Effect of Perched Water Tables on Aluminosilicate Stability and Soil Genesis

1A73Pedosphere 10(3): 247~256, 2000247ISSN 1002-0160/CN 32-1315/P回1999 SCIENCE PRESS, BEIJINGEffect of Perched Water Tables on AluminosilicateStability and Soil Genesis*ZHANG MIN1, GONG ZITONG2 and A. D. KARATHANASIS1 College of Resources and Environment, Shandong Agricultural University, Tai'an 271018 (China)2Institute of Soil Science, the Chinese Academy of Sciences, Narnjing 210008 (China)3 College of Agriculture, Universily of Kentucky, Lexington, KY 40546-0091 (USA)(Received January 26, 2000; revised June 6, 2000)ABSTRACTThe mineral stability and solute activitics of soil solution extracted from selected borizons of seven studiedpedons of Al6sols in Kentucky, USA, and the relationship between distribution of iron-manganeee concretionsand the retrictive layers were investigated. The results sbowed that the genesis and development of thesesoils and mineral weathering trends were strongly infuenced by the depth of bedrock and the presence ofperched water tables at lithic (imestone) interfaces due to the dissolution and buffering efet of limestonebedrock. The extractable Mg/Ca ratio as depth function and soil depth above bedrock could be used因indice of weathering and degree of soil development. Maximum iron manganese concretion accumulationwas found to occur in the horizon overlying clay horizon (> 40% clay) with & sharp increase in clay content(>10%), which suggested that zoncs of FrMn concretion accumulation in soils of the Inner Bluegrass Regionappeared to be a sensitive genetic indicator of arilic horizons with restrictive permeability.Key Words: iron- manganese concretion, perched water table, soil environment, soil genesisBedrock weathering and residual soil formation on limestone parent materials have beenstudied extensively by Plaster and Sherwood (1971), Levine et al. (1989), Karathanasis(1991a), Rabenhorst and Wilding (1984), etc. These studies showed that soils derived fromlinestone residues were related to the quantity and kind of impurities of limestone. Olson etal. (1980) reported that there were insuficient insoluble residues contained in the limestoneto produce soils over 5 m thick. Therefore, depth above the bedrock should be a sensitiveindicator for the degree of soil development on the limestone. Whereas, regolith materialsthat result from weathering and pedogenesis of crystalline rocks are much different fromthose derived from limestone. The formers can be divided into soil, transition zone betweensoil and saprolite, saprolite and weathering rock (Stolt et al, 1991). However, the lattersonly consist of soil and weathering zone (transition zone or lithic interface) between soil andbedrock. Transition zone thickness depends on rock type. Stolt et al. (1991) found thickertransition zones of soil with a greater degree of profile development.Soil solution plays an extremely important role in many soil processes; its compositionis infuenced by the solubility of contacting minerals and by variable fuxes of matter fromlProject (No. Y97D02061) supported by the Natural Science Foundation of Shandong Province, China.中国煤化工MYHCNMHG48M. ZHANG et al.the surrounding environment. While external conditions (landscape, drainage and climate)determine the nature and rates of weathering processes in soils, the actual clay mineral suiteis largely determined by the composition of the soil solution (Karathanasis, 1989). Watermovement and distribution is the principal reason for differences in soils on slopes. Althoughoverland fow is most obvious and often dramatic process of water distribution, it is nowevident that water movement in the soil horizons below the surface is more important thanoverland flow in soils of humid region (Hall, 1983). Blume et al. (1987) emphasized theimportance of a perched water table, which influences the soil morphology, ion exchange, pHand mineral stability.Iron-manganese concretions in which Fe and Mn oxides are concentrated relative to soilmatrix are commonly found in soils with restricted internal drainage, where the