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1.
The fate of added nitrogen in submerged soils was studied using 15N-labelled ammonium sulfate and alanine. After 8 weeks of incubation 25 and 22%, respectively, of nitrogen from ammonium sulfate and alanine were recovered in the soil. Under the experimental conditions used nitrogen added to presubmerged soils was lost rapidly outside of the soil-water system, regardless of whether the nitrogen was organic or inorganic. Fractionation studies revealed that the amount of tagged N incorporated into exchangeable ammonium, residual fractions, volatilized as NH3 and chemically fixed nitrogen was not enough to account for the nitrogen loss. The nitrogen loss was attributed to nitrification and subsequent denitrification during the incubation period.

The effect of N-Serve [2-chloro-6-(trichloromethyl)pyrimidine] on nitrification of 15N-labelled (NH4)2SO4-in submerged soils was studied. About 15% more nitrogen was recovered from non-presubmerged soils, and less nitrate was accumulated in presubmerged soils where N-Serve coated (NH4)2SO4 was applied, than from soils where (NH4)2SO4 was applied without N-Serve. Presubmerged soils provided a more favorable environment for nitrification than for denitrification under the experimental conditions used.  相似文献   

2.
Nitrification inhibitors (N-Serve, ATC, and CS2) were added to soils without N fertilizers. While the amount of nitrification of NH4+-N was reduced, so was the amount of ammonification of soil N. This effect was greater with ATC and CS2 than with N-Serve. In three field experiments, the application in the fall of ATC at 22 kg ha?1 mixed into the soil reduced the loss of soil mineral N in early spring. Apparently, the inhibition suppressed both ammonification and nitrification of soil N during the winter, and consequently there was less NO?3 in soil when the wet period occurred in the spring.  相似文献   

3.
Incubation studies (5 weeks at 30°C) of nitrification were made in an acid (pH 5.8) and a neutral (pH 7.1) soil receiving varying concentrations of pig slurry and (NH4)2SO4 solution. Mineral-N and pH changes were observed at weekly intervals and inorganic salts media were used to obtain separate estimates of the numbers of NH4-N- and NO2-N-oxidizing bacteria. In the acid soil, pig slurry NH4-N was nitrified to a greater extent than (NH4)2SO4. In the neutral soil, slurry additions resulted in the accumulation of NO2?-N and, in one case, the complete inhibition of nitrification for 4 weeks. Slurry raised the pH of both soils more than (NH4)2SO4 and nitrification in the acid soil was most rapid in a 2 week period of elevated pH following slurry applications. Numbers of Nitroxomonas isolated from the acid soil were considered high enough to account for NH4-N oxidation in slurry-treated samples. Numbers of nitrifiers recovered from the incubated neutral soil samples were variable but frequently high enough (>104/g dry soil) to account for observed rates of nitrification. Results are discussed in relation to heterotrophic nitrification in soils, and the practical implications of spreading slurry on agricultural land.  相似文献   

4.
Peanut (Arachis hypogea cv. Shulamit) grown on very high calcium carbonate (CaCO3) content soils is showing iron (Fe) chlorosis symptoms. Supplying the plant with ammonium sulphate ((NH4)2SO4) in the presence of nitrapyrin (N‐Serv) for preventing nitrification reduced Fe chlorosis. Nitrate (NO‐ 3) developed in the soil with time, even with nitrapyrin present. When ammonium (NH+ 4) was even less than 20% of the total mineral N in the soil, no Fe‐stress could be observed, suggesting that the NH+ 4 uptake by the plant and the consequence of hydrogen (H+) efflux occurs from the root to the rhizosphere, resulting in a decrease of redox potential near the root, and solubilizing enough Fe near the root to overcome the chlorosis.  相似文献   

5.
In the symbiosis between nodulated legume roots and arbuscular mycorrhizal (AM) fungi, the C and N economy can be influenced by the source of N-supply from either AM-derived NH4+ uptake or nodule-derived biological nitrogen fixation (BNF). This relationship was investigated in terms of NH4+ supply and BNF by the two symbionts. Nodulated Phaseolus vulgaris seedlings with and without AM, were hydroponically grown with either 0 N or 1 mM NH4+ supply. Plants were harvested at 30 days after emergence and measurements were taken for biomass, N2 fixation, photosynthesis, CO2 and O2 root respiration, calculated C and N economy. AM roots had higher NH4+ uptake and this was associated with the suppression of BNF and nodule growth. The higher NH4+ uptake in AM roots occurred with lower root maintenance respiration, compared to when N was derived from BNF. There was also an increase in the below-ground sink strength of NH4+ fed AM roots compared to NH4+ fed non-AM roots, as evidenced by the increases in root CO2 and O2 respiration and photosynthetic stimulation. These results indicate that although the AM root had higher total below-ground respiratory costs during NH4+ nutrition, there were lower respiratory C costs associated with N derived from AM symbionts in comparison to N from BNF.  相似文献   

