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Cumhur Aydınalp Uludag University, Faculty of Agriculture, Department of Soil Science, 16059 Bursa, Turkey. Abstract Vertisols were identified in a soil survey of the area of Bursa plain in northwestern Turkey. These are generally deep, dark colored with well-developed structure, high in CEC and base saturation, and can hold and supply sufficient amounts of water and nutrients for crops. Vertisols occupy quite large and important part of the agricultural land in the western part of the plain where rain-fed agriculture practiced. Some of the area is also irrigated for valuable crops in the region. The soils of the plain have a great potential for field crops such as wheat, sunflower and sugarbeet, as well as for horticultural crops such as tomato, pepper and melon. The aim of this research was to determine physical, chemical and morphological properties of irrigated Vertisols under intensive agricultural actives in the region. Twelve irrigated sites were selected to present Vertisols. All the studied soils had high clay contents and CEC values throughout the profiles. The high CEC/clay ratio suggests montmorillonitic and mixed mineralogy. Calcium (Ca) was the dominant cation followed by magnesium (Mg), potassium (K), and sodium (Na) in all the soil profiles. The electrical conductivity values are low throughout the soil profiles indicate the low leaching rate, eluviation and illuviation process within these soils. The studied soils were also classified according to FAO/UNESCO (1990) as Eutric Vertisol and USDA Soil Taxonomy (1998) as Typic Haploxerert. Introduction This paper focuses on Vertisols occurring in the Bursa province of Turkey. The province occupies an area of 1.104.301 ha. Vertisols comprise 23.436 ha of the land area and occur in the western side of the plain (Anonymous, 1995). These soils derived from marl parent material in the region. They have been mapped and described in limited resource surveys (Anonymous, 1971), but details of soil morphological, physical, chemical and mineralogical characteristics have been documented for only a few studies in this region (Aydınalp, 1996 and 2001). In recent years, land use has changed dramatically from agricultural use to urbanization and industrialization. Vertisols are under intensive agricultural activities in the region. Most of the arable land has dry farming system for wheat, sunflower and sugarbeet production. The soils with irrigation facilities enable high quality crops such as tomato, pepper, melon etc., in the region. The Nilüfer River, the Ayvalı Canal and ground water sources are the main irrigation water resources in study area. The detailed studies of the morphological, physical and chemical properties of selected soils were performed. The primary objectives of the work herein reported were to assess the potential of the irrigated Vertisols of the Bursa plain, Turkey to provide basic information for agricultural development; and to characterize the soils, on basis of their properties, according to the FAO/UNESCO (1990) and USDA Soil Taxonomy (1998). Material and Methods Twelve sites were chosen in this research. The soil profiles were located on west side of the Bursa plain in northwestern Turkey. Soil pits excavated to parent material and samples were collected according to different horizon. The profiles were described according to Soil Survey Manual (Soil Survey Division Staff, 1993). The soils were analyzed for particle-size distribution (Gee and Bauder, 1982), pH in a 1:2 soil:water ratio (McLean, 1982), organic carbon (Nelson and Sommers, 1982), total nitrogen (Bremner and Mulvaney, 1982), calcium carbonate (Nelson, 1982), EC (SCS, 1972), free iron oxide (SCS, 1972), CEC (Rhoades, 1982), exchangeable cations (Thomas,1982) and available phosphor (Olsen, 1982). Horizon nomenclature and classification of the soils carried out according to FAO/UNESCO (1990) and USDA Soil Taxonomy (1998). Results The morphological properties of the soils are given in Table 1. These soils were formed on marl parent material and irrigated with ground water in the research area. The soils occur in a climatic zone with strongly contrasted seasonal climate. During the wet season, soils are almost saturated conditions and become dry and desiccated throughout the profile in the summer season. The cracks were developed to a depth of about 90 cm in all the studied profiles. Their width at the soil surface ranged from 3 to 6 cm. Slickensides were observed and the paralleled structures were attributed to the soil texture, swelling, and shrinkage and pedoturbation in these soils. The soils are deep and dark coloured in the studied profiles. The all horizon had 10YR hue with value 2 to 3 and chroma 2 to 3. The data on particle size distribution is presented in Table 2. Data on particle size distribution support the observations made during the morphological studies. All the soils are clay textured, containing clay between 40.9 to 69.9%. Clay increases with depth in all the soil profiles and highest at the Bw horizons. Sand fraction varied from 9.5 to 42.7% and highest in the Ck horizons.   