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1.
A long-term fertilizer experiment investigating cotton-based cropping systems established in 1990 in central Asia was used to quantify the emissions of CO 2, CH 4 and N 2O from April 2012 to April 2013 to better understand greenhouse gas (GHG) emissions and net global warming potential (GWP) in extremely arid croplands. The study involved five treatments: no fertilizer application as a control (CK), balanced fertilizer NPK (NPK), fertilizer NPK plus straw (NPKS), fertilizer NPK plus organic manure (NPKM), and high rates of fertilizer NPK and organic manure (NPKM+). The net ecosystem carbon balance was estimated by the changes in topsoil (0–20 cm) organic carbon (SOC) density over the 22-year period 1990–2012. Manure and fertilizer combination treatments (NPKM and NPKM+) significantly increased CO 2 and slightly increased N 2O emissions during and outside the cotton growing seasons. Neither NPK nor NPKS treatment increased SOC in spite of relatively low CO 2, CH 4 and N 2O fluxes. Treatments involving manure application showed the lowest net annual GWP and GHG intensity (GHGI). However, overuse of manure and fertilizers (NPKM+) did not significantly increase cotton yield (5.3 t ha ?1) but the net annual GWP (?4,535 kg CO 2_eqv. ha ?1) and GHGI (?0.86 kg CO 2_eqv. kg ?1 grain yield of cotton) were significantly lower than in NPKM. NPKS and NPK slightly increased the net annual GWP compared with the control plots. Our study shows that a suitable rate of fertilizer NPK plus manure may be the optimum choice to increase soil carbon sequestration, maintain crop yields, and restrict net annual GWP and GHGI to relatively low levels in extremely arid regions. 相似文献
2.
Reducing tillage intensity and diversifying crop rotations may improve the sustainability of irrigated cropping systems in semi-arid regions. The objective of this study was to compare the greenhouse gas (GHG) emissions, soil organic matter, and net global warming potential (net GWP) of a sugar beet ( Beta vulgaris L.)-corn ( Zea mays L,) rotation under conventional (CT) and reduced-tillage (RT) and a corn-dry bean ( Phaseolus vulgaris L.) rotation under organic (OR) management during the third and fourth years of 4-year crop rotations. The gas and soil samples were collected during April 2011–March 2013, and were analyzed for carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) emissions, water-filled pore space (WFPS), soil nitrate (NO 3 ?–N) and ammonium (NH 4 +–N) concentrations, soil organic carbon (SOC) and total nitrogen (TN), and net global warming potential (net GWP). Soils under RT had 26% lower CO 2 emissions compared to 10.2 kg C ha ?1 day ?1 and 43% lower N 2O emissions compared to 17.5 g N ha ?1 day ?1 in CT during cropping season 2011, and no difference in CO 2 and N 2O emissions during cropping season 2012. The OR emitted 31% less N 2O, but 74% more CO 2 than CT during crop season 2011. The RT had 34% higher SOC content than CT (17.9 Mg ha ?1) while OR was comparable with CT. Net GWP was negative for RT and OR and positive for CT. The RT and OR can increase SOC sequestration, mitigate GWP and thereby support in the development of sustainable cropping systems in semiarid agroecosystems. 相似文献
3.
The contribution of ploughing permanent grassland and leys to emissions of N 2O and CO 2 is not yet well known. In this paper, the contribution of ploughing permanent grassland and leys, including grassland renovation, to CO 2 and N 2O emissions and mitigation options are explored. Land use changes in the Netherlands during 1970–2020 are used as a case study. Three grassland management operations are defined: (i) conversion of permanent grassland to arable land and leys; (ii) rotations of leys with arable crops or bulbs; and (iii) grassland renovation. The Introductory Carbon Balance Model (ICBM) is modified to calculate C and N accumulation and release. Model calibration is based on ICBM parameters, soil organic N data and C to N ratios. IPCC emission factors are used to estimate N 2O-emissions. The model is validated with data from the Rothamsted Park Grass experiments. Conversion of permanent grassland to arable land, a ley arable rotation of 3 years ley and 3 years arable crops, and a ley bulb rotation of 6 years ley and one year bulbs, result in calculated N 2O and CO 2 emissions totalling 250, 150 and 30 ton CO 2-equivalents ha –1, respectively. Most of this comes from CO 2. Emissions are very high directly after ploughing and decrease slowly over a period of more than 50 years. N 2O emissions in 3/3 ley arable rotation and 6/1 ley bulb rotation are 2.1 and 11.0 ton CO 2-equivalents ha –1 year –1, respectively. From each grassland renovation, N 2O emissions amount to 1.8 to 5.5 ton CO 2-equivalents ha –1. The calculated total annual emissions caused by ploughing in the Netherlands range from 0.5 to 0.65 Mton CO 2-equivalents year –1. Grassland renovation in spring offers realistic opportunities to lower the N 2O emissions. Developing appropriate combinations of ley, arable crops and bulbs, will reduce the need for conversion of permanent pasture. It will also decrease the rotational losses, due to a decreased proportion of leys in rotations. Also spatial policies are effective in reducing emissions of CO 2 and N 2O. Grassland ploughing contributes significantly to N 2O and CO 2 emissions. The conclusion can be drawn that total N 2O emissions are underestimated, because emissions from grassland ploughing are not taken into account. Specific emission factors and the development of mitigation options are required to account for the emissions and to realise a reduction of emissions due to the changes in grassland ploughing. 相似文献
4.
