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1.
Agricultural practices affect the production and emission of carbon dioxide (CO 2) from paddy soils. It is crucial to understand the effects of tillage and N fertilization on soil CO 2 flux and its influencing factors for a better comprehension of carbon dynamics in subtropical paddy ecosystems. A 2-yr field study was conducted to assess the effects of tillage (conventional tillage [CT] and no-tillage [NT]) and N fertilization (0 and 210 kg N ha ?1) on soil CO 2 fluxes during the 2008 and 2009 rice growing seasons in central China. Treatments were established following a split-plot design of a randomized complete block with tillage practices as the main plot and N fertilizer level as the split-plot treatment. The soil CO 2 fluxes were measured 24 times in 2008 and 17 times in 2009. N fertilization did not affect soil CO 2 emissions while tillage affected soil CO 2 emissions, where NT had similar soil CO 2 emissions to CT in 2008, but in 2009, NT significantly increased soil CO 2 emissions. Cumulative CO 2 emissions were 2079–2245 kg CO 2–C ha ?1 from NT treatments, and 2084–2141 kg CO 2–C ha ?1 from CT treatments in 2008, and were 1257–1401 kg CO 2–C ha ?1 from NT treatments, and 1003–1034 kg CO 2–C ha ?1 from CT treatments in 2009, respectively. Cumulative CO 2 emissions were significantly related to aboveground biomass and soil organic C. Before drainage of paddy fields, soil CO 2 fluxes were significantly related to soil temperature with correlation coefficients ( R) of 0.67–0.87 in 2008 and 0.69–0.85 in 2009; moreover, the Q 10 values ranged from 1.28 to 1.55 and from 2.10 to 5.21 in 2009, respectively. Our results suggested that NT rice production system appeared to be ineffective in decreasing carbon emission, which suggested that CO 2 emissions from integrated rice-based system should be taken into account to assess effects of tillage. 相似文献
2.
The wetlands play an important role in global carbon and nitrogen storage, and they are also natural sources of greenhouse gases such as methane (CH 4) and nitrous oxide (N 2O). Land-use change is an important factor affecting the exchange of greenhouse gases between wetlands and the atmosphere. However, few studies have investigated the effect of land-use change on CH 4 and N 2O emissions from freshwater marsh in China. Therefore, a field study was carried out over a year to investigate the seasonal changes of the emissions of CH 4 and N 2O at three sites ( Deyeuxia angustifolia marsh, dryland and rice field) in the Sanjiang Plain of Northeast China. Marsh was the source of CH 4 showing a distinct temporal variation. Maximum fluxes occurred in June and the highest value was 20.69 ± 2.57 mg CH 4 m ?2 h ?1. The seasonal change of N 2O fluxes from marsh was not obvious, consisted of a series of emission pulses. The marsh acted as a N 2O sink during winter, while became a N 2O source in the growing season. The results showed that gas exchange between soil/snow and the atmosphere in the winter season contributed greatly to the annual budgets. The winter season CH 4 flux was about 3.24% of the annual flux and the winter uptake of N 2O accounted for 13.70% of the growing-season emission. Conversion marsh to dryland resulted in a shift from a strong CH 4 source to a weak sink (from 199.12 ± 39.04 to ?1.37 ± 0.68 kg CH 4 ha ?1 yr ?1), while increased N 2O emissions somewhat (from 4.07 ± 1.72 to 4.90 ± 1.52 kg N 2O ha ?1 yr ?1). Conversion marsh to rice field significantly decreased CH 4 emission from 199.12 ± 39.04 to 94.82 ± 9.86 kg CH 4 ha ?1 yr ?1 and N 2O emission from 4.07 ± 1.72 to 2.09 ± 0.79 kg N 2O ha ?1 yr ?1. 相似文献
3.
