Yield-scaled N2O Emissions Research Articles

Effects of long-term nitrogen fertilization on N2O, N2 and their yield-scaled emissions in a temperate semi-arid agro-ecosystem

Nitrous oxide (N2O) measured simultaneously with di-nitrogen (N2) emissions from soils are greatly uncertain due to large temporal and spatial variations. This study aims to report N2O, N2, N2/N2O, 15N-N2O, wheat-maize annual grain yields, and yield-scaled N2O and N2O plus N2 emissions on the responses to different nitrogen (N) fertilizer rates in a winter wheat-summer maize cropping system. Furthermore, this study also seeks to determine controlling factors for N2O, N2, and N2/N2O emissions and significantly investigate the relationship between the soil-climate measured factors and 15N-N2O. Three N inputs and control treatments, 0, CK; 200, LN; 400, MN; and 600, HN kg N ha−1 year−1 were set since 1998. Direct measurement method has been used to quantify N2O and N2 emissions. Our results indicated that the effects of long-term N fertilization significantly increased N2O and N2 and also reduced N2/N2O emission ratios as described by exponential functions. Using structural equation modeling (SEM), NH4+, WFPS, NO3-, and DOC were revealed to be main controlling factors for N2O, while N2 by DOC, NO3-, WFPS, and temperature finally N2/N2O was positively related to temperature. Furthermore, the 15N-N2O was positively related to N2/N2O ratios, indicating that denitrification is the dominant process at the study site. The yield-scaled N2O emissions followed the order HM>MN>LN>CK, and they were 1.56, 1.47, and 1.07 times greater than CK, respectively. Total yield-scaled N2O plus N2 were in the order of CK>HN>MN>LN. N fertilization has shown strong impact not only on N2O, N2, and N2/N2O emissions but also on yield-scaled N2O and N2O plus N2 emissions. High agronomic nitrogen use efficiency (NUE), low yield-scaled N2O emissions, and low cumulative N2O plus N2 emissions were observed at 200-LN treatment, suggesting this rate to be an optimum and sustainable agricultural management practice with no significant crop yield reduction as compared to the current farmers’ practice of 400 kg N ha−1 year−1.

Nitrous oxide emissions and maize yield as influenced by nitrogen fertilization and tillage operations in upland soil

Previous studies simply focused on determining nitrous oxide (N2O) emissions from the soil under different tillage operations and nitrogen (N) fertilizations without considering crop yield. Therefore, the objective of this study was to determine the effects of different tillage operations and N fertilizations on N2O emissions and crop yield from upland soil. Two different tillage operations [conventional tillage (CT) and no-tillage (NT)] and N fertilizations [without urea (WOU) and with 186 kg N ha−1 of urea (WU)] were established in a randomized block design with three replications on upland soil. Maize (Zea mays) was cultivated from 6th July to 4th October, 2018 (year 1), and from 15th April to 26th July, 2019 (year 2). The daily N2O flux did not peak soon after tillage operation and N fertilization, but it was more related to the change in water-filled pore space (WFPS). The mean value of WFPS across N fertilizations and seasons (years) was higher in CT than in NT. The changes of nitrification and denitrification rates could be attributed to the differences in WFPS between CT and NT. Nitrification was the predominant process producing N2O with CT, but denitrification was with NT. The application of urea increased cumulative N2O emissions, while CT also increased it compared with NT. The order of the mean values of cumulative N2O emissions across seasons from the highest to the lowest was as follows: CT + WU (7.12 kg N2O ha−1 year−1) > NT + WU (5.69 kg N2O ha−1 year−1) ≥ CT + WOU (5.02 kg N2O ha−1 year−1) > NT + WOU (4.24 kg N2O ha−1 year−1). Tillage operation did not affect the grain yield of maize or yield-scaled N2O emissions (YSNE). However, the application of urea increased the grain yield of maize and decreased YSNE, implying it could reduce N2O emission per unit of maize grain production. No-tillage management did not decrease YSNE value compared to CT operation, but N fertilization significantly decreased YSNE in the current study.

