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Total soluble nitrogen in forest soils as determined by persulfate oxidation and by high temperature catalytic oxidation.

Introduction

Soil soluble nitrogen (N) pools, including mineral N (N[H.sub.4.sup.+], N[O.sub.3.sup.-], and N[O.sub.2.sup.-]) and soluble organic fractions (e.g. amino acids and peptides), play a vital role in N cycling in forest ecosystems and in global biogeochemical cycling of N at the broader scale (Qualls and Haines 1991; Jones et al. 2004). It has been suggested that boreal forest plants utilise not only mineral N from soil but also soil organic N directly (Nasholm et al. 1998) and about half or more of N in soil solution occurs in organic form in forest ecosystems (Currie et al. 1996; Qualls et al. 2000; Yu et al. 2002). Soil soluble N is used as a sensitive indicator for soil N status (Zhong and Makeschin 2003). Moreover, soil soluble N also represents major inputs of N to surface water in forested watersheds and affects water quality (Hedin et al. 1995). The measurement of total soil soluble N is thus critical both for accurately estimating N fluxes in forest ecosystems and for predicting the potential for N pollution in associated water bodies (e.g. eutrophication).

Water and a range of salt solutions (e.g. Ca[Cl.sub.2], KCl, [K.sub.2]S[O.sub.4]) have been used for extracting soluble N from soil (Murphy et al. 2000; Zhong and Makeschin 2003). Acid Kjeldahl digestion is the classical method for determining total N in water samples and soil extracts (Kjeldahl 1883; Bremner and Mulvaney 1982; Cornell et al. 2003). This method is based on the conversion of organic N to N[H.sub.4.sup.+]-N in hot and concentrated [H.sub.2]S[O.sub.4] solution with selenium as catalyst. The N[H.sub.4.sup.+]-N is then distilled and determined by titration. However, this method is slow and cumbersome. Various persulfate ([K.sub.2][S.sub.2][O.sub.8]) oxidation (PO) methods have been introduced as alternatives for measuring total N in water and soil extracts (Ebina et al. 1983; Keroleff 1983; Cabrera and Beare 1993; Yu et al. 2003; Doyle et al. 2004). Using this method, both N[H.sub.4.sup.+]-N and organic N are converted to N[O.sub.3.sup.-]-N by the persulfate oxidising agent. The reaction takes place either in an autoclave or under the influence of ultraviolet light. The N[O.sub.3.sup.-]-N is determined colourimetrically (Cabrera and Beare 1993; Williams et al. 1995; Sparling et al. 1996). This method is simple, sensitive, reliable, and suitable for processing a large number of samples. However, total soluble N at higher concentrations (>9 mg/L) may be underestimated compared with Kjeldahl digestion (Cabrera and Beare 1993). High temperature oxidation (HTO) and high temperature catalytic oxidation (HTCO) were originally developed to determine the total N in seawater (Suzuki et al. 1985; Badr et al. 2003; Cornell et al. 2003). These methods convert all forms of N to NO or N[O.sub.2] by oxidising the samples in a high-temperature furnace, and the NO is coupled with ozone ([O.sub.3]) to produce N[O.sub.2.sup.*], which is measured subsequently by chemiluminescence. These methods are simple to perform and give excellent precision in water samples (Badr et al. 2003). Recently, the HTCO method has been used to measure dissolved soil N and throughfall N and N in diluted [K.sub.2]S[O.sub.4] extracts of soil (Merriam et al. 1996; Alavoine and Nicolardot 2001). However, only 5 soils with similar chemical properties and a single salt extract ([K.sub.2]S[O.sub.4]) were tested for determination of soil soluble N by the HTCO method (Alavoine and Nicolardot 2001). In this paper we compared the PO and the HTCO methods for determination of total N in a wide range of water and salt extracts (2 M KCl and 0.5 M [K.sub.2]S[O.sub.4]) from forest soils.

Materials and methods

Soil sampling

Twenty-four surface forest soil samples (0-0.10 m) were collected from south-east Queensland, Australia (from 25[degrees]46"29'S, 151[degrees]56"41'E to 27[degrees]00"28'S, 153[degrees]08"26'E). These encompass a range of soil types, forest types, management practices and levels of fertility (Table 1). Ten soil cores (60 mm in diameter) at the depth of 0-0.10 m were randomly taken from an area of 10 m by 20 m of each location in March 2002 and bulked as a composite sample. Field moist soil samples were passed through a 2-mm sieve and stored at 4[degrees]C before analysis. A subsample of each soil was air-dried and stored at room temperature. Analyses of soil pH, total C, total N, CEC, conductivity, particle size, and hot-water-extractable total N were carried out on air-dried soils, whereas water-soluble total N and KCl- and [K.sub.2]S[O.sub.4]-extractable total N were measured on field-moist soils. All results are expressed on an oven-dry soil basis.

