首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
The effects of seven insecticides and six fungicides on denitrification of nitrate in soils were studied by determining the effects of 10 and 50μgg?1 soil of each pesticide on the amounts of nitrate lost and the amounts of nitrite, N2O and N2 produced when soil samples were incubated anaerobically after treatment with nitrate. The insecticides used were lindane, fenitrothion, fonofos, malathion, phorate, terbufos and carbofuran. The fungicides used were mancozeb, maneb, thiram, benomyl, captan and terrazole.None of the insecticides studied had a significant effect on denitrification when applied at the rate of 10 μgg?1 soil. When applied at the rate of 50μgg?1 soil, lindane, fonofos and malathion enhanced denitrification in the three soils studied, whereas fenitrothion, phorate, terbufos and carbofuran either had no appreciable effect on denitrification in these soils, or enhanced denitrification in at least one of the soils.None of the fungicides studied had an appreciable effect on denitrification when applied at the rate of 10μgg?1 soil, but thiram increased the ratio of N2 to N2O in the gaseous products of denitrification. Captan inhibited denitrification in two of three soils studied when applied at the rate of 50μgg?1 soil. The other five fungicides either had no significant effect on denitrification, or enhanced denitrification, when applied at this rate. Reports that maneb, thiram and terrazole inhibit denitrification in soil were not confirmed.  相似文献   

2.
Sorption, persistence and transport of herbicides in soils depend on the relative saturation of soils with cations from various soil amendments. Current research was conducted to study the effect of preequilibration of a Candler fine sand (Hyperthermic uncoated typic Quartzipsamments; 0–30 cm depth) with AlCl3, CaCl2, CuCl2, FeCl3, or KCl salt solutions on sorption in bromacil, simazine, norflurazon, and diuron herbicides commonly used in Florida citrus groves. Preequilibration of the soil with either FeCl3, or AlCl3 significantly decreased the sorption and therefore increased internal leaching potential, of all four herbicides as compared to their sorption in untreated soil. This decrease in sorption was much greater for bromacil and simazine (24 to 35%) than for norflurazon and diuron (7 to 8%). The desorption of bromacil and diuron in 1M NH4OAc was also significantly lower in soils preequilibrated with FeCl3 or AlCl3 than the untreated soil. However, the reverse was true in the case of simazine and norflurazon. Preequilibration of the soil with CuCl2, KCl, and CaCl2 resulted in a significant decrease in sorption of norflurazon, diuron, and simazine but did not affect bromacil sorption. Accordingly, the species of adsorbed cation had varying effects on the sorption/desorption of each of the herbicides and varied their leaching potential.  相似文献   

3.
The potential for surface and groundwater contamination of soil applied herbicides is partly dependent on soil properties. Sorption and desorption of diuron and norflurazon were studied in seven soils representative of the southern citrus-belt of Florida using the batch-equilibrium technique. Sorption of herbicides was influenced by soil properties. Sorption coefficients (K d) ranged from 0.84 to 3.26 mL g?1 for diuron and 0.63 to 2.20 mL g?1 for norflurazon indicating weak to moderate binding of herbicides to soil. For norflurazon, K dwas significantly related to organic C content, soil pH, and cation exchange capacity. For diuron, absence of a significant relationship between K dand selected soil properties suggests that the soil properties other than those studied may play a role in determining sorption on these soils. Desorption studies showed that higher amounts of diuron and norflurazon was desorbed by water than by 0.5 M CaCl2. An inverse relationship was apparent between herbicides sorbed and that which was desorbed among the soils studied. The soil which exhibited higher sorption had lower desorption and the soil which exhibited lower sorption had higher desorption.  相似文献   

