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1.
A laboratory-based aerobic incubation was conducted to investigate nitrogen(N) isotopic fractionation related to nitrification in five agricultural soils after application of ammonium sulfate((NH4)2SO4). The soil samples were collected from a subtropical barren land soil derived from granite(RGB),three subtropical upland soils derived from granite(RQU),Quaternary red earth(RGU),Quaternary Xiashu loess(YQU) and a temperate upland soil generated from alluvial deposit(FAU). The five soils varied in nitrification potential,being in the order of FAU YQU RGU RQU RGB. Significant N isotopic fractionation accompanied nitrification of NH+4. δ15N values of NH+4 increased with enhanced nitrification over time in the four upland soils with NH+4 addition,while those of NO-3 decreased consistently to the minimum and thereafter increased. δ15N values of NH+4 showed a significantly negative linear relationship with NH+4-N concentration,but a positive linear relationship with NO-3-N concentration. The apparent isotopic fractionation factor calculated based on the loss of NH+4 was 1.036 for RQU,1.022 for RGU,1.016 for YQU,and 1.020 for FAU,respectively. Zero- and first-order reaction kinetics seemed to have their limitations in describing the nitrification process affected by NH+4 input in the studied soils. In contrast,N kinetic isotope fractionation was closely related to the nitrifying activity,and might serve as an alternative tool for estimating the nitrification capacity of agricultural soils.  相似文献   

2.
Land-use and management practices can affect soil nitrification. However, nitrifying microorganisms responsible for specific nitrification process under different land-use soils remains unknown. Thus, we investigated the relative contribution of bacteria and fungi to specific soil nitrification in different land-use soils (coniferous forest, upland fields planted with corn and rice paddy) in humid subtropical region in China. 15N dilution technique in combination with selective biomass inhibitors and C2H2 inhibition method were used to estimate the relative contribution of bacteria and fungi to heterotrophic nitrification and autotrophic nitrification in the different land-use soils in humid subtropical region. The results showed that autotrophic nitrification was the predominant nitrification process in the two agricultural soils (upland and paddy), while the nitrate production was mainly from heterotrophic nitrification in the acid forest soil. In the upland soils, streptomycin reduced autotrophic nitrification by 94%, whereas cycloheximide had no effect on autotrophic nitrification, indicating that autotrophic nitrification was mainly driven by bacteria. However, the opposite was true in another agricultural soil (paddy), indicating that fungi contributed to the oxidation of NH4+ to NO3?. In the acid forest soil, cycloheximide, but not streptomycin, inhibited heterotrophic nitrification, demonstrating that fungi controlled the heterotrophic nitrification. The conversion of forest to agricultural soils resulted in a shift from fungi-dominated heterotrophic nitrification to bacteria- or fungi-dominated autotrophic nitrification. Our results suggest that land-use and management practices, such as the application of N fertilizer and lime, the long-term waterflooding during rice growth, straw return after harvest, and cultivation could markedly influence the relative contribution of bacteria and fungi to specific soil nitrification processes.  相似文献   

3.
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   

4.
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   

5.
The effect of acidic deposition on the soil under red pine forest in Chunchon, Korea was investigated. Precipitation, stream water, and soil solution chemistry were monitored at the watershed from 1997 to 1998. Acidity of the open-bulk precipitation was often neutralized by large amounts of ammonia (NH3) that might have originated from livestock farming and fertilization. Estimated elemental budget at the watershed showed a positive correlation between loss of base cations and proton (H+) production due to nitrogen transformation in soil (ΔH+ NT: ([NH4 +]in-[NH4 +]out)- ([NO3 ?]in-[NO3 ?]out)). When ΔH+ NT increased, concentrations of nitrate in soil solutions also increased. Consequently, pH values of soil solutions decreased, although ion exchange with base cations contributed to buffer reaction. Since acid buffering capacity of the red pine forest soil was small, it was concluded that the input of ammonium nitrogen enhanced nitrification in soil thus causing soil acidification represented by loss of base cations from the watershed.  相似文献   

