Scientific registration n : 123 Symposium n : 30 Presentation : poster. HSEU Zeng-Yei, CHEN Zueng-Sang *, LEU Ing-Yih

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1 Scientific registration n : 123 Symposium n : 30 Presentation : poster Relations between Iron-Manganese Concretions and Hydrogeomorphology in the Ultisols with Anthraquic Conditions Relations entre concrétions ferri-manganiques, hydrologie et géomorphologie dans les Ultisols sous conditions anthropiques pour la production de riz HSEU Zeng-Yei, CHEN Zueng-Sang *, LEU Ing-Yih Soil Survey and Classification Laboratory, Graduate Institute of Agricultural Chemistry, National Taiwan University, Taipei 10617, TAIWAN. (*Corresponding author: fax: , SOILCHEN@CCMS.NTU.EDU.TW) INTRODUCTION Iron-manganese concretion is one of the redoximorphic features which are characterized by wetness and attributed to the reduction and oxidation of Fe and Mn compounds in the soil after saturation with water and dry, respectively. Wherever Fe and Mn are oxidized and precipitated, they form either soft masses or hard concretions or nodules (Soil Survey Staff, 1992). Iron-manganese concretions are formed within a soil which apparently started as pore infillings (Cescas et al., 1970), presumably owing to periodic redox changes due to seasonal changes in soil moisture status (Polteva and Sokolova, 1967; Schwertmann and Fanning, 1976). In soil morphology, the boundaries between Fe-Mn concretions and surrounding matrix may be diffuse or sharp, depending on the degree of gleyification; a low chroma of the matrix is generally associated with sharpbounded concretions. As these are frequently surrounded by a granostriated b-fabric, we can infer that they are no longer active (Tucker et al., 1994). Other investigators pointed out that diffuse concretions imply a more active hydromorphism (Stoops and Eswaran, 1985; Hseu and Chen, 1996). Previous investigations have reported on zones of maximum concretion development in the E horizon of podzolic soils (Smith, 1936; Drosdorf and Nikiforoff, 1940). Phillippe et al. (1972) observed a maximum of concretion contents in the middle Bt horizons of moderately well-drained or somewhat poorly-drained soils. In northern Taiwan, many redoximorphic features generally occur in rice-growing soils with anthraquic conditions, particularly for Fe-Mn concretions. Although Chen (1984) investigated the chemical and mineralogical properties of selected Fe-Mn concretions in these soils, the relation of Fe-Mn concretions to the landscape with different anthraquic conditions has seldom been mentioned. Therefore, this study attempts to (i) illustrate the distribution and morphological characteristics of Fe-Mn concretion in the soil, (ii) understand the soil hydrology associated with the redox processes of Fe and Mn with anthraquic 1

2 conditions, and (iii) clarify the relationship between Fe-Mn concretion and hydrogeomorphology. MATERIALS AND METHODS (a) Site description. The study area is located at Taoyuan county in northern Taiwan, about 40 km southwest of Taipei city, Taiwan (Fig. 1). Soils are developed on an alluvial terrace from Quarternary. Based on the climatic data, mean air temperature in summer is 27 and 13 in the winter. Annual rainfall in 1996 was 1,320 mm, i.e. slightly lower than the mean value of around 1,560 mm for the last decade. The annual rainfall always exceeds the annual evapo-transpiration in this area. Roughly 2 km from the seashore, three representatively rice-growing (paddy) soils with plinthite were selected for this study along a transect on the Chungli Terrace. Slopes range from 2 to 6% over a distance of 4 km, they are Houhu, Hsinwu, and Lungchung series. All three