Upload
c-v
View
220
Download
2
Embed Size (px)
Citation preview
Genesis and Profile Development of Success Soils,Northern New HampshireJ. A. Freeland and C. V. Evans*
ABSTRACTModels of podzolization for northern New England soils are largely
limited to organo-chelate models, which are adequate to explain ort-stein development but are inadequate to explain other types of indur-ated horizons, such as those observed in the Success series (sandy-skeletal, mixed, frigid, ortstein Typic Haplorthod). In order to betterunderstand the genesis of these soils, which have light-colored, in-durated horizons below ortstein horizons, oxalate-extractable Si, Al,Fe, total C, pH, and micromorphological properties were determinedfor six pedons. Profile distributions of Si and Al and Fe and C werepositively correlated (r2 > 0.90 and =0.7, respectively), but Fe andAl, Al and C, Si and Fe, and C and Si were not significantly related.Estimated allophane contents calculated from Si and Al were signifi-cantly higher in Bsm and BCm horizons than in Bhs and Bhsm ho-rizons, as were pH values, while Bsm and BCm horizons hadsignificantly less C and Fe than Bhs and Bhsm horizons. The Bsmhorizons also had significantly lower pH values and higher estimatedallophane values than BCm horizons. Allophanic grain cutans (allans)form intergrain bridges in BCm horizons, and grains in Bhsm andBsm horizons have additional dark cutans abruptly adjacent to theallans. This suggests two separate phases of translocation, in whichinorganic sesqnioxide and allophanic sols are deposited during an in-itial phase that forms Bsm and BCm horizons, and organic compoundsare illuviated in a subsequent phase, creating Bhs and Bhsm horizons.
INDURATED HORIZONS occur in many New HampshireSpodosols, including the Success Series. Most of
these horizons are ortstein — Bsm or Bhsm horizonscemented by organically complexed Fe or Al. Theortstein materials are considered to be pedogenic, andare widely recognized products of podzolization(Schnitzer and Skinner, 1964; Farmer, 1982; Mc-Keague et al., 1983). Although the Success series lim-its require the presence of ortstein, Success soils alsohave one or more indurated layers — BCm horizons— below ortstein horizons, which are dissimilar toortstein. The ortstein typically has both value andchroma of <3, and hues of SYR to 7.5YR (dark red-dish brown, dark brown, or black), but the SuccessBCm horizons are lighter colored, with values of 4 or5 and chroma of 3 to 6. They are also typically lessred, with hues of 7.5YR and even 10YR (brown oryellowish brown).
Earlier work in Canada (McKeague and Kodama,1981; McKeague and Sprout, 1975) proposed that someindurated horizons below spodic horizons were ce-mented by amorphous oxides of Fe, Al, or Si thatwere either illuvial accumulations or in situ weather-ing products. Studies involving Spodosols in Scotland(Anderson et al., 1982) have documented significantquantities of allophane and imogolite that form thickcutans on quartz grains in lower B horizons, some of
Dep. of Natural Resources, Univ. of New Hampshire, Durham,NH 03824. Scientific Contribution no. 1770 form the New Hamp-shire Agric. Exp. Stn. Received 1 May 1992. * Correspondingauthor.
Published in Soil Sci. Soc. Am. J. 57:183-191 (1993).
which are cemented. These studies were supported byfurther work indicating that allophane and imogoliteprecipitate from inorganic Fe oxide-silica-alumina-water sols, suggesting that uncomplexed allophanicmaterials are significant products of podzolization(Farmer and Fraser, 1982). These models of podzo-lization are by no means universally accepted, how-ever, and others (Schnitzer and Skinner, 1964;McKeague et al., 1983; Buurman and Van Reeuwijk,1984) have emphasized the role of organic chelates inthe illuviation of sesquioxides.
The light colors of the BCm horizon contraindicatea strong influence of organic matter or Fe as cement-ing agents, however, so genesis of Success BCm ho-rizons may best be explained by an alternative processor processes. Although considerable work has beendone in the U.S. Northeast (e.g., Rourke et al., 1988)to correlate field and laboratory definitions of spodichorizons, most of the recent work addressing modelsof podzolization has come from other countries (Fannerand Fraser, 1982; Childs et al., 1983; Wang et al.,1986) or from regions of the USA where the need todistinguish between Andisols and Spodosols hasprompted such research (Ugolini et al., 1991). If Suc-cess BCm horizons are a type of spodic horizon, itwould require that the organic-complex models ofpodzolization most widely held in New Hampshire beexpanded to consider multiple models of podzoliza-tion. Alternatively, a new concept may need to bedeveloped that might combine features of the modelscited above.
