Rolf Russow

Quantification of airborne N-input in long-term field experiments and its validation through measurements using 15N isotope dilution

The N-deposition in Germany is commonly calculated as values of about 20—30 kg/ha·yr. This range is based on the measurements of the nitrate and ammonium nitrogen bulk deposition, which does not include the gaseous N-deposition and the direct N-uptake by plants.  The calculation of airbone N-deposition from N-balances of the Static Fertilization Experiment Bad Lauchstadt came to 50—58 kg/ha·yr. This is consistent with results from other European long-term experiments.  Using the newly developed 15N-based ITNI-system, the total airborne N-deposition can be determined. For Bad Lauchstadt analogous to results of former measuring periods an annual N-deposition of 65 kg/ha·yr was measured in 1998, a figure greater than the balanced values.  The balanced and measured values show, that airborne N-deposition is often underestimated and amounts to at least 50 kg/ha·yr, which is a significant burden on natural ecosystems. By taking this extra N-input into account in calculations for fertilizer recommendations in agriculture a decrease of N-losses can be achieved which, in turn can also induce a decrease in airborne N-deposition. uantifizierung der atmospharischen Stickstoffdeposition in Dauerfeldversuchen und ihre Validierung durch Messungen basierend auf der 15N-Isotopenverdunnungsmethode  Fur die atmogene Stickstoffdeposition werden bisher in Deutschland durchschnittlich 20—30 kg/ha und Jahr veranschlagt. Diese Werte basieren jedoch uberwiegend auf Messungen des Nitrat- und Ammoniumstickstoffs der Bulkdepositionen, welche die gasformige N-Deposition und die N-Direktaufnahme durch die Pflanze nicht beinhaltet.  Die Ableitung der atmogenen Stickstoffdeposition aus Stickstoffbilanzen der Dauerfeldversuche ergab fur den Standort Bad Lauchstadt Werte von 50—58 kg/ha und Jahr. Diese Grosenordnung wird durch andere Dauerfeldversuche in Deutschland und Europa bestatigt.  Mit dem neu entwickelten, 15N-gestutzten ITNI-Messsystem kann der atmogene Gesamt-N-Input in ein Boden-Pflanze System direkt bestimmt werden. Fur den Standort Bad Lauchstadt wurde 1998 analog zu den Ergebnissen aus den Vorjahren (Mehlert et al., 1996; Russow et al., 1997) eine Gesamt-Deposition von 65 kg/ha und Jahr atmogenes N gemessen, die damit noch uber den bilanzierten Werten liegt.  Die bilanzierten und gemessenen Werte zeigen, dass die atmogene Stickstoffdeposition bisher unterschatzt wird und mit mehr als 50 kg/ha kalkuliert werden sollte. Diese Grosenordnung stellt fur naturnahe Okosysteme eine wesentliche Belastung dar. Fur landwirtschaftliche Flachen muss dieser Input bei der Bemessung der Dungergaben berucksichtigt werden. Durch Einbeziehung der atmogenen Gesamt-N-Deposition in die Dungungsempfehlung kann langfristig eine Reduzierung der N-Verluste und damit ruckgekoppelt auch der N-Depositionen erreicht werden.

Using the natural 15N abundance to assess the main nitrogen inputs into the sand dune area of the North-Western Negev desert (ISRAEL)

The variation of the natural 15N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to use this approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system: i. Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N2-fixing vascular plants (e.g. the shrub Retama raetam); ii. Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition. Samples were taken from selected environmental compartments such as biological crusts, sand underneath these crusts (down to a depth of 90 cm), N2-fixing and non-N2-fixing plants, atmospheric bulk deposition as well as soil from arable land north of the sandy area in three field campaigns in March 1998, 1999 and 2000. The δ15N values measured were in the following ranges: grass −2.5‰ to +1.5‰; R. reatam: +0.5‰ to +4.5‰; non-N2-fixing shrubs +1‰ to +7‰; sand beneath the biological crusts +4‰ to +20‰ (soil depth 2–90 cm); and arable land to the north up to 10‰. Thus, the natural 15N abundance of the different N pools varies significantly. Accordingly, it should be feasible to assess different input pathways from the various 15N abundances of nitrogen. For example, the biological N fixation rates of the Fabaceae shrub R. reatam from the 15N abundances measured were calculated to be 46–86% of biomass N derived from the atmosphere. The biological crusts themselves generally show slight negative 15N values (−3‰ to −0.5‰), which can be explained by biological N fixation. However, areas with a high share of lichens, which are unable to fix atmospheric nitrogen, show very negative values down to −10‰. The atmospheric N bulk deposition, which amounts to 1.9–3.8 kg N/ha yr, has a 15N abundance between 4.4‰ and 11.6‰ and is likely to be caused by dust from the arable land to the north. Thus, it cannot be responsible for the very negative values of lichens measured either. There must be an additional N input from the atmosphere with negative δ15N values, e.g. gaseous N forms (NO x , NH3). To explain these conflicting findings, detailed information is still needed on the wet, particulate and gaseous atmospheric deposition of nitrogen.

