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1.
Intensively managed grasslands on organic soils are a major source of nitrous oxide (N 2O) emissions. The Intergovernmental Panel on Climate Change (IPCC) therefore has set the default emission factor at 8 kg N–N 2O ha −1 year −1 for cultivation and management of organic soils. Also, the Dutch national reporting methodology for greenhouse gases uses
a relatively high calculated emission factor of 4.7 kg N–N 2O ha −1 year −1. In addition to cultivation, the IPCC methodology and the Dutch national methodology account for N 2O emissions from N inputs through fertilizer applications and animal urine and faeces deposition to estimate annual N 2O emissions from cultivated and managed organic soils. However, neither approach accounts for other soil parameters that might
control N 2O emissions such as groundwater level. In this paper we report on the relations between N 2O emissions, N inputs and groundwater level dynamics for a fertilized and grazed grassland on drained peat soil. We measured
N 2O emissions from fields with different target groundwater levels of 40 cm (‘wet’) and 55 cm (‘dry’) below soil surface in
the years 1992, 1993, 2002, 2006 and 2007. Average emissions equalled 29.5 kg N 2O–N ha −1 year −1 and 11.6 kg N–N 2O ha −1 year −1 for the dry and wet conditions, respectively. Especially under dry conditions, measured N 2O emissions exceeded current official estimates using the IPCC methodology and the Dutch national reporting methodology. The
N 2O–N emissions equalled 8.2 and 3.2% of the total N inputs through fertilizers, manure and cattle droppings for the dry and
wet field, respectively and were strongly related to average groundwater level ( R
2 = 0.74). We argue that this relation should be explored for other sites and could be used to derive accurate emission data
for fertilized and grazed grasslands on organic soils. 相似文献
2.
Agriculture is a main contributor of diffuse emissions of N and P to the environment. For N the main loss pathways are NH 3-volatilization, leaching to ground and surface water and N 2(O) emissions. Currently, imposing restraints on farm inputs are used as policy tool to decrease N and P leaching to ground
water and to surface water, and the same measure is suggested to combat emissions of N 2O. The response, however, to these measures largely depends on the soil type. In this study nutrient flows of three dairy
farms in The Netherlands with comparable intensity on sand, peat and clay soils were monitored for at least 2 years. The first
aim was to provide quantitative data on current nutrient loss pathways. The second aim was to explore the responses in partitioning
of the nutrient loss pathways when farm inputs were altered. Mean denitrification rates ranged from 103 kg N ha −1 year −1 for the sandy soil to 170 kg N ha −1 year −1 for the peat soil and leaching to surface water was about 73 kg N ha −1 year −1 for the sandy soil, 15 kg N ha −1 year −1 for the clay soil and 38 kg N ha −1 year −1 for the peat soil. For P, leaching to surface water ranged from 2 kg P ha −1 year −1 for the sandy site to 5 kg P ha −1 year −1 for the peat site. The sandy soil was most responsive to changes in N surpluses on leaching to surface water, followed by
the peat soil and least responsive was the clay soil. For P, a similar sequence was found. This article demonstrates that
similar reductions of N and P inputs result in different responses in N and P loss pathways for different soil types. These
differences should be taken into account when evaluating measures to improve environmental performance of (dairy) farms. 相似文献
3.
To better understand the effects of increased N input and dry periods on soil nitrous oxide (N 2O) emission, we examined a unique data-set of weather, soil microclimate, N input, and N 2O emissions (using the eddy covariance method), measured at a fertilized grassland over the period 2003–2008. We found that
the N 2O emission (11.5 kg N ha −1 year −1), the ratio of N 2O emission to N input (3.4), and the duration of elevated N 2O flux (57 days) in 2003 were about two times greater than those of the following years. 2003 had the highest annual N input
(343 kg N ha −1 year −1) which exceeded the agronomical requirements for Irish grasslands (up to 306 kg ha −1 year −1). In the summer of 2003, the site had a significantly higher soil temperature, lower WFPS and lowest rainfall of all years.
Large N 2O emission events followed rainfall after a long dry period in the summer of 2003, attributed to dominant nitrification processes.