Simulations with the process oriented Forest-DNDC model showed reasonable to good agreement with observations of soil water contents of different soil layers, annual amounts of seepage water and approximated rates of nitrate leaching at 79 sites across Germany. Following site evaluation, Forest-DNDC was coupled to a GIS to assess nitrate leaching from German forest ecosystems for the year 2000. At national scale leaching rates varied in a range of 0–>80 kg NO 3–N ha −1 yr −1 (mean 5.5 kg NO 3–N ha −1 yr −1). A comparison of regional simulations with the results of a nitrate inventory study for Bavaria showed that measured and simulated percentages for different nitrate leaching classes (0–5 kg N ha −1 yr −1:66% vs. 74%, 5–15 kg N ha −1 yr −1:20% vs. 20%, >15 kg N ha −1 yr −1:14% vs. 6%) were in good agreement. Mean nitrate concentrations in seepage water ranged between 0 and 23 mg NO 3–N l −1. 相似文献
4.
We calculated farm, land, and soil N-budgets for countries in Europe and the EU27 as a whole using the agro-economic model CAPRI. For EU27, N-surplus is 55 kg N ha −1 yr −1 in a soil budget and 65 kg N 2O–N ha −1 yr −1 and 67 kg N ha −1 yr −1 in land and farm budgets, respectively. NUE is 31% for the farm budget, 60% for the land budget and 63% for the soil budget. NS values are mainly related to the excretion (farm budget) and application (soil and land budget) of manure per hectare of total agricultural land. On the other hand, NUE is best explained by the specialization of the agricultural system toward animal production (farm NUE) or the share of imported feedstuff (soil NUE). Total N input, intensive farming, and the specialization to animal production are found to be the main drivers for a high NS and low NUE. 相似文献
5.
Different land uses in subtropics play an important role in regulating the global environmental changes. To reduce uncertainties of greenhouse gas (GHG) emissions of agricultural soils in subtropical ecosystem, a four years campaign was started to determine the temporal GHG (CO 2 and CH 4) fluxes from seven sites of four land use types (1 vegetable field, 3 uplands, 2 orchards, 1 pine forest). The mean annual budgets of CO 2, and CH 4 were 6.5~10.5 Mg CO 2 ha ?1 yr ?1, and +0.47 ~ ?2.37 kg CH 4 ha ?1 yr ?1, respectively. Pine forest had significantly lower CO 2 emission and higher CH 4 uptake than agriculture land uses. Tilled orchard emitted more CO 2 and oxidized less CH 4 than non-tilled orchard. Upland crops had higher CO 2 emissions than orchards, while abrupt differences of CH 4 uptake were observed between upland crops and orchards. Every year, the climate was warm and wet from April to September (the hot–humid season) and became cool and dry from October to March (the cool–dry season). Driven by seasonality of temperature and WFPS, CO 2 fluxes were significantly higher in the hot–humid season than in cool–dry season. Soil temperature, WFPS, NO 3?–N and NH 4+–N contents interactively explained CH 4 uptake which was significantly higher in cool–dry season than in hot–humid season. We conclude that soil C fluxes from different land uses are strongly under control of different climatic predictors along with soil nutrient status, which interact in conjunction with each other to supply the readily available substrates. 相似文献
6.
Cadmium (Cd) levels in paddy fields across Taiwan have increased due to emission from industry. To ensure the production of rice that meets food quality standards, predictive models or suitable soil tests are needed to evaluate the quality of soils to be used for rice cropping. Levels of Cd in soil and rice grains were measured in 19 paddy fields across the western plains in Taiwan. Cadmium levels in soil range from less than 0.1 mg kg ?1 to 30 mg kg ?1. Measured Cd levels in brown rice were predicted very well ( R2 > 0.8) based on Cd and Zinc in a 0.01 M CaCl 2 extract or a soil–plant transfer model using the reactive soil Cd content, pH, and cation exchange capacity. In contrast to current soil quality standards used in Taiwan, such models are effective in identifying soils where Cd in rice will exceed food quality standards. 相似文献
7.
Based on multi-year measurements of CH 4 exchange in sub-daily resolution we show that clear-cutting of a forest in Southern Germany increased soil temperature and moisture and decreased CH 4 uptake. CH 4 uptake in the first year after clear-cutting (−4.5 ± 0.2 μg C m −2 h −1) was three times lower than during the pre-harvest period (−14.2 ± 1.3 μg C m −2 h −1). In contrast, selective cutting did not significantly reduce CH 4 uptake. Annual mean uptake rates were −1.18 kg C ha −1 yr −1 (spruce control), −1.16 kg C ha −1 yr −1 (selective cut site) and −0.44 kg C ha −1 yr −1 (clear-cut site), respectively. Substantial seasonal and inter-annual variations in CH 4 fluxes were observed as a result of significant variability of weather conditions, demonstrating the need for long-term measurements. Our findings imply that a stepwise selective cutting instead of clear-cutting may contribute to mitigating global warming by maintaining a high CH 4 uptake capacity of the soil. 相似文献
8.