6.
Ammonium salts used as fertilizers may cause soil acidification by two different processes: nitrification in soil and net release of protons from roots. Their influence on soil pH may vary depending on the distance from root surface. The aim of this study was to distinguish between these two processes. For this purpose rape seedlings were grown 10 d in a system which separated roots from soil by a fine-meshed screen. As a function of distance from the plane root layer formed on the screen, pH, titratable and exchangeable acidity and NO3- and NH4-nitrogen were determined. The soil, a luvisol from loess, was supplied with no N or (NH4)2SO4 either with or without a nitrification inhibitor (DCD). The bulk soil pH remained unaffected when no N or 400 mg NH4? N kg?1 soil plus DCD was applied but it decreased from 6.6 to 5.8 without DCD. In contrast, rhizosphere pH decreased in all cases, mainly within a distance of 1 mm from the root plane only, but with gradients extending to between 2 and 4 mm into the soil. The strongest pH decrease, from 6.6 to 4.9, occurred at the root surface of plants treated with both NH4-N and DCD where most of the mineral N remained as ammonium. In this case Al was solubilized in the rhizosphere as indicated by exchangeable acidity. Total soil acidity produced in the NH4 treatment without DCD was mainly derived from nitrification compared to root released protons. However, acidification of the rhizosphere was diminished by nitrification because nitrate ions taken up by the roots counteracted net proton release. It is concluded that nitrification inhibitors may reduce proton input from ammonium fertilizers but enhance acidification at the soil-root interface which may cause Al toxicity to plants.  相似文献   

7.
The effects on nitrification and acidification in three subtropical soils to which (NH4)2SO4 or urea had been added at rate of 250 mg N kg−1 was studied using laboratory-based incubations. The results indicated that NH4+ input did not stimulate nitrification in a red forest soil, nor was there any soil acidification. Unlike red forest soil, (NH4)2SO4 enhanced nitrification of an upland soil, whilst urea was more effective in stimulating nitrification, and here the soil was slightly acidified. For another upland soil, NH4+ input greatly enhanced nitrification and as a result, this soil was significantly acidified. We conclude that the effects of NH4+ addition on nitrification and acidification in cultivated soils would be quite different from in forest soils. During the incubation, N isotope fractionation was closely related to the nitrifying capacity of the soils.  相似文献   

8.
 N2O emissions from a transplanted irrigated rice grown on a Typic Ustochrept soil at New Delhi, India, were studied to evaluate the effect of N fertilizers, i.e. urea and (NH4)2SO4, alone and in combination with the nitrification inhibitors dicyandiamide (DCD) and thiosulphate. The addition of urea and (NH4)2SO4 increased N2O emissions considerably when compared to no fertilizer N application (control). N2O measurement in the field was done by a closed-chamber method for a period of 98 days. The application of urea with DCD and thiosulphate reduced N2O fluxes considerably. The highest total N2O-N emission (235 g N2O-N ha–1) was from the (NH4)2SO4 treatment, which was significantly higher than the total N2O-N emission from the urea treatment (160 g N2O-N ha–1). DCD reduced N2O-N emissions by 11% and 26% when applied with urea and(NH4)2SO4, respectively, whereas thiosulphate in combination with urea reduced N2O-N emissions by 9%. Total N2O-N emissions were found to range from 0.08% to 0.14% of applied N. N2O emissions were low during submergence and increased substantially during drainage of standing water. Received: 20 October 1999  相似文献   