soils are classified as Ultisols: a Typic Plinthaquult (Houhu), a Typic Plinthudult (Hsinwu), and a Plinthaquic Paleudult (Lungchung) according to Keys to Soil Taxonomy (Soil Survey Staff, 1996), or classified as Plinthitic Ferralsols based on FAO/UNESCO classification systems (FAO/UNESCO, 1988). The agricultural lands on the Chungli Terrace have been used for rice-growing soils since In the growing seasons from March to November, rice is harvested twice annually, and lands are fallowed in the winter. The soils are seasonally flooded. (b) Hydrological monitoring. A monitoring plot for short-term observation was established at each study site. The following information was recorded on bi-weekly intervals in 1996: (i) depth to water table, (ii) soil water tension at 50- and 100-cm depths, and (iii) soil redox potential at 50- and 100-cm depths, respectively (in triplicate). From these data, the duration time below the water table, the saturation conditions (soil water pressure head 0 cm), and reducing conditions (Eh < 250 mv at soil ph 5.5) were calculated for various depths. In addition, the reducing condition was discerned by the onset of Fe reduction from an Eh-pH phase diagram (Collins and Buol, 1970). (c) Soil analysis. A soil pit was excavated at each study site. The morphological characteristics and redoximorphic features of three selected soils were described and classified according to the Keys to Soil Taxonomy (Soil Survey Staff, 1996). To determine the Fe-Mn concretion, duplicate fresh subsamples from the bulk samples (2 kg approximately) were wet sieved; in addition, coarse (>15 mm), medium (15-5 mm), and fine (<5 mm) concretion fractions were collected and weighed. Next, undisturbed soil blocks were collected with Kubiena boxes for the micromorphological studies. After air drying, vertical and horizontal oriented thin sections with a thickness of 30 micrometer were prepared by Spectrum Petrographics, Inc., Oregon, USA. Finally, thin sections were observed with a polarized microscope (Nikon, AFX-II Type) and described according to the terminology of Bullock et al. (1985) and Brewer (1964). RESULTS AND DISCUSSION (a) Iron-manganese concretion distribution in the soil pedons Due to seasonal high water tables and strong Fe segregation, various redoximorphic features occurred in each pedon (Table 1). Although plinthites and Fe-Mn concretions were found in all Btv horizons, some differences arose in distributions within the 2

3 profile and on the landscape. Plinthites increased with soil depth in the individual profile, e.g. 25% in the Btv1 horizon increases to 70% in the Btv4 horizon of Hsinwu pedon. In addition, the depth of plinthite increased with increasing drainage in the following order: Houhu < Hsinwu < Lungchung. On the other hand, the maximum content of Fe-Mn concretion always occurred in the middle Btv horizons in all pedons. Restated, they are Btv3 horizon of Houhu pedon (15%), Btv3 horizon of Hsinwu pedon (30%), and 2Btv2 horizon of Lungchung pedon (25%). In Fe-Mn concretion, increasing contents generally implied larger sizes. Schwertmann and Fanning (1976) found that hydromorphism in the soils led to concretion formation; the intensity of which appears to have a maximum in the wetter, but not the wettest soils. Consequently, the least amounts of Fe-Mn concretion through the profile were found in Houhu pedon, which contained the poorest drainage and was closest to the sea level (Fig. 1). Moreover, although there were significantly more shapes of Fe-Mn concretion in the upper Btv horizons such as angular, pellet, slice, and elliptic shapes, only subangular or inperfectly round shaped was found in the lower Btv horizons for the three