in the literature through comparisons of total N2O emission. Hence, information is scarce on the effect of these management practices on specific N sources affecting N2O emissions (i.e., N fertilizer, soil, above and belowground crop residues) – a knowledge gap explored in this study with the use of 15N tracers. The isotope approach enabled refinement on global N2O budget by directly determining the emission factors (EF) of above and belowground crop residues that vary in chemical composition and comparison with default EF values (e.g., IPCC EFs). Our experiment was conducted over the full-cycle of long-term crop rotations to (i) compare N2O totals and intensity, under no-tillage and conventional tillage, simple and diverse rotation; (ii) partition total N2O emissions into soil, N fertilizer, above and belowground crop residue N sources; (iii) compare the 12-month EF of crop residue against the default values proposed by IPCC (2019). For the tillage effect, annual N2O emissions were from 1.2- to 2.0-times higher on CT than NT soil due to 40% increased soil N derived N2O emission in CT. The diversified crop rotation emitted 1.3-times higher N2O than the simple rotation over the full-cycle of the rotations, but the effect was due to differences in N fertilizer rate between the rotations since emissions were equivalent when scaled by N rate. Finally, our results suggested that default IPCC EF are overestimated for crop residues under CT and NT, simple and diverse rotations as measured EFs never surpassed 0.1%.

Contribution of Different Quantities of Leaf Litter to Nitrous Oxide Emission from a Temperate Deciduous Forest

Leaf litter cover on forest floors regulates the nitrogen dynamics in soil and affects soil-atmospheric exchange of nitrous oxide (N2O). “The effect of ‘different mass’ of leaf litter on N2O” emission is, however, unclear. In this study, we measured N2O emission from variable leaf litter applications in (IN) and on (ON) soil such as 0 (control), 370, 730, and 1,009 g dry weight m−2. Closed chambers were installed at an experimental site in Korea to measure N2O emission from the soil. Average N2O emission was decreased by 1.15 µg N2O-N m−2 h−1 with leaf litter removal in ON-0 and increased by 2.38 µg N2O-N m−2 h−1 with soil tilling in IN-0 treatment. Average N2O emission was increased by 3.75 µg N2O-N m−2 h−1 and 3.06 µg N2O-N m−2 h−1 with increasing leaf litter from 370 to 730 g m−2 in both ON and IN treatments, respectively. N2O emission was decreased by 4.04 µg N2O-N m−2 h−1 and 1.51 µg N2O-N m−2 h−1 in ON-1009 and IN-1009 treatments as compare to ON-730 and IN-730 treatments, respectively due to high soil water content and carbon to nitrogen ratio, respectively. Average annual N2O emission in different types of temperate forests around the World ranged between 13.5 to 21,10.0 g N2O-N ha−1 y−1, while 1,007.4 g N2O-N ha−1 y−1 was observed in this study. Soil temperature exhibited a weak correlation with N2O emission in all treatments of both IN and ON treatments. Average N2O emission in IN-0, IN-370, IN-730, and IN-1009 was 45.0, 53.0, 27.0, and 86.0% higher than ON-0, ON-370, ON-730, and ON-1009 treatments, respectively. Results of N2O emission from this study can be used to estimate N2O emission from forest soils in Korea and extended worldwide to countries with similar soil and climatic conditions.

Reducing N2O emissions with enhanced efficiency nitrogen fertilizers (EENFs) in a high-yielding spring maize system.