Preparation of soil extracts

Water extracts were prepared by mixing 20 g (dry weight equivalent) of field-moist soil samples with 50 mL of distilled water (soil:water ratio 1:2.5) in an end-to-end shaker for 1 h and filtering through a Whatman 42 paper and then a 0.45-[micro]m filter membrane. Hot water extracts were obtained according to the method described by Sparling et al. (1998). In brief, 4.0g (dry weight equivalent) of air-dried soil was incubated with 20 mL water in a capped test-tube at 70[degrees]C for 18 h. The test-tubes were then shaken on an end-to-end shaker for 5 min, and filtered through a Whatman 42 paper, followed by a 0.45-[micro]m filter membrane. For the KCl extracts, 5 g (dry weight equivalent) of field-moist soil samples were extracted with 50 mL of 2 M KCl in an end-to-end shaker for 1 h and filtered through a Whatman 42 paper. The 0.5 M [K.sub.2]S[O.sub.4] extracts of chloroform (CH[Cl.sub.3])-fumigated and non-fumigated soil samples were prepared using the method described by Vance et al. (1987). In brief, 2 portions of 25g of field-moist soils (dry weight equivalent) were weighed, and one of them was directly extracted with 100mL 0.5 M [K.sub.2]S[O.sub.4] in an end-to-end shaker for 30 min, and filtered through a Whatman 42 paper. The other portion of soil was fumigated with CH[Cl.sub.3] vapour for 24 h, and then extracted as above. All above soil extracts were stored at -20[degrees]C before analysis.

Analysis of soluble N in soil extracts

Total soluble N in soil extracts was simultaneously measured by both the PO and the HTCO methods. The PO procedure described by Cabrera and Beare (1993) was adopted to convert all N in soil extracts (including water, hot water, 2 M KCl and 0.5 M [K.sub.2]S[O.sub.4]) to N[O.sub.3.sup.-]-N, which was then determined colourimetrically using a LACHAT Quickchem Automated Ion Analyser (QuikChem Method 10107-04-1-H for N[O.sub.3]/N[O.sub.2], Colorado, USA). All soil extracts with > 10 mg N/L were diluted before measurement. Five standard urea solutions, each containing 5 mg N/L, were used to measure persulfate oxidising efficiency in each run. Recovery of urea N by the PO method was 92.8%, 98.2%, and 98.6% for 2 M KCl, 0.5 M [K.sub.2]S[O.sub.4], and water matrices, respectively. For the HTCO method, soil extracts were combusted using medical grade 02 (purity >99.6%) at 720[degrees]C, total N in the extracts being converted to NO. The gas stream containing the NO was then cooled and dehumidified by the electronic dehumidifier, and the NO detected by chemiluminesce gas analyser. We use a SHIMADZU [TOC-.sub.VCPH/CPN] analyser (fitted with a TN unit) (Kyoto, Japan) for this work. It generally takes 10-12 min to analyse one sample. Water and hot water extract samples were analysed without dilution, but 2 M KCl and 0.5 M [K.sub.2]S[O.sub.4] extracts were diluted 5-fold before measurement to minimise the precipitation of salts on the surface of Pt/[Al.sub.2][O.sub.3] catalysts with resulting decrease in catalyst efficiency. Water and diluted salt solution blanks were checked in each run and were found to be <0.06 mg N/L. The repeatability and drift of sensitivity for the HTCO method was checked by the coutinuous analyses of 20 standard solutions (5 mg N/LKN[O.sub.3]) in 0.4 M KCl, 0.1 M [K.sub.2]S[O.sub.4], or water.

Standard solutions of N-(1-naphthyl) ethylenediamine dihydrochloride (NED), sulfanilamide, glycine, L-aspartic acid, sodium nitrite, urea, ethylenediaminetetraacetic acid disodium salt (EDTA), ammonium chloride, L-glutamic acid sodium salt and L-arginine, each containing 5 mg N/L, were used to determine N recovery (against KN[O.sub.3] standard solution) by the HTCO method. All the above analyses were carried out in triplicate.

