Published online 11 January 2008
Published in Soil Sci Soc Am J 72:135-142 (2008)
DOI: 10.2136/sssaj2007.0092
© 2008 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
SOIL BIOLOGY & BIOCHEMISTRY
Shortcomings in the Commercialized Barometric Process Separation Measuring System
Joachim Ingwersena,*,
Ulrich Schwarza,
Claus Florian Stangeb,
Xiaotang Juc and
Thilo Strecka
a Univ. of Hohenheim, Institute of Soil Science and Land Evaluation, Biogeophysics Section, D-70593 Stuttgart, Germany
b UFZ, Helmholtz Centre for Environmental, Research Dep. of Soil Physics, Theodor-Lieser-Strasse 4, D-06120 Halle/Saale, Germany
c China Agricultural Univ., College of Agricultural Resources and Environmental Sciences, Beijing, 10009, P.R. China
* Corresponding author (jingwer{at}uni-hohenheim.de).
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ABSTRACT
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In a growing number of studies, the barometric process separation (BaPS) method has been applied for measuring gross nitrification rates in soil. In 2000, the company Umweltanalytische Mess-Systeme (UMS) GmbH (Munich, Germany) presented the first and only commercially available automatic BaPS measuring system. In an ongoing project, we have used the UMS BaPS system to measure gross nitrification rates in two alkaline agricultural soils. During data evaluation, we came across certain shortcomings in the UMS data evaluation routine. We identified three problems: (i) a unit error in the calculation of the carbonate equilibrium, (ii) an erroneous calculation when the respiration quotient is unequal to unity, and (iii) an inappropriate procedure for handling a negative rate of N gases produced by denitrification (
NxOy). Particularly the error in calculating the carbonate equilibrium caused a significant overestimation of the gross nitrification rate at pH values >6. A literature review showed that the BaPS method works well in acidic to weakly acidic soils. For soils with higher pH values, its performance remains unclear. More research is needed to test the applicability of the BaPS method in neutral and alkaline soils.
Abbreviations: BaPS, barometric process separation • UMS, Umweltanalytische Mess-Systeme GmbH
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INTRODUCTION
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Nitrification is a central process in the soil N cycle. The standard method for measuring gross nitrification rates in soil is the 15N pool dilution technique (Kirkham and Bartholomew, 1954). Despite some methodological difficulties such as the homogeneous application of the labeled material, this method is well established and has been proven to be applicable to a wide range of soils and conditions (Murphy et al., 2003). An alternative method, the barometric process sepa ration (BaPS) method, has been proposed by Ingwersen et al. (1999). Advantages of the BaPS method include the fact that no labeled material must be added to the soil. In addition, the equipment is relatively inexpensive, widely available, easy to operate, and the measurement is quick. In the BaPS method, a soil sample is incubated in a closed chamber under isothermal conditions. Then, the O2 net consumption and the CO2 net production from the soil sample, as well as the total net gas balance of the chamber's atmosphere, are monitored, typically for 12 to 24 h. By solving balance equations for O2, CO2, and total gas, the BaPS method yields soil respiration, nitrification, and denitrification rates. Several studies tested the BaPS method against the 15N pool dilution technique and found good agreement (Breuer et al., 2002; Kiese et al., 2002). A pronounced systematic overestimation of gross nitrification rates by the BaPS method was observed by Müller et al. (2004) in a study with a grassland soil. But by manipulating the respiration quotient, they adjusted the outcome of the BaPS method to the results of the 15N pool dilution technique.
In 2000, the company Umweltanalytische Mess-Systeme (UMS) GmbH (Munich, Germany) presented the first commercially available automatic BaPS measuring system. It consists of a water-cooled aluminum chamber that holds up to seven 100-cm3 soil cores. In the head of the chamber, O2, CO2, pressure, and temperature sensors are installed. The data are evaluated by integrated software. In an ongoing project, we have used the UMS BaPS system to measure gross nitrification rates in two alkaline agricultural soils. During data evaluation, we discovered errors in the calculations implemented in the UMS data evaluation software. In this study, we identified these errors and determined how they affect the result of the BaPS calculation. Here we review the literature for studies that have used the UMS BaPS system and discuss whether erroneous calculations might have affected data interpretation.
