Greenhouse gas emissions from decomposition of biosolids as affected by stabilization method and soil moisture

Computational models are useful to estimate agricultural greenhouse gas emissions at regional scales. However, empirically based parameter values are required for the models to accurately represent carbon (C) and nitrogen (N) mineralization rates of different organic amendments in more and less humid regions or during wet and dry periods of the growing season. A controlled environment study was conducted to assess the rates of C and N mineralization in differently processed sewage sludge (biosolids) in wet and dry soil. Parameter values were estimated for use in modelling the degradation of three types of biosolids. A loam soil with either 49% water-filled pore space (WFPS) or 29% WFPS was amended with mesophilic anaerobically digested (digested), alkaline-stabilized, or composted biosolids. Headspace samples were collected and analysed for carbon dioxide (CO₂) and nitrous oxide (N₂O), and soil samples for nitrate (${\mathrm{NO}}_3^{-}$) and ammonium (${\mathrm{NH}}_4^{+}$). Four different first-order models were fitted to the cumulative CO₂–C and N₂O–N data (R² > 0.98), and soil ${\mathrm{NO}}_3^{-}$ (R² > 0.65) and ${\mathrm{NH}}_4^{+}$ (R² > 0.93) concentrations. CO₂–C data indicated that C mineralization was higher in soil with 49% WFPS than in soils with 29% WFPS. Seventy-nine percent of the C compounds in digested biosolids degraded in soil with 49% WFPS, compared with 52% for alkaline-stabilized biosolids and 8% for composted biosolids. The fitted coefficient values were similar for all of the four first-order models used in this study and provide useful information for parameterizing more sophisticated mechanistic models of the degradation of biosolids in soil.     

Nitrous oxide emissions from grain legumes as affected by wetting/drying cycles and crop residues

Grain legume production with rhizobial inoculation has drawn attention not only because of the economic value of nitrogen (N) fixation by grain legumes, but also because of the concern that N₂ fixation by grain legumes may enhance emissions of nitrous oxide (N₂O), a powerful greenhouse gas. However, the relationship between N₂O emissions and biological N₂ fixation by grain legumes is not well understood. The objective of this study was to quantify N₂O emissions associated with N₂ fixation by grain legumes as affected by wetting/drying cycles and crop residues. Two grain legumes, lentil (Lens esculenta Moench) and pea (Pisum sativum L.), either inoculated with two Rhizobium leguminosarum biovar viciae strains, 99A1 and RGP2, respectively, or fertilized with ¹⁵N-labeled fertilizer were grown in a controlled environment under three wetting/drying cycles. Profile N₂O concentrations and surface N₂O emissions were measured from the soil–plant systems, which were compared with those from a cereal, spring wheat (Triticum aestivum L. ac. Barrie). After harvest, crop residues were incorporated into soils that were seeded to spring wheat to evaluate the effect of crop residues on N₂O emissions. Results indicated that: (1) inoculating grain legumes with non-denitrifying rhizobia did not enhance N₂O emissions and the presence of grain legumes did not increase N₂O emissions compared with the cereal crop, and (2) profile N₂O accumulation and surface emissions were not related to the type of crop residues added to the soil, but related to the residual N applied previously as N fertilizer. This suggests that N₂O emissions are not directly related to biological N₂ fixation by grain legumes, and on a short time scale, N rich residues of N₂-fixing crops have a limited impact on N₂O emissions compared with N fertilization.     

