influence of vegetation on water repellency in selected western wisconsin soils1
TRANSCRIPT
Influence of Vegetation on Water Repellency in Selected Western Wisconsin Soils1
J. L. RICHARDSON AND F. D. HotE2
ABSTRACTWater repellency in several western Wisconsin soils was character-
ized by three tests: wetting angle (0), wetting drop penetration-time(WDPT), and 90°-surface tension (?,,). It appears that the highcontents of organic matter in the A horizon of Mollisols and ALfisolsare associated with slight repellency as measured by 0 and WDPT.Frequent burning of a prairie on a Mollisol increased persistence(WDPT) and y^, as compared with soil at a nearby control site, buthad no influence on 0, indicating that repellency is present at initialwater contact but is unstable and disappears with prolonged watercontact.
Mor Utter layers having observable fungal mycelia had repellentsurfaces as measured by all three of the above tests. These repellentmaterials were observed in Spodosols under red pine (Pinus resinosa),hemlock (Tsuga canadensis), and under a mixed hard and soft woodstand with dense ericaceous shrub understory. The repellency of morhorizons of Spodosols may relate in some significant way to process ofgenesis of Spodic horizon.
Additional Index Words: wetting angle and surface tension.Richardson, J. L. and F. D. Hole. 1978. Influence of vegetation on waterrepellency in selected western Wisconsin soils. Soil Sci. Soc. Am. J.42:465-467.
WATER INFILTRATION into soils can be profoundlyinfluenced by degree of water repellency (DeBano
and Letey, 1969; Letey et al., 1975). In California, severeerosion and flood damage have resulted from runoff inburned chaparral watersheds where soils exhibited a highdegree of water repellency. The infiltration of water intosuch soils is lowered by water-repellent natural surfactantscovering soil particles (Pelishek et al., 1962). Undernatural conditions, water repellency of soil also appears tobe related to certain plant communities including fungi(Letey et al., 1975). Organic matter that has been translo-cated to the Bh horizon may be highly water repellent(Holzhey et al., 1975). Bond (1969) noted that coarse-textured soils are more likely to be water repellent thanfiner ones. Hillel and Berliner (1974) studied the re-lationship of aggregate size and stability to water repellencyand reported that large, water-repellent aggregates actuallycan greatly increase infiltration. However, if aggregate sizefalls below a certain value, infiltration is decreased. Dasand Das (1972) have used various measures of waterrepellency as a fundamental soil characterization criteria ofselected Indian soils.
Little information exists on water repellency in coolhumid regions. Singer and Ugolini (1976) studied waterrepellency in Washington but no studies have been pub-lished for the midwest or the northeast especially in relationto vegetation. This study attempts to relate repellency inselected soils to associated plant communities in westernWisconsin soils.
'Research supported by a Univ. of Wis. Agric. Coop. Res. Grant no.WIS01013-M. Received 12 Sept. 1977. Approved 9 Jan. 1978.
"Assistant Professor, N. Dak. State Univ. and Professor, Univ. of Wis.,Madison, respectively. Senior author formerly Assistant Professor, Univ.of Wis., River Falls.
METHODS AND MATERIALS
MethodsThe liquid-solid contact angle was determined by the indirect or
comparative capillary rise method outlined by Letey et al. (1962).This method utilized the capillary rise equation
he = 2ycos6 I rpg
where he is the height of rise, y surface tension of the liquid, 9 isthe liquid-solid contact angle, r is the capillary radius, p is theliquid density, and g is gravity constant. For soil columns with agreat many capillaries, r is the "effective" radius of capillarityporosity. In this method a reference liquid (ethanol in this case),which is assumed to wet all soils readily at a 0° wetting angle, isused first to calculate the effective radius of capillary porosity.The process is repeated with water to determine the calculatedwetting angle 0. Tubes 2 cm in diameter were filled with soil thathad been air dried and passed through a 2-mm sieve. The soil wasuniformly packed by dropping the tubes 25 times a distance of 2cm. A constant low negative head was maintained throughouteach test. Each test was allowed to continue for 48 hours whichappeared in most cases to allow equilibrium to be reached. Thismethod assumes constant pore geometry in the soil-filled tubesand equillibrium of capillary rise. The contact angles calculatedby this method are relative and not absolute values. This methoddoes not evaluate initial resistance to wetting which is important(Watson and Letey, 1970). Each sample was replicated threetimes and the median value is recorded in this report.
The water drop penetration time (WDPT) test used was amodification of the technique described by Letey et al. (1975).The test estimates initial wetability of a soil and also stability ofthe water-repellency or persistence in resisting wetting as afunction of time. An evaporation dish 8.6 cm in diameter is nearlyfilled level with air-dried soil, onto which 2 ml of water werequickly poured. When the water beads up and does not penetratewithin 8—10 sec, 6 > than 90°. Each test was reolicated at leasttwice, and usually three times by two different operators. Themeans of the four to six replications on each sample are reportedhere. Soils with a WDPT > 8 sees were assumed to be waterrepellent. By using 2 ml instead of a single drop, repeatability ofthe tests was improved; also the increased ease of observationallowed more accurate timing of the results.