Increasing soil pH reduces fertiliser derived N2O emissions in intensively managed temperate grassland

Soil pH is generally considered a master variable, controlling a wide range of physical, chemical and biological properties, including a significant effect on microbial processes responsible for production and consumption of nitrous oxide (N2O), a potent greenhouse gas. Evidence of this pH impact on microbial denitrification mainly stems from observations in controlled laboratory experiments, while the results from field studies are mainly short-term, more variable and circumstantial. Soil pH is also one of the main factors controlling the availability of soil phosphorous (P), which has been also linked with N2O emissions. Here, we utilised an existing intensive grassland liming and P trial to investigate the effect of longer-term lime and P management and their interaction on N2O emissions and grassland productivity. The treatment plots were subject to different liming and P fertilisation strategies over 8 years and had a wide gradient of soil pH (5.1–6.9) and extractable P (2.3–8.3 mg kg−1). All plots received a total of 300 kg ha−1 of fertiliser nitrogen (N), applied in 8 splits across the growing season. N2O emissions, soil mineral N and grass yields were measured over 12-month period. We found a negative linear relationship between soil pH and cumulative N2O emissions, with a decrease in N2O emissions up to 39 % from limed plots compared to the unlimed control. The same effect was observed in relation to N2O emission factors and yield-scaled N2O emissions. Extractable soil P content had positive effect on yields, but no effect of P or P and pH interaction was observed in terms of direct N2O emissions or yield-scaled N2O emissions. We estimated that the increase in soil pH of grasslands in Ireland over the last 12 years potentially reduced national N2O emissions by 95 Gg CO2-eq yr−1, with potential for a further reduction by up to 254 Gg CO2-eq yr−1 if all the remaining acidic soils are brought up to optimal pH.

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

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

Decreased nitrous oxide emissions associated with functional microbial genes under bio-organic fertilizer application in vegetable fields

Bio-organic fertilizers enriched with plant growth-promoting microbes (PGPMs) have been widely used in crop fields to promote plant growth and maintain soil microbiome functions. However, their potential effects on N2O emissions are of increasing concern. In this study, an in situ measurement experiment was conducted to investigate the effect of organic fertilizer containing Trichoderma guizhouense (a plant growth-promoting fungus) on soil N2O emissions from a greenhouse vegetable field. The following four treatments were used: no fertilizer (control), chemical fertilizer (NPK), organic fertilizer derived from cattle manure (O), and organic fertilizer containing T guizhouense (O+T, referring to bio-organic fertilizer). The abundances of soil N cycling-related functional genes (amoA) from ammonium-oxidizing bacteria (AOB) and archaea (AOA), as well as nirS, nirK, and nosZ, were simultaneously determined using quantitative PCR (qPCR). Compared to the NPK plot, seasonal total N2O emissions decreased by 11.7% and 18.7% in the O and O+T plots, respectively, which was attributed to lower NH4+-N content and AOB amoA abundance in the O and O+T plots. The nosZ abundance was significantly greater in the O+T plot, whilst the AOB amoA abundance was significantly lower in the O+T plot than in the O plot. Relative to the organic fertilizer, bio-organic fertilizer application tended to decrease N2O emissions by 7.9% and enhanced vegetable yield, resulting in a significant decrease in yield-scaled N2O emissions. Overall, the results of this study suggested that, compared to organic and chemical fertilizers, bio-organic fertilizers containing PGPMs could benefit crop yield and mitigate N2O emissions in vegetable fields.

Nitrification inhibitor nitrapyrin does not affect yield-scaled nitrous oxide emissions in a tropical grassland

Urea is the most common nitrogen (N) fertilizer used in the tropics but it has the risk of high gaseous nitrogen (N) losses. Use of nitrification inhibitor has been suggested as a potential mitigation measure for gaseous N losses in N fertilizer-applied fields. In a field trial on a tropical Andosol pastureland in Costa Rica, gaseous emissions of ammonia (NH3) and nitrous oxide (N2O) and grass yield were quantified from plots treated with urea (U; 41.7 kg N ha–1 application–1) and urea plus the nitrification inhibitor nitrapyrin (U + NI; 41.7 kg N ha–1 application–1 and 350 g of nitrapyrin for each 100 kg of N applied) and control plots (without U and NI) over a six-month period (rainy season). Volatilization of NH3 (August to November) in U (7.4% ± 1.3% of N applied) and U + NI (8.1% ± 0.9% of N applied) were not significantly different (P > 0.05). Emissions of N2O in U and U + NI from June to November were significantly different (P < 0.05) only in October, when N2O emission in U + NI was higher than that in U. Yield and crude protein production of grass were significantly higher (P < 0.05) in U and U + NI than in the control plots, but they were not significantly different between U and U + NI. There was no significant difference in yield-scaled N2O emission between U (0.31 ± 0.10 g N kg–1 dry matter) and U + NI (0.47 ± 0.10 g N kg–1 dry matter). The results suggest that nitrapyrin is not a viable mitigation option for gaseous N losses under typical N fertilizer application practices of pasturelands at the study site.

