Highest Cumulative N2O Emissions Research Articles

Winter cover crops decreased soil mineral N contents and increased soil organic C stocks and N2O emission

Cover crops (CC) can contribute to climate protection as a result of their effects on soil nitrogen (N) cycling and nitrous oxide (N2O) emission and by increasing soil organic carbon (SOC) stocks. This study explored the influence of different winter CC (saia oat, winter rye and spring vetch) compared with bare fallow, followed by silage maize on N2O emissions and soil mineral N (SMN) dynamics, as well as on SOC stocks in year-round replicated field plot experiments in four fields located at two sites in northern Germany (Kiel, Uelzen) over two consecutive years (2018/19 and 2019/20). Non-legume CC decreased SMN contents in 0–30 cm during the CC period, but this did not result in decreased cumulative N2O emissions over that time. Decreased emissions during CC growth were offset by increased emissions during CC mineralisation after frost and incorporation. Higher cumulative N2O emissions during the maize period in all CC treatments compared with bare fallow (significant for non-legume CC) indicated that the incorporated CC biomass still boosted N2O emissions under the following crop. Overall, including CC in the cropping system increased annual and yield-related N2O emissions compared with bare fallow (significant only for non-legumes). The increase in annual N2O emissions of 0.84 ± 1.06 kg N2O-N ha−1 yr−1 was only partly offset by the estimated mitigation potential for indirect N2O emissions of 0.52 ± 0.14 kg N2O-N ha−1 yr−1. The mean annual increase in SOC induced by growing CC every fourth year over a 50-year period was 40–60 kg C ha−1 yr−1. In summary, CC had both positive and negative effects on greenhouse gas exchange. Site and crop rotation optimised CC systems, and a more precise and site-specific consideration of fertilising effects might help improve the net greenhouse gas budget of CC.

Long-term application of controlled-release urea reduced ammonia volatilization, raising the risk of N2O emissions and improved summer maize yield

ContextWith the extensive promotion of controlled-release urea (CRU), its N-release pattern has been shown to match the crop’s N-demand period and improve crop yield by reducing N losses. Nevertheless, the impacts of CRU on summer maize yield, especially on greenhouse gas emissions, have rarely been reported during its long-term use. ObjectiveIt is necessary through long-term positioning field experiment with CRU application to investigate the regulatory mechanisms of maize yield formation, nitrogen use efficiency (NUE), ammonia volatilization and greenhouse gas emissions. MethodsThe long-term fertilizer positioning experiment for ten years, four treatments were performed: polymeric-coated controlled-release urea (CRF, 42% N, 3-months controlled-release period), sulfur-coated controlled-release urea (SCF, 35% N, 3-months controlled-release period), common urea (CCF, 46% N) and no nitrogen fertilizer (CK). ResultsResults showed that the two coated controlled-release fertilizers significantly increased NUE and dry matter accumulation in summer maize, and ultimately improved grain yield. Compared to CCF, CRF and SCF treatments increased post-silking dry matter accumulation by 16.3% and 13.3%; NUE by 42.3% and 28.9%. The 2-year mean grain yield of CRF and SCF treatment increased 9.0% and 12.4% compared to CCF treatment. CRF treatment significantly increased the NO3--N content in 0–60 cm soil layer; while CRF and SCF treatments showed a significantly higher NH4+-N concentration in the 0–20 cm soil layer than CCF treatment. Compared to CCF treatment, the CRF and SCF treatments significantly reduced peak ammonia volatilization, and the average cumulative emissions of ammonia volatilization of two years were reduced by 80.8% and 53.2%, respectively. CRF treatment had lower peak of N2O emissions but longer N2O emission duration than other N application treatments. The two-year average cumulative N2O emissions from CRF treatment increased by 49.6%, and SCF treatment increased by 61.1% compared to CCF treatment. Compared to CK treatment, total cumulative CH4 uptake was 36.1% lower in CRF treatment, 60.9% in SCF and 78.9% in CCF treatment. The higher cumulative N2O emissions from CRF and SCF treatment resulted in a significantly higher global warming potential (GWP) than CCF treatment. The two-year mean increase in greenhouse gas intensity (GHGI) was 36.2% for CRF treatment and 44.7% for SCF treatment compared to CCF treatment. ConclusionsLong-term application of coated controlled-release fertilizers could achieve high yields and nitrogen use efficiency. However, there is a risk of increased N2O emissions, causing elevated GHGI. SignificanceIn the future, it is necessary to strengthen the research on the comprehensive effects of long-term reduced application of CRU on crop yield and greenhouse gas emissions, in order to promote the wide application of environmentally friendly CRU in the field.