Analysis of other soil properties

Soil total C and total N were analysed using an isotope ratio mass spectrometer with a Eurovector Elemental Analyser (Isoprime-EuroEA 3000, Milan, Italy). Soil particle size, pH, CEC, and conductivity were measured the methods reported by Xu et al. (1995).

Statistical analysis

Regression analyses on relationships between the values of total soluble N measured by the PO and the HTCO methods in various matrices were carried out in STAWSTLX for Window, version 2.2. The t-tests to compare the slopes of regression equations with 1 (the slope when values of total soluble N determined by 2 methods are identical, namely y = x) were carried out according to the method described by Zar (1999). Paired t-tests for N recovery of N-containing compounds in different matrices were carried out in Microsoft Excel 2000.

Results and discussion

Soil characteristics

Because the chemical and physical properties of the soils in Table 1 vary so widely, they make a good test-bed for comparing the HTCO and the PO methods. Soil pH ranged from 3.6 to 7.0, organic C from 0.609 to 8.295%, total N from 0.02 to 0.71%, CEC from 2.2 to 57.9 cmol/kg, conductivity from 0.013 to 0.773 dS/m, clay content from < 1.0% to 49.2%, silt from < 1.0% to 29.3%, and sand from 27.7% to 97.9%.

Assessment of the HTCO method

Preliminary studies showed that without dilution (2 M KCl and 0.5 M [K.sub.2]S[O.sub.4]), large amounts of salts were deposited on the Pt/[Al.sub.2][O.sub.3] catalyst pellets, leading to poor reproducibility and to decreases in the oxidation efficiency by c. 30% for 2M KCl matrix and by c. 10% for 0.5 M [K.sub.2]S[O.sub.4] matrix in the first 20 samples (data not shown). Similar results were also reported by Alavoine and Nicolardot (2001). For this reason, all the 2 M KCl and 0.5 M [K.sub.2]S[O.sub.4] soil extracts were diluted 5-fold (i.e. to final concentrations of 0.4M KCl and 0.1 M [K.sub.2]S[O.sub.4]) before measurement of total soluble N by the HTCO method. The ranges of total soluble N measured by the HTCO method, with an injection volume of 50 [micro]L, were 0.511-3.829 mg/L for diluted KCl extracts, 0.518-14.114 mg/L for diluted [K.sub.2]S[O.sub.4] extracts of fumigated and non-fumigated soils, and 0.823-31.08 mg/L for water and hot water extracts of soils (without dilution). These were within the designated detection limits of total soluble N by the HTCO method using the SHIMADZU [TOC-.sub.VCPH/CPN] analyser (0.1-4000 mg/L), which were much wider than the detection limits of the PO method (Cabrera and Beare 1993).

Drifts of sensitivity of signals in diluted KCl (0.4 M), [K.sub.2]S[O.sub.4] (0.1 M) and water matrices by the HTCO method were very minor, with <2% in KCl matrix and <3% in [K.sub.2]S[O.sub.4] and water matrices (Table 2). This was consistent with the result of signal sensitivity tests for standard solution in a 0.025 M [K.sub.2]S[O.sub.4] matrix by the HTCO method (Alavoine and Nicolardot 2001).

Nitrogen recoveries from different standard N-containing compounds (5 mg/L) analysed by the HTCO technique (against KN[O.sub.3] standard solution) in all matrices tested (water, [K.sub.2]S[O.sub.4], and KCl) were >94% except for sulfanilamide (c. 85-89%) (Table 3). These N recoveries are comparable to those found in other studies (Walsh 1989; Merriam et al. 1996; Alvarez-Salgado and Miller 1998; Alavoine and Nicolardot 2001: Doyle et al. 2004). For example, Merriam et al. (1996) reported that N recoveries by the HTCO method for NaN[O.sub.2], EDTA, NED, caffeine, and glycine dissolved in water were >90%, for N concentrations of 0.5-10.0 mg/L. They also found that the HTCO method gained low recovery of sulfanilamide N (85.7% at 5 mg/L). Alavoine and Nicolardot (2001) observed nitrogen recoveries >98% for 12 different standard N compounds (at 10 mg/L) in 0.025 M [K.sub.2]S[O.sub.4] matrix by the HTCO method. Doyle et al. (2004) also reported N recovery of >97% of N recoveries from glycine, lysine, urea, yeast extract, and nicotinamide by the HTCO method, all higher than the corresponding recoveries by the PO method (92-96%). The N recoveries from L-aspartic acid, NaN[O.sub.2], and N[H.sub.4]Cl in all matrices tested exceeded 100% in our study, indicating that the N in these compounds was more completely oxidised to NO than the standard KN[O.sub.3] used to calibrate the analyser. Alavoine and Nicolardot (2001) also found that recovery of N from NaN[O.sub.2] in 0.025 M [K.sub.2]S[O.sub.4] by HTCO was over 100%. A paired t-test showed that there were no significant differences observed in N recovery for N-containing compounds among different matrices in our study (P > 0.05) (Table 3). This further indicates that the HTCO method is suitable for determining total soluble N in both water and diluted salt extracts of forest soils.