6.
Chemical fixation of NH3 to soil organic matter was studied in two Swedish soils with different contents of organic matter: a clay soil with 2.3% C and an organic soil with 36.6% C. 15N‐labelled urea was applied at different rates to both sterilized and non‐sterilized soils. After 10 days, the soils were extracted and washed with K2SO4 and determined for total N and atom% 15N excess. Urea N was recovered as non‐extractable N in sterilized soil corresponding to 9.7% of supplied l5N‐labelled urea in the organic soil and 2.2% in the clay soil. Since no biological immobilization is thought to occur in the sterile soil, this non‐extractable N is suggested to be chemically fixed to soil organic matter. Owing to urea hydrolysis in the clay soil, pH increased from 6.3 to 9.3 and in the organic soil from 5.7 to 6.9 and 8.8, respectively, at the low and high urea supply.  相似文献   

7.
LAN Ting  HAN Yong  CAI Zu-Cong 《土壤圈》2017,27(1):112-120
Although to date individual gross N transformations could be quantified by ~(15)N tracing method and models,studies are still limited in paddy soil.An incubation experiment was conducted using topsoil(0-20 cm) and subsoil(20-60 cm) of two paddy soils,alkaline and clay(AC) soil and neutral and silt loam(NSL) soil,to investigate gross N transformation rates.Soil samples were labeled with either ~(15)NH4_NO_3 or NH_4~(15)NO_3,and then incubated at 25 °C for 168 h at 60%water-holding capacity.The gross N mineralization(recalcitrant and labile organic N mineralization) rates in AC soil were 1.6 to 3.3 times higher than that in NSL soil,and the gross N nitrification(autotrophic and heterotrophic nitrification) rates in AC soil were 2.4 to 4.4 times higher than those in NSL soil.Although gross NO_3~- consumption(i.e.,NO_3~- immobilization and dissimilatory NO_3~- reduction to NH_4~+ rates increased with increasing gross nitrification rates,the measured net nitrification rate in AC soil was approximately 2.0 to 5.1 times higher than that in NSL soil.These showed that high NO_3~- production capacity of alkaline paddy soil should be a cause for concern because an accumulation of NO_3~- can increase the risk of NO_3~- loss through leaching and denitrification.  相似文献   

8.
Abstract

Release of native and added K+ and NH+ 4 from two soils was monitored during a 166 day incubation/leaching experiment. One soil (Brookston) represented a major soil series In Ontario whereas the other (Harriston) was suspected having a relatively large fixation capacity. Treatments were imposed involving addition of 50 μM g‐1 soil of K+(KCl) or NH+ 4 (NH4Cl) only or one added after the other on successive days. The addition of either K+ or NH+ 4 on day 2 tended to inhibit the release of the other added on day I. Also the addition of either K+ or NH+ 4 on day 1 tended to inhibit the sorption or fixation of the other on day 2. The release rate of K+ during the 10 to 166 day period was almost constant and not affected by the addition of NH+ 4. Alternatively, the addition of K+ on day 2 slowed the release rate of NH+ 4 measured by NO? 3 appearance from day 10 to 40 but had no effect thereafter. At the end of the experiment considerably more K+ than NH+ 4 was retained suggesting that K+ was more firmly fixed. However, the continuing nitrification of NH+ 4 must be contrasted with periodic removal of K+ by leaching with 0.01 M CaCl2 solution since the equilibrium between exchangeable and fixed ions was affected. There were no notable differences between the two soils inspite of a considerable difference in clay content.  相似文献   

9.
塿土固定态NH4+释放动力学的研究   总被引：8，自引：0，他引：8  
樊小林  张一平  李玲 《土壤学报》1996,33(3):287-292
  相似文献   

10.
Agricultural systems that receive high or low organic matter (OM) inputs would be expected to differ in soil nitrogen (N) transformation rates and fates of ammonium (NH4+) and nitrate (NO3−). To compare NH4+ availability, competition between nitrifiers and heterotrophic microorganisms for NH4+, and microbial NO3− assimilation in an organic vs. a conventional irrigated cropping system in the California Central Valley, chemical and biological soil assays, 15N isotope pool dilution and 15N tracer techniques were used. Potentially mineralizable N (PMN) and hot minus cold KCl-extracted NH4+ as indicators of soil N supplying capacity were measured five times during the tomato growing season. At mid-season, rates of gross ammonification and gross nitrification after rewetting dry soil were measured in microcosms. Microbial immobilization of NO3− and NH4+ was estimated based on the uptake of 15N and gross consumption rates. Gross ammonification, PMN, and hot minus cold KCl-extracted NH4+ were approximately twice as high in the organically than the conventionally managed soil. Net estimated microbial NO3− assimilation rates were between 32 and 35% of gross nitrification rates in the conventional and between 37 and 46% in the organic system. In both soils, microbes assimilated more NO3− than NH4+. Heterotrophic microbes assimilated less NH4+ than NO3− probably because NH4+ concentrations were low and competition by nitrifiers was apparently strong. The high OM input organic system released NH4+ in a gradual manner and, compared to the low OM input conventional system, supported a more active microbial biomass with greater N demand that was met mainly by NO3− immobilization.  相似文献   