Induration processes independent of podzolizationare also well known, including glacial compaction,clay bridging (Lindbo and Veneman, 1989), amor-phous silica (Steinhardt et al., 1982) and quartz ce-mentation (Harder and Flehmig, 1970), and quartzpressure solution (Robin, 1978). Unlike the Cd hori-zons created by glacial compaction, Success BCm ho-rizons lack the coarse platy alignment of basal till, areusually massive and randomly fractured, and, even inthe field, an intergranular cementing agent is visible.Both clay bridging and amorphous silica accumula-tions have been proposed as binding agents of fragi-pans (B[t]x horizons) in humid climates. Either ofthese would be consistent with the colors observed inthe Success subsoil horizons, but Success BCm ho-rizons lack the coarse prismatic structure or bleachedcoatings most researchers associate with fragipans(Smeck and Ciolkosz, 1989). Silica is also the essen-tial agent of duripan formation; however, duripansform primarily in xeric and semiarid climates, wherehigh soil solution pH enables mobilization of signifi-cant quantities of silica (McKeague et al., 1983).Therefore, the acidic materials and humid climatesthat favor Spodosol formation are inconsistent withconcurrent development of duripans, although the tax-onomic system (Soil Survey Staff, 1990) provides forDuric subgroups of Spodosols.
183
184 SOIL SCI. SOC. AM. J., VOL. 57, JANUARY-FEBRUARY 1993
As each of the above tentative explanations for thegenesis of Success soils was questionable, this workwas undertaken to investigate the genesis of these soils.Two hypotheses were examined most closely: (i) Suc-cess soils represent a sequential podzolization profilethat included BCm horizons as ortstein-like horizons;and (ii) Success soils consist of an upper podzolizedprofile and a lower cemented profile in which indur-ation is independent of podzolization.
MATERIALS AND METHODSStudy Sites
Six Success pedons were selected for study in Coos County,New Hampshire (Fig. 1). Success soils are well drained andderived from glacial till that has its source in the AmmonoosucFormation, an Ordovician metamorphosed volcanic complex.Two pedons (Jericho Pond 1 and 2) were sampled on JerichoPond Road in Berlin, NH; two others (Nash Stream 1 and 2)from the Nash Stream area of Stratford, NH; one pedon nearCascade, NH; and the sixth pedon near Randolph, NH. JerichoPond 1 is the type location for the Success series. Profileswere described according to standard terminology (Soil SurveyStaff, 1990), and a BCm designation was tentatively used forthe lighter-colored indurated horizons under study (Table 1).
Laboratory AnalysesSlake tests were performed on BCm clods to help identify
the cementing agent(s). In this study, water was used to testfor fragipan cementation (Soil Survey Staff, 1990, p. 16-17)and 0.05 M NaOH and 0.1 M HCI were used for further slaketests, based on pH-dependent solubility rates of Fe, Al, andSi (Lindsay, 1979). The duripan test in Soil Survey Staff (1990,
71° 26' 30" 71° 11'30"
44° 42' 30"
440 22.
44° 42' 30"
- 44° 22' 00"
NEW HAMPSHIRE
p. 15) relies on these relationships to identify Si as a cementingagent, since Si is relatively soluble in bases, but very sparinglysoluble in acids. Conversely, Al is relatively soluble at bothrelatively high and relatively low pH, while Fe is quite solublein acidic solutions, but much less soluble in more basic solu-tions as long as Eh remains constant. Thus, indurated clodsthat are cemented with Si should slake in NaOH, but not HCI;if Al is the cementing agent, clods should slake in both NaOHand HCI but, if Fe is the cementing agent, clods should slakeonly in HCI.
Soil pH of all E, B, and C horizons was measured in 1:1soilwater slurries with distilled water and 0.01 M CaCl2(McLean, 1982). Total C, assumed to be organic, was calcu-lated for these horizons from weight loss on ignition (Schulteet al., 1991). After H2O2 pretreatment to destroy organic mat-ter (Kunze and Dixon, 1986), paired replicate samples fromE, B, and C horizons were reacted with 0.2 M ammonium
Table 1. Profile descriptions.