The zero tillage (ZT) system is used in a large area (>24 Mha) of crop production in Brazil. This management system can contribute
to soil C sequestration, but many studies in other countries have registered greater nitrous oxide emissions under ZT compared
to conventional tillage (CT), which may reduce greenhouse gas mitigation benefits. The aim of this study was to estimate the
emission of N 2O from cropping systems under conventional and zero tillage in an 18-year-old experiment conducted on a Rhodic Ferralsol in
the South of Brazil. Fluxes of N 2O were measured over two years using static-closed chambers in the two tillage systems with three crop rotations. Soil water
filled pore space (%WFPS) and soil mineral N were monitored along with rainfall and air temperature. Estimates of N 2O emissions were obtained by integrating the fluxes with time and also by applying the IPCC direct emission factor (EF1 = 1%)
to the amounts of N added as fertilisers and returned as crop residues. Fluxes of N 2O were relatively low, apart from a short period at the beginning of measurements. No relationship between N 2O fluxes and %WFPS or mineral N were observed. Nitrous oxide emissions were not influenced either by tillage system or crop
rotation. For the crop rotation receiving high rates of N fertiliser in the second year, field-measured N 2O emissions were significantly underestimated by the IPCC emission factor 1 (EF1). For the other treatments measured N 2O emissions fell within the EF1 uncertainty range, but always considerably lower than the EF1 estimate, which suggests IPCC
EF1 overestimates true N 2O emissions for the Ferralsol under evaluation. 相似文献
5.
Recent interest in integrated crop-livestock (ICL) systems has prompted numerous investigations to quantify ecosystem service tradeoffs associated with management. However, few investigations have quantified ICL management effects on net global warming potential (GWP), particularly in semiarid regions. Therefore, we determined net GWP for grazed and ungrazed cropland in a long-term ICL study near Mandan, ND USA. Factors evaluated for their contribution to net GWP included carbon dioxide (CO2) emissions associated with production inputs and field operations, methane (CH4) emissions from enteric fermentation by beef cattle, change in soil carbon stocks, and soil-atmosphere CH4 and nitrous oxide (N2O) fluxes. Net GWP was significantly greater for grazed cropland (946 kg CO2equiv. ha-1 yr-1) compared to ungrazed cropland (200 kg CO2equiv. ha-1 yr-1) (P=0.0331). The difference in net GWP between treatments was largely driven by emissions from enteric fermentation (602 kg CO2equiv. ha-1 yr-1). Among other contributing factors, CO2 emissions associated with seed production and field operations were lower under ungrazed cropland (P?=?0.0015 and 0.0135, respectively), while soil CH4 uptake was greater under grazed cropland (P?=?0.0102). Soil-atmosphere N2O flux from each system negated nearly all the CO2equiv. sink capacity accrued from soil carbon stock change. As both production systems resulted in net greenhouse gas (GHG) emissions to the atmosphere, novel practices that constrain GHG sources and boost GHG sinks under semiarid conditions are recommended. 相似文献
6.