Accumulated deposition of salts on the surface of catalyst can gradually reduce oxidation efficiency of the catalyst for the HTCO method. Dilution of salt extracts can reduce this impact and enhance the sensitivity of measurement. The performance of the catalyst can be checked by analysing a set of standard solutions. We suggest that it is necessary to perform the regeneration of the catalyst after each run on the SHIMADZU [TOC-.sub.VCPH/CPN] analyser and the catalyst needs to be replaced after measurement of about 1000-1500 samples in 0.4 M KCl matrix and 1500-2000 samples in 0.1 M [K.sub.2]S[O.sub.4] matrix.

Comparing the PO and the HTCO methods for the determination of total soluble N

The results of total soluble N measured by the PO and the HTCO methods are shown in Table 4. The values of total soluble N in 2M KCl extracts measured by 2 methods were well correlated ([r.sup.2] = 0.989, P < 0.01) (Fig. 1). The PO method tended to give lower values for total soluble N than the HTCO method, while the slope of the regression curve (0.975) was not significantly different from 1 (Fig. 1). Total soluble N in 0.5 M [K.sub.2]S[O.sub.4] extracts of unfumigated soils determined by both methods was significantly correlated ([r.sup.2] = 0.992, P < 0.01), similarly for fumigated soils ([r.sup.2] = 0.996, P < 0.01) (Fig. 2). The slope of regression curve (1.051) for unfumigated soils was not significantly different from 1, whereas the slope of the regression curve (1.254) for fumigated soils was significantly different from 1 (P < 0.05) (Fig. 2). These results showed that the PO method underestimated total soluble N in [K.sub.2]S[O.sub.4] extracts compared with the HTCO method, particularly with high concentrations of N (e.g. [K.sub.2]S[O.sub.4] extracts of fumigated soils), even though dilution procedures were carried out when total N in the extracts was > 10 mg/L. Doyle et al. (2004) also reported that the PO method recovered 95% of dissolved organic N in soil [K.sub.2]S[O.sub.4] extracts compared with the HTCO method. More N released by fumigation was measured by the HTCO method than by the PO method (Table 4, Fig. 3). The regression slope was significantly different from 1 (P < 0.05) although the values obtained by 2 methods were significantly correlated (Fig. 3).

[FIGURES 1-3 OMITTED]

The values for total soluble N in water extracts obtained by the 2 methods were significantly correlated (Fig. 2), and similar when concentrations of total soluble N were low (<~ 115 mg/kg soil) (Table 2, Fig. 4). The regression slope was not significantly different from 1. The values of hot-water-extractable total N measured by the HTCO method were generally greater than by the PO method, particularly for high N concentrations (Table 2, Fig. 5). The regression slope was also significantly different from 1. Merriam et al. (1996) also found that the values of total soluble N measured by the HTCO and the PO methods in throughfall and soil solutions were highly correlated within a range from <0.5 to 110 mg/L, but that the HTCO method produced slightly greater values than the PO method. Maita and Yanada (1990) also reported a similar result with a range of N concentrations from 0 to 50 [micro]g/L. The underestimation of total soluble N by the PO method compared with the HTCO method may be due to more complete oxidation of soluble N by the HTCO method. For some chemical compounds (such as amino-antipyrine caffeine), efficiency of N recovery by the PO method could be as low as c. 50-85%. (e.g. Zhu and Carreiro 2004). It is also possible that N[H.sub.4]-N is lost through evolution of N[H.sub.3] under the alkaline condition of the persulfate oxidation (Ross 1992).