Horizon
EBhsBhsmBsmBCmC
EBhslBhs2BsmBCmClC2
EBhBhsmBsmBCmC
AEBBhsBsmlBsm2BCmC
AEBhsmBsmBCmC
AEBhsBhsmBCmlBCBCm2
Depth
cm
5-2020-3030-4040-5353-7474-90 +
0-55-10
10-303<M141-7676-9191-120 +
0-1313-1515-2020-3030-5151-81 +
0-1010-2020-2828-4141-6161-7979-100 +
0-1818-3030-5151-7171-9999-120 +
0-1818-3636-5151-9191-127127-142142-160
Moistcolor Texturef
Jericho Pond no. 110YR 5/2 fslSYR 3/4 IsSYR 4/6 Is7.5YR 4/6 Is10YR 5/6 gs2.SYR 4/2 vgs
Jericho Pond no. 27.5YR 6/2 IsSYR 2.5/2 IsSYR 3/4 Is7.5YR 4/4 vgs10YR 5/3 vgs2.5YR 4/4 vgs2.5YR 5/2 gs
Nash Stream no. 110YR 5/1 IsSYR 3/2 Is2.5YR 2.5/2 Is7.5YR 4/4 vgs10YR 3/3 vgs10YR 4/3 vgs
Nash Stream no. 27.5YR 3/2 fsl7.5YR 5/2 fslSYR 2.5/2 IfsSYR 3/4 vgsSYR 3/4 sg10YR 4/4 sg10YR 5/3 sg
Cascade10YR 3/2 vgls10YR 4/1 vgls10YR 2/2 vglcos7.5YR 3/2 vglcos7.5YR 4/6 vgcos10YR 4/6 vgcos
Randolph10YR 2/1 gfsl10YR 5/2 fsl7.5YR 3/2 vglcosSYR 3/4 vglcos7.5YR 4/4 vgcos7.5YR 4/4 g7.5YR 4/4 vgcos
Structure:):
mIfsbk
mmm
Icpl
Ifgr2fgr
Imsbkmmm
Icpl
IfgrIfsbk
mmm
Icpl
IfgrIfgr
Ifsbkmmm
Icpl
Ifgrmmmmsg
Ifgrsg
Ifsbkmmsgm
Cement
%
nonenone
609090
none
nonenonenone
3060
nonenone
none20
1007020
none
nonenonenone
805030
none
nonenone
908070
none
nonenonenone
8050
none40
Fig. 1. approximate location of study sites in Coos County,New Hampshire.
t Texture: f = fine, 1 = loam(y), s - sand, Icos = loamy coarse sand,g = gravel(ly), and vg = very gravelly.
t Structure: 1 = weak, f = fine, m = moderate, c = coarse, sbk =subangular blocky, pi = platy, gr = granular, and m = massive.
FREELAND & EVANS: GENESIS AND PROFILE DEVELOPMENT OF SUCCESS SOILS 185
oxalate adjusted to pH 3 (Jackson et al., 1986). Oxalate so-lutions were examined for Fe, Al, and Si content using induc-tively coupled plasma spectroscopy.
Iron, Si, Al, and C values of each horizon were evaluatedboth within individual profiles and among all profiles for rel-ative rank levels. Rank numbers for each constituent were usedto evaluate coincident depth distributions by obtaining corre-lation coefficients of simple linear relationships between eachpair of constituents (Wolfram Research, 1991).
As allophanic materials (sometimes referred to as protoimo-golite) are the only significant source of oxalate-extractable Siin soils (Parfitt and Hemni, 1982; Farmer et al., 1983), allo-phane estimates were calculated from Al and Si data. Calcu-lations were based on earlier work (Parfitt and Hemni, 1982;Childs et al., 1983; Parfitt and Kimble, 1989) which deter-mined that allophane in humid, acidic soils contains 14% Siand has an average oxalate-soluble Al to Si ratio of 2:1. Wanget al. (1991) also used this value to calculate imogolite content.
Significance of differences in pHH20, pHCaC12, C, Fe, andestimated allophane were evaluated with a Student's West(Wolfram Research, 1991) applied to mean value pairs fromsix groups of genetic horizons. Horizon groupings used were:BCm horizons, Bhs horizons, Bsm horizons, Bhsm horizons,B(h)sm horizons, which included both Bhsm and Bsm hori-zons, and Bhs(m) horizons, which included both Bhs and Bhsmhorizons.
Oriented samples of ortstein and BCm horizons from eachpedon were collected and made into thin sections that wereexamined optically and described according to Brewer (1976).
RESULTS AND DISCUSSIONIndurated BCm clods did not slake in water or in 0.05
M NaOH, ruling out both the fragipan and duripan ascurrently defined by Soil Survey Staff (1990). Clods didslake in 0.1M HC1, which is consistent with expectationsof sesquioxide cement.
