Lime-nitrogen application reduces N2O emission from a vegetable field with imperfectly-drained sandy clay-loam soil

Abstract

We studied the effect of lime-nitrogen (calcium cyanamide, CaCN₂) application on the emission of nitrous oxide (N₂O) from a vegetable field with imperfectly-drained sandy clay-loam soil. Lime-nitrogen acts as both a pesticide and a fertilizer. During the decomposition of lime-nitrogen in the soil, dicyandiamide (DCD), a nitrification inhibitor, is formed, and as a result lime-nitrogen application may mitigate N₂O emission from the soil. The study design consisted of three different nitrogen-application treatments in field plots with a randomized block design. The nitrogen application treatments were: CF (chemical fertilizer), LN (all nitrogen fertilizer applied as lime-nitrogen), and CFD (chemical fertilizer containing DCD). Soil nitrification activity was lower in the LN and CFD plots than in the CF plots, and nitrification was inhibited for a longer period in the LN plots than in the CFD plots. In the LN plots, N₂O emission was lower than those of other treatments from 20 to 40 days after fertilization, a period when large peaks of N₂O emission were observed after rainfall in the CF and CFD plots. Cumulative N₂O emission over 63 days in the CF plots (mean ± standard deviation: 30.2 ± 14.4 mg N₂O m^?2) and CFD plots (24.3 ± 10.8 mg N₂O m^?2) was significantly higher than that in the LN plots (10.7 ± 1.2 mg N₂O m^?2; P < 0.05). Our results suggested that lime-nitrogen application decreased N₂O emission by inhibiting both nitrification and denitrification.     

Gaseous losses of fertilizer nitrogen from a citrus orchard in the red soil hilly region of Southeast China

The gaseous losses of fertilizer nitrogen (N) applied to agroecosystems are a major contributor to a host of environmental problems, inefficient production systems, and decreased N-use efficiency. These losses lead to the wastage of resources, increasing the greenhouse effect and harming human health. The red soil hilly region of Southeast China houses the biggest orchard area of the world, and nitrogen fertilizers are usually heavily applied to the orchard systems in China. Therefore, this study aimed to measure the gaseous losses of the fertilizer N by ammonia (NH₃) volatilization and denitrification losses using the venting method and acetylene inhibition method respectively, and to assess the potential environmental risk of NH₃ and nitrous oxide (N₂O) emission from this orchard system based on the recent orchard management practices. An experiment was conducted in an Ougan citrus (Citrus reticulata Blanco ‘Suavissima’) orchard in the red soil hilly region of Southeast China. Three fertilization treatments, including the control (no N fertilizer, CK), poultry manure (at a rate of 6.3 t/ha, OM), and conventional fertilization (OM 6.3 t/ha + chemical fertilizer 393 kg N/ha, CF), were used. In all treatments, the fertilizers were incorporated into the soil after application. The test results, which were continuously determined within one year, indicated that the NH₃ volatilization losses accounted for 4.5% of the OM nitrogen (OM-N) and 2.9% of the CF nitrogen (CF-N), whereas the denitrification N losses accounted for 2.1% of the OM-N and 2.9% of the CF-N. Overall, the total gaseous N losses (including NH₃ volatilization losses and denitrification N losses) were 5.8% in the CF treatment. A relatively higher N₂O flux, accounting for 1.8% of the CF-N, emitted from the CF treatment.     

N2O and NO emissions from an Andisol field as influenced by pelleted poultry manure