Furthermore, in the non summer periods, when temperature was lower and WFPS was higher and when there were prior N applications,
lower N 2O emissions occurred and were attributed to dominant denitrification processes. Throughout the study period, the N input and
soil dryness related factors (duration of WFPS under 50%, summer average WFPS, and low rainfall) showed exponential relationships
with N 2O emission and the ratio of N 2O emission to N input. Based on these findings, we infer that the observed anomalously high N 2O emission in 2003 may have been caused by the combined effects of excess N input above the plant uptake rate, elevated soil
temperature, and N 2O flux bursts that followed the rewetting of dry soil after an unusually long dry summer period. These results suggest that
high N input above plant uptake rate and extended dry periods may cause abnormal increases in N 2O emissions. 相似文献
4.
Recent interests in improving agricultural production while minimizing environmental footprints emphasized the need for research on management strategies that reduce nitrous oxide (N2O) emissions and increase nitrogen-use efficiency (NUE) of cropping systems. This study aimed to evaluate N2O emissions, annualized crop grain yield, emission factor, and yield-scaled- and NUE-scaled N2O emissions under continuous spring wheat (Triticum aestivum L.) (CW) and spring wheat–pea (Pisum sativum L.) (WP) rotations with four N fertilization rates (0, 50, 100, and 150 kg N ha?1). The N2O fluxes peaked immediately after N fertilization, intense precipitation, and snowmelt, which accounted for 75–85% of the total annual flux. Cumulative N2O flux usually increased with increased N fertilization rate in all crop rotations and years. Annualized crop yield and NUE were greater in WP than CW for 0 kg N ha?1 in all years, but the trend reversed with 100 kg N ha?1 in 2013 and 2015. Crop yield maximized at 100 kg N ha?1, but NUE declined linearly with increased N fertilization rate in all crop rotations and years. As N fertilization rate increased, N fertilizer-scaled N2O flux decreased, but NUE-scaled N2O flux increased non-linearly in all years, regardless of crop rotations. The yield-scaled N2O flux decreased from 0 to 50 kg N ha?1 and then increased with increased N fertilization rate. Because of non-significant difference of N2O fluxes between 50 and 100 kg N ha?1, but increased crop yield, N2O emissions can be minimized while dryland crop yields and NUE can be optimized with 100 kg N ha?1, regardless of crop rotations. 相似文献
5.
Midseason aeration (MSA) of rice paddy fields functions to mitigate CH 4 emission by a large margin, while simultaneously promoting N 2O emission. Alternation of timing and duration of MSA would affect CH 4 and N 2O emissions from intermittently irrigated rice paddies. A pot trial and a field experiment were conducted to study the effect
of timing and duration of MSA on CH 4 and N 2O emissions from irrigated lowland rice paddy soils in China. Four different water regimes, i.e., early aeration, normal aeration
(the same as the local practice in timing and duration of aeration), delayed aeration, and prolonged aeration, were adopted
separately and compared with respect to global warming potential (GWP) of CH 4 and N 2O emissions and rice yields as well. Total emission of CH 4 from the rice fields ranged from 28.6 to 64.1 kg CH 4 ha −1, while that of N 2O did from 1.71 to 6.30 kg N 2O–N ha −1 during the study periods. Compared with the local practice, early aeration reduced CH 4 emission by 13.3–16.2% and increased N 2O emission by 19.1–68.8%, while delayed aeration reduced N 2O emission by 6.8–26.0% and increased CH 4 emission by 22.1–47.3%. The lowest GWP of CH 4 and N 2O emissions occurred in prolonged aeration treatment, however, rice grain yield was reduced by 15.3% in this condition when
compared with normal practice. It was found in the experiments that midseason aeration starting around D 30 after rice transplanting,
just like the local practice, would optimize rice yields while simultaneously limiting GWPs of CH 4 and N 2O emissions from irrigated lowland rice fields in China. 相似文献
6.