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THEORY OF THE BAROMETRIC PROCESS SEPARATION METHOD
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The theory of the BaPS method has been described in detail elsewhere (Ingwersen et al., 1999). In brief, the central equation of the BaPS method is
 | [1] |
where NxOy (mol s–1) stands for the rate of N gases produced by denitrification, n (mol s–1) denotes the net rate of total gas production or consumption, while CO2 (mol s–1) and O2 (mol s–1) are the net rates of CO2 formation and O2 depletion, respectively, in the chamber's headspace atmosphere.
For the net O2 consumption, we may write
 | [2] |
and the net CO2 production may be expressed as
 | [3] |
where the subscripts R, N, and D refer to respiration, nitrification, and denitrification, respectively. Note that in the case of a gas-producing process, the value of a rate has a positive sign (e.g., CO2,R), and when gas is consumed, the rate is negative (e.g., O2,N). The terms O2,aq and CO2,aq take into account that, due to concentration changes during incubation, O2 is released from the soil solution to the chamber's atmosphere and CO2 is transferred from the chamber's atmosphere to the soil solution. In the study of Ingwersen et al. (1999), the term O2,aq was not included in the calculation because of the much lower water solubility of O2 compared with CO2. In the UMS BaPS system, this term has been introduced. Its calculation is based on Henry's law.
Inserting Eq. [2] and [3] into Eq. [1] and rearranging the resulting equation for n, we may write the equation for the rate of total net gas production or consumption (mol s–1) as
 | [4] |
The relationship between O2 consumption and CO2 assimilation during autotrophic nitrification is described in the BaPS system using the 
ratio:
 | [5] |
The BaPS method uses a literature value of = 7.3. Substituting the term O2,N in the total net gas balance equation (Eq. [4]) with the term CO2,N (see Eq. [5]), the rate of CO2 assimilated by nitrifiers (mol s–1) may be calculated by
 | [6] |
Note that Eq. [6] is valid only for autotrophic nitrification and presumes that the respiration quotient (RQ) equals unity! In the notation of this study, RQ is defined as the negative ratio between CO2,R and O2,R:
 | [7] |
In the case of RQ = 1, CO2,R may be directly replaced with –O2, and vice versa.
In the study of Ingwersen et al. (1999), the calculation of CO2,aq was restricted to the physical dissolution of CO2 into water using Henry's law. This was feasible because the studied soil's pH was <4 and therefore the other two species of the carbonate equilibrium, HCO3– and CO3–, were negligible. At pH values >6, however, these two species become significant (Sparks, 2003). In the UMS BaPS system, a calculation of the total carbonate concentration in pure water as a function of the CO2 partial pressure and pH was therefore originally added to the evaluation algorithm. Using the law of mass action, the sum of all carbonate species dissolved in pure water (CO2,aq, mol L–1; see e.g., Sparks, 2003) is
 | [8] |
where KH (mol L–1 Pa–1) is the Henry constant, which depends on temperature and ionic strength, and (Pa) is the partial pressure of CO2. The symbols (mol L–1) and (mol L–1) denote the dissociation constants of H2CO3 and HCO3–, respectively, and [H+] (mol L–1) stands for the H ion concentration. Note that the developers of the UMS BaPS system do not differentiate between concentrations and activities.