Animal manures from intensive livestock operations can be pelleted to improve handlings and recyclings of embodied nutrients. The aim of this study was to evaluate the influence of pelleted poultry manure on N₂O and NO fluxes from an Andisol field. In autumn 2006 and summer 2007, poultry manure (PM), pelleted poultry manure (PP), and chemical fertilizer (CF) were applied at a rate of 120 kg N ha⁻¹ in each cultivation period to Komatsuna (Brassica rapa var. peruviridis). Nitrous oxide and NO fluxes were measured using an automated monitoring system. A soil incubation experiment was also conducted to determine the influence of intact and ground pelleted manure on N₂O, NO, and CO₂ production with a water-filled pore space (WFPS) of 30 or 50%. In the field measurements, N₂O emission rates from the organic fertilizer treatments were larger than that from the CF treatment, possibly because organic C stimulated denitrification. The highest N₂O flux was observed from the PP treatment after a rainfall following fertilization, and the cumulative emission rate (2.72 ± 0.22 kg N ha⁻¹ y⁻¹) was 3.9 and 7.1 times that from the PM and CF treatments, respectively. In contrast, NO emission rates were highest from the CF treatment. The NO/N₂O flux ratio indicated that nitrification was the dominant process for NO and N₂O production from the CF treatment. Cumulative N₂O emission rates from all treatments were generally higher during the wetter cultivation period (autumn 2006) than during the drier cultivation period (summer 2007). In contrast, NO emission rates were higher in the drier than in the wetter cultivation period. The incubation experiment results showed a synergistic effect of soil moisture and the pelleted manure form on N₂O emission rates. The intact pelleted manure with the 50% WFPS treatment produced the highest N₂O and CO₂ fluxes and resulted in the lowest soil NO₃⁻ content after the incubation. These results indicate that anaerobic conditions inside the pellets, caused by rainfall and heterotrophic microbial activities, led to denitrification, resulting in high N₂O fluxes. Controlling the timing of N application by avoiding wet conditions might be one mitigation option to reduce N₂O emission rates from the PP treatment in this study field.     

施肥对夏玉米季紫色土N2O排放及反硝化作用的影响

采用原状土柱-乙炔抑制培养法研究了施肥对紫色土玉米生长季土壤N2O排放通量和反硝化作用的影响.结果表明:玉米季施肥显著增加土壤N2O排放和反硝化损失,同时,各施肥处理间N2O排放与反硝化损失量差异显著.猪厩肥、猪厩肥配施氮磷钾肥、氮肥、氮磷钾肥和秸秆配施氮磷钾肥等处理的土壤N,O排放量分别为3.01、2.86、2.51、2.19和1.88 kg hm-2,分别占当季氮肥施用量的1.63％、1.53％、1.30％、1.09％和0.88％,反硝化损失量分别为6.74、6.11、5.23、4.69和4.12 kg hm-2,分别占当季氮肥施用量的3.97％、3.55％、2.97％、2.61％和2.23％,不施肥土壤的N2O排放量和反硝化损失量仅为0.56和0.78 kg hm-2.施肥是紫色土玉米生长前期(2周内)土壤N2O排放和反硝化速率出现高峰的主要驱动因子,土壤铵态氮和硝态氮含量是影响土壤N2O排放、土壤硝化和反硝化作用的限制因子,土壤含水量是重要影响因子,降雨是主要促发因素.土壤N2O排放量与反硝化损失量的比值介于0.45 ～0.72之间,土壤反硝化损失量极显著高于土壤N2O排放量,说明土壤反硝化作用是紫色土玉米生长季氮肥损失的重要途径.     

Effect of the number of tillages in fallow season and fertilizer type on greenhouse gas emission from a rice (Oryza sativa L.) paddy field in Ehime,southwestern Japan