9.
Plants have the ability to suppress microbial nitrification process through secondary metabolites released from their root exudates or/and leaf litter. For decades, grasses were suggested to control nitrification process, and recently, Brachiaria humidicola accession 26159 (BH) as a tropical and subtropical grass has been shown to reduce nitrification rates under laboratory and soil conditions. In this study, experiments were conducted under controlled conditions in nutrient solution culture to investigate whether the reported release of natural nitrification inhibitors from root exudates of BH is an active or passive phenomenon. So different variables such as N-form (nitrate vs. ammonium), collecting medium (distilled water vs. 1 mM NH4Cl) and collecting period (6 vs. 24 hrs) were included to study the hypothesis. Results showed when root exudates were collected in distilled water there was no nitrification inhibition activity for all ammonium and nitrate grown plants. However, when collection was done in a medium containing 1 mM NH4Cl, root exudates showed significant nitrification inhibition activity similar to results obtained by Subbarao et al. The observed nitrification inhibition activity had a positive correlation to ammonium treatment particularly in collection medium, probably due to root cells damage induced by low pH and membrane depolarization under ammonium nutrition. This was more supported by application of shoot homogenates of NH4+, NO3? or NH4NO3 grown plants that showed significant nitrification inhibition activity compared to distilled water and DMPP controls in a bioassay test, independent of N-form. Potassium concentrations in root exudates (as a result of potassium leakage) were found to increase in root washings of plants, which were grown with ammonium, particularly when root exudates were collected in 1 mM NH4Cl solution. In addition, higher electric conductivity of root washings after collection of root exudates in ammonium containing medium (low pH) and also in nitrate containing medium which adjusted to pH 3 by applying H2SO4, strongly suggest that release of natural nitrification inhibitors from root exudates of B. humidicola may not be an active process, but instead it is rather a passive phenomenon by ammonium induced root physicochemical damages.  相似文献   

10.
Emissions of N2O and CH4 and CH4 oxidation rates were measured from Lolium perenne swards in a short-term study under ambient (36 Pa) and elevated (60 Pa) atmospheric CO2 at the Free Air Carbon dioxide Enrichment experiment, Eschikon, Switzerland. Elevated pCO2 increased (P<0.05) N2O emissions from high N fertilised (11.2 g N m−2) swards by 69%, but had no significant effect on net emissions of CH4. Application of 13C-CH4 (11 μl l−1; 11 at.% excess 13C) to closed chamber headspaces in microplots enabled determination of rates of 13C-CH4 oxidation even when net CH4 fluxes from main plots were positive. We found a significant interaction between fertiliser application rate and atmospheric pCO2 on 13C-CH4 oxidation rates that was attributed to differences in gross nitrification rates and C and N availability. CH4 oxidation was slower and thought to be temporarily inhibited in the high N ambient pCO2 sward. The most rapid CH4 oxidation of 14.6 μg 13C-CH4 m−2 h−1 was measured in the high fertilised elevated pCO2 sward, and we concluded that either elevated pCO2 had a stimulatory effect on CH4 oxidation or inhibition of oxidation following fertiliser application was lowered under elevated pCO2. Application of 14NH415NO3 and 15NH415NO3 (10 at.% excess 15N) to different replicates enabled determination of the respective contributions of nitrification and denitrification to N2O emissions. Inhibition of CH4 oxidation in the high fertilised ambient pCO2 sward, due to competition between NH3 and CH4 for methane monooxygenase enzymes or toxic effects of NH2OH or NO2− produced during nitrification, was hypothesised to increase gross nitrification (12.0 mg N kg dry soil−1) and N2O emissions during nitrification (327 mg 15N-N2O m−2 over 11 d). Our results indicate that increasing atmospheric concentrations of CO2 may increase emissions of N2O by denitrification, lower nitrification rates and either increase or decrease the ability of soil to act as a sink for atmospheric CH4 depending on fertiliser management.  相似文献   

11.
The effects of 15N-labelled urea, (NH4)2SO4 and KNO3 on immobilization, mineralization, nitrification and ammonium fixation were examined under aerobic conditions in an acid tropical soil (pH 4.0) and in a neutral temperate soil (pH 6.8). Urea, (NH4)2SO4 and KNO3 slightly increased net mineralization of soil organic nitrogen in both soils. There was also an apparent Added Nitrogen Interaction (ANI) i.e. added labelled NH4-N stood proxy for unlabelled NH4-N that would otherwise have been immobilized. So far as immobilization and nitrification were concerned, urea and (NH4)2SO4 behaved very similarly in each soil. Immobilization of NO3-N was negligible in both soils. Some of the added labelled NH4-N was rapidly fixed, more by the temperate soil than by the tropical soil. This labelled fixed NH4-N decreased during incubation, in contrast to labelled organic N, which did not decline.  相似文献   