Profile distributions of Si, Al, and Fe are shown inFig. 2a through 2f. In each of the six pedons, Si and Almaxima were coincident. In five of the six profiles, thiscomaximum occurred in lower B horizons — Bsm orBCm — while Fe was most concentrated in upper Bhs(m)horizons. The Jericho Pond 2 profile was unique in hav-ing Fe, Al, and Si maxima together in the Bhs2 horizon.The association of Si and Al is also strongly supportedby high r2 values (>0.9) when relative levels of theseelements were regressed against each other (Table 2).Not only is there a strong correlation within profiles, asalso indicated by Fig. 2a through 2f, but, when all ho-rizons of all six pedons were evaluated as a single group,the strong correlation was maintained. This suggests thatcoilluviation, coprecipitation, or relatively rapid sequen-tial accumulation of Si and Al are important processesin the formation of Success profiles. It also suggests thatallophanic materials are a significant weathering productin these soils.
The Fe maxima in Bh(sm) horizons evident in Fig. 2ato 2f are supported by a more modest correlation (r2 <0.7) between Fe and C in Table 2. All profiles exceptNash Stream 1 had C and Fe comaxima in the same Bhorizon, suggesting at least partial organic complexationof iron in some spodic subhorizons. This agrees withstudies (Anderson et al., 1982; Childs et al., 1983; Wanget al., 1986), in which pyrophosphate-extracted Fe wasinterpreted as being organically bound. Generally, dis-tribution data for Al, Si, Fe, and C strongly suggest thatSuccess profiles are the product of (at least) two distinct
sets of processes: one in which Fe and organic matterare mobilized and concentrated, and another in which Aland Si are mobilized and concentrated. These data havetwo corollary implications, as well: first, the low cor-relation between Fe and Al indicates that unexaminedusage of the generic term sesquioxides to refer to tan-demized Fe and Al oxyhydroxide illuviation during pod-zolization is unwarranted; secondly, the notably lowcorrelations between Al and C and between Si and Csupport earlier data proposing that some podzolic con-stituents move as primarily inorganic sols.
Mean values for pH, organic C, Fe, and estimatedallophane are presented in Table 3. In all profiles, pHincreased with depth, although the Randolph BC horizonhad slightly higher pH values (4.7 in water and 4.5 inCaCl2) than the underlying BCm2 horizon (4.5 and 4.2).As would be expected, organic C levels were highest inBh, Bhs, and Bhsm horizons and lowest in E and Chorizons. Horizons were grouped according to their fielddesignations because of their genetic connotations, andtwo hybridized groups, B(h)sm and Bhs(m), were alsocreated in order to evaluate possible contrasts betweenprocesses that accumulate organic matter and those thatproduce cementation. This was done because the pre-sumed role of organic matter in ortstein cementation con-trasts notably with the lower organic C levels of the BCmhorizons.
In all profiles in this study, Bhs horizons (if present)overlie Bhsm horizons (if present), which overlie Bsmhorizons (if present). This is a typical sequence in manySpodosol profiles (McKeague et al., 1983), which, inthe Success series, overlies the BCm horizon(s). Thus,horizon groupings of soil properties, as in Table 3, alsoprovide an insight into depth distributions of those prop-erties. This is particularly useful if it is suspected thatsoil-forming processes are partitioned in a depth-depen-dent fashion. For example, it has already been pointedout that organic C values have consistent maxima andminima in certain horizons, and these trends are evidentin Table 3, as are those along which pH increases froma minimum in Bhs horizons to a maximum in BCm ho-rizons.
Estimated allophane values (Table 3) display a strongmaximum in Bsm horizons, with somewhat lower valuesin BCm and B(h)sm horizons. The B(h)sm group alsoincludes Bsm horizons, however, and this mean value isstrongly influenced by the Bsm horizons included within.It is clear from examining the high standard deviationvalue for this property, as well as the much lower esti-mated allophane value of the Bhsm group, that only Bsmhorizons actually contain more estimated allophane thanBCm horizons. Note also that allophane estimates areextremely disparate among Bhs horizons, which have thenext highest mean value. This is due primarily to theanomalously high value (33.9 g kg"1) calculated for theBhs2 horizon in the second pedon sampled at JerichoPond. If this horizon is excluded, the remaining Bhshorizons have an estimated allophane mean of 2.96 gkg"1, and range from 2.3 to 4.3 g kg"1. As mentionedabove, this is also the only horizon in this study in whichFe, Al, and Si are all at their maximum profile valuessimultaneously. In fact, only two of the six profiles inthis study fail to display an estimated allophane distri-bution that increases in the order Bhs < Bhsm < BCm
186 SOIL SCI. SOC. AM. J., VOL. 57, JANUARY-FEBRUARY 1993
x:E.O)Q
O
CLo>Q
o
Q.<DQ
tu ,
-40-
-60-
-80-
-100-
-120-0 -
1
-50-
-100-
-150-
0 -
-20-
-40-
-60-
-80-
-100-
H-
3Df +
D3H-OO
OEM- O O+ Fe OAI D Si2 a) Cascade
a- o• i •
B-n CD + +D «0
+ Fe O Al DSiO3-+ O O
2b) Randolphra+oo
CE + O O
i
3-
^T«»-IB 00
+a a>
-BO - ——————————————— |2c) Nash Stream #1+ Fe o Al a Si
1 1 •
0
-20
-40
-60
-80
-1000
-20
-40
-60
-80
-100
-1200
-20
-40
-60
-80
mn0 10 20
g/kg soil
0 -
I-20-
-40-
-60-
-80-
-100-0 -
-20-
-40-
-60-
-80-
-100-
-120-0 -
-20-
-40-
-60-
-80-
_inn -
B
n o + +a +&0 2e) Jericho Pond #1•^ C0 + Fe 0 Al D Si
-B 0
BO
• 1 ' 1 ^ 1 '
2) -fi-eri ++ o o
-IHD O O
-Ktn oo2f) Jericho Pond #2
a o+ Fe O A I D Si
•BO)
i
30 -H-30) -1- +
•B O 0
B- OO
"* u u 2d) Nash Stream #2
* + Fe O Al D Si
BhsBhsm
Bsm
BCm
EBhs1Bhs2Bsm
BCm
C1
C2
ffi
Bhs
Bsm1
Bsm2
BCm
C.
