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1.
Heterotrophic and autotrophic nitrification in two acid pasture soils   总被引：1，自引：0，他引：1  
Laboratory incubation experiments, using 15N-labeling techniques and simple analytical models, were conducted to measure heterotrophic and autotrophic nitrification rates in two acid soils (pH 4.8-5.3; 1/5 in H2O) with high organic carbon contents (6.2-6.8% in top 5 cm soil). The soils were from pastures located near Maindample and Ruffy in the Northeast Victoria, Australia. Gross rates of N mineralization, nitrification and immobilization were measured. The gross rates of autotrophic nitrification were 0.157 and 0.119 μg N g−1 h−1 and heterotrophic nitrification rates were 0.036 and 0.009 μg N g−1 h−1 for the Maindample and Ruffy soils, respectively. Heterotrophic nitrification accounted for 19% and 7% of the total nitrification in the Maindample and Ruffy soils, respectively. The heterotrophic nitrifiers used organic N compounds and no as the substrate for nitrification.  相似文献   

2.
Using a soilless culture system mimicking tropical acidic peat soils, which contained 3 mg of gellan gum and 0.5 mg NO3?-N per gram of medium, a greenhouse gas, N2O emitting capability of microorganisms in acidic peat soil in the area of Palangkaraya, Central Kalimantan, Indonesia, was investigated. The soil sampling sites included a native swamp forest (NF), a burnt forest covered by ferns and shrubs (BF), three arable lands (A-1, A-2 and A-3) and a reclaimed grassland (GL) next to the arable lands. An acid-tolerant Janthinobacterium sp. strain A1-13 (Oxalobacteriaceae, β-proteobacteria) isolated from A-1 soil was characterized as one of the most prominent N2O-emitting bacteria in this region. Physiological characteristics of the N2O emitter in the soilless culture system, including responses to soil environments, substrate concentration, C-source concentration, pH, and temperature, suggest that the N2O emitting Janthinobacterium sp. strain A1-13 is highly adapted to reclaimed open peatland and primarily responsible for massive N2O emissions from the acidic peat soils. Regulation of N2O emitters in the reclaimed peatland for agricultural use is therefore one of the most important issues in preventing the greenhouse gas emission from acidic peat soil farmlands.  相似文献   

3.
Soil of the former lake Texcoco is alkaline saline with pH often >10 and electrolytic conductivity (EC) >70 dS m?1 with rapidly changing water contents. Little is known how fertilizing this area with urea to vegetate the soil would affect emissions of carbon dioxide (CO2) and dynamics of N. Texcoco soil with electrolytic conductivity (EC) 2.3 dS m?1 and pH 8.5 (TEXCOCO A soil), EC 2.0 dS m?1 and pH 9.0 (TEXCOCO B soil) and 200 dS m?1 and pH 11.2 (TEXCOCO C soil) was amended with or without urea and incubated at 40% of water holding capacity (WHC), 60% WHC, 80% WHC and 100% WHC, while emissions of nitrous oxide (N2O) and CO2 and dynamics of ammonium (NH4+), nitrite (NO2?) and nitrate (NO3?) were monitored for 7 days. An agricultural soil served as control (ACOLMAN soil). The emission of CO2 increased in the urea amended soil 1.5 times compared to the unamended soil, it was inhibited in TEXCOCO C soil and was >1.2 larger in soil incubated at 40%, 60% and 80% WHC compared to soil incubated at 100% WHC. The emission of N2O increased in soil added with urea compared to the unamended soil, was similar in TEXCOCO A and B soils, but was <0.2 mg N kg?1 soil day?1 in TEXCOCO C soil and generally larger in soil incubated at 60% and 80% WHC compared to soil incubated at 40% and 100% WHC. The water content of the soil had no significant effect on the mean concentration of NH4+, but addition of urea increased it in all soils. The concentration of NO2? was not affected by the water content and the addition of urea except in TEXCOCO A soil where it increased to values ranging between 20 and 40 mg N kg?1. The concentration of NO3? increased in the ACOLMAN, TEXCOCO A and TEXCOCO B soil amended with urea compared to the unamended soil, but not in the TEXCOCO C soil. It decreased with increased water content, but not in TEXCOCO C soil. It was found that the differences in soil characteristics, i.e. soil organic matter content, pH and EC between the soils had a profound effect on soil processes, but even small changes affected the dynamics of C and N in soil amended with urea.  相似文献   

