Nitrogen transformations of ammonium sulfate and alanine in submerged Maahas clay

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.     

Nitrification activity in submerged soils and its relation to denitrification loss

Summary Nitrification activity (formation of NO ₂ ^– + NO ₃ ^– per unit soil weight) was measured in the surface layer of 15 presubmerged soils incubated in petri dishes under flooded but aerobic conditions. soils with pH above 5 nitrified quickly, whereas soils with pH below this level did not nitrify or nitrified slowly. The pH values between 7 and 8.5 were optimal for nitrification. Organic-matter levels in the 15 soils of our study did not influence their nitrification activities. In a follow-up greenhouse pot study, after a period of 3 weeks, ¹⁵N-balance measurements showed that the loss of N through apparent denitrification did not follow the nitrification patterns of the soils observed in the petri dishes. Apparent denitrification accounted for 16.8% and 18.9% loss of ¹⁵N from a soil with insignificant nitrification activity and a soil with high nitrification activity, respectively. These results, thus, indicate a lack of correspondence between the nitrification activities of soil and the denitrification loss of N when the former was measured in the dark and the latter was estimated in the light. Soils that nitrified in the darkness of the incubator did not nitrify in the daylight in the greenhouse.     

Some factors influencing denitrification and nitrogen immobilization in a clay soil

Nitrate-N, enriched with ¹⁵N, was added to small cores of the 0–10 cm layer of a clay soil. The base of each core was sealed, then water, equivalent to 0, 10, 20 or 30mm of rain, was added to the soil surface. The cores were incubated for 1 week at 10, 20, or 30°C in the presence or absence of wheat straw. The recovery of ¹⁵N in the soil mineral-N and organic-N fractions was then measured.No significant losses of ¹⁵N were detected in the cores which received 0–10 mm of added water, and in which the soil water content was close to 0.56 g g^?1 (?10 kPa). However, ¹⁵N losses, assumed due to denitrification, were rapid from cores receiving 20 or 30 mm of water and incubated at 20–30°C. The onset of denitrification was quite sudden as the amount of added water increased from 10 to 20 mm. In this range, a small increment of added water apparently sealed a relatively large volume of soil from atmospheric O₂ diffusion. This phenomenon was strongly temperature-dependent since no losses were detected from any cores at 10°C even though the 30mm addition of water produced a thin layer of free water across the soil surface.The addition of straw did not promote denitrification in soil at water contents close to 0.56 g g^?1. At high soil water contents, adcling straw increased immobilization of labelled NO₃^? and so reduced denitrification losses. The response of immobilization to changing soil water and temperature conditions was very different from that of denitrification.     

土壤熏蒸剂对土壤硝化、反硝化作用的影响

采用化学分析和变性梯度凝胶电泳(DGGE)技术,以大田威百亩、棉隆、溴甲烷、硫酰氟熏蒸100 d土壤为研究对象,探究土壤熏蒸对土壤硝化活性、反硝化活性及amoA基因型硝化型细菌、nirS基因型反硝化细菌群落结构影响。研究表明,威百亩、棉隆、硫酰氟熏蒸剂处理下,土壤硝化活性与对照无显著差异;而溴甲烷处理的硝化活性比对照降低13.19%,差异显著(P0.05);熏蒸剂之间土壤硝化活性无显著差异。4种熏蒸剂之间以及与对照之间土壤反硝化活性无显著差异。4种熏蒸剂中溴甲烷处理土样amoA型硝化细菌多样性指数、均匀度显著低于对照土样和其他3种熏蒸剂处理土样;而丰富度指数无显著差异。威百亩、棉隆和硫酰氟熏蒸土样之间及与对照之间amoA型硝化细菌3种生态指数无明显差异。4种熏蒸剂处理土壤nirS型反硝化细菌多样性指数、均匀度与对照无显著差异(P0.05);熏蒸剂之间存在显著差异(P0.05)。研究表明,溴甲烷对土壤硝化活性的抑制是通过抑制amoA型硝化细菌的多样性而实现,其他3种熏蒸剂对土壤硝化活性无显著影响。4种熏蒸剂对土壤反硝化活性无显著影响。     

Column studies of denitrification in soil

Small columns, 2.5 cm dia and of different lengths, were filled with an air-dried. Hanford sandy loam and leached with CaCl₂ (0.001 n) and nitrate (10–100 μg/ml N) for 3 weeks. The average NO₃ N concentration of the leachate during the last 12 days of the experiment was used to calculate denitrification rates. The net reaction of NO₃^? appeared to be zero order with the 50 and 100 μg/ml NO₃ N applications with a rate constant of 0.27 μg/ml/h N residence time for columns 5–50 cm long. Nitrate was not completely lost with the lower NO₃^? N applications; this implies that greater than zero order reactions can also occur. Although N₂ gas evolution was not measured, most N was doubtless volatilized since analysis of selected soil samples at the end of the experiment indicated no net assimilation of the NO₃ N.     

