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1.
Abstract

Diffusion methods for quantitative determination and isotope‐ratio analysis of inorganic N in soil extracts were modified for use with Kjeldahl digests. The digest was diluted to 25 mL with deionized water, and an aliquot (to 6 mL) was transferred in a shell vial (17 mm dia., 60 mm long) to a 473‐mL (1‐pint) wide‐mouth Mason jar containing 15 mL of 8 M NaOH. The NH3 liberated by overturning the vial inside the sealed jar was collected for 48 h at room temperature (24 h with orbital shaking) in 3 mL of boric acid‐indicator solution in a Petri dish, or in an acidified glass‐fiber disk, suspended from the Mason‐jar lid. Determinations of N and 15N by diffusion were in close agreement with analyses using conventional steam‐distillation and concentration techniques.  相似文献   

2.
Abstract

Very low recovery of NH4+‐N was observed in total N determination of (NH4)2SO4 in KC1 solutions by a semimicro Kjeldahl method using permanganate and reduced iron to recover NO3‐ and NO2‐, whereas complete recovery was obtained in analysis of NH4+‐N in water, and of NO3 ?‐N or NO2 ?‐N in either water or KC1 solutions. The loss of NH4 +‐N observed with KC1 was attributed to the formation of NCl3 upon reaction of NH4 + with Cl2 generated during oxidation of Cl? by MnO4 ?. This difficulty is avoided by using K2SO4 instead of KC1 for extraction of inorganic N from soil. Complete recovery was obtained by adding 15N‐labeled NH4+, NO3‐, or NO2‐ to 0.5 M K2SO4 soil extracts, and total 15N analyses of the labeled extracts were in good agreement with values calculated from the additions of 15N and the total N contents of the soil extracts.  相似文献   

3.
Abstract

Studies to evaluate the use of diffusion for automated 15N analysis of inorganic N in soil extracts showed that serious error can arise from use of the Devarda's alloy recommended for steam distillations and that the error can be avoided by using a commercial product of higher purity. These studies showed that serious error can also arise when NO3 ‐‐N is diffused following NH4 +‐N and that separate diffusions should be performed for NH4 +‐N and (NH4 + + NO3‐)‐N. Other work demonstrated that the plastic specimen containers employed for diffusion can be reused if acid‐washed, that diffusions can be performed using either light or heavy MgO without ignition to decompose carbonate, and that labeled NO2‐is completely removed from soil extracts by treatment with sulfamic acid before diffusion. A comparison of 15N analyses by steam distillation and diffusion using extracts from two soils revealed better agreement for the soil having a lower content of organic matter. Substantial differences in analyses by the two techniques for the soil having a higher organic‐matter content were attributed to enzymatic conversions of inorganic N during the 6‐d diffusion period.  相似文献   

4.
The aim of this study was to examine the effect of the nitrification inhibitor nitrapyrin on the fate and recovery of fertilizer nitrogen (N) and on N mineralization from soil organic sources. Intact soil cores were collected from a grassland field. Diammonium phosphate (DAP) and urea were applied as N sources. Cores were equilibrated at –5 kPa matric potential and incubated at 20 °C for 42 to 56 days. Changes in NH4+‐N, accumulation of NO3–‐N, apparent recovery of applied N, and emission of N2O (acetylene was used to block N2O reductase) were examined during the study. A significant increase in NH4+‐N released through mineralization was recorded when nitrapyrin was added to the control soil without N fertilizer application. In the soils to which N was added either as urea or DAP, 50–90 % of the applied N disappeared from the NH4+‐N pool. Some of this N (8–16 %) accumulated as NO3–‐N, while a small proportion of N (1 %) escaped as N2O. Addition of nitrapyrin resulted in a decrease and delay of NH4+‐N disappearance, accumulation of much lower soil NO3–‐N contents, a substantial reduction in N2O emissions, and a 30–40 % increase in the apparent recovery of added N. The study indicates that N recovery can be increased by using the nitrification inhibitor nitrapyrin in grassland soils at moisture condition close to field capacity.  相似文献   

