Infrared spectra of humic acids from soils formed under grass or trees

Gec~erma -- Elsevier Publishing Company, Amsterdam Printed in The Netherlands

INFRARED SPECTRA OF HUMIC ACIDS FROM ~ I L S FORMED UNDEi~ GRASS OR TREES J. F. DORMAAR Research Station, Canada Department of Agriculture, Lethbridge, Alta. (Canada) (Received April 20, 1967) SUMMARY The i n f r a r e d absorption s p e c t r a of various humic acids ha'~e been exa.nined to establish whether the 2, 500-1,800 cm -1 spectral region may be used to distinguish between soils formed under g r a s s or under t r e e s or to separate Chernozemic from Podzolic organic matter. I t appears evident that the spectral slope o r configuration in this region is r e l a t e d to tbe molecular weight of the m a t e r i a l examined and to the vegetation under which the humic substances a r e f o r m e d or t r a n s f o r m e d . Tbe change f r o m Podzolic to C h e r nozemic organic m a t t e r o c c u r r e d within a few years. The change iv the opposite direction took a number of y e a r s , and even then Podzolic c h a r a c t e r i s tics of the organic m a t t e r as m e a s u r e d by the configuration of the spectral region between 2, 500 and 1, 800 cm -1 f i r s t became evident in the Bt horizon. The same r e s u l t s were obtained under poplar as well as under coniferous trees. INTRODUCTION Absorption s p e c t r a of soil humtc acids usually a r e discussed with r e f e r e n c e to the a s s i g n m e n t of specific absorption bands r a t h e r than to slope or configuration of the spectra over a certain range of wavelengths. Yet slope or peaks of high t r a n s m i s s i o n have been used in discussions of both visible and i n f r a r e d spectra. Tan (1966) noted that it may be possible to determine the n a t u r e of humic compounds by studying the slope of spectrog r a m s in the region of 300-700 m/~. He suggested that the slope should give an indication of the degree of polymerisation, the s t e e p e r the slope the lower would be the molecular weight of the humic substances. Sloping b~:selines in the i n f r a r e d region have been used as a c h a r a c t e r i s t i c to identify polymers such as nylon (Lindley, 1965). If humlc substances a r e considered to be high molecular weight compounds (Scheffer und Ulrich, 1960; Kononova, 1961) and if podzolisation leads to humic substances with a s m a l l e r molecular weight (Kononova, 1961), the change in spectral pattern between 2, 500 and 1.800 cm -x of electrodialysed humic acids from v a r i o u s horizons of a biosequence of soil profiles found under encroaching poplar t r e e s (Dormaar and L ,'twick, 1966) could be vatuable, It is possible that the change of slope of the spectral line in the region of 2, 500-1, 800 cm -1 may have to do with the molecular weight of the humie Geoderma, 1, 1967

37

substances analysed. S o m e evidence for. this hypothesis can be obtained from an examination of infrared absorption spectra of humic acids separated on a Sephadex G-50 column (Kleinhempel und Hieke, 1965). Spectra of humic and fulvic acids of several humic allophane soils produced by Tokudome and Kanno (1965) reveal a striking difference in the configuration of the spectral region from 2, 500-1,800 c m -I. Similarly, the infrared spectra of humicand fulvic-acid samples from plant roots showed the same change in configuration in this region (Scharpenseel ~t al., 1964). Scheffer and Ulrich (1960) indicated that humic acids have a mo.'e complex structure and larger molecular weight but less acid character tim~ fulvic acids. Yet none of the above authors mentioned these differences in spectral configuration. The purpose of this study was to evaluate the s p e c t r a l configuration in the region from 2, 5 0 0 - 1 , 8 0 0 cm - I of humic acids from s e v e r a l softs formed under v a r i o u s vegetation. If a definite relationship e~ists between s p e c t r a l configuration and humic acids from soils f o r m e d under g r a s s or t r e e s , it could be used to advantage in soil g e n e s i s and classification studies. This informati_on would also be d e s i r a b l e from the standpoint of b u r i e d soils p r o vided no changes had o c c u r r e d following b u r i a l .

