Nitrous oxide production at different soil moisture contents in an arable soil in China

Abstract

Laboratory incubations were conducted to investigate nitrous oxide (N₂O) production from a subtropical arable soil (Typic Plinthodults) incubated at different soil moisture contents (SMC) and with different nitrogen sources using a 10% (v/v) acetylene (C₂H₂) inhibitory technique at 25°C. The production of N₂O and CO₂ was monitored during the incubations and changes in the contents of KCl-extractable NO^? ₃-N and NH⁺ ₄-N were determined. The production of N₂O increased slightly with an increase in SMC from 40% water-holding capacity (WHC) to 70% WHC, but increased dramatically at 100% WHC. After incubation the NO^? ₃-N content increased even at a SMC of 100% WHC. At a SMC of 100% WHC, the addition of NH⁺ ₄-N promoted the production of N₂O and CO₂, whereas the addition of NO^? ₃-N decreased N₂O production. Compared with the incubation without C₂H₂, the presence of C₂H₂ increased NH⁺ ₄-N content, but decreased NO^? ₃-N content, and there was no significant difference in N₂O production. These results indicate that heterotrophic nitrification contributes to N₂O production in the soil.     

Soil Moisture Controls the Denitrification Loss of Urea Nitrogen from Silty Clay Soil

Relative control of soil moisture [30, 60, and 80 percent water-holding capacity (WHC)] on nitrous oxide (N₂O) emissions from Fargo-Ryan soil, treated with urea at 0, 150, and 250 kg N ha^?1 with and without nitrapyrin [2-chloro-(6-trichloromethyl) pyridine] (NP), was measured under laboratory condition for 140 days. Soil N₂O emissions significantly increased with increasing nitrogen (N) rates and WHC levels. Urea applied at 250 kg N ha^?1 produced the greatest cumulative N₂O emissions and averaged 560, 3919, and 15894 µg kg^?1 at 30, 60, and 80 percent WHC, respectively. At WHC ≤ 60 percent, addition of NP to urea significantly reduced N₂O losses by 2.6- to 4.8-fold. Additions of NP to urea reduced N₂O emission at rates similar to the control (0 N) until 48 days for 30 percent WHC and 35 days for 60 and 80 percent WHC. These results can help devise urea-N fertilizer management strategies in reducing N₂O emissions from silty-clay soils.     

Soil N Losses by Denitrification Evaluated Using the 15N Tracer Method

Molecular nitrogen (N₂) and nitrous oxide (N₂O) generated by denitrification increase N losses in the soil–plant system. This study aimed to quantify N₂ and N₂O from potassium nitrate (K¹⁵NO₃) applied to soils with different textures and moisture contents in the absence and presence of a source of carbon (C) using the ¹⁵N tracer method. In the three soils used (sandy texture (ST), sandy clay loam texture (SCLT), and clayey texture (CT)), three moisture contents were evaluated (40%, 60%, and 80% of the water holding capacity (WHC)) with (D⁺) and without (D^?) dextrose added. The treatments received 100 mg N kg^?1 (KNO₃ with 23.24 atom% ¹⁵N). N₂ emissions occurred in all of the treatments, but N₂O emissions only occurred in the D⁺ treatment, showing increases with increasing moisture content. SCLT with 80% WHC in the D⁺ treatment exhibited the highest accumulated N emission (48.26 mg kg^?1). The ¹⁵N balance suggested trapping of the gases in the soil.     