On those soils with a WDPT > 8 sec, y^ (90°-surface tension)was determined following the technique of Watson and Letey(1970). This method utilizes an array of aqueous-ethanol solutionsof various surface tensions. Starting with the solution of highestsurface tension, a drop of each solution was-placed on the soil andthe disappearance rate observed. The test was repeated withdecreasing surface tensions until the liquid persisted < 8 sec. Thesurface tension of the liquid preceding the above liquid wasrecorded as y,,. Both WDPT and y,, adapt well to field use duringdry periods.
MaterialsThe soils selected for study are representative soil series of
western Wisconsin, developed under a variety of native plantcommunities. The series belong to three soil orders and fivesuborders. Table 1 lists the soil subgroups, condition of plantcover, and location of the sites. Except in the case of the PortByron, each sampled pedon was representative of an extensivesoil body.
465
466 SOIL SCI. SOC. AM. J . , VOL. 42, 1978
Table 1—Selected soils and plant cover used.
Subgroup
Typic ArgiudollTypic Argiudoll
Typic ArgiudollTypic HapludalfTypic GlossoboralfAlficHaplorthodEntic Haplorthod
Entic Haplaquod
Series
DakotaDakota
Port ByrontSea tonSantiagoPadusVilas
AuGres
Surface texture
Sandy loamSandy loam
Silt loamSilt loamSandy loamFine sandy loamLoamy sand
Sandy loam
Nature and condition of plant cover
Frequently burned natural prairieUnder a rotation of corn (Zea mays), oats (Avena
sp.), and 3 years of alfalfa (Medicago sp.)Continuous corn (Zea mays)Second growth sugar maple (Acer saccharum) forestSecond growth oak-hickory (Quercus-Carya sp.)Mature hemlock (Tsuga canadensis) forestRed pine (Pinus resinosa) plantation 20 years old
approximatelyMixed northern hardwood-conifer forest
Location of site
Pierce County, Wis.Pierce County, Wis.
St. Croix County, Wis.Pierce County, Wis.St. Croix County, Wis.Bayfield County, Wis.Oneida County, Wis.
Oneida County, Wis.
t This pedon is an inclusion in a large body of Pillott silt loam.
RESULTS AND DISCUSSIONThe purpose of this study was to compare representative
pedons from prairie, deciduous forest, and conifer forestplant communities in Wisconsin (Table 1). The only nativeprairie used was a Dakota sandy loam that had beenfrequently burned. An ecology class at the University ofWisconsin at River Falls had burned vegetation at this place2 months before sampling. The site was compared to anadjacent one in a cultivated field and to a cultivated PortByron silt loam a few kilometers away. All three pedonspossess well-developed Mollic Epipedons. The deciduousforest soils were represented by a Hapludalf presently undersugar maple (Acer saccharum) and a Glossoboralf underoak-hickory (Quercus sp. - Carya sp.). The thin understoryshrubs were not members of the Ericaceae family. Threediffering conifer stands, all with ericaceous shrub under-story, were examined: (i) an Haplorthod under maturehemlock (Tsuga canadensis), (ii) an Haplorthod under a redpine (Pinus resinosa) plantation, and (iii) an Haplaquodunder mixed hardwood-softwood forest with a denseericaceous shrub understory.
In the Udolls, the surface layer of the Mollic epipedonwas compared with the underlying B horizon. The PortByron and Dakota epipedons had higher contact angles(67°, 59°, and 59°, respectively) than the 48° of the PortByron B horizon (Table 2). Remarkably little differences ineffective porosity, capillary rise, and wetting angle wereobserved between the two Dakota epipedons. The two soilsdiffered with respect to WDPT and y^. The burned-overprairie soil did not wet initially, but the repellencyapparently was unstable and disappeared after an average of9 sec of water contact. Schwartzendruber et al. (1954) hadnoted similar repellency or wetting angle phenomena in theA horizon in their studies of soil structure in some prairiesoils of Iowa.
The Alii sols supporting deciduous trees had B horizonsthat wet rapidly. The B horizon of the pedon in theSantiago series, a Boralf, had a low contact angle (51°) andwet readily (WDPT of 3.5 sec). The A2 horizon displayedmodest repellency. The litter layer and Al horizon of theSeaton, a Udalf, wet easily. The trees surrounding theSeaton pedon were maples (Acer saccharum) with a sparseunderstory and little fungal mycelia in the litter materialover the mull A horizon.
Samples of pedons of Orthods, one (Vilas) under pine(Pinus resinosa) and the other (Padus) under hemlock(Tsuga canadensis) showed water repellency. The Ohorizon of the Vilas loamy sand, a thin mor with abundant
Table 2—Data from the three tests used to measurewater repellency.