追肥时间对小麦拔节-成熟期氧化亚氮排放的影响

2007～2008年采用3种追肥时间(雨前追肥、雨时追肥和雨后追肥)进行田间试验,观测小麦拔节-成熟期N2O排放,以探讨追肥时间对麦季N2O排放的影响。结果表明,与雨前追肥和雨时追肥相比,雨后追肥小麦拔节-成熟期N2O排放量分别减少37%～67%和22%～46%。各处理小麦产量无显著差异(p>0.05)。土壤水分含量是影响小麦拔节-成熟期N2O排放的关键因素。雨后趁墒追肥能显著减少小麦拔节-成熟期N2O排放且不影响小麦产量,是较为合理的追肥方式。     

Greenhouse gas emissions from a wastewater sludge-amended soil cultivated with wheat (Triticum spp. L.) as affected by different application rates of charcoal

Applying biochar to soil is an easy way to sequester carbon in soil, while it might reduce greenhouse gas (GHG) emissions and stimulate plant growth. The effect of charcoal application (0, 1.5, 3.0 and 4.5%) on GHG emission was studied in a wastewater sludge-amended arable soil (Typic Fragiudepts) cultivated with wheat (Triticum spp. L.) in a greenhouse. The application of charcoal at ≥1.5% reduced the CO₂ emission rate significantly ≥37% compared to unamended soil (135.3 g CO₂ ha⁻¹ day⁻¹) in the first two weeks, while the N₂O emission rate decreased 44% when 4.5% charcoal was added (0.72 g N₂O ha⁻¹ day⁻¹). The cumulative GHG emission over 45 days was 2% lower when 1.5% charcoal, 34% lower when 3.0% charcoal and 39% lower when 4.5% charcoal was applied to the sludge-amended soil cultivated with wheat. Wheat growth was inhibited in the charcoal-amended soil compared to the unamended soil, but not yields after 135 days. It was found that charcoal addition reduced the emissions of N₂O and CO₂, and the cumulative GHG emissions over 45 days, without altering wheat yield.     

Least limiting water range and crop yields as affected by crop rotations and tillage

Crop rotation and the maintenance of plant residues over the soil can increase soil water storage capacity. Root access to water and nutrients depends on soil physical characteristics that may be expressed in the Least Limiting Water Range (LLWR) concept. In this work, the effects of crop rotation and chiselling on the soil LLWR to a depth of 0.1 m and crop yields under no‐till were studied on a tropical Alfisol in São Paulo state, Brazil, for 3 yr. Soybean and corn were grown in the summer in rotation with pearl millet (Pennisetum glaucum, Linneu, cv. ADR 300), grain sorghum (Sorghum bicolor, L., Moench), congo grass (Brachiaria ruziziensis, Germain et Evrard) and castor bean (Ricinus comunis, Linneu) during fall/winter and spring, under no‐till or chiselling. The LLWR was determined right after the desiccation of the cover crops and before soybean planting. Soil physico‐hydraulic conditions were improved in the uppermost soil layers by crop rotations under zero tillage, without initial chiselling, from the second year and on, resulting in soil quality similar to that obtained with chiselling. In seasons without severe water shortage, crop yields were not limited by soil compaction, however, in a drier season, the rotation with congo grass alone or intercropped with castor resulted in the greatest cover crop dry matter yield. Soybean yields did not respond to modifications in the LLWR.     

An empirical model for estimating nitrate leaching as affected by crop type and the long-term N fertilizer rate

Abstract. An empirical model was developed for prediction of annual average nitrate leaching as affected by the long-term rate of N fertilization and crop type. The effect of N fertilization was estimated from annual values of nitrate leaching obtained from two Danish investigations of drainage from pipe drains with four rates of N fertilization on a loamy sand and sandy clay loam from 1973-89. The effect of crop at normal N fertilization was estimated from 147 observations of annual nitrate leaching obtained from field measurements. The nitrate leaching model consists of a relative N fertilization submodel and an absolute submodel for specific combinations of crop, soil and drainage at the normal rate of N fertilization. The relative submodel is Y/Y _lN= exp[0.7l(N/ N₁– I)], where Y is the nitrate leaching (kg N/ha per year) at fertilization rate N , and Y _IN and N₁ are the corresponding values at the normal rate of N fertilization. The relative submodel is valid for cereals, root crops and grass leys fertilized with mineral fertilizer at N/N ₁ < 1.5, and on the prerequisite that the fertilization rate N has been constant for some years. To illustrate the use of the relative leaching submodel, estimated values of Y _IN corrected to mean annual drainage for 1970 to 1990 in Denmark for spring cereals and grass on sandy and loamy soils are given as input to the relative leaching submodel. The model can be used for sandy to loamy soils to estimate the mean nitrate leaching over a number of years.     