5.
An incubation experiment under aseptic and septic conditions using 15N-labelled NH4+-N and NO3–-N, was carried out to study the effect of N transformations after flooding on NH4+ fixation in a paddy soil from China. After flooding ammonification was favoured, providing NH4+ for fixation by clay minerals. NH4+ fixation was more pronounced under low redox potential (Eh) conditions. Close correlations existed between exchangeable NH4+, Eh, and non-exchangeable NH4+. Therefore, two major conditions for NH4+ fixation induced by flooding in paddy soil were found, namely flooding promoted net production of NH4+ due to the deamination of organic N and, in addition, decreased the Eh of the soil. A lower Eh was caused by reduction and dissolution of Fe oxide coating on the clay minerals' surfaces, eliminating the obstacles for NH4+ diffusing into or out of the interlayers of clay minerals. A higher concentration of exchangeable NH4+ from deamination of organic N would drive NH4+ diffusing from the soil solution into the interlayers of clay minerals. 15N-labelled NO3– incorporated into the flooded soil was not reduced to NH3. The addition of NO3– retarded the decrease in the soil Eh and, therefore, NH4+ fixation.  相似文献   

6.
The soil nitrogen (N) cycle exhibits a variety of complex biochemical reactions in which N species such as NO2−, NO and N2O are produced and consumed by co‐existing processes that respond differently to the local environmental conditions. Key to understanding the soil N cycle in its full complexity is the development and application of methods that allow a quantification of individual pathways and processes that are responsible for the build‐up and/or emission of N compounds. Triplet 15N tracer experiments (TTE) have been developed and applied to allow a source‐related quantification of N species such as NO2−, and N2O by different biochemical pathways (e.g. ammonia oxidation and nitrate reduction) that are related to multiple N sources (NH4+, NO3− and Norg). An analysis of a TTE requires the application of either a numerical or analytical model. Because of the ease of application it is desirable to use analytical models. However, available analytical solutions suffer from serious drawbacks concerning the quantification of N fluxes related to soil organic N. In this paper we describe the development and application of a new inverse abundance approach (IAA) to analyse a TTE. Theoretical and experimental data sets of soil N2O release were analysed by the new method. The IAA was also applied to an already existing data set to identify fractions of the soil nitrite pool related to NH4+, NO3− and Norg. We show that the IAA provides a reliable and comprehensive data evaluation of a TTE.  相似文献   

7.
Abstract

This study determined the effects of soil preservation methods on inorganic nitrogen (N) analysis and evaluated methods of soil inorganic N analysis. Soils were preserved by oven‐drying at 55'C, air‐drying at 27°C, and freezing at ‐ 7°C. Inorganic N results were compared with initial N levels prior to imposing preservation treatments. Soil preservation effects on ammonium‐nitrogen (NH4 +‐N) were not consistent across soil types. Soil nitrate‐nitrogen (NO3 ‐‐N) levels after air‐drying and freezing compared most favorably with initial levels indicating that both are acceptable methods of soil inorganic‐N preservation. Levels of NH4 +‐N averaged across soils were 3.9 mg/kg for steam distillation, 4.2 mg/kg for sodium salicylate‐hypochlorite, and 3.7 mg/kg for indophenol blue. When compared with steam distillation averaged across soils, NO3 ‐‐N for cadmium‐copper (Cd‐Cu) reduction was 4 mg/kg greater, followed by nitrate electrode at 3 mg/kg, and salicylic acid at 2 mg/kg. Recovery of added N ranged from 83.3 to 94.8% for the NH4+‐N methods and from 74.8 to 112.4% for the NO3 ‐‐N methods with the nitrate electrode averaging 98.3%.  相似文献   

8.
The inherent features of Acrisols with their increasing clay content with depth are conducive to reducing nutrient losses by nutrient adsorption on the matrix soil surfaces. Ammonium (NH4+) and nitrate (NO3?) adsorption by a Plinthic Acrisol from Lampung, Indonesia was studied in column experiments. The peak of the H218O breakthrough occurred at 1 pore volume, whereas the median pore volumes for NH4+ and NO3? ranged from 6.4 to 6.9 and 1.1 to 1.6, respectively. The adsorption coefficients (Ka in cm3 g–1) measured were 1.81, 1.51, 1.64 and 1.47 for NH4+ and 0.03, 0.09, 0.10 and 0.17 for NO3?, respectively, in the 0–0.2, 0.2–0.4, 0.4–0.6 and 0.6–0.8 m soil depth layers. The NH4+ and NO3? adsorption coefficients derived from this study were put in to the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model to evaluate their effect on leaching in the context of several cropping systems in the humid tropics. The resulting simulations indicate that the inherent ‘safety‐net’ (retardation mechanism) of a shallow (0.8–1 m) Plinthic Acrisol can reduce the leaching of mineral N by between 5 and 33% (or up to 2.1 g m?2), mainly due to the NH4+ retardation factor, and that the effectiveness in reducing N leaching increases with increasing depth. However, the inherent ‘safety‐net’ is useful only if deep‐rooted plants can recover the N subsequently.  相似文献   