Airborne Nitrogen Input at Four Locations in the German State of Saxony-Anhalt - Measurements using the 15N-Based ITNI-System

Abstract The amount of atmospheric N deposition in Germany is actual rather uncertain. Estimates using standard methods indicate an N deposition of 30–35 kg N/ha × year. However, the results of long-term field experiments and newly by the ITNI (Integrated Total Nitrogen Input) system could prove a much higher N input of about 50–60 kg N/ha × year. The reason for this difference is that standard methods use wet-only or bulk collectors, which neglect gaseous and organic N deposition as well as direct N uptake by aerial plant parts. By contrast, the ITNI-system is able to measure the total atmospheric N input using the 15N isotope dilution method. The input of airborne N into a soil/plant system leads to a dilution of the abundance of a previously applied 15N tracer over a defined time period. The atmospheric N deposition can be calculated from this dilution. To estimate the actual N input in Central Germany, ITNI measurements were carried out from autumn 1998 to autumn 2000 at four locations in the German state of Saxony-Anhalt. Atmospheric N depositions between 45 and 75 kg N/ha × year were determined depending on the location. These results closely match to N balances of longterm field experiments. Furthermore, a relationship was found between N deposition and the plant species used as well as plant development.

A New Approach to Determine the Total Airborne N Input into the Soil/Plant System Using 15N Isotope Dilution (ITNI): Results for Agricultural Areas in Central Germany

The atmospheric deposition of nitrogen (N) in the environment is of great concern due to its impact on natural ecosystems including affecting vegetation, reducing biodiversity, increasing tree growth in forests, and the eutrophication of aquatic systems. Taking into account the average annual N emission into the atmosphere in Germany of about 2 million t N (ammonia/ammonium, NOx), and assuming homogeneous distribution throughout Germany, an average N deposition of 45 kg/ha x year can be calculated. Such high atmospheric N deposition could be confirmed by N balances from long-term field experiments in Central Germany (e.g., the Static Fertilization Experiment in Bad Lauchstädt). By contrast, estimates by standard methods indicate a deposition of only about 30 kg N/ha x year. This is because the standard methods are using wet-only or bulk collectors, which fail to take into account gaseous deposition and the direct uptake of atmospheric N by aerial plant parts. Therefore, a new system was developed using N isotope dilution methodology to measure the actual total atmospheric N input into a soil/plant system (Integrated Total Nitrogen Input, ITNI). A soil/plant system is labeled with [N]ammonium-[N]nitrate and the total input of airborne N is calculated from the dilution of this tracer by N from the atmosphere. An average annual deposition of 64 ± 11 kg/ha x year from 1994–2000 was measured with the ITNI system at the Bad Lauchst?dt research farm in the dry belt of Central Germany. Measurements in 1999/2000 at three other sites in Central Germany produced deposition rates of about 60 kg/ha x year. These data clearly show that the total atmospheric N deposition into the soil/plant system determined by the newly developed ITNI system significantly exceeds that obtained from standard wet-only and bulk collectors. The higher atmospheric N depositions found closely match those postulated from the N balances of long-term agricultural field experiments.