11.
水分状况与供氮水平对土壤可溶性氮素形态变化的影响   总被引：3，自引：0，他引：3  
采用通气培养试验,研究比较了两种水稻土在不同水分和供氮水平下的矿质氮(TMN)和可溶性有机氮(SON)的变化特征。结果表明,加氮处理及淹水培养均显著提高青紫泥的NH4+-N含量;除加氮处理淹水培养第7 d外,潮土NH4+-N含量并未因加氮处理或淹水培养而明显升高。无论加氮与否,控水处理显著提高两种土壤的NO3--N含量,其中潮土始见于培养第7 d,青紫泥则始于培养后21 d;加氮处理可显著提高淹水培养潮土NO3--N含量,却未能提高淹水培养青紫泥NO3--N含量。两种土壤的SON含量从开始培养即逐步升高,至培养21～35 d达高峰期,随后急剧下降并回落至基础土样的水平;SON含量高峰期,潮土SON/TSN最高达80%以上,青紫泥也达60%。综上所述,潮土不仅在控水条件下具有很强硝化作用,在淹水条件下的硝化作用也不容忽视,因此氮肥在潮土中以硝态氮的形式流失的风险比青紫泥更值得关注;在SON含量高峰期,两种土壤的可溶性有机氮的流失风险也应予以重视。  相似文献   

12.
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   

13.
Measurements of N transformation rates in tropical forest soils are commonly conducted in the laboratory from disturbed or intact soil cores. On four sites with Andisol soils under old-growth forests of Panama and Ecuador, we compared N transformation rates measured from laboratory incubation (at soil temperatures of the sites) of intact soil cores after a period of cold storage (at 5 °C) with measurements conducted in situ. Laboratory measurements from stored soil cores showed lower gross N mineralization and NH4+ consumption rates and higher gross nitrification and NO3− immobilization rates than the in-situ measurements. We conclude that cold storage and laboratory incubation change the soils to such an extent that N cycling rates do not reflect field conditions. The only reliable way to measure N transformation rates of tropical forest soils is in-situ incubation and mineral N extraction in the field.  相似文献   

14.
Agricultural systems that receive high amounts of inorganic nitrogen (N) fertilizer in the form of either ammonium (NH4+), nitrate (NO3−) or a combination thereof are expected to differ in soil N transformation rates and fates of NH4+ and NO3−. Using 15N tracer techniques this study examines how crop plants and soil microbes vary in their ability to take up and compete for fertilizer N on a short time scale (hours to days). Single plants of barley (Hordeum vulgare L. cv. Morex) were grown on two agricultural soils in microcosms which received either NH4+, NO3− or NH4NO3. Within each fertilizer treatment traces of 15NH4+ and 15NO3− were added separately. During 8 days of fertilization the fate of fertilizer 15N into plants, microbial biomass and inorganic soil N pools as well as changes in gross N transformation rates were investigated. One week after fertilization 45-80% of initially applied 15N was recovered in crop plants compared to only 1-10% in soil microbes, proving that plants were the strongest competitors for fertilizer N. In terms of N uptake soil microbes out-competed plants only during the first 4 h of N application independent of soil and fertilizer N form. Within one day microbial N uptake declined substantially, probably due to carbon limitation. In both soils, plants and soil microbes took up more NO3− than NH4+ independent of initially applied N form. Surprisingly, no inhibitory effect of NH4+ on the uptake and assimilation of nitrate in both, plants and microbes, was observed, probably because fast nitrification rates led to a swift depletion of the ammonium pool. Compared to plant and microbial NH4+ uptake rates, gross nitrification rates were 3-75-fold higher, indicating that nitrifiers were the strongest competitors for NH4+ in both soils. The rapid conversion of NH4+ to NO3− and preferential use of NO3− by soil microbes suggest that in agricultural systems with high inorganic N fertilizer inputs the soil microbial community could adapt to high concentrations of NO3− and shift towards enhanced reliance on NO3− for their N supply.  相似文献   