Nitrous oxide emissions from three ecosystems in tropical peatland of Sarawak,Malaysia

Abstract

Nitrous oxide (N₂O) emissions were measured monthly over 1 year in three ecosystems on tropical peatland of Sarawak, Malaysia, using a closed-chamber technique. The three ecosystems investigated were mixed peat swamp forest, sago (Metroxylon sagu) and oil palm (Elaeis guineensis) plantations. The highest annual N₂O emissions were observed in the sago ecosystem with a production rate of 3.3 kg N ha^?1 year^?1, followed by the oil palm ecosystem at 1.2 kg N ha^?1 year^?1 and the forest ecosystem at 0.7 kg N ha^?1 year^?1. The N₂O emissions ranged from –3.4 to 19.7 µg N m^?2 h^?1 for the forest ecosystem, from 1.0 to 176.3 µg N m^?2 h^?1 for the sago ecosystem and from 0.9 to 58.4 µg N m^?2 h^?1 for the oil palm ecosystem. Multiple regression analysis showed that N₂O production in each ecosystem was regulated by different variables. The key factors influencing N₂O emissions in the forest ecosystem were the water table and the NH⁺ ₄ concentration at 25–50 cm, soil temperature at 5 cm and nitrate concentration at 0–25 cm in the sago ecosystem, and water-filled pore space, soil temperature at 5 cm and NH⁺ ₄ concentrations at 0–25 cm in the oil palm ecosystem. R² values for the above regression equations were 0.57, 0.63 and 0.48 for forest, sago and oil palm, respectively. The results suggest that the conversion of tropical peat swamp forest to agricultural crops, which causes substantial changes to the environment and soil properties, will significantly affect the exchange of N₂O between the tropical peatland and the atmosphere. Thus, the estimation of net N₂O production from tropical peatland for the global N₂O budget should take into consideration ecosystem type.     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.     

高氮和NO2-对中亚热带森林土壤N2O和NO产生的影响

利用15N同位素标记方法,研究在两种水分条件即60％和90％ WHC下,添加硝酸盐(NH4NO3,N 300 mg kg-1)和亚硝酸盐(NaNO2,N 1 mg kg-1)对中亚热带天然森林土壤N2O和NO产生过程及途径的影响.结果表明,在含水量为60％ WHC的情况下,高氮输入显著抑制了N2O和NO的产生(p＜0.01);但当含水量增为90％ WHC后,实验9h内抑制N2O产生,之后转为促进.所有未灭菌处理在添加NO2-后高氮抑制均立即解除并大量产生N2O和NO,与对照成显著差异(p＜0.01),在60％ WHC条件下,这种情况维持时间较短(21 h),但如果含水量高(90％ WHC)这种情况会持续很长时间(2周以上),说明水分有效性的提高和外源NO2-在高氮抑制解除中起到重要作用.本实验中N2O主要来源于土壤反硝化过程,而且加入未标记NO2-后导致杂合的N2O(14N15NO)分子在实验21 h内迅速增加,表明这种森林土壤的反硝化过程可能主要是通过真菌的“共脱氮”来实现,其贡献率可多达80％以上.Spearman秩相关分析表明未灭菌土壤NO的产生速率与N2O产生速率成显著正相关性(p＜0.05),土壤含水量越低二者相关性越高.灭菌土壤添加NO2-能较未灭菌土壤产生更多的NO,但却几乎不产生N2O,表明酸性土壤的化学反硝化对NO的贡献要大于N2O.     

Nitrous oxide and methane fluxes during the growing season from cultivated peat soils,peaty marl and gyttja clay under different cropping systems

Drainage of peatlands affects the fluxes of greenhouse gases (GHGs). Organic soils used for agriculture contribute a large proportion of anthropogenic GHG emissions, and on-farm mitigation options are important. This field study investigated whether choice of a cropping system can be used to mitigate emissions of N₂O and influence CH₄ fluxes from cultivated organic and carbon-rich soils during the growing season. Ten different sites in southern Sweden representing peat soils, peaty marl and gyttja clay, with a range of different soil properties, were used for on-site measurements of N₂O and CH₄ fluxes. The fluxes during the growing season from soils under two different crops grown in the same field and same environmental conditions were monitored. Crop intensities varied from grasslands to intensive potato cultivation. The results showed no difference in median seasonal N₂O emissions between the two crops compared. Median seasonal emissions ranged from 0 to 919?µg?N₂O?m^?2?h^?1, with peaks on individual sampling occasions of up to 3317?µg?N₂O?m^?2?h^?1. Nitrous oxide emissions differed widely between sites, indicating that soil properties are a regulating factor. However, pH was the only soil factor that correlated with N₂O emissions (negative exponential correlation). The type of crop grown on the soil did not influence CH₄ fluxes. Median seasonal CH₄ flux from the different sites ranged from uptake of 36?µg CH₄?m^?2?h^?1 to release of 4.5?µg?CH₄?m^?2?h^?1. From our results, it was concluded that farmers cannot mitigate N₂O emissions during the growing season or influence CH₄ fluxes by changing the cropping system in the field.     