CH4 and N2O Emission and Grain Yield Performance of Three Main Rice-Farming Patterns in Central China

This study focuses on the development of more cropping systems in response to global warming and food security concerns. A two-year field experiment (2017–2018) was conducted to investigate the effects of greenhouse gases (GHGs), soil environmental factors and yield on traditional double-cropping rice (DR), maize rice (MR) and ratooning rice (Rr). The results showed a significant annual effect of temperature and rainfall on GHG emissions under different cropping systems. Annual CH4 emissions under MR and Rr were significantly lower than under DR. Compared to DR, the highest cumulative N2O emissions were observed in MR (14.9 kg·ha−1) with a reduction of 23.7% in Rr. In addition, the upland crops significantly reduced CH4 emissions for late rice, while N2O emissions increased by 20.6%. Compared with DR and Rr, global warming potential (GWP) and greenhouse gas intensity (GHGI) were significantly lower for MR (p < 0.05). Meanwhile, the annual yield of MR (16.40 t·ha−1) was 8.1% and 2.4% higher than that of DR and Rr, respectively. This study further found that soil temperature and NH4+-N content were positively correlated with CH4 and N2O emissions, and soil moisture was positively correlated with N2O emission. Thus, we concluded that MR has the greatest potential to improve crop yield and mitigate GHG emissions in central China.

Episodic N2O emissions following tillage of a legume–grass cover crop mixture

Abstract. Nitrogen (N) fertilizer inputs to agricultural soils are a leading cause of nitrous oxide (N2O) emissions. Legume cover crops are an alternative N source that can reduce agricultural N2O emissions compared to fertilizer N. However, our understanding of episodic N2O flux following cover crop incorporation by tillage is limited and has focused on single-species cover crops. Our study explores whether increasing cover crop functional diversity with a legume–grass mixture can reduce pulse emissions of N2O following tillage. In a field experiment, we planted crimson clover (Trifolium incarnatum L.), cereal rye (Secale cereal L.), a clover–rye mixture, and a no-cover control at two field sites with contrasting soil fertility properties in Michigan. We hypothesized that N2O flux following tillage of the cover crops would be lower in the mixture and rye compared to the clover treatment because rye litter can decrease N mineralization rates. We measured N2O for approximately 2 weeks following tillage to capture the first peak in N2O emissions in each site. Across cover crop treatments, the higher-fertility site, CF, had greater cover crop biomass, 2-fold-higher aboveground biomass N, and higher cumulative N2O emissions than the lower-fertility site, KBS (413.4±67.5 vs. 230.8±42.5 g N2O-N ha−1; P=0.004). There was a significant treatment effect on daily emissions at both sites. At CF, N2O fluxes were higher following clover than the control 6 d after tillage. At KBS, fluxes from the mixture were higher than rye 8 and 11 d after tillage. When controlling for soil fertility differences between sites, clover and mixture led to approximately 2-fold-higher N2O emissions compared to rye and fallow treatments. We found partial support for our hypothesis that N2O would be lower following incorporation of the mixture than clover. However, treatment patterns differed by site, suggesting that interactions between cover crop functional types and background soil fertility influence N2O emissions during cover crop decomposition.

Effects of different tillage systems and cropping sequences on soil physicochemical properties and greenhouse gas emissions

The greenhouse gas emissions (GHGE) are major contributor to climate change and farmlands are prominent source of GHGE that are affected by soil chemical and physical properties. Field management practices e.g. no-till (NT) and cropping sequences (CSs) can regulate GHGE by changing soil physicochemical properties. To understand the role of soil physicochemical properties on GHGE under different tillage and CSs, a field experiment was conducted during 2019 and 2020 consisting of two tillage systems (NT and rotary tillage (RT)) and CSs (maize-wheat-soybean-wheat (MWS), soybean-wheat-maize-wheat (SWM), wheat-soybean (SW) and wheat-maize (WM)). The results showed that N2O emissions were higher in 2019, mainly under SWM and SW as compared to other CSs. Higher cumulative N2O emissions (28.89% (2019) and 37.94% (2020)) under RT were observed than NT. RT had higher CH4 sink in 2019 (20.93%) and 2020 (19.6%) in comparison to NT. Moreover, CH4 uptake was increased almost 91.49% in 2020 as compared to 2019. These inter-annual changes between GHGE were mainly due to water filled pore spaces (WFPS) induced by inter-annual precipitation anomalies, where higher precipitation (79.91%) in 2019 increased about 50.71% WFPS as compared to 2020. The global warming potential (GWP) was negatively correlated to TN, PON, SOC, POC and SOC stock, but positively correlated to WFPS. These results suggested that RT could negatively impact WFPS, SOC, TN and their associated fractions in different CSs and enhance GWP. In conclusion, NT with diversified CSs could offer a solution for decreasing GWP and improving maize equivalent yield.