4.
Denitrification loss from a loam under a cut ryegrass sward receiving 0, 250 and 500 kg N ha?1 a?1 in four equal amounts was measured during 14 months using the acetylene-inhibition technique. The rate of denitrification responded rapidly to changes in soil water content as affected by rain. Mean rates of denitrification exceeded 0.2 kg N ha?1 day?1 only when the soil water content was >20% (w/w) and nitrate was >5μ N g?1 in the upper 20 cm of the profile and when soil temperature at 2 cm was >5–8°C. When the soil dried to a water content <20%, denitrification decreased to <0.05 kg N ha?1 day?1. Highest rates (up to 2.0 kg N ha?1 day?1) were observed following application of fertilizer to soil at a water content of about 30% (w/w) in early spring. Denitrification in the control plot during this period was generally about a hundredth of that in plots treated with ammonium nitrate. High rates of N2O loss (up to 0.30 kg N ha?1 day-1) were invariably associated with high rates of denitrification (> 0.2 kg N ha?1 day?1). However, within 2–3 weeks following application of fertilizer to the plot receiving 250 kg N ha?1 a?1 the soil acted as a sink for atmospheric N2O when its water content was >20% and its temperature >5–8°C. Annual N losses arising from denitrification were 1.6, 11.1 and 29.1 kg N ha?1 for the plots receiving 0, 250 and 500 kg N ha?1 a?1, respectively. More than 60% of the annual loss occurred during a period of 8 weeks when fertilizer was applied to soil with a water content >20%.  相似文献   

5.
Denitrification losses from a horticultural soil as affected by mineral N-fertilization To investigate denitrification in the Ap-horizon from a horticultural cambisol as affected by mineral N-fertilization, measurements of N2O-release from the soil surface and N2O-production in the upper 10 cm soil layer were carried out. The acetylene inhibition technique was used. The loamy sand was amended with 86 and 186 kg N·ha?1 (ammonium nitratecalcium carbonate mixture). The field was cropped with celeriac (Apium graveolens L. var. rapaceum). Denitrification rates as well as soil temperature, moisture, nitrate and watersoluble carbon were measured from mid July until the end of October. In both N treatments denitrification rates were low, but higher rates could be measured in the higher N-treatment. They reached amounts of 0.6 to 134.3 g N2O-N·ha?1day?1. Estimated N-loss by denitrification totalled about 3.5 in the low and 4.9 kg N·ha?1 in the high N-treatment for the whole sampling period (107 days). Spatial variability of denitrification rates was high (39–283%). The relationship between soil temperature, moisture, nitrate content as well as watersoluble carbon and denitrification rate was shown by regression analysis.  相似文献   

6.
Calcium nitrate fertilizer containing 92.3 atoms % excess nitrogen-15 was applied on 5 May 1981 at a rate equivalent to 100 kg N ha?1 to a clay soil in southern England cropped to winter wheat. Samples of the soil gases were collected frequently during the following 3 weeks. The soil oxygen concentration declined to 5% after 60 mm rain. A maximum of 1.5 ± 0.5 atom % N-15 enrichment in labelled N2 gas (29N2) was detected in the soil atmosphere on 28 May. Total denitrification losses, calculated from air-filled pore space and rates of gas loss from the soil estimated using a Fick's law approximation, were 9.5 kg N ha?1 with a daily rate of 0.30 ± 0.07 kg N ha?1. Estimated total losses were greater than 30 kg N ha?1, 93% in the form N2, but the estimation depends on several assumptions about the amount of double labelled gas (30N2), rates of gas diffusion and flux.  相似文献   