Effects of the nitrification inhibitor nitrapyrin and the plant growth regulator gibberellic acid on yield-scale nitrous oxide emission in maize fields under hot climatic conditions

Nitrification inhibitors are widely used in agriculture to mitigate nitrous oxide (N2O) emission and increase crop yield. However, no concrete information on their mitigation of N2O emission is available under soil and environmental conditions as in Pakistan. A field experiment was established using a silt clay loam soil from Peshawar, Pakistan, to study the effect of urea applied in combination with a nitrification inhibitor, nitrapyrin (2-chloro-6-tri-chloromethyl pyridine), and/or a plant growth regulator, gibberellic acid (GA3), on N2O emission and the nitrogen (N) uptake efficiency of maize. The experimental design was a randomized complete block with five treatments in four replicates: control with no N (CK), urea (200 kg N ha–1) alone, urea in combination with nitrapyrin (700 g ha–1), urea in combination with GA3 (60 g ha–1), and urea in combination with nitrapyrin and GA3. The N2O emission, yield, N response efficiency, and total N uptake were measured during the experimental period. The treatment with urea and nitrapyrin reduced total N2O emission by 39%–43% and decreased yield-scaled N2O emission by 47%–52%, relative to the treatment with urea alone. The maize plant biomass, grain yield, and total N uptake increased significantly by 23%, 17%, and 15%, respectively, in the treatment with urea and nitrapyrin, relative to the treatment with urea alone, which was possibly due to N saving, lower N loss, and increased N uptake in the form of ammonium; they were further enhanced in the treatment with urea, nitrapyrin, and GA3 by 27%, 36%, and 25%, respectively, probably because of the stimulating effect of GA3 on plant growth and development and the reduction in biotic and abiotic stresses. These results suggest that applying urea in combination with nitrapyrin and GA3 has the potential to mitigate N2O emission, improve N response efficiency, and increase maize yield.

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.

Effects of the nitrification inhibitor nitrapyrin and mulch on N2O emission and fertilizer use efficiency using 15N tracing techniques

Nitrous oxide (N2O), is a potent greenhouse gas (GHG) that shares 7% of global warming around the world. Among different sources, agricultural systems account for approx. 60% of global anthropogenic N2O emissions. These N2O emissions are associated with the activity of nitrifiers and denitrifiers that contribute to >4 Tg (teragrams) N2O-N emission per year. Application of nitrogen (N) fertilizers and manures in agricultural fields plays an imperative role in this regard. On the other hand nitrification inhibitors are an effective approach to minimize N2O-N emissions from agricultural fields. Here we examined the effects of applying urea with a nitrification inhibitor (Ni) nitrapyrin and mulch (Mu) on urea transformation, nitrous oxide (N2O) emissions, grain yield and nitrogen (N) uptake efficiency. The treatments include a control (zero N), urea (U) applied at 200 kg N ha−1, U + Ni (Ni applied at 700 g ha−1), U+ Mu (Mu applied at 4 t ha−1) and U + Ni + Mu. The N2O emission factor (EF) was 66% and 75% when U and Mu were applied, respectively. Yield-scaled N2O emissions were lower in U and Mu by 45% and 55%, respectively. The Ni coupled with Mu enhanced urea-15N recovery by 58% and wheat grain yield by 23% and total N uptake by 30% compared with U alone. In conclusion, Ni usage is an effective strategy to mitigate N2O emissions under field conditions.