Agricultural fields, including rice (Oryza sativa L.) paddy fields, constitute one of the major sources of atmospheric methane (CH₄) and nitrous oxide (N₂O). Organic matter application, such as straw and organic fertilizer, enhances CH₄ emission from paddy fields. In addition, rice straw management after harvest regulates CH₄ emissions in the growing season. The interaction of tillage times and organic fertilizer application on CH₄ and N₂O emissions is largely unknown. Therefore, we studied the effects of fallow-season tillage times and fertilizer types on CH₄ and N₂O emissions in paddy fields in Ehime, southwestern Japan. From November 2011 to October 2013, four treatments, two (autumn and spring) or one (spring) in the first year, or two (autumn and spring) or three (autumn, winter, and spring) in the second year times of tillage with chemical or organic fertilizer application, were established. Gas fluxes were measured by the closed-chamber method. Increasing the number of tillage times from one to two decreased succeeding CH₄ emission and the emission factor for CH₄ (EF_CH4) in the rice-growing season, suggesting that the substrate for CH₄ production was reduced by autumn and spring tillage in the fallow season. Higher EF_CH4 [1.8–2.0 kg carbon (C) ha^?1 d^?1] was observed when more straw was applied (6.9–7.2 Mg ha^?1) in the second year. Organic fertilizer application induced higher CH₄ emission just after the application as basal and supplemental fertilizers, especially at a lower straw application rate. This indicated that EF_CH4 in the organically managed fields should be determined individually. Organic fertilizer application with two tillage times induced N₂O efflux during the rice-growing season in the second year, but N₂O emissions were not affected by winter tillage. Although paddy fields can act as an N₂O sink because of reduced soil conditions when straw application was high, application of organic C and nitrogen as fertilizer can enhance N₂O production by the denitrification process during the growing season, especially in the ripening stage when soil anaerobic conditions became moderate. These results suggest that negative emission factors for N₂O (EF_N2O) can be applied, and EF_N2O of organic fertilizer should be considered during the estimation of N₂O emission in the paddy field.     

Effects of application of lime nitrogen and dicyandiamide on nitrous oxide emissions from green tea fields

Abstract

The aim of this study was to assess the mitigating effects of lime nitrogen (calcium cyanamide) and dicyandiamide (DCD) application on nitrous oxide (N₂O) emissions from fields of green tea [Camellia sinensis (L.) Kuntze]. The study was conducted in experimental tea fields in which the fertilizer application rate was 544 kg nitrogen (N) ha^?1 yr^?1 for 2 years. The mean cumulative N₂O flux from the soil between the canopies of tea plants for 2 years was 7.1 ± 0.9 kg N ha^?1 yr^?1 in control plots. The cumulative N₂O flux in the plots supplemented with lime nitrogen was 3.5 ± 0.1 kgN ha^?1, approximately 51% lower than that in control plots. This reduction was due to the inhibition of nitrification by DCD, which was produced from the lime nitrogen. In addition, the increase in soil pH by lime in the lime nitrogen may also be another reason for the decreased N₂O emissions from soil in LN plots. Meanwhile, the cumulative N₂O flux in DCD plots was not significantly different from that in control plots. The seasonal variability in N₂O emissions in DCD plots differed from that in control plots and application of DCD sometimes increased N₂O emissions from tea field soil. The nitrification inhibition effect of lime nitrogen and DCD helped to delay nitrification of ammonium-nitrogen (NH₄⁺-N), leading to high NH₄⁺-N concentrations and a high ratio of NH₄⁺-N /nitrate-nitrogen (NO₃^–-N) in the soil. The inhibitors delayed the formation of NO₃^–-N in soil. N uptake by tea plants was almost the same among all three treatments.     

Nitrous oxide emissions are greater in silt loam soils with a legacy of manure application than without

Soil carbon (C) content, often found at elevated levels in manured soils, can play a critical role in regulating nitrous oxide emissions. Nitrate availability and oxygen status are the other primary drivers of emissions, yet the interaction of these three variables and the dynamics of the denitrification process are inadequately known. Emissions of N₂O and N₂ were measured from two New York State soils that were historically managed either with regular cattle manure applications (M) or without manure (NM). For 168 h, repacked soil cores were maintained at 80 % water-filled pore space after the application of 0, 50, 100, and 200 kg ha^?1 of labeled K¹⁵NO₃. Significant differences were found in the N₂O emission profiles between the two treatments with a simultaneous increasing trend in emissions with higher fertilizer applications. The M soil produced 53-, 15.5-, and 8.6-fold increases in N₂O emissions over the NM soil at the 50-, 100-, and 200-kg ha^?1 N rates, respectively. Additionally, the mean ratio of nitrous oxide to total denitrification (N₂O/(N₂O + N₂)) was higher for M soil. It increased to values of 0.17, 0.25, and 0.43 for fertilizer rates of 50, 100, and 200 kg ha^?1, respectively, in contrast to ratios in the NM soil of 0.01, 0.03, and 0.14.     