Enhanced efficiency nitrogen fertilizers (EENFs), including nitrification inhibitors (NIs) and slow-release fertilizer (SRF), are considered promising approaches for mitigating nitrous oxide (N2O) emissions while improving crop yield. This study investigated the combined application of EENFs with improved water and fertilizer management in an intensively irrigated spring maize rotation over five years in Northwestern China. High-frequency measurements of N2O fluxes were made throughout each year (both during crop growth and the fallow season) in five treatments: no N fertilizer as a control (CK), conventional N fertilization and irrigation (Con), optimum N fertilization and irrigation (Opt, 33% reduction in N fertilizer and 25% reduction of irrigation water), optimum N fertilization and irrigation with nitrification inhibitor (Opt+NI), and optimum N fertilization and irrigation with slow-release fertilizer (Opt-SRF). Annual mean cumulative N2O emissions reached 0.31±0.07, 3.66±0.19, 1.87±0.16, 1.23±0.13, and 1.61±0.16kg N2O-N ha-1 for CK, Con, Opt, Opt+NI, and Opt-SRF, respectively, with annual mean nitrogen use efficiency (NUE) of 36, 54, 61 and 59% for Con, Opt, Opt+NI, and Opt-SRF, respectively. The Opt, Opt+NI and Opt-SRF treatments significantly reduced cumulative N2O emissions by 49%, 66%, and 56% (P<0.05), respectively, and increased NUE by 51%, 70%, and 66% (P<0.05), respectively, relative to Con. However, mean above-ground N uptake (288-309kgN ha-1) and mean grain yields (12.7-12.8Mgha-1) did not differ significantly between the Con, Opt, Opt+NI, and Opt-SRF treatments during the five-year study. High N2O emissions mainly occurred within a few days of fertilization with irrigation, which could have been produced by microbially-mediated nitrifier or nitrifier denitrification processes. The fallow seasons had significantly lower cumulative N2O emissions, which were mainly attributed to the low temperature, low N inputs of crop residues, and low soil moisture conditions. Our study clearly indicated that the combined application of EENFs with optimum N fertilization and irrigation management can reduce environmental impacts while maintaining high crop yields in dryland regions such as Northwest China.

Nitrous Oxide and Methane Emissions from Beef Cattle Feedyard Pens Following Large Rainfall Events

HighlightsNitrous oxide and methane emissions were measured from a commercial beef feedyard following large rainfall events.Nitrous oxide emissions dropped below detection levels for ten days following a 77 mm rainfall event.Daily N2O and CH4 emissions followed a diel pattern, peaking at manure temperatures of 36°C to 38°C.Results will be used to refine empirical models for predicting GHG emissions from open-lot feedyards.Abstract. More than six million beef cattle are fed annually in feedyards on the semiarid Southern Great Plains (SGP). Manure deposited on the open-lot pen surfaces contributes to greenhouse gas (GHG) emissions. Nitrous oxide (N2O) and methane (CH4) are GHGs linked to climate change, and both have global warming potentials greater than carbon dioxide (CO2). Two sampling campaigns were conducted in 2019 to quantify N2O and CH4 emissions from open-lot pen surfaces. The occurrence of large, unforecast rainfall events during both campaigns provided an opportunity to compare GHG emissions from the dry manure before rainfall and from the wetted pen surface for one to two weeks following precipitation. Temporal variability was quantified by continuous sampling using six to eight automated flux chambers, a multiplexer system, and real-time analyzers. Spatial variability was quantified using a recirculating portable chamber on a 5 × 8 grid. Nitrous oxide emissions dropped below detection levels for ten days after the precipitation event. Nitrous oxide emissions were related to nitrification or other aerobic processes. Methane emissions dropped below detection levels for five days after the precipitation event and then increased to pre-rainfall levels by day 8. When present, N2O and CH4 emissions followed a diel pattern, with the highest emissions occurring during the afternoon when manure pack temperatures at the 25 mm depth were 36°C to 38°C and ambient temperatures were 31°C to 32°C. Average CH4 emissions from the feedyard pen surface were 96-fold lower than estimated enteric CH4 emissions. The results of this field research will be used to refine empirical models for predicting annual N2O and CH4 emissions from open-lot beef cattle feedyards on the semiarid SGP. Keywords: Beef cattle, Flux chamber, Greenhouse gas, Manure, Nitrous oxide, Rainfall.

Fertilization and clear-cutting effects on greenhouse gas emissions of pinewood nematode damaged Masson pine plantation

ABSTRACT Introduction: Management practices are essential for maintaining forest ecological functions under increasing diseases and pest disasters. The effects of nitrogen fertilization (NF) and clear-cutting (CC) on the soil microbial community structure and greenhouse gases emission were investigated of pinewood nematodes (Bursaphelenchus xylophilus)-infected Masson pine (Pinus massoniana) plantations. Outcomes: CC increased the soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) contents relative to the control (CK). NF increased the SMBN but had no significant effect on the SMBC content. The total fungal and bacterial abundances increased in the CC treatment compared with the CK, but there was no significant difference between the NF and CK. The cumulative soil CO2 emission (2.35 t C·hm−2) was higher than that of CK (1.65 t C·hm−2) in summer, and the cumulative annual N2O emission (16.90 kg N·hm−2 yr−1) of NF was approximately 47 times of CK (0.36 t N·hm−2·yr−1). CC increased the CO2 flux (2.21 t C·hm−2) in summer but have no significantly effects on N2O emission. Conclusion: These results indicated that NF and CC practices changed forest soil microbial community structure and affected soil greenhouse gas emissions in pinewood nematodes -infected Masson pine plantations. The CO2 emission rates increased in the NF and CC treatments, which reduced the carbon sequestration function of forests and had a negative impact on climate change.