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MATERIALS AND METHODS
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Samples were taken from two slightly alkaline soils. The first soil was sampled from the top 20 cm of a winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) rotation field at the Dongbeiwang Agricultural Experimental Station of the China Agricultural University (40°4.8' N, 116°16.8' E), Beijing, China. The station is situated in the North China Plain within a continental monsoon zone with a hot and rainy summer and a dry and cold winter. Mean annual temperature is 11.8°C with an average annual precipitation of 578 mm (Schröder, 2000). The soil is classified as a Calcaric Cambisol (FAO, 1998) or Calcixerept (Soil Survey Staff, 2006). The soil texture is silt loam, with an organic C content of 11.0 g kg–1. The soil pH is 7.6 in 0.01 mol L–1 CaCl2 and 8.0 in water. The second soil was sampled at the Julius-Kühn-Feld long-term experimental station in Halle (Saale) (51°30.8' N, 11°59.9' E), Germany. The experimental station is situated in a plain of the eastern foreland of the Harz Mountains. The site belongs to the central German arid region. The annual precipitation is highly variable and ranged during the last decades from 258 to 700 mm. The average annual temperature is 9.2°C. Soil samples were taken from an Ap horizon directly adjoining the Eternal Rye Trial. The soil is a Haplic Phaeozem (FAO, 1998) or Hapludoll (Soil Survey Staff, 2006) with an A horizon of about 60 cm. The organic C content is 13.0 g kg–1. The pH of the soil sample is 7.4 in 0.01 mol L–1 CaCl2 and 7.8 in water. For further details, see Merbach et al. (2000). From each site, about 3.5 kg of fresh soil was taken, sieved to <2 mm, homogenized, divided in three about equal parts, and stored in plastic bags at –18°C.
Gross nitrification rates were determined simultaneously using the BaPS method (Ingwersen et al., 1999) and 15N pool dilution technique (Kirkham and Bartholomew, 1954). Measurements with the BaPS method were performed and evaluated using the BaPS system (Version 2.1.1) from UMS GmbH. The BaPS calculation was performed with delta values. The ratio between N2 and N2O produced during denitrification was set to 2:1. The respiration coefficient was assumed to be unity and the fraction of heterotrophic nitrification was fixed to zero. As recommended by the manufacturer, sensors were calibrated annually. The UMS BaPS system includes a Microsoft Excel worksheet that performs the rate calculations in the same way as the integrated UMS data evaluation software. Based on this worksheet, we retraced the calculations.
The frozen soil was put into a refrigerator (4°C) 5 d before the experiment commenced. After defrosting, the soil was homogeneously labeled by spraying it with a solution containing 7 mg K15NO3 (99 atom%), yielding a 10 atom% 15N enrichment. The volumetric water content was adjusted to 25%. Subsequently, the soil sample was preincubated for 2 h and split into two subsamples. The first subsample was transferred to seven 100-cm3 soil cores and compacted to a bulk density of 1.3 g cm–3. The cores were then placed in the BaPS container. After constant temperature was achieved, soil samples were incubated for 20 h at 17°C. The second subsample was used to determine the initial 15N abundance and concentration of the NO3 pool in quadruplicate. Nitrate was extracted from the soil with 1 mol L–1 KCl (12.5 g soil/50 mL KCl solution). After incubation, three soil cores were removed from the BaPS container and used to measure the final concentration and 15N abundance of the NO3 pool. From each of the three cores, three subsamples of 12.5 g were taken and extracted with 50 mL of KCl solution. The NO3 concentration in the KCl extracts was determined using flow injection colorimetry, and the 15N/14N ratio was measured using the SPINMAS technique (Stange et al., 2007). For each site, the incubation experiment was repeated three times.
The statistical analysis of the data was performed with SPSS Version 12.0.1 (SPSS, 2003). Calculated gross nitrification rates were compared between the different computation routines by a one-way ANOVA followed by Fisher's LSD post hoc test for significant differences between means. The LSD test was performed as a two-tailed test using a 0.05 significance level.
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RESULTS AND DISCUSSION
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Error in the Calculation of the Carbonate Equilibrium
As mentioned above, the evaluation algorithm of the UMS BaPS system was extended for the calculation of the total carbonate concentration in water as a function of the CO2 partial pressure and pH. This calculation, however, is erroneous due to a unit error. The soil pH in the Excel spreadsheet is given in units of millimoles per liter but the dissociation constants are given in moles per liter. This results in a highly significant underestimation of CO2,aq at soil pH values >6 (Fig. 1
); this, in turn, leads to a pronounced underestimate of the O2 consumption by respiration and consequently significantly overestimates O2 consumption by nitrification (i.e., the gross nitrification rate). The resulting error (in moles) is given by the following equation (for derivation, see Eq. [A1–A6] in the Appendix):
 | [9] |
where Vaq (L) is the total soil water volume in the cores. Besides temperature (KH is a function of the temperature) and the soil water content, the size of the error depends on the soil pH and the change in the CO2 partial pressure during the experiment (Fig. 2
). Increasing soil pH by one unit increases the error by a factor of 10. The error given in Eq. [9] is an absolute error. Because the error does not depend on O2,N, the relative error can be immediately calculated by dividing the absolute error by O2,N.