9.
Spatiotemporal heterogeneity of soil available nitrogen (AN) (sum of NO3−–N and NH4+–N) is the essential basis for soil management and highly correlates to crop yield. Both geostatistical and traditional analyses were used to describe the spatiotemporal distribution of AN in the 0–20‐cm soil depth on typical Mollisol slopes (S1 and S2) in Northeast China. The concentration of NO3−–N dynamics at slope positions was typically opposite to NH4+–N. The peak values of AN typically moved from the summit of the slope to the bottom from spring to autumn and were mainly influenced by the content of NO3−–N (S1, 7·9–18·9 mg kg−1; S2, 1·2–103·6 mg kg−1), both of NO3−–N (S1, 3·9–8·3 mg kg−1; S2, 2·2–28·0 mg kg−1) and NH4+–N (S1, 21·4–30·5 mg kg−1; S2, 2·1–23·3 mg kg−1), and NH4+–N (S1, 10·5–28·9 mg kg−1; S2, 5·0–39·0 mg kg−1) in the seedling stage, vegetative growth stage, and reproductive growth stage, respectively. The spatial autocorrelation of AN was strong and was mainly influenced by structural factors during crop growth stages. This was mainly determined by soil erosion–deposition (SED) and soil temperature–moisture (STM) in the seedling stage; this was also mainly influenced by SED, STM, crop type, and crop growth in the vegetative growth stage and by early STM and early SED in the reproductive growth stage. Generally, the content of AN, NO3−–N, and NH4+–N on the whole slope was mainly determined by the early SED and local fertilizer application, while their spatiotemporal heterogeneity, especially the evenness, was mainly changed by SED, STM, crop growth, and crop types on the slope scale. In order to increase more crop yields, additional N fertilizer application on both the summit and the bottom during the vegetative growth stage and conservation tillage systems or additional soil amendments on the back slopes was necessary. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

10.
Soil NH+4-N and NO?3-N at five soil depths (0–10, 10–20, 20–40, 40–60, 60–80 cm) and some environmental variables were measured in a field trial under fallow and wheat for 9 months.Significant linear and quadratic relationships were obtained relating soil NH+4-N, NO?3-N, NH+4-N + NO?3-N, and NH+4-N + NO?3 + total-N uptake by wheat to soil heat accumulation (temperature), moisture, and rainfall. R2 values generally decreased with soil depth and the maximum value (37%) was obtained for NO?3-N changes in the topsoil (0–10 cm).Although a considerable amount of variation in the inorganic values recorded is not included in the equations, our results suggest that the development of the above relationships particularly of the quadratic type are useful to predict crop requirements for N by measurement of environmental variables in the field.  相似文献   

11.
Inorganic nitrogen (N) in soils is a primary component of soil‐plant N buffering. This study was conducted to determine if non‐exchangeable ammonium‐nitrogen (NH4‐N) could serve as an index of potentially mineralizable organic N which is an important sink in N buffering. Four long‐term winter wheat (Triticum aestivum L.) experiments that had received annual fertilizer N at 0 to 272 kg N ha‐1 were used. Soils from these experiments were extracted by four 10 mL portions of 2M potassium chloride (KC1) at room temperature followed by extraction with 20 mL of 2M hot KC1. Extraction at 100°C for four hours using 3 g soil and 20 mL 2M KC1 was found to be the most effective. Hot KC1‐extractable NH4‐N minus room temperature KCl‐extractable NH4‐N was considered non‐exchangeable NH4‐N. Non‐exchangeable NH4‐N was correlated with the long‐term N rates, and believed to be a reliable index of potentially mineralizable organic N. The relationship was linear for NH4‐N where the lowest N rate had the lowest extractable N. The mean non‐exchangeable NH4‐N concentration ranged from 8.42 to 16.34 mg kg‐1; whereas, nitrate‐nitrogen (NO3‐N) ranged from 0.07 to 1.87 mg kg1. Total inorganic N extracted was similar to that mineralized in a 42‐day aerobic water saturated incubation. In addition, using a linear‐plateau model, extractable NH4‐N was highly correlated with long‐term average yield (R2=0.92). For the soils evaluated, this method provided a rapid measure of potentially mineralizable N.  相似文献   

12.
Abstract

Tomato plants were grown in sand culture with NH+ 4, and NO? 3, forms of N and three levels of light. Plants supplied with NH+ 4, nutrition under high light intensity had symptoms of stunting, leaf roll, wilting, interveinal chlorosis of the older leaves, and one third the dry weight of N03‐fed plants. In contrast, growth of plants receiving NH+ 4, nutrition under shade appeared normal although dry weight was reduced. NH4‐N nutrition suppressed K, Ca and Mg accumulation in tissues and increased P contents as compared to NO3‐N nutrition.  相似文献   