4.
A phylogenetic analysis of the archaeal community in the soil of the former Lake Texcoco showed that some of the clones identified were affiliated to Archeae that reduce nitrate (NO3?) to nitrite (NO2?) and NO2? to unknown products under aerobic conditions. Previous research suggested that this indeed might occur when an easily decomposable C-substrate is available, but little is known about the factors that control the possible processes involved. The sandy clay loam soil with pH 10 and electrolytic conductivity 56 dS m?1 was spiked with 1000 mg glucose-C kg?1 soil (GLUCOSE pre-treatment), 200 mg NO3?-N kg?1 soil (NITRATE pre-treatment), or left unamended (CONTROL pre-treatment) and conditioned for eight days. Pre-treated soil was then added with 1000 mg glucose-C kg?1 soil and 200 mg NO3?-N kg?1 soil and amended with ammonium (NH4+) (AMM treatment) and l-glutamine (GLUT treatment), acetylene (C2H2) (ACE treatment), oxygen (O2) (OXI treatment), left untreated (CON treatment) or sterilized. No abiotic factors affected concentrations of NH4+, NO2? or NO3?. In the CONTROL pre-treatment, concentration of NO3? decreased 170 mg N kg?1 soil within 72 h, in the GLUCOSE pre-treatment with 182 mg N kg?1 soil within 2 h and in the NITRATE pre-treatment with 272 mg N kg?1 soil within 168 h. Mean concentration of NO2? was 3.2 mg N kg?1 soil in unamended soil, 5.7 mg N kg?1 soil in the CONTROL pre-treatment, but >20 mg kg?1 soil in the GLUCOSE pre-treatment and ≥40 mg kg?1 in the NITRATE pre-treatment. The application of NO3? and glucose increased the mean concentration of NH4+ compared to the unamended soil independently of pre-treatment. It was found that microorganisms in the alkaline saline soil of the former Lake Texcoco can reduce concentrations of NO3? while releasing NO2? under aerobic conditions when an easy decomposable substrate is available without it being directly related to microbial activity and this being more outspoken when glucose or nitrate were previously added.  相似文献   

5.
Meat and bone meal (MBM) utilization for animal production was banned in the European Union since 2000 as a consequence of the appearance of transmissive spongiform encephalopathies. Soil application could represent a lawful and effective strategy for the sustainable recycling of MBM due to its relevant content of nutritive elements and organic matter. The effectiveness of MBM as organic fertilizer needs to be thoroughly investigated since there is a lack of knowledge about the mineralization dynamics of MBM in soil and the impact of such residues, in particular the high content of lipids, on soil biochemical and microbiological properties. For this aim, a defatted (D) and the correspondent non-defatted (ND) MBM were added at two rates (200 and 400 kg N ha?1) to two different moist soils and incubated at 15 and 20 °C for 14 d. MBM mineralization dynamics was studied by measuring CO2 evolution. Water extractable organic C, K2SO4-extractable NO3? and NH4+, microbial biomass ninhydrin-reactive N, enzymatic activities (FDA, urease, protease, alkaline phosphatase) and microbial composition (aerobic and anaerobic bacteria, fungi) were measured 2 and 14 d after MBM addition to the soil. The rate of CO2 evolution showed a maximum 2–3 d after the addition of MBM, followed by a decrease approaching the control. MBM mineralization was fast with, on average, 54% of total CO2 evolved in the first 4 d of incubation at 20 °C. The percentage of added C which was evolved as CO2 at the end of the incubation period ranged between 8% and 16% and was affected by temperature, soil type and MBM treatment (ND > D). Soil amendment with MBM caused a noteworthy increase in both extractable NH4+ and NO3? (about 50% of added N) which was higher for ND. The addition of MBM also enhanced microbial content and activity. Microbial biomass increased as a function of the rate of application and was higher for ND with respect to D. The increase in numbers of aerobic and anaerobic bacteria and fungi caused by MBM addition was, in general, more pronounced with ND. Enzymatic activity in amended soils showed an enhancement in nutrient availability and element cycling. At the rate of application of present work, lipids did not cause adverse effects on soil microorganisms.The potential of MBM as effective organic fertilizer was supported by the large increase in available N and the enhancement of the size and activity of soil microorganisms.  相似文献   