Tillage system affects fertilizer-induced nitrous oxide emissions

Since the development of effective N2O mitigation options is a key challenge for future agricultural practice, we studied the interactive effect of tillage systems on fertilizer-derived N2O emissions and the abundance of microbial communities involved in N2O production and reduction. Soil samples from 0–10 cm and 10–20 cm depth of reduced tillage and ploughed plots were incubated with dairy slurry (SL) and manure compost (MC) in comparison with calcium ammonium nitrate (CAN) and an unfertilized control (ZERO) for 42 days. N2O and CO2 fluxes, ammonium, nitrate, dissolved organic C, and functional gene abundances (16S rRNA gene, nirK, nirS, nosZ, bacterial and archaeal amoA) were regularly monitored. Averaged across all soil samples, N2O emissions decreased in the order CAN and SL (CAN = 748.8 ± 206.3, SL = 489.4 ± 107.2 μg kg−1) followed by MC (284.2 ± 67.3 μg kg−1) and ZERO (29.1 ± 5.9 μg kg−1). Highest cumulative N2O emissions were found in 10–20 cm of the reduced tilled soil in CAN and SL. N2O fluxes were assigned to ammonium as source in CAN and SL and correlated positively to bacterial amoA abundances. Additionally, nosZ abundances correlated negatively to N2O fluxes in the organic fertilizer treatments. Soils showed a gradient in soil organic C, 16S rRNA, nirK, and nosZ with greater amounts in the 0–10 than 10–20 cm layer. Abundances of bacterial and archaeal amoA were higher in reduced tilled soil compared to ploughed soils. The study highlights that tillage system induced biophysicochemical stratification impacts net N2O emissions within the soil profile according to N and C species added during fertilization.

Tillage, residue and nitrogen management effects on methane and nitrous oxide emission from rice–wheat system of Indian Northwest Indo-Gangetic Plains

Zero-tillage, residue management and precision nutrient management techniques are being promoted in the rice–wheat (RW) production system of Indo-Gangetic Plains (IGPs) to enhance climate change adaptation and increase food production. These management practices may also influence greenhouse gas emissions through their effects on various soil processes such as oxidation-reduction and nitrification–denitrification. We measured soil fluxes of CH4 and N2O in RW system under three tillage and residue management systems layered with four nitrogen (N) management treatments. The tillage and residue management systems comprised: conventional tillage (CT), zero-tillage without residue retention (ZT − R) and ZT with full residue retention (ZT + R) for both the crops. The four N management treatments for rice were: (a) basmati cultivar with recommended dose of nitrogen (RDN) applied in three splits, (b) basmati cultivar with 80% RDN as basal dose followed by Green Seeker (GS) guided N application, (c) hybrid cultivar with RDN applied in three splits and (d) hybrid with 80% RDN as basal dose followed by GS guided N application. The four N management treatments for wheat comprised combinations of RDN with and without relay green gram (GG), and 80% of RDN as basal dose followed by GS guided N application with and without relay GG. We employed the static chamber method to collect gas samples from the experimental plots which were subsequently analysed using gas chromatograph. Significant CH4 emissions were detected only in the CT rice system during the initial phase of continuous flooding, irrespective of N management strategies. N fertilization management affected the pattern of N2O emission with higher emission rates during crop establishment phase under 80% RDN as basal followed by GS guided N application than conventional RDN. In case of wheat, 80% RDN as basal followed by GS guided N application also induced higher cumulative N2O emissions than applying RDN at three regular splits. In rice, ZT-based RW system emitted more N2O than CT-based system. Overall ZT-based RW system reduced CH4 emission but this benefit is counterbalanced by higher N2O production compared to CT-based RW system.