Reduced tillage with residue retention and nitrogen application rate increase N2O fluxes from irrigated wheat in a subtropical floodplain soil

Nitrous oxide (N2O) emissions were measured in irrigated wheat (Triticum aestivum) in an annual wheat- mungbean (Vigna radiata)-rice (Oryza sativa L) rotation that had been running for seven consecutive years. Effect of two soil disturbance levels (strip vs. conventional tillage; ST vs. CT both with 30 % residue retention) and three nitrogen (N) fertilizer rates (60, 100 and 140 % of the recommended N fertilizer dose, RD; called hereafter 60RD, 100RD and 140RD, respectively) were assessed. Mean N2O fluxes were about 110 % higher in ST than in CT. The rate of N fertilizer application influenced the mean and cumulative N2O fluxes with significantly higher fluxes in ST than in CT. Based on the respective maximum grain yields (CT: 140RD, 3.52 t ha−1; ST: 60RD, 3.19 t ha−1) yield-scaled N2O emissions were higher in ST than those in CT. However, tillage vs. N rate interactions showed both the highest and lowest yield-scaled N2O fluxes in ST with 140RD and 60RD, respectively. Soil microbial biomass carbon (MBC), organic carbon (SOC), total N (TN), nitrate (NO3- -N), aggregate mean weight diameter (MWD) and larger aggregate size classes (2.0‒0.85 and >2.0 mm) were significantly higher in ST and positively correlated with N2O fluxes. Our results highlight that, despite increased N2O emissions, ST with residue can trade-off emissions to improve soil macro aggregation, C sequestration and retention of N and crop yield with the lower N fertilizer and other energy inputs. Reduction of the recommended N fertilization rate could be considered if ST is adopted.

Soil N-oxide emissions decrease from intensive greenhouse vegetable fields by substituting synthetic N fertilizer with organic and bio-organic fertilizers

In order to reduce soil and environmental quality degradation associated with the use of synthetic nitrogen (N), substituting chemical fertilizer with organic or bio-organic fertilizer has become an increasingly popular option. However, components of this fertilizer strategy related to mitigation of soil N-oxide emissions and maintenance of crop yield remain uncertain. Here, we evaluated the effects of three different fertilizer strategies, with equal amounts of N, on nitrous oxide (N2O) and nitric oxide (NO) emissions, vegetable yield, and yield-scaled N2O and NO emissions under three consecutive cucumber growing seasons. The three treatments were chemical fertilizer (NPK, urea), organic fertilizer (O, composted cattle manure), and bio-organic fertilizer (O + T, O combined with Trichoderma.spp). Results showed that the NPK plot had the highest area-scaled emissions of N2O (13.1 ± 0.48 kg N ha−1 yr−1) and NO (5.01 ± 0.34 kg N ha−1 yr−1), which were 1.3–1.4 and 3.1–3.7 times greater than the O and O + T plots, respectively. The annual direct emission factors for N2O and NO were 2.08% and 0.92% for the NPK plot, which declined to 1.34% and 0.09% in the O plot, and 1.12% and 0.03% in the O + T plot, respectively. The annual vegetable yield was 117 ± 2.9 t ha−1 for NPK plot and 122 ± 2.0 t ha−1 for O + T plot, which was higher than 111 ± 1.7 t ha−1 for O plot. The yield-scaled N2O + NO emissions differed significantly with fertilization treatment, with the lowest value observed in the O + T plot. We attributed the lower soil N-oxide emissions following organic fertilizer application to the slow release of available N and enhanced denitrification caused by the increase of soil dissolved organic carbon and pH. Compared with the use of organic fertilizer alone, the addition of Trichoderma.spp significantly increased the potential denitrification rate but decreased N2O emissions, which may have promoted the reduction of N2O to N2. Therefore, our results suggest that adopting composted organic fertilizer mixtures with microbial inoculants could be a win-win practice to mitigate gaseous N losses and simultaneously improve crop yield in intensively managed vegetable cropping systems.

Variations in nitrous oxide emissions as manipulated by plastic film mulching and fertilization over three successive years in a hot pepper-radish rotated vegetable production system