13.
坡缕石包膜对尿素氮行为的影响   总被引：3，自引：1，他引：2  
采用静态吸收和土柱淋溶试验方法,分析对比了3种不同用量坡缕石包膜尿素与普通尿素施入土壤后对尿素氮行为的影响,结果表明:在土壤中施用坡缕石包膜尿素较普通尿素减少10.38%～26.24%的氨挥发损失,减少5.88%～27.74%的氮素(NO3--N+NH4+-N)淋溶损失,20%的坡缕石包膜尿素能显著提高土柱土壤NH4+-N含量,3种坡缕石包膜尿素都能极显著提高土柱土壤NO3--N含量.坡缕石包膜后能减少尿素氨的挥发,降低NH4+-N和NO3--N的淋失,提高土壤NH4+-N和NO3--N含量,以20%的坡缕石包膜尿素的综合生态效应最好.  相似文献   

14.
Pearl millet [Pennisetum glaucum (L.) R. Br.] is a potentially productive, high‐yielding grain crop in the southeastern USA. A lack of response in pearl millet grain yield to fertilizer N in field studies indicates pearl millet may be able to remobilize N from vegetative to reproductive tissue. The N remobilization capabilities of a plant can be affected by the form of N supplemented. The objectives of this study were to evaluate the effects of N‐form ratio (NH4 + : NO3 ‐) on the N remobilization capabilities of pearl millet when N is removed from the nutrient solution at the boot stage and to evaluate the effects of changing N‐form ratios at the boot stage on the seed yield and N content of pearl millet. Pearl millet was grown in solution culture under greenhouse conditions. There were 10 treatments: an initial NH4 + : NO3 ‐ ratio of 3:1 followed by a change at the boot stage to either all NO3 ‐, no N, or a continuation of the initial ratio; an initial NH4 + : NO3 ‐ ratio of 1:1 followed by a change at the boot stage to either all NO3 ‐, all NH4 + no N, or a continuation of the initial ratio; and an initial NH4 + : NO3 ‐ ratio of 1:3 followed by a change at the boot stage to either all NH4 + no N, or a continuation of the initial ratio. Pearl millet dry matter accumulation was insensitive to changes in N‐form ratio or N removal at the boot stage. The lack of seed yield response to removal of N was a result of pearl millet utilizing N present in culms and leaves for seed production. Applications of N after the boot stage did not increase seed yield, but led to luxury consumption of N.  相似文献   

15.
Sandy loam soil, with added glucose, was incubated anaerobically under N2 and subjected to repeated 1-h C2H2 reduction assays. In the presence of 1% glucose the addition of 50 μg NH4+ ?N/g or of 20 μg NO?3 N/g (untreated soil contained 1.2 μg NH+4?N and 7.10 μg NO?3-N/g) caused at least some suppression of nitrogenase activity. Activity developed when the KCl-extractable soil inorganic nitrogen concentration dropped below 35 μg/g. In the presence of 0.1 or 0.05% glucose the addition of 5 μg NH+4?N/g caused some suppression of nitrogenase activity. However, activity developed when the soil NH4+-N concentration dropped below about 4 μg/g. With 0.1% glucose and 5 μg added NO?2 N/g, activity did not develop until the soil NO?2 -N concentration dropped to zero. Added NO?3 N was rapidly reduced and denitrified to NO?2- N, N2O-N and NH+4 N and furthermore caused some inhibition of CO2 evolution. The data from NH4?-addition experiments are consistent with a nitrogenase repression/ derepression threshold of 4 and 35μg NH+4-N/g at 0.05 and 1% glucose concentrations, respectively. The data from NO?2- and NO?3-addition experiments suggest a combination of repression and toxicity effects in the presence of added NO?3 N.  相似文献   