Global greenhouse vegetable production systems are hotspots of soil N2O emissions and nitrogen leaching: A meta-analysis.

Vegetable production in greenhouses is often associated with the use of excessive amounts of nitrogen (N) fertilizers, low NUE (15-35%), and high N losses along gaseous and hydrological pathways. In this meta-analysis, we assess the effects of application rate, fertilizer type, irrigation, and soil properties on soil N2O emissions and nitrogen leaching from greenhouse vegetable systems on the basis of 75 studies. Mean±standard error (SE) N2O emissions from unfertilized control plots (N2Ocontrol) and N leaching (NLcontrol) of greenhouse vegetable systems were 3.2±0.4 and 91±20kgN ha-1 yr-1, respectively, indicating legacy effects due to fertilization in preceding crop seasons. Soil organic carbon concentrations (SOC) and irrigation were significantly positively correlated with NLcontrol losses, while other soil properties did not significantly affect N2Ocontrol or NLcontrol. The annual mean soil N2O emission from fertilized greenhouse vegetable systems was 12.0±1.0kg N2O-N ha-1 yr-1 (global: 0.067Tg N2O-N yr-1), with N2O emissions increasing exponentially with fertilization. The mean EFN2O was 0.85%. The mean annual nitrogen leaching (NL) was 297±22kgN ha-1 yr-1 (global: 1.66TgN yr-1), with fertilization, irrigation, and SOC explaining 65% of the observed variation. The mean leaching factor across all fertilizer types was 11.9%, but 18.7% for chemical fertilizer. Crop NUE was highest, while N2O emissions and N leaching were lowest, at fertilizer rates <500kgN ha-1 year-1. Yield-scaled N2O emissions (0.05±0.01kg N2O-N Mg-1 yr-1) and nitrogen leaching (0.79±0.08kgN Mg-1 yr-1) were lowest at fertilizer rates <1000kgN ha-1 yr-1. Vegetables are increasingly produced in greenhouses, often under management schemes of extreme fertilization (>1500kgN ha-1 yr-1) and irrigation (>1200mm yr-1). Our study indicates that high environmental N2O and N leaching losses can be mitigated by reducing fertilization rates to 500-1000kgN ha-1 yr-1 (mean: ∼762kgN ha-1 yr-1) without jeopardizing yields.

Nitrous oxide emissions in response to long-term application of the nitrification inhibitor DMPP in an acidic luvisol

One of the options recommended by the Intergovernmental Panel on Climate Change (IPCC) to reduce N2O emissions from agricultural soils is the application of nitrification inhibitors (NIs). However, the effects of long-term in situ application of 3,4-dimethylpyrazole phosphate (DMPP), one of the important NIs, on N2O emissions from agricultural soils are not well documented. In this study, a field trial was conducted to determine N2O emissions in response to DMPP application for six consecutive years (2010–2015) on a rainfed acidic luvisol planted with maize in Northeast China, as well as the effects on the soil microbial communities after six years. Three treatments were used, i.e., no urea (CK), urea (SU), and urea plus DMPP (DMPP). The results showed large intra- and interannual variations in the N2O fluxes for all treatments. The N2O mitigation efficiency of DMPP varied from 18.4 to 50.3% across the six cycles, which was mainly attributed to the amount of precipitation and its annual distribution. The annual N2O emissions and N2O emissions factor during the six years were significantly mitigated by DMPP applications, with mean reductions of 29.9 and 47.9%, respectively. The abundances of bacterial 16S rRNA genes, ammonia oxidizer genes, and denitrifier functional genes in the soils collected 10 days after fertilization in May 2015 and again in September were determined. In May 2015, DMPP application significantly decreased the ammonia-oxidizing bacteria (AOB) amoA gene copy number by 77.7% and increased the nosZ gene copy number by 116.8%. However, in September 2015, even after the six-year application period assessed in May, there was no significant effect on gene abundance due to DMPP. Overall, the repeated annual application of DMPP in the spring effectively reduced N2O emissions from acidic luvisol soil, yielding no significant long-term shifts in soil bacterial communities.