7.
Denitrification losses from puddled rice soils in the tropics   总被引：4，自引：0，他引：4  
Summary Although denitrification has long been considered a major loss mechanism for N fertilizer applied to lowland rice (Oryza sativa L.) soils, direct field measurements of denitrification losses from puddled rice soils in the tropics have only been made recently. This paper summarizes the results of direct measurement and indirect estimation of denitrification losses from puddled rice fields and reviews the status of research methodology for measurement of denitrification in rice fields. The direct recovery of (N2+N2O)-15N from 15N-enriched urea has recently been measured at sites in the Philippines, Thailand, and Indonesia. In all 12 studies, recoveries of (N2+N2O)-15N ranged from less than 0.1 to 2.2% of the applied N. Total gaseous N losses, estimated by the 15N-balance technique, were much greater, ranging from 10 to 56% of the applied urea-N. Denitrification was limited by the nitrate supply rather than by available C, as indicated by the values for water-soluble soil organic C, floodwater (nitrate+nitrite)-N, and evolved (N2+N2O)-15N from added nitrate. In the absence of runoff and leaching losses, the amount of (N2+N2O)-15N evolved from 15N-labeled nitrate was consistently less than the unrecovered 15N in 15N balances with labeled nitrate, which presumably represented total denitrification losses. This finding indicates that the measured recoveries of (N2+N2O)-15N had underestimated the denitrification losses from urea. Even with a probable two-or threefold underestimation, direct measurements of (N2+N2O)-15N failed to confirm the appreciable denitrification losses often estimated by the indirect difference method. This method, which determines denitrification losses by the difference between total 15N loss and determined ammonia loss, is prone to high variability. Measurements of nitrate disappearance and 15N-balance studies suggest that nitrification-denitrification occurs under alternate soil drying and wetting conditions both during the rice cropping period and between rice crops. Research is needed to determine the magnitude of denitrification losses when soils are flooded and puddled for production of rice.  相似文献   

8.
The production of gaseous hydrocarbons has been studied in a clayey, loamy and sandy soil. The soil samples were incubated under closed conditions at field capacity and under waterlogged conditions. Additions of 100 or 300 μgg?1 nitrate were made to some of the soil samples. It was found that hydrocarbons were produced in two phases: at the beginning of the incubation period, coinciding with the high microbial activity after rewetting a dry soil and after obtaining anaerobic conditions in the flasks. Under anaerobic conditions, the concentration of methane was higher than the concentration of ethylene, ethane and propane. Methane production was high in the neutral soil, and of minor importance in the acid soils, while ethylene production was important in the soil with the highest organic matter content. Waterlogged conditions were much more favourable for hydrocarbon production than field capacity conditions. The addition of nitrate, in general, decreased hydrocarbon production, especially at 300μgg?1 for all treatments. In some treatments and for some gases, the influence of 100μgg?1 was less significant.  相似文献   

9.
Denitrification has long been considered a major mechanism of N loss when N fertilizer is applied to flooded rice paddies. However, the direct determination of denitrification in soils is almost impossible because of the high atmospheric background of dinitrogen (N2). Dissolved N2 in a small water sample can be rapidly and precisely measured through membrane inlet mass spectrometry (MIMS). This study is the first to directly measure N2 flux through MIMS in flooded rice paddy plots that received different amounts of urea. Ammonia (NH3) volatilization was measured simultaneously to verify whether NH3 volatilization and denitrification are complementary loss mechanisms. The average cumulative N2–N loss measured by MIMS 21 days after fertilization was 4.7?±?1.7 % of the applied N, which was within the range of the reported values obtained by cumulative recovery of (N2 + N2O)–15N and 15N-balance technique. Underestimation or overestimation of denitrification can be prevented in MIMS given that N2 can be measured directly without 15N-labeled fertilizer. A good positive correlation was found between the dissolved in situ N2 concentrations of floodwater and the denitrification rates of intact soil cores. Urea incorporation reduced NH3 volatilization unlike surface broadcasting. However, urea incorporation significantly increased cumulative N2–N loss during the 21 days after fertilization. Correlation analysis showed that nitrate (NO3 ?–N) concentration in floodwater could be the primary restricting factor for soil denitrification in the experimental field. Results suggest that MIMS is a promising technique for the measurement of denitrification in a flooded rice paddy.  相似文献   