Some chemical properties of soils are presented in Table 3. The soil pH ranged from 7.7 to 8.1 and values increased with depth. The CEC values varied 30.8 to 61.5 cmol (+) kg-l, and, along with clay content of the soils, increased with depth (Table 2). Ca values ranged from 23.7 to 55.3 cmol (+) kg-l and increased to Bw horizons. Mg values varied from 3.5 to 4.5 cmol (+) kg-l and increased with depth and highest in the Ck horizons of all the studied soils. K and Na values ranged from 1.6 to 2.3 and from 1.3 to 2.1 cmol (+) kg-l respectively, and values slightly decreased with depth. Base saturation is 100% throughout all the soil profiles due to the presence of free CaCO3. The organic C and total N values varied from 0.5% to 2.1% and from 0.04% to 0.15% respectively decreased with depth. C/N ratios ranged from 11.7 to 16.7. The CaCO3concentration varied from 2.0% to 6.8% and increased with depth. The high CEC values indicate high fertility potential for all the studied soils. The high CEC/clay ratio (Table 3) indicated that smectite is the contributor to the high CEC values. Electrical conductivity values showed that the highest value was 0.62 dS m-l in the profile 12. Values of EC ranged from 0.22 to 0.62 dS m-l indicating that these soils are not saline. Free iron oxide values varied from 0.72 to 1.14% and decreased with depth. Available phosphorous values ranged from 7.17 to 35.08 ppm and decreased with depth. The upper horizons showed highest values and levels of phosphorous were adequate in the studied soils.  Conclusion Generally, these irrigated soils are non-saline and slightly alkaline with pH around 7.8. The studied soils have high cation exchange capacity that is contributed largely by clays despite the low organic matter content. Clay content is high in the soils. The high CEC/clay ratio suggests montmorillonitic and mixed mineralogy. The similar distribution of soil properties indicates the low leaching rate, eluviation, illuviation processes, slow rate of weathering and soil development within these irrigated sites. All the studied soils were classified according to FAO/UNESCO (1990) as Eutric Vertisol and USDA Soil Taxonomy (1998) as Typic Haploxerert. References . Anonymous., 1971. Susurluk havzası toprakları. Toprak Su Genel Müdürlüğü Yayınları: 258, Raporlar Serisi: 46, Ankara. . Anonymous., 1995. Bursa ili arazi varlığı. T.C. Başbakanlık Köy Hizmetleri Genel Müdürlüğü Yayınları. İl Rapor No: 16, Ankara. . Aydınalp, C., 1996. Characterization of the main soil types in the Bursa province, Turkey. PhD thesis, The University of Aberdeen, Aberdeen, UK. . Aydınalp, C., 2001. Characterization of some Vertisols in northwestern Turkey. 1st International Conference on Soils and Archaeology. pp 172-176. 30 May-03 June, Szazhalombatta, Hungary. . Bremner, J.M. & Mulvaney, C.S., 1982. Nitrogen-total. In: A.L. Page, R.H. Miller, and D.R. Keeney (eds.), Methods of Soil Analysis. Part 2: Chemical and Microbiological Properties. 2nd ed. American Society of Agronomy, Madison, WI, pp. 595-624. . Gee, G.W. & Bauder, J.W., 1982. Particle-size analysis. In: A. Klute (ed.), Methods of Soil Analysis. Part I: Physical and Mineralogical Methods. 2nd ed. American Society of Agronomy, Madison, WI, pp. 383-412. . FAO/UNESCO., 1990. Soil map of the world, revised legend, World Soil Resources Report 60, Rome. . McLean, E.O., 1982. Soil pH and lime requirement. In: A.L. Page, R.H. Miller, and D.R. Keeney (eds.), Methods of Soil Analysis. Part 2: Chemical and Microbiological Properties. 2nd ed. American Society of Agronomy, Madison, WI, pp. 199-224. . Nelson, D.W. & Sommers, L.E.,1982. Total carbon, organic carbon, and organic matter. In: A.L. Page, R.H. Miller, and D.R. Keeney (eds.), Methods of Soil Analysis. Part 2: Chemical and Microbiological Properties. 2nd ed. American Society of Agronomy, Madison, WI, pp. 538-580. . Nelson, R.E., 1982. Carbonate and gypsum. In: A.L. Page, R.H. Miller, and D.R. Keeney (eds.), Methods of Soil Analysis. Part 2: Chemical and Microbiological Properties. 2nd ed. American Society of Agronomy, Madison, WI, pp. 181-198. . Olsen, S.R. & Sommers, L.E., 1982. Phosphorus. pp. 403-430. In: A.L. Page, R.H. Miller, and D.R. Keeney (eds.), Methods of soil analysis. Part 2: Chemical and Microbiological Properties. 2nd ed. American Society of Agronomy, Madison, WI. . Rhoades, J.D., 1982. Cation exchange capacity. In: A.L. Page, R.H. Miller, and D.R. Keeney (eds.), Methods of Soil Analysis. Part 2: Chemical and Microbiological Properties. 2nd ed. American Society of Agronomy, Madison, WI, pp. 149-158. . Thomas, G.W., 1982. Exchangeable cations. In: A.L. Page, R.H. Miller, and D.R. Keeney (eds.), Methods of Soil Analysis. Part 2: Chemical and Microbiological Properties. 2nd ed. American Society of Agronomy, Madison, WI, pp. 159-166. . Soil Conservation Service., 1972. Soil survey laboratory methods and procedures for collecting soil samples. U.S. Dep. of Agriculture Soil Survey Investigations Rep. No. 1. U.S. Government Printing Office, Washington, D.C. . Soil Survey Division Staff., 1993. Soil survey manual. USDA, Washington, D.C. . USDA., 1998. Soil taxonomy: Keys to soil taxonomy, Sixth Edition, p. 293. |