Nitrate enhances N2O emission more than ammonium in a highly acidic soil

Purpose

Nitrous oxide (N₂O) is produced naturally in soils through microbial processes of nitrification and denitrification. In recent years, the long-term application of nitrogen-heavy fertilizers has led to the acidification of tea orchard soils with high N₂O emission. The present research aimed at finding out which process (nitrification or denitrification) dominates in N₂O production, whether certain fertilizer managements could reduce N₂O emission, and the effects of fertilizer management on the abundance of functional genes.

Materials and methods

Two nitrification inhibitors, 3, 4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD), combined with different N fertilizers (ammonium sulfate and potassium nitrate) were applied to highly acidic tea orchard soil in an aerobic incubation experiment. Both amoA and nosZ gene abundances from different treatments were determined by quantitative PCR. An anaerobic nitrate effect test was carried out using C₂H₂ inhibition method.

Results and discussion

The application of nitrate fertilizers significantly (P?<?0.05) enhanced total N₂O emission. A linear regression analysis between total N₂O emission and average nitrate contents indicated that denitrification is the dominant source of N₂O in this tea orchard soil. In the anaerobic incubation, no significant difference of N₂O emission was observed between KNO₃ and no KNO₃ treatments before 96 h. Quantitative PCR revealed lower copy numbers of nosZ in nitrate-associated fertilizer-treated soils than the soils from other treatments. Compared with the control, ammonium fertilizers with DCD or DMPP significantly (P?<?0.05) inhibited nitrate production as well as N₂O.

Conclusions

These results showed that denitrification is the dominant source of N₂O in this highly acidic soil. Nitrate addition could significantly inhibit the abundance of nitrous oxide reductase, therefore causing high N₂O emission. The application of ammonium fertilizers with DCD or DMPP could significantly reduce N₂O emission, possibly due to the effective inhibition of nitrate production.     

Effect of Inorganic N Composition of Fertilizers on Nitrous Oxide Emission Associated with Nitrification and Denitrification

We studied the effect of repeated application (once every 2 d) of a fertilizer solution with different ratios of NH₄ ⁺ - and NO₃ ^?-N on N₂O emission from soil. After the excess fertilizer solution was drained from soil, the water content of soil was adjusted to 50% of the maximum water-holding capacity by suction at 6 × 10³ Pa. Repeated application of NH₄ ⁺- rich fertilizer solution stimulated nitrification in soil more than NO₃ ^?-rich fertilizer. Although the evolution of N₂O through nitrifier denitrification tended to increase with the repeated addition of a fertilizer solution rich in NH₄ ⁺ rather than in NO₃ ^?, the contribution of nitrifier denitrification remained at levels of 20 to 36% of the total emission regardless of the inorganic N composition. The total emission of N₂O also tended to increase with the application of NH₄ ⁺- rather than NO₃ ^?-rich fertilizer. It was suggested that the coupled process of nitrification and denitrification at micro-aerobic sites became important when fertilizer rich in NH₄ ⁺ was applied to soil under relatively aerobic conditions.     

Impact of Long-Term Application of Fertilizers on N2O and NO Production Potential in an Intensively Cultivated Sandy Loam Soil