团头鲂池塘养殖生态系统晒塘阶段温室气体排放通量分析

为探讨团头鲂池塘养殖生态系统晒塘阶段温室气体的排放规律及综合增温潜势,采用静态暗箱——气相色谱法对团头鲂池塘养殖生态系统晒塘阶段温室气体(CO2,CH4,N2O)的排放进行原位测定。结果显示,团头鲂池塘养殖生态系统晒塘阶段均表现为CO2,CH4和N2O的排放源,其中CO2排放通量达(86.72±12.46)g/m2,CH4排放量达(2.01±0.34)g/m2,N2O排放量达(7.44±0.98)mg/m2;在100 a的时间尺度上,团头鲂池塘养殖生态系统在晒塘阶段综合增温潜势为(157.28±24.31)g/m2,团头鲂池塘养殖生态系统温室气体减排空间较大。     

Boron absorption by crop plants as affected by other nutrients of the medium

Numerous reports on boron nutrition of plants have been published since WARINGTON (15), using Vicia faba, first discovered in 1923 that boron is essential for the growth of higher plants. Inorganic (7, 9, 11) and organic (1) constituents of the growth medium and climatic conditions such as light intensity (13), photoperiod (5, 16), and drying and wetting of the soil (10) are some of the factors affecting boron uptake by plants.     

Growth of cassava cultivar TMS 30572 as affected by alley-cropping and mycorrhizal inoculation

The effect of inoculation with Glomus clarum, a vesicular-arbuscular mycorrhiza fungus, and alley-cropping on the growth of the cassava cultivar, TMS 30572, was investigated under field conditions in a low nutrient tropical soil. Cassava was grown either interplanted between two hedgerow tree species (alley-cropped) or sole-cropped. Sub-plots were either inoculated with G. clarum or were not inoculated. No effort was made to destroy the indigenous mycorrhizal fungi. Three months after planting, no significant influence of G. clarum inoculation was observed on the growth of roots, shoots or leaf area index (LAI). However, with time, inoculation and system of cropping enhanced these growth parameters. Nine months after planting, the total biomass of alley-cropped cassava was significantly higher than that of inoculated and non-inoculated sole-cropped cassava. Inoculation had led to an increase in the fresh tuber yield of both the alley- and sole-cropped cassava 12 months after planting. The LAI of both alley- and sole-cropped cassava inoculated with G. clarum increased. Received: 6 December 1996     

Soil microbial biomass and nitrogen supply in an irrigated lowland rice soil as affected by crop rotation and residue management

 Processes that govern the soil nitrogen (N) supply in irrigated lowland rice systems are poorly understood. The objectives of this paper were to investigate the effects of crop rotation and management on soil N dynamics, microbial biomass C (C_BIO) and microbial biomass N (N_BIO) in relation to rice N uptake and yield. A maize-rice (M-R) rotation was compared with a rice-rice (R-R) double-cropping system over a 2-year period with four cropping seasons. In the M-R system, maize (Zea mays L.) was grown in aerated soil during the dry season (DS) followed by rice (Oryza sativa L.) grown in flooded soil during the wet season (WS). In the R-R system, rice was grown in flooded soil in both the DS and WS. Three fertilizer N rates (0, 50 or 100 kg urea-N ha^–1 in WS) were assigned to subplots within the cropping system main plots. Early versus late crop residue incorporation following DS maize or rice were established as additional treatments in sub-subplots in the second year. In the R-R system, the time of residue incorporation had a large effect on NO₃ ^–-N accumulation during the fallow period and also on extractable NH₄ ⁺-N, rice N uptake and yield in the subsequent cropping period. In contrast, time of residue incorporation had little influence on extractable N in both the fallow and rice-cropping periods of the M-R system, and no detectable effects on rice N uptake or yield. In both cropping systems, C_BIO and N_BIO were not sensitive to residue incorporation despite differences of 2- to 3-fold increase in the amount of incorporated residue C and N, and were relatively insensitive to N fertilizer application. Extractable organic N was consistently greater after mid-tillering in M-R compared to the R-R system across N rate and residue incorporation treatments, and much of this organic N was α-amino N. We conclude that N mineralization-immobilization dynamics in lowland rice systems are sensitive to soil aeration as influenced by residue management in the fallow period and crop rotation, and that these factors have agronomically significant effects on rice N uptake and yield. Microbial biomass measurements, however, were a poor indicator of these dynamics. Received: 31 October 1997     