6.
Contradictory effects of simultaneous available organic C and N sources on nitrous oxide (N2O), carbon dioxide (CO2) and nitric oxide (NO) fluxes are reported in the literature. In order to clarify this controversy, laboratory experiments were conduced on two different soils, a semiarid arable soil from Spain (soil I, pH=7.5, 0.8%C) and a grassland soil from Scotland (soil II, pH=5.5, 4.1%C). Soils were incubated at two different moisture contents, at a water filled pore space (WFPS) of 90% and 40%. Ammonium sulphate, added at rates equivalent to 200 and 50 kg N ha?1, stimulated N2O and NO emissions in both soils. Under wet conditions (90% WFPS), at high and low rates of N additions, cumulative N2O emissions increased by 250.7 and 8.1 ng N2O–N g?1 in comparison to the control, respectively, in soil I and by 472.2 and 2.1 ng N2O–N g?1, respectively, in soil II. NO emissions only significantly increased in soil I at the high N application rate with and without glucose addition and at both 40% and 90% WFPS. In both soils additions of glucose together with the high N application rate (200 kg N ha?1) reduced cumulative N2O and NO emissions by 94% and 55% in soil I, and by 46% and 66% in soil II, respectively. These differences can be explained by differences in soil properties, including pH, soil mineral N and total and dissolved organic carbon content. It is speculated that nitrifier denitrification was the main source of NO and N2O in the C-poor Spanish soil, and coupled nitrification–denitrification in the C-rich Scottish soil.  相似文献   

7.
Recovery of soil organic matter, organic matter turnover and mineral nutrient cycling is critical to the success of rehabilitation schemes following major ecosystem disturbance. We investigated successional changes in soil nutrient contents, microbial biomass and activity, C utilisation efficiency and N cycling dynamics in a chronosequence of seven ages (between 0 and 26 years old) of jarrah (Eucalyptus marginata) forest rehabilitation that had been previously mined for bauxite. Recovery was assessed by comparison of rehabilitation soils to non-mined jarrah forest references sites. Mining operations resulted in significant losses of soil total C and N, microbial biomass C and microbial quotients. Organic matter quantity recovered within the rehabilitation chronosequence soils to a level comparable to that of non-mined forest soil. Recovery of soil N was faster than soil C and recovery of microbial and soluble organic C and N fractions was faster than total soil C and N. The recovery of soil organic matter and changes to soil pH displayed distinct spatial heterogeneity due to the surface micro-topography (mounds and furrows) created by contour ripping of rehabilitation sites. Decreases in the metabolic quotient with rehabilitation age conformed to conceptual models of ecosystem energetics during succession but may have been more indicative of decreasing C availability than increased metabolic efficiency. Net ammonification and nitrification rates suggested that the low organic C environment in mound soils may favour autotrophic nitrifier populations, but the production of nitrate (NO3?) was limited by the low gross N ammonification rates (≤1 μg N g?1 d?1). Gross N transformation rates in furrow soils suggested that the capacity to immobilise N was closely coupled to the capacity to mineralise N, suggesting NO3? accumulation in situ is unlikely. The C:N ratio of the older rehabilitation soils was significantly lower than that of the non-mined forest soils. However, variation in ammonification rates was best explained by C and N quantity rather than C:N ratios of whole soil or soluble organic matter fractions. We conclude that the rehabilitated ecosystems are developing a conservative N cycle as displayed by non-mined jarrah forests. However, further investigation into the control of nitrification dynamics, particularly in the event of further ecosystem disturbance, is warranted.  相似文献   