Determination of 15N in 15N-enriched nitrite and nitrate in aqueous samples by reaction continuous flow quadrupole mass spectrometry

The 15N tracer method is the most suitable method for studying complex N transformation processes in microbiology and biochemistry. It entails the constant determination of the 15N abundance of the inorganic nitrogen (N) compounds nitrite and nitrate. However, 15N analytical methods are time-consuming, difficult to automate, and require at least 10 µg of N per determination. An additional obstacle in the case of nitrite is that it usually only occurs in very small amounts (ppb) dwarfed by much larger quantities of nitrate (ppm). More useful is an approach in which the N compound is selectively converted into a gaseous form suitable for direct measurement by mass spectrometry. By using this ‘reaction continuous-flow mass spectrometry’ (R/CFMS) we developed methods for the 15N determination of nitrite and nitrate from tracer experiment samples, i.e. artificially enriched in 15N. Because both methods are based on the same principle, one continuous flow setup connected directly to a quadrupole mass spectrometer for all determinations was used. Nitrite and nitrate are reduced to NO by iodide and titanium(III) chloride, respectively. The technique developed ensures a precision of relative standard deviation ≤3% if at least 0.5 and 2 µg N with an abundance of ≥1 at.% are to be measured for nitrite and nitrate, respectively. Copyright

Measuring of the Integral Airborne Nitrogen-Input into a Soil-Plant System by the 15N-Isotope Dilution Method

Abstract Airborne nitrogen-inputs so far have only been measured in single fractions (deposition on plant surfaces or on soil and direct absorption of nitrogen containing gases by plants) by intensive exposition experiments in gas chambers, measurement of wet and dry N-deposition in the field and very expensive micrometereological field measurements. It is very difficult to estimate any overall N-input with practical relevance from these single N-component measurements. In this introduced field experiment an isolated measuring system is labelled with a 15N-tracer since it is not possible to label the nitrogen compounds of the atmosphere (e.g. NH3, NOx) which are to be absorbed. Through the dilution of this 15N-tracer by nitrogen derived from the atmosphere the total input of airborne nitrogen is determined. As soil resembling substrate sand was used and summer wheat was planted. With the regular and automated irrigation of nitrogen-free nutrient solution and the collection of precipitation surpluses this ...

Denitrification in the River Estuaries of the Northern Baltic Sea

Abstract Estuaries have been suggested to have an important role in reducing the nitrogen load transported to the sea. We measured denitrification rates in six estuaries of the northern Baltic Sea. Four of them were river mouths in the Bothnian Bay (northern Gulf of Bothnia), and two were estuary bays, one in the Archipelago Sea (southern Gulf of Bothnia) and the other in the Gulf of Finland. Denitrification rates in the four river mouths varied between 330 and 905 μmol N m−2 d−1. The estuary bays at the Archipelago Sea and the Gulf of Bothnia had denitrification rates from 90 μmol N m−2 d−1 to 910 μmol N m−2 d−1 and from 230 μmol N m−2 d−1 to 320 μmol N m−2 d−1, respectively. Denitrification removed 3.6–9.0% of the total nitrogen loading in the river mouths and in the estuary bay in the Gulf of Finland, where the residence times were short. In the estuary bay with a long residence time, in the Archipelago Sea, up to 4.5% of nitrate loading and 19% of nitrogen loading were removed before entering the sea. According to our results, the sediments of the fast-flowing rivers and the estuary areas with short residence times have a limited capacity to reduce the nitrogen load to the Baltic Sea.

Atmogener N‐Eintrag in Boden und Pflanze am Standort Bad Lauchstädt: Ergebnisse aus 15N‐Gestützten direktmessungen (ITNI‐System) im Vergleich zur indirekten Quantifizierung aus N‐Bilanzen des Statischen Dauerdüngungsversuches