Arable soils are a significant source of nitric oxide (NO), a precursor of tropospheric ozone, and thereby contribute to ozone pollution. However, their actual impact on ozone formation is strongly related to their spatial and temporal emission patterns, which warrant high-resolution estimates.Here, we combined an agro-ecosystem model and geo-referenced databases to map these sources over the 12 000 km 2 administrative region surrounding Paris, France, with a kilometric level resolution. The six most frequent arable crop species were simulated, with emission rates ranging from 1.4 kg N-NO ha −1 yr −1 to 11.1 kg N-NO ha −1 yr −1. The overall emission factor for fertilizer-derived NO emissions was 1.7%, while background emissions contributed half of the total NO efflux. Emissions were strongly seasonal, being highest in spring due to fertilizer inputs. They were mostly sensitive to soil type, crops' growing season and fertilizer N rates. 相似文献
9.
Due to the high temporal and spatial variability of N 2O fluxes, estimates of N 2O emission from temperate forest ecosystems are still highly uncertain, particularly at larger scales. Although highest N 2O emissions with up to 7.0 kg N ha −1 yr −1 were mainly reported for soils affected by stagnant water, most of the reported gas flux measurements were performed at forest sites with well-aerated soils yielding mostly to low mean annual emission rates less than 1.0 kg N ha −1 yr −1. This study compares N 2O fluxes from upland ( Cambisols) and temporally water-logged ( Gleysols, Histosols) soils of the Central Black Forest (South-West Germany) over a period of 2 yr. Mean annual N 2O fluxes from investigated soils ranged between 0.2 and 3.9 kg N ha −1 yr −1. The fluxes showed a large variability between the different soil types. Emissions could be clearly ranked in the following order: Cambisols (0.26–0.75 kg N ha −1 yr −1)< Gleysols (1.37–2.68 kg N ha −1 yr −1)< Histosol (3.66–3.95 kg N ha −1 yr −1). Although the Cambisols cover two-thirds of the investigated area, only about half of the overall N 2O is emitted from this soil type. Therefore, regional or national N 2O fluxes from temperate forest soils are underestimated if soils characterised by intermediate aeration conditions are disregarded. 相似文献
10.
Throughfall and bulk precipitation chemistry were studied for five years (June 1994–May 1999) at two high elevation forest sites (Val Gerola and Val Masino) which were known to differ in terms of tree health, as assessed by live crown condition. The ion concentration of bulk precipitation samples did not differ significantly between sites, except for Mg 2+, while the throughfall concentrations differed in the measured values of H +, N-NO 3−, Cl −, Na +, K +, DOC and weak organic acids. The results of the application of the canopy exchange model indicated a higher contribution from the dry deposition of N-NO 3−, N-NH 4+ and H + at Val Gerola, where the damage symptoms were more evident. In addition, the canopy leaching of Ca 2+, K + and weak organic acids were 47%, 21% and 27% higher at Val Gerola than at Val Masino. Annual SO 42− deposition fluxes (21.3 kg ha −1 yr −1 at Val Masino and 23.6 kg ha −1 yr −1 at Val Gerola) were similar to those reported for moderately polluted European and U.S. sites. Annual N loads were 13.6 and 13.1 kg ha −1 yr −1 in the bulk input, and 15.0 and 18.0 kg ha −1 yr −1 in throughfall inputs, at Val Masino and Val Gerola, respectively. The contribution of the organic fraction to the total N atmospheric deposition load is significant, constituting 17% of the bulk flux and 40% of the throughfall flux. Measured nitrogen loads exceed the critical nutrient loads by several kg N ha −1 at both stations. In particular the nitrogen throughfall load at Val Gerola was about 3 times higher than the critical values. 相似文献
11.