Lack of local data limits estimation of nitrous oxide (N 2O) emissions from different land uses of Uruguay. As a first step towards obtaining local information, we measured from August
2003 to September 2004 N 2O fluxes from a rotation-by-tillage experiment established in 1993 and from a nearby natural pasture (NP). Nitrous oxide emission
rates were measured on an event-driven basis by using the closed chamber technique with six replicates per treatment. Fluxes
varied considerably with time and the higher rates (more than 30 g N ha −1 day −1) were generally associated with periods of high soil water content, high temperature, and/or decreasing soil nitrate. We
could not identify, however, any statistically significant correlation between flux and these variables. Throughout the evaluation
period, fluxes from crops or cultivated pastures tended to be higher than those from NP, but the effects of tillage (no-till
and conventional tillage) or rotation (continuous tillage and rotation with pasture) were not consistent. The application
of 112 kg N ha −1 to barley did not increase N 2O fluxes probably due to a high fertilizer use efficiency caused by the recommended three-split application and by the lack
of rain during this period. The annual cumulative flows of different treatments compared well with those estimated using IPCC
methodology, but the high spatial and temporal variability observed in this one-year study indicate that further research
is needed to obtain reliable data on N 2O fluxes from agricultural soils of Uruguay. 相似文献
7.
Several technologies have been developed to improve the recovery efficiency of N (RE N) but their impacts on greenhouse gas (GHG) emission, N loss and economic implication are rarely analysed. A decision support
system (DSS) has been developed to quantify inputs, outputs and balance of N in soil; GHG emission and RE N with the prominent N management technologies in rice. This DSS, named InfoNitro (Information on Nitrogen Management Technologies
in Rice), integrated analytical and expert knowledge with databases on bio-physical, agronomic and socio-economical features
to establish input–output relationships related to N management in rice. Sixteen technologies, which differed in terms of
water regime, method of N application, forms of N and tools of fertilizer recommendation were analysed for their RE N, N losses, GHG emission and economic return in Haryana, a rice growing region in India. In the current farmers’ practice,
RE N was 32.7%, which increased up to 40.8% with various technologies except in mid-season drainage and alternate flooding technologies
where it decreased up to 29.3%. Loss of N through leaching, volatilization and denitrification in the farmers’ practice (67.5 kg N ha −1) decreased up to 40.5 kg N ha −1 except in mid-season drainage and alternate flooding technologies where it increased. The technologies also reduced global
warming potential (GWP) by 1 to 9%. However, the technologies except no tillage, mid-season drying and alternate flooding
reduced the net income of the farmers. When the environmental cost (cost of N loss and GWP) was included net income with various
technologies was either at par or more than the farmers’ practice. The marginal abatement cost of N loss was Rs. 8 to 134 kg −1 N and for GWP was Rs. 766 to 4854 Mg −1 CO 2 eq. Resource conserving technology was the most cost effective strategy to reduce N loss and GHG emission whereas integrated
N management cost high for mitigating GHG emission. 相似文献
8.
Drainage and cultivation of peat soils stimulates soil organic matter (SOM) mineralization, which substantially increases
CO 2 emissions from soils. Large uncertainties are associated with this CO 2 flux, and little data are available, especially in Norway. The objective of the present research was to estimate C losses
from cultivated peatlands in West Norway by three independent methods: (1) long-term monitoring of subsidence rates, (2) changes
in ash contents, and (3) soil CO 2 flux measurements. Subsidence of cultivated peat soils averaged about 2.5 cm year −1. We estimated that peat loss and compaction were respectively responsible for 38% and 62% of the total subsidence during
a 25-year period after drainage. Based on this estimate the corresponding C loss equals 0.80 kg C m −2 year −1. The observed increase in mineral concentration of the topsoil of cultivated peat is proportional to their C loss, providing
no mineral particles other than lime and fertilizers are added to the soil. Using this novel approach across 11 sites, we
estimated a mean C loss of 0.86 kg C m −2 year −1. Soil CO 2 flux measurements, corrected for autotrophic respiration, yielded a C loss estimate from cultivated peat soils of 0.60 kg C m −2 year −1. The three methods yielded fairly similar estimates of C losses from Norwegian cultivated peatlands. Cultivated peatlands
in Norway cover an estimated 63,000 ha. Total annual C losses from peat degradation were estimated to range between 1.8 and
2 million tons CO 2 year −1, which equals about 3–4% of total anthropogenic greenhouse gas emissions from Norway. 相似文献
9.