alternatingreducing and oxidizing environments are thus created. In Fe Mn concretions, iron contentwas 2 to 4 times higher than in bulk soils and manganese was 63.5 times higher than inbulk soils in some Vertisols of China (Zhang and Gong, 1989). Concretion distributionwithin soil profles varies among soil types. Maximum concentration of concretions (up to7.5%) occurred in the upper B horizon (about 50-cm in depth), approaching the surface withincreasing wetness in hydrosequences of soils in loess in Bavaria, Germany (Schwertmannand Fanning, 1976). Soil concretions were observed in all borizons with a maximum of 46%by weight in a Maury C horizon (Phillippe et al, 1972). These indicates that the zone ofmaximum Fe-Mn concretion acumulation relates to the depth of a restricting layer withthe abilty to reduce infltration and create perched water tables during wet seasons (Zhangand Karathanasis, 1997). The horizon above the restricting layer is representative of a soilzone that receives the effect of alternating wetting and drying, and reducing and oxidizingconditions.The Inner Bluegrass Region of Kentucky is characterized by undulating topographycaused by diferential weathering of Ordovician limestone with variable impurities (Karathanasis, 1991b; USDA-SCS, 1983a, 1983b). Soil development is strongly infuenced by surfacewater movement on hillslopes and by seasonal perched water tables at lithic interfaces withthe limestone bedrock and restrictive clayey argillic horizons (Pillippe et al, 1972). Thisstudy was conducted to investigate the effect of perched water tables above the limestonebedrock on aluminosilicate mineral weathering trends, composition and stability, and therelationship between the depth of the limestone bedrock and the degree of soil development;to examine the distribution of Fe-Mn concretions affected by perched water tables; and toassess the maximum accumulation of concretions as an indicator of the presence of restrictivelayers.MATERIALS AND METHODSSeven pedons representing four soil series (Hagerstown, Faywood, Caleast and Maury)of Alfisols were sampled from the research farms of University of Kentucky in the InnerBluegrass Region of Kentucky, USA. They were sampled by horizon and described accordingto procedures of the Soil Conservation Service (Soil Survey Staff, 1984). The sites wereselected on the sideslope landscape. Six pedons were sampled to the depth of limestone中国煤化工MYHCNMHGPERCHED WATER TABLE EFFECT ON SOIL GENESIS249bedrock and Pedon SRF in the South Research Farm was sampled to the depth of 350 cm,but no bedrock was found.Soil solution was extracted from each bulked soil sample at field moisture content bycentrifugation within 24 hours of sampling (Adams et al, 1980). The samples were spunat 3 000 r min-1 for 2 h using a DAMON-ICE DPR-6000 refrigerated centrifuge with thetemperature adjusted at 25 °C. The extracted solution was stored in refrigerator for analysesof Al, Si, Ca, Mg, K, Na, Fe, Mn, so2- , NO8-, P and C1- except pH, Eh and EC whichwere determined immediately after extraction. The methods and procedures used in theanalysis are outlined by American Public Health Association (1981) and Karathanasis etal. (1983). Ionic activities of solution components were calculated using the MINTEQAspeciation program.Iron- manganese concretions were separated from air-dried subsamples of the bulk soilsamples by wet shaking over night and passing through 2-, 1-, 0.5- and 0.25-mm sieves,respectively. Soil particles were readily removed by spraying deionized water on the concretions. The concretions were separated into coarse (> 2 mm), medium (2~1 mm), fine (1~0.5mm) and very fine (0.5~0.25 mm) fractions. Coarse and medium concretions were purifedby visual inspection fllowing hand-picking with tweezers, and fine and very fine concretionswere purifed using a strong magnet but still contained a very small proportion of impurities,such as quartz sand, grains and cheat.RESULTS AND DISCUSSIONEfect of bedrock depth on soil developmentThe extractable Mg/Ca ratios as a function of depths of six pedons are shown in Fig. 1.The