Soils are a significant source for atmospheric NO. However, due to the limited number of measurements and in view of the high temporal and spatial variability of NO emissions, as originating from dependencies from a series of environmental constraints such as soil properties, meteorology or N fertilization, inventories of soil NO emissions are still highly uncertain. In this work, the agricultural DNDC model was modified and applied on site scale in order to evaluate its capability to simulate soil NO emissions. DNDC captured differences in the magnitude of NO emissions between sites, but was less successful when simulating observed day-by-day variations. However, major peak emission events, e.g. due to fertilizer application or following rainfall events, were mostly simulated. DNDC as well as its forest version Forest-DNDC were finally linked to a GIS to calculate NO emissions from agricultural and forest soils across Europe. Using the same databases for agricultural soils, we also compared our estimate with other commonly used methodologies (Skiba-EMEP/CORINAIR, Yienger and Levy, Stehfest and Bouwman). A canopy reduction factor was not applied in this study. Estimates for NO emissions for agricultural soils for EU15 states varied in a range of 48.9–189.8 kt NO-N for the year 2000 depending on the approach used (Yienger and Levy > DNDC > Stehfest and Bouwman > Skiba-EMEP/CORINAIR). For forests, using the model Forest-DNDC as the only approach, we calculated soil NO emissions to be 75.1 kt NO-N yr ?1. The results show that soils in EU15 states are significant sources of atmospheric NO, though the share of soil NO emissions on total NO x emissions (incl. NO x emissions by combustion processes) in EU15 was only 4–6%. Given that soil NO emissions are largely driven by the availability of inorganic nitrogen (fertilization) and temperature, emissions are larger during the vegetation period. Especially during early summer when fertilizer-induced NO emissions from agricultural soils are peaking, the contribution of soil emissions to total NO x emissions may most likely be well above 10%. 相似文献
12.
We present a methane (CH 4) budget for the area of the Baiyinxile Livestock Farm, which comprises approximately 1/3 of the Xilin river catchment in central Inner Mongolia, P.R. China. The budget calculations comprise the contributions of natural sources and sinks as well as sources related to the main land-use in this region (non-nomadic pastoralism) during the growing season (May–September). We identified as important CH 4 sources floodplains (mean 1.55 ± 0.97 mg CH 4–C m ?2 h ?1) and domestic ruminants, which are mainly sheep in this area. Within the floodplain significant differences between investigated positions were detected, whereby only positions close-by the river or bayous emitted large amounts of CH 4 (mean up to 6.21 ± 1.83 mg CH 4–C m ?2 h ?1). Further CH 4 sources were sheepfolds (0.08–0.91 mg CH 4–C m ?2 h ?1) and pasture faeces (1.34 ± 0.22 mg CH 4–C g ?1 faeces dry weight), but they did not play a significant role for the CH 4 budget. In contrast, dung heaps were not a net source of CH 4 (0.0 ± 0.2 for an old and 0.0 ± 0.3 μg CH 4–C kg ?1 h ?1 for a new dung heap). Trace gas measurements along two landscape transects (volcano, hill slope) revealed expectedly a mean CH 4 uptake (volcano: 76.5 ± 4.3; hill: 28.3 ± 5.3 μg CH 4–C m ?2 h ?1), which is typical for the aerobic soils in this and other steppe ecosystems. The observed fluxes were rarely influenced by topography.The CH 4 emissions from the floodplain and the sheep were not compensated by the CH 4 oxidation of aerobic steppe soils and thus, this managed semi-arid grassland did not serve as a terrestrial sink, but as a source for this globally important greenhouse gas. The source strength amounted to 1.5–3.6 kg CH 4–C ha ?1 during the growing season, corresponding to 3.5–8.7 kg C ha ?1 yr ?1. 相似文献
13.