Conclusions

The values of total soluble N in various extracts of forest soils measured by PO and HTCO methods were highly correlated, but the HTCO method gave more complete oxidation and thus appeared to give greater values for total soluble N than the PO method. We consider the HTCO method to be a simple, automated, rapid, quantitative, and reliable method, with a wider concentration range, for determining total soluble N in both water extracts and diluted salt extracts of forest soils. However, the HTCO method using the SHIMADZU [TOC-.sub.VCPH/CPN] analyser also has some constraints for concentrated salt extracts of soils. Salt extracts of soil require dilution before measurement and the catalysts have to be replaced more often. We suggest that the catalyst needs to be replaced after measurement of ~1000-1500 samples in 0.4 M KCl matrix and 1500-2000 samples in 0.1 M [K.sub.2]S[O.sub.4] matrix.

Acknowledgments

The access to the experimental sites of DPI Forestry, Queensland and Department of Primary Industries and Fisheries, Queensland, Horticulture and Forestry Sciences is acknowledged. The authors would like to thank Mr John Simpson, Tim Smith, and Mark Podberscek of Queensland Forest Research Institute for access to site information details and Mr John Simpson for his helpful comments on this manuscript.

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Manuscript received 7 September 2004, accepted 2 March 2005

C.R. Chen (A,D), Z.H. Xu (A), P. Keay (B), and S. L. Zhang (C)

(A) Faculty of Environmental Sciences, Griffith University, Nathan, Qld 4111, Australia.

(B) DPI Forestry Queensland, Fraser Road, Gympie, Qld 4570, Australia.

(C) Current address: College of Resources and Environment, Northwest Sci-Tech University of Agriculture and Forestry, Yangling, Shaanxi 712100, P. R. China.

(D) Corresponding author. Email: c.chen@griffith.edu.au
Table 1. Chemical and physical properties determined for the forest
soils (0-0.10m) collected

Locations Soil type (A) Vegetations and/or management

 1. Toolara Grey Kandosol Pinus elliottii var. elliottii
 2. Toolara Grey Kandosol 6-year-old [F.sub.1] hybrid Pinus
 elliottii x Pinus caribaea, double
 residue retention
 3. Toolara Grey Kandosol 6-year-old [F.sub.1] hybrid Pinus
 elliottii x Pinus caribaea, all
 residue removed
 4. Toolara Red Kurosol Native eucalypt (E. racemosa, E.
 tindaliae, E. intermedia,
 E. acmenioides)
 5. Toolara Red Kurosol 31-year-old Pinus elliottii var.
 elliottii
 6. Tuan Podosol 7-year-old [F.sub.1] hybrid Pinus
 elliottii x Pinus caribaea
 7. Tuan Podosol Native eucalypt (E. umbra, Banksia
 aemula, Allocasuarina littoralis)
 8. Tuan Podosol 14-year-old Pinus caribaea var.
 hondurensis
 9. Tuan Red Kurosol 10-year-old hybrid [F.sub.1] hybrid
 Pinus elliottii x Pinus caribaea
10. Beerburrum Yellow Kandosol 30-year-old Pinus elliottii var.
 elliottii
11. Beerburrum Yellow Kandosol 1.2-year-old hybrid [F.sub.1] hybrid
 Pinus elliottii x Pinus caribaea
12. Imbil Red Ferrosol Dry subtropical rainforests
13. Imbil Red Ferrosol 2-year-old Araucaria cunninghamii
14. Beerburrum Red Kandosol Native eucalypt (E. racemosa,
 E. tindaliae, E. intermedia,
 Angophora floribunda)
15. Beerburrum Red Kandosol 13-year-old [F.sub.1] hybrid Pinus
 elliottii x Pinus caribaea
16. Beerburrum Arenic Rudosol 1-year-old [F.sub.1] hybrid Pinus
 elliottii x Pinus caribaea
17. Yarraman Black Dermosol Dry subtropical rainforests
18. Yarraman Black Dermosol 2nd rotation Araucaria cunninghamii
19. Yarraman Red Ferrosol 2nd rotation Araucaria cunninghamii
20. Yarraman Red Ferrosol Dry subtropical rainforests
21. Beerburrum Yellow Kandosol Native eucalypt (E. microcorys,
 E. pilularis, E. racemosa,
 E. siderophloia)
22. Toolara Red Kurosol Native eucalypt (E. microcorys,
 E. pilularis, E. racemosa,
 E. siderophloia)
23. Beerburrum Podosol E. racemosa, E. intermedia,
 Melaleuca quinquenervia
24. Yarraman Red Ferrosol Native Araucaria cunninghamii