Mg/Ca ratio deceased with depth in most pedons. Higher Mg/Ca ratios were foundin Pedons STF1 and POFB2, because these two pedons had deeper soil solums. Using theMg/Ca ratio as an index of weathering, these would indicate a more advanced weatheringstage and also higher degree of soil development for the pedons that were deeper in bedrockdepth.Exchangoable Mg/Ca ratoBaso saturarbin (%)0.05 0.100.15 0.20)0204060801020 t. 60r= -0.876*+ n=1230 t120180100 t120 t140300160 t360Fig. 1 Exchangeable Mg/Ca ratio a a function of depths of six pedons.Fig. 2 Relationship between base saturation at the critical taxonomic depth and bedrock depth.中国煤化工MYHCNMHG50M. ZHANG et al.Relationship between base saturation (BS) at the critical taxonomic depth and bedrockdepth is ilustrated in Fig. 2. Significant negative correlation between BS and depth of thebedrock suggested that the degree of the weathering and soil development be strongly infu-enced by the bedrock depth. In the less developed Faywood and Hagerstown pedons (POFA1and POFA2), base saturation was greater than 50% in all horizons and increased with depth.Mg/Ca ratio was <0.1 in all horizons, decreased with depth and reached the minimum of0.011 and 0.021 in the lithic interfaces of Pedons POFA1 and POFA2, respectively. In twoHagerstown soil pedons (POFB1 and POFB2), the base saturation in tbe upper part of solumwas less than 50%, and increased with depth. Two Caleast soil pedons (STF1 and STF2)had lower base saturation in the upper part of the profles. Their base saturation increasedwith depth, and the Mg/Ca ratio also decreased with depth.Soil solution chemistrySolute activities of soil solutions extracted from selected horizons of the studied pedonssampled from the research farms of University of Kentucky, USA, in the spring, 1993 aregiven in Table I. All the pH values of in-situ soil solutions at the lithic interfaces of the sixpedons were over 7, and the base saturation >65%. Whereas, the pH values of the overlyinghorizons were below 6 in the upper part of the sideslope and 6~7 in the lower part of thesideslope. Ca2+ and Na+ had the same trend with pH. In contrast, the activities of Al3+,Mn2+, Fe2+ and Fe3+ in the solutions were much lower in the interfaces of limestone bedrockthan in other horizons. This would contrlbute to the dissolution of the limestone due to thepresence of perched water table created by bedrock. The activities of H4SiO4, H2POq, C-and so4- in soil solutions of the horizons immediately above the lithic interfaces were higherthan in the lithic interfaces, especially in the lower position of the sideslope and the pedonswith shallower depth of bedrock, which indicated the efect of fuctuation of perched watertable.The dependency of pAl3+ and pFe3+ on solution pH was ilustrated by tbeir good cor-relations (0.966** and 0.815**, respectively). Otber positive significant correlations werefound between pH, and pH2POq (0.545**) and pMn2+ (0.289*), respectively. These rela-tionships suggested that the activities of these solutes were affected by mineral dissolutionreactions enhanced by low pH. Negative significant correlations were found between pH, andpCa2+(-0.710**), pMg2+(-0.553**) and pH4SiO4 (-0.267*), respetivly, which rflectedthe association of these components with weathering silicate minerals. All the pH valuesof the solutions at the lithic interfaces of six pedons were over 7, and the values of basesaturation were all over 65%. Therefore, the dissolution of the weathered limestone bedrockand presence of the perched water tables strongly retarded the weathering trends of alumi-nosilicate minerals and the soil development processes.The good relationships between the amounts of FeMn concretions, and pFe2+ (-0.468**)and pNOz (-0.541**) indicated that the concretion formation was favored in the zones withhigher levels of Fe2+ and NO3 , such as conditions of frequently alternating oxidation andreduction cycles. However, siguifcant correlation between Fe-Mn concretions and pH2POq(0.453**) suggested that the alternating oxidation and reduction condition may result in