pedons. (b) Seasonal water table, water potential and redox potential fluctuations At the beginning of annual rice planting in mid-spring, the soil is flooded primarily throughout the growing seasons from March to October, subsequently raising the water table to the surface. Therefore, water potentials and redox potentials in the depths of 50- and 100 cm seasonally fluctuate depending on the water tables associated with irrigation and drainage for rice production and the distribution of annual rainfall. All the soils were saturated and reduced in summer and autumn with a higher rainfall. In Houhu pedon, the soils were markedly reduced and saturated in the depths of 50- and 100 cm throughout the year except for the fallow season in winter (Table 2). In Hsinwu pedon, alternative wet and dry cycles were more frequent because the water tables raised and falled sharply. The duration of saturation in the depth of 50 cm was 45% of the year; that in the depth of 100 cm was 50% of the year. The soils within 100 cm in Hsinwu pedon were reduced for roughly four months during the year. Although the soil in Lungchung pedon was the most well drained in this hydrosequence, less reduction and saturation occurred during the year even though the soils were frequently flooded in summer. (c) Genetic processes of iron-manganese concretions When reoxidized condition existed in the soil, Fe and Mn were accumulated as coatings and infillings in the voids, root channels, and macropores, particularly in the root channels and other biopores caused by human activities during rice production. After alternative redox processes, irregular soft masses were concentrated close to the pedosurface; Fe-Mn concretions were further formed as well. Therefore, plinthites included soft masses and hard concretions. According to our results, many coarse grains were embedded in Fe-Mn concretions. In addition, these concretions were formed as Fe coatings on the surfaces of coarse grain and sand. In hardness, the Fe-Mn concretions of Houhu pedon were markedly less than those of Hsinwu and Lungchung pedon, as attributed to the strong reducing conditions in the soil of Houhu pedon with the poorest drainage. 3

4 CONCLUSIONS Results in this study demonstrate that although iron-manganese concretions are found in the three soils with anthraquic conditions, the maximums amount and size occur in the optimum reducing and saturation conditions for Hsinwu pedon. Reverse effects in the development of Fe-Mn concretion are excessive submergence and less saturation and reduction. The fact that there are much more void types like root channels and other biopores near the plow layer (caused by human activities for rice production) accounts for why the patterns of Fe-Mn concretion tend to have diverse shapes such as angular, pellet, slice, and elliptic shapes in the upper Btv horizons and subangular or inperfectly round shapes in the lower Btv horizons. ACKNOWLEDGMENTS The authors would like to thank the National Science Council of the Republic of China for partial financially supporting this research under Contract No. NSC B REFERENCES Brewer, R Fabric and mineral analysis of soils. J. WileySons, New York, 470pp. Bullock, P., N. Fedoroff, A. Jongerius, G. Stoops, and T. Tursina Handbook for soil thin section description. Waine Research Publications, Wolverhampton, U.K. Cescas, M. P., E. H. Tyner, and R. S. Harmer III Ferromanganiferous soil concretions: a scanning electron microscope study of their micropore structures. Soil Sci. Soc. Am. Proc. 34: Chen, Z. S A model for the nowadays soil survey and classification of paddy soils in Taiwan: the study on the formation, genesis, and classification of the seashore district paddy