Yield and N uptake as affected by soil tillage and catch crop

Two field trials with spring barley (Hordeum vulgare L.) were conducted at two locations in Denmark in order to evaluate the effects of tillage and growth of a catch crop on yield parameters under temperate coastal climate conditions. Ploughing in autumn or spring in combination with perennial ryegrass (Lolium perenne L.) as a catch crop was evaluated on a coarse sand (Orthic Haplohumod) from 1987 to 1992 at three rates of N fertiliser application (60, 90 and 120 kg N ha⁻¹ year⁻¹). Rotovating and direct drilling were also included as additional tillage practices. The experiment was conducted on a 19-year-old field trial with continuous production of spring barley. Ploughing in autumn or spring in combination with stubble cultivation and a catch crop, in addition to minimum tillage, was evaluated in a newly established field trial on a sandy loam (Typic Agrudalf) from 1988 to 1992. Yield parameters and N concentrations in grain and straw were determined. On the coarse sand, N uptake in the grain in ploughed plots without a catch crop was significantly greater when spring ploughed as opposed to autumn ploughed, but grain and straw yields did not differ significantly. Grain yield, straw yield and total N uptake did not differ significantly between direct drilled and autumn ploughed plots, but the trend was for grain yield to be lower with direct drilling. After 19 years of catch crop use, yield parameters in ploughed plots were greater than in plots without catch crops. This was most pronounced in the autumn ploughed plots. Rotovating the catch crop in the spring decreased grain yield compared with underploughing the catch crop in autumn or spring. No significant interactions were found between tillage and N rates. On the sandy loam, grain as well as straw yield and total N uptake were not significantly affected by catch crop or time of ploughing. Grain yield was significantly lower with reduced tillage (stubble cultivation in autumn) than in all other treatments.     

Trace gas emissions from soil of the central highlands of Mexico as affected by natural vegetation: a laboratory study

In the central highlands of Mexico, mesquite (Prosopis laevigata) and huisache (Acacia schaffneri), N₂-fixing trees or shrubs, dominate the vegetation and are currently used in a reforestation program to prevent erosion. We investigated how natural vegetation or cultivation of soil affected oxidation of CH₄, and production of N₂O. Soil was sampled under the canopy of mesquite (MES treatment) and huisache trees (HUI treatment), outside their canopy (OUT treatment) and from fields cultivated with maize (ARA treatment) at three different sites while production of CO₂, and dynamics of CH₄, N₂O and inorganic N (NH₄⁺, and NO₃^–) were monitored in an aerobic incubation. The production of CO₂ was 2.3 times higher and significantly greater in the OUT treatment, 3.0 times higher in the MES treatment and 4.0 times higher in the HUI treatment compared to the ARA treatment. There was no significant difference in oxidation of CH₄ between the treatments, which ranged from 0.019 g CH₄–C kg^–1 day^–1 for the HUI treatment to 0.033 CH₄–C kg^–1 day^–1 for the MES treatment. The production of N₂O was 30 g N₂O–N kg^–1 day^–1 in the MES treatment and >8 times higher compared to the other treatments. The average concentration of NO₃^– was 2 times higher and significantly greater in the MES treatment than in the HUI treatment, 3 times greater than in the OUT treatment and 10 times greater than in the ARA treatment. It was found that cultivation of soil decreased soil organic matter content, C and N mineralization, but not oxidation of CH₄ or production of N₂O.     

