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Hasan Özcan 1 , Erhan Akça 2 , Selim Kapur 2 , Oğuz Dinç 2 1 The Sixth Regional Directorate of State Hydraulic Works, Planning Section, 01330 Seyhan-ADANA/TURKEY 2 University of Çukurova, Faculty of Agriculture, Department of Soil Science, 01330 Balcalı-ADANA/TURKEY ABSTRACT Long term changes in soil salinity of a 10000 ha area of theYüreğir plain was studied considering irrigation, drainage, soil and topographic properties, using soil salinity data obtained in 1959 and 1979, with recently analysed soils (surface horizon 0-15, 15-30 cm) collected from previously determined soil series. Results revealed that non-saline, slightly and moderately saline soils were 93% of the study area in 1959, 73 % in 1979, and 72% in 1999. Strongly and very strongly saline areas did not increase in comparison to the 1979 and 1999. The problem area in 1979 has been reclaimed by newly opened drainage canals, whereas areas with no salinity problems, surrounded by the Akyatan lagoon and its overflowed area, reveal increased salinity. The saline areas in the local lowlands have not significantly changed within a 40 year-period due to soil and topographic conditions. Land covered with natural vegetation exposes increased salinity at the top soil due to the increasing capillarity by roots, whereas parts devoted to agriculture have revealed decrease of salinity at the surface and increase with depth due to increased leaching by tillage. INTRODUCTION It is generally known that soil productivity changes based on its physical and chemical properties. The most important factors effecting soil productivity are soil salinity, alkalinity and ground water levels. Soil salinity and alkalinity are mainly caused by natural and cultural (secondary salinisation) factors. While climate, natural drainage, topographic properties, geologic structure, parent material, distance to the sea are natural factors; unsuitable irrigation methods and water quality, insufficient drainage, poor land management are cultural factors. Saline, saline-alkaline and alkaline soils are usually seen in the hollow and flat topographies in the arid and semi arid climatic conditions. In these areas, the upward movement of high groundwater, waterflood and excess evapotranspiration can cause salt accumulation at the soil surface (Dinç, 1987; Mehanni, 1998; Özcan and Çetin, 1998). The salt caused both by natural and cultural effects on soil can be of chemical, physical and biological origin. Chemical effects are the cation exchanges and the interaction among salts. Whereas the major physical effects are on permeability where a non-permeable subsoil layer can partly or completely prevent salt leaching from soil (Dinç et al., 1990; Smedema and Rycroft, 1983). Biological effects are the changes in osmotic pressure and alteration of protoplasmatic actions in plants (Özgül, 1974; FAO, 1985; Smedema and Rycroft, 1983). The study area has no outflow to the sea and is composed of alluvial deposits which are more suitable for salinisation. The south section towards the Mediterranean Sea of the Lower Seyhan Plain (ASO), one of the earlier irrigation projects of Turkey, has been highly effected by salinisation. The salt effected soil series are Helvacı, Arıklı, Arpacı, Gemisüre and the dominant salt type is halite (according to Nuns, 1960 and Dinç et al., 1990). Yüzgeç (1985) investigated salt changes in the surface horizons of the Çukurova Region between 1956 and 1984. Results revealed that the strongly saline areas decreased from 16,8 % to 2,1% with irrigation and saline soils from 105639 ha to 60898 ha. Özcan and Çetin (1996) examined maximum soil salinity and alkalinity in a soil profile (within 150 cm) from 1956 to 1979 in the fourth project area of ASO. They pointed out that there had been 2,5 and 1,5 fold increases in saline-alkaline and strongly saline areas respectively, with a 1,5 fold decrease in saline soils. The reasons of these changes were; vicinity leakage owing to upper catchement irrigation, irrigation from drainage canals and the highly saline groundwater. The northern part of the area intended for investigation has been under irrigation since 1960 following the Seyhan dam construction. But, the study area has not had irrigation infrastructure and the drainage canals have been partly constructed since 1990 as is the usual practice in many similar cases. Thus the aim of the study seeks to evaluate the drainage and irrigation effects on soil salinity and monitoring of changes since 1959 in selected saline areas ( about 10000 ha) of the Yüregir plain. MATERIALS AND METHODS The study area was decided to represent the ASO fourth project area. Hence, having considered the topographic condition and soil series, about a 10000 ha area with complex soil series was selected for the study. The area is located between the Adana province and Karataş town and surrounded by the YD3 main drainage canal and the Akyatan Lagoon. The Mediterranean climate prevails within annual precipitation of 772,3 mm/year, average temperature of 18,1 °C and total evaporation of 1580,1 mm. From a topographic perspective the area is flat with 0-0,05 % slope. The altitude is 2,5 m in the north, 2 m in the south with some local depressions. The 1/25000 scaled topographic map, land classification report of the Yuregir plain (TGAE, 1959), land classification report of the Lower Seyhan plain fourth project area (DSİ, 1979) and the detailed soil