10.
Summary The influence of 28 nitrification inhibitors on denitrification of nitrate in soil was studied by determining the effects of different amounts of each inhibitor on the amounts of nitrate lost and the amounts of nitrite, N2O and N2 produced when soil samples were incubated anaerobically after treatment with nitrate or with nitrate and mannitol. The inhibitors used included nitrapyrin (N-Serve), etridiazole (Dwell), potassium azide, 2-amino-4-chloro-6-methylpyrimidine (AM), sulfathiazole (ST), 4-amino-1,2,4-triazole(ATC),2,4-diamino-6-trichloromethyl-s-triazine (CL-1580), potassium ethylxanthate, guanylthiourea (ASU), 4-nitrobenzotrichloride, 4-mesylbenzotrichloride, sodium thiocarbonate (STC), phenylmercuric acetate (PMA), and dicyandiamide (DCD).Only one of the nitrification inhibitors studied (potassium azide) retarded denitrification when applied at the rate of 10 g g–1 soil, and only two (potassium azide and 2,4-diamino-6-trichloromethyl-s-triazine) inhibited denitrification when applied at the rate of 50 g g–1 soil. The other inhibitors either had no appreciable effect on denitrification, or enhanced denitrification, when applied at the rate of 10 or 50 g g–1 soil, enhancement being most marked with 3-mercapto-1,2,4-triazole. Seven of the inhibitors (potassium azide, sulfathiazole, potassium ethylxanthate, sodium isopropylxanthate, 4-nitrobenzotrichloride, sodium thiocarbonate, and phenylmercuric acetate) retarded denitrification when applied at the rate of 50 g g–1 soil to soil that had been amended with mannitol to promote microbial activity.Reports that nitrapyrin (N-Serve) and etridiazole (Dwell) inhibit denitrification when applied at rates as low as 0.5 g g–1 soil could not be confirmed. No inhibition of denitrification was observed when these compounds were applied at the rate of 10 g g–1 soil, and enhancement of denitrification was observed when they were applied at the rate of 50 or 100 g g–1 soil.  相似文献   

11.
The environmental behaviour of metolachlor and diuron was studied in the Central-western region of Brazil, by means of a field study where six experimental plots were installed. The soil was classified as a Latosol, and the soil horizons were characterized. Sorption of metolachlor and diuron was evaluated in laboratory batch experiments. Metolachlor and diuron were applied to the experimental plots on uncultivated soil in October 2003. From this date to March 2004, the following processes were studied: leaching, runoff and dissipation in top soil. K oc of metolachlor varied from 179 to 264 mL g?1 in the soil horizons. K oc of diuron in the Ap horizon was 917 mL g?1, decreasing significantly in the deeper horizons. Field dissipation half-lives of metolachlor and diuron were 18 and 15 days, respectively. In percolated water, metolachlor was detected in concentrations ranging from 0.02 to 2.84 μg L?1. In runoff water and sediment, metolachlor was detected in decreasing concentrations throughout the period of study. Losses of 0.02% and 0.54% of the applied amount by leaching and runoff, respectively, were observed confirming the high mobility of this herbicide in the environment. In percolated water, diuron was detected with low frequency but in relatively high concentrations (up to 6.29 μg L?1). In runoff water and soil, diuron was detected in decreasing concentrations until 70 days after application, totalizing 13.9% during the whole sampling period. These results show the importance of practices to reduce runoff avoiding surface water contamination by these pesticides, particularly diuron.  相似文献   

12.
The effect of 25 herbicides and herbicide combinations, in amounts comparable to those used in agriculture, on microbial activity in two soil types was determined in the laboratory. Herbicides did not affect respiration, assayed by CO2 evolution and dehydrogenase activity, in either silty clay loam or loamy sand. Organic matter decomposition, determined by the amount of CO2 evolved and inorganic N formed from decomposing alfalfa tissue, was also not affected. Alteration in soil pH or moisture content did not affect herbicide action. Addition of herbicides 3 weeks before amendment, or fertilizer application, also did not influence herbicide activity. Selected herbicides (trifluralin, linuron, dinoseb) at concentrations 100-fold higher than the recommended rates did not affect alfalfa decomposition. Solubilization of Ca3(PO4)2 in soil was not affected by herbicides. S oxidation to SO2?4 in soil, however, was increased by most herbicides. In silty clay loam, 18 of the 25 herbicides and herbicide combinations increased S oxidation almost up to 3-fold. Results in loamy sand were similar. Dinoseb effectively reduced the algal population in loamy sand by more than 90%. Trifluralin, linuron, and metribuzin did not inhibit algal populations.  相似文献   

