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1.
Abstract

A sandy soil was amended with various rates (20 – 320 g air-dry weight basis of the amendments per kg of air-dry soil) of chicken manure (CM), sewage sludge (SS), and incinerated sewage sludge (ISS) and incubated for 100 days in a greenhouse at 15% (wt/wt) soil water content. At the beginning of incubation, NH4-N concentrations varied from 50 – 280 mg kg?1 in the CM amended soil with negligible amounts of NO3-N. Subsequently, the concentration of NH4-N decreased while that of NO3-N increased rapidly. In soil amended with SS at 20 – 80 g kg?1 rates, the NO3-N concentration increased sharply during the first 20 days, followed by a slow rate of increase over the rest of the incubation period. However, at a 160 g kg?1 SS rate, there were three distinct phases of NO3-N release which lasted for160 days. In the ISS amended soil, the nitrification process was completed during the initial 30 days, and the concentrations of NH4-N and NO3-N were lower than those for the other treatments. The mineralized N across different rates accounted for 20 – 36%, 16 – 40%, and 26 – 50% of the total N applied as CM, SS, and ISS, respectively.  相似文献   

2.
Increased use of nitrogenous fertilizers in agriculture has led to the increased pollution of ground water and atmosphere. Certain plant products can be used as coating materials onto urea to reduce the N losses. We evaluated the effectiveness of citronella and palmarosa grass oils as nitrification inhibitors in a soil incubation study. The treatments (14) were combinations of 4 N sources (neem, citronella and palmarosa oil coated prilled ureas, and uncoated prilled urea), 2 coating thicknesses of oils (500 and 1000 mg kg?1) and 2 N levels (75 and 150 kg N ha?1), replicated thrice in a randomized block design. N levels at 75 and 150 kg ha?1 were equivalent to 34 and 68 mg N kg?1 soil, respectively. Results showed that N sources citronella (CCPU1000) and neem oil (NCPU1000) coated prilled ureas at 1000 mg kg?1 coating thickness with 75 kg ha?1 released similar amount of ammonical-N to uncoated prilled urea at 150 kg N ha?1, suggesting the beneficial effect of coated ureas. The highest nitrification inhibition (%) was recorded with NCPU1000, the reference nitrification inhibitor, which was significantly greater to all the other N sources at 7 days after incubation (DAI), and at par to CCPU1000 at 14 and 21 DAI.  相似文献   

3.
Sodium chloride, at rates up to 100 mg g?1, was added to a Sassafras sandy loam amended with finely-ground alfalfa to determine the effect of NaCl on CO2 evolution, ammonification, and nitrification in a 14-week study. A NaCl concentration of 0.25 mg g?1 significantly reduced CO2 evolution by 16% in unamended soil and 5% in alfalfa-amended soil. Increasing NaCl progressively reduced CO2 evolution, with no CO2 evolved from the soil receiving 100 mg NaCl g?1. A 0.50 mg NaCl g?1 rate was required before a significant reduction in decomposition of the alfalfa occurred. The NO?2-N + NO?3-N content of the soil was significantly reduced from 40 to 37 μg g?1 at 0 and 0.25 mg NaCl g?1, respectively in the unamended soil. In the alfalfa amended soil, nitrification was significantly reduced at 5 mg NaCl g?1. At 10 mg NaCl g?1, nitrification was completely inhibited, there being only 6 and 2 μg NO?2-N + NO?3-N g?1 in the alfalfa amended and unamended soil, respectively. In the alfalfa amended soil NH+4-N accumulated from 6 μg g?1 at the 0 NaCl rate to a maximum of 54 μg g?1 with 25 mg NaCl g?1. These higher NH+4-N values resulted in a 0.5 unit increase in the pHw over that of the 0 NaCl rate in the alfalfa amended soil. At NaCl concentrations above 25 mg g?1 there was a reduction in NH+4-N. The addition of alfalfa to the soil helped to alleviate the adverse affects of NaCl on CO2 evolution and nitrification.  相似文献   