soils in Taoyuan, Taiwan. Ph.D. dissertation. Graduate Institute of Agricultural Chemistry, National Taiwan University, Taipei, TAIWAN. Collins, J. F., and S. W. Buol Effects of fluctuations in the Eh-pH environment on iron and/or manganese equilibria. Soil Science 110: Drosdoff, M., and C. C. Nikiforoff Iron-manganese concretions in Dayton soils. Soil Sci. 49: FAO/UNESCO FAO/Unesco Soil map of the world, Revised Legend, with corrections. World Soil Resources Report 60, FAO, Rome. Reprinted as technical paper 20, ISRIC, Wageningen, Hseu, Z. Y., and Z. S. Chen Saturation, reduction, and redox morphology of seasonally flooded Alfisols in Taiwan. Soil Sci. Soc. Am. J. 60: Phillippe, W. R., R. L. Blevins, R. I. Barnhisel, and H. H. Bailey Distribution of concretions from selected soils of the inner bluegrass region of Kentucky. Soil Sci. Soc. Am. Proc. 36: Polteva, R. N., and T. A. Sokolova Investigation of concretions in a strongly podzolic soil. Sov. Soil Sci. 10: Schwertmann, U., and D. S. Fanning Iron-manganese concretions in hydrosequences of soils in loess in Bavaria. Soil Sci. Soc. Am. J. 40: Smith, W. O Sorption in an ideal soil. Soil Sci. 41: Soil Survey Staff Keys to Soil Taxonomy. Soil Management Support Service Tech. Monographs No. 19, 5th ed., Pocahontas Press, Blacksburg, VA, USA. Soil Survey Staff Keys to Soil Taxonomy. Soil Management Support Service Tech. Monographs No. 19, 7th ed., NRCS-USDA, Washington, D.C. Stoops, G and H. Eswaran p Morphological characteristics of wet soils. In: Wetland soils: Characterization, classification, and utilization. IRRI, Los Banos, Philippines. 4

5 Tucker, R. J., L. R. Drees, and L. P. Wilding Signposts old and new: active and inactive redoximorphic features; and seasonal wetness in two Alfisols of the gulf coast region of Texas, U.S.A. p In: Ringrose-Voase A. J. and Humphreys G. S. (eds.), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsvile, Australia, July Developments in Soil Science 22, Elsevier, Amsterdam. Key words: iron-manganese concretions, hydrogeomorphology, Ultisols, anthraquic conditions, micromorphology Mots clés : concrétions ferri-manganiques, hydrogéomorphologie, Ultisols, conditions hydriques anthropiques, micromorphologie Table 1. Morphological characteristics of soil pedons. Horizon Depth Texture+ Matrix color Redoximorphic features ++ cm Houhu pedon (Typic Plinthaquult) Ap 0-34 CL 2.5Y 4/2 MP 5YR 4/4 AB SiCL 2.5Y 4/1 CP 7.5YR 5/8 Bt SiCL 10YR 4/3 CP 7.5YR 5/8 Btv SiC 10YR 5/3 CP 7.5YR 5/8, CP 2.5YR 4/8, CD 10YR 6/1 Btv SiC 10YR 6/1 MP 2.5YR 5/8, CP 2.5YR 4/8 Btv SiC 7.5YR 6/1 MP 2.5YR 5/8, CP 2.5YR 4/8 Btv C 7.5YR 6/1 MD 5YR 5/8, MF 7.5YR 5/6, CP 2.5YR 4/8 Btv5 >150 SiC 7.5YR 5/6 CP 2.5YR 4/8, CD 7.5YR 3/1, MD 7.5YR 6/1 Hsinwu pedon (Typic Plinthudult) Ap 0-15 SiL 2.5Y 4/3 AB SiL 2.5Y 4/1 CF 2.5Y 4/2 Bt SiC 10YR 5/4 CD 7.5YR 4/4, FF 10YR 5/8 Bt SiC 10YR 5/6 CD 5YR 5/8, FF 10YR 5/8 Btv CL 10YR 5/2 MP 2.5YR 4/4, MF 10YR 5/3, CP 2.5YR 4/4 Btv C 2.5YR 4/8 CP 10YR 6/3, MD 2.5YR 4/4, CP 10YR 6/2 Btv C 2.5YR 4/8 CD 2.5YR 2/1, MD 2.5YR 4/4, CP 10YR 6/2 Btv C 2.5YR 4/8 CD 2.5YR 4/4, MP 10YR 7/1 Lungchung pedon (Plinthic Paleaquult) Ap 0-20 SiC 2.5Y 4/2 Bw SiC 10YR 5/2 CD 5YR 5/8 2A SiCL 10YR 4/2 CP 2.5YR 3/4 2Bt SiC 10YR 4/4 CD 7.5YR 5/6, CD 10YR 5/8 2Btv SiC 10YR 5/3 CD 2.5YR 5/8, CD 2.5YR 3/2, CP 2.5YR 4/8 2Btv SiC 10YR 6/2 MP 2.5YR 5/6, CP 2.5YR 3/2, MP 2.5YR 4/8 2Btv SiC 10YR 6/1 MP 2.5YR 5/8, CP 2.5YR 4/8, CP 2.5YR 6/1 2Btv4 >180 SiC 10YR 6/1 MP 2.5YR 5/8, CP 2.5YR 4/8, CP 2.5YR 6/1 + : SiL=Silty loam, SiCL=Silty clay loam, CL=Clay loam, SiC=Silty clay, C=Clay. ++ : C=coarse, M=medium, F=fine; P=predominant, D=distinct, F=faint. 5

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