Organic Carbon Content and Rates of Sequestration in Soils of AlbaniaPandi Zdruli, Hari Eswaran,* and John Kimble

ABSTRACTSoil organic carbon (SOC) was measured in 17 pedons, representing

major agricultural soils in Albania. The soils studied were Inceptisols,Vertisols, Mollisols, and Alfisols. Within each order, the wet members(aquic suborders) had 10 times or more SOC than their well-drainedcounterparts. Radiocarbon dates were determined on wood fragmentsfound in a few of the soils. The steady-state rates of accumulationrange from 20 to 60 g m"1 m"2 yr"1 in the wet soils. Only onewell-drained soil was available for comparison and this had an accumu-lation rate of SOC of<l gm""1 m ~ 2 yr ~'. Drainage of the wet soilsresults in a marked decrease in SOC. The rate of decrease is muchsmaller (26 g m ~ ] m " * yr ~' during a 38-yr period) than the accumula-tion rate, which was about 210 g m"1 m"2 yr"1 (during 2000 yr)in the one pedon studied. In the same climatic environment, thewell-drained soils accumulate SOC at significantly lower rates thantheir poorly drained counterparts, making the former inefficient sinksof SOC. Thus, from the point of view of sinks of atmospheric COi,emphasis must be given to the wetland soils.

INFORMATION ON THE VOLUMETRIC CONTENT Of SOCin soils is slowly increasing. Though organic C is

routinely measured during the characterization of soilsin a soil survey program, information on the bulk densityof corresponding horizons for volumetric computationsis frequently not available. However, with recent interestin the content and fate of SOC, more complete dataon SOC-volume relationships is becoming available,thereby permitting the collation of regional and globaldatabases. The preliminary study of Eswaran etal. (1993)is a first estimate of the contents of SOC in named soilsof the world. This study complements previous studiesof Bohn (1982) and others.

Recently, interest has increased in mitigating technolo-gies to enhance the content of SOC (Johnson and Kerns,1991; Downing and Cataldo, 1992; Lugo, 1992). Amajor impetus toward these heightened interests resultfrom the expected increases in atmospheric COa, as soilsare considered an important C sink (Duxbury, 1991).Knowledge of baseline accumulation rates thus becomeimportant as few comprehensive measurements exist dueto inherent difficulties in making such measurements.

The objective of this study was to employ radiocarbondating techniques to obtain estimates of the age of depositsand thereby estimate steady-state rates of SOC accumula-tion. Such measurements are fraught with errors (Schar-penseel and Schifrman, 1977; Scharpenseel and Becker-Heidmann, 1992) and uncertainties but provide somebenchmark values of sequestration rates (Eswaran et al.,1993).

Contribution from the World Soil Resources, USDA Natural ResourcesConservation Service, P.O. Box 2890, Washington, DC 20013. Received4 Jan. 1995. Corresponding author.

Published in Soil Sci. Soc. Am. J. 59:1684-1687 (1995).

MATERIALS AND METHODSThe Republic of Albania is located in the Balkan Peninsula,

between 39°38' and 42°39' N, and 19°16' and 21°40' E. Thenorth and northeast part of the country borders the Republicof Yugoslavia and former Yugoslav Republic of Macedonia,in the south it is bordered by Greece, and in the west by theAdriatic and Ionian Seas. Total surface area of the country is28 748 km2, and of this area, only 16.2% is less than 100 mabove sea level. It is very mountainous, with many variedlandscapes including bare rock. Agriculture is well distributedwithin the country, but is most intensive in the western coastallowland. Albania has a total agricultural land area of about700 000 ha, confined mainly to the western coastal plains anda few of the larger intermontane basins.

Seventeen pedons were sampled in the agricultural areas ofAlbania. The sites were selected based on previous publishedinformation (Veshi and Spaho, 1988) and the representativenessof the soil with respect to the soils of the country. Soils wereanalyzed by the National Soil Survey Laboratory of the USDANatural Resources Conservation Service (formerly USDA-SCS), using prescribed methods (Soil Survey Staif, 1995).Soil organic C was determined with the wet digestion method.Bulk density was measured on saran-coated clods. The weightpercentages of SOC were converted to volume content andthen summed to provide values for total amounts to a 1-mdepth. Table 1 lists the amounts for the 17 pedons. The soilswere classified according to soil taxonomy (Soil Survey Staff,1994). Detailed pedon descriptions with supporting character-ization data is given by Zdruli (1995, unpublished data).