4.
Two series of laboratory-scale vertical flow systems (flooded and nonflooded columns) were designed to compare nitrogen removal performance, nitrous oxide emission, and ammonia volatilization under different water levels upon treating diluted digested livestock liquid. In these systems, influent was supplied at three hydraulic loading rates (HLRs of 1.25, 2.5, and 5 cm day?1) during stage 1 and the rates were doubled during stage 2 when the water levels of nonflooded columns were elevated from zero to half the height of the soil column. After hydraulic loading rates doubled, the average removal rates of total nitrogen in flooded columns varied from 1.27 to 2.94 g?2 day?1 and those in nonflooded columns ranged from 1.23 to 3.88 g?2 day?1. The T-N removal at an HLR of 10 cm day?1 in the nonflooded column with an elevated water table level had higher efficiency than that in the flooded column, suggesting T-N removal is enhanced in the nonflooded column probably due to the improved coupled nitrification–denitrification process under the elevated water table level condition. On the other hand, there was a significant correlation (r 2 = 0.532, p < 0.001) between the N2O flux and redox potential that mainly corresponded to water levels and HLRs, suggesting anoxic or aerobic conditions stimulate N2O emission by enhancing the nitrification (nitrification–denitrification) process. In contrast, NH3 volatilization had a high flux in the anaerobic condition mainly because of flooding. Based on the experimental results, it is hypothesized a nonflooded condition with higher water table level (Eh range of ?160 to +260 mV) would be suitable to reduce N2O emission and NH3 volatilization peak value by at least half while maintaining relatively efficient nitrogen removal performance.  相似文献   

5.

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO3 ?) leaching and nitrous oxide (N2O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g?1 soil) and biomass N (63 to 28 μg N g?1), protease (361 to 694 μg tyrosine g?1 soil h?1) and deaminase (4.3 to 5.6 μg NH4 + g?1 soil h?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?109 to 2.77?×?109 g?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?107 to 3.01?×?108 g?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.  相似文献   

6.

Purpose

Dicyandiamide (DCD) has been used commercially in New Zealand to reduce nitrate leaching and N2O emissions in grazed pastures. However, there is a lack of information in the literature on the optimum rate of DCD to achieve the environmental benefits while at the same time reducing the cost of the technology. The objective of this study was to determine the effect of DCD application rate on its effectiveness to inhibit ammonia oxidizer growth and nitrification rate in a grazed pasture soil.

Materials and methods

The soil was a Templeton silt loam (Immature Pallic Soil; Udic Haplustepts) collected from Lincoln University Research Dairy Farm with a mixed pasture consisting of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) and was incubated alone (control) or with cow urine at 700 kg N/ha with 6 rates of DCD [0, 2.5, 5, 7.5, 10 (applied twice), 15 and 20 kg/ha] in incubation vessels. The incubation vessels were placed randomly in an incubator with a constant temperature of 12 °C. During 112 days of incubation, soil subsamples were taken at different time intervals to measure the concentrations of NO3 ?-N and NH4 +-N and the amoA gene copy numbers of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA).

Results and discussion

DCD applied at all the different rates inhibited nitrification in urine-treated soils, but the effectiveness increased with DCD application rate. In addition, AOB growth and the amounts of nitrate-N in the soil were significantly related to the application rate of DCD. However, AOA population abundance showed no relationship to the application rate of DCD. The DCD rate at which the AOB growth rate and nitrate-N concentration were halved (effective dosage that causes 50 % reduction in nitrification rate, or ED50) was about 10 kg DCD/ha.

Conclusions

These results suggest that DCD applied at relatively low rates still slowed down the nitrification rate, and the current recommended rate of 10 kg DCD/ha for DCD use in New Zealand grazed pastures would result in a 50 % reduction in nitrification rate in this soil. The actual rate of DCD application used would depend on the cost of the product and the environmental and agronomic benefits that would result from its use.  相似文献   