Literature reports on N₂O and NO emissions from organic and mineral agricultural soil amended with N-containing fertilizers have reached contradictory conclusions. To understand the influence of organic manure (OM) and chemical fertilizer application on N₂O and NO emissions, we conducted laboratory incubation experiments on an agricultural sandy loam soil exposed to different long-term fertilization practices. The fertilizer treatments were initiated in 1989 at the Fengqiu State Key Agro-ecological Experimental Station and included a control without fertilizer (CK), OM, mineral NPK fertilizer (NPK), mineral NP fertilizer (NP), and mineral NK fertilizer (NK). The proportion of N emitted as NO and N₂O varied considerably among fertilizer treatments, ranging from 0.83% to 2.50% as NO and from 0.08% to 0.36% as N₂O. Cumulative NO emission was highest in the CK treatment after NH ₄ ⁺ -N was added at a rate of 200 mg N kg^?1 soil during the 612-h incubation period, whereas the long-term application of fertilizers significantly reduced NO emission by 54–67%. In contrast, the long-term application of NPK fertilizer and OM significantly enhanced N₂O emission by 95.6% and 253%, respectively, compared to CK conditions. The addition of NP fertilizer (no K) significantly reduced N₂O emission by 25.5%, whereas applications of NK fertilizer (no P) had no effect. The difference among the N-fertilized treatments was due probably to discrepancies in the N₂O production potential of the dominant ammonia-oxidizing bacteria (AOB) species rather than AOB abundance. The ratio of NO/N₂O was approximately 24 in the CK treatment, significantly higher than those in the N-fertilized treatments (3–11), and it decreased with increasing N₂O production potential in N-fertilized treatments. Our data suggests that the shift in the dominant AOB species might produce reciprocal change in cumulative NO and N₂O emissions.     

Gross nitrogen transformations and related N2O emissions in uncultivated and cultivated black soil

A better understanding of the nitrogen (N) cycle in agricultural soils is crucial for developing sustainable and environmentally friendly N fertilizer management and to propose effective nitrous oxide (N₂O) mitigation strategies. This laboratory study quantified gross nitrogen transformation rates in uncultivated and cultivated black soils in Northeast China. It also elucidated the contribution made by nitrification and denitrification to the emissions of N₂O. In the laboratory, soil samples adjusted to 60 % water holding capacity (WHC) were spiked with ¹⁵NH₄NO₃ and NH₄ ¹⁵NO₃ and incubated at 25 °C for 7 days. The size and ¹⁵N enrichment of the mineral N pools and the N₂O emission rates were determined between 0 and 7 days. The results showed that the average N₂O emission rate was 21.6 ng N₂O-N kg^?1 h^?1 in cultivated soil, significantly higher than in the uncultivated soil (11.6 ng N₂O-N kg^?1 h^?1). Denitrification was found to be responsible for 32.1 % of the N₂O emission in uncultivated soil, and the ratio increased significantly to 43.2 % in cultivated soil, due to the decrease in soil pH. Most of the increase in net N₂O-N emissions observed in the cultivated soil was resulting from the increased production of N₂O through denitrification. Gross nitrification rate was significantly higher in the cultivated soil than in the uncultivated soil, and the ratio of gross nitrification rate/ammonium immobilization rate was 6.87 in cultivated soil, much larger than the uncultivated soil, indicating that nitrification was the dominant NH₄ ⁺ consuming process in cultivated soil, and this will lead to the increased production of nitrate, whereas the increased contribution of denitrification to N₂O emission promoted the larger emission of N₂O. This double impact explains why the risk of N loss to the environment is increased by long-term cultivation and fertilization of native prairie sites, and controlling nitrification maybe effective to abate the negative environmental effects.     

Linkage of N2O emissions to the abundance of soil ammonia oxidizers and denitrifiers in purple soil under long-term fertilization

Abstract

Microbial nitrification and denitrification are responsible for the majority of soil nitrous (N₂O) emissions. In this study, N₂O emissions were measured and the abundance of ammonium oxidizers and denitrifiers were quantified in purple soil in a long-term fertilization experiment to explore their relationships. The average N₂O fluxes and abundance of the amoAgene in ammonia-oxidizing bacteria during the observed dry season were highest when treated with mixed nitrogen, phosphorus and potassium fertilizer (NPK) and a single N treatment (N) using NH₄HCO₃as the sole N source; lower values were obtained using organic manure with pig slurry and added NPK at a ratio of 40%:60% (OMNPK),organic manure with pig slurry (OM) and returning crop straw residue plus synthetic NH₄HCO₃fertilizer at a ratio of 15%:85% (SRNPK). The lowest N₂O fluxes were observed in the treatment that used crop straw residue(SR) and in the control with no fertilizer (CK). Soil NH₄⁺provides the substrate for nitrification generating N₂O as a byproduct. The N₂O flux was significantly correlated with the abundance of the amoA gene in ammonia-oxidizing bacteria (r = 0.984, p < 0.001), which was the main driver of nitrification. During the wet season, soil nitrate (NO₃^?) and soil organic matter (SOC) were found positively correlated with N₂O emissions (r = 0.774, p = 0.041 and r = 0.827, p = 0.015, respectively). The nirS gene showed a similar trend with N₂O fluxes. These results show the relationship between the abundance of soil microbes and N₂O emissions and suggest that N₂O emissions during the dry season were due to nitrification, whereas in wet season, denitrification might dominate N₂O emission.     