10
g/kg soil20
Fig. 2. Profile distributions of oxalte-extractable Si, Fe, and Al for the sampled soils, (a) Cascade location; (b) Randolph location;(c) Nash Stream location, Profile 1; (d) Nash Stream location, Profile 2, (e) Jericho Pond location, Profile 1; (f) Jericho Pondlocation, Profile 2.
< Bsm, with an estimated allophane bulge in a Bsmhorizon above the BCm. The other exception is the Cas-cade profile, in which the BCm is the maximum, with13.5 vs. the 8.5 g kg"1 estimated for the Bsm.
Mean Fe values for horizon groups in Table 3 alsoverify Fe distributions in Fig. 2a to 2f and the correlationbetween Fe and C distributions in Table 2. The Fe bulgeis in Bhs horizons, where pH is lowest and organic C ishighest, and Fe decreases through Bhsm and Bsm hori-zons, to a subsoil minimum in the BCm horizon, wherepH is highest and organic C is lowest.
Thus, profile distributions of Al, Si, Fe, and C for theSuccess soils indicate that (estimated) allophane is concen-trated in the lower B horizons in all profiles, while ses-quioxides are concentrated in upper, and more acidic, B
horizons. These relationships corroborate previous results(Farmer et al., 1980; Farmer and Fraser, 1982; Farmer,1984; Wang et al., 1986) suggesting that Al compoundsare more soluble than Fe compounds at low pH levels, andmay move differentially in the soil profile.
Means of each soil property value for each horizongroup in Table 3 were compared with means of that sameparameter for each of the other horizon groups, and sig-nificant differences are reported in Table 4. In general,differences in pH and organic C were most significant,while differences in iron and estimated allophane levelswere less significant. The most substantial and consistentdifferences are found between the BCm horizons andboth the Bhs and Bhs(m) horizons. The BCm horizonsdiffer strongly from these upper B horizons in both pH
FREELAND & EVANS: GENESIS AND PROFILE DEVELOPMENT OF SUCCESS SOILS 187
Table 2. Regression correlation coefficients (r2) for depthdistributions of Fe, Al, Si, and organic C (OC).
Al Si Fe OC
SiFeOC
SiFeOC
0.9550.1730.018
0.9090.2180.031
Ranked within profiles0.121
0 121 _o!o05 0.661
Ranked among all profiles
0.0930.005
0.093
0.666
0.0050.661
0.0050.666
and in organic C, representing the strongest contrast amongall horizon groups.
The strongest difference between BCm horizons andBsm horizons was due to differences in pHCaa2. Twoother points are notable here, as well. First, both pHqaCi2and pHH20 values from Bsm horizons are equally distinctfrom those properties in Bhs horizons, except that therelationship is reversed. Differences in pHCaC12 betweenBsm and Bhs(m) horizons are also different at the P <0.001 level; thus, Bs horizons are significantly less acidicthan Bhs and Bhs(m) horizons, while they are signifi-cantly more acidic than BCm horizons. This suggeststhat they are transitional, as well as intermediate, hori-zons. Secondly, organic C levels of Bsm and BCm ho-rizons are not significantly different at any level, whileboth Bsm and BCm horizons have significantly less or-ganic C than Bhs, B(h)sm, and Bhs(m) horizons, as wellas being significantly less acidic than these upper hori-zons. Thus, the difference in acidity between Bsm andBCm horizons is the only such difference that seemsunrelated to organic matter content, suggesting that Bsmhorizons are simply more intensively leached than BCmhorizons.