7.
Abstract

Two experiments were conducted to evaluate the inhibitory effects of 2-chloro-6 (trichloromethyl) pyridine (nitrapyrin) and dicyandiamide on nitrous oxide (N2O), a greenhouse gas, emission from soils amended with ammonium sulfate. In the two experiments, samples of an Andosol and a Gray Lowland soil were kept in glass vessels sealed with a butyl rubber cap and incubated at 25°C. In the first experiment, nitrapyrin (1 µg g?1 dry soil) and dicyandiamide (10 µg g?1 dry soil) were applied to samples of a water-saturated Andosol and a Gray Lowland soil to which ammonium sulfate had been applied at a rate of 0.1 mg N g?1 dry soil. Nitrapyrin decreased N2O emissions from the Andosol and the Gray Lowland soil by 71% and 24%, respectively. Dicyandiamide decreased N2O emissions from the Andosol and Gray Lowland soil by 31% and 18%, respectively. In the second experiment, nitrapyrin (1 µg g?1 dry soil) was applied to samples of an Andosol at 51% water-filled pore space to which ammonium sulfate had been applied at rates of 0.01, 0.1 and 0.5 mg N g?1 dry soil. Nitrapyrin decreased N2O emissions by 62%, 83% and 74%, respectively. Changes in the NH+ 4 and NO? 2 + NO? 3 concentrations in soil showed that nitrapyrin and dicyandiamide slowed down the nitrification process, but did not completely stop the process at any time. The results reveal the potential of nitrification inhibitors to decrease N2O emission from fertilized soil in a wide range of moisture conditions and nitrogen levels.  相似文献   

8.
Steaming of narrow soil bands prior to sowing is a new technique that reduces the need for intra-row weeding in herbicide-free row crops. However, the steam treatment may eliminate both weed seeds and non-target soil organisms, thereby affecting the nutrient cycling in the soil. This study tested the effect of band-steaming on N and C dynamics in a sandy loam soil that was steamed in situ to maximal temperatures of 70–90°C using a prototype band-steamer. Soil samples (0–5 cm depth) were collected during 90 days from band-steamed soil, undisturbed control soil, and control soil treated just mechanically with the band-steamer. In the steamed soil, ammonium concentrations increased from 1.1 to 20.3 μg NH 4 + -N g?1 dry weight during 28 days. This coincided with an immediate and persistent inhibition of potential nitrification (33–61% inhibition during 90 days). Assays of the temperature response of potential nitrification confirmed the temperature sensitivity and showed an optimum temperature of 27.1°C and a temperature coefficient (Q 10) of 1.9. The effects of band-steaming on concentrations of nitrate and water-soluble carbon were divergent and stimulatory, respectively, but generally not statistically significant. Mechanical effects of band-steaming were negligible. The observed ammonium surplus could be of agronomic benefit and should be evaluated in integrated studies of the effects of band-steaming on crop growth and plant N uptake.  相似文献   

9.
The effects of phenmedipham, propham, carbetamide, lenacil and benzthiazuron on soil nitrification was studied in the laboratory using a perfusion technique. The nitrification process was markedly retarded at a phenmedipham concentration of 50–500μg g?1 soil, so that 55–150 days were required for complete oxidation of supplied NH+4-N as compared with 33 days for the untreated control. Phenmedipham caused a reduction in both the maximum population and the proliferation rate of nitrifying organisms, as evaluated from kinetic parameters. These inhibitory effects showed a low persistance probably due to herbicide breakdown. The effects of 100 μg g?1 soil of propham, carbetamide, lenacil or benzthiazuron on the nitrification process was very weak, although the kinetics of the nitrification process was affected by all these herbicides.  相似文献   