Agricultural soils may account for 10% of anthropogenic emissions of NO, a precursor of tropospheric ozone with potential impacts on air quality and global warming. However, the estimation of this biogenic source strength and its relationships to crop management is still challenging because of the spatial and temporal variability of the NO fluxes.Here, we present a combination of new laboratory- and field-scale methods to characterise NO emissions and single out the effects of environmental drivers.First, NO fluxes were continuously monitored over the growing season of a maize-cropped field located near Paris (France), using 6 automatic chambers. Mineral fertilizer nitrogen was applied from May to October 2005. An additional field experiment was carried out in October to test the effects of N fertilizer form on the NO emissions. The automatic chambers were designed to measure simultaneously the NO and N 2O gases. Laboratory measurements were carried out in parallel using soil cores sampled at same site to test the response of NO fluxes to varying soil N–NH 4 and water contents, and temperatures. The effects of soil core thickness were also analysed.The highest NO fluxes occurred during the first 5 weeks following fertilizer application. The cumulative loss of NO–N over the growing season was estimated at 1.5 kg N ha ?1, i.e. 1.1% of the N fertilizer dose (140 kg N ha ?1). All rainfall events induced NO peak fluxes, whose magnitude decreased over time in relation to the decline of soil inorganic N. In October, NO emissions were enhanced with ammonium forms of fertilizer N. Conversely, the application of nitrate-based fertilizers did not significantly increase NO emissions compared to an unfertilized control. The results of the subsequent laboratory experiments were in accordance with the field observations in magnitude and time variations. NO emissions were maximum with a water soil content of 15% (w w ?1), and with a NH 4–N content of 180 mg NH 4–N kg soil ?1. The response of NO fluxes to soil temperature was fitted with two exponential functions, involving a Q10 of 2.0 below 20 °C and a Q10 of 1.4 above. Field and laboratory experiments indicated that most of the NO fluxes originated from the top 10 cm of soil. The characterisation of this layer in terms of mean temperature, NH 4 and water contents is thus paramount to explaining the variations of NO fluxes. 相似文献
14.
Effects of elevated N deposition on forest aboveground biomass were evaluated using long-term data from N addition experiments and from forest observation plots in Switzerland. N addition experiments with saplings were established both on calcareous and on acidic soils, in 3 plots with Fagus sylvatica and in 4 plots with Picea abies. The treatments were conducted during 15 years and consisted of additions of dry NH 4NO 3 at rates of 0, 10, 20, 40, 80, and 160 kg N ha −1 yr −1. The same tree species were observed in permanent forest observation plots covering the time span between 1984 and 2007, at modeled N deposition rates of 12-46 kg N ha −1 yr −1. Experimental N addition resulted in either no change or in a decreased shoot growth and in a reduced phosphorus concentration in the foliage in all experimental plots. In the forest, a decrease of foliar P concentration was observed between 1984 and 2007, resulting in insufficient concentrations in 71% and 67% of the Fagus and Picea plots, respectively, and in an increasing N:P ratio in Fagus. Stem increment decreased during the observation period even if corrected for age. Forest observations suggest an increasing P limitation in Swiss forests especially in Fagus which is accompanied by a growth decrease whereas the N addition experiments support the hypothesis that elevated N deposition is an important cause for this development. 相似文献
15.
Simulation models are one of the approaches used to investigate greenhouse gas emissions and potential effects of global warming on terrestrial ecosystems. DayCent which is the daily time-step version of the CENTURY biogeochemical model, and DNDC (the DeNitrification–DeComposition model) were tested against observed nitrous oxide flux data from a field experiment on cut and extensively grazed pasture located at the Teagasc Oak Park Research Centre, Co. Carlow, Ireland. The soil was classified as a free draining sandy clay loam soil with a pH of 7.3 and a mean organic carbon and nitrogen content at 0–20 cm of 38 and 4.4 g kg ?1 dry soil, respectively. The aims of this study were to validate DayCent and DNDC models for estimating N 2O emissions from fertilized humid pasture, and to investigate the impacts of future climate change on N 2O fluxes and biomass production. Measurements of N 2O flux were carried out from November 2003 to November 2004 using static chambers. Three climate scenarios, a baseline of measured climatic data from the weather station at Carlow, and high and low temperature sensitivity scenarios predicted by the Community Climate Change Consortium For Ireland (C4I) based on the Hadley Centre Global Climate Model (HadCM 3) and the Intergovernment Panel on Climate Change (IPCC) A1B emission scenario were investigated. DayCent predicted cumulative N 2O flux and biomass production under fertilized grass with relative deviations of +38% and (?23%) from the measured, respectively. However, DayCent performs poorly under the control plots, with flux relative deviation of (?57%) from the measured. Comparison between simulated and measured flux suggests that both DayCent model’s response to N fertilizer and simulated background flux need to be adjusted. DNDC overestimated the measured flux with relative deviations of +132 and +258% due to overestimation of the effects of SOC. DayCent, though requiring some calibration for Irish conditions, simulated N 2O fluxes more consistently than did DNDC. We used DayCent to estimate future fluxes of N 2O from this field. No significant differences were found between cumulative N 2O flux under climate change and baseline conditions. However, above-ground grass biomass was significantly increased from the baseline of 33 t ha ?1 to 45 (+34%) and 50 (+48%) t dry matter ha ?1 for the low and high temperature sensitivity scenario respectively. The increase in above-ground grass biomass was mainly due to the overall effects of high precipitation, temperature and CO 2 concentration. Our results indicate that because of high N demand by the vigorously growing grass, cumulative N 2O flux is not projected to increase significantly under climate change, unless more N is applied. This was observed for both the high and low temperature sensitivity scenarios. 相似文献
16.