In the following study N 2O emissions from 3 different grasslands and from 3 different arable lands, representing major agriculture areas with different
soil textures and normal agricultural practices in Belgium, have been monitored for 1 to 2 years. One undisturbed soil under
deciduous forest was also included in the study. Nitrous oxide emission was measured directly in the field from vented closed
chambers through photo-acoustic infrared detection. Annual N 2O emissions from the arable lands ranged from 0.3 to 1.5 kg N ha −1 y −1 and represent 0.3 to 1.0% of the fertilizer N applied. Annual N 2O emissions from the intensively managed grasslands and an arable land sown with grass were significantly larger than those
from the cropped arable lands. Emissions ranged from 14 to 32 kg N ha −1 y −1, representing fertilizer N losses between 3 and 11%. At the forest soil a net N 2O uptake of 1.3 kg N 2O-N ha −1 was recorded over a 2-year period. It seems that the N 2O-N loss per unit of fertilizer N applied is larger for intensively managed and heavily fertilized (up to 500 kg N ha −1) grasslands than for arable lands and is substantially larger than the 1.25% figure used for the global emission inventory.
Comparison of the annual emission fluxes from the different soils also indicated that land use rather than soil properties
influenced the N 2O emission. Our results also show once again the importance of year-round measurements for a correct estimate of N 2O losses from agricultural soils: 7 to 76% of the total annual N 2O was emitted during the winter period (October–February). Disregarding the emission during the off-season period can lead
to serious underestimation of the actual annual N 2O flux.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
N 2O emissions from a fertilized humid grassland near Cork, Ireland were continuously measured during 2003 using an eddy covariance
system. For most of the year emissions were close to zero and 60% of the emissions occurred in eight major events of 2–20 days’
duration. Two hundred and seven kg ha −1 of synthetic N and 130 kg ha −1 organic N were applied over the year and the total measured annual N 2O emission was 11.6 kg N ha −1. The flux data were used to test the prediction of N 2O emissions by the DNDC (DeNitrification – DeComposition) model. The model predicted total emissions of 15.4 kg N ha −1, 32 % more than the observed emissions. On this basis the model was further used to simulate (a) background (non-anthropogenic)
N 2O emissions and (b) the effect on N 2O emissions of future climate perturbations based on the Hadley Center model output of the IS92a scenario for Ireland. DNDC
predicts 1.7 kg N ha −1 year −1 of background N 2O emissions, accounting for 15% of the observed emissions. Climate shifts will increase total annual modeled N 2O emissions from 15.4 kg N ha −1 to 22.4 kg N ha −1 if current levels of N applications are maintained, or to 21.2 kg N ha −1 if synthetic N applications are reduced to 170 kg N ha −1 to comply with recent EU water quality legislation. Thus the projected increase in N 2O emissions due to climate change is far larger than the decrease expected from reduced fertilizer applications. 相似文献
11.
Estimation of nitrous oxide (N 2O) emissions from arable soils, in relation to crop fertilization, is essential to devise strategies to mitigate the impact
of agriculture on global warming. This paper presents the development and test of a N 2O model resulting from the linkage of a dynamic soil-crop simulation model (CERES) with two sub-models of N 2O production and reduction in soils. These sub-models (NOE and NGAS) account for both the nitrification and denitrification
pathways. The resulting models (CERES–NOE and CERES–NGAS) were tested against experimental data collected on three contrasting
wheat-cropped soils representative of the Beauce agricultural region in France. Although the input variables for the N 2O modules were correctly simulated, CERES–NGAS was over-responsive to soil water content in a Haplic Calcisol, and strongly
over-estimated the N 2O fluxes as a result. On the other hand, CERES–NOE predicted correct mean N 2O emission levels for all sites, but failed to simulate the peak fluxes observed in the weeks following fertilizer application
in the most N 2O-productive soil. Both models achieved root mean squared errors in the 23–26 g N–N 2O ha −1 day −1 range, significantly higher than the average experimental error on the measurements. On the other hand, their mean deviations
were acceptable, being lower than 2.2 g N–N 2O ha −1 day −1, compared with a mean observed flux of 7.9 g N–N 2O ha −1 day −1. Overall, the response of CERES–NOE to soil type was more accurate, but this came at the cost of costly, site-specific characterization
on the soils’ biological properties. The development of pedo-transfer functions to infer these parameters from basic soil
characteristics appears as a pre-requisite for the use of CERES–NOE on a wider scale. 相似文献
12.
