Rozpuszczalny węgiel organiczny w glebie płowej w różnych systemach nawożenia i zmianowania roślin

http://www.degruyter.com/view/j/ssa (Read content)

Vol. 64 No 3/2013: 114–119

* email: tomasz_sosulski@sggw.pl

DOI: 10.2478/ssa-2013-0015

INTRODUCTION

The recently increasing interest in the changes in carbon compounds in the natural environment that lead to the retention of this element in the soil, or to the release of CO₂ from the soil into the atmosphere, has intensified studies on the levels of different forms of carbon in the soil, including the amounts of disso-lved organic carbon (DOC) (Rees and Parker, 2005; Gonet and Dêbska, 2006; McDowell et al., 2006; von Lützow et al., 2007; Gjettermann et al., 2008; Mari-nari et al., 2010; Sosulski et al., 2011). In these stu-dies, various methods are usually used for the extrac-tion of DOC from the soil, employing soluextrac-tions of various chemical compounds at different concentra-tions, and with different proportions of extraction solution and soil. Because of the considerable varia-tions in the methodology, researchers obtain signifi-cant differences in test results. Meanwhile, since the mid-1990s, increasing importance in fertilization dia-gnostics has been gained by the soil extraction me-thod with a weak extraction solution – 0.01 mol×dm–3 CaCl₂, proposed by Houba (1983) for the extraction of soluble nitrogen from the soil. In this method, the ratio of extraction solution to soil is 10:1, and the duration of the extraction is 2 hours. Another method described in literature is the method of Zsolnay (1996) of extracting soil DOC also by means of 0.01 mol×dm–3

CaCl₂ solution, but under different conditions – extraction for 10 minutes at a ratio of extraction so-lution : soil = 2:1.

The aim of study was to evaluate the amount of organic dissolved carbon in Luvisol profile under different fertilization and crop rotation. Extraction organic dissolved carbon from soil was made by Ho-uba (1983) and Zsolnay (1996) methods. Because the two methods employ the same extraction solu-tion, while the extraction conditions are different, it seemed appropriate to the authors of this study to compare the results of measurements of soil DOC with the use of the two extraction methods in terms of the possibility of using the method described by Houba (1983) to assess the DOC content in the soil as a uni-versal soil test.

MATERIALS AND METHODS

The long-term fertilization experiments in Skier-niewice have been conducted in a fixed system since 1922. They are the oldest fertilization experiments in Poland and some of the oldest in Europe. They are located in central Poland on a Luvisol with a clay fraction (Æ <0.002 mm) of 14–17% in the Ap hori-zon, 10–12% in the Eet horihori-zon, and 25% in the Bt horizon. In 2011, soil samples were taken in two pe-riods: in the spring before the beginning of vegeta-TOMASZ SOSULSKI*, EWA SZARA, WOJCIECH STÊPIEÑ

Warsaw University of Life Science, Department of Soil Environments Science, Nowoursynowska 159, 02-766 Warszawa

Dissolved organic carbon in Luvisol under different fertilization

and crop rotation

Abstract: The study was conducted on selected plots of long-term experiments in Skierniewice with different fertilization systems and crop rotation having an effect on the amounts of dissolved organic carbon (DOC) in the soil. The aim of the study was to compare the results of measurements of DOC by two methods, Zsolnay’s and Houba’s, which use the same extraction solution (0.01 mol×dm–3

CaCl2), but the extraction is carried out with different proportions of extraction solution and soil, and for different durations. Soil

samples for analyses were collected in the spring and autumn of 2011 from three soil horizons: Ap (0–25 cm), Eet (25–45 cm) and Bt (45–65 cm). Using the same solution to extract soil DOC (0.01 mol×dm–3 _CaCl

2), but extending the extraction time from 10 minutes to

2 hours and expanding the ratio of extraction solution : soil from 2:1 to 10:1 (Zsolnay’s method and Houba’s method, respectively) causes an approximately 2.4-fold increase in the amount of DOC extracted from the soil. The results obtained by the two extraction methods were characterized by statistically significant differences in precision and accuracy. The observed differences in the assessment of DOC levels in the soil obtained by the two methods were particularly pronounced at lower concentrations of dissolved organic carbon in the soil. The differences demonstrate that it is not possible to substitute Zsolnay’s soil test, dedicated to measuring the DOC content in the soil, with Houba’s universal test designed to measure the levels of active forms of nutrients.