Radiocarbon dating (13C) was determined by a commerciallaboratory. The samples were first washed with deionizedwater and then subject to an alternate acid-alkali treatment toremove carbonates and secondary organic acids. The SOC wasthen synthesized to benzene, measured for '4C content, andcalculated for radiocarbon age. Table 2 gives the adjusted I3Cage (the radiocarbon ages are converted to calendar ages).The vendors indicated an error of ±50 yr in the calibratedresults.

RESULTS AND DISCUSSIONThe SOC varied from about 5 to >75 kg m~' m~2 in

the 17 pedons (Table 1). The smaller values were in thewell-drained soils. The largest value was in Pedon 007,which was located in a concave depression where thesoils grade to Histosols. Within the same order, thewetter soils (aquic suborders) had greater SOC levelsthan their better drained counterparts.

The magnitude of the SOC content in the well-drainedsoils of Albania was similar to soils in other parts ofthe world with equivalent soil temperature and moistureregimes. This was confirmed by comparing the SOCcontents in the Albanian soils with data from the databaseof the World Soil Resources of the USDA (Eswaran etal., 1993). The STR is thermic in the southern part ofAlbania and mesic in the north and in die highlandregions. Table 1 lists the STR of the sampled pedons.

Abbreviations: SOC, soil organic carbon; STR, soil temperature regime;SMR, soil moisture regime; BP, years before present.

1684

ZDRULI ET AL.: ORGANIC CARBON CONTENT AND SEQUESTRATION RATE 1685

Table 1. Organic C content of some soils of Albania.

Pedonno.

001008004009

016012010014

007003002015006Oil

017005013

Classification

Vertic HalaqueptUdifluventic UstochreptUdic UstochreptFluventic Xerochrept

Typic EndoaquertAquic HaploxerertUdic HaploxerertChromic-Udic Haplustert

Pachic CalciustollVertic ArgiaquollPachic CalcixerollFluventic HaplustollUdic CalciustollTypic Argiudoll

Aquic HaplustalfUdic HaplustalfUdic Rhodustalf

STR

InceptisolsTTMT

VertisolsTMTT

MollisolsMTTTMT

AlfisolsTMM

0-30 cm

3.97.33.54.4

18.77.65.14.1

29.010.57.47.94.25.5

6.24.94.6

Total organic C

0-50 cm

6.011.54.56.7

30.911.28.55.0

47.716.510.811.36.48.2

9.07.18.2

0-100 cm

11.017.55.1

11.0

56.714.615.07.4

76.531.114.518.88.5

15.4

12.410.011.6

t STR is soil temperature regime; M = mesic; T = thermic.

The soils of the central and southwestern coastal plainshave a xeric SMR, which changes to ustic northward.The eastern part of the country and the mountainousareas have a udic soil moisture regime. In the well-drained soils, the soil composition and environment,including SMR and STR, determine the rate and amountof SOC production. The net accumulation is also deter-mined by the extent of losses or gains through erosion.In the wetter soils, in comparison, the accumulation ratesand thus the net amounts are accentuated by the prevalentanaerobic conditions. Most of the poorly drained soilsoccur in basin or depression landscape situations with ahigh input of SOC through erosion products. Micromor-phological analysis (Zdruli, 1995, unpublished data)showed microstrata of partially decomposed SOC in thesesoils of sedimentary origin.

Wetness also influences the depth of SOC accumulation(Table 1). In well-drained soils, most SOC accumulationoccurs in the top 30 cm of the soil. In the poorly drainedsoils, more than 50% of SOC is present at depths >50cm. This is due to stratification in the soils, as shownin the micromorphological study (Zdruli, 1995, unpub-lished data).

Table 2 provides the radiocarbon age of wood frag-

Table 2. Rate of organic C (OC) accumulation in Albanian soils.

ments hand picked at the depths shown. The amount ofSOC in the layers above this depth was computed andfrom this, rates of SOC accumulation were calculated(Table 2). The rates are expressed both on a 1-m soildepth over an area of 1 m2 and also on a hectare basis.In the soils with high water table, the steady-state rateof accumulation ranges from 20 to 60 g m"1 m~2 yr"1

(or 0.2-0.6 kg irT1 ha~' yr"1). The only pedon (Pedon005) of a well-drained soil (from which wood fragmentswere available for dating) snowed a value <1 g m"1 m~2

yr-'.Pedon 16 was collected from an area previously de-

scribed as peat by Bajraktari and Xinxo (1972). Themapped area is about 2000 ha. Radiocarbon dating of awood fragment at about 1-m depth indicated an ageof 2300 BP. Unpublished archaeological observationssuggest that the area was colonized about 2000 yr ago.This date corresponds with the radiocarbon age determi-nation and suggests that much of the sedimentation ofthe swamp took place after that time period. The sedimen-tation rate (assuming no subsidence) initially was about4 mm yr"1 and later (since 1800 BP) reduced to about3 mm yr"1.