Locations Soil type (A) Soil Organic C Total N
 pH (%) (%)

 1. Toolara Grey Kandosol 5.1 2.39 0.12
 2. Toolara Grey Kandosol 4.6 2.45 0.06
 3. Toolara Grey Kandosol 5.1 1.00 0.03
 4. Toolara Red Kurosol 4.8 1.48 0.06
 5. Toolara Red Kurosol 4.7 1.94 0.05
 6. Tuan Podosol 3.6 1.81 0.03
 7. Tuan Podosol 4.0 1.32 0.03
 8. Tuan Podosol 3.9 1.93 0.04
 9. Tuan Red Kurosol 4.8 0.61 0.02
10. Beerburrum Yellow Kandosol 4.9 1.40 0.04
11. Beerburrum Yellow Kandosol 4.8 1.44 0.05
12. Imbil Red Ferrosol 6.2 6.45 0.63
13. Imbil Red Ferrosol 7.0 8.30 0.69
14. Beerburrum Red Kandosol 4.7 1.70 0.05
15. Beerburrum Red Kandosol 4.3 2.39 0.06
16. Beerburrum Arenic Rudosol 4.1 0.87 0.02
17. Yarraman Black Dermosol 5.4 4.11 0.25
18. Yarraman Black Dermosol 6.1 4.09 0.24
19. Yarraman Red Ferrosol 5.8 5.41 0.43
20. Yarraman Red Ferrosol 5.3 7.26 0.62
21. Beerburrum Yellow Kandosol 4.9 0.88 0.04
22. Toolara Red Kurosol 3.9 2.13 0.08
23. Beerburrum Podosol 5.2 2.48 0.10
24. Yarraman Red Ferrosol 5.7 7.14 0.71

Locations Soil type (A) CEC Conductivity Clay
 (cmol/kg) (dS/m) (%)

 1. Toolara Grey Kandosol 12.9 0.031 12.4
 2. Toolara Grey Kandosol 6.8 0.035 4.4
 3. Toolara Grey Kandosol 4.4 0.015 4.2
 4. Toolara Red Kurosol 6.3 0.029 4.1
 5. Toolara Red Kurosol 8.4 0.032 5.2
 6. Tuan Podosol 5.1 0.040 <1.0
 7. Tuan Podosol 3.9 0.021 <1.0
 8. Tuan Podosol 8.4 0.026 <1.0
 9. Tuan Red Kurosol 2.2 0.012 3.2
10. Beerburrum Yellow Kandosol 5.3 0.023 4.0
11. Beerburrum Yellow Kandosol 6.5 0.028 7.9
12. Imbil Red Ferrosol 54.3 0.157 40.5
13. Imbil Red Ferrosol 57.9 0.285 38.9
14. Beerburrum Red Kandosol 7.6 0.027 6.4
15. Beerburrum Red Kandosol 8.9 0.046 5.2
16. Beerburrum Arenic Rudosol 2.5 0.013 1.8
17. Yarraman Black Dermosol 24.9 0.065 14.6
18. Yarraman Black Dermosol 26.0 0.057 19.2
19. Yarraman Red Ferrosol 32.5 0.082 42.2
20. Yarraman Red Ferrosol 41.4 0.115 49.2
21. Beerburrum Yellow Kandosol 3.9 0.026 2.75
22. Toolara Red Kurosol 9.4 0.037 8.9
23. Beerburrum Podosol 10.2 0.033 1.0
24. Yarraman Red Ferrosol 45.3 0.773 32.4

Locations Soil type (A) Silt Sand
 (%) (%)

 1. Toolara Grey Kandosol 22.1 65.6
 2. Toolara Grey Kandosol 7.6 88
 3. Toolara Grey Kandosol 7.4 88.4
 4. Toolara Red Kurosol 11.2 84.7
 5. Toolara Red Kurosol 11.9 82.9
 6. Tuan Podosol 1.8 97.9
 7. Tuan Podosol 1.9 97.8
 8. Tuan Podosol 4.6 95.4
 9. Tuan Red Kurosol 6.3 90.5
10. Beerburrum Yellow Kandosol 8.4 87.6
11. Beerburrum Yellow Kandosol 9.8 82.0
12. Imbil Red Ferrosol 24.1 35.4
13. Imbil Red Ferrosol 20.1 41.0
14. Beerburrum Red Kandosol 7.8 85.8
15. Beerburrum Red Kandosol 6.3 88.5
16. Beerburrum Arenic Rudosol >1.0 98.0
17. Yarraman Black Dermosol 29.3 56.1
18. Yarraman Black Dermosol 6.3 74.6
19. Yarraman Red Ferrosol 16.7 41.1
20. Yarraman Red Ferrosol 23.1 27.7
21. Beerburrum Yellow Kandosol 8.7 88.6
22. Toolara Red Kurosol 8.9 82.2
23. Beerburrum Podosol 2.9 96.1
24. Yarraman Red Ferrosol 36 31.7