15.
陕西省几种代表性土壤NH4+吸附、解吸动力学特征研究   总被引：3，自引：0，他引：3  
薛泉宏  尉庆丰  高彦  石辉  曲东 《土壤学报》1996,33(2):129-137
采用连续液流法测定了五种土壤吸附、解吸ＮＨ＾＋４的动力学性质。研究表明：（１）ＮＨ＾＋４吸附、解吸平衡时间及反应速率，平衡时的吸附、解吸量及吸附平衡常数均随土壤粘粒和ＣＥＣ不同而变化；（２）不同动力学模型及同一模型对不同土壤的拟合性不同。  相似文献   

16.
In the tropics,frequent nitrogen(N)fertilization of grazing areas can potentially increase nitrous oxide(N2O)emissions.The application of nitrification inhibitors has been reported as an effective management practice for potentially reducing N loss from the soil-plant system and improving N use efficiency(NUE).The aim of this study was to determine the effect of the co-application of nitrapyrin(a nitrification inhibitor,NI)and urea in a tropical Andosol on the behavior of N and the emissions of N2O from autotrophic and heterotrophic nitrification.A greenhouse experiment was performed using a soil(pH 5.9,organic matter content 78 g kg-1,and N 5.6 g kg-1)sown with Cynodon nlemfuensis at 60%water-filled pore space to quantify total N2O emissions,N2O derived from fertilizer,soil ammonium(NH4+)and nitrate(NO3-),and NUE.The study included treatments that received deionized water only(control,NI).No significant differences were observed in soil NH4+content between the UR and UR+NI treatments,probably because of soil mineralization and NO3-produced by heterotrophic nitrification,which is not effectively inhibited by nitrapyrin.After 56 d,N2O emissions in UR(0.51±0.12 mg N2O-N concluded that the soil organic N mineralization and heterotrophic nitrification are the main processes of NH4+and NO3-production.Additionally,it was found that N2O emissions were partially a consequence of the direct oxidation of the soil's organic N via heterotrophic nitrification coupled to denitrification.Finally,the results suggest that nitrapyrin would likely exert significant mitigation on N2O emissions only if a substantial N surplus exists in soils with high organic matter content.  相似文献   

17.
Limited research has been conducted on how atmospheric carbon dioxide (CO2) affects water and soil nitrogen (N) transformation in wetland ecosystems. A stable isotope technique is suitable for conducting a detailed investigation of mechanistic nutrient transformations. Nutrient ammonium sulfate (NH4)2SO4 input in culture water under elevated CO2 (700 μL L?1) and ambient CO2 (380 μL L?1) was studied to analyze N transformations with N blanks for both water and soil. It was measured by 15N pool dilution using analytical equations in a riparian wetland during a 3-month period. Soil gross ammonium (NH4 +) mineralization and consumption rates increased significantly by 22% and 404%, Whereas those of water decreased greatly by??57% and??57% respectively in enriched CO2. In contrast, gross nitrate (NO3 ?) consumption and nitrification rates of soil decreased by??11% and??14% and those of water increased by 29% and 27% respectively in enrichment CO2. These may be due to the extremely high soil microbial biomass nitrogen (MBN), which increased by 94% in elevated soil. The results can show when CO2 concentrations are going to rise in the future. Consequently soil microbial activity initiates the decreased N concentration in sediment and increased N concentration in overlying water in riparian wetland ecosystems.  相似文献   