10.
The effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N transformations and composition of ammonia-oxidizing bacteria (AOB) communities was investigated at the centimeter scale in a microcosm experiment under laboratory conditions. After 28 days, samples were collected from soil treated with urea or urea and DMPP at increasing distance from the fertilizer zone; this distance ranged from 0 to 5 cm in both horizontal and vertical directions. The results showed that DMPP application significantly increased soil pH and NH 4 + -N and mineral N (NH 4 + -N, NO 3 ? -N, and NO 2 ? -N) concentrations but decreased (NO 3 ? + NO 2 ? )-N concentration, and such effect was decreased by increasing the distance from the fertilizer zone. Fingerprint profiles of denaturing gradient gel electrophoresis showed that the number of bands decreased by increasing the distance from the fertilizer zone due to decreasing NH 4 + -N concentrations in the urea treatment. Compared to urea applied alone, DMPP application increased NH 4 + -N concentrations and decreased AOB diversity from 0 to 3 cm but promoted diversity from 3 to 5 cm distance from the fertilizer zone. A phylogenetic analysis showed that AOB communities were dominated by Nitrosospira cluster 3. Therefore, the nitrification inhibitor DMPP modified the composition of AOB communities by increasing the distance from the fertilizer zone and this probably was related to the changes in soil pH and inorganic N concentration.  相似文献   

11.
The fate of added 15N-labelled nitrite (15NO2?-N) was investigated in a laboratory experiment with two acidic pasture soils collected from northeast Victoria (Maindample and Ruffy) and an alkaline soil collected from Waurn Ponds, Victoria, Australia. Two and a half hours after mixing and extraction, the 15NO2?-N recovered in 2 M KCl extracts was 22% and 33% of the applied NO2? in Maindample and Ruffy soils, respectively, and 100% in the Waurn Ponds soil. There was no difference in NO3? recovered with and without NaClO3 addition during this procedure, suggesting that biological oxidation of the applied NO2? was not the cause of the low recovery. Of the applied 15NO2?-N, 21% and 20% in the acidic Maindample and Ruffy soils, respectively, were recovered from the organic pool where it is believed to have been chemically fixed, leaving the total loss of 15NO2? as 57% and 47% from these two soils, most likely due to chemical self-decomposition to NO and NO2. When extracted with 0.005 M KCl, the salt concentration used in the short-term nitrification assay (SNA) 51% and 42% of applied 15NO2? were recovered in the extract from Maindample and Ruffy soils, respectively, but the total losses were only 9% and 10% of the applied 15NO2?-N, respectively. The chemical fixation and self-decomposition of NO2? in acidic soils are likely to cause an underestimate of nitrification rates by SNA.  相似文献   

12.
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   

13.
The effects of temperature, moisture content and the addition of pig slurry on nitrification in two soils were studed. There was no accumulation of NO2?-N under the incubation conditions investigated and the accumulation of NO3?-N was linear for additions of 50–250 μg NH4+-N g? soil, either as ammonium sulphate or as pig slurry. Nitrate formation was treated as a single step, zero order process to enable a rate constant to be calculated. Nitrification rate increased with increasing moisture content up to the highest level tested, soil water potential ?8.0 kPa, corresponding to approximately 60% of water holding capacity in both soils. Measurable nitrification was found in both soils at the lowest moisture content (soil water potential ?1.5 MPa) and temperature (5° C) tested. The nitrification rate constant in soils treated with 50 μg NH4+-N g? soil was not significantly affected (P = 0.05) by the form of ammonium added. Addition of 250 μg NH4+-N as ammonium sulphate caused a marked inhibition of nitrification at all moisture contents and temperatures. Addition of 250 μg NH4+-N as pig slurry caused a marked increase in nitrification rate, the increase being greater at the higher temperatures and moisture contents.  相似文献   

14.
硝化反应是土壤、特别是干旱半干旱地区农业土壤N2O产生的重要途径之一。但是,目前环境条件对硝化反应中N2O排放的影响研究较少,而在国内外通用的几个模型中均用固定比例估算硝化反应过程中N2O的排放。本文通过砂壤土培养试验,研究了土壤温度、水分和NH4+-N浓度对硝化反应速度及硝化反应中N2O排放的影响,并用数学模型定量表示了各因素对硝化反应的作用,用最小二乘法最优拟合求得该土壤的最大硝化反应速度及N2O最大排放比例。结果表明,随着温度升高,硝化反应速度呈指数增长;水分含量由20%充水孔隙度(WFPS)增加到40%WFPS时,反应速度增加,水分含量增加到60%WFPS时反应速度略有降低;NH4+-N浓度增加对硝化反应速度起抑制作用。用米氏方程描述该土壤的硝化反应过程,其最大硝化反应速度为6.67mg·kg?1·d?1。硝化反应中N2O排放比例随温度升高而降低;随NH4+-N浓度增加而略有增加;20%和40%WFPS水分含量时,硝化反应中N2O排放比例为0.43%～1.50%,最小二乘法求得的最大比例为3.03%,60%WFPS时可能由于反硝化作用,N2O排放比例急剧增加,还需进一步研究水分对硝化反应中N2O排放的影响。  相似文献   