Nitrous oxide emissions from wetland soil amended with inorganic and organic fertilizers

Agricultural soils are a primary source of anthropogenic trace gas emissions, and the subtropics contribute greatly, particularly since 51% of world soils are in these climate zones. A field experiment was carried out in an ephemeral wetland in central Zimbabwe in order to determine the effect of cattle manure (1.36% N) and mineral N fertilizer (ammonium nitrate, 34.5% N) application on N₂O fluxes from soil. Combined applications of 0 kg N fertilizer + 0 Mg cattle manure ha^?1 (control), 100 kg N fertilizer + 15 Mg manure ha^?1 and 200 kg N fertilizer + 30 Mg manure ha^?1 constituted the three treatments arranged in a randomized complete block design with four replications. Tomato and rape crops were grown in rotation over a period of two seasons. Emissions of N₂O were sampled using the static chamber technique. Increasing N fertilizer and manure application rates from low to high rates increased the N₂O fluxes by 37–106%. When low and high rates were applied to the tomato and rape crops, 0.51%, 0.40%, and 0.93%, 0.64% of applied N was lost as N₂O, respectively. This implies that rape production has a greater N₂O emitting potential than the production of tomatoes in wetlands.     

Nitrate Transformation and N2O Emission in a Typical Intensively Managed Calcareous Fluvaquent Soil: A 15-Nitrogen Tracer Incubation Study

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO₃-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N₂O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO₃-N decreased. When ¹⁵NO₃-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg^?1 only 1.1 ± 0.4 mg kg^?1 NO₃-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N₂O-N emissions were at levels of only micrograms kg^?1 soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N₂O.     

Effects of land-use type and nitrogen addition on nitrous oxide and carbon dioxide production potentials in Japanese Andosols

Land-use type and nitrogen (N) addition strongly affect nitrous oxide (N₂O) and carbon dioxide (CO₂) production, but the impacts of their interaction and the controlling factors remain unclear. The aim of this study was to evaluate the effect of both factors simultaneously on N₂O and CO₂ production and associated soil chemical and biological properties. Surface soils (0–10 cm) from three adjacent lands (apple orchard, grassland and deciduous forest) in central Japan were selected and incubated aerobically for 12 weeks with addition of 0, 30 or 150 kg N ha^–1 yr^–1. Land-use type had a significant (p < 0.001) impact on the cumulative N₂O and CO₂ production. Soils from the apple orchard had higher N₂O and CO₂ production potentials than those from the grassland and forest soils. Soil net N mineralization rate had a positive correlation with both soil N₂O and CO₂ production rates. Furthermore, the N₂O production rate was positively correlated with the CO₂ production rate. In the soils with no N addition, the dominant soil properties influencing N₂O production were found to be the ammonium-N content and the ratio of soil microbial biomass carbon to nitrogen (MBC/MBN), while those for CO₂ production were the content of nitrate-N and soluble organic carbon. N₂O production increased with the increase in added N doses for the three land-use types and depended on the status of the initial soil available N. The effect of N addition on CO₂ production varied with land use type; with the increase of N addition doses, it decreased for the apple orchard and forest soils but increased for the grassland soils. This difference might be due to the differences in microbial flora as indicated by the MBC/MBN ratio. Soil N mineralization was the major process controlling N₂O and CO₂ production in the examined soils under aerobic incubation conditions.     