MATERIALS Humic acids w e r e extracted from s e v e r a l soils collected in a valley enclosing the headwaters of the Oldman R i v e r on the e a s t e r n slope of the Rocky Mountains in southwestern Alberta (Jeffrey et al., 1.~7) to s u r e e y the r e l a t i o n ship between configuration of infrared s p e c t r a of electrodialysed humic acids and established tree and g r a s s stands. T h r e e soils were sampled at the P . F . R . A . T r e e Nu,-sery, Indian Head (Sask.), to obtain further evidence on the change in configuration that r e s u l t s from planting t r e e s on Chernozemic soils. Sites 1 and 2 have had Scots pine (Pinus sylvestris L.) since 1910 while site 4 r e p r e s e n t s the adjacent undisturbed Black Chernozem. Four Che~nozemic Ah horizons w e r e collected in the Black soil zone of southern Alberta to e s t a b l i s h whether texture would influe,~ce the configuration of the s p e c t r a of humic acids f r o m soils developed under g r a s s . Two soils formed under t r e e s , and that have been under g r a s s for a number of y e a r s , were sampled to d e t e r m i n e whether the change of the spect r a l slope was r e v e r s i b l e . One soil was the Ae horizon of a Bisequa Gray Wooded with g r a s s for 5 and 11 y e a r s , and one was the Ae of a Podzo Regosol with g r a s s for 25 y e a r s . Soil group and horizon designations a r e those r e c o m m e n d e d by the Canadian N~tio~al Soil Survey Committee (1965).

METHODS Humic acids w e r e obtained by extract~ug the soil for 16h with a solution that corresponds to 0.1M Na4P207 and to 0. IN NaOH. The soil-solvent ratio was 1/10 and the pH of the solution was about 13. The e x t r a c t was acidified with concentrated H2SO 4 to pH 1.0. The humic acids w e r e titrated with NaOH to about pH 11 and purified Lnder nitrogen by exhaustive e l e c t r o 38

Geoderma, 1,, 1967

dialysis (Dormaar and T y r r e l l , 1965). The purified humic acid solutions were lyophilised. Sephadex G-100 (40-120 p) was allowed to swell in excess water and left to stand for t h r e e days with inte. mittent s t i r r i n g and decantation. A g l a s s column (22 x 400 mm) equipped with a capillary outlet (1 × 50 ram) was then filled and p r e p a r e d as described by Flodin (1961; t e e also Anonymous, date unknown). The gel bed was 350 m m high. One-half g r a m of electrodialysed humic acid of the Ah horizon of the ,.mdisturbed Black Chernozem f r o m the Indian Head T r e e N u r s e r y was dissolved in some 0.5N NaOH and placed beneath a layer of eluent on top of the gel bed. Distilled water was used as the eluent. The flow rate was r e g u lated at 3.0 m l / m i n . The f i r s t five fractions of 50 ml each were collected, acidified, and the precipitate was washed and lyophilised. All spectra presented herein were taken on KBr pellets. Two m i l l i g r a m s of lyophilised, electrodialysed humic acids were mixed with 400 mg of KBr for 3 rain in a React-R-Mill, Model E (manufactured by Udo Analyzer Company, Pullman, Washington), then t r a n s f e r r e d to a P e r k i n o E l n i e r Y ~ r die and evacuated. The pellets were c o m p r e s s e d at a total load of 10 tons for 5 min. All spectra were recorded on a P e r k i n - E l m e r ~ o d e l 137 Infracord Spectrophotometer. An i n c r e a s e in the time of grinding- or pressing or in the total load had no effect on the sloping baselines.

RESULTS AND DISCUSSION The Mull Regosols, found under g r a s s above the t r e e line, can be differentiated from the Acid Brown Wooded and PodzoUc soils formed under t r e e s (Fig. 1). The positive slope f r o m left to right Jn the region of 2, 5001,800 cm-1 has been denoted as having "Chernozemtc c h a r a c t e r " , and the zero to negative slope has been denoted as having "Podzolic cha~'acter" (Dormaar and Lutwick, 1966). The spectrum of the humic acids obtained from the Bfj horizon of the Brown Wooded soil still shows "Che~-nozemic charact e r " in this spectral region. However, this soil was situated under an open forest stand with enough g r a s s to form a minimal Ah horizon. The Gleyed Mull Regosol, Acid Brown Wooded, and Podzol soils o c c u r r e d on non-calcareous m a t e r i a l (less than 1% carbonates), while the Mull Regosol, Brown Wooded, and Gray Wooded soils were found on calcareous parent m a t e r i a l s (more than 1% carbonates). Yet the spectral configuration does not s e e m to be influenced by this difference in parent material. It is, therefore, a c h a r a c t e r i s t i c of the organic m a t t e r (Chern~zemic vs. Podzo]ic), indepe,~dent of the pH of the soil The configuration of the spectral regiow of 2, 500-1, 800 cm -1 fo~ the Mull Regosols and the Brown Wooded soil is s i m i l a r to that for lignin (Durie et al., 1960), lignin-derived m a t e r i a l s ( F a r m e r and Morrison, 1960), and r e s i d u e s from acid hydrolysis of ligno-protei~s extracted f r o m compost (Goulden and Jenkinson, 1959). The s p e c t r a l configurations of the humic acids of the Acid Brown Wooded and PodzoUc soils r e s e m b l e those obtained for a c i d - a n d alkaline-soluble soft organic matter (Tokudome and Kanno, 1965). Geoderma