Our study showed (Table 1) that the organic C content

Pedonno.

003005007007016016016t016t

Depth

cm85-112

112-14477-95

160-18049-6995-11949-6995-119

Cis age

640 BP8490 BP1850 BP2420 BP1770 BP2300 BP17702330

Total OC inoverlying layers

kg m~' m"2

26.910.366.480.130.352.7

194.7210.3

g m~' m"2 yr"1

541

50203023

11091

Rate ofaccumulation

kg m"1 ha"1 yr"1

0.50.010.50.20.30.2

11.09.1

t These are based on the soil OC content prior to drainage in 1956.

1686 SOIL SCI. SOC. AM. J., VOL. 59, NOVEMBER-DECEMBER 1995

Table 3. Changes in soil organic C (SOC) due to drainage inPedon 16.

Samplingdate

195619701994

0-30 cm

90.338.6 (57.2)t17.5 (80.6)

Total SOC

0-50 cm. _, _ 2

141.152.7 (62.7)30.3 (78.5)

0-100 cm

221.487.5 (60.5)65.6 (70.4)

t Percentage loss from 1956 (year of drainage) in parentheses.

of the surface soil material in Pedon 16 was too low toclassify as a histic material, so the soil was classified asa Vertisol. Prior to 1956, the area was a swamp butwas drained and reclaimed for agricultural use in 1956.Bajraktari and Xinxo (1972) studied the soils beforeand after reclamation and showed a marked decrease inorganic C content. Table 3 and Fig. 1 show this decline(the 1994 data coming from our study). In the 1-mcontrol section, there was a 60% decrease in total SOCduring the period 1956 to 1972 and, for the period1956 to 1994, the decrease was about 70%. The rate ofdecrease is about 0.026 kg m~' m~2 yr~ ' . Part of thedecrease is due to oxidation of the SOC and part is dueto subsidence. As the organic component of even thetopsoil is not high, subsidence was not expected to con-tribute significantly to the SOC decrease.

The rate of SOC decrease resulting from drainage ismuch smaller (26 g m~' m~2 yr~ ' during the 38-yrperiod) than the SOC accumulation rate, which was about210 g m~' nT2 yr~ ' (during 2000 yr) in the one pedonstudied. For the accumulation rate, the SOC contentprior to drainage of the soil (Table 2) was used forcomparison. Most of the decrease was probably due tooxidation and mineralization of the non- or partiallydecomposed woody tissue materials.

250

200

1150ocaK<<j<j 100zoato

50-

SO1L LAYER

0-30 cm +0-50 cm -*-0-100 cm

fe-_

'+..._

1956—\——}——1970

YEAR

1994

Fig. 1. Change in soil organic C (SOC) with drainage and cultivationin Pedon 16, a Typic Endoaquert (SOC data of 1956 and 1970from Bajraktari and Xinxo (1972).

Despite the small number of sampling points, it appearsthat the rates of SOC accumulation in the wet soils areabout 40 times those of well-drained soils in this climaticzone. Total SOC amounts vary about 10-fold. The twosources of accumulation were (i) additions from erosion,and (ii) in situ accumulation associated with slower de-composition rates in anaerobic environments. Erosionwas probably a more important SOC contributor. Obser-vations of upland soils indicated that water erosion hadcaused major soil losses. The soils of sedimentary originthus, particularly the wet ones, were relatively largersinks of SOC than the upland soils.

CONCLUSIONMore than 65 % of Albania is composed of hills and

mountains, mostly heavily eroded with shallow soils andeven bare rock. The eroded sediments form the westerncoastal plains and the intermontane valleys. The soils onthese sedimentary deposits have acquired SOC throughthe erosion products and in addition have accumulatedsome SOC from the vegetation on them. The measuredvalues of SOC provide a steady-state amount. It is notpossible to differentiate the two processes.

It is evident that anaerobic conditions in the soil pro-mote rapid accumulation of SOC. A 10-fold differencein rate was shown in this study. The study also showsthe very rapid decline in SOC content following drainage.The ability to accumulate SOC and the ease of its oxida-tion after drainage are characteristics of wetland soils,making them very efficient sources and sinks of CO2.This represents another dimension to the fragility ofwetlands and provides a very valid reason for theirprotection and preservation. In the same climatic environ-ment, the well-drained soils accumulate SOC at signifi-cantly lower rates. These latter soils are inefficient sinksof SOC. Thus, from the point of view of sinks of atmo-spheric CO2, emphasis must be given to the wetlandsoils.

AGBENIN & TIESSEN: PHOSPHORUS FORMS IN FRACTIONS OF BRAZILIAN TOPOSEQUENCE 1687