8.
Nitrous oxide emissions were monitored at three sites over a 2-year period in irrigated cotton fields in Khorezm, Uzbekistan, a region located in the arid deserts of the Aral Sea Basin. The fields were managed using different fertilizer management strategies and irrigation water regimes. N2O emissions varied widely between years, within 1 year throughout the vegetation season, and between the sites. The amount of irrigation water applied, the amount and type of N fertilizer used, and topsoil temperature had the greatest effect on these emissions.Very high N2O emissions of up to 3000 μg N2O-N m?2 h?1 were measured in periods following N-fertilizer application in combination with irrigation events. These “emission pulses” accounted for 80–95% of the total N2O emissions between April and September and varied from 0.9 to 6.5 kg N2O-N ha?1.. Emission factors (EF), uncorrected for background emission, ranged from 0.4% to 2.6% of total N applied, corresponding to an average EF of 1.48% of applied N fertilizer lost as N2O-N. This is in line with the default global average value of 1.25% of applied N used in calculations of N2O emissions by the Intergovernmental Panel on Climate Change.During the emission pulses, which were triggered by high soil moisture and high availability of mineral N, a clear diurnal pattern of N2O emissions was observed, driven by daily changes in topsoil temperature. For these periods, air sampling from 8:00 to 10:00 and from 18:00 to 20:00 was found to best represent the mean daily N2O flux rates. The wet topsoil conditions caused by irrigation favored the production of N2O from NO3? fertilizers, but not from NH4+ fertilizers, thus indicating that denitrification was the main process causing N2O emissions. It is therefore argued that there is scope for reducing N2O emission from irrigated cotton production; i.e. through the exclusive use of NH4+ fertilizers. Advanced application and irrigation techniques such as subsurface fertilizer application, drip irrigation and fertigation may also minimize N2O emission from this regionally dominant agro-ecosystem.  相似文献   

9.
Dicyandiamide (DCD, C2H4N4) is a nitrification inhibitor that has been studied for more than 80 years. However, there are few papers that have examined the use of DCD on dairy farms where cattle graze pasture and where urine is the primary form of nitrogen (N) deposited onto soils. After DCD was applied (10 kg DCD ha?1) with bovine urine (700–1200 kg N ha?1) to five soils throughout New Zealand, the reduction in direct nitrous oxide (N2O) emissions was significant and remarkably consistent (71 ± 8%, average ± standard error). The application of DCD to these soils occurred in autumn and winter; daily average soil temperature (T) was reported but these data were not further analysed. Perusal of the literature suggested no consensus on the temperature dependence of DCD degradation in soils. Based on published data from controlled-environment studies of soils sampled in four countries, we quantified the relation between T and the time for DCD concentration in soils to decline to half its application value (t½) as t½ (T) = 168e?0.084T with parameter standard errors of ±16 d and ±0.011 d?1, respectively (n = 16). For example, at 5 °C a 1 °C increase in T reduced t½ from 110 to 101 d whereas at 25 °C the reduction was 20–19 d. Analysing T data from the New Zealand trials using our t½ (T) function, over 43–89 d when direct N2O emissions from treated plots became indistinguishable from the controls, the estimated percentage of applied DCD remaining in the soil averaged 43 ± 10%. These calculations suggested the apparently remaining DCD was ineffective with respect to direct N2O emissions. In the absence of measurements, explanations for this interpretation included vertical displacement of the DCD and sorption onto organic matter in soils. The consistent DCD efficacy from these trials corresponded with T generally <10 °C, so it is suggested as an application criteria for the reduction of direct N2O emissions from pastoral soils subjected to urine excretion by grazing cattle.  相似文献   

10.
N2O emissions from soils treated with NH4+-N under aerobic conditions in the laboratory were 3- to 4-fold higher than those from controls (no extra N added) or when NO3?-N was added. Although the emission of N2O-N in these field and laboratory experiments represented only 0.1–0.8% of the applied fertilizer NH4+-N and are therefore not significant from an agronomic standpoint, these studies have conclusively demonstrated that the oxidation of applied ammoniacal fertilizers (nitrification) could contribute significantly to the stratospheric N2O pool.Like N-serve, acetylene was shown to be a potent inhibitor of nitrification as it stopped the oxidation of NH4+-N to (NO3+-N + NO2?)-N and hence reduced the evolution of N2O from nitrification within 60 min after its addition.Although high amounts of NO3?-N were present, the rate of denitrification was very low from soils with moisture up to 60% saturation. The further increase in the degree of saturation resulted in several-fold increase of denitrification which eventually became the predominant mechanism of gaseous N losses under anaerobic conditions.  相似文献   