Keywords: Luvisol, dissolved organic carbon, extraction with 0.01 mol×dm–3 _CaCl 2

tion and in the autumn after the harvest of crop plants grown in three experiments: A – with arbitrary crop rotation without legumes and without manure, E – with a five-field crop rotation with a papilionaceous plant and manure (potatoes + 30 t manure·ha–1_, bar-ley, yellow lupin, wheat, rye), and D – with a mono-culture of rye (Tab. 1). The experiment with arbitrary crop rotation (A) is carried out in 3 replications, whe-reas the experiments with a five-field rotation (E) and rye monoculture (D) are carried out in 5 replications. Since 1976, the plots with mineral fertilization (CaNPK and NPK) have been fertilized with ni-trogen in the form of ammonium nitrate at a dose of 90 kg N·ha–1_{, phosphorus in the form of single} superphosphate at a dose of 26 kg P·ha–1_{, and} potas-sium as potaspotas-sium salt at a dose of 91 kg K·ha–1_. De-tailed information on the chemical and physicoche-mical properties of the soil in the long-term fertiliza-tion experiments in Skierniewice can be found in the work by Mercik and Stêpieñ (2005).

The study was conducted on selected plots with fertilization combinations of the three experiments allowing to test the effect of different fertilization systems (mineral, mineral-organic and organic), used on limed and acidic soils, and of crop rotation on the DOC content of the soil (Tab. 1). In both study pe-riods, soil samples were collected from three soil horizons: Ap (0–25 cm), Eet (25–45 cm) and Bt (46–65 cm). The total number of soil samples collec-ted and analyzed in 2011 was 246.

The soil subjected to extraction was in its natural state with respect to moisture content. Measurements of soil moisture content after drying at 105°C allo-wed the calculation and expression of soil DOC con-tent on a dry weight basis. The soil samples were sub-jected to extraction in accordance with the metho-dologies described by Zsolnay (1996) and Houba (1983). In both methods, the extraction solution is 0.01 mol×dm–3 _CaCl

2. In the method for extracting DOC described by Zsolnay (1996), the ratio of soil to extraction solution is 1:2, and the extraction time

is 10 minutes. In the method described by Houba (1983), used also for extracting mineral N from the soil, the ratio is 1:10, and the extraction lasts 2 hours. The soil extracts obtained by the two methods were subjected to vacuum filtration using Æ 0.45 µm What-man filters allowing to isolate the low molecular or-ganic compounds from solution. In the soil solutions thus obtained, the amounts of dissolved organic car-bon (DOC) were measured by the direct method of infrared (IR) spectrometry – PN-EN 1484: 1999 using a solution of glycine at a concentration of 1000 mg·dm–3 to prepare the calibration solutions needed to compile the standard curve. The results of the DOC content analyses obtained for the two extraction methods were compared using Student’s test (t) and Fischer test (F) to assess the significance of the differences in the ac-curacy and precision of the measurements.

Accuracy and precision are the parameters charac-terizing the analytical method and determine the po-ssibility of replacing one another analytical method. Accuracy is the degree of conformity between the ac-tual value and the average of the results obtained for the study parameter (systematic error), which is esti-mated using the Student’s test (t).The precision of the method is the degree of agreement between the results obtained with multiple repetitions of analysis carried out under defined conditions (random error) and esti-mated to be in the Fischer test (F) (Mercik, 2004).