12.
Methane mitigation in flooded Louisiana rice fields   总被引：6，自引：0，他引：6  
Summary A field experiment was conducted to determine whether selected nitrification inhibitors (encapsulated calcium carbide and dicyandiamide) and SO inf4 sup-2 -containing compounds [(NH4)2SO4 and Na2SO4] had mitigating effects on CH4 emissions from flooded rice. Microplots were established within a rice bay drill-seeded with the Texmont rice cultivar and CH4 fluxes were measured over the main rice cropping season. Methane emissions over the 77-day sampling period were approximately 230, 240, 260, 290, 310, and 360 kg CH4 ha-1 from the calcium carbide, Na2SO4-rate II, Na2SO4-rate I, (NH4)2SO4, dicyandiamide, and urea (control) treatments, respectively. Reductions in CH4 evolution, compared to the control, ranged from 14 to 35%, depending on treatment. The selected inhibitors and SO inf4 sup-2 -containing compounds appear to be effective in reducing the CH4 emitted from flooded rice fields.  相似文献   

13.
Abstract

Captan [N‐(trichloromethylthio)‐4‐cyclo‐hexene‐l, 2‐dicarboximide] and benomy1[methyl 1‐(butylcarbamoyl)‐2‐benzimidazolecarbamate] were evaluated as nitrification inhibitors and compared with nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine]. Nitrapyrin, captan, and benorayl were applied at 0, 20, 40, and 60 mg/kg with three nitrogen sources, KNO3, (NH4)2SO4, and urea, at 300 mg N/kg to ‘Cherry Belle’ radish (Raphanus sativusL). Nitrapyrin and captan inhibited nitrification effectively, but benomyl was not an effective inhibitor. Growth of radish roots and shoots was restricted with application of nitrapyrin and captan combined with (NH4)2SO4or urea relative to the comparable KNO3treatments. The concentrations of Ca, Mg, and NO3‐N in plants, especially in shoots, fell, and the percentage of ? was increased with the addition of nitrapyrin and captan. Benomyl did not affect plant growth or composition  相似文献   

14.
Abstract

Degradation of dicyandiamide (DCD) was assayed in laboratory studies at 8, 15, and 22 C in a Decatur silt loam and in a Norfolk loamy sand. Dicyandiamide was very short lived at 22 C, with half‐lives of 7.4 and 14.7 days in the Decatur and Norfolk soils, respectively. In the Norfolk soil at 8 C, half‐life increased to 52.2 days. In a nitrificaton study of both soils at 22 C, 80 mg (NH4)2SO4‐N kg‐1 of soil was applied with 20 mg DCD‐N kg‐1 of soil and 100 mg kg‐1 (NH4)2S04‐N was added with 5% nitrapyrin. Distinct lag phases preceded zero order nitrification with the inhibitor treatments. Lag periods were 2 and 2.6 times the half life of DCD in the degradation study for Decatur and Norfolk soils, respectively. Like most nitrification inhibitors, the effectiveness of DCD decreases with increasing temperature. In the Norfolk loamy sand, nitrification inhibition by DCD was equal to nitrapyrin for up to 42 days, but in Decatur silt loam, DCD was less potent to nitrapyrin as a nitrification inhibitor.  相似文献   

15.
Abstract

Nitrapyrin, terrazole and simazine were evaluated as chemical inhibitors of biological nitrification and denitrification. Corn (Zea mays L. cv. Hybrid Pioneer 3343) was grown in 60‐liter pots filled with a 50/50 (V/V) sand/Cecil clay mixture. Chemical treatments consisted of weekly applications of 0.25 ppm nitrapyrin, terrazole and/or simazine concurrently with 20 ppm N as either (NH4)2SO4 or Ca(NO3)2 for 9 weeks. Thereafter, only N (20 ppm per pot) was applied to the media every three days for 4 weeks. Nitrapyrin, terrazole and simazine reduced nitrification resulting in both higher total plant N and residual soil NH4 content relative to the control plants and soil. Plant growth was reduced by the inhibitory effects of the chemicals on nitrification and subsequent NH4 accumulation in the medium. All chemicals reduced denitrification with terrazole being more effective than nitrapyrin as reflected by higher N contents of plants and residual soil NO3‐N. Nitrapyrin and/or terrazole applied with Ca(NO3)2 increased plant biomass, but simazine, by inducing higher N02 concentration in the plant tissues, sharply reduced plant growth relative to the other treatments. When simazine was part of the chemical treatment, its effects on plant growth and total N contents generally outweighed or masked those of nitrapyrin or terrazole.  相似文献   

16.
The simultaneous nitrification and diffusion of NH4+, applied as ammonium sulphate to laboratory columns, was followed experimentally and with a simulation model. Ammonium was applied as a fertilizer band at levels equivalent to 69 kg N ha?1 to a 1 cm depth. The concentration profiles of NH4+, NO3?, SO2?4 and pH were measured in two columns for incubation times of 214 and 286 h. The simulation model provided for the precipitation and ion pair formation of CaSO4, the adsorption equilibria of NH4+ and soil acid with the soil solid phase, and nitrifier growth and activity. In general, good agreement was found between the experimental and simulated concentration profiles. The effect of CaSO4 precipitation on the diffusion of N was investigated using model simulations of the diffusion of NH4+ in the absence of nitrification. The simulations suggested that the reactions of SO2?4 in the soil could markedly affect the spread of NH4+ from a band of (NH4)2SO4.  相似文献   