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The infrared spe~ctra of the humic acids extracted from the undisturbed Black Chernozem s~m~led at the Indian Head T r e e Nursery displayed the typical s p e c t r a l configuraLion of humic acids obtained from soils formed under FREQUENCY (cm - ~ ) 250")

1725 IBO0 1525

3000

Ah MULL REGOSOL

Ah GLEYED MULL ~EGOSOL Bfj BROWN WOODED

Bfj ACID BRO

WOODED

Ae GRAY WOODED

1

Bt

Ae

PODZOL

Be

"5

4

5

6

?

WAVELENGTH (p)

Fig. 1. Infrared s p e c t r a of dialysed humic acids extracted from soils developed in the Upper Oldman R i w r Basin, Alberta.

g r a s s (Fig. 2). It was noted elsewhere (Dormaar and Lutwick, 1966) that when soils t r a n s f o r m e d from a Chernozemic to a Podzolic soil as a r e s u l t of t r e e encroachment a change in the spectral configuration started to occur in the humic acids extracted from the Bt horizon. This initial observation can now be substantiRted w i ~ the spectra of the humic acids of the soils planted to Scots pine, It has b~en suggested (Wright and Schnitzer, 1963) that fulvic acid on its path down the profile durin~ the podzolisat~on p r o c e s s f o r m s metalloorganic complexes, ~hlch precipitate lower in the profile. If it can be assure40

Geoderma, 1, 1967

F R E Q U E N C Y { O m "l ) ESoO 1725 1800 tS2S

~000

1 SiTE 4 Ab Im m

ll--'lE SITE I

"l

A&I~ St1

lit i

]

IIm

SITE AID! Altl~

I

4 S S WAVELENGTH ( p )

7

Fig. 2. Infrared spectra of dialysed humic acidF, extracted from a Black Cherno~em (site 4) and Black Chernozems planted t,, Scots pine (Pi~s sy!vestris L.) in 1910 (sites I and 2).

ed tha~ the negative slope from left to right in the spectral region of 2, 5001,800 c m -I is related to organic materials of lower molecular weight than those found under grass and since Scheffer and Ulrich (1960) showed that the molecular weight of fulvlc acids is less than that of humic acias, it seems reasonable to expect a change in spectral configuration of the organic material obtained from the Bt horizon. The Bt z spectrum of site 2 shows particularly strong "Podzollc character". The initialmorphological description of the profile called only for one Bt horizon. However, the results show the value of having sampled both an upper and a lower half. This change in spectral configuration happened under trees, that is, under both Po~lus species (Dormaar mid Lutwick, 1966) and conifer species Geoderma, I, 1967

41

(Fig. 1, 2). It i s likely then to be a c h a r a c t e r i s t i c o£ the t r a n s f o r m a t i o n f r o m C h e r n o z e m i c to Podzolic o r g a n i c m a t t e r within the soil, independent of the t r e e s p e c i e 3 growing in the soil. The t e x t u r e of the Ah horizon does not ~eem to influence the s p e c t r a l configuration in the r e g i o n between 2, 500 ~md 1,800 cm -1 (Fig. 3). The i n c r e a s e e shoulder at 1,725 c m -1 with an i n c r e a s e in p e r c e n t a g e of sand is of interest.

(,~m - i ) FREQUENCY 17;~5 2500 1800 1525 5000 '

Ill

]'

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BLACK CHERNOZ EMS

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Fig. 3. Infrared s p e c t r a of dialysed humic a c i d s e x t r a c t e d f r o m f~ur Black C h e r n o z e m i c Ah h o r i z o n s of different t e x t u r e .