15.
Soils stored in stockpiles during opencast mining operations accumulate significant quantities of ammonium (of the order of 200 μg NH4+-N g?1 soil) within the predominantly anaerobic cores of mounds. Upon stockpile dismantling and land restoration, this NH+4-N is rapidly oxidized to NO?3-N, which is readily lost from newly restored soil ecosystems by leaching and denitrification. Experiments were set up to examine how these significant reserves of mineral N might be conserved in such situations. Application of the nitrification inhibitor dicyandiamide was successful in minimizing NO3?-N lost by leaching, though large concentrations of NH4+-N were detected in drainage waters. Straw incorporation decreased nitrate leaching by up to 40%; biomass C was some 40% greater in straw-amended than in unamended soils after 14 weeks, though biomass N was similar in both. Addition of nitrogen-free organic materials (glucose, starch and cellulose) produced different results, with glucose amendment showing the greatest reduction in nitrate leaching in the short term (due to an apparent stimulation of denitrification) whereas addition of cellulose resulted in the most effective conservation of nitrogen over 14 weeks; this was due, at least in part, to uptake of mineral N by the soil microbial biomass.  相似文献   

16.

Purpose

Input of N as NH4 + is known to stimulate nitrification and to enhance the risk of N losses through NO3 ? leaching in humid subtropical soils. However, the mechanisms responsible for this stimulation effect have not been fully addressed.

Materials and methods

In this study, an acid subtropical forest soil amended with urea at rates of 0, 20, 50, 100 mg N kg?1 was pre-incubated at 25 °C and 60 % water-holding capacity (WHC) for 60 days. Gross N transformation rates were then measured using a 15N tracing methodology.

Results and discussion

Gross rates of mineralization and nitrification of NH4 +-N increased (P?<?0.05), while gross rate of NO3 ? immobilization significantly decreased with increasing N input rates (P?<?0.001). A significant relationship was established between the gross nitrification rate of NH4 + and the gross mineralization rate (R 2?=?0.991, P?<?0.01), so was between net nitrification rate of NH4 + and the net mineralization rate (R 2?=?0.973, P?<?0.05).

Conclusions

Stimulation effect of N input on the gross rate of nitrification of NH4 +-N in the acid soil, partially, resulted from stimulation effect of N input on organic N mineralization, which provides pH-favorable microsites for the nitrification of NH4 + in acid soils (De Boer et al., Soil Biol Biochem 20:845–850, 1988; Prosser, Advan Microb Physiol 30:125–181, 1989). The stimulated gross nitrification rate with the decreased gross NO3 ? immobilization rate under the elevated N inputs could lead to accumulation of NO3 ? and to enhance the risk of NO3 ? loss from humid forest soils.
  相似文献   

17.
Inhibition of nitrification as a mitigation tool to abate nitrogen (N) losses and improve N use efficiency (NUE) is a promising technology. Nitrification inhibitor (dicyandiamide, DCD) was evaluated in two consecutive wheat-maize rotations (2015–2017), with two different N fertilizer levels applied in wheat (160, 220 kg N ha?1) and maize (180, 280 kg N ha?1). More NH4+-N contents (101% and 102% in wheat and 74% and 73% in maize) and less NO3–-N contents (37% and 43% in wheat and 46% and 57% in maize) were observed at both N levels treated with DCD compared to without DCD. Higher pH, lower EC and reduced NO3–-N accumulation were the other benefits of DCD. The NO3–-N accumulation within the 0–200 cm soil profile was significantly less at both N levels with DCD (66 mg kg?1 and 121 mg kg?1) compared to without DCD (96 mg kg?1 and 169 mg kg?1). Application of DCD also improved the growth and yield in both crops. Increase in NUE from 38% to 49% in wheat and 27% to 33% in maize with DCD at higher N level was also observed. Overall, the effectiveness of DCD in retarding the nitrification process was higher in wheat than maize.  相似文献   