These suggestions are supported by Fe and estimatedallophane data, among which the most substantial dif-ference is that between estimated allophane levels of Bsm
Table 3. Mean and standard deviation (SD) values of pH,organic C (OC), Fe, and estimated allophane for selectedhorizon groupsf.
Parameter B(h)sm BCm Bsm Bhs(m) Bhsm Bhs
nmean pHH20SD pHH omean pHc.̂SD pHCaC,,mean OC (g kg-1)SDOCmean Fe (g kg-')SDFemean estim.
allophane (g kg-1)SD estim.
allophane
104.360.223.920.25
33.521.22.841.05
14.3
8.85
74.590.194.310.119.63.11.860.83
12.9
2.01
64.450.224.070.10
22.810.32.470.67
19.1
7.54
93.970.323.470.32
84.940.59.329.998.31
10.28
44.230.173.700.25
49.524.53.401.377.10
5.01
53.760.263.280.25
113.224.114.0611.619.28
13.78
t B(h)sm = all Bhsm and Bsm horizons; Bhsm = Bhsm horizons only;Bhs(m) = all Bhs and Bhsm horizons; Bsm = Bsm horizons only;Bhs = Bhs horizons only; and BCm = BCm horizons only.
and Bhsm horizons. The Bhsm/Bsm horizon boundaryappears also to represent a shift in process. As noted inthe discussion of profile distribution of Al, Fe, Si, andC, Success profiles seem to be the product of two distinctprocesses. Differences in mean values of Fe, estimatedallophane, and organic C indicate that these processesare not concurrent, but are sequential, or compartment-alized, in a fashion similar to that decribed by Ugoliniet al. (1991). The transitional pH values of Bsm hori-zons, coupled with the distinctive shift in estimated al-lophane (Si and Al) above the Bsm horizon, argues thatBsm and BCm horizons are products of one process, orset of processes, while horizons above the Bsm are prod-ucts of another.
This boundary does not appear to be abrupt, however,nor do the Success soils seem to be bisequal in the usualsense. Migration of Fe, Si, Al, and C in these profilesseems to occur in stages that have a specific order, inwhich Bsm and BCm horizons are simply precursors ofBhs and Bhsm horizons. Although means of Fe and al-
Table 4. Probability levels of significant difference of means tests for selected horizons groups.Property
pHH2o
pHCaC,2
Organic C
P =
BCm >Bsm >
Bhsm >
Bsm >Bhsm >
Bhsm >Bhs(m) >
0.05
B(h)smBhsmBhs(m)
BhsmBhs
BCmBhsm
P =
B(h)sm >B(h)sm >
Bsm >BCm >Bhsm >BCm >
B(h)sm >
B(h)sm >B(h)sm >Bhs(m) >
Bhs >
0.01
Bhs(m)BhsBhs(m)BhsmBhsBhsmBhs(m)
BCmBhs(m)BsmBhsm
P =
Bsm >
B(h)sm >BCm >Bsm >
Bhs(m) >
0.001
Bhs
BhsBsmBhs
Bsm
P <
BCm ;BCm >
BCm >BCm >BCm >Bsm >Bhs >Bhs >Bhs >
Bhs(m) >
: 0.001
• Bhs(m)• Bhs
• Bhs(m)• Bhs• B(h)sm• Bhs(m)• B(h)sm• Bsm• BCm• BCm
Fe
Estimatedallophane
BCmBCmBCmBCmBsmBsm
B(h)smB(h)sm
BsmBsm
BCmB(h)sm
B(h)smBhs(m)BhsmBhsBhs(m)Bhs;Bhs(m)BhsBCmBhs(m)BhsmBhsm
Bsm > Bhsm
188 SOIL SCI. SOC. AM. J., VOL. 57, JANUARY-FEBRUARY 1993
lophane estimates are less significantly different than pHand organic C means, they strongly parallel those dif-ferences. Iron values decrease through the sequence: Bhsand Bhs(m) > B(h)sm > Bsm and BCm, while esti-mated allophane values increase in a similar order. Theonly interruption in these sequences occurs between es-timated allophane levels of Bsm and BCm horizons. Asalready discussed, estimated levels of allophane are higherin Bsm horizons than in BCm horizons. When allophaneestimates for BCm horizons are compared with those of
Bsm and Bhsm horizons, however, the enrichment inBCm horizons with respect to Bhsm horizons is as greatas that of Bsm horizons with respect to BCm horizons.Since pHCaC12 was the most significant difference be-tween the Bsm and BCm horizons, it may be that pH-controlled precipitation of allophanic constituents con-stitutes such an impediment. Again, this is consistentwith proposals cited above (Farmer et al., 1980; Farmerand Fraser, 1982; Farmer, 1984; Wang et al., 1986), aswell as with observations of Wang et al. (1991).