17.
Soil was incubated under greenhouse conditions with plant residues having varying phenolic and nitrogen contents. The total plant material added in staggered applications every 4 months was 15 g kg?1 soil and the total incubation period was 12 months.The N-mineralization in these plant residues as influenced by their phenol and N contents was examined. The nitrification of applied (NH4)2SO4 in these amended soils was also investigated under optimum conditions of pH.A high plant-N content resulted in increased N-mineralization of plant residue, but this effect was lowered by the presence of high concentrations of polyphenols in the decomposing residue, most probably due to increased participation of N with polyphenols in the formation of humus fractions.Soils amended with phenol-rich residues did not show any inhibition of nitrification of applied (NH4)2SO4. Possible reasons are discussed. In organic matter decomposition, the quality of the leaf polyphenols appears to determine the degree of inhibition to soil nitrification.  相似文献   

18.
The effects of urea, (NH4)2SO4, KNO3, and NH4NO3 on nitrous oxide (N2O) emission from soil at field capacity and submerged condition were studied during 120 days in the laboratory. Soils in both moisture regimes gave higher emissions in the beginning, which were reduced later. Total emission of N2O was higher at submergence as compared to field capacity regardless of fertilizer type. At field capacity soil fertilized with ureaemitted the highest amount of N2O (1903 μg N2O-N kg-1 soil) during 120 days while at submerged condition, soil with NH4NO3 gave the highest emission (4843 μg N2O-N kg-1 soil). In another study, the efficacy of seven nitrification inhibitors in reducing the emission of N2O-N from soil fertilized with urea was tested in the laboratory. Nitrapyrin, 2-amino-4-chloro-6-methylpyrimidine (AM), and dicyandiamide (DCD) reduced the emission to 12, 24, and 63% that of urea, respectively, whereas sodium thiosulphate, sulphur, acetylene,and thiourea had no effect on emission of N2O. In submerged conditions none of the inhibitors reduced the emission.  相似文献   

19.
For understanding the effects of nitrification ability on nitrogen (N) use efficiency and N losses via denitrification in paddy soils under flooding conditions, six paddy soils with different nitrification activities were sampled from various sites of China and a pot experiment was conducted. Rice plants at tillering stage were transplanted into pots and harvested 7.5 days after transplanting, 15N-(NH4)2SO4 was applied 2.5 days after rice transplanting under continuously flooding conditions. The N losses by denitrification were determined by the unrecovered 15N applied as 15NH4 + and the N use efficiency (NUE) was calculated by 15N taken up by rice plants. Plant height (from 33.8 to 37.3 cm) and biomass (from 1.07 g pot?1 to 1.52 g pot?1) increased significantly with the native NH4 + concentration in the studied soils (P < 0.01). The NUE decreased, whereas the N losses via denitrification increased due to the increase in the nitrification rate of soils determined at 60% water holding capacity (P < 0.05). The results implied that the nitrification activity of paddy soils is a key factor in controlling NUE and N losses via denitrification.  相似文献   

20.
Abstract

The persistence of the effects of four nitrification inhibitors (2‐ethynylpyridine, nitrapyrin, etridiazole, 3‐methylpyrazole‐l‐carboxamide) on nitrification in soil was assessed by measuring the ability of two soils to nitrify NH4 + [added as (NH4)2SO4] after they had been treated with 5 μg inhibitor g‐1 soil and incubated at 10, 20, or 30°C for 0, 21, 42, 84, 126, or 168 days. The soils used differed markedly in organic‐matter content (1.2 and 4.2% organic C). The data obtained showed that the persistence of the effects of the inhibitors studied decreased markedly with increase in soil temperature from 10 to 30°C and that, whereas the initial inhibitory effects of the test compounds on nitrification were greatest with the soil having the lower organic‐matter content, the persistence of their effects at 20 or 30°C was greatest with the soil having the higher organic‐matter content. The inhibitory effects of 2‐ethynylpyridine and etridiazole on nitrification were considerably more persistent than those of nitrapyrin or 3‐methylpyrazole‐l‐carboxamide and were significant even after incubation of inhibitor‐treated soil at 20°C for 168 days.  相似文献   

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