the中国煤化工MYHCNMHG詩TABLEISolute activities of soil solutions extracted from selected horizons of the studied pedonsFarmPedon Soil Beries Horizon MSIa) pH pA13+ pH4SiO PCa2+ pMg2+ pK+ pNa+ pMn2+ pPe2+ pCI- pNO5 pSO- pHzPOqPin Oak POFA1 Faywood Ap0.67 6.86 10.76 4.124.13 5.564.71 5.239.03 5.73 4.43 4.04 4.936.22Bt14.744.87 4.089.06 5.40 3.57 4.07 4.07 5.79Bt30.685.65 6.72 3.803.76 4.784.19 4.026.645.27 3.49 4.69 3.78 5.41Bt40.53 7.75 10.76 4.083.29 4.559.10 5.56 3.56 4.44 3.667.33POFA2 Hagerstown Ap0.55 7.13 10.83 4.163.37 4.15 2.94 4.14 6.78 5.27 3.00 3.15 3.73 6.00Btl0.63 6.49 9.75 4.19.62 4.4423 4.126.47 5.84 3.44 3.92 3.70 6.140.60 6.10 7.95 3.993.54 4.274.54 4.16.666.26 3.29 6.02 3.585.5266 7.52 12.92 4.003.464.46.91 4.056.72 5.85 3.72 6.02 3.576.32POFB1 Hagerstown Ap0.857.0511.07 4.124.235.283.483.833.505.66Bt20.66 5.69 7.16 4.313.644.354.43 4.096.395.56 3.59 4.13 3.795.83BC0.75 5.52 6.58 4.37. 3.89 4.88 4.66.74 5.56 3.69 5.41 3.635.13CB0.73 7.10 11.47 4.033.50 4.45 2.69 4.17 6.72 5.74 2.59 5.18 4.185.18POFB2 Hagerstown Ap0.91 7.08 10.96 4.163.624.25 4.53 4.346.59 5.13 3.69 4.61 3.455.990.70 5.57 6.56 4.223.704.60 4.64 4.666.785.73 3.48 4.47 3.765.02Bt60.70 7.00 10.97 4.043.724.674.60 4.077.345.79 3.67 6.02 3.655.140.767.62 13.22 4.054.301.45 4.407.14Spindle- STF1 CaleastAp.75 5.81 6.78 4.033.826.64 5.43 3.63 4.27 3.784.88top0.72 5.61 6.77 4.163.86 5.17 4.52 4.18 6.60 5.58 3.62 4.65 3.844.82Parm0.69 5.58 6.65 4.283.974.86 4.55 4.266.85 6.11 3.75 5.71 3.814.62.79 7.58 13.06 4.023.534.75 4.08 4.749.076.03 3.99 6.02 4.135.94STF2 Caleast0.65 5.74 6.75 4.363.654.364.29 4.246.655.27 3.57 3.45 3.753. 844.30 4.266.795.463.586.023.585.26.55 10.46 3.983.864.574.44 4.166.67 6.03 3.70 5.41 3.704.89 .0.77 7.03 10.96 4.024.53 3.84 4.26 7.52 5.95 3.93 4.97 3.93South SRF Maury0.757.30 12.52 4.093.424.094.16 4.32 6.69 5.21 3.56 3.46 3.82 5.39Research0.86 5.31 7.23 4.204.044.784.16 4.20 6.68 5.46 3.77 4.23 4.006.040.75 6.36 9.09 4.083.874.552.66 4.016.74 5.86 2.59 4.29 4.635.79工:30.96 5.95 8.58 3.804.114.143.87.015.67 3.52 4.84 4.734.64nl叫Soil moisture saturation index.昌252M. ZHANG et al.occlusion of phosphate and antagonistic effects in dissolution- precipitation of Fe-Mn oxideand aluminosilicate minerals.Mineral compsittion and stability affected by perched water tableIn terms of mineral composition (Table II), the most obvious diference between thelithic interfaces and the upper part of the profles (Ap, Bt1 and/or Bt2 horizons) was thehigh apatite content in the lithic interfaces or in the horizons just above the interfaces,which was also affected by the fuctuation of perched water table and the dissolution of thelimestone beds. This explained the presence of the fragments in these horizons due to thelow solubility of apatite. The 2:1 expanding mineral components included mainly a weaklyAl-bydroxyinterlayered vermiculite (collapsing readily with K+ saturation) (KarathanasisTABLE IIMineralogical compoaition of clay (< 2 pm) fractions of the soil horizons studiedFarm Pedon Hori- HISVa) Sm/Vb) Ilite Kao Quar- Apar Feldspar Interstratifed Fe2O3 Hydroxylzonlinite ttitemineralH2O lossPin Oak POFA1 Ap 36030105.8FarmBt1 543.5Bt343.5Bt4 227.0POFA2 Ap 45324108147.5Btl 308.28.3Bt3 40Bt4 2620128.5POFBI Ap 2610 29 10.73t2 207.83C4:8.8;B419.5POFB2 Ap 4317Bt2 35,.3Bt6 -1044121739.8Spindle- STF1 Ap 24).2.3topBt2 32BC24182281CB28STF2 Ap 243t1 25Bt49.03322South SRFp 4032ResearchBt3 4412.526)3212010503.7)Weakly Al-hydroxyinterlayered vermiculite with minor amounts of smectite; )Weakly hydroxyinterlayeredsmectite with minor amounts of vermiculite.