Fig. 3. Allophane cementation and grain bridging in BCm horizon.
Fig. 4. Cutan zoning on grains of BCm horizon.
FREELAND & EVANS: GENESIS AND PROFILE DEVELOPMENT OF SUCCESS SOILS 189
MicromorphologyPlasmic fabrics of Success B horizons were primarily
skelsepic, and secondarily vosepic and insepic. Most voidswere either vughs or interconnected vughs, althoughchannels — probably associated with desiccation of spodicmaterials — were also evident. Allophane is opticallyidentified as a yellow isotropic substance (Farmer et al.,1985), and it was found in Success horizons as an in-tergrain cement, particularly in BCm horizons (Fig. 3),and as cutans (allans) on grains and in voids. Micro-graphs (Fig. 4 and 5) show grain cutans consisting of aninner light-colored to transparent layer — the allan —and an outer dark layer — the organosesquan — whichform bridges between grains. Boundaries between theallans and organosesquans are most sharp and abrupt inBCm horizons (Fig. 4). In B(h)sm horizons, the bound-ary is degraded, and, in some cases, the allophane ap-pears to be engulfed by the organosesquan (Fig. 5).Compound cutans that appear similar to those in Fig. 4and 5 were reported by McKeague and Wang (1980; inMcKeague et al., 1983), along with energy dispersivex-ray spectra of each cutan. The cutans in Fig. 4 and 5have two important differences from those in the earlierwork. First, the innermost cutan of McKeague and Wang(1980) is described as anisotropic material, which is in-terpreted by those authors as silicate clay; those in Suc-cess horizons are largely isotropic, which is consistentwith the optical properties of allophane. Secondly,McKeague and Wang's (1980) inner cutan has a higherSi than Al peak, also consistent with silicate clay. Ex-traction data for Success soils indicate considerably moreAl than Si, however, which is more consistent with al-lophane composition. Thus, both chemical and micro-morphological evidence make it plausible that anincremental and superimposed podzolization is respon-sible for the Success soils and that cementation of Bsm
and BCm horizons may be primarily due to the accu-mulation of allophane.
Genetic MechanismsSeveral models of podzolization and allophane for-
mation have been proposed. Three models, briefly sum-marized here, indicate that allophane is a weatheringproduct in Spolosols, but disagree about the mechanismsof weathering and precipitation. One model (Buurmanand Van Reeuwijk, 1984) emphasizes organic chelationof sesquioxides by mobile fulvates. According to thismodel, sesquioxides are first liberated from parent ma-terials by organic acids. Next, continued production oforganic acids leads to chelation of metals by organiccomplexes, chiefly fulvates. Mobile fulvates migrate downthe profile, where they apparently lose mobility as metalconcentrations reach critically high levels, and precipi-tate in the B horizon. Here, microbes break down theorganic complexes, remobilizing the sesquioxides. Fi-nally, alumina combines with low concentrations of dis-solved silica to form allophane, while Fe forms oxyhy-droxides.
Another model, proposed by Anderson et al. (1982)and Farmer (1984), disputes the mobile fulvate model,claiming that sesquioxides and silica migrate as inor-ganic colloids. According to this model, small organicacids, such as citric, carbonic, and oxalic acids, liberatesesquioxids and silica from parent materials. Next, elec-tropositive mixed Al2O3-Fe2O3-SiO2-H2O colloids leachout of the A horizon, forming an eluviated horizon, andprecipitate as allophane and Fe oxides in the Bs horizon.Once the E horizon is established by the removal ofelectropositive sesquioxides, electronegative organiccolloids are free to migrate deeper into the profile, wherethey precipitate on top of the positively charged Bs ho-rizon. Lowering of pH by organic processes causes Al
Fig. 5 . Degraded intercutanic boundary between allan and organosesquan of Bhsm horizon.
190 SOIL SCI. SOC. AM. J., VOL. 57, JANUARY-FEBRUARY 1993
to dissolve and move to greater depth. Iron oxides andFe-organic complexes are less susceptible to acid attackand remain effectively immobile in the uppermost Bhshorizon. Additional hydroxy-Fe, hydroxy-Al, and Si formby in situ weathering of parent materials in the Bs ho-rizon. Humic complexes form in the B horizon primarilyby in situ decomposition of roots, and heavy precipita-tion promotes periodic leaching of organic complexesinto the B horizon.