13.
In modern agriculture, long‐term soil fertility and crop productivity are maintained by a combination of inorganic fertilizers and pesticide inputs which, in turn, create environmental and health concerns. Therefore, studies were initiated to evaluate two commonly used herbicides (atrazine and simazine) and two biological nitrification inhibitors (nitrapyrin and terrazole) applied with NO3‐N source fertilizer for their effects on denitrification and on corn (Zea mays L.) growth and yields. Each chemical applied at the rate of 10, 50, or 100 mg a.i. L‐1 suppressed denitrification of NO3 ‐ in a liquid medium inoculated with a Tifton loamy sand in a laboratory study. Nitrapyrin and terrazole selectively suppressed NO3 ‐ or NO2 ‐ or both reduction while atrazine and simazine suppressed NO2 ‐ or N2O or both reduction. In greenhouse pot culture studies, chemical application resulted in higher percent N recovery relative to the control. When atrazine or simazine was part of the chemical treatment, concentrations of NO3 ‐ and NO2 ‐ in corn (Zea mays L.) plants increased, and plant growth was restricted due to NO2 ‐ toxicity. During two consecutive years of field studies using split‐banded applications of N fertilization with nitrapyrin and terrazole, corn ear yields increased 78% and 25% in the first and second year, respectively. With atrazine and simazine, however, yields increased significantly in the first season only. Mixing either herbicide with nitrapyrin or terrazole had no effect on yields during both seasons.

Chemical Names: atrazine = [2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine]; simazine = [2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine]; nitrapyrin = [2‐chloro‐6‐(trichloromethyl)pyridine]; terrazole = [ethoxy‐3‐trichloromethyl‐1,2,4‐thiadiazole].  相似文献   

14.

Purpose

Rice-paddy-dominated watersheds in eastern China are intensively cultivated, and lands with two crops receive as much as 550–600 kg?ha–1?year–1 of nitrogen (N), mainly through the addition of N-based fertilizers. However, stream N concentrations have been found to be relatively low. Waterways in the watersheds are assumed to be effective “sinks” for N, minimizing its downstream movement. We directly measured net sediment denitrification rates in three types of waterways (ponds, streams/rivers, and a reservoir) and determined the key factors that control net sediment denitrification. Such information is essential for evaluating the impact of the agricultural N cycle on the quality of surface water.

Materials and methods

The pond–stream–reservoir continuum was sampled every 2 months at nine sites in an agricultural watershed between November 2010 and December 2011. Net sediment N2 fluxes/net sediment denitrification rates were determined by membrane inlet mass spectrometry and the N2/Ar technique. A suite of parameters known to influence denitrification were also measured.

Results and discussion

Net denitrification rates ranged between 28.2?±?18.2 and 674.3?±?314.5 μmol N2–N?m–2?h–1 for the streams, 23.7?±?23.9 and 121.2?±?38.7 μmol N2–N?m–2?h–1 for the ponds, and 41.8?±?17.7 and 239.3?±?49.8 μmol N2–N?m–2?h–1 for the reservoir. The mean net denitrification rate of the stream sites (173.2?±?248.4 μmol N2–N?m–2?h–1) was significantly higher (p?<?0.001) than that of the pond sites (48.3?±?44.5 μmol N2–N?m–2?h–1), and the three types of waterways all had significantly higher (p?<?0.01) mean net denitrification rates in summer than in other seasons. Linear regression and linear mixed effect model analysis showed that nitrate (NO3 ?–N) concentration in surface water was the primary controlling factor for net sediment denitrification, followed by water temperature. Using monitoring data on NO3 ?–N concentrations and temperature of the surface water of waterways and an established linear mixed effect model, total N removed through net sediment denitrification in the pond–stream–reservoir continuum was estimated at 46.8?±?24.0 t?year–1 from July 2007 to June 2009, which was comparable with earlier estimates based on the mass balance method (34.3?±?12.7 t?year–1), and accounted for 83.4 % of the total aquatic N. However, the total aquatic N was only 4.4 % of the total N input to the watershed, and thus most of the surplus N in the watershed was likely to be either denitrified or stored in soil.