RESULTS AND DISCUSSION

Regardless of the differences in the measured amount of dissolved organic carbon extracted by two methods from soil samples collected in the spring of 2011 from three genetic horizons of the soil of selec-ted test plots in three experimental fields, the DOC content in the deeper soil horizons was higher than in the humus accumulation horizon. This indicates inten-se leaching of organic compounds from the topsoil during winter and early spring. In autumn, by contrast, on the plots with only mineral fertilization applied to

m e t s y s n o it a zi li tr e F Mineralfetrliziaiton Organcifetrliziaiton Expeirment Croprotaiton l a r e n i M CaNPK K P N none A arbirtaryrotaitonwtihout elgumes K P N a C K P N D ryemonocutlure ci n a g r o -l a r e n i M CaNPK 30tmanure·ha–1 _every4years K P N a C K P N 30tmanure·ha 1 – _{every5years E ifve-feildcroprotaitonwtihelgumes} ci n a g r O Ca a h · e r u n a m t 0 2 –1 _{everyyear D ryemonocutlure} TABLE 1. Scheme of treatments

the experimental fields with arbitrary crop rotation (A) and rye monoculture (D), the most DOC was in the Ap horizon, and less in the deeper horizons of the soil pro-file. During the same period, on the plots fertilized with mineral fertilizers and manure and the plots fertilized with manure only in the experimental fields E and D, larger amounts of DOC were found in the deeper hori-zons of the soil (Bt and Eet) than in the arable layer (the Ap horizon). This means that in the case of mine-ral fertilization only the release of DOC in the soil during the growing season is determined largely by the inflow of crop residues. On the other hand, under organic-mineral and organic fertilization, non-specific compounds of low molecular weight are constantly forming in the soil during the decomposition of orga-nic matter, which under favourable conditions are easily washed out of the topsoil to deeper soil horizons

(Dêb-ska and Gonet, 2002; McDowell et al., 2006; Marinari et al., 2010)

Regardless of the study period and the soil hori-zon, a larger amount of DOC was extracted from the soil after 2 hours at a ratio of extraction solution : soil = 10:1 than after 10 minutes at a ratio of 2:1 (Tab. 2). Prolonging the time of extraction while expanding the ratio of extraction solution to soil resulted in an average increase of about 2.4 times in the measured amount of DOC in the soil. Larger differences in the amounts of DOC extracted from the soil by the two methods were found at the lower levels of DOC in the soil. The minimum DOC content in the soil when extracting with Zsolnay’s method was 4.12 mg C·kg–1_, and with Houba’s method 13.01 mg C·kg–1_{. On the} other hand, the maximum DOC content in the soil determined by the two methods was, respectively,