Effect of crop residue C:N ratio on N2O emissions from Gray Lowland soil in Mikasa,Hokkaido, Japan

Abstract

We studied the effect of crop residues with various C:N ratios on N₂O emissions from soil. We set up five experimental plots with four types of crop residues, onion leaf (OL), soybean stem and leaf (SSL), rice straw (RS) and wheat straw (WS), and no residue (NR) on Gray Lowland soil in Mikasa, Hokkaido, Japan. The C:N ratios of these crop residues were 11.6, 14.5, 62.3, and 110, respectively. Based on the results of a questionnaire survey of farmer practices, we determined appropriate application rates: 108, 168, 110, 141 and 0 g C m^?2 and 9.3, 11.6, 1.76, 1.28 and 0 g N m^?2, respectively. We measured N₂O, CO₂ and NO fluxes using a closed chamber method. At the same time, we measured soil temperature at a depth of 5 cm, water-filled pore space (WFPS), and the concentrations of soil NH⁺ ₄-N, NO^? ₃-N and water-soluble organic carbon (WSOC). Significant peaks of N₂O and CO₂ emissions came from OL and SSL just after application, but there were no emissions from RS, WS or NR. There was a significant relationship between N₂O and CO₂ emissions in each treatment except WS, and correlations between CO₂ flux and temperature in RS, soil NH⁺ ₄-N and N₂O flux in SSL and NR, soil NH⁺ ₄-N and CO₂ flux in SSL, and WSOC and CO₂ flux in WS. The ratio of N₂O-N/NO-N increased to approximately 100 in OL and SSL as N₂O emissions increased. Cumulative N₂O and CO₂ emissions increased as the C:N ratio decreased, but not significantly. The ratio of N₂O emission to applied N ranged from ?0.43% to 0.86%, and was significantly correlated with C:N ratio (y = ?0.59 ln [x] + 2.30, r ² = 0.99, P < 0.01). The ratio of CO₂ emissions to applied C ranged from ?5.8% to 45% and was also correlated with C:N ratio, but not significantly (r ² = 0.78, P = 0.11).     

The effects of rice (Oryza sativa L. ssp. japonica) husk biochar on nitrogen dynamics during the decomposition of hairy vetch in two soils under high-soil moisture condition

ABSTRACT

Legumes, including hairy vetch (Vicia villosa Roth), are widely used as green manures. They fix nitrogen (N) and provide the N to other crops when they decompose, and thus are considered alternatives for chemical N fertilizers. However, N-rich plant residues, including hairy vetch, are also sources of soil nitrous oxide (N₂O) emissions, a greenhouse gas. On one hand, rice (Oryza sativa L. ssp. japonica) husk biochar is widely used as a soil conditioner in Japan and has been reported as a tool to mitigate soil N₂O emissions. We conducted a soil core incubation experiment (1.5 months) to compare the N₂O emissions during the decomposition of surface-applied hairy vetch (0.8 kg dried hairy vetch m^?2 soil) under semi-saturated soil moisture conditions (~100% water-filled pore space (WFPS)), using two soil types, namely Andosol and Fluvisol. Throughout the incubation period, the use of biochar suppressed soil NH₄⁺-N concentrations in Andosol, whereas the effect of biochar on NH₄⁺-N was not clear in Fluvisol. Biochar increased the nitrate (NO₃^?-N) levels both in Andosol and Fluvisol, suggesting a negative influence on denitrification and/or a positive influence on nitrification. Biochar application did not influence the cumulative N₂O emissions. Our study suggests that rice husk biochar is not a good option to mitigate N₂O emissions during the decomposition of surface-applied hairy vetch, although this study was performed under laboratory conditions without plants. However, the trends of the inorganic-N concentration changes followed by the addition of hairy vetch and biochar were markedly different between the two soil types. Thus, factors behind the differences need to be further studied.     