Twenty-two long-term measurements of direct N 2O emissions from soils in an intensive agricultural area were used for the validation of the process-based DNDC model (version 8.3P). Model simulations were evaluated for temporal patterns of N 2O, NH 4+, NO 3− and water-filled pore space (WFPS) and total N 2O emissions. Several soil and crop input parameter adjustments to the model were evaluated but only the recalculation of the WFPS at wilting point and at field capacity, using pedotransfer functions, resulted in a clear improvement of the simulated variables (WFPS in all cases, N 2O in some cases). Therefore, only this adjustment was made to DNDC 8.3P. This change, however, resulted for some cases (both cropland and grassland) in retardation of nitrate leaching and to a lesser extent of NH 4+ to the deeper soil layers. The goodness of fit of the simulated temporal pattern of N 2O varied considerably between sites. The total simulated N 2O emissions from cropland showed a good agreement with the measurements, although there was a systematic overestimation of 7.4 kg N 2O-N ha −1. Grassland soils, in contrast, gave a low agreement between total simulated and measured N 2O losses. On the basis of all measured data a regional emission factor of 3.16 with a 95% confidence interval of −0.89 to 7.21 could be calculated. DNDC simulations resulted in an emission factor of 6.49 with a 95% confidence interval of 4.04–8.93. The overall outcome of the N 2O emission measurements and DNDC simulations were compared with several empirical regression models, which may be applicable for a temperate climate system. All of the tested regression models showed reliable results up to a N 2O emission of 10 kg N 2O-N ha −1. Higher emissions, however, were systematically underestimated. Though DNDC both under- and overestimated specific sites, the general agreement, over the whole range between measurements and simulations of total N 2O losses (simulations=0.82×meas.+6.2), was better than for the different regression models. 相似文献
17.
An automated system for continuous measurement of N 2O fluxes on an hourly basis was employed to study N 2O emissions in an intensively managed low carbon calcareous soil under sub-humid temperate monsoon conditions. N 2O emissions occurred mainly within two weeks of application of NH 4+-based fertilizer and total N 2O emissions in wheat (average 0.35 or 0.21 kg N ha −1 season −1) and maize (average 1.47 or 0.49 kg N ha −1 season −1) under conventional and optimum N fertilization (300 and 50-122 kg N ha −1, respectively) were lower than previously reported from low frequency measurements. Results from closed static chamber showed that N 2O was produced mainly from nitrification of NH 4+-based fertilizer, with little denitrification occurring due to limited readily oxidizable carbon and low soil moisture despite consistently high soil nitrate-N concentrations. Significant reductions in N 2O emissions can be achieved by optimizing fertilizer N rates, using nitrification inhibitors, or changing from NH 4+- to NO 3ˉ-based fertilizers. 相似文献
18.