Environmental benefits associated with reduced rates of nitrogen (N) application, while maintaining economically optimum yields
have economic and social benefits. Although N is an indispensable plant nutrient, residual soil N could leach out to contaminate
groundwater and surface water resources, particularly in sandy soils. A 2-year field study was conducted in an established
bermudagrass ( Cynodon dactylon) pasture in the Lower Suwannee Watershed, Florida, to evaluate N application rates on forage yield, forage quality, and nitrate
(NO 3-N) leaching in rapidly permeable upland sandy soils. Four N application rates (30, 50, 70, and 90 kg N ha −1 harvest −1) corresponding to 0.33, 0.55, 0.77 and IX, respectively, of recommended N rate (90 kg N ha −1 harvest −1) for bermudagrass hay production in Florida were evaluated vis-à-vis an unfertilized (0 N) control. Suction cups were installed
near the center of each plot at two depths (30 and 100 cm) to monitor NO 3-N leaching. The grass was harvested at 28 days intervals to determine dry matter yield, N uptake, and herbage nutritive value.
Nitrogen application at the recommended rate produced the greatest total dry matter yield (~18.4 Mg ha −1 year −1), but a modeled economically optimum N rate of ~57 kg N ha −1 harvest −1 (~60% of the recommended N rate) projected an average dry matter yield of ~17.3 Mg ha −1 year −1, which represents >90% of the observed maximum yield. Nitrogen application increased nutritive quality of the grass, but
increases in N application rate above 30 kg N ha −1 did not result in significant increases in in vitro digestible organic matter concentration, and tissue crude protein was
not significant above 50 kg N ha −1. Across the sampling period, treatments with N rates ≤50 kg N ha −1 harvest −1 had leachate NO 3-N concentration below the maximum contaminant limit of <10 mg l −1. Conversely, applying N at rates ≥70 kg N ha −1 harvest −1 resulted in leachate N concentration that exceeded the maximum contaminant limit, and suggest high risk of impacting groundwater
quality, if such rates are applied to soils with coarse (sand) textures. The study demonstrates that recommendation of a single
N application rate may not be appropriate under all agro-climatic conditions and, thus, a site-specific evaluation of best
N management strategy is critical. 相似文献
13.
The denitrification process and the associated nitrous oxide (N 2O) production in soils have been poorly documented, especially in terms of soil profiles; most work on denitrification has
concentrated on the upper layer (first 20 cm). The objectives of this study were to examine the origin of N 2O emission and the effects of in situ controlling factors on soil denitrification and N 2O production, also allowing the (N 2O production)/(NO 3
−–N reduction) ratio to be determined through (1) the position on a slope reaching a river and (2) the depth (soil horizons:
10–30 and 90–110 cm). In 2009 and 2010, slurry batch experiments combined with molecular investigations of bacterial communities
were conducted in a corn field and an adjacent riparian buffer strip. Denitrification rates, ranging from 0.30 μg NO 3
−–N g −1 dry soil h −1 to 1.44 μg NO 3
−–N g −1 dry soil h −1, showed no significant variation along the slope and depth. N 2O production assessed simultaneously differed considerably over the depth and ranged from 0.4 ng N 2O–N g −1 dry soil h −1 in subsoils (the 90–110-cm layer) to 155.1 ng N 2O–N g −1 dry soil h −1 in the topsoils (the 10–30-cm layer). In the topsoils, N 2O–N production accounted for 8.5–48.0% of the total denitrified NO 3
−–N, but for less than 1% in the subsoils. Similarly, N 2O-consuming bacterial communities from the subsoils greatly differed from those of the topsoils, as revealed by their nosZ DGGE fingerprints. High N 2O-SPPR (nitrous oxide semi potential production rates) in comparison to NO 3-SPDR (nitrate semi potential reduction rates) for the topsoils indicated significant potential greenhouse N 2O gas production, whereas lower horizons could play a role in fully removing nitrate into inert atmospheric N 2. In terms of landscape management, these results call for caution in rehabilitating or constructing buffer zones for agricultural
nitrate removal. 相似文献
14.