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Fig. 1. Sum of carbonate species as implemented in the Umweltanalytische Mess-Systeme (UMS) barometric process separation (BaPS) system and the corrected calculation as a function of pH (see Eq. [8]). The calculations were performed assuming a CO2 partial pressure of 30 Pa and a temperature of 10°C (dissociation constants used were log KH = –6.298 mol L–1 Pa–1, log KH2CO3 = –6.35 mol L–1, and log KHCO3= –10.33 mol L–1).
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Fig. 2. Nomogram for the error in the calculation of the O2 nitrification rate caused by a pH unit error in calculating the carbonate equilibrium in the Umweltanalytische Mess-Systeme barometric process separation (BaPS) data evaluation algorithm. The calculation (see Eq. [9]) was performed for 10°C and assuming that the incubation chamber was loaded with seven 100-cm3 soil cores with a volumetric water content of 25% (water volume = 0.175 L). The dissociation constants used were log KH = –6.298 mol L–1 Pa–1, log KH2CO3 = –6.35 mol L–1, and log KHCO3 = –10.33 mol L–1.
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Erroneous Calculation for Respiration Quotient Not Unity
In the UMS BaPS system, Eq. [6] is used to calculate the CO2 assimilated by autotrophic nitrifiers. Equation [6], however, holds only for RQ = 1. Only in this case do the terms O2,R and CO2,R cancel out in Eq. [4]. In the event that RQ 
1, the following equation must be used (for derivation, see Eq. [A7–A8] in the Appendix):
 | [10] |
The error with regard to O2,N caused by the use of Eq. [6] for RQ 1 is (for derivation, see Eq. [A9–A15] in the Appendix)
 | [11] |
For an RQ >1, the UMS BaPS system underestimates the gross nitrification rate, and for RQ <1, the UMS BaPS system overestimates it (Fig. 3
). Compared with the error induced by the erroneous calculation of the carbonate equilibrium, this error is small. In the range of reasonable RQ and CO2,R values, the absolute error of O2,N does not exceed 5 µmol.
Inappropriate Procedure for Handling a Negative Denitrification Nitric Gas Production Rate
The BaPS calculation might result in a negative value for NxOy (Müller et al., 2004). In the UMS BaPS system, the value of NxOy is set to zero in such a case, and the subsequent calculation of the gross nitrification rate is performed as usual. Below, we will show that this procedure yields a gas balance error and violates the previous assumption regarding the ratio. We propose to use one of the following two procedures.
Distributed Error Adjustment
The term NxOy is computed based on three measurements: n, O2, and CO2. Each of these measurements is subject to error. In the "distributed error adjustment" approach, a negative value of NxOy is regarded as the sum of these measurement errors, and each measurement is adjusted by its weight to the total error. Using the law of propagation of error (Meschede, 2006), the total variance of the derived NxOy value may be calculated as
 | [12] |
The subscripts n, O2, and CO2 refer to the corresponding measurements. In this study, the variance of each measuring device was derived by running a water-cooled empty BaPS container for 2 h, collecting data on O2, CO2, and pressure, and computing the variance of the readings. The fraction of a single measurement in the total error may be calculated by dividing the error of the respective measurement by the total variance of NxOy. The fraction of the CO2 measurement in the total variance, for example, may be calculated as
 | [13] |
For the weights, we found wn = 0.21, WO2 = 0.27, and WCO2 = 0.52. Based on these weights, the error (NxOy) was distributed across the three measurements as follows:
 | [14] |
 | [15] |
 | [16] |
Unknown Process
In this approach, a negative NxOy value is assumed to be caused by an unknown gas-consuming process X, which consumes neither O2 nor CO2 (e.g., heterotrophic N2 fixation by free-living bacteria, etc.). Then the gas balance becomes
 | [17] |
Here, we encounter the problem of two unknown variables but only one equation. Equation [17] is solvable only if we assume that the term NxOy is zero, i.e., that denitrification is negligible in the soil under study. Accepting this assumption, for the CO2 produced by respiration we have
 | [18] |
Equation [18] may be derived in analogy to Eq. [A16] (see Appendix). Based on CO2,R, the remaining terms can be calculated stepwise.