Conclusions

High doses of N in a rice-paddy-dominated watershed did not lead to high stream N concentrations due to limited input of N into waterways and the high efficiency of waterways in removing N through denitrification.  相似文献   

15.
In order to evaluate the climatic and soil variables which control the denitrification processes in the field, measurements of N2O-losses using the C2H2 inhibition technique were carried out in an Inceptisol cropped with spring wheat. The silty sand was amended with mineral fertilizer (120 kg N ha?1) or additionally with sewage sludge (620 kg total N ha?1). Soil temperature, moisture, nitrate and available carbon, the release of nitrous oxide (N2O) from the soil surface as well as the N2O concentrations along the soil profile were measured from March until November 1985 The N2O surface fluxes from the inorganically fertilized field were well correlated with those from the sewage sludge amended plots (r = 0.76). Multivariate correlation analyses show that particularly soil moisture and nitrate content had a significant effect on the nitrate respiration. The correlation with the soil water content was more clearly expressed by the N2O surface fluxes than by the N2O concentrations of the soil air. The N2O surface fluxes during 1985 totalled about 3 kg N ha?1 in the minerally fertilized field. Sewage sludge amendments increased the N2O evolution by 5 times. Spatial variability was high and the N2O surface fluxes were not well correlated (r = 0.4) with the N2O concentrations in the soil atmosphere. These experiments provide the background data for a denitrification model and better knowledge about the variables which have to be considered for its validation.  相似文献   

16.
A better understanding of the nitrogen (N) cycle in agricultural soils is crucial for developing sustainable and environmentally friendly N fertilizer management and to propose effective nitrous oxide (N2O) mitigation strategies. This laboratory study quantified gross nitrogen transformation rates in uncultivated and cultivated black soils in Northeast China. It also elucidated the contribution made by nitrification and denitrification to the emissions of N2O. In the laboratory, soil samples adjusted to 60 % water holding capacity (WHC) were spiked with 15NH4NO3 and NH4 15NO3 and incubated at 25 °C for 7 days. The size and 15N enrichment of the mineral N pools and the N2O emission rates were determined between 0 and 7 days. The results showed that the average N2O emission rate was 21.6 ng N2O-N kg?1 h?1 in cultivated soil, significantly higher than in the uncultivated soil (11.6 ng N2O-N kg?1 h?1). Denitrification was found to be responsible for 32.1 % of the N2O emission in uncultivated soil, and the ratio increased significantly to 43.2 % in cultivated soil, due to the decrease in soil pH. Most of the increase in net N2O-N emissions observed in the cultivated soil was resulting from the increased production of N2O through denitrification. Gross nitrification rate was significantly higher in the cultivated soil than in the uncultivated soil, and the ratio of gross nitrification rate/ammonium immobilization rate was 6.87 in cultivated soil, much larger than the uncultivated soil, indicating that nitrification was the dominant NH4 + consuming process in cultivated soil, and this will lead to the increased production of nitrate, whereas the increased contribution of denitrification to N2O emission promoted the larger emission of N2O. This double impact explains why the risk of N loss to the environment is increased by long-term cultivation and fertilization of native prairie sites, and controlling nitrification maybe effective to abate the negative environmental effects.  相似文献   