Fungal N2O production in an arable peat soil in Central Kalimantan,Indonesia

Abstract

To clarify the microbiological factors that explain high N₂O emission in an arable peat soil in Central Kalimantan, Indonesia, a substrate-induced respiration-inhibition experiment was conducted for N₂O production. The N₂O emission rate decreased by 31% with the addition of streptomycin, whereas it decreased by 81% with the addition of cycloheximide, compared with a non-antibiotic-added control. This result revealed a greater contribution of the fungal community than bacterial community to the production of N₂O in the soil. The population density of fungi in the soil, determined using the dilution plate method, was 5.5 log c.f.u. g^?1 soil and 4.9 log c.f.u. g^?1 soil in the non-selective medium (rose bengal) and the selective medium for Fusarium, respectively. The N₂O-producing potential was randomly examined in each of these isolates by inoculation onto Czapek agar medium (pH 4.3) and incubation at 28°C for 14 days. Significant N₂O-producing potential was found in six out of 19 strains and in five out of seven strains isolated from the non-selective and selective media, respectively. Twenty-three out of 26 strains produced more than 20% CO₂ during the 14-day incubation period, suggesting the presence of facultative fungi in the soil. These strains were identified to be Fusarium oxysporum and Neocosmospora vasinfecta based on the sequence of 18S rDNA, irrespective of the N₂O-producing potential and the growth potential in conditions of low O₂ concentration.     

Effect of Alternating Furrow Irrigation and Nitrogen Fertilizer on Nitrous Oxide Emission in Corn Field

The objectives of this 2-year field study were to assess the effects of irrigation and nitrogen (N) application on nitrous oxide (N₂O). Soil N₂O flux was determined using open-bottomed chambers. Nitrous oxide concentrations were determined with gas chromatography. The results showed that in 2008, N₂O emission rates ranged from 2.0 to 50.0 g N ha^?1 d^?1 in the alternating furrow irrigation and N application treatments (AFINA) and from 2.4 to 68.4 g N ha^?1 d^?1 in the conventional every-furrow irrigation and fertilization treatment (CIF). In 2009, cumulative N₂O-N loss in the optimal combination with greater yields and lower N₂O emission in AFINA was 1277 g N ha^?1 compared to 1695 g N ha^?1 with CIF. The study indicated that AFINA practices combined with optimum N fertilizer and irrigation rates could reduce soil N₂O emission and water input compared to CIF practices without causing a decline in corn yield.     

Drivers of nitrous oxide fluxes from the semi-arid Leymus chinensis grassland in Inner Mongolia,China

Nitrous oxide (N₂O) flux in the semi-arid Leymus chinensis (Trin.) Tzvel. grassland in Inner Mongolia, China was measured for two years (from January 2005 to December 2006) with the enclosed chamber technique. The measurements were made twice per month in the growing season and once per month in the non-growing season. To evaluate the effect of aboveground vegetation on N₂O emission, the ecosystem N₂O flux over the grassland was measured, and concurrently soil N₂O flux was measured after the removal of all the aboveground biomass. The possible effect of water-heat factors on N₂O fluxes was statistically examined. The ecosystem N₂O flux ranged from 0.21 to 0.26?kg nitrous oxide-nitrogen (N₂O–N) ha^{? 1} year^{? 1}, indicating that the Leymus chinensis grassland of Inner Mongolia was a source for the atmospheric N₂O. There was no significant difference between the ecosystem N₂O flux and the soil N₂O flux. The ecosystem N₂O flux was under similar environmental control as the soil N₂O flux. Soil moisture was the primary driving factor of the N₂O fluxes in the growing season of both years; the changes in water–filled pore space (WFPS) of soil surface layers could explain 45–67% of the variations in N₂O fluxes. The high seasonal variation of the N₂O fluxes in the growing seasons was regulated by the distribution of effective rainfall, rather than the precipitation intensity. While in the non-growing season, the N₂O fluxes were restricted much more by air temperature or soil temperature, and 83–85% of the variations of the N₂O fluxes were induced by changes in temperature conditions.     