Plastic film mulching (FM) is widely applied in agro-ecosystems to improve soil hydrothermal conditions for better crop productivities. However, effects of such FM practices on nitrous oxide (N2O) emissions are not well known in high nitrogen (N) input vegetable fields. Using static chambers under no-mulching (NM) and FM with four N application rates N2O emissions were monitored in a hot pepper (Capsicum annuum)-radish (Raphanus sativus) rotation in southwest China over three years (Cycle 1, 2 and 3) from May 2014 to February 2017. These four N application rates for each vegetable crop were 0, 150, 300 and 450 kg N ha−1 and 0, 100, 200 and 300 kg N ha-1 in the respective hot pepper and radish seasons. Compared to NM, FM insignificantly reduced N2O emissions in the hot pepper season owing to lower soil moisture, while significantly increased N2O emissions in the radish season owing to higher soil NH4++NO3− and temperature. Additionally, FM had no remarkable effects on N2O EFs or crop yields of hot pepper or radish. N application exerted stronger effects on N2O emissions under FM and NM in Cycle 1 than in other two cycles during the hot pepper season owing to higher temperature and rainfall, resulting in very high N2O EFs (2.56 %–7.43 %). The average seasonal EF was 1.52 % (0.15 %–7.43 %), while the average annual EF was 1.74 % (0.16 %–5.32 %), which was comparable to the 2006 IPCC defaulted of 1.00 %. Yield-scaled N2O emissions under FM were significantly increased in the radish season, but not in the hot pepper season. Additionally, N application remarkably increased N2O emissions and crop yields in the hot pepper season, with a bigger effect on N2O emissions than on crop yields, leading to increased yield-scaled N2O emissions with increasing N application between 0 and 450 kg N ha-1. Moreover, the stimulation effect of N application on crop yield was strongest under 150 kg N ha-1 with lower yield-scaled emissions. In addition, N application remarkably increased N2O emissions and crop yields, but were more prominent on crop yields than N2O emissions during the radish season, resulting in insignificant increase of yield-scaled N2O emissions between 0 and 300 kg N ha-1. Our results demonstrated that no-mulching with 150 or 300 kg N ha-1 fertilization in the hot pepper or radish season is a more suitable agronomic practice to simultaneously mitigate N2O emissions while increasing crop yields in subtropical vegetable fields.

Four-year continuous residual effects of biochar application to a sandy loam soil on crop yield and N2O and NO emissions under maize-wheat rotation

Biochar application has been reported to effectively mitigate N2O emissions and increase crop yield; however, its long-term residual effects remain largely unknown. A four-year field experiment was designed in the North China Plain (NCP) to evaluate the residual effect of biochar on N2O and NO emissions and crop yield under maize-wheat rotation. The study included five treatments: no N fertilization (Control), N fertilizer application (CN), and N fertilizer plus maize-straw biochar application at 3 (NB3), 6 (NB6) and 12 t ha−1 (NB12). Biochar amendment had no effect on maize yield during the four-year rotation, but increased maize grain N uptake by 12.9 − 14.1 % and fertilizer N use efficiency by 13.8 % in the fourth year. Meanwhile, NB12 treatment decreased wheat yield by 11.7 − 15.5 % in each year, except the second, while decreased average wheat yield. Biochar application significantly reduced N2O emissions by 31.5 − 42.4 % during the first maize season, and by 6.9 − 21.3 % in the third and fourth years primarily due to reduction in NH4+ availability for nitrification. Furthermore, this mitigation effect was positively related to soil moisture content and decreased with time after biochar application. Cumulative N2O emissions during the four wheat seasons were 0.25 − 0.85 kg N2O-N ha−1, and only decreased by 8.9 − 9.9 % under biochar amendment in the third and fourth years probably because low soil temperature suppressed N2O production. Biochar addition in the third and fourth years significantly reduced NO emissions by 9.0 − 20.1 % during the maize growing seasons and 10.5 − 19.1 % during the wheat growing seasons, especially under NB6 treatment. The average yield-scaled N2O and NO emissions were lowest in the NB6 treatment during the maize and wheat season. Overall, these findings suggest that 6 t ha−1 is the optimal biochar application rate for reducing N2O/NO emissions and yield-scaled N2O/NO emission under four-year maize-wheat rotation in the NCP.