18.
Abstract

Herbicides have potential for economical and efficient site preparation following timber harvest. The effects of tebuthiu‐ron, one of the herbicides approved for this use, on soil nitrogen (N) mineralization and nitrification were determined in laboratory incubations. Tebuthiuron was added at rates from 0 to 1000 μg g‐1 to three soils. There was no effect of tebuthiuron additions of less than 1 μg g‐1 on soil N mineralization and nitrification. Tebuthiuron reduced nitrification in all soils at 1000 μg g‐1 and in two of the soils at 100 μg g‐1 . All soils had increased net mineralization with tebuthiuron added at 100 and 1000 μg g‐1. The addition of 50 μg NH+ 4‐N and 1000 μg tebuthiuron g‐1 resulted in increased net mineralization in the three soils. Nitrification was affected differently in each of the three soils by the addition of both NH+ 4‐N and tebuthiuron. The added NH+ 4‐N either removed the inhibition of nitrification by the herbicide or had no effect on the inhibition in two of the soils. In the third soil, nitrification was reduced by the addition of NH+ 4‐N.

The presence of NO‐ 3‐N in these acid soils and the effects of added NH+ 4‐N on NO‐ 3‐N production suggest that heterotrophic nitrification occurs in at least two of the soils. The findings of this study indicate that any effects of tebuthiuron on N mineralization and nitrification at the currently recommended application rates are likely to be transient and localized.  相似文献   

19.
The occurrence of nitrification in some acidic forest soils is still a subject of debate. Identification of main nitrification pathways in acidic forest soils is still largely unknown. Acidic yellow soil (Oxisol) samples were selected to test whether nitrification can occur or not in acidic subtropical pine forest ecosystems. Relative contributions of autotrophs and heterotrophs to nitrification were studied by adding selective nitrification inhibitor nitrapyrin. Soil NH4+-N concentrations decreased, but NO3--N concentrations increased significantly for the no-nitrapyrin control during the first week of incubation, indicating that nitrification did occur in the acidic subtropical soil. The calculated net nitrification rate was 0.49 mg N kg-1 d-1 for the no-nitrapyrin control during the first week of incubation. Nitrapyrin amendment resulted in a significant reduction of NO3--N concentration. Autotrophic nitrification rate averaged 0.28 mg N kg-1 d-1 and the heterotrophic nitrification rate was 0.21 mg N kg-1 d-1 in the first week. Ammonia-oxidizing bacteria (AOB) abundance increased slightly during incubation, but nitrapyrin amendment significantly decreased AOB amoA gene copy numbers by about 80%. However, the ammonia-oxidizing archaea (AOA) abundance showed significant increases only in the last 2 weeks of incubation and it was also decreased by nitrapyrin amendment. Our results indicated that nitrification did occur in the present acidic subtropical pine forest soil, and autotrophic nitrification was the main nitrification pathway. Both AOA and AOB were the active biotic agents responsible for autotrophic nitrification in the acidic subtropical pine forest soil.  相似文献   

20.
烤烟钾素库源关系生理调控措施研究   总被引：8，自引：2，他引：8  
在大田生产条件下 ,采用单株挂牌设置处理的研究方法 ,研究涂抹生长素与其它不同生长调节剂和烟株顶端调控等措施对烤烟钾吸收及其在库源中再分配的影响。结果表明 ,现蕾后不打顶或打顶结合生长素处理茎断面均有利于不同部位叶片含钾量的提高 ,以打顶结合涂抹生长素效果更好 ;内源生长素和外源生长素都有利于烟株体内的钾素向叶片中分配 ,其中外源生长素的活性更强 ,能更有效地提高烟株叶片的含钾量 ,且涂抹 2次比涂抹 1次的效果好 ,但涂抹次数间差异不显著。  相似文献   

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