洁霉素在黏土和有机质土中的吸附特性研究

抗生素一般是指由细菌、霉菌或其他微生物在繁殖过程中产生的,能够杀灭或抑制其他微生物的一类物质及其衍生物。目前,抗生素被广泛应用于人们的日常生活与水产及畜牧等产业。美国每年应用于水产养殖的抗生素达9.25×104～19.6×104 kg[1],应用于动物养殖中的抗生素每年约8.5×106～11.2×106 kg[2]。     

Participation of iron in denitrification in waterlogged soil

A study was made of the formation of anaerobiosis in a waterlogged soil. A dilute soil suspension containing NO^?₃, Fe³⁺, sodium citrate, a limited amount of O₂, and trace elements was used as a model of waterlogged soil. Polarography was used to detect dissolved O₂, Fe³⁺ and Fe²⁺. The fates of the NO^?₃ and Fe³⁺ during and after O₂ consumption by the microorganisms were studied in a specially designed vessel. A close correspondence was obtained between the reduction of NO^?₃, NO^?₂ and Fe³⁺ and the growth of denitrifying bacteria in the closed system employed. From the experimental results we presume that microorganisms which respire NO^?₃ are also capable of utilising Fe³⁺ in their respiration. The mechanisms of reduction of these chemical species by the microorganisms are also discussed, emphasising the possibility of the participation of chemical reduction of NO^?₂ by Fe²⁺ in the over-all reduction process.     

Nitrogen losses from the field: denitrification and leaching in intensive winter cereal production in relation to tillage method of a clay soil

Abstract. Losses of soil and fertilizer nitrogen by leaching and denitritication from a clay soil in southern England have been measured over four years. Nitrate losses in drainage water from direct-drilled land averaged 20–30 kg N ha 'a' with wide seasonal variation. Ploughing and conventional cultivations increased this loss. Denitritication from direct-drilled land averaged 5–10 kg N ha 'a' with wide seasonal variation. Ploughing and drainage both diminished denitritication losses but cultivation had the greater effect. These nitrogen losses occurred mainly in autumn and spring.
Nitrogen losses, in drainage water or by denitritication after spring fertilizer applications, were related to the rainfall in the 28 days following top dressing. Approximately 40 mm rain was needed to cause a loss of 10% of the nitrogen applied but in practice losses were quite variable.     

Phases of denitrification following oxygen depletion in soil

The short-term response of soil denitrification to reduced aeration was studied using the acetylene inhibition method for the assay of denitrification. Two distinct phases of denitrification rate were observed. An initial constant rate, termed phase I, was not decreased by chloramphenicol, was increased slightly or not at all by organic carbon amendment, and lasted for 1–3 h. Phase I was attributed to the activity of pre-existing denitrifying enzymes in the soil microflora. Following phase I the denitrification rate increased; chloramphenicol inhibited this increase. In soils without organic-C amendment a second linear phase, termed phase II, was attained after 4–8 h of anaerobic incubation. The linearity of this phase was attributed to the full derepression of denitrifying enzyme synthesis by the indigenous population and to the lack of significant growth of denitrifiers. Phase I rate was dependent on the initial or in situ aeration state of the soil sample; phase II was not. Therefore, phase I may be more directly related to field denitrification rates.Denitrification rate changes following water saturation of soils in aerobic atmospheres were also examined. Rates were greatly increased by wetting but only after a lag of several hours. Our interpretation is that following wetting of natural soils, anaerobic or partially anaerobic conditions are established by respiration and reduced O₂ diffusion rate; this first eliminates O₂ inhibition then derepresses the synthesis of denitrifying enzymes. Although denitrifying enzymes are apparently present even in relatively dry soils, their activity is low until O₂ inhibition is eliminated. From this evidence we reason that most N is lost from soils during brief periods beginning a few hours after irrigation or a rainfall.     