Nitrous oxide (N 2O) emissions were measured over two years from an intensively managed grassland site in the UK. Emissions from ammonium nitrate (AN) and urea (UR) were compared to those from urea modified by various inhibitors (a nitrification inhibitor, UR(N), a urease inhibitor, UR(U), and both inhibitors together, SU), as well as a controlled release urea (CR). N 2O fluxes varied through time and between treatments. The differences between the treatments were not consistent throughout the year. After the spring and early summer fertilizer applications, fluxes from AN plots were greater than fluxes from UR plots, e.g. the cumulative fluxes for one month after N application in June 1999 were 5.2 ± 1.1 kg N 2O-N ha –1 from the AN plots, compared to 1.4 ± 1.0 kg N 2O-N ha –1 from the UR plots. However, after the late summer application, there was no difference between the two treatments, e.g. cumulative fluxes for the month following N application in August 2000 were 3.3 ± 0.7 kg N 2O-N ha –1 from the AN plots and 2.9 ± 1.1 kg N 2O-N ha –1 from the UR plots. After all N applications, fluxes from the UR(N) plots were much less than those from either the AN or the UR plots, e.g. 0.2 ± 0.1 kg N 2O-N ha –1 in June 1999 and 1.1 ± 0.3 kg N 2O-N ha –1 in August 2000. Combining the results of this experiment with earlier work showed that there was a greater N 2O emission response to rainfall around the time of fertilizer application in the AN plots than in the UR plots. It was concluded that there is scope for reducing N 2O emissions from N-fertilized grassland by applying UR instead of AN to wet soils in cool conditions, e.g. when grass growth begins in spring. Applying UR with a nitrification inhibitor could cut emissions further. 相似文献
7.
About 40% of the agricultural land in the European Union (EU) is grassland used for animal production. When grassland is tilled, organically bound carbon and nitrogen are released, providing substrates for nitrifying and denitrifying microorganisms. The aim of this study was to examine the immediate effects of tillage of a perennial grassland carried out on different dates, on the emissions of nitric oxide (NO) and nitrous oxide (N 2O), monitored intensively over a 5-day period, in a humid, dairy farming area of northern Spain. Soil was tilled 12 days and 2 days prior to fertiliser application. Tillage, time of tillage, and N fertiliser application affected NO and N 2O emissions. Tillage 12 days before the start of the flux measurements resulted in higher emissions than tillage one day before, the difference being related to differences in soil mineral N and water-filled pore space (WFPS). Emissions of NO peaked at a WFPS of 50–60%, while N 2O fluxes peaked at 70–90% WFPS. Loss of N was greater as N 2O than as NO. The total loss of N as N 2O plus NO ranged from 0.027 kg N ha –1 in unfertilised plots to 0.56 kg N ha –1 in the tilled and N fertilised plot. Thereafter emissions decreased rapidly to low values. The results of this study indicate that tillage of perennial grassland may release large amounts of NO and N 2O, the amounts also depending on moisture conditions and addition of N fertiliser. We suggest that in order to reduce such emissions, application of N fertiliser should not immediately follow tillage of perennial grassland, as there is an extra supply of N from mineralisation of organic matter at this time. 相似文献
8.
Grazed pastures contribute significantly to anthropogenic emissions of N 2O but the respective contributions of archaea, bacteria and fungi to codenitrification in such systems is unresolved. This study examined the relative contributions of bacteria and fungi to rates of denitrification and codenitrification under a simulated ruminant urine event. It was hypothesised that fungi would be primarily responsible for both codenitrification and total N 2O and N 2 emissions. The effects of bacterial (streptomycin), fungal (cycloheximide), and combined inhibitor treatments were measured in a laboratory mesocosm experiment, on soil that had received 15N labelled urea. Soil inorganic-N concentrations, N 2O and N 2 gas fluxes were measured over 51 days. On Days 42 and 51, when nitrification was actively proceeding in the positive control, the inhibitor treatments inhibited nitrification as evidenced by increased soil NH 4 + -N concentrations and decreased soil NO 2 ? -N and NO 3 ? -N concentrations. Codenitrification was observed to contribute to total fluxes of both N 2O (≥ 33%) and N 2 (≥ 3%) in urine-amended grassland soils. Cycloheximide inhibition decreased NH 4 + – 15N enrichment and reduced N 2O fluxes while reducing the contribution of codenitrification to total N 2O fluxes by ≥ 66 and ≥ 42%, respectively. Thus, given archaea do not respond to significant urea deposition, it is proposed that fungi, not bacteria, dominated total N 2O fluxes, and the codenitrification N 2O fluxes, from a simulated urine amended pasture soil. 相似文献
9.