Humic a c i d s from the Ae horizons of the B i s e q u a G r a y Wooded soil and the Podzo Regosol show "Podzolic c h a r a c t e r " in the s p e c t r a l rc~ion between 2, 500 and 1, 800 c m -1 (Fig. 4). However, a s soon a s p e r m a n e n t p a s t u r e w a s e s t a b l i s h e d the configuration a c q u i r e d " C h e r n o z e m i c c h a r a c t e r " . Humic acids obtained from even a 2 - y e a r - o l d p a s t u r e showed s o m e "Podzolic c h a r a c t e r " . Kononova (1961) c o n s i d e r s humic acid f o r m a t i o n to be a polycondensation p r o c e s s . She feels that u n d e r high mo~isture conditions r e m o v a l of condensation b y p r o d u c t s such a s w a t e r i s prevented and this, in turn, h i n d e r s the growth of the molecule. C h e r n o z e m s , on the other hand, a r e char~.cterized 42

Geoderma, 1, 1967

by a periodic m o i s t u r e deficit that c r e a t e s conditions favourable for the r e m o v a l of byproducts and the formation of more complex humic acids. The configurations (Fig. 4) suggest that the m o l e c u l a r weight of the humic substances would i n c r e a s e within a few years. On the other hand, the change in c h a r a c t e r of organic m a t t e r f r o m Chernozemic to Podzolic takes longer. The f i r s t signs of such a change in s p e c t r a l pattern a r e found in the Bt horizon (Fig. 2 and D o r m a a r and Lutwick, 1966). FREQUENCY 2500 3000 "1

O/

'

(cm

"l)

1725 18 DO !525, , I '

I

I

I

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Ap

(11 YEARS)

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REGOSOL

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4 6 G WAVELENGTH (p)

7

Fig. 4. Infrared s p e c t r a of dialysed humic acids extracted from the Ae horizons of a Podzo Regosol and a Bisequa Gray Wooded and adjacent Ap horizons with various ages of permanent pasture. The separation by Sephadex G-100 of humic acid from a soil formed under g r a s s is interesting (Fig. 5). The f i r s t 50-ml fraction still shows "Chernozemi~ c h a r a c t e r " of the original sample in the s p e c t r a l region of 2,500-~800 cm-1. Although the fractionation range of molecular weight limits of Se~hadex G-100 within which molecules can be separated by size is 5, 0 0 0 100, 000, it does not n e c e s s a r i l y mean that fraction 1 contains material with a molecular weight l a r g e r than 100, 000. Nevertheless, each successive f r a c tion will contain molecules of d e c r e a s i n g molecular size. F r a c t i o n 2 s t a r t s to flatten in the s p e c t r a l region under consideration, while fraction 5 ~hows complete "Podzolic c h a r a c t e r " . It may thus be concluded that the slope of the i n f r a r e d spectrum of humic acids in the region of 2, 500-1,800 cm -1 is influenced by the moiecular weight of these humic acids. Without an actual determination of m o l e c u l a r weight, however, the size of the molectde at which the slope of the baseline s t a r t s to change remains a m a t t e r of conjecture. The data p r e s e n t e d support the belief that the slope o r configuration of infrared spectra of humic acids in the region of 2, 500-1,800 cm -z is r e l a t e d Geoderma, 1, 1967

43

F R E O U E K C ' q (©m-~) 2 50~ 1725 3000 18OO 1525

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WAVELENGTH (p)

Fig. 5. Infrared s p e c t r a of a dialysed humic acid extracted from a Black Chernozemic Ah horizon and of successive fractions eluted f r o m a Sephadex G- 100 column. to ~he molecular weight of the m a t e r i a l and to the vegetation under which these humic substances a r e formed. Duti! and Juste (1965) presented infrared s p e c t r a of humic aci.is extracted f r o m Black Palaeosols found in the Sahara (Hoggar) and f o r m e d during the last humid climate cycle about 3000 B.C. Two of the soils they studied have v e r t i s o l i c c h a r a c t e r i s t i c s and were formed under a predominantly g r a s s vegetation (P. Dutil, p e r s o n a l communication, date unknown). One of the s p e c t r a shows "Chernozemic c h a r a c t e r " . In the d e p r e s s i o n a l a r e a s woody plants such as Acacia and Eucalyptus a r e common genera. ~]ince the other s p e c t r u m shows "Podzolic c h a r a c t e r " it may be speculated that this soil came from one of these depressional a r e a s with woody plants or that changes have o c c u r r e d following burial. ACKNOWLEDGEMEN'rs I am indebted to Dr. D. K. McBeath, R e s e a r c h Station, Lacombe, Alberta, who supplied the Bisequa Gray Wooded s a m p l e s from n e a r Chedderville, Alta.; to Mr. J. A. Shields, Saskatchewan Institute of Pedology, Saskatoon, Sask., 44