t n e m ir e p x E Fetrliziers Soli n o zi r o h Spirng2011 Autumn2011 e r u n a M Mineral DOC1:2 DOC1:10 DOC1:2 DOC1:10 g k · C g m –1_DW A None CaNPK Ap t e E t B n a e M 3 1 . 5 9 5 . 7 9 3 . 7 0 7 . 6 1 2 . 6 1 7 5 . 1 2 4 0 . 9 1 4 9 . 8 1 5 4 . 1 1 2 1 . 6 9 9 . 0 1 2 5 . 9 9 6 . 6 2 5 5 . 7 1 2 2 . 4 2 2 8 . 2 2 K P N Ap t e E t B n a e M 3 8 . 4 5 8 . 4 0 6 . 7 6 7 . 5 5 4 . 5 1 9 4 . 4 1 8 3 . 9 1 4 4 . 6 1 6 1 . 9 -0 9 . 4 8 0 . 9 1 7 . 7 6 5 . 3 2 4 4 . 6 1 3 2 . 2 2 4 7 . 0 2 D None CaNPK Ap t e E t B n a e M 1 8 . 9 5 8 . 7 5 0 . 4 1 7 5 . 0 1 3 4 . 4 2 2 6 . 2 2 8 6 . 2 3 8 5 . 6 2 7 0 . 8 1 0 . 6 2 5 . 6 7 8 . 6 8 4 . 2 2 1 5 . 7 1 6 7 . 9 1 2 9 . 9 1 K P N Ap t e E t B n a e M 8 0 . 0 1 6 8 . 8 3 0 . 6 1 6 6 . 1 1 2 3 . 3 2 2 3 . 1 2 3 5 . 4 3 9 3 . 6 2 5 2 . 7 6 2 . 6 6 6 . 0 1 6 0 . 8 0 2 . 9 1 3 2 . 8 1 7 7 . 4 2 3 7 . 0 2 a h · t 0 3 –1_every s r a e y 4 CaNPK AEept t B n a e M 5 6 . 1 1 2 8 . 5 1 8 6 . 4 1 5 0 . 4 1 9 . 8 2 7 3 . 1 3 4 1 . 0 3 4 1 . 0 3 1 1 . 0 1 8 5 . 5 4 4 . 5 1 8 3 . 0 1 3 0 . 5 2 8 6 . 7 1 4 0 . 2 3 2 9 . 4 2 a h · t 0 2 –1 y lr a e y Ca AEept t B n a e M 0 2 . 5 1 3 4 . 0 1 6 3 . 5 1 6 6 . 3 1 5 7 . 3 3 5 6 . 5 2 8 9 . 4 3 6 4 . 1 3 1 1 . 9 5 6 . 2 1 7 6 . 2 1 8 4 . 1 1 1 1 . 2 2 7 1 . 0 3 7 5 . 9 2 8 2 . 7 2 E 30t·ha–1_every s r a e y 5 Ca AEept t B n a e M 5 3 . 2 1 7 3 . 1 1 9 1 . 3 1 0 3 . 2 1 6 2 . 9 2 6 4 . 4 2 2 8 . 7 2 8 1 . 7 2 6 2 . 7 1 4 . 7 5 4 . 6 1 7 3 . 0 1 6 9 . 9 1 1 4 . 0 2 6 0 . 4 3 1 8 . 4 2 K P N a C Ap t e E t B n a e M 9 7 . 1 1 1 9 . 9 9 3 . 4 1 3 0 . 2 1 4 5 . 9 2 8 1 . 7 2 3 2 . 1 3 2 3 . 9 2 3 3 . 7 9 0 . 8 5 8 . 1 1 9 0 . 9 7 6 . 1 2 2 0 . 1 2 9 6 . 7 2 6 4 . 3 2 K P N Ap t e E t B n a e M 6 4 . 2 1 1 9 . 0 1 6 2 . 5 1 8 8 . 2 1 7 . 8 2 8 0 . 5 2 6 4 . 9 2 5 7 . 7 2 0 7 . 0 1 3 8 . 7 1 1 . 9 1 2 . 9 5 4 . 5 2 2 . 1 2 3 2 . 4 2 3 6 . 3 2 TABLE 2. DOC content (mg C·kg–1 _{DW) in three soil horizons (Ap, Eet, Bt) depending on method of extraction}

18.45 mg C·kg–1 _{and 38.18 mg C·kg}–1_{. Statistical} ana-lysis of the data based on the population of 246 soil samples showed the significance of differences in the mean amount of DOC extracted from the soil by both methods and the significance of differences in varian-ce for data obtained by both methods when testing at a significance level of a = 0.05 (Tab. 3). This means that the two methods differ significantly in terms of accuracy and precision of measurement.

In both study periods, each method of extraction had a different effect on the amount of DOC released from different soil horizons. Both in the spring and autumn, despite considerable differences in the

con-rizons resulting from the use of two different extrac-tion methods were caused by the amounts of various non-specific organic compounds appearing at the time in the soil , the nature and amount of which do not depend on the type of the soil-forming process.

Like for the whole population of results obtain for 246 soil samples, comparisons of the average amounts of DOC and variances calculated individu-ally for the results obtained within the individual soil horizons (Ap, Eet and Bt) also re-vealed significant differences, at a significance level of a = 0.05, in the accuracy and precision of measurements after extraction by the two methods, Zsolnay’s and Houba’s.

Table 4 shows linear regres-sion equations describing the re-lationship between the amount of DOC extracted from the soil by Zsolnay’s method and Houba’s method. Both in the whole soil profile to a depth of 65 cm and in the individual soil horizons (Ap, Eet and Bt), strong association was found between the amounts of DOC extracted by the two me-thods, as determined by the value of the correlation coefficient r, which ranged from 0.93 to 0.95. The regression equations describing the mathemati-cal relationship between the amount of DOC extrac-ted by Zsolnay’s and Houba’s methods fitextrac-ted the expe-rimental data very well (R2 _{= 0.85–0.89). However,} it should be noted that the degree of fit between the function and the experimental data obtained for the Eet horizon was slightly lower than for the Ap and Bt horizons. This might be due to a different nature of the processes taking place in each soil horizon.