Agroecosystems rely on inputs of nitrogen (N) to sustain productivity. But added N can leak into adjacent environments, affecting the health of other ecosystems and their inhabitants. Worries about global warming have cast further attention on the N cycle in farmlands because farms are a main source of N 2O, and because carbon sequestration, proposed to help reduce CO 2 loads, requires a build-up of N. Our objective was to estimate, as an illustrative example, the net N balance of Canadian agroecosystems in 1996 and then infer some hypotheses about the routes of N loss, their magnitude, and ways of reducing them. We defined agroecosystems as all agricultural lands in Canada including soil to 1 m depth and all biota, except humans. Only net flows of N across those boundaries were counted in our balance – all others represent internal cycling. Based on our estimates, about 2.35 Tg N entered Canadian agroecosystems from biological fixation, fertilizers, and atmospheric deposition (excluding re-deposited NH 3). In the same year, about 1.03 Tg N were exported in crop products and 0.19 Tg were exported in animals and animal products. Consequently, N inputs exceed exports in products by about 1.13 Tg, a surplus that is either accumulating in agroecosystems or lost to the environment. Because potential soil organic matter gains can account for only a small part of the surplus N, most is probably lost to air or groundwater. Our finding, that N losses amount to almost half of N added, concurs with field experiments that show crop recovery of added N in a given year is often not more than 60%. Better management may reduce the fraction lost somewhat but, because N in ecosystems eventually cycles back to N 2, substantive gains in efficiency may not come easily. As well as trying to reduce losses, research might also focus on steering losses directly to N 2, away from more harmful intermediates. If some of the `missing N' can be assimilated into organic matter, agricultural soils in Canada may need little added N to achieve C sequestration targets. 相似文献
10.
When appraising the impact of food and fiber production systems on the composition of the Earth's atmosphere and the ‘greenhouse’
effect, the entire suite of biogenic greenhouse gases – carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) – needs to be considered. Storage of atmospheric CO 2 into stable organic carbon pools in the soil can sequester CO 2 while common crop production practices can produce CO 2, generate N 2O, and decrease the soil sink for atmospheric CH 4. The overall balance between the net exchange of these gases constitutes the net global warming potential (GWP) of a crop
production system. Trace gas flux and soil organic carbon (SOC) storage data from long-term studies, a rainfed site in Michigan
that contrasts conventional tillage (CT) and no-till (NT) cropping, a rainfed site in northeastern Colorado that compares
cropping systems in NT, and an irrigated site in Colorado that compares tillage and crop rotations, are used to estimate net
GWP from crop production systems. Nitrous oxide emissions comprised 40–44% of the GWP from both rain-fed sites and contributed
16–33% of GWP in the irrigated system. The energy used for irrigation was the dominant GWP source in the irrigated system.
Whether a system is a sink or source of CO 2, i.e. net GWP, was controlled by the rate of SOC storage in all sites. SOC accumulation in the surface 7.5 cm of both rainfed
continuous cropping systems was approximately 1100 kg CO 2 equivalents ha −1 y −1. Carbon accrual rates were about three times higher in the irrigated system. The rainfed systems had been in NT for >10 years
while the irrigated system had been converted to NT 3 years before the start of this study. It remains to be seen if the C
accrual rates decline with time in the irrigated system or if N 2O emission rates decline or increase with time after conversion to NT. 相似文献
11.
Soil N 2O emissions were measured during four seasons from two highly productive grass-clover dairy pastures to assess the influences of soil moisture, temperature, availability of N (NH
4
+
and NO
3
–
) and soluble C on N 2O emissions, and to use the emission data to validate and refine a simulation model (DNDC). The soils at these pasture sites (Karapoti fine sandy loam, and Tokomaru silt loam) differed in texture and drainage characteristics. Emission peaks for N 2O coincided with rainfall events and high soil moisture content. Large inherent variations in N 2O fluxes were observed throughout the year in both the ungrazed (control) and grazed pastures. Fluxes averaged 4.3 and 5.0 g N 2O/ha/day for the two ungrazed sites. The N 2O fluxes from the grazed sites were much higher than for the ungrazed sites, averaging 26.4 g N 2O/ha/day for the fine sandy loam soil, and 32.0 g N 2O/ha/day for the silt loam soil. Our results showed that excretal and fertiliser-N input, and water-filled pore space (WFPS) were the variables that most strongly regulated N 2O fluxes. The DNDC model was modified to include the effects of day length on pasture growth, and of excretal-N inputs from grazing animals; the value of the WFPS threshold was also modified. The modified model NZ-DNDC simulated effectively most of the WFPS and N 2O emission pulses and trends from both the ungrazed and grazed pastures. The modified model fairly reproduced the real variability in underlying processes regulating N 2O emissions and could be suitable for simulating N 2O emissions from a range of New Zealand grazed pastures. The NZ-DNDC estimates of total yearly emissions of N 2O from the grazed and ungrazed sites of both farms were within the uncertainty range of the measured emissions. The measured emissions changed with changes in soil moisture resulting from rainfall and were about 20% higher in the poorly drained silt loam soil than in the well-drained sandy loam soil. The model accounts for these climatic variations in rainfall, and was also able to pick up differences in emissions resulting from differences in soil texture. 相似文献
12.