Methanogenesis during rice growth as related to the water regime between crop seasons

In a long-term pot experiment with paddy rice, the effect of a wet or dry fallow on methanogenesis was studied during the ninth season. At times of CH₄ measurement, the oxidation of CH₄ was suppressed by C₂H₂. Methanogenesis started earlier in continuously flooded soil and was higher during the entire rice-growing period than in soil kept dry during the fallow and rewetted again before transplanting the rice seedlings. Increased CH₄ emission from the wet fallow treatment was, in contrast to the dry fallow treatment, associated with constantly low redox potentials. The experiment shows that the water regime during the fallow period is important to methanogenesis during the growth of rice plants.     

Nitrogen and phosphorus transformations as affected by crop residue management practices and their influence on crop yield

Abstract. A 15-year field experiment investigated crop residue management practices, with crop residue removal, burning and incorporation as the main treatments and nitrogen levels as subtreatments. The effects of crop residue management practices on rice and wheat yield were measured for 11 years. Surface soil samples were taken to study nitrogen and phosphorus immobilization/adsorption and their release under laboratory conditions. The field experiment indicated that residue burning and residue removal resulted in greater grain yields of rice (5.57 and 5.53 t/ha, respectively) and wheat (4.12 and 4.02 t/ha, respectively) than residue incorporation (4.51 t/ha rice and 3.72 t/ha wheat). Laboratory experiments indicated that by the addition of crop residues nitrogen and phosphorus were converted to unavailable forms through immobilization and adsorption, respectively.
Crop residue management practices were discontinued after 13 years and wheat and maize crops were grown in sequence. There were significantly greater yields of wheat (3.57 t/ha in 1992–93 and 3.6 t/ha in 1993–94) and of maize (2.1 t/ha in 1993) in plots where the residues had previously been incorporated than where the residues were previously either removed or burned. This is attributed to release of nitrogen and phosphorus from the incorporated residues.     

Nitrous oxide and nitric oxide emissions from maize field plots as affected by N fertilizer type and application method

N₂O and NO emissions from an Andisol maize field were studied. The experimental treatments were incorporation of urea into the plough layer at 250 kg N ha^-1 by two applications (UI250), band application of urea at a depth of 8 cm at 75 kg N ha^-1 plus incorporation of urea into the plough layer at 75 kg N ha^-1 (UB150), band application of polyolefin-coated urea at a depth of 5 cm at 150 kg N ha^-1 (CB150), and a control (without N application). N₂O fluxes from UI250 and UB150 peaked following the incorporation of supplementary fertilizer, and declined to the background level after that, while the N₂O flux from CB150 was relatively low but remained at a constant level until shortly after harvest. Accordingly, the total N₂O emissions during the whole cultivation period from the three treatments were not significantly different. The fertilizer-derived N₂O-N losses from UI250, UB150 and CB150 were 0.15%, 0.27% and 0.28% of the applied N, respectively. However, it was suggested that, due to the low plant N recovery, UI250 had a significantly larger potential for indirect N₂O emission than the other treatments. On the other hand, NO emissions from UI250 and UB150 were 12 times higher than that from CB150, and the fertilizer-derived NO-N losses from the three treatments were 0.16%, 0.27% and 0.026% of the applied N, respectively. Significant NO fluxes were detected only when urea-N fertilizer was surface-applied and incorporated into plough-layer soil.     