11.
Soils in Mexico are often contaminated with hydrocarbons and addition of waste water sludge and earthworms accelerates their removal. However, little is known how contamination and subsequent bioremediation affects emissions of N2O and CO2. A laboratory study was done to investigate the effect of waste water sludge and the earthworm Eisenia fetida on emission of N2O and CO2 in a sandy loam soil contaminated with the polycyclic aromatic hydrocarbons (PAHs): phenanthrene, anthracene and benzo(a)pyrene. Emissions of N2O and CO2, and concentrations of inorganic N (ammonium (NH4+), nitrite (NO2?) nitrate (NO3?)) were monitored after 0, 5, 24, 72 and 168 h. Adding E. fetida to the PAHs contaminated soil increased CO2 production rate significantly 2.0 times independent of the addition of sludge. The N2O emission rate from unamended soil expressed on a daily base was 5 μg N kg?1 d?1 for the first 2 h and increased to a maximum of 325 μg N kg?1 d?1 after 48 h and then decreased to 10 μg N kg?1 d?1 after 168 h. Addition of PAHs, E. fetida or PAHs + E. fetida had no significant effect on the N2O emission rate. Adding sludge to the soil sharply increased the N2O emission rate to >400 μg N kg?1 d?1 for the entire incubation with a maximum of 1134 μg N kg?1 d?1 after 48 h. Addition of E. fetida, PAHs or PAHs + E. fetida to the sludge-amended soil reduced the N2O emission rate significantly compared to soil amended with sludge after 24 h. It was found that contaminating soil with PAHs and adding earthworms had no effect on emissions of N2O. Emission of N2O, however, increased in sludge-amended soil, but addition of earthworms to this soil and contamination reduced it.  相似文献   

12.
We used natural gradients in soil and vegetation δ13C signatures in a savannah ecosystem in Texas to partition soil respiration into the autotrophic (Ra) and heterotrophic (Rh) components. We measured soil respiration along short transects from under clusters of C3 trees into the C4 dominated grassland. The site chosen for the study was experiencing a prolonged drought, so an irrigation treatment was applied at two positions of each transect. Soil surface CO2 efflux was measured along transects and CO2 collected for analysis of the δ13C signature in order to: (i) determine how soil respiration rates varied along transects and were affected by localised change in soil moisture and (ii) partition the soil surface CO2 efflux into Ra and Rh, which required measurement of the δ13C signature of root- and soil-derived CO2 for use in a mass balance model.The soil at the site was unusually dry, with mean volumetric soil water content of 8.2%. Soil respiration rates were fastest in the centre of the tree cluster (1.5 ± 0.18 μmol m?2 s?1; mean ± SE) and slowest at the cluster–grassland transition (0.6 ± 0.12 μmol m?2 s?1). Irrigation produced a 7–11 fold increase in the soil respiration rate. There were no significant differences (p > 0.5) between the δ13C signature of root biomass and respired CO2, but differences (p < 0.01) were observed between the respired CO2 and soil when sampled at the edge of the clusters and in the grassland. Therefore, end member values were measured by root and soil incubations, with times kept constant at 30 min for roots and 2 h for soils. The δ13C signature of the soil surface CO2 efflux and the two end member values were used to calculate that, in the irrigated soils, Rh comprised 51 ± 13.5% of the soil surface CO2 efflux at the mid canopy position and 57 ± 7.4% at the drip line. In non-irrigated soil it was not possible to partition soil respiration, because the δ13C signature of the soil surface CO2 efflux was enriched compared to both the end member values. This was probably due to a combination of the very dry porous soils at our study site (which may have been particularly susceptible to ingress of atmospheric CO2) and the very slow respiration rates of the non-irrigated soils.  相似文献   