The number of published N 2O and NO emissions measurements is increasing steadily, providing additional information about driving factors of these emissions and allowing an improvement of statistical N-emission models. We summarized information from 1008 N 2O and 189 NO emission measurements for agricultural fields, and 207 N 2O and 210 NO measurements for soils under natural vegetation. The factors that significantly influence agricultural N 2O emissions were N application rate, crop type, fertilizer type, soil organic C content, soil pH and texture, and those for NO emissions include N application rate, soil N content and climate. Compared to an earlier analysis the 20% increase in the number of N 2O measurements for agriculture did not yield more insight or reduced uncertainty, because the representation of environmental and management conditions in agro-ecosystems did not improve, while for NO emissions the additional measurements in agricultural systems did yield a considerable improvement. N 2O emissions from soils under natural vegetation are significantly influenced by vegetation type, soil organic C content, soil pH, bulk density and drainage, while vegetation type and soil C content are major factors for NO emissions. Statistical models of these factors were used to calculate global annual emissions from fertilized cropland (3.3 Tg N 2O-N and 1.4 Tg NO-N) and grassland (0.8 Tg N 2O-N and 0.4 Tg NO-N). Global emissions were not calculated for soils under natural vegetation due to lack of data for many vegetation types. 相似文献
13.
Direct nitrous oxide emissions from a light-textured arable soil typical of North-Western Russia and subject to different
management systems were measured during three growing seasons (May–September) in 2003–2005. Cumulative fluxes varied between
0.26 ± 0.06 and 2.98 ± 1.56 kg N 2O–N ha −1, with the lowest flux produced where no N was added as mineral fertilizers/manures or where green manure/low inputs of mineral
fertilizer were used as a source of N. Highest cumulative fluxes were measured from the plots where high inputs of farmyard
manure were used. Of the crops studied, potatoes produced the highest N 2O fluxes; this was attributed to the use of furrows, in which the soil tended to be more compact with higher water-filled
pore space, making the soil more prone to denitrification than that in fields without furrows. The available N content of
the soil at the start of each growing season was quite low and cumulative N 2O fluxes were significantly affected by N-fertilizer application within one growing season. However, for different growing
seasons with highly changeable rainfall patterns and with different soil management for different crops, the quite high yearly
correlation between N application and N 2O fluxes was much reduced. 相似文献
14.
N 2O and NO fluxes from grassland soil after the application of cattle and swine excreta were measured by a closed chamber method
in the autumn and winter of 1994 to 1995. Fresh excrement and urine were spread on the grassland experimental plots and these
gas fluxes were measured one or two times a week. In the autumn experiment, N 2O and NO fluxes began to increase several days after the application, the NO flux reaching a maximum after 16 days. In the
winter experiment, N 2O and NO fluxes began to increase 45 days after the application and reached a maximum after 80 days. Nitrous oxide flux was
influenced by soil water content, high water content leading to high N 2O flux. The ratio of NO-N/N 2O-N in the flux was in the range of 1.1 to 13.7, and negatively correlated to the soil water content. In the winter experiment,
the total emission rate of NO was 0.48% and 0.45% of total nitrogen in the applied cattle and swine excreta, respectively.