Nitrogen use efficiency, crop water productivity and nitrous oxide emissions from Chinese greenhouse vegetables: A meta-analysis

Greenhouse vegetable cultivation is a substantial source of nitrous oxide (N2O) emissions in China due to intensive managements with nitrogen (N) fertilizers and irrigation water. We hypothesize that reducing input rates of N fertilizers or irrigation water to optimal levels would mitigate N2O emissions without significant loss of vegetable yields. The primary aims of this study are to (i) quantify the variations in vegetable yields, N2O emissions, nitrogen use efficiency (NUE) and crop water productivity (CWP) under greenhouse cultivation conditions; (ii) determine the major regulating factors of vegetable yields, N2O emissions, emission factors (EFs), yield-scaled N2O emissions, NUEs and CWPs; and (iii) evaluate the effectiveness of fertilization and irrigation strategies for N2O mitigation. We compiled a comprehensive dataset from 44 peer-reviewed publications, which includes 408 determinations of seasonal N2O emissions from greenhouse vegetable systems across China between 2006 and 2019. An emission coefficient of 0.95% was obtained as the slope of the linear regression between N2O emissions against N input rates (r2 = 0.480, n = 322, p < 0.001) for treatments that were unfertilized and fertilized with conventional fertilizers. For fruit vegetables, N2O emissions responded to NUEs following a linear-plateau model (r2 = 0.539, n = 115, p < 0.001), which suggests that management practices aiming to increase NUEs are effective for decreasing N2O emissions at NUEs below 0.15 t kg−1. The results of meta-analyses revealed that applications of biochar or enhanced efficiency fertilizers (EEFs) decreased EFs and yield-scaled N2O emissions (ranging from −42% to −34%) but did not significantly increase NUEs. Reducing the input rates of N fertilizers (approximately 50% of the total N input) or irrigation water (approximately 20% of the full irrigation water) provided advantages for maintaining vegetable yields (ranging from −7% to 3%), decreasing N2O emissions (ranging from −68% to −59%), increasing NUEs (ranging from 76% to 157%), and subsequently reducing the reactive N released into the environment.

Soil greenhouse gas fluxes from maize cropping system under different soil fertility management technologies in Kenya

Few studies have quantified soil greenhouse gas (GHG) −CH4, CO2 N2O – annual fluxes directly from smallholder maize cropping systems under different soil fertility management technologies in Sub Saharan Africa. We quantified soil GHG annual fluxes from smallholder maize cropping systems under four different soil fertility management technologies in the Central Highlands of Kenya. We regularly sampled GHG from 2nd March 2018 to 1st March 2019 (1 year) in three maize farms using a static chamber technique. The fertility management technologies were: inorganic fertilizer, animal manure, animal manure combined with inorganic fertilizer, and a Control (No external input). The experimental design was a randomized complete block design replicated thrice. Cumulative annual soil fluxes ranged from -2.40 kg CH4-C ha−1 yr−1 from the control treatment to −1.62 kg CH4-C ha−1 yr−1 from the manure combined with inorganic fertilizer treatment, 4810 kg CO2-C ha−1 yr−1 from the control treatment to 6576 kg CO2-C ha−1 yr−1 from the inorganic fertilizer treatment, and 0.21 kg N2O-N ha−1 yr−1 from the control treatment to 0.38 kg N2O-N ha−1 yr−1 from the inorganic fertilizer treatment for CH4, CO2, and N2O fluxes, respectively. Fertilizer treatment produced the highest CO2 emissions (p < 0.001), N2O emissions (P < 0.001), and yield-scaled N2O emissions (YSE), (0.028 g N2O-N kg−1 grain yield). A combination of manure and inorganic fertilizer produced the highest CH4 fluxes (p = 0.035) across treatments. We concluded that a judicious combination of organic resources (animal manure) and inorganic resources (fertilizer) has the potential to enhance food security while mitigating soil greenhouse gas emissions in SSA.

Effect of Water-Fertilizer-Gas Coupling on Soil N2O Emission and Yield in Greenhouse Tomato