Example Measurements
The BaPS measurement of the Dongbeiwang soil showed a negative NxOy value of –5.9 µmol h–1 on average. A negative value was treated using either the UMS approach, which was corrected for the pH unit error before calculation, or using one of the two approaches proposed here. By way of example for one of the replicates, the outcomes of the three procedures are compared in Table 1
. In the UMS approach, the gas balance check shows that setting a negative NxOy value to zero causes a gas balance error (see n' in Table 1). Moreover, in the UMS approach, the resulting O2,N/CO2,N ratio deviates from the preassigned value of 7.3. Instead of 7.3, the resulting O2,N/CO2,N ratio is 3.2. With regard to O2,N, the UMS approach gives about a 15% lower rate than the "unknown process" procedure. In the "distributed error adjustment" approach, the computed O2 consumption by nitrification is about twice as high as in the UMS approach. Note that the difference between the two approaches depends on the size of NxOy. The larger the deficit, the larger the difference between the approaches.
Figures 4
and 5
compare the results of the UMS BaPS system with the results obtained with the proposed calculation routines. For the Dongbeiwang soil, the UMS BaPS system overestimated the gross nitrification rate, as determined by the 15N pool dilution technique, by a factor of about four (Fig. 4). Because of the pH unit error, the term CO2,aq was strongly underestimated in the UMS BaPS system. Instead of using a pH(CaCl2) value of 7.6, for example, the UMS BaPS system calculated the carbonate equilibrium for a pH of 4.6. As a consequence, in the example measurement, the UMS BaPS calculation had a low sensitivity to pH, and therefore the use of pH(CaCl2) or pH(H2O) yielded very similar gross nitrification rates. In the corrected results, this was totally different. In this case, the results depended strongly on the method used to measure soil pH, reflecting the high pH sensitivity of the CO2,aq term in the neutral to alkaline pH range. After recalculation and using pH(H2O), the results of the BaPS method and the 15N pool dilution technique were in the same range. Using pH(CaCl2), the BaPS method still overestimated the gross nitrification rate measured by the 15N pool dilution technique by a factor of 2 to 3.
The main findings for the Julius-Kühn-Feld soil were very similar to those obtained for the Dongbeiwang soil. With two of the three replicates, the NxOy value was slightly positive (0.1 and 0.2 µmol h–1). For these two replicates, it was not necessary to adjust the measured O2, CO2, and n data before evaluation. For the third replicate, the NxOy value was slightly negative (–1.0 µmol h–1). This replicate was evaluated using the "unknown process" procedure. The "distributed error adjustment" procedure yielded a slightly higher gross nitrification rate than the "unknown process" procedure [e.g., for pH(CaCl2), 38 µg N kg–1 h–1 using the "unknown process" procedure vs. 43 µg N kg–1 h–1 using the "distributed error adjustment" approach]. The UMS BaPS system overestimated the 15N gross nitrification rate by a factor of about four (Fig. 5), and the method chosen for measuring the soil pH had no effect on the outcome. Correcting the calculation for the CO2,aq term improved the agreement between the 15N pool dilution technique and the BaPS method. After correction and using pH(H2O), the gross nitrification rate measured with the latter method (15 ± 3 µg N kg–1 h–1) was very close to the rate determined with the former technique (17 ± 7 µg N kg–1 h–1). Both rates were not significantly different at 
= 0.05. As was the case for the Dongbeiwang soil using pH(CaCl2), the BaPS method overestimated the 15N gross nitrification rate by a factor of 2.4. The significant difference between the rates obtained with pH(CaCl2) or pH(H2O) underlines the high sensitivity of the BaPS method with regard to soil pH or, more specifically, the CO2,aq term in neutral to alkaline soils.