The total emission rate of N 2O was 0.085% and 0.098% in the applied cattle and swine excreta, respectively.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
We reviewed the factors and processes relevant to C (Carbon) stocks and dynamics in the soils of Hindu Kush-Himalayan region (HKH) in general, and Nepal in particular. Included in this paper are reviews of land use change, soil types, erosion, soil fertility status, land management and other pertinent information in relation to the SOC (Soil Organic Carbon) stock, dynamics and sequestration. Watershed degradation in the HKH region appears to be a serious problem affecting the SOC pool, which may be primarily attributed to deforestation, land use changes, forest degradation, soil erosion and fertility decline. Soils under degraded forest and grazing land and red soils were reported to have less than 1% SOC; however, well managed forests have considerably higher organic matter (SOC = 4%) levels than those cleared for cultivation. Our estimates show that both the soil and SOC losses are site specific, being as high as 256 kg C ha –1 y –1. Estimated net CO 2 losses from the erosion displaced SOC varied between <1 and 42 kg C ha –1 y –1 depending on initial SOC content and soil erosion rates in the specific sites. The land cover changes in the past 18 years in the two Nepalese watersheds, Mardi and Fewa, may have resulted in net loss of SOC stock (29% losses for Mardi and 7% losses for Fewa) compared to land cover in the base year (1978). The processes contributing to C pool, fluxes and sequestration are inadequately studied, and particularly in the HKH region, there is a lack of data on several essential aspects needed for estimating soil C fluxes and C sequestration potential. Systematic soil survey and long term experiments are needed on dominant soil types and land use systems of the HKH region for developing the database on soil fertility and SOC relationships to site specific management practices. Future research should focus upon generating data on spatial and temporal variation, depth distribution, quantification of various pools, and transport/translocation of SOC, as well as the establishment of soil/SOC databases, in relation to specific land use and management practices. 相似文献
16.
We measured fluxes of three greenhouse gases (N 2O, CO 2O and CH 4) from soils of six different land-use types at 27 temporary field sites in Jambi Province, Sumatra, Indonesia. Study sites included natural and logged-over forests; rubber plantation; oil palm plantation; cinnamon plantation; and grassland field. The ranges of N 2O, CO 2 and CH 4 fluxes were 0.13–55.8 gN m-2h-1; 1.38–5.16 g C m-2d-1; –1.27–1.18 mg C m-2d-1, respectively. The averages of N 2O, CO 2 and CH 4 fluxes at 27 sites were 9.4 gN m-2h-1,3.65 g C m-2d-1, –0.45 mg C m-2d-1, respectively. The values of CO 2 and CH 4 fluxes were comparable with those in the reports regarding other humid tropical forests, while the N 2O flux was relatively lower than those of previous reports. The N 2O fluxes in each soil type were correlated with the nitrification rates of soils of 0–5 cm depth. In Andisols, the ratio of the N 2O emission rate to the nitrification rate was possibly smaller than that of the other soil types. There was no clear relationship between N 2O flux and the soil water condition, such as water-filled pore space. Seventeen percent of CH 4 fluxes were positive; according to these positive fluxes, we did not find a good correlation between CH 4 uptake rate and soil properties. Although we performed a chronosequence analysis to produce some hypotheses about the effect of land-use change by a limited amount of sampling at one point in time, further tests are required for the future. 相似文献
17.
Emissions of nitrous oxide (N 2O) from N-fertilized silage grassland in the UK were modelled with a hybrid part-empirical part-mechanistic model, B-LINE 2. N 2O fluxes were predicted from combinations of three soil variables: soil water-filled pore space (WFPS), soil temperature (T) and soil mineral N content (N min). Pooled field “training” data from several sites and seasons were used to parameterise the model. N 2O fluxes were assigned one of three values: the geometric means of the ranges 1–10, 10–100 and 100–1,000 g N 2O-N ha ?1 day ?1, respectively, depending on threshold lines (a) relating flux and N min and (b) relating flux, WFPS and T. The model was applied to give daily and seasonal total fluxes, and the overall relationships with measured emissions from ammonium nitrate treatments were analysed separately for those site-seasons not used as a source of training data, for the training data site-seasons, and for all site-seasons together. Results for both training and non-training site-seasons showed, with some exceptions, reasonable agreement with experimental measurements in the timings of main emission peaks, and also in the magnitude of daily flux rate variations over time. Generally, modelled seasonal N 2O emissions were somewhat higher than measured values, possibly because at very high WFPS values the actual N 2O flux was lower than predicted as a result of greater reduction of nitrate to N 2, rather than release as N 2O. However, one site was an outlier, with predicted emissions much lower than those observed. Overall, the modelling results compared well with those obtained elsewhere with other models. 相似文献
18.