To reveal the effect of water, fertilizer, and gas coupling on soil N2O emissions in greenhouse tomato soil and suggest appropriate measures for increasing yield and reducing N2O emissions, static chamber-gas chromatography was used to study the effects of soil N2O emissions. The variation laws of soil temperature, water-filled pore space (WFPS), NO3--N content, and O2 content and the influence mechanism of N2O emission under the condition of water-fertilizer-gas coupling were analyzed. Aerated conditions comprised two water levels, 0.6 W and 1.0 W (representing 40% deficit irrigation and full irrigation, W represents when sufficient irrigation water was available), and three nitrogen levels (120 kg·hm-2, 180 kg·hm-2, and 240 kg·hm-2, representing low, medium, and high nitrogen, respectively, with 50% F, 75% F, and F, F is the recommended amount of nitrogen application locally). Three levels of fertilization were used as controlled unaerated full irrigation (O representing aeration, and CK representing conventional drip irrigation). Nine treatments were designed in the experiment. The results showed that the tomato field cumulative emission of N2O under full irrigation (W2F1O, W2F2O, and W2F3O) increased by an average of 55.7% compared with the corresponding treatment at W1 level (P<0.05). The N2O emissions of W1F3O, W2F3O, and W2F3CK fields significantly increased by 13.4% and 43.8% compared with medium nitrogen W1F2O, W2F2O, and W2F2CK and low nitrogen W1F1O, W2F1O, and W2F1CK treatments, respectively (P<0.05).Compared with the corresponding unaerated full irrigation, the emissions (W2F1O, W2F2O, and W2F3O) significantly increased by 11.2% (P<0.05). Aeration, the increase of nitrogen rate, and irrigation amount resulted in the increment of tomato yield and yield-scaled N2O emissions. Compared with medium nitrogen, the yield and yield-scaled N2O emission of high nitrogen treatment increased by 12.5% (P<0.05) and 3.9% (P>0.05), respectively. Compared with low nitrogen treatment, the yield and yield-scaled N2O emission of high nitrogen treatment increased by 30.4% and 9.6% (P<0.05), respectively. The yield and yield-scaled N2O emissions of aerated full irrigation significantly increased by 29.7% and 18.7%, respectively, compared with aerated deficient irrigation. Compared with unaerated irrigation treatment, the yield under aerated treatment increased by 10.4% (P<0.05), and the yield-scaled N2O emission increased by 3.9% (P>0.05). Under the conditions of increasing irrigation water, decreasing fertilizer application, and aeration, partial factor productivity, and irrigation water use efficiency (IWUE) can be significantly increased. After comprehensive consideration of cumulative N2O emissions, tomato production, nitrogen fertilizer utilization efficiency, IWUE, and yield-scaled N2O emission, it can be concluded that aerated low nitrogen full irrigation is an optimal management mode. The results provide reference for increasing yield and reducing emissions of greenhouse tomato.

Effect of organic amendments on yield-scaled N2O emissions from winter wheat-summer maize cropping systems in Northwest China.

The effect of dairy manure amendments to agricultural soil on the yield-scaled nitrous oxide (N2O) emissions remains unclear. We hypothesize that an optimum ratio of dairy manure to synthetic fertilizers leads to large nitrogen use efficiency (NUE) and small yield-scaled N2O emissions. The aims of this study were to (1) quantify the variations in the crop yields and N2O emissions from winter wheat-summer maize cropping systems in Northwest China, (2) determine the responses of the NUE and yield-scaled N2O emission to the ratio of organic materials to synthetic fertilizers, and (3) evaluate the relationship between the NUE and yield-scaled N2O emissions. Field measurements were conducted within long- and short-term fertilization experiments between the years of 2014 and 2016. Treatments included synthetic fertilizers, synthetic fertilizers plus crop residues, and synthetic fertilizers plus dairy manure at both sites. The annual grain yields and N2O emissions varied from 13.3 to 18.0 Mg ha-1 and from 1.3 to 3.6 kg N ha-1, respectively, across the treatments. The yield-scaled N2O emissions related negatively to the NUE, suggesting that agronomic aims of improving NUE are an effective approach to mitigate N2O emissions. The ratio of organic materials to synthetic fertilizers was not a significant limit on the NUE and yield-scaled N2O emissions. We conclude that organic amendments appeared to play a minor influence on the promotion of the NUE and N2O mitigation.

Finding the optimal fertilizer type and rate to balance yield and soil GHG emissions under reclaimed water irrigation