13.
The treatment of manures may improve their agricultural value and environmental quality, for instance with regards to greenhouse gases mitigation and enhancement of carbon (C) sequestration. The present study verified whether different pig slurry treatments (i.e. solid/liquid separation and anaerobic digestion) changed slurry composition. The effect of the slurry composition on N2O and CO2 emissions, denitrification and soil mineral nitrogen (N), after soil incorporation, was also examined during a 58-day mesocosm study. The treatments included a non-treated pig slurry (NT), the solid fraction (SF), and the liquid fraction (LF) of a pig slurry and the anaerobically digested liquid fraction (DG). Finally, a non-fertilized (N0) and a treatment with urea (UR) were also present.The N2O emissions measured represented 4.8%, 2.6%, 1.8%, 1.0% and 0.9% of N supplied with slurry/fertilizer for NT, LF, DG, SF and UR, respectively. Cumulative CO2 emissions ranged from 0.40 g CO2-C kg?1 soil (0.38 Mg CO2-C ha?1) to 0.80 g CO2-C kg?1 soil (0.75 Mg CO2-C ha?1). They were highest for SF (56% of C applied), followed by NT (189% of C applied), LF (337% of C applied) and DG (321% of C applied). Ammonium was detected in the soil for all treatments only at day one, while nitrate concentration increased linearly from day 15 to day 58, at a rate independent of the type of slurry/fertilizer applied. The nitrate recovery at day 58 was 39% of the N applied for NT, 19% for SF, 52% for LF, 67% for DG, and 41% for UR. The solid fraction generally produced higher potential denitrification fluxes (75.3 for SF, 56.7 for NT, 53.6 for LF, 47.7 for DG and 39.7 mg N2O + N2-N kg?1 soil for UR). The high variability of actual denitrification results obfuscated any treatment effect.We conclude that treatment strongly affects slurry composition (mainly its C, fibre and NH4+ content), and hence N2O and CO2 emission patterns as well as denitrification processes and nitrate availability. In particular, the solid fraction obtained after mechanical separation produced the most pronounced difference, while the liquid fraction and the anaerobically digested liquid fraction did not show significant difference with respect to the original slurry for any of the measured parameters. Combining data from the different fractions we showed that separation of slurry leads to reduced N2O emissions, irrespective of whether the liquid fraction is digested or not. Furthermore, our results suggested that the default emission factor for N2O emissions inventory is too low for both the non-treated pig slurry and its liquid fraction (digested or not), and too high for the separated solid fraction and urea.  相似文献   

14.
In recent years alternative farming practices have received considerable attention from Canadian producers as a means to improve their net return from grain and oilseed production. Enhancing the efficiency of nitrogen fertilizer use, including a pulse crop in the rotation, reducing tillage and pesticide use are seen as viable options to reduce reliance on fossil fuel, lower input costs and decrease the risk of soil, air and water degradation. The objective of this study was to determine the effects of 16 alternative management practices for a 2-year spring wheat (Triticum aestivum L.)–field pea (Pisum sativum L.) rotation on economic returns, non-renewable energy use efficiency, and greenhouse gas emissions. The alternative management methods for wheat consisted of a factorial combination of high vs. low soil disturbance one pass seeding, four nitrogen (N) fertilizer rates (20 kg N ha?1, 40 kg N ha?1, 60 kg N ha?1 and 80 kg N ha?1), and recommended vs. reduced rates of in-crop herbicide application. Alternative management practices for field pea were high vs. low soil disturbance one pass seeding. The resulting 16 cropping systems were evaluated at the whole farm level based on 4 years (two rotation cycles) of data from field experiments conducted on two Orthic Black Chernozem soils (clay loam and loam textures) in Manitoba, Canada. The highest net returns on the clay loam soil were for the high disturbance system with 60 kg N ha?1 applied to wheat and the recommended rates of in-crop herbicides. The lowest application rate of N, together with low disturbance seeding, provided the highest economic returns on the loam soil. Energy use efficiency was highest for the lowest rate of N application for both tillage systems. The highest rate of N fertilizer and recommended rates of in-crop herbicide produced little additional yield response, lower net returns, and higher GHG emissions. An increase in N fertilizer application from 20 kg ha?1 to 80 kg ha?1 increased whole farm energy requirements by about 40%, while reducing herbicide rates had negligible effects on grain yields and total energy input. Overall, as N fertilizer rate increased, the associated GHG emissions were not offset by an increase in carbon retained in the above-ground crop biomass. Moderate to high soil test NO3-N levels at experimental sites reduced the potential for positive yield responses to N fertilizer in this study, thus minimizing the economic benefits derived from N fertilizer application.  相似文献   