N2O and NO Emissions as Affected by the Continuous Combined Application of Organic and Mineral N Fertilizer to a Soil on the North China Plain

A field experiment was conducted to evaluate the influence of the continuous application of organic and mineral N fertilizer on N2O and NO emissions under maize and wheat rotation on the North China Plain. This study included eight treatments: no fertilizer (control); mineral N fertilizer (Nmin) at a rate of 200 kg N ha−1 per season; 50% mineral fertilizer N plus 50% cattle manure N (50% CM), 50% chicken manure N (50% FC) or 50% pig manure N (50% FP); 75% mineral fertilizer N plus 25% cattle manure N (25% CM), 25% chicken manure N (25% FC) or 25% pig manure N (25% FP). The annual N2O and NO emissions were 2.71 and 0.39 kg N ha−1, respectively, under the Nmin treatment, with an emission factor of 0.50% for N2O and 0.07% for NO. Compared with the Nmin treatment, N2O emissions did not differ when 50% of the mineral N was replaced with manure N (50% CM, 50% FC and 50% FP), while annual NO emissions were significantly reduced by 49.0% and 27.8% under 50% FC and 50% FP, respectively. In contrast, annual N2O emissions decreased by 21–38% compared to the Nmin treatment when 25% of the mineral N was replaced with manure N (25% CM, 25% FC and 25% FP). Most of the reduction occurred during the maize season. The 25% CM, 25% FC and 25% FP treatments had no effect on NO emissions compared to the Nmin treatment. There was no obvious difference in annual N2O and NO emissions among the organic manures at the same application rate, probably due to their similar C/N ratio. Replacing a portion of the mineral fertilizer N with organic fertilizer N did not significantly affect crop grain yield, except for the 50% FC treatment in the wheat season. Overall, the results suggest that the combined application of 25% organic manure N plus 75% mineral fertilizer N had the most potential to mitigate N2O emissions while not affecting crop yield in the maize and wheat rotation system in this area of China.

Effects of Nitrogen Fertilizer and Straw Returning Methods on N2O Emissions in Wheat-Maize Rotational Soils

In order to explore the impacts of nitrogen fertilizer and straw returning methods on N2O emissions, a two-factor split-zone design was adopted for experimentation under the winter wheat-summer maize rotation model in the Guanzhong area of Shanxi, China. The main areas of interest were conventional nitrogen (G) and reduced nitrogen (70% G); the sub-areas were straw no return (N), straw return (S), and straw return + biochar (SB); we analyzed their impacts on N2O emissions and crop yield, and the relationships with related impact factors. The results showed that the N2O emissions peaks appeared in the wheat season and maize season treatments within 5-16 days after fertilization, and also appeared after rainfall. The N2O flux was significantly and positively correlated with soil temperature and NH4+-N content. Regardless of the wheat season, maize season, or annual total N2O emissions, the 70% GSB treatment was the lowest and the GS treatment was the highest. At the same level of nitrogen application, S treatment increased N2O emissions, SB treatment could reduce N2O emissions, both S and SB treatments could significantly increase crop yields, and SB production increased more; 70%G-level annual N2O emissions, when compared with the G level, had been reduced by 40% to 48%, while the yield has not decreased significantly. Through comprehensive consideration, a reduction of nitrogen by 30% was achieved through the combination of straw + biochar on the basis of conventional nitrogen application, while ensuring high crop yields and the best N2O emissions reduction.

Enhanced nitrous oxide emissions caused by atmospheric nitrogen deposition in agroecosystems over China.

Atmospheric nitrogen (N) deposition in China has been the largest worldwide. Yet the impacts of atmospheric N deposition on soil N2O emissions were often ignored by previous studies. Thus, we investigated how N deposition affected N2O emissions over China using the process-based model (DNDC, DeNitrification-DeComposition). Total soil N inputs were 194kgNha-1 in agricultural systems over China in 2010, including chemical N fertilizer (78%), atmospheric N deposition (12%), and crop residues N (10%). Annual N2O emissions induced by N deposition were estimated at 97Gg N, occupying 43% of total soil N2O emissions (228Gg N) in agricultural systems over China. In particular, the largest N2O emissions caused by atmospheric N deposition were found in South China, followed by North China Plain and Southwest China. The efficiency of N deposition generating N2O emissions (3.0%) over China was 4 times than that of N fertilizer (0.7%). N2O emissions induced by N deposition increased from 81Gg in 2000 to 93Gg in 2014 (by 1% yr-1), which was consistent with the long-term trend of N deposition. This suggests N deposition accelerated soil N2O emissions largely contributing to global warming. Our results also indicated that 62% and 10% of soil N2O emissions were reduced by applying a nitrification inhibitor and N fertilizer with 20% decrease. We highlight the significance of considering N deposition in determining total soil N2O emissions over China. The results provide an important scientific basis for the prediction of greenhouse effect caused by N deposition over China.