Literature Review
From 1999 to 2006, 10 publications applied the BaPS method to measure gross nitrification rates in soil (Table 2
). Seven of these 10 studies used the UMS BaPS system. As shown above, the error in calculating the carbonate equilibrium becomes significant at soil pH values >6. Among the studies that used the UMS BaPS system, three measured gross nitrification rates in soils exceeding this critical pH value. These cases require reevaluating the BaPS data to quantify the extent to which the UMS BaPS system's shortcomings have affected the results.
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Table 2. Summary of published studies that used the barometric process separation (BaPS) method for measuring gross nitrification rates.
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Müller et al. (2004) measured gross nitrification rates from a Fluvic Gleysol at a grassland site. In comparing the UMS BaPS method to the 15N pool dilution technique, they found that the former yielded 1.5 to 2.5 times higher rates. They hypothesized that an RQ <1 caused this overestimation. By manipulating the RQ, the BaPS results were adjusted to the rates determined by the 15N pool dilution technique. In light of our recent findings, however, such an overestimation could also be explained at least partly by the error in calculating the carbonate equilibrium.
The high sensitivity of the BaPS calculation with regard to RQ was also shown theoretically by Ingwersen et al. (1999). Based on a sensitivity analysis, they demonstrated that a discrepancy between the RQ used in the BaPS calculation and the real RQ in soil may cause large errors in the obtained gross nitrification rate. For example, if the BaPS calculation assumes an RQ = 1 but it is actually 0.95, then—depending on the CO2,R/O2,N ratio—the gross nitrification rate may be overestimated by up to 80%. The present study, however, focuses not on this problem but on the fact that the UMS BaPS calculation uses an inappropriate equation when RQ 1. Even if the RQ used in the BaPS calculation agrees with the soil RQ, the calculation remains erroneous in the UMS BaPS system because of the wrong use of Eq. [6].
The review shows that the BaPS method is suited to measure gross nitrification rates from acidic to weakly acidic soils. For soils with a higher pH, however, applying the BaPS is currently problematic. Besides this study, only one other study has tested the BaPS method against the 15N pool dilution technique for neutral to alkaline soils. Heidenfelder (2002) studied gross nitrification rates from a Rendzic Leptosol derived from Jurassic limestone. The BaPS method—neglecting HCO3– formation due to a higher CO2 concentration during incubation—led to a strong overestimation compared with the 15N pool dilution data. Incorporating HCO3– formation improved the agreement between the two methods, but the agreement was still much less satisfactory than for studies with acidic soils. This researcher concluded that Eq. [8], which describes the carbonate equilibrium in pure water, can only estimate the total carbonate concentration in soil solutions whose ionic composition is complex and variable. Our findings point in a similar direction. The choice of the method used to measure soil pH strongly affected the BaPS calculation: accurately quantifying the CO2,aq term is essential when applying this method at neutral to alkaline sites.
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CONCLUSIONS
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This study identified three shortcomings in the UMS BaPS system: (i) a unit error in the calculation of the carbonate equilibrium, (ii) an erroneous calculation if RQ 1, and (iii) an inappropriate procedure for handling a negative NxOy value. The error in calculating the carbonate equilibrium caused a significant overestimation of the gross nitrification rates at weakly neutral to alkaline pH. We recommend that future studies report the value of NxOy and state how a negative value was handled. For a negative value, we propose the use of either the "unknown process" or the "distributed error adjustment" procedure. Which of these two procedures performs best for a variety of soils remains to be established in further experimental studies. The literature review showed that, in acidic to weakly acidic soils, the BaPS method is well suited for measuring gross nitrification rates. At pH >6, the outcome of the BaPS method becomes highly sensitive to accurately quantifying the transfer of gaseous CO2 from the incubation chamber's atmosphere to the soil solution. Future research is needed to adapt the BaPS method to neutral and alkaline soils and to reliably quantify this CO2 transfer during incubation.