Nitrous oxide fluxes and denitrification sensitivity to temperature in Irish pasture soils

Nitrous oxide (N₂O) emissions from grazed pastures constitute approximately 28% of total global anthropogenic N₂O emissions. The aims of this study were to investigate the effect of inorganic N fertilizer application on fluxes of N₂O, quantify the emission factors (EFs) for a sandy loam soil which is typical of large areas in Ireland and to investigate denitrification sensitivity to temperature. Nitrous oxide flux measurements from a cut and grazed pasture field for 1 year and denitrification laboratory incubation were carried out. The soil pH was 7.3 and had a mean organic C and N content at 0–20 cm of 44.1 and 4.4 g/kg dry weight, respectively. The highest observed peaks of N₂O fluxes of 67 and 38.7 g N₂O‐N per hectare per day were associated with times of application of inorganic N fertilizer. Annual fluxes of N₂O from control and fertilized treatments were 1 and 2.4 kg N₂O‐N per hectare, respectively. Approximately 63% of the annual flux was associated with N fertilizer application. Multiple regression analysis revealed that soil nitrate and the interaction between soil nitrate and soil water content were the main factors controlling N₂O flux from the soil. The derived EF of 0.83% was approximately 66% of the IPCC default EF value of 1.25% as used by the Irish EPA to estimate greenhouse gases (GHGs) in Ireland. The IPCC‐revised EF value is 0.9%. A highly significant exponential regression (r² = 0.98) was found between denitrification and incubation temperature. The calculated Q₁₀ ranged from 4.4 to 6.2 for a temperature range of 10–25 °C and the activation energy was 47 kJ/mol. Our results show that denitrification is very sensitive to increasing temperature, suggesting that future global warming could lead to a significant increase in soil denitrification and consequently N₂O fluxes from soils.     

Effect of Organic Residues with Varied Carbon–Nitrogen Ratios on Grain Yield,Soil Health,and Nitrous Oxide Emission from a Rice Agroecosystem

Experiments were conducted in an attempt to study the impact of using different organic residues as fertilizers on grain yield, magnitude of nitrous oxide (N₂O) emissions, and soil characteristics. Five fertilizer treatments including conventional nitrogen (N) fertilizer, cow manure, rice straw, poultry manure, and sugarcane bagasse were applied in the rice field in 2012. The maximum reduction in seasonal N₂O emissions (10–27%) was observed under the influence of rice straw application over conventional N fertilizer. The experiment was repeated for a second season in 2013 with the same treatments for further confirmation of the results obtained during the first year of experimentation. The application of rice straw also showed a slight advantage by increasing grain yield (4.38 t ha^?1) compared to control. Important soil properties and plant growth parameters were studied and their relationships with N₂O emission were worked out. The incorporation of organic residues helped in restoring and improving the soil health and effectively enhancing grain yield with reduced N₂O emission from rice fields.     

Effect of biochar and nitrapyrin on nitrous oxide and nitric oxide emissions from a sandy loam soil cropped to maize