Effect of urease inhibitors on denitrification in soil

Abstract. The influence of three urease inhibitors, hydroquinone (HQ), phenyl phosphorodiamidate (PPDA) and N-(n-butyl) phosphorothioic triamide (NBPT) on denitrification of nitrate in soil was studied in an incubation experiment under waterlogged conditions, at 25°C and in the presence of increasing amounts (0.0, 0.1 and 1 %) of ground barley straw. Two hundred milligrams of nitrate-N (as potassium nitrate) was added with the respective urease inhibitors.
Addition of barley straw increased the denitrification rate in the soil. Within 2 days the added nitrate-N was completely reduced. This result was confirmed by the measurement of nitrous oxide. HQ decreased gaseous nitrogen loss by decreasing the activity of the denitrifiers in the soil. The inhibitory effect was increased by adding increasing amounts of HQ. Because denitrification is stimulated by readily decomposable organic matter, the retardation seems to be a short-term effect. The other urease inhibitors, PPDA and NBPT, had no significant influence on the denitrification process when they were applied at the rate of 4 mg per kilogram of soil.     

Effects of organic solvents on denitrification in soil

Summary Although organic solvents such as methanol and ethanol have been shown to act as energy sources for denitrifying microorganisms, no studies on the influence of organic solvents on denitrification in soil have been reported. Organic solvents have been used as an aid in the application of pesticides and other agricultural chemicals to soil, in studying the effects of these chemicals on denitrification in soil. During these applications, the soil is often aerated or heated to remove the solvent while leaving the chemical in the soil. The work reported here shows that treating soils with methanol, ethanol, or acetone had a very marked effect on their denitrifying ability, even when the soils were aerated thoroughly or heated at 50°C to remove these solvents. This indicates either that it is not possible to effect complete removal of organic solvents from soils by aeration or heating or that organic solvents promote denitrification by solubilizing a fraction of soil organic matter that is not available to denitrifying microorganisms before the addition of these solvents. Experiments using phenylmercuric acetate (a herbicide and nitrification inhibitor) showed that although this compound had a marked inhibitory effect on denitrification when added to soil in methanol, ethanol, or acetone, it had no inhibitory effect on denitrification when added to soil in water. The work reported shows that the use of an organic solvent in adding an agricultural chemical to soil can lead to erroneous conclusions in studies on the effects of the chemical on soil denitrification.     

Animal treading stimulates denitrification in soil under pasture

The effects of animal treading on denitrification in a mixed ryegrass-clover pasture were studied. A single treading event of moderate or severe intensity was applied in plots during spring by using dairy cows at varying stocking rates (4.5 cows 100 m⁻² for 1.5 or 2.5 h, respectively). Treading caused a significant short-term 21 days) increase in denitrification. Denitrification rates reached a maximum of 52 g N₂O-N ha⁻¹ day⁻¹ at 8 days after severe treading compared to 2.3 g N₂O-N ha⁻¹ day⁻¹ under nil treading. Thereafter, denitrification rates declined, and were similar to non-trodden control plots after 28 days. Soil aeration, was significantly reduced by treading as expressed by water-filled porosity. In addition, soil NH₄⁺-N and NO₃⁻-N concentrations were also increased by treading. We propose that the underlying processes involved in increasing denitrification under treading were two-fold. Firstly, treading caused a temporary (e.g. 3 days after treading) reduction in soil aeration through soil physical damage, and secondly, reduced soil N utilisation prompted by reduced plant growth led to increased soil NH₄⁺-N and NO₃⁻-N availability. This study shows that treading, without the influence of other grazing animal factors (e.g. excretion), can cause a large short-term stimulation of denitrification in grass-clover pastures.     

Participation of soluble and oxidizable soil organic compounds in denitrification

Summary The role of soluble organic carbon (SOC) in denitrification in four mineral soils and one organic soil was evaluated in laboratory studies. Denitrification capacities and SOC concentrations were determined by nitrate loss from air-dried flooded soil treated with a solution containing 100 g/ml N0₃ ^–-N, while the rate of consumption was measured by Warburg manometry on 20 g air-dried soils to which 10 ml water had been added. High correlation coefficients (r > 0.93) were obtained between denitrification capacities, SOC, and oxygen consumption in the five soils. A mineral soil was amended with extracts of an organic soil. After incubating for 1 week, denitrification capacity was enhanced and SOC concentrations decreased in that soil. Extracted mineral soil had a lower denitrification capacity than an unextracted one. Decreases in concentrations of SOC were related to color change. Infrared spectra of precipitates from soil extracts indicated that absorption at wave number 1420–1440 cm -1 was also related to the color changes. It was implied that low molecular weight fulvic acid like compounds represented the SOC mineralized in denitrification, and that their supply to soil solution by solubilization of organic matter influenced the denitrification rate in the soil.     