Nitrogen stocks and flows in an acid sulfate soil

Besides causing acidification, acid sulfate (AS) soils contain large nitrogen (N) stocks and are a potential source of N loading to waters and nitrous oxide (N2O) emissions. We quantified the stocks and flows of N, including crop yields, N leaching, and N2O emissions, in a cultivated AS soil in western Finland. We also investigated whether controlled drainage (CD) and sub-irrigation (CDI) to keep the sulfidic horizons inundated can alleviate N losses. Total N stock at 0–100 cm (19.5 Mg ha−1) was smaller than at 100–200 cm (26.6 Mg ha−1), and the mineral N stock was largest below 170 cm. Annual N leaching (31–91 kg N ha−1) plus N in harvested grain (74–122 kg N ha−1) was 148% (range 118–189%) of N applied in fertilizers (90–125 kg N ha−1) in 2011–2017, suggesting substantial N supply from soil reserves. Annual emissions of N2O measured during 2 years were 8–28 kg N ha−1. The most probable reasons for high N2O emission rates in AS soils are concomitant large mineral N pools with fluctuating redox conditions and low pH in the oxidized subsoil, all favoring formation of N2O in nitrification and denitrification. Although the groundwater level was higher in CD and CDI than in conventional drainage, N load and crop offtake did not differ between the drainage methods, but there were differences in emissions. Nitrogen flows to the atmosphere and drainage water were clearly larger than those in non-AS mineral soils indicating that AS soils are potential hotspots of environmental impacts.

Assessing the impacts of diversified crop rotation systems on yields and nitrous oxide emissions in Canada using the DNDC model

Process-based models are effective tools for assessing the sustainability of agricultural productivity and environmental health under various management practices and rotation systems. The objectives of this study were to (1) calibrate and evaluate the DeNitrification-DeComposition (DNDC) model using measurements of yields, nitrogen (N) uptake, soil inorganic N, soil temperature, soil moisture and nitrous oxide (N2O) emissions under long-term fertilized continuous corn (CC) and corn-oats-alfalfa-alfalfa (COAA) rotation systems in southwest Ontario from 1959 to 2015, Canada, and (2) explore the impacts of four diverse rotation systems (CC, COAA, corn-soybean-corn-soybean (CSCS) and corn-soybean-winter wheat (CSW)) on corn yields and annual N2O emissions under long-term climate variability. DNDC demonstrated “good” performance in simulating corn, oats and alfalfa yield (normalized root mean square error (nRMSE) < 20%, Nash-Sutcliffe efficiency (NSE) > 0.5 and index of agreement (d) > 0.8). The model provided “fair” to “good” simulations for corn N uptake and soil inorganic N (NSE > 0.2 and d > 0.8), and also daily soil temperature and soil moisture (nRMSE <30% and d > 0.7) for both calibration and validation periods. The model demonstrated “good” performance in estimating daily and cumulative N2O emissions from both the continuous and rotational corn, whereas it produced “poor” to “good” predictions for N2O emissions from the rotational oats and alfalfa crops, however, the emissions from these crops were very low and the relative magnitude of these emissions between all crops investigated were well predicted. The lowest N2O emissions were from COAA followed by CSCS, CSW then CC. The highest corn yields were from COAA, followed by CSW, CSCS, then CC. This study highlights how modelling approaches can help improve the understanding of the impacts of diversified rotations on crop production and greenhouse gas emissions and contribute towards developing policies aimed at improving the sustainability and resiliency of cropping systems.