中国煤化工MYHCNMHGPERCHED WATER TABLE EFFECT ON SOIL GENESIS253et al, 1983) with some amounts of smectite (expansion to 1.8 nm with glycerol). Apatite,smectite and ilite, the weatherable minerals, appeared to be concentrated more in the lowerhorizons of the profiles, especially in the lithic interfaces, while more resistant mineralssuch as kaolinite, HISV (weakly Al-hydroxyinterlayered vermiculite with minor amounts ofsmectite), and quartz were found in the surface and upper Bt horizons.Table III shows the saturation index (SI) of the soil solutions in selected horizons ofthe six pedons relative to the solubility of common soil minerals.Most of the minerals(with the exception of gibbsite) were present in the samples studied. The q (ion activityproduct) values for these minerals were calculated from their respective dissolution reactions(Table II). The SI values for the 2:1 expanding minerals indicated that all solutions werestrongly supersaturated with respect to the minerals with vermiculitic behavior. However,the solutions seemed to be near equilibrium or slightly undersaturated with respect to theTABLE ISaturation index (SI) values*) for soil solution samples from the selected horizons studied with respect 切ocommon soil mineralsFarmPedon Horizon V-gmb) Sn-vc) Kaolinite Halloysite Gibbsite mlite Feldspar ApatitePin Oxk POFA1 Ap5.02 - 1.084.280.921.77-0.07 -2.3-5.753t14.36 -1.74.180.821.86- -0.66 -2.25-5.30st13t34.85 -1.255.742.382.18-1.03-9.943t46.26 0.163.560.201.372.53 -0.4:1.35POFA2 Ap7.28 1.195.682.322.513.46 1.27 0.605.83 -0.274.961.601.35 -0.91-4.36t35.93 -0.175.602.242.300.74 - 1.00-6.024.16801.592.46 -0.751.92POFB1 Ap4.802.031.58 -0.470.563.29- -2.81 4.080.721.86 -1.63 -2.76 - 10.3C2.52- -3.584.100.741.93-2.86 -3.25 -10.6B6.140.044.481.121.783.01 1.152.206.780.685.121.72.232.33 -0.65-0.973t23.78- -2.324.742.10-1.53-2.58-9.033t66.32 0.224.861.981.82 -0.60.526.71 0.614.060.70.78 -0.344.26Spindle- STF1 Ap6.122.762.600.58 -0.63-7.53top3.76 - 2.344.68-1.15 -2.33-8.95BC3.29- 2.814.50.142.04-1.83 -2.72-9.116.700.604.200.81.63 3.15 0.12 3.13STF2lp4.41 -1.695.102.420.57- -2.16- 7.175.04 - 1.06.4.821.460.55 -1.30 - 6.393.301.14-0.30 - 1.646.65 0.551.742.082.62 0.260.76 .SouthSRF5.35 -0.753.46101.331.29 -0.753.37Research-0.26 - 6.361.88-1.480.65-5.28 - -3.75-15.63C4.79 - 1.31.4.701.941.02 0.45 -6.66)33.91 -2.19 3.820.461.22-0.26 -1.32 -7.28Reference pKgL)-7.30 - -13.40 -7.12- 10.48-8.05 - -7.00 -1.00 - 14.46)Logarithm of the ratio of ion activity product (9) to equilibrium constant (K) (pK-pQ); positive sI valuesindicate oversaturation, negative undersaturation, and values of zero equilibriun; b) Vermiculite with minoramounts of smectite;。) The same mineral treated s smectite; d) Reference pKs from Karathanasis (1991b).中国煤化工.一MYHCNMHG254M. ZHANG et al.minerals with smectitic behavior.Similar solution supersaturation trends were found with respect to kaolinite and hal-loysite minerals (Table II).- All the solutions were supersaturated relative to kaolinite, butonly slightly oversaturated relative to halloysite, being closer to equilibrium in the lithicinterfaces, slightly supersaturated relative to gibbsite and/or very near equilibrium with mi-crocrystalline gibbsite. The SI values relative to ilite suggested strong supersaturation inthe lithic interfaces of all six pedons, near equilibrium in the surface and the Bt horizons.Potassium feldspars were only present in the surface and/or subsurface horizons of the up-per sideslope pedons (Table II), due to the Pleistocene loess contributions (Barnhisel et al,1971; Karathanasis, 1991b) and seemed unstable (solutions slightly undersaturated) in otherhorizons. Apatite showed similar dissolution trends with smectite. The solutions were su-persaturated in the lithic interfaces and undersaturated in the Bt horizons with respect toapatite.Depth distribution of concretionsIron- manganese concretions were observed in all horizons of all soils studied. The dis-tribution of concretions by depth showed a maximum concretion concentration in upperhorizons (Fig. 3A). Although the distributions of concretions in four sites and seven pedonshad the same trend, the maximum accumulations by depth were diferent. The number,size and depth of maximum accumulation of concretions were usually associated with soilleaching and development, landscape position and soil erosion (Phillippe et al, 1972; Rhotonet al, 1993).Concentratlon (%)0510152040B0&20-AB◆言4010012+ -StF2160Fig 3 Depth distribution of Fe-Mn concretions (A) and clay fractions (B).Zones with maximum concretion accumulation in all the seven pedons were found tooccur just above