18.
宁夏引黄灌区稻田氮素浓度变化与迁移特征   总被引：3，自引：0，他引：3  
过量施氮与不合理灌水是农田面源污染加剧的主要原因。为了寻求较优的水氮管理模式以促进农业生产和减少农田退水对黄河水体的污染, 在宁夏引黄灌区典型稻田中开展了不同水氮条件下稻田氮素迁移转化规律研究。结果表明: 不同水氮条件下稻田田面水NH4+-N 与NO3--N 浓度伴随施肥出现明显峰值, NO3--N 峰值出现时间较NH4+-N 晚, 且变化较平缓。3 次追肥时期和整个生育期田面水NH4+-N 平均浓度与施氮量和灌水量都呈显著相关, 田面水NO3--N 平均浓度与施氮量呈显著正相关, 与灌水量相关性不显著。稻田30 cm与60 cm 深度的直渗水NH4+-N 浓度受施肥影响较大, 与田面水NH4+-N 浓度变化规律相似, 90 cm 处直渗水NH4+-N 浓度峰值出现较为滞后, 且浓度较上层土体低, 120 cm 处直渗水NH4+-N 浓度大体呈现持续上升趋势,整个生育期直渗水NH4+-N 平均浓度与施氮量呈显著相关, 仅30 cm 处NH4+-N 平均浓度与灌水量呈负相关, 其他土层深度不显著。30 cm 与60 cm 直渗水NO3--N 浓度在首次灌水后急剧下降, 在施肥后有较小幅度上升, 90 cm 与120 cm 直渗水NO3--N 浓度下降缓慢, 仅30 cm 处NO3--N 平均浓度与施肥量显著正相关。总的结果表明减少施肥或灌水均可达到减少农田氮素淋失的目的。  相似文献   

19.
The contribution of nitrification to the emission of nitrous oxide (N2O) from soils may be large, but its regulation is not well understood. The soil pH appears to play a central role for controlling N2O emissions from soil, partly by affecting the N2O product ratios of both denitrification (N2O/(N2+N2O)) and nitrification (N2O/(NO2−+NO3−). Mechanisms responsible for apparently high N2O product ratios of nitrification in acid soils are uncertain. We have investigated the pH regulation of the N2O product ratio of nitrification in a series of experiments with slurries of soils from long-term liming experiments, spanning a pH range from 4.1 to 7.8. 15N labelled nitrate (NO3−) was added to assess nitrification rates by pool dilution and to distinguish between N2O from NO3− reduction and NH3 oxidation. Sterilized soil slurries were used to determine the rates of chemodenitrification (i.e. the production of nitric oxide (NO) and N2O from the chemical decomposition of nitrite (NO2−)) as a function of NO2− concentrations. Additions of NO2− to aerobic soil slurries (with 15N labelled NO3− added) were used to assess its potential for inducing denitrification at aerobic conditions. For soils with pH?5, we found that the N2O product ratios for nitrification were low (0.2-0.9‰) and comparable to values found in pure cultures of ammonia-oxidizing bacteria. In mineral soils we found only a minor increase in the N2O product ratio with increasing soil pH, but the effect was so weak that it justifies a constant N2O product ratio of nitrification for N2O emission models. For the soils with pH 4.1 and 4.2, the apparent N2O product ratio of nitrification was 2 orders of magnitude higher than above pH 5 (76‰ and 14‰). This could partly be accounted for by the rates of chemodenitrification of NO2−. We further found convincing evidence for NO2−-induction of aerobic denitrification in acid soils. The study underlines the role of NO2−, both for regulating denitrification and for the apparent nitrifier-derived N2O emission.  相似文献   

20.
In soil incubation experiments we examined if there are differences in the kinetic parameters of atmospheric methane (CH4) oxidation in soils of upland forests and forested peatlands. All soils showed net uptake of atmospheric CH4. One of the upland forests included also managed (clear-cut with or without previous liming or N-fertilization) study plots. The CH4 oxidation in the forested peat soil had a higher Km (510 μl l−1) and Vmax (6.2 nmol CH4 cm−3 h−1) than the upland forest soils (Km from 5 to 18 μl l−1 and Vmax from 0.15 to 1.7 nmol CH4 cm−3 h−1). The forest managements did not affect the Km-values. At atmospheric CH4 concentration, the upland forest soils had a higher CH4 oxidation activity than the forested peat soil; at high CH4 concentrations the reverse was true. Most of the soils oxidised CH4 in the studied pH range from 3 to 7.5. The pH optimum for CH4 oxidation varied from 4 to 7.5. Some of the soils had a pH optimum for CH4 oxidation that was above their natural pH. The CH4 oxidation in the upland forest soils and in the peat soil did not differ in their sensitivities to (NH4)2SO4 or K2SO4 (used as a non-ammonium salt control). Inhibition of CH4 oxidation by (NH4)2SO4 resulted mainly from a general salt effect (osmotic stress) though NH4+ did have some additional inhibitory properties. Both salts were better inhibitors of CH4 oxidation than respiration. The differences in the CH4 oxidation kinetics in the forested peat soil and in the upland forest soils reveal that there are differences in the physiologies of the CH4 oxidisers in these soils.  相似文献   

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