16.
Diffusion methods previously developed for inorganic-N analysis of soil extracts were modified to improve reliability, increase the dynamic range, extend the scope of applications, and simplify the processing of samples for N-isotope analysis. In these methods, the soil extract is treated with MgO, or MgO plus Devarda‘s alloy, in a 473-ml (1-pint) wide-mouth Mason jar to convert NH4 +-N, NO3 –-N, and/or NO2 –-N to NH3-N. The NH3 thereby liberated is collected in H3BO3-indicator solution in a Petri dish suspended from the Mason-jar lid and determined quantitatively by acidimetric titration. With the modifications described, analyses can be performed on 10- to 100-ml samples of water, 0.5MK2SO4, 1MKCl, 2MKCl, or 4MKCl, at temperatures between 20 and 30°C. Recovery from 10 or 20ml was quantitative in 18–80h with up to 4mgN; recovery from 50 or 100ml was quantitative in 3–13 days with up to 2mgN. Removal of H3BO3 for N-isotope analysis by the Rittenberg process was effected using methanol. Mason-jar diffusion methods are much simpler and more convenient than conventional steam distillations. Comparative studies showed that quantitative determinations are more accurate and precise by diffusion than by distillation. Received: 15 May 1996  相似文献   

17.
Abstract

Rapid, sensitive analysis of NH4 ‐ NO3 ‐, and NO2 ‐ in 1–150 μL of soil extract or water was achieved using a modified indophenol blue technique adapted to microtiter plate format. The microplate technique was similar to conventional steam distillation in accuracy and precision. By varying aliquot volume, a wide linear dynamic range (0.05 to 1000 mg of NH4 +‐ or NO3 ‐‐NL‐1) was achieved without the need for sample dilution or concentration. High sample throughput (250–500 NH4 + analyses d‐1) was accomplished manually, but could be significantly increased by automation. Of considerable importance was the very low waste stream produced by the method. All equipment and supplies required are commercially available and need no modifications for this use. The microtiter plate format could be used for other soil colorimetric analyses with little or no down time for equipment setup, a major consideration for commercial soil‐testing laboratories. The method and equipment used are well suited to quality control and quality assurance programs, as required under FIFRA Good Laboratory Practices.  相似文献   

18.
Laboratory incubations were conducted to study the effect of sodium chloride (NaCl) on denitrification and respiratory gases (CO2, O2) from soil treated with ammonium or nitrate and incubated at 20 % moisture. The same samples were assayed for denitrifying enzyme activity (DEA) after incubation at 40 % moisture with glucose and NO3–. Under aerobic conditions (20 % water content), a flush of activity was observed at 6 hours after start of incubation and subsided to negligible levels at 12 hours. Sodium chloride significantly depressed N2O and CO2 emissions and O2 consumption. Significantly more loss of N2O occurred from NH4+‐ than NO3–‐treated soil at all NaCl levels and was attributed to higher microbial activity. A highly significant positive correlation was obtained between N2O emission and respiratory gases. The respiratory quotient (CO2 evolved/O2) was higher for NH4+‐treated soil and decreased with the amount of NaCl. At 40 % moisture, N2O emissions were higher than at 20 % and peaked at 37 hours followed by a sharp decrease. Short‐term incubations of soil with NH4+ or NO3– did not have an effect on denitrifying enzyme activity (DEA) while NaCl had a positive effect, particularly in previously NO3–‐treated soil.  相似文献   

19.
The availability of C and N to the soil microbial biomass is an important determinant of the rates of soil N transformations. Here, we present evidence that changes in C and N availability affect the 15N natural abundance of the microbial biomass relative to other soil N pools. We analysed the 15N natural abundance signature of the chloroform‐labile, extractable, NO3–, NH4+ and soil total N pools across a cattle manure gradient associated with a water reservoir in semiarid, high‐desert grassland. High levels of C and N in soil total, extractable, NO3–, NH4+ and chloroform‐labile fractions were found close to the reservoir. The δ15N value of chloroform‐labile N was similar to that of extractable (organic + inorganic) N and NO3– at greater C availability close to the reservoir, but was 15N‐enriched relative to these N‐pools at lesser C availability farther away. Possible mechanisms for this variable 15N‐enrichment include isotope fractionation during N assimilation and dissimilation, and changes in substrate use from a less to a more 15N‐enriched substrate with decreasing C availability.  相似文献   

20.
We tested how amendments of different forms of nitrogen (N) affect microbial respiration rates by adding six different forms of N (NH4NO3, (NH2)2CO (urea), KNO3, NH4Cl, (NH4)2SO4, Ca(NO3)2) to three distinct soils. All inorganic N forms led to a net reduction in microbial respiration, and the magnitude of the observed response (up to 60 % reduction) was consistent across all soils and negatively correlated with N concentration. Urea also reduced respiration rates in nearly all cases, but the effect was attenuated by the associated input of labile organic carbon. We observed decreases in respiration regardless of soil type, the specific N counter ion, N added as NH4+ or NO3−, or the effects of N form on soil pH, suggesting that decreases in respiration rates were mainly a direct result of the increase in soil N availability, rather than indirect effects caused by the form of N added.  相似文献   

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