Geoderma, 1, 1967

who supplied the f i e l d d a t a of t h e Indian Head T r e e N u r s e r y s o i l s ; and to M e s s r s . R. A. M i l n e , R e s e a r c h Station, L e t h b r i d g e , Alta., and G. E m m o n d , E x p e r i m e n t a l F a r m , Indian Head, Sask., who s a m p l e d the Indian Head T r e e N u r sery soils.

REFERENCES Anonymous, date unknown. Sephadex, Theory and Experimental Technique. Pharmacia, Uppsala, (Sweden), 23 pp. Dormaar, J. F. and Lutwick, L. E., 1966. A biosequence of soils of the rough fescue prairie-poplar transition in southerwestern Alberta. Can. J. Earth Sci., 3: 457-471. Dormaar, J. F. and Tyrrell, C., 1965. The use of a solenoid water valve in an electrodialysis system. Can. J. Soil Sci., 45: 235-237. Durie, R. A., Lynch, B. M. and Sternhall, S., 1960. Comparative studies of brown coal and lignin. 1. Infra-red spectra. Australian J. Chem., 13: 156-168. Dutil P. et Juste, C., 1965. Etude de la composition de la mati~re organique de pal~)sols sahariens; interpretation et consequences pour l'h~ritage organique des sols. Compt. Rend., 261: 4791-4794. F a r m e r , V. C. and Morrison, R.I. 1960. Chemical and infrared studies on Phragmites peat and its humic acid. Sci. Proc. Roy. Dublin Soc., Ser.A(1): 85-104. Flodin, P., 1961. Methodological aspects of gel filtration with special referer, ce to desalting operations. J. Chromatog., 5: 103-115. Goulden, J. D. S. and Jenkinson, D.S., 1959. S~mdies on the organic material extracted from soils and composts. 2. The infra-red spectra of ligno-proteins isolated from compost. J. Soil Sci., 10: 264-270. Jeffrey, W. W., Bayrock, L.A., Lutwick, L. E. and Dormaar, J. F., 1967. Land-vegetation typology in the Upper Oldman River Basin, Alberta. Can. Dept. Forestry, Tech. Bull., in press. Kleinhempel, D. und Hieke, W., 1965. Zur Trennung yon Huminsliuren durch Geldiffusion. Albrecht Thaer Arch., 9: 165-172. Kononova, M.M., 1961. Soil Organic Matter. Pergamon, New York, N.Y., 450 pp. L~ndley, G., 1965. The identification of polymers by filament pyrolysis and infra-red spectrometry. Lab. Pract., 14: 826-831. National Soil Survey Committee of Canada, 1965. Report. Can. Dept. Agr., Ottawa, Ont., 132 pp. Scharpenseel, H. W., K'dnig, E. und Menthe, E., 1964. Infrarot- und Differential-The, ,,o o Analyse an Huminsliureproben aus verschiedenen Bodentypen, aus Wurmkot ~md Streptomyceten. Z. Pflanzenern~lhr. D~mg. Bodenk., 106: 134-150. Scheffer, F. und Ulrich, B., 1960. Lehrbuch der Agrtkttlturchemie ULJ Do¢lenmmde. 3. Teil. Humus and Humusdiingung. Band 1. Morphologie, Biol.gie, Chemie trod Dynamik des Humus. Enke, Stuttgart, 266 S. Tan, K. H. 1966. On the pedogenetic role of organic matter in volcanic ash soils uncler tropical conditions. Soil Sci. Plant Nutr. (Tokyo), 12: 34-38. Tokudome, S. and Kanno, I., 1965. Nature of the humus of humic aHophane soils in Japan. Part 2. Some physico-chemical properties of humic and fulvic acids. Soil Sct. Plant Nutr. (Tokyo), 11: 193-199. Wright, J. R. and Schnltzer, M., 1963. Metallo-organic interactions associated with podzolizaUon. Soil Sci. Soc. Am. Proc. 27, 171-176.

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