Nitrous oxide emissions and nitrogen use efficiency in wheat: Nitrogen fertilization timing and formulation, soil nitrogen, and weather effects

AbstractImproving N fertilization in croplands could minimize soil emissions of nitrous oxide (N2O) and mitigate climate change. This study investigated the effects of spring vs. fall N applications of conventional vs. enhanced‐efficiency N fertilizers (EENFs) on N2O emissions and N use efficiency in spring wheat (Triticum aestivum L.) over 2.5 yr in Alberta, Canada. Fertilizers were anhydrous ammonia and urea and the EENF formulations included urease and nitrification inhibitors and a polymer coating. We measured a fertilizer N2O emission factor of 0.31 ± 0.04%. Irrespective of N fertilizer and timing options peak N2O emissions were evident following soil thawing and major rainfalls. Because most of the annual N2O emissions were associated with soil thawing, spring‐applied N emitted half the N2O of the fall‐applied N during the second study year (P &lt; .001). Conversely, the opposite was observed for the first study year when overall N2O emissions were 36% larger for spring‐ than fall‐applied N (P = .031) as major rainfalls occurred shortly after the spring N fertilization. Nevertheless, within this first study year, EENFs significantly reduced N2O emissions (by 26% on average; P = .019), with a tendency for 11% higher grain yield across springtime EENFs than for conventional fertilizers. Concomitantly, spring‐applied N doubled the fertilizer N recovery efficiency in the same year (P = .023). The soil at the study site inherently had high N availability (NH4 and NO3) and this probably moderated the beneficial effects of EENFs on N2O emissions and grain yields. Results suggest that spring EENFs can mitigate the risk for N2O emissions while sustaining high yields even under scenarios with high availability of native soil N.

Are annual nitrous oxide fluxes sensitive to warming and increasing precipitation in the Gurbantunggut Desert?

AbstractTemperate desert soils are an important source of atmospheric nitrous oxide (N2O). However, it is uncertain how N2O emissions respond to warming, increased rainfall and nitrogen (N) addition in such soils. A multifactorial field manipulation study was carried out in the Gurbantunggut Desert, China's second largest desert, to investigate how these factors influence desert soil N2O emissions and to assess inter‐year variation. In our 3‐year study, under current climatic conditions, the annual flux of N2O in this temperate desert soil was 0.13 ± 0.02 kg N ha−1 yr−1, with the period of no plant growth contributing 43% of the annual emission. Surprisingly, there was no significant change in annual N2O flux under warming (+1°C) or increased precipitation (30%, +60 mm yr−1). In contrast, N2O emissions were significantly affected by extreme drought followed by precipitation. Additional N input, at 30 or 60 kg N ha−1 yr−1, greatly elevated annual N2O emission by 55–133%. The combined impact of N deposition and increasing rainfall on N2O emission was greater than that of any single factor, except for N deposition. This suggests that N2O emissions in this desert are driven primarily by soil available N content and are less sensitive to variations in soil temperature and moisture.

Rubber-leguminous shrub systems stimulate soil N2O but reduce CO2 and CH4 emissions

Rubber plantations represent 13 million hectares in the world. Many researchers have focused on the environmental sustainability of rubber plantations, with rubber-legume systems better approach for ameliorating soil environments. This study investigated the effect of introducing Flemingia macrophylla (a leguminous shrub) to different-aged rubber plantations on the emissions of CO2, N2O, and CH4. As trees aged in the rubber plantations, the annual emissions of CO2, N2O, and CH4 significantly decreased. The introduction of F. macrophylla to different-aged rubber plantations significantly decreased CO2 and CH4 flux but increased N2O flux. The CO2 and N2O fluxes were mainly affected by soil temperature at 10 cm depth, and CH4 flux was mainly affected by both soil water content in the 0–10 cm soil layer and soil temperature at 10 cm depth. Compared to the same-aged rubber plantations, annual total CO2 flux of young and mature rubber–F. macrophylla plantations decreased 154,000 and 64000 kg ha−1, CH4 flux decreased 0.50 and 0.78 kg ha−1 (17.0 and 26.5 kg CO2 eq ha−1), and N2O flux increased 0.15 and 0.55 kg ha−1 (44.7 and 163.9 kg CO2 eq ha−1), respectively. The rubber-leguminous shrub systems significantly improved soil organic carbon sequestration rate, relative to the same aged rubber plantations. In conclusion, the emissions of CO2, N2O and CH4 decreased as the trees aged in the rubber plantations, and rubber-leguminous shrub systems could mitigate local climate warming by reducing reduce greenhouse gas emissions and improving soil organic sequestration rate.