(A) Soil type was classified according to Isbell (1996).

Table 2. Sensitivity drifts with standard solutions (5 mg N/L,
KN[O.sub.3]) in KCl, [K.sub.2]S[O.sub.4], and water matrixes by
the HTCO method

 KCl [K.sub.2]S[O.sub.4]
Test
no. (mg/L) Recovery (%) (mg/L) Recovery (%)

 1 5.00 100.0 4.99 99.9
 2 5.03 100.6 5.03 100.6
 3 4.95 99.1 4.89 97.8
 4 5.02 100.5 4.94 98.7
 5 4.93 98.6 5.02 100.4
 6 4.87 97.3 5.06 101.2
 7 4.95 99.0 4.91 98.3
 8 4.95 99.0 4.87 97.4
 9 4.92 98.4 4.97 99.5
10 4.96 99.2 4.87 97.4
11 5.03 100.7 4.95 99.0
12 5.07 101.5 4.91 98.2
13 5.06 101.1 4.90 98.1
14 4.95 99.0 4.97 99.3
15 4.94 98.8 4.87 97.3
16 5.01 100.1 4.86 97.1
17 4.91 98.3 4.93 98.7
18 4.93 98.6 4.85 97.0
19 4.97 99.4 4.93 98.7
20 4.95 99.0 4.92 98.4
Mean 4.97 99.0 4.93 98.6
s.d. 0.05 1.1 0.06 1.20

 Water
Test
no. (mg/L) Recovery (%)

 1 5.08 101.5
 2 4.95 99.1
 3 5.03 100.6
 4 5.09 101.7
 5 5.01 100.2
 6 4.90 97.9
 7 5.00 100.0
 8 5.03 100.5
 9 4.92 98.4
10 4.96 99.2
11 4.96 99.1
12 5.10 101.9
13 5.13 102.7
14 5.03 100.6
15 4.97 99.4
16 5.08 101.7
17 4.89 97.8
18 4.95 99.0
19 5.05 100.9
20 5.03 100.6
Mean 5.01 100.1
s.d. 0.07 1.4

Table 3. Recoveries of N compounds (5 mg N/L) dissolved in water, 0.1 M
[K.sub.2]S[O.sub.4], and 0.4 M KCl matrix and measured by the HTCO
method (standard deviations of the mean in parentheses)

N compound Recovery (%) in:

 Water [K.sub.2] KCl
 S[O.sub.4]

N-(1-Naphthyl) 99.9 (0.11) 102.9 (1.16) 103.5 (1.26)
 ethylenediamine
 dihydrochloride
Sulfanilamide 84.6 (1.57) 85.3 (1.16) 88.8 (0.17)
Glycine, anminoacetic, 97.8 (0.91) 99.1 (0.34) 99.7 (0.23)
 glycocll
L-aspartic acid 103.3 (0.49) 102.1 (0.48) 104.9 (0.48)
Sodium nitrite 103.2 (0.14) 102.6 (1.33) 103.9 (0.14)
Urea 96.0 (1.12) 94.1 (0.34) 100.6 (1.62)
Ethylenediaminetetra- 99.1 (1.44) 98.2 (1.17) 99.3 (0.54)
 acetic acid
 disodium salt
Ammonium chloride 102.2 (0.08) 101.9 (0.74) 104.6 (0.48)
L-glutamic acid 101.7 (0.49) 96.6 (1.91) 95.3 (0.49)
 sodium salt
L-Arginine 94.6 (0.82) 96.2 (0.14) 94.2 (0.11)
Mean 98.2 97.9 99.5

Table 4. Soluble N pools extracted by KCl, [K.sub.2]S[O.sub.4], cold
water, and hot water and determined by persulfate oxidation (PO) and
by high temperature catalytic oxidation (HTCO)