Water and inorganic nitrogen fertilizer have a notable impact on crop yield and greenhouse gas (GHG) emissions from soil. Reclaimed water (RW) is widely used for irrigation when there are shortages of water resources. It is very important to control yield and greenhouse gas emissions by fertilization under reclaimed water irrigation (RWI). The study consisted of a continuous test that evaluated three types of fertilizer treatments (urea, amine, and slow-release fertilizer) and a no-fertilizer treatment under three-year RWI and four fertilizer levels (150, 200, 250 and 300 kg.N.ha−1) under one-year RWI to determine the best fertilizer to support maize production and reduce GHG (CO2 and N2O) emissions from soil; further, the applicability of RWI in the DNDC model was verified. For many years, GHG emissions under RWI showed an increasing trend, but the effect was not significant. A strong correlation was found between the GHG emissions flux and fertilizer amount, and a threshold fertilization amount existed between 220 and 260 kg.N.ha−1 that minimized yield-scaled N2O emissions and the ratio of GHG cumulative emission to yield (GHG/Y). The results indicated that the optimal amounts of SF and UF under RWI were 240 and 225 kg.N.ha−1 by second-order equation and the DNDC model, respectively, and the rate better balanced the yield and GHG emissions.

Nitrous oxide emissions from oilseed rape cultivation were unaffected by flash pyrolysis biochar of different type, rate and field ageing

Nitrous oxide (N2O) emission from winter oilseed rape (WOSR) cultivation may compromise the sustainability of oilseed rape biodiesel. Typically, greenhouse gas budgets of WOSR cultivation assume an N2O emission factor (EF) of 1% of the N added in fertilizer and crop residues. Management options to reduce direct soil emissions of N2O include the application of biochar, but efficacy and mechanisms of N2O suppression are elusive. We measured N2O emissions in a WOSR field trial on a sandy loam soil in Denmark over 402 days in 2017–2018, comparing biochar applications from two feedstocks (wheat straw and pig manure fibers), two application rates (1.5 and 15 Mg ha−1) and field ageing of up to three years. Further, a controlled incubation experiment was performed to examine the effect of biochar dose and ageing on N2O production and consumption by denitrification. Biochar treatments had no significant effects on cumulative N2O emissions (1.71–2.78 kg N ha−1 yr−1). Likewise, no significant effects were found on crop yield, yield-scaled N2O emission, soil mineral N content, gravimetric soil moisture or pH. The fertilizer induced EF was 0.51% which is well below the IPCC Tier 1 EF of 1%. High doses of fresh, but not field-aged biochar suppressed N2O production under anoxic conditions ex situ, suggesting that biochar with sufficient liming capacity could mitigate N2O emissions from denitrification also under field conditions. Yet, rates of up to 15 Mg ha−1 flash pyrolysis biochar in the current in situ study, which comprised a pronounced summer drought, showed no significant N2O mitigation. This highlights the need for selecting dedicated biochars and doses and test them in multi-year studies to conclude on their N2O mitigating effect. Yet, in relation to sustainability of WOSR cultivation for biodiesel, the current study suggests that C sequestration by biochar is not compromised by increased N2O emissions.

Optimal biochar amendment rate reduced the yield-scaled N2O emissions from Ultisols in an intensive vegetable field in South China

Nitrous oxide (N2O) emissions, vegetable yields, and soil microbial properties were studied in response to different rates of rice-straw biochar applied to an intensive vegetable soil (Ultisol) in South China. The study was conducted over a one-year period as a block-designed field experiment (n = 3) with two successive crops and five harvests in total. Biochar was applied at rates of 0, 10, 20, 30 and 40 Mg ha−1 and splits of nitrogen (N) fertilizer were added in the form of urea (1010 kg N in total). References without biochar and N fertilization were included. Biochar significantly decreased the cumulative annual N2O emissions by 34–67%, which concurred with decreased denitrification enzyme activity and increased nosZ gene abundance in the vegetable soil. The absolute N2O mitigation increased with increasing flux rates, which were positively correlated to soil temperature and water-filled pore space. Conversely, weak increases of N2O emissions were recurrently induced by biochar when the soil temperature was lower than 20 °C and the absolute fluxes were low. A significant 17–29% increase in vegetable yield was induced by biochar, which also ameliorated soil fertility by increasing the soil carbon content and the cation exchange capacity. Overall, biochar significantly decreased the yield-scaled N2O emissions by 44–71% with the lowest yield-scaled N2O emissions for the intermediate biochar application rate of 20 Mg ha−1. Higher biochar application rates failed to further decrease the yield-scaled N2O emissions, but rather caused weak increases. Based on the present results, a biochar application rate of 20 Mg ha−1 combined with N fertilization seemed to be recommendable to achieve highest vegetable yield with lowest N2O emissions in intensive vegetable production in South China.