The role of nitrogen (N) in acidification of soil and water has become relatively more important as the deposition of sulphur has decreased. Starting in 1991, we have conducted a whole-catchment experiment with N addition at Gårdsjön, Sweden, to investigate the risk of N saturation. We have added 41 kg N ha −1 yr −1 as NH 4NO 3 to the ambient 9 kg N ha −1 yr −1 in fortnightly doses by means of sprinkling system. The fraction of input N lost to runoff has increased from 0% to 10%. Increased concentrations of NO 3 in runoff partially offset the decreasing concentrations of SO 4 and slowed ecosystem recovery from acid deposition. From 1990-2002, about 5% of the total N input went to runoff, 44% to biomass, and the remaining 51% to soil. The soil N pool increased by 5%. N deposition enhanced carbon (C) sequestration at a mean C/N ratio of 42-59 g g −1. 相似文献
19.
The iron (Fe) (hydro)oxides deposited around rice roots play an important role in arsenic (As) sequestration in paddy soils, but there is no systematic study on the relative importance of Fe (hydro)oxides on root surface and in rhizosphere soil in limiting As bioavailability. Twenty-seven rice genotypes were selected to investigate effects of Fe (hydro)oxides on As uptake by rice in an alkaline paddy soil. Results indicated that the As content was positively correlated with the Fe content on root surface, and most of As (88–97%) was sequestered by poorly crystalline and crystalline Fe (hydro)oxides in the alkaline paddy soil. The As sequestration by Fe (hydro)oxides on root surface (IASroot 16.8–25.0 mg As/(g Fe)) was much higher than that in rhizosphere (IASrhizo 1.4–2.0 mg As/(g Fe)); therefore, in terms of As immobilization, the Fe (hydro)oxides on root surface were more important than that in rhizosphere. However, the As content in brown rice did not have significant correlation with the As content on root surface but was significantly correlated (R2?=?0.43, P?<?0.05) with the partition ratio (PRAs?=?IASroot/IASrhizo) of As sequestration on root surface and in rhizosphere, which suggested that Fe (hydro)oxides on root surface did not play the controlling role in lowering As uptake, and the partition ratio PRAs would be a better indicator to evaluate effects of Fe (hydro)oxides around roots on As uptake by rice. 相似文献
20.
Combination of divergent active principles to achieve broad-spectrum control is gaining popularity to manage the weed menace in intensive agriculture. However, such application could have non-target impacts on the soil processes affecting soil ecology and environmental interactions. A field experiment was conducted to investigate the impact of separate and combined applications of herbicides bensulfuron methyl and pretilachlor on the emission of N 2O and CH 4, and related soil and microbial parameters in a flooded alluvial field planted to rice cv Lalat. Single application of the herbicide bensulfuron methyl or pretilachlor resulted in a significant reduction of N 2O and CH 4 emissions while the combination of these two herbicides distinctly increased N 2O and CH 4 emissions. Cumulative N 2O emissions (kg N 2O-N) followed the order of bensulfuron methyl (0.35 kg ha −1) < pretilachlor (0.36 kg ha −1) < control (0.45 kg ha −1) < bensulfuron methyl 0.6% + pretilachlor 6.0% single dose (0.49 kg ha −1) < bensulfuron methyl 0.6% + pretilachlor 6.0% double dose (0.54 kg ha −1). Cumulative CH 4 emissions (kg CH 4), on the other hand, followed the order of bensulfuron methyl (47.89 kg ha −1) < pretilachlor (73.17 kg ha −1) < bensulfuron methyl 0.6% + pretilachlor 6.0% single dose (93.50 kg ha −1) < control (106.54 kg ha −1) < bensulfuron methyl 0.6% + pretilachlor 6.0% double dose (124.67 kg ha −1). The inhibitory effect of separate application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% on N 2O emission was linked to lower mineral N, lower denitrifying and nitrifying activity and low denitrifier and nitrifier populations. Inhibitory effect on CH 4 emission, on the contrary, was linked to prevention in the drop of redox potential, lower readily mineralizable carbon (RMC) and microbial biomass carbon (MBC) contents as well as lower methanogenic and higher methanotrophic bacterial population. Admittedly, stimulatory effect of combined application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% at double dose on N 2O and CH 4 emission was related to reversal of the identified indicators of inhibition. Results indicate that while individual application of herbicides bensulfuron methyl 0.6% or pretilachlor 6.0% can reduce N 2O and CH 4 emission from flooded soil planted to rice, their combined application at normal dose can keep the emission at a comparatively lower level with significantly higher grain yield as compared to the herbicides applied alone. 相似文献
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