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NOTE ADDED IN PROOF
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Our results have led to a revision and extension of the UMS BaPS evaluation software according to this paper. The revised software (Version 2.2) is available at the company's website (http:/www.ums-muc.de).
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APPENDIX
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Derivation of the Error Caused by the Unit Error in the Commercial System
The error in calculating the O2 consumption by autotrophic nitrification caused by the unit error is
 | [A1] |
where O2,N* is the erroneous calculation of the UMS BaPS system. By combining the total gas balance (Eq. [4]) with the ratio (Eq. [5]), the rate of O2 consumption by nitrification may be expressed as
 | [A2] |
In the UMS BaPS system, the erroneous term CO2,aq* is used for computation, and Eq. [A2] may be written as
 | [A3] |
Inserting Eq. [A2] and [A3] into Eq. [A1] gives
 | [A4] |
Inserting Eq. [8] into Eq. [A4] with and without the pH unit error yields
 | [A5] |
and rearranging Eq. [A5] gives
 | [A6] |
The unit of the error in Eq. [A6] is moles per liter. By multiplying Eq. [A6] with Vaq, the error may also be expressed in moles.
Derivation of the Error for Respiration Quotient Not Unity
In the UMS BaPS system, Eq. [6] is used to calculate CO2,N. When RQ 1, this calculation becomes erroneous. The general form of Eq. [6] is
 | [A7] |
Equation [A7] may be immediately derived by replacing O2,N with CO2,N (see Eq. [5]) in the total gas balance (Eq. [4]) and rearranging the resulting equation for CO2,N. When RQ 1, the terms CO2,R and O2,R do not cancel out in Eq. [A7] and the relation O2,R = (–1/RQ)CO2,R must be used in further calculations (see Eq. [7]). Using this RQ relation, Eq. [A7] may be rewritten as
 | [A8] |
The error in calculating the O2 consumption by nitrification caused by the wrong use of Eq. [6] when RQ 1 may be written as
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| [A9] |
where O2,N* is the erroneous calculation of the UMS BaPS system. Combining Eq. [2] with the RQ relation gives the rate of O2 consumption by nitrification as
 | [A10] |
and the error in the UMS BaPS calculation may be rewritten as
 | [A11] |
where CO2,R* is the UMS BaPS calculation for CO2,R. For CO2,R, we may write (see Eq. [3])
 | [A12] |
and the erroneous calculation of CO2,R may be expressed as
 | [A13] |
wher e CO2,N* is the erroneous calculation of the CO2 consumed during autotrophic nitrification. Inserting Eq. [A12] and Eq. [A13] into Eq. [A11] gives
 | [A14] |
Inserting Eq. [A8] and Eq. [6] into Eq. [A14] gives, for the error,
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| [A15] |
The term CO2,R may be computed using the following equation:
 | [A16] |
Equation [A16] may be derived from the ratio:
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| [A17] |
Using Eq. [2] in the numerator and Eq. [4] in the denominator, Eq. [A17] may be rewritten as
 | [A18] |
Finally, we substitute the RQ ratio into O2,R in the numerator, replace O2,N with Eq. [2] in the denominator, and rearrange the resulting equation for CO2,R.
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ACKNOWLEDGMENTS
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We thank Dr. H. Eißner from the Martin-Luther University Halle-Wittenberg for his support. This work was funded by the German Research Foundation (DFG) in the framework of the Sino-German Research Training Group "Sustainable Resource Use in North China".
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NOTES
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All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication March 5, 2007.
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REFERENCES
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- Breuer, L., R. Kiese, and K. Butterbach-Bahl. 2002. Temperature and moisture effects on nitrification rates in tropical rain-forest soils. Soil Sci. Soc. Am. J. 66:834–844.[Abstract/Free Full Text]
- Brüggemann, N., P. Rosenkranz, H. Papen, K. Pilegaard, and K. Butterbach-Bahl. 2005. Pure stands of temperate forest tree species modify soil respiration and N turnover. Biogeosci. Discuss. 2:303–331.