Managed grasslands are occasionally ploughed up and reseeded in order to maintain or increase the sward productivity. It has
been reported that this renovation of grassland is associated with a flush of soil organic nitrogen (N) mineralization and
with a temporary increase in soil mineral N contents. Here, we report on the effects of method and time of grassland renovation
on herbage yield, nitrate (NO 3
−) leaching and nitrous oxide (N 2O) emission. Field experiments were carried out at three sites (two sandy soils and a clay soil) in the Netherlands for three
years. Renovation of grassland increased the percentage of Perennial ryegrass from 48–70% up to more than 90%. However, averaged
over three years, dry matter yields were higher for the reference (not reseeded) swards (on average 13.6 Mg ha −1 for the highest N application rate) than for the renovated grasslands (12.2–13.1 Mg ha −1 dry matter). Grassland renovation in April did not increase N leaching in comparison to the reference. However, renovation
in September increased the risk of leaching, because mineral N contents in the 0–90 cm were in November on average 46–77 kg N
ha −1 higher than in the reference. Contents of dissolved organic N (DON) in the soil were not affected by renovation. Renovation
increased N 2O emissions by a factor of 1.8–3.0 relative to the reference grassland. Emissions of N 2O were on average higher after renovation in April (8.2 kg N 2O-N ha −1) than in September (5.8 kg N 2O-N ha −1). Renovation without ploughing (i.e. only chemically destruction of the sward) resulted in a lower percentage of perennial
ryegrass (60–84%) than with ploughing (>90%). Moreover, N 2O emissions were higher after renovation without ploughing than with ploughing. Clearly, farmers need better recommendations
and tools for determining when grassland renovation has beneficial agronomic effects. Losses of N via leaching and N 2O emission after renovation can probably not be avoided, but renovation in spring in stead of autumn in combination with ploughing
and proper timing of fertilizer application can minimize N losses. 相似文献
15.
Even though nitrogen (N) is a key nutrient for successful cranberry production, N cycling in cranberry agroecosystems is not
completely understood. Prior research has focused mainly on timing and uptake of ammonium fertilizer, but the objective of
our study was to evaluate the potential for additional N contributions from hydrologic inputs (flooding, irrigation, groundwater,
and precipitation) and organic matter (OM). Plant biomass, soil, surface and groundwater samples were collected from five
cranberry beds (cranberry production fields) on four different farms, representing both upland and lowland systems. Estimated
average annual plant uptake (63.3 ± 22.5 kg N ha −1 year −1) exceeded total average annual fertilizer inputs (39.5 ± 11.6 kg N ha −1 year −1). Irrigation, precipitation, and floodwater N summed to an average 23 ± 0.7 kg N ha −1 year −1, which was about 60% of fertilizer N. Leaf and stem litterfall added 5.2 ± 1.2 and 24.1 ± 3.0 kg N ha −1 year −1 respectively. The estimated net N mineralization rate from the buried bag technique was 5 ± 0.2 kg N ha −1 year −1, which was nearly 15% of fertilizer N. Dissolved organic nitrogen represented a significant portion of the total N pool in
both surface water and soil samples. Mixed-ion exchange resin core incubations indicated that 80% of total inorganic N from
fertilizer, irrigation, precipitation, and mineralization was nitrate, and approximately 70% of recovered inorganic N from
groundwater was nitrate. There was a weak but significant negative relationship between extractable soil ammonium concentrations
and ericoid mycorrhizal colonization (ERM) rates ( r = −0.22, P < 0.045). Growers may benefit from balancing the N inputs from hydrologic sources and OM relative to fertilizer N in order
to maximize the benefits of ERM fungi in actively mediating N cycling in cranberry agroecosystems. 相似文献
16.