Tillage and crop residue management significantly affects N-trace gas emissions during the non-rice season of a subtropical rice-wheat rotation

Field operations of tillage and residue incorporation could have potentially important influences on N-trace gas fluxes, though poorly quantified. Here we studied the effects of straw incorporation in the preceding rice season and no-tillage prior to wheat sowing on nitric oxide (NO) and nitrous oxide (N₂O) emissions during the non-rice period of a typical rice-wheat rotation in the Yangtze River Delta. Compared to conventional management practice (no straw incorporation along with rotary harrowing tillage to 10 cm before wheat sowing), straw incorporation alone decreased cumulative N₂O emissions over the entire non-rice period by 32% (1.53 vs. 2.24 kg N ha^-1, P < 0.05) but did not affect NO emissions (0.88 vs. 0.87 kg N ha⁻¹). In contrast, no-tillage alone increased N₂O emissions by 75% (P < 0.05) while reducing NO emissions by 48% (P < 0.01). Combination of no-tillage and straw incorporation led to no change in N₂O emissions but a reduction in NO emissions compared to the conventional management regime. The direct N₂O emission factors (EF_ds) of applied nitrogen fertilizers during the non-rice season ranged from 0.29% to 1.35% with a coefficient of variation (CV) as large as 68% among the investigated management regimes. The EF_ds for NO ranged from 0.13% to 0.32% with a CV of 50%. Adoption of these new EF_ds will allow us to account for management effects on N-trace gas emissions when calculating emission inventories. Nevertheless, it is noteworthy that the uncertainty remains high, since the effects of soil properties such as texture or pH on management practices are not yet well defined.     

Fate of nitrogen from crop residues as affected by biochemical quality and the microbial biomass

Net mineralization of N from a range of shoot and root materials was determined over a period of 6 months following incorporation into a sandy-loam soil under controlled environment conditions. Biochemical “quality” components of the materials showed better correlation with net N mineralization than did gross measures of the respiration and N content of the soil microbial community during decomposition. The quality components controlling net N mineralization changed during decomposition, with water-soluble phenolic content significantly correlated with net N mineralization at early stages, and water-soluble N, followed by cellulose at later stages. C-to-N and total N were correlated with net N mineralization towards the end of the incubation only. Cumulative microbial respiration during the early stages of decomposition was correlated with net N mineralization measured after 2 months, at which time maximum net N mineralization was recorded for most residues. However, there was no relationship between microbial-N and net N mineralization. Biochemical quality factors controlling the C and N content of the residue remaining at the end of the incubation as light fraction organic matter (LFOM) were also investigated. Both C and N content of LFOM derived from the residues were correlated with residue cellulose content, and the chemical characteristics of LFOM were highly correlated with those of the original plant material. Incorporation of low cellulose, high water-soluble N-containing shoot residues resulted in more N becoming mineralized than had been added in the residues, demonstrating that net mineralization of native soil organic matter had occurred. Large amounts of N were lost from the mineral-N pool during the incubation, which could not be accounted for by microbial immobilization.     

Nitrogen conservation in soil and crop residues as affected by crop rotation and soil disturbance under Mediterranean conditions

We investigated conservation and cycling of N under oat–oat and lupine–oat rotations in disturbed and undisturbed soil, when roots or roots plus aboveground residues were retained. Crop residues were labelled with ¹⁵N in Year 1, and differential soil disturbance was imposed after harvest. In Year 2, plant growth, N transfer from residue into the various sinks of the second crop (plant, soil, and residual residues), and changes in microbial activity and numbers were determined. Oat biomass was greater after lupine than after oat due to differences in supply of N from these residues. Buried residues of both crops appeared to decompose faster than when left on the soil surface. Lupine residues decomposed faster than oat residues. Oat biomass was not affected by soil disturbance if grown after lupine but decreased when oat straw was buried in the soil. More residue N was recovered from soil than from the crop. Most ¹⁵N was recovered from disturbed soil, which also had greater dehydrogenase activity and more culturable fungi. At the end of the oat–oat rotation, 20 and 5 kg N ha⁻¹ were derived from the roots of the first crop in undisturbed or disturbed soil, respectively. Equivalent values for the lupine–oat rotation were 18 and 44 kg N ha⁻¹. Returning aboveground residues provided an extra 52–80 kg N ha⁻¹ for oat and 61–63 kg N ha⁻¹ for lupine relative to treatments where they were removed. Over a year, lupine contributed 9 to 20 kg N ha⁻¹ more to the agroecosystem than did oat.     