17.
Nitrous oxide (N2O) and nitric oxide (NO) released from soil is a concern since it can act as a potential atmospheric pollutant and it represents a loss of N from the soil. These gases are present in the atmosphere in trace amounts and are important to atmospheric chemistry and earth's radiative balance. Nitric oxide (NO) does not directly contribute to the greenhouse effect, but it contributes to climate forcing through its role in photochemistry of hydroxyl radicals and ozone and plays a key role in air quality issues. Nitrification and denitrification have been identified as major controlling microbial processes in soils responsible for the formation of NO and N2O. To elucidate the contribution of both processes to the release of NO and N2O from loess-black earth soils under field conditions—i.e. to evaluate nitrate and ammonium as sources of NO and N2O emission—two field experiments with either [15N] nitrate (NO3?) or [15N] ammonium (NH4+) labelling have been conducted at two sites differing in soil organic matter content (high and normal SOM). [15N] nitrate treatments revealed that denitrification of NO3? represents the main pathway of soil N2O release. On average 76% and 54% of N2O was emitted during denitrification from soils with high and normal SOM content, respectively. Contrarily, denitrification contributed on average only 17% and 12% of released NO from soil with high and normal SOM content, respectively. The [15N]ammonium treatments revealed that nitrification of NH4+ is the major process responsible for soil NO emission. SOM content of the loess-black earth soil significantly influenced NO and N2O emission. The soil with the higher SOM content showed lower NO emission but drastically increased N2O emission after nitrate fertilisation. In particular the soil with high SOM content exhibited a high sorption capacity for ammonium ions which led to unexpected results after fertilisation with [15N]ammonium. To explain this results a revised concept containing three different interacting soil ammonium pools have been hypothesised.  相似文献   

18.
Laboratory studies were conducted to determine if acetylene affects the rate of NO3? reduction to N2O and N2, if C2H2 ist anaerobically metabolized in the presence of nitrate, and if C2H2 affects soil carbon metabolism. These studies in water saturated soil, incubated under air or N2 atmosphere, with or without acetone-free acetylene, show that C2H2 can accelerate NO3? reduction. Acetylene inhibited carbon mineralization when NO3? was limited but accelerated it when sufficient NO3? was available. After three days, only two per cent or less of the added C2H2 was directly oxidized to CO2, however, up to 28 % of the added C2H2 carbon remained in the soil. The residual C2H2 carbon was oxidized aerobically and anaerobically when NO3? was added. These data suggest that when C2H2 is used in denitrification studies, the results must be carefully scrutinized. Once a soil is exposed to C2H2 it should not be used again soon to assess denitrification.  相似文献   

19.
Adsorption and desorption of the herbicides glyphosate [N-phosphonomethyl-aminoaceticacid], simazine [6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine] and atrazine [6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine] were studied in four sandy soils from Western Australia. Distribution coefficients (Kds) were calculated from breakthrough curves (BTCs) resulting from leaching step changes in concentrations through small saturated columns of soil at flow rates ranging from 0.3 to 30 m day–1. A comparison was made with Kds obtained after batch equilibrating solutions of the herbicides with the same soils. The Kds of herbicides in soils decreased with increasing flow rate and most strongly for glyphosate in soils rich in clay content. Resulting increases in mobility of about 40–50% were estimated for simazine and atrazine and > 50% for glyphosate at flow rates of 3 m day–1. Adsorption and desorption rates were estimated by fitting numerically simulated BTCs to experimental BTCs. Best fits were obtained with a time-dependent Freundlich adsorption equation. The resulting coefficient for time dependency in the equation suggests that the rates of adsorption and desorption are controlled mainly by diffusion in an adsorbing layer on or in soil particles.  相似文献   

20.
An incubation experiment was conducted to examine the effects of phosphorus (P) addition with and without ammonium, nitrate, or glucose on N2O and NO emissions from soil taken under Acacia mangium plantation and incubated at 100 % water-filled pore space (WFPS). Additions of NO 3 ? stimulated the N2O and NO emissions while NH 4 + did not, showing that denitrification was the main process of N2O and NO production in the study condition. When NO 3 ? was added with P significantly (P?<?0.05) increased N2O emissions regardless of the ratio of the added nitrogen and carbon, suggesting that P addition stimulated denitrification activity. The activation of denitrification by P addition is possibly attributed to two mechanisms: (1) the added-P stimulated denitrification by relieving P shortage for denitrifying bacteria and (2) the added-P stimulated activity of heterotrophic soil microflora with increased O2 consumption promoting the development of anaerobic conditions with stimulation of denitrification.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号