Agricultural soils are a major source of atmospheric N 2O. This study was conducted to determine the effect of different crop-specific field management and N fertilization rates
on N 2O emissions from a fine-loamy Dystric Eutrochrept. Fluxes of N 2O were measured for two years at least once a week on plots cropped with potatoes ( Solanum tuberosum) fertilized with 50 or 150 kg N ha −1 a −1, winterwheat ( Triticum aestivum) fertilized with 90 or 180 kg N ha −1 a −1, corn ( Zea mays) fertilized with 65 or 130 kg N ha −1 a −1, and on an unfertilized, set-aside soil planted with grass (mainly Lolium perenne and Festuca rubra). The mean N 2O emission rate from the differently managed plots was closely correlated to the mean soil nitrate content in the Ap horizon
for the cropping period (April to October, r
2 = 0.74), the winter period (November to March, r
2 = 0.93, one outlier excluded), and the whole year ( r
2 = 0.81). N 2O emissions outside the cropping period accounted for up to 58% of the annual emissions and were strongly affected by frost-thaw
cycles. There was only a slight relationship between the amount of fertilizer N applied and the annual N 2O emission ( r
2 = 0.20). The mean annual N 2O-N emission from the unfertilized set-aside soil was 0.29 kg ha −1. The annual N 2O-N emission from the fertilized crops for the low and the recommended rates of N fertilization were 1.34 and 2.41 kg ha −1 for corn, 2.70 and 3.64 kg ha −1 for wheat, and 5.74 and 6.93 kg ha −1 for potatoes. The high N 2O emissions from potato plots were due to (i) high N 2O losses from the interrow area during the cropping season and (ii) high soil nitrate contents after the potato harvest. The
reduction of N fertilization (fertilizer was applied in spring and early summer) resulted in decreased N 2O emissions during the cropping period. However, the emissions during the winter were not affected by the rate of N fertilization.
The results show that the crop-specific field management had a great influence on the annual N 2O emissions. It also affected the emissions per unit N fertilizer applied. The main reasons for this crop effect were crop-specific
differences in soil nitrate and soil moisture content.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
An in-depth understanding of nutrient management variability on the regional scale is urgently required due to rapid changes
in cropping patterns and farmers’ resource use in peri-urban areas of China. The soil surface nitrogen (N) balances of cereal,
orchard and vegetable systems were studied over a 2-year period on smallholder fields in a representative peri-urban area
of Beijing. Positive soil surface N balances were obtained across all three cropping systems. The mean annual N surplus of
the vegetable system was 1,575 kg N ha −1 year −1, or approximately 3 times the corresponding values in the cereal (531 kg N ha −1 year −1) and orchard systems (519 kg N ha −1 year −1). In the vegetable system, animal manure (1,443 kg N ha −1 year −1 on average) was the major source of N input (65 % of the total N input) and the factor with strongest impact on the N surplus.
In the cereal system, however, about 74 % of the total N input originated from mineral fertilizer application which was the
major contributor to the N surplus, while in the orchard system, the N surplus was strongly and positively correlated with
both mineral fertilizer and animal manure applications. Furthermore, within each cropping system, N fertilization, crop yields
and N balances showed large variations among different smallholder fields, especially in orchard and vegetable systems. This
study highlights that differences in farming practices within or among cropping systems should be taken into account when
calculating nutrient balances and designing strategies of integrated nutrient management on a regional scale. 相似文献
18.