A field experiment was conducted to evaluate the combined or individual effects of biochar and nitrapyrin (a nitrification inhibitor) on N₂O and NO emissions from a sandy loam soil cropped to maize. The study included nine treatments: addition of urea alone or combined with nitrapyrin to soils that had been amended with biochar at 0, 3, 6, and 12 t ha^?1 in the preceding year, and a control without the addition of N fertilizer. Peaks in N₂O and NO flux occurred simultaneously following fertilizer application and intense rainfall events, and the peak of NO flux was much higher than that of N₂O following application of basal fertilizer. Mean emission ratios of NO/N₂O ranged from 1.11 to 1.72, suggesting that N₂O was primarily derived from nitrification. Cumulative N₂O and NO emissions were 1.00 kg N₂O-N ha^?1 and 1.39 kg NO-N ha^?1 in the N treatment, respectively, decreasing to 0.81–0.85 kg N₂O-N ha^?1 and 1.31–1.35 kg NO-N ha^?1 in the biochar amended soils, respectively, while there was no significant difference among the treatments. NO emissions were significantly lower in the nitrapyrin treatments than in the N fertilization-alone treatments (P?<?0.05), but there was no effect on N₂O emissions. Neither biochar nor nitrapyrin amendment affected maize yield or N uptake. Overall, our results showed that biochar amendment in the preceding year had little effect on N₂O and NO emissions in the following year, while the nitrapyrin decreased NO, but not N₂O emissions, probably due to suppression of denitrification caused by the low soil moisture content.     

Effect of calcareous and siliceous amendments on N2O emissions of a grassland soil

Liming of acidic agricultural soils has been proposed as a strategy to mitigate nitrous oxide (N₂O) emissions, as increased soil pH reduces the N₂O/N₂ product ratio of denitrification. The capacity of different calcareous (calcite and dolomite) and siliceous minerals to increase soil pH and reduce N₂O emissions was assessed in a 2-year grassland field experiment. An associated pot experiment was conducted using homogenized field soils for controlling spatial soil variability. Nitrous oxide emissions were highly episodic with emission peaks in response to freezing–thawing and application of NPK fertilizer. Liming with dolomite caused a pH increase from 5.1 to 6.2 and reduced N₂O emissions by 30% and 60% after application of NPK fertilizer and freezing–thawing events, respectively. Over the course of the 2-year field trial, N₂O emissions were significantly lower in dolomite-limed than non-limed soil (p < .05), although this effect was variable over time. Unexpectedly, no significant reduction of N₂O emission was found in the calcite treatment, despite the largest pH increase in all tested minerals. We tentatively attribute this to increased N₂O production by overall increase in nitrogen turnover rates (both nitrification and denitrification) following rapid pH increase in the first year after liming. Siliceous materials showed little pH effect and had no significant effect on N₂O emissions probably because of their lower buffering capacity and lower cation content. In the pot experiment using soils taken from the field plots 3 years after liming and exposing them to natural freezing–thawing, both calcite (p < .01) and dolomite (p < .05) significantly reduced cumulative N₂O emission by 50% and 30%, respectively, relative to the non-limed control. These results demonstrate that the overall effect of liming is to reduce N₂O emission, although high lime doses may lead to a transiently enhanced emission.     

The effect of urea and pig slurry fertilization on denitrification, direct nitrous oxide emission, volatile fatty acids, water-soluble carbon and anthrone-reactive carbon in maize-cropped soil from the Po plain (Modena, Italy)

 The use of zootechnical slurries in agriculture can increase N losses as N₂O by direct emission and by denitrification. The aim of this research was to determine the influence of pig slurry, as well as its combination with mineral N, on N₂O emissions in the field and their relationships with some fractions of soil organic matter, with soil moisture and with rainfall. In spite of varying amounts of organic substance applied, the diverse agronomic treatments did not produce substantial differences in N losses due to denitrification. Wide variations between the slurry fertilized and the urea-fertilized plots were not found, whereas the combination of pig slurry with urea usually produced an increase both in N₂O emissions due to denitrification and in direct N₂O emissions (N losses corresponding to about 50% of those due to denitrification). The greatest losses of N₂O-N occurred in the first month following fertilizer administration. N₂O emissions due to denitrification were highest in the days immediately following the administration of fertilizers and lowest in a later period. N₂O emissions due to nitrification occurred later. Therefore, N₂O emission via nitrification differed from N₂O losses via denitrification which, under optimal conditions, presented peaks of activity during the whole growth cycle. The N₂O-N losses were highly influenced by physical parameters, particularly rain. An increase in micropore water creates conditions of scarce oxygenation or of anaerobiosis which influence oxidation-reduction processes and, at the same time, can limit the diffusion of bacteria-produced gas towards the soil surface. Received: 14 January 1998     