Predicting and mitigating the net greenhouse gas emissions of crop rotations in Western Europe

Nitrous oxide, carbon dioxide and methane are the main biogenic greenhouse gases (GHGs) contributing to net greenhouse gas balance of agro-ecosystems. Evaluating the impact of agriculture on climate thus requires capacity to predict the net exchanges of these gases in a systemic approach, as related to environmental conditions and crop management. Here, we used experimental data sets from intensively monitored cropping systems in France and Germany to calibrate and evaluate the ability of the biophysical crop model CERES-EGC to simulate GHG exchanges at the plot-scale. The experiments involved major crop types (maize-wheat-barley-rapeseed) on loam and rendzina soils. The model was subsequently extrapolated to predict CO₂ and N₂O fluxes over entire crop rotations. Indirect emissions (IE) arising from the production of agricultural inputs and from use of farm machinery were also added to the final greenhouse gas balance. One experimental site (involving a maize-wheat-barley-mustard rotation on a loamy soil) was a net source of GHG with a net GHG balance of 670 kg CO₂-C eq ha⁻¹ yr⁻¹, of which half were due to IE and half to direct N₂O emissions. The other site (involving a rapeseed-wheat-barley rotation on a rendzina) was a net sink of GHG for −650 kg CO₂-C eq ha⁻¹ yr⁻¹, mainly due to high C returns to soil from crop residues. A selection of mitigation options were tested at one experimental site, of which straw return to soils emerged as the most efficient to reduce the net GHG balance of the crop rotation, with a 35% abatement. Halving the rate of N inputs only allowed a 27% reduction in net GHG balance. Removing the organic fertilizer application led to a substantial loss of C for the entire crop rotation that was not compensated by a significant decrease of N₂O emissions due to a lower N supply in the system. Agro-ecosystem modeling and scenario analysis may therefore contribute to design productive cropping systems with low GHG emissions.     

水分状态、土壤类型和氮素种类对氧化亚氮和甲烷排放的影响

Specific management of water regimes, soil and N in China might play an important role in regulating N2O and CH4 emissions in rice fields. Nitrous oxide and methane emissions from alternate non-flooded/flooded paddies were monitored simultaneously during a 516-day incubation with lysimeter experiments. Two N sources （^15N-（NH4）2SO4 and ^15N-labeled milk vetch） were applied to two contrasting paddies： one derived from Xiashu loess （Loess） and one from Quaternary red clay （Clay）. Both N2O and CH4 emissions were significantly higher in soil Clay than in soil Loess during the flooded period. For both soil, N2O emissions peaked at the transition periods shortly after the beginning of the flooded and non-flooded seasons. Soil type affected N2O emission patterns. In soil Clay, the emission peak during the transition period from non-flooded to flooded conditions was much higher than the peak during the transition period from flooded to non-flooded conditions. In soil Loess, the emission peak during the transition period from flooded to non-flooded conditions was obviously higher than the peak during the transition period from non-flooded to flooded conditions except for milk vetch treatment. Soil type also had a significant effect on CH4 emissions during the flooded season, over which the weighted average flux was 111 mg C m^-2 h^-1 and 2.2 mg C m^-2 h^-1 from Clay and Loess, respectively. Results indicated that it was the transition in the water regime that dominated N2O emissions while it was the soil type that dominated CH4 emissions during the flooded season. Anaerobic oxidation of methane possibly existed in soil Loess during the flooded season.