the argillic horizons, in which a sharp increase (>10%) in clay content to> 40% was observed (Fig. 3B). These arillic borizons restricted permeability to some extent,leading to occurrence of water-saturated zones or perched water tables of short durationduring wet seasons. Apparently the short duration of saturation in the upper argillic horizonscaused primary soil Mn solubilization, and precipitation (or coprecipitation) of solubilizedMn with some Fe along existing Fe oxide-coated surfaces or FeMn concretionary centersduring subsequent dry cycles. Few concretions were found within the perched water table-中国煤化工MYHCNMHGPERCHED WATER TABLE EFFECT ON SOIL GENESIS255affected zones associated with the lithic interfaces of the limestone bedrock due to longerduration or greater frequency of saturation. This allows considerably higher amounts of Feand Mn to dissolve and produce observable gray chrome matrix with common distinct orprominent bright Fe (ferrans) and black Mn (mangans) soft masses. However, these soilzones are saturated or moisture-enriched for too long to allow extensive hardening of Mnand Fe (concretion formation) to occur.Size distributions of concretionsThe same trend in development of concretions of different sizes with total content ofconcretions was obvious in these soils. Correlation analysis ilustrated that all size frac-tions of concretions had signifcant correlation with total concretions (Table IV). The verysignificant correlation between the total amount of concretions and the amount of coarseconcretions (0.904**) suggested that the size of concretions increased along with the amountof concretions.TABLE IvCorrelation matrix for total number, various sizes of concretions and soil clay content (n= 84)Total FeMn CoarseFineVery fineconcretions concretions concretions concretionsconcretions(>2 mm) (2~1 mm) (1~0.5 mm)(0.5~0.25 mm)Coarse concretionsMedium concretions0.857**0.589**Fine concretions0.705**0.380**0.786**Very fine concretions0.407**0.1590.391**0.655**Clay-0.561*-0.612**-0.640***ignificant at the 0.01 probability level.Significant negative correlation of total amount of concretions with clay content indicatedthat maximum formation of concretions and concretions of larger size sbould occur in soilswith a medium to high air conductivity that had a large quick change in aeration (e.g, .air volume changed from 2% to 12% or Eh changed from -100 to +600 mV in less than2 weeks) (Schwertmann and Fanning, 1976). Periodic oxidation and drying appeared to beessential for process of concretion formation whereas permanent wetness led to motling oreven complete loss of Fe and Mn. This may explain why the maximum accumulation ofconcretions was always above the restricting layer and why the fuctuation of perched watertable occurred frequently; whereas, the maximumn dark, gray mottle development was foundat the lithic interfaces of limestone bedrock where the perched water table kept permanent.REFERENCES! Adams, F., Burmester, C, Hue, N. V. and Long, F. L.1980. A comparison of columndisplacement andcentrifuge methods for obtaining soil solutions. Soil Science Society of America Joumal. 44: 733~735.中国煤化工MYHCNMHG56M. ZHANG et al.American Public Health Association (APHA). 1981. Standard Methode for Examination of Water andWastewater. 15th ed. APHA, Washington, DC. pp. 5~120.3 Barnhised, R. I., Bailey, H. H. and Matongdong, S. 1971. 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Soil Science Society of America Joumnal. 55: 1 067~1 075.1usDA-SCS. 19838. Soil Survey of Fayette County, Kentucky. US. Government Printing Offce, Washington,DC. pP.15~108. .i USDA-SCS. 1983b. Soil Survey of Jessanine and Woodford Counties, Kentucky. U.S. Government PrintingOfice, Washington, DC. pp.55~124.21 Zhang, M. and Gong, z. T. 1989. Some geochemical characteristics of the formation of calcarous Vertisolsin China. Soilo (in Chinesc). 21(5): 226~233.SVZhang, M. and Karathanaeis, A. D.19979. Characterization of iron manganese concretions in KentuckyAlfisols with perched water tables. Clays and Clay Minerals,. 45(3): 428~439.中国煤化工一-:MYHCNMHG