The effects of silicon fertilizer on denitrification potential and associated genes abundance in paddy soil

This study evaluated the effect of silicate fertilizer on denitrification and associated gene abundance in a paddy soil. A consecutive trial from 2013 to 2015 was conducted including the following treatments: control (CK), mineral fertilizer (NPK), NPK plus sodium metasilicate (NPK + MSF), and NPK plus slag-based silicate fertilizer (NPK + SSF). Real-time quantitative PCR (qPCR) was used to analyze the abundances of nirS, nirK, and nosZ genes. Potential N₂O emissions and ammonium and nitrate concentrations were related to the nirS and nirK gene abundance. Compared with the NPK treatments, the addition of a Si fertilizer decreased N₂O emission rates and denitrification potential by 32.4–66.6 and 22.0–59.2%, respectively, which were probably related to increased rice productivity, soil Fe availability, and soil N depletion. The abundances of nirS and nirK genes were decreased by 17.7–35.8% and 21.1–43.5% with addition of silicate fertilizers, respectively. Rates of total N₂O and N₂O from denitrification (DeN₂O) emission were positively correlated with the nirS and nirK gene abundance. Nitrate, exchangeable NH₄ ⁺, and Fe concentrations were the main factors regulating the nirS and nirK gene abundance. Silicate fertilization during rice growth may serve as an effective approach to decreasing N₂O emissions.     

菜地土壤中氮肥的反硝化损失和N2O排放

A field experiment was conducted on Chinese cabbage （Brassica campestris L. ssp. pekinensis （Lour.） Olsson） in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates： zero chemical fertilizer N （CK）; urea at rates of 300 kg N ha^-1 （U300） and 600 kg N ha^-1 （U600）, both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N ha^-1 （PCU180） as a basal application. The acetylene inhibition technique was used to measure denitrification （N2 ＋ N2O） from intact soil cores and N2O emissions in the absence of acetylene. Results showed that compared to （3K total denitrification losses were significantly greater （P ≤ 0.05） in the PCU180, U300, and U600 treatments,while N2O emissions in the U300 and U600 treatments were significantly higher （P ≤ 0.05） than （3K. In the U300 and U600 treatments peaks of denitrification and N2O emission were usually observed after N application. In the polymer-coated urea treatment （PCU180） during the period 20 to 40 days after transplanting, higher denitrification rates and N2O fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and N2O emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N2O emissions tended to decrease. A significant （P ≤0.01） positive correlation occurred between denitrification （r = 0.872） or N2O emission （r = 0.781） flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season.     

Inoculation with N2-generating denitrifier strains mitigates N2O emission from agricultural soil fertilized with poultry manure

Pelleted poultry manure is recommended for use with agricultural soil as a replacement for chemical fertilizers; however, application of the manure stimulates nitrous oxide (N₂O) emission from the soil through denitrification. To mitigate the N₂O emission caused by application of pelleted poultry manure, soil microcosms were set up; each microcosm was inoculated with one of the following N₂-generating denitrifier strains previously been isolated from paddy soil: Azoarcus, Dyella, Dechloromonas, Niastella, and Burkholderia. When pelleted poultry manure was incubated on its own, N₂O was produced by denitrification. In contrast, N₂O emission was significantly lowered when the manure was inoculated with most of the N₂-generating strains. In soil microcosms, N₂O was emitted during incubation after application of the pelleted manure, while N₂O flux was significantly lowered when the soil was inoculated with Azoarcus sp. KS11B, Niastella sp. KS31B, or Burkholderia sp. TSO47-3 on the 12th day of incubation. In addition, when pelleted manure was inoculated with the strains prior to application in the soil microcosms, the level of N₂O emission was significantly lowered to ca. 40–60 % that from the non-inoculated control. Our study provides the prototype of a technique that uses microbial technology to mitigate N₂O emission from agricultural soil fertilized with pelleted poultry manure.