Ugolini et al. (1991) studied tephra-derived Spo-dosols and postulated that soil profiles were composedof two weathering compartments. The E and Bhs ho-rizons occupied the upper compartment, in which "or-ganic acid chelators drive weathering processes, whileBs, BC, and C horizons comprised the lower com-partment, in which carbonic acid is the main protondonor. At least some of the carbonic acid is suppliedby decomposition of the Bhs horizon, but the rest isproduced by root decay.
According to this model, imogolite (a thread-like min-eral chemically similar to allophane) is produced in situin the lower compartment after incongruent dissolutionof primary minerals. They cite evidence to indicate thatthe formation of imogolite in the upper compartment isblocked by chelators and low pH, and made possible inthe lower compartment where such chemical inhibitorsare absent. Like the model proposed by Farmer (1984)and Anderson et al., (1982), this one acknowledges thatthe development of the Bs horizon precedes the Bhs. Inour study, the clear tendency for the allophanic cutansto immediately surround grains and the darker cutansto collect outside of the allans appears to support thepodzolization model proposed by Anderson et al. (1982)and Farmer (1984), where allophane initially precipi-tates in the B horizon, followed by translocation ofhumic substances. It seems difficult to account for thedistinct segregation of the allophanic and organic-richcutans into single separate zones if one assumes thatsesquioxides initially precipitate from organic com-plexes, as is proposed in the Buurman and Van Reeu-wijk (1984) model.
Continuous translocation of metal-fulvates with sub-sequent decay and allophane precipitation seems morelikely to produce either relatively homogeneous mixed,organic-allophanic cutans or cutans consisting of mul-tiple, alternating, thin layers of allophanic and humicsubstances. The cutanic zonation is also difficult to ac-count for if imogolite is presently forming in situ in thelower horizons of the Success profiles. Such a processwould require a mechanism to pass Al, and nothing else,from the soil solution, through the organic-rich cutans,to the edges of quartz grains where free silica and waterwere available to form allophanic materials. Still, noth-ing in our study rules out the possibility of allophaneprecipitating according to the model proposed by Ugoliniet al. (1991). In an earlier stage of pedogenesis, prior tothe accumulation of substantial amounts of humic sub-stances, allophane may well have precipitated as a resultof carbonic acid weathering. Some question remains,however, as to whether enough carbonic acid would existin early stages of weathering to produce the weatheringenvironment proposed by this model, since at least someof the carbonic acid was attributed to decomposition ofthe Bhs horizon.
CONCLUSIONSProfile distributions and correlations of Fe, Al, C, and
Si within Success profiles indicated a strong associationof Al and Si, which is at least partially due to pedogenicallophane. The distribution of Fe and C corresponded tolower soil pH, while maximum estimated allophane con-tents and coexisted with higher pH values. By far, mostof the C was concentrated in the upper parts of the Bhorizons, which is consistent with several studies of Spo-dosols. Chemical data collected in this study are consis-tent with a multiple-stage podzolization process in whichacidification and subsequent migration of inorganic Al-rich compounds are the initial stages. These compoundsare apparently precipitated in Bsm and BCm horizonswhen pH levels exceed optimum levels for Al solubility.Removal of these materials seems to precede accumu-lations of C- and Fe-rich compounds in upper Bhs andBhsm horizons. Petrographic observations revealed strongevidence in support of a mobile inorganic sol model ofpodzolization, with allophanic cutans coating grains, anddarker, organic-rich cutan outside of the allans, illus-trating initial migration and deposition of allophanic ma-terials, and either secondary migration and deposition orin situ deposition of humic substances. Allophane ap-peared primarily responsible for cementation of the in-durated horizons, with organic complexes, perhaps,playing a secondary role.
These data support the need for further investigationsof podzolization processes in northern New England andelsewhere, where consideration of these processes hasbeen largely limited to organo-chelate models. Successsoils are well-drained soils derived from metamorphosedvolcanic materials, and it is not known whether, or towhat extent, either or both of these factors creates theessential environment for their genesis. Both soil drain-age conditions (Wang et al., 1991) and modern volcanicmaterials (Ugolini et al., 1991) have been associatedwith pedogenic production of allophanic substances, soboth of these factors should be considered in further stud-ies. Such studies should lead to an understanding of howvariable podzolization processes are within the region.They should also focus on determining which soil-form-ing factors and processes will dominate particular kindsof pediogenic episodes.
ACKNOWLEDGMENTSThe Success series was brought to the attention of the au-
thors by John Handler, USDA-SCS, Lancaster, NH, who alsogenerously provided site locations and descriptive data for someof the profiles. We also thank C.T. Smith, Jr., for a helpfulreview of an earlier version of this manuscript.
FREELAND & EVANS: GENESIS AND PROFILE DEVELOPMENT OF SUCCESS SOILS 191