The statistically significant differences observed in the results of measurements of DOC extracted from the soil with the same extraction solution, but at a different ratio of extraction solution to soil and diffe-centration of soil DOC measured by the two methods,

it was generally possible to identify the same soil hori-zon in which the DOC content was the highest. Howe-ver, with smaller amounts of DOC in the other soil horizons, the use of Zsolnay’s extraction method very often gave a different result of the assessment of DOC content in the individual soil horizons than the use of Houba’s extraction method. This allows the conclu-sion that the solubility of various organic compounds in a 0.01 mol·dm–3

solu-tion of CaCl₂ depends on the length of time the extraction solution acts on the soil and on the adop-ted ratio of extraction so-lution : soil. Therefore, it can be assumed that the differences in the asses-sment of the DOC content in the individual soil

ho-TABLE 4. The linear model describing the relationship between the variables DOC_1:2 and DOC_1:10 determined in the soil using two methods of extraction, the determination coefficient (R2_{) and the}

correlation coefficient (r) significant at a<0.05 li o S n o zi r o h Equaiton R2 r m c 5 6 – 0 DOC1:2=-4.00667+0.574363·DOC1:10 0.90 0.95 p A DOC_1:2=-2.81606+0.515717·DOC_1:10 0.89 0.94 t e E DOC1:2=-3.82012+0.562605·DOC1:10 0.85 0.93 t B DOC1:2=-3.88898+0.581678·DOC1:10 0.88 0.94 n o zi r o H Statystyka DOC1:2 DOC1:10 F t 5 6 – 0 Standarddevaiiton e c n ai r a V e g a r a v A f D 1 3 . 3 9 9 . 0 1 9 3 . 0 1 5 4 2 7 4 . 5 7 9 . 9 2 6 0 . 5 2 5 4 2 * 3 7 . 2 35.96* p A Standarddevaiiton e c n ai r a V e g a r a v A f D 1 6 . 2 1 8 , 6 5 8 . 9 1 8 8 7 . 4 5 8 . 2 2 5 5 . 4 2 1 8 * 6 3 . 3 24.45* t e E Standarddevaiiton e c n ai r a V e g a r a v A f D 0 9 . 2 0 4 . 8 2 9 . 7 1 8 7 7 . 4 4 7 . 2 2 5 9 . 2 2 1 8 * 1 7 . 2 22.02* t B Standarddevaiiton e c n ai r a V e g a r a v A f D 6 1 . 3 1 0 . 0 1 9 5 . 2 1 1 8 2 1 . 5 1 2 . 6 2 3 3 . 8 2 1 8 * 2 6 . 2 23.62* TABLE 3. Comparative statistics two extraction methods of dissolved organic carbon from Luvisol

rent extraction time, despite the high correlation of the data obtained by the two methods, do not allow substitution of the original Zsolnay’s method, dedi-cated to measurements of DOC in the soil, by the universal method for extracting active forms of nu-trients from the soil proposed by Houba.

CONCLUSIONS

1. The result of the measurement of dissolved organic carbon (DOC) content in the soil is dependent on the conditions of extraction (the ratio of extraction solution to soil and the length of time the extraction solution acts on the soil). When using the same extraction solution (1 mol·dm–3 _CaCl

2) to extract

DOC from the soil, prolonging the extraction time from 10 minutes to 2 hours, with the ratio of extrac-tion soluextrac-tion to soil increased from 2:1 to 10:1 (Zsol-nay’s method and Houba’s method, respectively) causes an approximately 2.4-fold increase in the amount of DOC extracted from the soil.