Carbon (C) sequestration and soil emissions of nitrous oxide (N 2O) affect the carbon dioxide (CO 2) advantage of energy crops. A long-term study has been performed to evaluate the environmental effects of energy crop cultivation
on the loamy sand soil of the drier northeast region of Germany. The experimental field, established in 1994, consisted of
columns (0.25 ha each) cultivated with short rotation coppice (SRC: Salix and Populus) and columns cultivated with annual crops. The columns were subdivided into four blocks, with each receiving different fertilization
treatments. The soil C content was measured annually from 1994 until 1997, and then in 2006. Soil N 2O levels were measured several times per week from 1999 to 2007. Water-filled pore space (WFPS) and soil nitrate measurements
have been performed weekly since 2003. Increased C stocks were found in SRC columns, and C loss was observed in blocks with
annual crops. The soil from fertilized blocks had higher levels of C than the soil from non-fertilized blocks. SRC cropping
systems on dry, loamy sand soils are advantageous relative to annual cropping systems because of higher C sequestration, lower
fertilized-induced N 2O emissions, and reduced background N 2O emissions in these soils. SRC cropping systems on dry, loamy sand soils have a CO 2 advantage (approximately 4 Mg CO 2 ha −1 year −1) relative to annual cropping systems. 相似文献
19.
Fluxes of CH 4 and N 2O were measured regularly in an agricultural field treated with 280 g m −2 of sewage sludge. In a nearby beech forest N 2O and CH 4 fluxes were measured in a well-drained (dry) area and in a wet area adjacent to a drainage canal. We observed brief increases
of both CH 4 and N 2O emissions immediately following soil applications of digested sewage sludge. Cumulated values for CH 4 emissions over the course of 328 days after sludge applications indicated a small net source in sludge treated plots (7.6
mg C m −2) whereas sludge-free soil constituted a small sink (-0.9 mg C m −2). The CH 4 emission amounted 0.01% of the sludge-C. Extrapolated to current rates of sludge applications in Danish agriculture this
amounts to 0.1% of the total agricultural derived CH 4. Sludge applications did not affect cumulated fluxes of N 2O showing 312 mg N 2O–N m −2 and 304 mg N m −2 with and without sludge, respectively. Four months after the sludge applications a significant effect on CO 2 and NO emissions was still obvious in the field, the latter perhaps due to elevated nitrification. Nitrous oxide emission
in the beech forest was about six times smaller (45 mg N m −2) than in the field and independent of drainage status. Methane oxidation was observed all-year round in the forest cumulating
to -225 mg C m −2 and -84 mg C m −2 in dry and wet areas. In a model experiment with incubated soil cores, nitrogen amendment (NH 4Cl) and perturbation significantly reduced CH 4 oxidation in the forest soil, presumably as a result of increased nitrification activity. Sludge also induced net CH 4 production in the otherwise strong CH 4 oxidising forest soil. This emphasises the potential for CH 4 emissions from sewage sludge applications onto land. The study shows, however, that emissions of N 2O and CH 4 induced by sewage sludge in the field is of minor importance and that factors such as land use (agriculture versus forest)
is a much stronger controller on the source/sink strengths of CH 4 and N 2O.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
The clearing of tropical rain forest in the Amazon basin has created large areas of cattle pasture that are now declining in productivity. Practices adopted by ranchers to restore productivity to degraded pastures have the potential to alter soil N availability and gaseous N losses from soils. We examined how soil inorganic N pools, net N mineralization and net nitrification rates, nitrification potential and NO and N 2O emissions from soils of a degraded pasture responded to the following restoration treatments: (1) soil tillage followed by replanting of grass and fertilization, (2) no-till application of non-selective herbicide, planting of rice, harvest followed by no-till replanting of grass and fertilization, and (3) the same no-till sequence with soybeans instead of rice. Tillage increased soil NH 4+ and NO 3? pools but NH 4+ and NO 3? pools remained relatively constant in the control and no-till treatments. Cumulative rates of net N mineralization and net nitrification during the first 6 months after treatment varied widely but were hightest in the tilled treatment. Emissions of NO and N 2O fluxes increased with tillage and with N fertilization. There were no clear relationships among rates of N fertilizer application, net N mineralization, net nitrification, NO, N 2O and total N oxide emissions. Our results indicate that pasture restoration sequences involving tilling and fertilizing will increase emissions of N oxides, but the magnitude of the increase is likely to differ based on timing of fertilizer application relative to the presence of plants and the magnitude of plant N demand. Emissions of N oxides appear to be decreased by the use of restoration sequences that minimize reductions in pasture grass cover. 相似文献
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