Influence of oxygen on denitrification and aerobic respiration in soil

Summary The influence of the partial pressure of oxygen on denitrification and aerobic respiration was investigated at defined P02 values in a mull rendzina soil. The highest denitrification and respiration rates obtained in remoistened, glucose- and nitrate-amended soil were 43 1 N₂0 h^–1g^–1 soil and 130 1 O₂ h^–1g^–1 soil, respectively. At -55 kPa matric water potential, corresponding to 40% water saturation, N₂0 was produced only below P0₂ 40 hPa. The K _m, for O₂ was 3.0 x 10^–6 M. Formation of N₂O and consumption of O₂ occurred simultaneously with half maximum rates at P0₂ 6.7–13.3 hPa. Nitrite accumulated in soil below 40 hPa and increased with decreasing pO₂. The upper threshold for N₂0 formation in amended soil was P0₂ 33–40 hPa (39-47 M O₂).     

Denitrification in drained and undrained arable clay soil

Emissions of nitrous oxide (N₂O) and nitrogen gas (N₂) from denitrification were measured using the acetylene inhibition method on drained and undrained clay soil during November 1980-June 1981. Drainage limited denitrification to about 65% of losses from undrained soil. Emissions from the undrained soil were in the range 1 to 12 g N ha^–1 h^–1 while those from the drained soil ranged from 0.5 to 6 g N ha^–1 h^–1 giving estimated total losses (N₂O + N₂) of 14 and 9 kgN ha^–1.
Drainage also changed the fraction of nitrous oxide in the total denitrification product. During December, emissions from the drained soil (1.8±0.6 gN ha^–1 h^–1) were composed entirely of nitrous oxide, but losses from the undrained soil (2.7 ± 1.1 g N ha^–1 h^–1) were almost entirely in the form of nitrogen gas (the fraction of N₂O in the total loss was 0.02). In February denitrification declined in colder conditions and the emission of nitrous oxide from drained soil declined relative to nitrogen gas so that the fraction of N₂O was 0.03 on both drainage treatments. The delayed onset of N₂O reduction in the drained soil was related to oxygen and nitrate concentrations. Fertilizer applications in the spring gave rise to maximum rates of emission (5–12g N ha^–1 h^–1) with the balance shifting towards nitrous oxide production, so that the fraction of N₂O was 0.2–0.8 in April and May.     

Nitrification and denitrification as sources of atmospheric nitrous oxide – role of oxidizable carbon and applied nitrogen

Laboratory incubation experiments were conducted to study the influence of easily oxidizable C (glucose) and mineral N (NH₄⁺ and NO₃^-) on N₂O emission, evolution of CO₂ and consumption of O₂. A flush of N₂O was always observed during the first few hours after the start of soil incubation, which was significantly higher with NH₄⁺ compared to NO₃^- applications. The increase in N₂O emission was attributed mainly to enhanced soil respiration and subsequent O₂ limitation at the microsite level. Application of NH₄⁺ helped to develop denitrifying populations since subsequent additions of NO₃^- and a C source significantly enhanced N₂O emissions. In soils treated with NH₄⁺, N₂O emissions declined rapidly, which was related to decreasing concentrations of easily oxidizable C. Addition of glucose in different amounts and pre-incubation of soil for different lengths of time (to create variation in the amount of easily oxidizable C) changed the pattern of N₂O emissions, which was ascribed to changes in soil respiration.     

Nitrification and denitrification in the rhizosphere of rice: the detection of processes by a new multi-channel electrode

 N turnover in flooded rice soils is characterized by a tight coupling between nitrification and denitrification. Nitrification is restricted to the millimetre-thin oxic surface layer while denitrification occurs in the adjacent anoxic soil. However, in planted rice soil O₂ released from the rice roots may also support nitrification within the otherwise anoxic bulk soil. To locate root-associated nitrification and denitrification we constructed a new multi-channel microelectrode that measures NH₄ ⁺, NO₂ ^–, and NO₃ ^– at the same point. Unfertilized, unplanted rice microcosms developed an oxic-anoxic interface with nitrification taking place above and denitrification below ca. 1 mm depth. In unfertilized microcosms with rice plants, NH₄ ⁺, NO₂ ^– and NO₃ ^– could not be detected in the rhizosphere. Assimilation by the rice roots reduced the available N to a level where nitrification and denitrification virtually could not occur. However, a few hours after injecting (NH₄)₂HPO₄ or urea, a high nitrification activity could be detected in the surface layer of planted microcosms and in a depth of 20–30 mm in the rooted soil. O₂ concentrations of up to 150 μM were measured at the same depth, indicating O₂ release from the rice roots. Nitrification occurred at a distance of 0–2 mm from the surface around individual roots, and denitrification occurred at a distance of 1.5–5.0 mm. Addition of urea to the floodwater of planted rice microcosms stimulated nitrification. Transpiration of the rice plants caused percolation of water resulting in a mass flow of NH₄ ⁺ towards the roots, thus supporting nitrification. Received: 23 July 1999