15.
Irrigation management has an important influence on emissions of nitrous oxide (N2O) and nitric oxide (NO) from irrigated agricultural soils. In order to develop strategies to reduce the emission of these gases, a field experiment was carried out to compare the influence of different irrigation systems: furrow (FI) and drip-irrigation (DI), on N2O and NO emissions from a soil during the melon crop season. Two fertilizer treatments were evaluated for each irrigation regime: ammonium sulphate (AS) as a mineral N fertilizer, at a rate of 175 kg N ha?1; and a control without any N fertilizer (Control). On plots where the AS treatment was applied, drip irrigation reduced total N2O and NO emissions (by 70% and 33% respectively) with respect to values for furrow irrigation. This was probably due to the lower amount of water applied and the different soil wetting pattern associated with DI. Dry areas of the drip-irrigated plots emitted a similar amount of N2O to the wet areas (0.45 kg N2O-N ha?1) in the Control and greater quantities in the AS treatment (0.92 kg N2O-N ha?1 for dry and 0.70 kg N2O-N ha?1 for wet areas). We suggest that the N oxide pulses observed throughout the irrigation period on DI plots could have been the result of frequent increases in the soil wetting volume after the addition of water. Denitrification losses (from depths of 0–10 cm) were estimated at 11.44 kg N2O- N ha?1 for the AS treatment under FI and at 4.96 kg N2O-N ha?1 for DI. Under DI, nitrification was an important source of N2O, whereas denitrification was the most important source under FI. The addition of NH4+ and the use of DI enhanced the N2O/N2 ratio of gases produced through denitrification. The quantity of dissolved organic C (DOC) in the soil generally decreased with addition of NH4+.This work showed that, in comparison with furrow irrigation, drip irrigation is a method that can be used to save water and mitigate emissions of the atmospheric pollutants NO and N2O.  相似文献   

16.
Surface samples (0–10 cm) of two equally-acidic soils (pH 4.5) exhibited very different net N mineralization rates. In an andic soil, it was negligible despite a high (46%) organic matter content, whereas it was appreciable in a colluvial soil of lower (14%) organic matter content. During incubation experiments no NO?3 was observed in the andic soil, whereas nitrification occurred in the colluvial soil. Incorporation of added 15NH4 is much higher in the andic soil, despite no greater biological immobilization than in the colluvial soil.Added 15NO2? and nitrapyrin experiments showed that incorporation of inorganic-N into the organic fraction of the andic soil can also proceed via a chemical pathway, NO2? self-decomposition and fixation on organic matter. This can be a limitation to NO3? appearance in this soil. The protective effect of amorphous aluminium is also considered to lower mineralization of organic-N. These two mechanisms could be responsible for low concentration of inorganic-N in many aluminous humic-rich acidic soils.  相似文献   

17.
To gain insight into the effects of drying and rewetting events on anaerobic respiration in ombrotrophic peat soils, we investigated bacterial sulfate (SO4) reduction and methane (CH4) production in anaerobic incubations of intact peat microcores from 30 to 40 cm depth of Mer Bleue bog, Ontario/Canada. Concentrations of dissolved SO4, carbon dioxide (CO2), CH4, acetate, and hydrogen (H2) were recorded and net turnover rates calculated from regression. Gross rates of bacterial sulfate reduction were determined by 35SO4 tracer incubation. After incubation, the peat was dried and rewetted, with saturated peat serving as control. CO2 production was initially rapid (up to <360 nmol cm?3 d?1) and slowed towards an endpoint of 2–3 mmol l?1, which was only partly related to thresholds of Gibbs free energies of the involved processes. Acetate rapidly accumulated to levels of 600–800 μmol l?1 and remained constant thereafter. CH4 production (0–2.8 nmol cm?3 d?1) was small and delayed, even after SO4 was depleted, by about 30–40 d. Hydrogenotrophic methanogenesis was endergonic and the process thus likely followed an acetotrophic pathway. Drying and rewetting replenished the SO4 pool, enhanced SO4 reduction rates and suppressed methanogenesis. The overall contribution of net SO4 reduction and methanogenesis to the CO2 production rate was small (0.5–22%) and only enhanced in replicates subjected to drying (35–62%). The major fraction of respiration in the incubated peat cores thus followed yet unidentified pathways.  相似文献   