2. Zsolnay’s and Houba’s soil extraction methods al-low measurements of DOC content in the soil with statistically proven different precision and accu-racy. The observed differences in the assessment of DOC content in different soil horizons by the two methods are particularly pronounced at lower concentrations of dissolved organic carbon in the soil. These differences are evidence that it is not possible to substitute Zsolnay’s soil test, dedica-ted to measuring the DOC content in the soil, with Houba’s universal test, designed for measuring the amounts of active forms of nutrients.

3. DOC content is higher in the deeper soil horizons than in the humus accumulation of Luvisol stu-died. This relationship is more pronounced in the spring than autumn and in soil fertilized with ma-nure, or with manure and mineral fertilizers than in soil fertilized with mineral fertilizers only.

ACKNOWLEDGEMENT

The results presented in this paper were obtained as part of the research project NN 305 060640 funded by the Polish National Centre for Research and

Deve-lopment in 2011–2014, and the data analysis perfor-med is the implementation of one of the project tasks.

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prak-tyczne. Wyd. SGGW, Warszawa: 281s.

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Received: June 28, 2013 Accepted: October 25, 2013

Streszczenie: Badania przeprowadzono na wybranych obiektach wieloletnich eksperymentów nawozowych w Skierniewicach (SGGW),

co umo¿liwi³o przebadanie wp³ywu ró¿nego systemu nawo¿enia (mineralnego, mineralno-organicznego i organicznego) oraz zmiano-wania roœlin na zawartoœæ rozpuszczalnego wêgla organicznego (DOC) w glebie. Próby gleby do analiz pobrano wiosn¹ i jesieni¹ 2011 roku z trzech poziomów gleby: Ap (0–25 cm), Eet (25–45 cm) i Bt (46–65 cm). Zawartoœci rozpuszczalnego wêgla organicznego (DOC) w glebie oznaczono dwiema metodami Zsolnay’a (1996) i Houby (1983), w których wykorzystywany jest taki sam roztwór ekstrakcyjny (0,01 mol·dm–3 _CaCl

2) lecz ekstrakcja prowadzona jest przy ro¿nej proporcji roztworu ekstrakcyjnego gleby i w ró¿nym czasie. Przy

zastosowaniu takiego samego roztworu ekstrakcyjnego do ekstrakcji DOC z gleby (0,01 mol·dm–3 _CaCl

2) wyd³u¿enie czasu ekstrakcji

z 10 minut do 2 godzin, przy jednoczesnym rozszerzeniu stosunku roztworu ekstrakcyjnego do gleby z 2:1 do 10:1 (odpowiednio metoda Zsolnay’a i metoda Houby) powoduje ok. 2,4-krotny przyrost iloœci wyekstrahowanego DOC z gleby. Metoda ekstrakcji gleby Zsolnay’a i Houby pozwala na przeprowadzenie pomiaru zawartoœci DOC w glebie, ze statystycznie udowodnion¹ ró¿n¹ precyzj¹ i dok³adnoœci¹. Stwierdzone ró¿nice w ocenie zawartoœci DOC w poziomach gleby jedn¹ i drug¹ metod¹ s¹ szczególnie wyraŸne przy mniejszej koncentracji rozpuszczalnego wêgla organicznego w glebie. Ró¿nice te dowodz¹ braku mo¿liwoœci zast¹pienia testu glebo-wego Zsolnay’a, dedykowanego pomiarowi zawartoœci DOC w glebie, uniwersalnym testem Houby przeznaczonym do pomiaru zawar-toœci aktywnych form sk³adników pokarmowych. Zawartoœæ DOC jest wy¿sza w g³êbszych poziomach gleby ni¿ w poziomie akumula-cji. Przy czym, zale¿noœæ ta jest wyraŸniejsza w okresie wiosennym ni¿ jesieni¹ oraz w glebach nawo¿onych obornikiem, a tak¿e obornikiem i nawozami mineralnymi, ni¿ w glebach nawo¿onych wy³¹cznie nawozami mineralnymi.

S³owa kluczowe: gleba p³owa, rozpuszczalny wêgiel organiczny, ekstrakcja 0,01 mol·dm–3 _CaCl 2

Rozpuszczalny wêgiel organiczny w glebie p³owej

w ró¿nych systemach nawo¿enia i zmianowania roœlin