Relationships between soil moisture content and nitrous oxide production during nitrification and denitrification

Summary The effect of soil water content [60%–100% water-holding capacity (WHC)] on N₂O production during autotrophic nitrification and denitrification in a loam soil was studied in a laboratory experiment by selectively inhibiting nitrification with a low C₂H₂ concentration (2.1 Pa). Nitrifiers usually produced more N₂O than denitrifiers. During an initial experimental period of 0–6 days the nitrifiers produced more N₂O than the denitrifiers by a factor ranging from 1.4 to 16.5, depending on the water content and length of incubation. The highest N₂O production rate by nitrifiers was observed at 90% WHC, when the soil had become partly anaerobic, as indicated by the high denitrification rate. At 100% WHC there were large gaseous losses from denitrification, while nitrification losses were smaller except for the first period of measurement, when there was still some O₂ remaining in the soil. The use of 10 kPa C₂H₂ to inhibit reduction of N₂O to N₂ stimulated the denitrification process during prolonged incubation over several days; thus the method is unsuitable for long-term studies.     

Denitrification,N2-fixation and fermentation during anaerobic incubation of soils amended with glucose and nitrate

Nitrate and glucose additions were investigated for their role in the C and N dynamics during anaerobic incubation of soil. A gas-flow soil core method was used, in which the net production of N₂, N₂O, NO, CO₂, and CH₄ under a He atmosphere could be monitored both accurately and frequently. In all experiments clayey silt loam soil samples were incubated for 9 days at 25 °C. Addition of nitrate (50 mg KNO₃-N kg^-1 soil) had no effect on total denitrification and CO₂ production rates, while the N₂O/N₂ ratio was affected considerably. The cumulative N₂O production exceeded the cumulative N₂ production for 6 days in the treatment with nitrate addition, compared to 1.2 days in the unamended treatment. Glucose addition stimulated the microbial activity considerably. The denitrification rates were limited by the growth rate of the denitrifying population. During denitrification no significant differences were observed between the treatments with 700 mg glucose-C kg^-1 and 4200 mg glucose-C kg^-1, both in combination with 50 mg KNO₃-N kg^-1. The N₂ production rates were remarkably low, until NO _inf3 ^sup- exhaustion caused rapid reduction of N₂O to N₂ at day 2. During the denitrification period 15–18 mg N kg^-1 was immobilised in the growing biomass. After NO _inf3 ^sup- shortage, a second microbial population, capable of N₂-fixation, became increasingly important. This change was clearly reflected in the CO₂ production rates. Net volatile fatty acid (VFA) production was monitored during the net N₂-fixation period with acetate as the dominant product. N₂-fixation faded out, probably due to N₂ shortage, followed by increased VFA production. In the high C treatment butyrate became the most important VFA, while in the low C treatment acetate and butyrate were produced at equal rates. During denitrification no VFA accumulation occurred; this does not prove, however, that denitrification and fermentation appeared sequentially. The experiments illustrate clearly the interactions of C-availability, microbial population and nitrate availability as influencing factors on denitrification and fermentation.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Effects of greenhouse intensive cultivation and organic amendments on greenhouse gas emission according to a soil incubation study

Soil cultivation changes and usage of agricultural wastes can have profound impacts on greenhouse gas (GHG) emission from soil. In this study, the effects of soil cultivation and organic amendment on GHG emission were investigated using aerobic incubation. Surface soil (0–20 cm) from (1) rice–legume consecutive rotation (Rice) and (2) recently (<3 years) converted from rice field to plastic-covered intensive vegetable and flower production (VegC) were collected in Kunming, P.R. China. Rose (Rosa rugosa Thunb.) residues and cattle manure were applied at 5% by weight. Results indicated that N₂O and CO₂ fluxes were significantly influenced by soil cultivation, organic amendment, incubation time and their interaction (p <0.05). Applying cattle manure increased, while rose residue decreased, cumulative N₂O emissions from soil (84 days). Rose residue application significantly increased cumulative CO₂ emissions with peak values of 6371 (Rice) and 7481 mg kg^?1 (VegC), followed by cattle manure addition figure of 2265 (VegC) and 3581 mg kg^?1 (Rice). Both were significantly higher (p <0.05) than the un-amended Control at 709 (VegC) and 904 mg kg^?1 (Rice). Our study demonstrates that a low C/N ratio in cattle manure is better than a high C/N ratio in rose residue in regard to reducing the global warming potential of agricultural soil.     