18.
Nitrogen (N) from urine excreted by grazing animals can be transformed into N compounds that have detrimental effects on the environment. These include nitrate, which can cause eutrophication of waterways, and nitrous oxide, which is a greenhouse gas. Soil microbes mediate all of these N transformations, but the impact of urine on microbes and how initial soil conditions and urine chemical composition alter their responses to urine are not well understood. This study aimed to determine how soil inorganic N pools, nitrous oxide fluxes, soil microbial activity, biomass, and the community structure of bacteria containing amoA (nitrifiers), nirK, and nirS (denitrifiers) genes responded to the addition of urine over time. Bovine urine containing either a high (15.0 g K+ l?1) or low salt content (10.4 g K+ l?1) was added to soil cores at either low or high moisture content (hereafter termed dry and wet soil respectively; 35% or 70% water-filled pore space after the addition of urine). Changes in soil conditions, inorganic N pools, nitrous oxide fluxes, and the soil microbial community were then measured 1, 3, 8, 15, 29 and 44 days after urine addition. Urine addition increased soil ammonium concentrations by up to 2 mg g d.w.?1, soil pH by up to 2.7 units, and electrical conductivity (EC) by 1.0 and 1.6 dS m?1 in the low and high salt urine treatments respectively. In response, nitrate accumulation and nitrous oxide fluxes were lower in dry compared to wet urine-amended soils and slightly lower in high compared to low salt urine-amended soils. Nitrite concentrations were elevated (>3 μg g d.w.?1) for at least 15 days after urine addition in wet urine-amended soils, but were only this high in the dry urine-amended soils for 1 day after the addition of urine. Microbial biomass was reduced by up to half in the wet urine-amended soils, but was largely unaffected in the dry urine-amended soils. Urine addition affected the community structure of ammonia-oxidising and nitrite-reducing bacteria; this response was also stronger and more persistent in wet than in dry urine-amended soils. Overall, the changes in soil conditions caused by the addition of urine interacted to influence microbial responses, indicating that the effect of urine on soil microbes is likely to be context-dependent.  相似文献   

19.
Mineral fertilizers, organic amendments, and pesticides are inputs commonly used in conventional farming practices. The aim of this study was to evaluate the effects of single or combined applications of spent grape marc-vermicompost, urea, and/or diuron on soil-enzyme activities and the persistence of this herbicide in soils with low organic carbon content. The application of vermicompost enhanced dehydrogenase (DHase) enzyme activity over time but altered soil urease activity to a very limited extent. The reduction in diuron concentrations and the increase in DHase activity indicated that the soil microorganisms were capable of degrading the ureic herbicide. Treatment with vermicompost and diuron had a stimulatory effect on soil microbial activity. On the whole, the application of diuron and urea to the vermicompost-amended soil raised DHase and urease activity to maximum levels (>3 μg INTF g?1 h?1 and >47 μg NH4+ g?1 h?1, respectively). The application of urea to the unamended and vermicompost-amended soil decreased diuron persistence from 18.8 and 33 d to 12.5 and 15 d, respectively. Our findings show that although vermicompost additions reduce diuron availability, this boosts diuron degradation when combined with urea. These additions, under different soil management conditions, minimize the bioavailability and persistence of diuron and consequently the risk of leaching and seepage into aquifers. Compared with untreated soils, these types of treated soils could also improve agricultural sustainability and the quality of the environment.  相似文献   

20.
Enchytraeid worms (Oligochaeta) are the dominant mesofauna in wet acidic habitats. They have key roles in biogeochemical cycling, and can be used as biological indicators. Here we report the response of these worms to in situ ammonia-N (NH3-N) deposition on an ombrotrophic bog. Three years of NH3-N fumigation from an automated release system has created a gradient of NH3-N concentrations downwind of the release pipe ranging from 83 μg m−3 (near source) to 4.5 μg m−3 NH3-N (60 m from release pipe); the ambient NH3-N concentration is 0.56 μg m−3 NH3-N. Peat pH and mineral N content have increased near the ammonia release pipe. We hypothesised that enhanced N deposition at the site would have improved litter quality and thus, enchytraeid distribution would be increased along the transect compared to ambient. However, neither litter quality nor enchytraeid abundance and diversity were affected by NH3-N despite increases in peat pH and mineral N. This suggests that three years of ammonia fumigation was not enough time for plant matter exposed to ammonia to become incorporated into the peat litter layer. Enchytraeids appear not to be sensitive indicators of NH3 fumigation because there was no effect below-ground of peat chemistry on litter quality.  相似文献   

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