- Chen, S., and Y. Huang. 2006. Determination of respiration, gross nitrification and denitrification in soil profile using BaPS system. J. Environ. Sci. 18:937–943.[CrossRef]
- FAO. 1998. World reference base for soil resources. World Soil Resour. Rep. 84. FAO, Rome.
- Heidenfelder, A. 2002. Einfluß von Klima und Bewirtschaftung auf am N-Umsatz beteiligte mikrobielle Prozesse in Waldböden. (In German, with English abstract.) Ph.D. diss. Albert-Ludwigs-Univ. Freiburg, Freiburg, Germany.
- Ingwersen, J., K. Butterbach-Bahl, R. Gasche, O. Richter, and H. Papen. 1999. Barometric process separation: New method for quantifying nitrification, denitrification, and nitrous oxide sources in soils. Soil Sci. Soc. Am. J. 63:117–128.[Abstract/Free Full Text]
- Kiese, R., H. Papen, E. Zumbusch, and K. Butterbach-Bahl. 2002. Nitrification activity in tropical rain forest soils of the coastal lowlands and Atherton tablelands, Queensland, Australia. J. Plant Nutr. Soil Sci. 165:682–685.[CrossRef]
- Kirkham, D., and W.V. Bartholomew. 1954. Equations for following nutrient transformations in soil, utilizing tracer data. Soil Sci. Soc. Am. Proc. 18:33–34.[Medline]
- Merbach, W., J. Garz, W. Schliephake, H. Stumpe, and L. Schmidt. 2000. The long-term fertilization experiments in Halle (Saale), Germany: Introduction and survey. J. Plant Nutr. Soil Sci. 163:629–638.[CrossRef]
- Meschede, D. (ed.). 2006. Gerthsen Physik. 23rd ed. (In German.) Springer Verlag, Berlin.
- Müller, C., M. Kaleem Abbasi, C. Kammann, T.J. Clough, R.R. Sherlock, R.J. Stevens, and H.J. Jäger. 2004. Soil respiratory quotient determined via barometric process separation combined with nitrogen-15 labeling. Soil Sci. Soc. Am. J. 68:1610–1615.[Abstract/Free Full Text]
- Murphy, D.V., S. Recous, E.A. Stockdale, I.R.P. Fillery, L.S. Jensen, D.J. Hatch, and K.W.T. Goulding. 2003. Gross nitrogen fluxes in soil: Theory, measurement and application of 15N pool dilution techniques. Adv. Agron. 79:69–118.
- Nübling, J. 1999. Development of a measuring device for determining gross nitrification rates in soil. (In German.) M.S. thesis. Univ. of Applied Sciences Offenburg, Offenburg, Germany.
- Rosenkranz, P., N. Brüggemann, H. Papen, Z. Xu, L. Horváth, and K. Butterbach-Bahl. 2006. Soil N and C trace gas fluxes and microbial soil N turnover in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary. Plant Soil 286:301–322.[CrossRef][Web of Science]
- Schröder, P. (2000): Die Klimate der Welt: Aktuelle Daten und Erläuterungen. Thieme, Stuttgart, Germany.
- Soil Survey Staff. 2006. Keys to Soil Taxonomy. 10th ed. Pocahontas Press, Blacksburg, VA.
- Sparks, D.L. 2003. Environmental soil chemistry. Academic Press, Amsterdam.
- SPSS. 2003. SPSS Version 12.0.1. SPSS, Chicago.
- Stange, C.F. 2007. A novel approach to combine response functions in ecological process modeling. Ecol. Modell. 204:547–552.[CrossRef][Web of Science]
- Stange, C.F., O. Spott, B. Apelt, and R.W.B. Russow. 2007. Automated and rapid online determination of 15N abundance and concentration of ammonium, nitrite, or nitrate in aqueous samples by the SPINMAS technique. Isotopes Environ. Health Stud. 43:227–236.[CrossRef][Web of Science][Medline]
- Sun, G., N. Wu, and P. Luo. 2005. Soil N pools and transformation rates under different land uses in a subalpine forest–grassland ecotone. Pedosphere 15:52–58.[Web of Science]
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ABSTRACT
INTRODUCTION