The DNDC (DeNitrification and DeComposition) model was tested against experimental data on CH 4 and N 2O emissions from rice fields at different geographical locations in India. There was a good agreement between the simulated
and observed values of CH 4 and N 2O emissions. The difference between observed and simulated CH 4 emissions in all sites ranged from −11.6 to 62.5 kg C ha −1 season −1. Most discrepancies between simulated and observed seasonal fluxes were less than 20% of the field estimate of the seasonal
flux. The relative deviation between observed and simulated cumulative N 2O emissions ranged from −237.8 to 28.6%. However, some discrepancies existed between observed and simulated seasonal patterns
of CH 4 and N 2O emissions. The model simulated zero N 2O emissions from continuously flooded rice fields and poorly simulated CH 4 emissions from Allahabad site. For all other simulated cases, the model satisfactorily simulated the seasonal variations
in greenhouse gas emission from paddy fields with different land management. The model also simulated the C and N balances
in all the sites, including other gas fluxes, viz. CO 2, NO, NO 2, N 2 and NH 3 emissions. Sensitivity tests for CH 4 indicate that soil texture and pH significantly influenced the CH 4 emission. Changes in organic C content had a moderate influence on CH 4 emission on these sites. Introducing the mid-season drainage reduced CH 4 emissions significantly. Process-based biogeochemical modeling, as with DNDC, can help in identifying strategies for optimizing
resource use, increasing productivity, closing yield gaps and reducing adverse environmental impacts. 相似文献
19.
High profile nitrate-nitrogen (N) accumulation has caused a series of problems, including low N use efficiency and environmental
contamination in intensive agricultural systems. The key objective of this study was to evaluate summer maize ( Zea mays L.) yield and N uptake response to soil nitrate-N accumulation, and determine soil nitrate-N levels to meet N demand of high
yield maize production in the North China Plain (NCP). A total of 1,883 farmers’ fields were investigated and data from 458
no-N plots were analyzed in eight key maize production regions of the NCP from 2000 to 2005. High nitrate-N accumulation (≥172 kg N ha −1) was observed in the top (0–90 cm) and deep (90–180 cm) soil layer with farmers’ N practice during maize growing season.
Across all 458 no-N plots, maize grain yield and N uptake response to initial soil nitrate-N content could be simulated by
a linear plus plateau model, and calculated minimal pre-planting soil nitrate-N content for maximum grain yield and N uptake
was 180 and 186 kg N ha −1, respectively, under no-N application conditions. Economically optimum N rate (EONR) decreased linearly with increasing pre-planting
soil nitrate-N content ( r
2 = 0.894), and 1 kg soil nitrate-N ha −1 was equivalent to 1.23 kg fertilizer-N ha −1 for maize production. Residual soil nitrate-N content after maize harvest increased exponentially with increasing N fertilizer
rate ( P < 0.001), and average residual soil nitrate-N content at the EONR was 87 kg N ha −1 with a range from 66 to 118 kg N ha −1. We conclude that soil nitrate-N content in the top 90 cm of the soil profile should be maintained within the range of 87–180 kg N ha −1 for high yield maize production. The upper limit of these levels would be reduce if N fertilizer was applied during maize
growing season. 相似文献
20.
The yield increases often recorded in maize following grain legumes have been attributed to fixed-N and ‘other rotation’ effects,
but these effects have rarely been separated. Field trials were conducted between 2003 and 2005 to measure these effects on
maize following grain legumes in the northern Guinea savanna of Nigeria. Maize was grown on plots previously cultivated to
two genotypes each of soybean (TGx 1448-2E and SAMSOY-2) and cowpea (IT 96D-724 and SAMPEA-7), maize, and natural fallow.
The plots were split into four N fertilizer rates (0, 30, 60 and 90 kg N ha −1) in a split plot design. The total effect was calculated as the yield of maize following a legume minus the yield following
maize, both without added N and the rotation effect was calculated as the difference between rotations at the highest N fertilizer
rate. The legume genotypes fixed between 14 and 51 kg N ha −1 of their total N and had an estimated net N balance ranging from −29.8 to 9.5 kg N ha −1. Positive N balance was obtained only when the nitrogen harvest index was greater than the proportion of N derived from atmosphere.
The results also indicated that the magnitude of the fixed-N and other rotation effects varied widely and were influenced
by the contributions of the grain legumes to the soil N-balance. In general, fixed-N effects ranged from 124 to 279 kg ha −1 while rotation effects ranged between 193 and 513 kg ha −1. On average, maize following legumes had higher grain yield of 1.2 and 1.3-fold compared with maize after fallow or maize
after maize, respectively. 相似文献
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