Earthworms reduce soil nitrous oxide emissions during drying and rewetting cycles

Nitrous oxide (N2O) is a greenhouse gas that is released from both nitrification and denitrification processes. Soil moisture content is a key controller of the biochemical pathways leading to N2O emission, causing a switch between nitrification and denitrification processes. Earthworms are reported to increase N2O emissions from soil under aerobic and anaerobic conditions, but how earthworm-induced N2O emissions are affected by soil drying and rewetting cycles is unknown. The objectives of this study were to (1) evaluate earthworm-induced N2O emissions from soils with aerobic, anaerobic, and fluctuating soil moisture conditions; and (2) determine the earthworm effects on soil denitrifiers responsible for N2O fluxes. Soils were kept in mesocosms (polyvinyl chloride plastic tubes, 10 cm diameter, filled with soil to 15 cm depth) at constant 33% water-filled pore space (WFPS), constant 97% WFPS or underwent three wetting-drying cycles (WD). Each soil moisture treatment had 2 earthworm treatments, including (1) a mixture of endogeic Aporrectodea turgida and anecic Lumbricus terrestris and (2) no earthworm treatment. These gave a total of 6 treatments in this study, with 5 replicates for each treatment. The N2O fluxes were quantified every one to three days, and the soil denitrifier activities were measured after 69 days, when the experiment ended. Soil moisture significantly affected N2O emissions and the WD treatment had the highest cumulative N2O emissions. Earthworms increased N2O emissions by 50% in the 33% WFPS treatment but decreased N2O emissions by 34% in the 97% WFPS treatment, probably due to more complete reduction of N2O to N2. Earthworms strongly reduced N2O emission rate in WD treatment, and they significantly reduced cumulative N2O emissions by 82%. Soil denitrification enzyme activity (DEA) increased significantly when earthworms were present. Abundance of 16S rRNA, nirS, and nosZ genes was affected significantly by the earthworm × soil moisture interaction, with the highest 16S rRNA and nosZ abundance in soil from the WD treatments. We conclude that the decrease in cumulative N2O emissions from soil at 97% WFPS and the WD treatment by earthworms was due to an alteration of the denitrifying bacterial community composition.

Carbon Dioxide and Nitrous Oxide Fluxes in Corn Grown under Two Tillage Systems in Southwestern Quebec

Agriculture has an important potential role in mitigating greenhouse gas emissions (GHG). However, practices that reduce CO2 emissions from soils and increase the soil organic C level may stimulate N2O emissions. This is particularly critical in Quebec where heavy soils and a humid climate may limit the adoption of agricultural practices designed to mitigate GHG. The objective of this work was to study the effects of two tillage and N fertilization regimes on CO2 and N2O fluxes and the seasonal variability in emissions of these gases, associated with corn (Zea mays L.) grown in southwestern Quebec. Different seasonal emission patterns of CO2 and N2O were observed. Higher N2O fluxes occurred during the spring and were associated with precipitation events, while higher CO2 fluxes occurred in mid‐season and were related to temperature. Conventional tillage (CT) had greater peaks of CO2 emissions than no‐till (NT) only after disking in the spring. Once corn was established, differences between tillage systems were small. Peaks of N2O emission occurred in both systems (NT and CT) following N application. Plots receiving 180 kg N ha−1 in both tillage systems had large peak of N2O emission rates during the wettest parts of the season. The CT and NT systems generally had similar cumulative CO2 emissions but NT had higher cumulative N2O emissions than CT. Our findings suggests that changing from CT to NT under the heavy soil conditions of Quebec may increase GHG, mainly as result of the increase in N2O emission. This negative effect of NT could be reduced by avoiding fertilizing when precipitation is more intense.

Winter grazing of forages - soil moisture and tillage methods impact nitrous oxide emissions and dry matter production

Grazing of winter forage crops can cause extensive compaction of soils that may reduce re-growth of crops and lead to large emissions of nitrous oxide (N2O). A field trial was undertaken to investigate the effects of cattle grazing at three soil moisture contents on N2O emissions and dry matter (DM) production of a winter forage crop established by intensive (IT), minimum (MT), or no tillage (NT) practices. A multi-grazing triticale (cv. Doubletake) was sown in the main tillage plots in March 2003. In June, the tillage plots (three replicates) were each divided into six split plots and additional treatments were imposed: simulated treading (+/-); soil moisture at treading (< field capacity (FC); FC; and >FC); and urine (+/-). Tillage practice and soil moisture content at treading affected soil compaction. The greatest increase in surface soil (0-7.5 cm) bulk density occurred in IT plots treaded at >FC. Treading wet soil greatly increased (up to 8 times) the amount of N2O emitted. The highest cumulative N2O emissions were from IT (14.9 kg N/ha) and MT (12.7 kg N/ha) urine-applied plots treaded at >FC. There was no difference in N2O emitted from treaded FC. Treading at FC also caused a significant loss of DM production in the IT plots but not in the MT plots. DM production in the NT plots was unaffected by treading. Establishing winter forage crops by direct drilling may be an important management option to mitigate N2O emissions and maintain high DM production of grazed forages, as will avoiding grazing when soils are wet. Keywords: forage crops, grazing, nitrous oxide, soil compaction, tillage, urine