Soils Total soluble N (mg/kg) Total soluble N (mg/kg)
 in KCl extracts in [K.sub.2]S[O.sub.4] extracts,
 unfumigated

 PO HTCO PO HTCO

 1 52.5 74.6 22.3 27.0
 2 19.8 31.2 14.2 17.9
 3 13.7 20.4 9.4 11.4
 4 34.3 48.7 21.4 26.4
 5 19.0 34.0 12.9 16.0
 6 17.5 23.0 10.1 11.8
 7 17.0 24.9 12.0 14.0
 8 21.9 31.5 13.9 17.5
 9 14.2 22.0 12.1 13.8
10 25.3 26.1 9.9 10.1
11 13.6 40.0 25.5 25.5
12 164.2 173.6 96.1 99.9
13 249.7 255.4 179.3 187.2
14 15.9 31.8 11.8 14.6
15 27.0 46.7 21.8 27.2
16 8.8 14.0 11.1 10.3
17 17.8 25.8 18.4 23.8
18 22.2 38.1 19.3 24.7
19 59.9 70.7 52.9 70.4
20 83.8 94.7 70.9 86.1
21 18.7 31.1 15.9 19.7
22 39.3 61.9 26.4 35.2
23 27.9 45.7 14.4 16.2
24 177.3 183.9 82.6 89.4
Mean 48.4 60.4 32.7 37.3
CV% 20.3 25.9 24.6 22.7

Soils Total soluble N (mg/kg) N flush (mg/kg) in
 [K.sub.2]S[O.sub.4] extracts, response to fumigation
 fumigated

 PO HTCO PO HTCO

 1 44.3 56.7 21.9 29.7
 2 24.6 34.0 10.4 16.1
 3 16.7 18.8 7.3 7.4
 4 32.2 43.8 10.8 17.4
 5 23.8 33.0 10.8 17.1
 6 18.6 22.9 8.5 11.0
 7 21.3 26.6 9.4 12.5
 8 22.8 28.6 8.9 11.1
 9 15.5 19.7 3.4 5.9
10 18.0 22.5 8.1 12.4
11 35.8 40.9 10.3 15.4
12 196.3 261.3 100.2 161.4
13 308.0 375.2 128.7 187.9
14 22.5 25.7 10.6 11.1
15 33.3 45.8 11.5 18.6
16 11.4 13.3 0.4 2.9
17 30.9 41.2 12.4 17.3
18 35.3 48.0 16.0 23.3
19 69.3 95.4 16.4 25.0
20 100.8 125.4 29.9 39.3
21 19.4 28.8 3.5 9.1
22 38.5 52.1 12.1 17.0
23 26.8 35.4 12.4 19.2
24 166.8 218.9 84.3 129.5
Mean 55.5 71.4 22.8 34.1
CV% 26.1 25.5 29.2 29.9

Soils Water soluble total N Hot water extractable
 (mg/kg) total N (mg/kg)

 PO HTCO PO HTCO

 1 20.1 21.2 41.6 50.9
 2 8.9 10.4 32.8 36.2
 3 4.4 5.3 18.6 20.1
 4 9.5 10.2 36.1 43.3
 5 6.3 6.8 26.2 32.2
 6 7.4 6.9 24.0 26.5
 7 5.8 5.7 29.7 30.1
 8 7.5 7.7 29.0 28.5
 9 4.5 4.5 16.5 16.6
10 11.0 11.4 24.4 23.6
11 16.4 16.0 33.3 33.4
12 156.5 189.6 177.6 209.5
13 205.6 271.4 154.5 222.7
14 4.2 4.9 22.3 20.2
15 10.4 11.9 38.5 38.2
16 4.9 3.5 18.1 16.7
17 16.9 16.1 77.9 84.6
18 17.0 13.3 57.4 72.6
19 34.6 35.3 126.6 141.7
20 51.5 51.6 183.7 236.8
21 9.7 9.6 27.6 25.9
22 15.6 15.4 48.5 51.9
23 11.7 11.2 40.9 39.9
24 107.5 113.3 435.4 658.9
Mean 31.1 35.5 71.7 90.0
CV% 33.8 37.6 26.4 31.4
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Article Details
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Author:Chen, C.R.; Xu, Z.H.; Keay, P.; Zhang, S.L.
Publication:Australian Journal of Soil Research
Geographic Code:8AUST
Date:Jul 1, 2005
Words:6709
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