Daytime,Temporal, and Seasonal Variations of N2O Emissions in an Upland Cropping System of the Humid Tropics

Abstract

Nitrous oxide (N₂O) contributes to global climate change, and its emission from soil–crop systems depend on soil, environmental, and anthropogenic factors. Thus, we evaluated the variability of N₂O emissions measured by microchambers (cross section: 184 cm²) from a groundnut–fallow–maize–fallow cropping system of the humid tropics. The crops received inorganic nitrogen (N) plus crop residues (NC), inorganic N alone as ammonium sulfate (RN), and half of the inorganic N along with crop residues and chicken manure (N_1/2CM), amounting for the crop rotation to 322, 180, and 400 kg N ha^?1 yr^?1, respectively. The N₂O fluxes during the groundnut–maize crop rotation were log‐normally distributed, and the frequency distributions were positively skewed. Daytime changes in N₂O fluxes were inconsistent, and the 50% of total N₂O emission during the 12 h measurement periods was attained earlier under maize (～11∶00 h) than groundnut covers (～13∶00 h). Spatial variability in each treatment with eight gas chambers was large but smaller during the cropping periods than the fallow, indicating masking efficiency of crop covers for the soil heterogeneity that was accelerated presumably by antecedent climatic variables. The temporal variability of N₂O emissions was also large (coefficients of variation, CV, ranged from 60 to 81%), involving both input differences between treatments and measurement periods. As such, the relative deviation from the annual mean of total N₂O emission was high during the period after a large N application with a maximum of +480%, due to addition of chicken manure. The seasonal contribution of summer and monsoon to N₂O emissions was insignificant. However, intensive rainfall negatively (?0.65**) and the amount of added N from either source positively (0.83***) correlated with the integrated N₂O emissions, and those were exponential. Results suggest that around noon (12∶00 h) gas collection could represent well the daily N₂O fluxes, increasing the number or size of the gas chambers could minimize the large variability, and mainly the rainfall and N inputs regulated its emissions in the humid tropics of Malaysia.     

Effects of organic material amendment and water content on NO, N2O, and N2 emissions in a nitrate-rich vegetable soil

Amending vegetable soils with organic materials is increasingly recommended as an agroecosystems management option to improve soil quality. However, the amounts of NO, N₂O, and N₂ emissions from vegetable soils treated with organic materials and frequent irrigation are not known. In laboratory-based experiments, soil from a NO ₃ ^? -rich (340 mg N?kg^?1) vegetable field was incubated at 30°C for 30 days, with and without 10 % C₂H₂, at 50, 70, or 90 % water-holding capacity (WHC) and was amended at 1.19 g?C kg^?1 (equivalent to 2.5 t?C ha^?1) as Chinese milk vetch (CMV), ryegrass (RG), or wheat straw (WS); a soil not amended with organic material was used as a control (CK). At 50 % WHC, cumulative N₂ production (398–524 μg N?kg^?1) was significantly higher than N₂O (84.6–190 μg N?kg^?1) and NO (196–224 μg N?kg^?1) production, suggesting the occurrence of denitrification under unsaturated conditions. Organic materials and soil water content significantly influenced NO emissions, but the effect was relatively weak since the cumulative NO production ranged from 124 to 261 μg N?kg^?1. At 50–90 % WHC, the added organic materials did not affect the accumulated NO ₃ ^? in vegetable soil but enhanced N₂O emissions, and the effect was greater by increasing soil water content. At 90 % WHC, N₂O production reached 13,645–45,224 μg N?kg^?1 from soil and could be ranked as RG?>?CMV?>?WS?>?CK. These results suggest the importance of preventing excess water in soil while simultaneously taking into account the quality of organic materials applied to vegetable soils.