Die durchschnittliche N‐Emission betrug in Deutschland Anfang der 90er Jahre 2,1 Mill, t N/a (Ammoniak/Ammonium und NOx). Daraus resultiert unter Berücksichtigung von Ex‐ und Import von Stickstoff in der Atmosphäre bei Annahme einer gleichmäßigen Verteilung über die gesamte Bundesrepublik eine durchschnittliche N‐Deposition von 45 kg/ha*a. Über die Höhe der tatsächlichen jährlichen N‐Deposition und dessen Verteilung herrscht jedoch noch große Unsicherheit. Die üblichen Bestimmungsmethoden, Wet Only‐ und Bulk‐Sammler, lieferten jedoch nur Werte von ca. 30 kg N/ha *a. Diese Werte beinhalten nicht die gasförmige Deposition und die direkte N‐Aufnahme durch die Pflanze. Zur exakten direkten Bestimmung des gesamten atmogenen N‐Eintrages in das System Boden‐Pflanze wurde daher das IT??‐Meßsystem (ITNI = Integral Total Nitrogen Input) entwickelt. Es basiert auf der 15N‐Isotopenverdünnungsmethode, d.h. anstatt die deponierten Stickstoflkomponenten der Atmosphäre zu markieren, was in Feldversuchen nicht möglich ist, wird in einem Gefäß mit Pflanzenbewuchs (Boden‐Pflanze‐System) ein [15N]Ammoniumnitrat‐Tracer eingesetzt und die Verdünnung dieses 15N‐Tracers durch den aufgenommenen atmogenen Stickstoff als Maß für die eingetragene N‐Menge gemessen. Mit diesem System wurden in den Jahren 1994 bis 1998 am Standort Bad Lauchstädt Gesamt‐N‐Einträge von durchschnittlich 64 ±12 kg/ha und Jahr gemessen. Eine Möglichkeit der indirekten Bestimmung des gesamten atmogenen N‐Eintrages in das System Boden‐Pflanze ergibt sich aus der Stickstoffbilanz von langjährigen Feldversuchen ohne N‐Düngung. Für den “Statischen Düngungsversuch Bad Lauchstädt”; erhält man danach jährliche Stickstoffdepositionen von 50–60 kg/ha und Jahr und bestätigt damit die mit dem ITNI‐System gemessenen Werte. Ferner wird diese Größenordnung durch andere Dauerfeldversuche in Deutschland und Europa erhärtet.

Release of nitrous oxide and dinitrogen from a transition bog under drained and rewetted conditions due to denitrification: results from a [15N]nitrate-bromide double-tracer study.

Denitrification is well known being the most important nitrate-consuming process in water-logged peat soils, whereby the intermediate compound nitrous oxide (N2O) and the end product dinitrogen (N2) are ultimately released. The present study was aimed at evaluating the release of these gases (due to denitrification) from a nutrient-poor transition bog ecosystem under drained and three differently rewetted conditions at the field scale using a 15N-tracer approach ([15N]nitrate application, 30 kg N ha−1) and a common closed-chamber technique. The drained site is characterized by a constant water table (WT) of –30 cm (here referred to as D30), while rewetted sites represent a constant WT of –15 cm, a constant WT of 0 cm (i.e. waterlogged), and an initial WT of 0 cm (which decreased slightly during the experiment), respectively, (here referred to as R15, R0, and R0d, respectively). The highest N2O emissions were observed at D30 (291 µg N2O–N m−2 h−1) as well as at R0d (665 µg N2O–N m−2 h−1). At the rewetted peat sites with a constant WT (i.e. R15 and R0), considerably lower N2O emissions were observed (maximal 37 µg N2O–N m−2 h−1). Concerning N2 only at the initially water-logged peat site R0d considerable release rates (up to 3110 µg N2–N m−2 h−1) were observed, while under drained conditions (D30) no N2 emission and under rewetted conditions with a constant WT (R15 and R0) significantly lower N2 release rates (maximal 668 µg N2–N m–2 h−1) could be detected. In addition, it has been found that natural WT fluctuations at rewetted peat sites, in particular a rapid drop down of the WT, can induce high emission rates for both N2O and N2.

Nitrate turnover in a peat soil under drained and rewetted conditions: results from a [15N]nitrate–bromide double-tracer study

Under natural conditions, peatlands are generally nitrate-limited. However, recent concerns about an additional N input into peatlands by atmospheric N deposition have highlighted the risk of an increased denitrification activity and hence the likelihood of a rise of emissions of the greenhouse gas nitrous oxide. Therefore, the aim of the present study was to investigate the turnover of added nitrate in a drained and a rewetted peatland using a [15N]nitrate–bromide double-tracer method. The double-tracer method allows a separation between physical effects (dilution, dispersion and dislocation) and microbial and chemical nitrate transformation by comparing with the conservative Br− tracer. In the drained peat site, low NO3− consumption rates have been observed. In contrast, NO3− consumption at the rewetted peat site rises rapidly to about 100% within 4 days after tracer application. Concomitantly, the 15N abundances of nitrite and ammonium in soil water increased and lead to the conclusion that, besides commonly known NO3− reduction to nitrite (i.e. denitrification), a dissimilatory nitrate reduction to ammonium has simultaneously taken place. The present study reveals that increasing NO3− inputs into rewetted peatlands via atmospheric deposition results in a rapid NO3− consumption, which could lead to an increase in N2O emissions into the atmosphere.