Soil
Udoll(Port Byron)Udoll(Dakota, plowed)Udoll(Dakota, prairie)Udalf(Seaton)Boralf(Santiago)Orthod(Vilas)Orthod(Padus)
Aquod(AuGres, No. 1)
Aquod(AuGres, No. 2)
Horizon
AB
A
A0&A1A2AB
0&A2
0BhirA2BhirBir0A2Bir
r
0.00160.0016
0.0016
0.00160.00160.00120.00120.0012
0.0013
0.00130.00130.00160.00260.0026
---
hc of water48 hours
cm ————3662T
48
4857605477T
36
4743471223.5--
-
e
67°48°
59°
59°52°60°64°51°
72°
67°69°59°78°65°---
WDPT
sec94
4
99
10.5153.5
75
18002
1541
688.56
Indyn/cm
72>72
>72
60726052
>72
52
38?607
>72
t Equilibrium had not been reached.
fungal mycelia, contained a small portion of the underlyingvery thin A2 horizon as a result of difficulty in sampling.This horizon had a 72° contact angle and a WSPT of 75 sec;y^ was 52 dynes/cm. The Padus sandy loam pedon, withthicker, more distinct horizons, was more easily sampledthan the Vilas soil. Here the O horizon was a "mor"humus with prominent fungal mycelia. The wetting anglewas 67°, and tfie WDPT phenomenal. No penetration ofwater was observed for at least 1800 sec. As a result,evaporation must have been faster than absorption, y^ was38 dynes/cm indicating low solid surface tension and highinitial repellency (Watson and Letey, 1970). The Bhir ofthis soil had an even higher wetting angle, 69°. However,the WDPT was only 2 sec. This apparent discrepancy maybe related to the macropores present in the sandy soil. If thepores in the Bhir horizon had exceeded the critical sizedetermined by Hillel and Berliner (1974) then WDPTwould not have been a valid measure of repellency. In thishorizon the critical size of the macropores probably wasexceeded and, therefore, WDPT measures do not reflect thepotential repellency.
The samples from an Aquod (AuGres series) undernorthern deciduous forest dominated by birchs (Betula sp.),with a dense understory of shrubs and other ericaceous
RICHARDSON & HOLE: VEGETATION ON WATER REPELLENCY IN WESTERN WISCONSIN 467
plants (Vaccinium sp.), yielded results similar to those for indication of mycelial growth, show little repellency.the Orthods already mentioned. The Bhir had a 78° wetting However, mor humus, with abundant observable fungalangle and a surprisingly low WDPT (4 sec). A second mycelia, are repellent under ericaceous shrubs and con-AuGres pedon gave the high reading of 84 sec for the Bhir. ifers. The better developed the mor horizon, the moreThe Albic A2 had a WDPT of 15 sec. However, the y^ was repellent the material.only 60 dynes/cm indicating a fairly high energy solid Bh horizons were not found to be consistently watersurface tension and a 6 of 59° partly substantiating this. repellent.
The influence of vegetation in Spodosol formation iswell known (Buol et al., 1973). Iron- and aluminum-hydrous oxides often react with organic matter (Thomas,1975) especially in acid soils. Holzhey et al. (1975) havereported that unusually thick Bh horizons in Aquods inNorth Carolina were repellent to water. When the organicmatter is adsorbed on iron- and aluminum-oxide colloids,the colloids may become repellent. If the organic materialcausing the repellency is destroyed or altered, the repel-lency may disappear. If the vegetation associated withSpodosols is altered such as by timber harvesting, therepellency will also change. The litter from maple (Acersaccharum), for instance is far less repellent than litter fromhemlock (Tsuga canadensis). As demonstrated by Hole(1975) invasion of maple (Acer saccharum) into hemlockstands (Tsuga canadensis) is associated in some forests ofnortheastern Wisconsin with a gradual disappearance of theBh horizon, which has a half-life of about 100 years asreported in terms of indices (cm thickness by percentorganic matter) of pedons.
The results of this study suggest that water when it doespenetrate through O or repellent Bh horizons moves bysaturated flow concentrated in macropores. Tonguing of theA2 and Bh horizons may be formed by this kind of watermovement with differing rates and depths of penetration. Inacid sandy soils or mor litter would be conducive to bothspodic development and water repellency such as underhemlock vegetation.
CONCLUSIONSThis study suggests that the burning of prairie grass in
Wisconsin increases water repellency of soil but not asmarkedly as reported from chaparral burns in California(DeBano and Krammes, 1966) or from forest fires in thePacific northwest (Meeuwig, 1971; Dyrness, 1976). Somenatural repellency does occur in Mollic epipedons even incultivated soils. B horizons below the Mollic epipedon,however, do wet readily.
Mull humus from deciduous forests, having little or no