map and report of the Çukurova Region (Dinç et al., 1990) were the basic materials used in the study area. The salinity classes of the 1959 and 1979 were considered together with the slopes for determining sampling points representing each mapping unit and the previous years' salinity classes. Soil samples were collected from 0-15 and 15-30 cm depths from the identified two hundred sampling points (october-november 1999). The soluble salt and pH analys of the soils were carried out on saturated pastes according to Bower and Wilcox (1965) and Jackson (1967) respectively. RESULTS Variations On The Salt Levels Over The Years The soils studied are on three different physiographic units (Dinç et al., 1990) of the Yüreğir plain (Figure 1). Helvacı, Arpacı and Oymaklı are the most common soils of the study area. The variations in the soil salinity levels (0-30 cm) of the study area over the years 1959-1999 are shown in Figure 2 and their maps are presented in Figures 3,4 and 5. The non-saline and slightly to moderately saline soil areas were about 93% before the irrigation project started, they decreased primarily to 73% in 1979 when irrigation was intensified at the upper part of the project area and then decreased to 72% in 1999 after constructions of the new main drainage were started. On the other hand the no changes in the strongly and very strongly saline soils between 1979 and 1999 seem to be misleading when Figures 3, 4 and 5 are examined by drawing out the following results; - Salinity has decreased except in the local depressions after the construction of the drainage canals at the north of the study areas. On the contrary, due to the insufficent outlet and the partly operating pump station even the non-saline areas (areas towards the Akyatan Lagoon and its vicinity ) are determined to have significantly increased in salinity.The salinity level of the water of the Akyatan Lagoon was more than 150 dS/m (strongly saline) due to the lack of water circulation and high groundwater levels in its western part (KHGM, 1997; DSİ, 1979). In addition, at the north of lagoon there is a 3000 ha saline-alkaline weed area with waterlogging developed from surface flow and intensive rainfall, especially in the winter season effecting the south of the area.  - Due to the low altitude of the southern part of the study area (2m), the bottom level of the open drainage canals is lower than the sea level, thus the south of the study area is effected by the sea as well.  Figure 1 shows the soils of the test area together with Figure 4 and 5 which show the increase of the strongly and very strongly saline soils in the delta and old terraces. The soil series which exist within these two physiographic units contain more than 50% clay with massive structures in the lower horizons due to low hydraulic conductivity levels.     SALT REMOVAL The salt movement in the top soils representing different physiographic units (0-15 cm and 15-30 cm) ) is given in Figure 6. The salinity of 14 out of 147 soil samples have decreased with depth whereas others have increased. Local lowlands and the area covered with natural vegetation expose increase of salinity at the top soil owing to capillarity, whereas parts devoted to agricultural management have effected capillary movement negatively by destruction of micro and macro pores. Destroyed pores cause a decrease in capillarity, inhibiting saline groundwater movement to the surface. Agricultural practices effect salinity of the area in two different ways. First destruction of the pores, second increasing leaching of salt related to crop patterns. CONCLUSIONS The following conclusions can be drawn from this study: 1. The annual precipitation ( about 772.3 mm/year) may improve salinity conditions by itself provided sufficient drainage is present. 2. Uncontrolled irrigation practices applied in the upper and some parts of the study area can cause 50 % over irrigation water use (Özcan and Çetin, 1995) with C2S1 quality water containing 0.45-0.50 dS/m salinity (DSİ, 1979). Thus applying 1000 mm irrigation water in the area leaves 3 ton/ha/year salt on the soil. This may be another way for increased salinisation under poor drainage conditions allowing insufficient percolation and drainage discharge. 3. High saline groundwater, soil and topographic conditions are more effective than the effects of the sea and the Akyatan Lagoon for salinity development. Especially in the lowland and delta areas very strong salinisation has not changed since 1956. 4. High evaporation rates increased salinisation in the wasteland and bare areas. 5. Absence and/or lack of well maintaned drainage networks are the main cause of developing salinity as elsewhere. REFERENCES Bower, C.A.; Wilcox, L.V., 1965. Soluble Salt Method of Soil Analysis. Methods of Soil Analysis Part 2, Am. Soc. Agron. No:9, Madison, Wilconsin USA, p:933-940. Dinç, U., 1987. Türkiye Toprakları Ders Notları. (Basılmamış). Adana. Dinç ve ark., 1990. Çukurova Bölgesi Toprakları. Ç.Ü.Z.F. Yardımcı Ders Kitabı, No:26, Ç.Ü.Z.F. Adana. DSİ, 1979. Aşağı seyhan Projesi Aşağı Seyhan Ovası IV. Merhale (7YP-8YP) Sahaları Planlama Arazi Tasnif Raporu. DSİ, Ankara. FAO, 1985. Guidelines: Land Evaluation For Irrigated Agriculture. FAO Soils Bulletin No. 55, Rome, FAO. 229 pp. General Directorate of Rural Services, 1997. Akyatan Lagoon Project. Anonymous. Jackson, M.L., 1967. Soil Chemical Analysis. Prentice Hall of India Private Ltd. New Delhi. Mehanni, A.H., 1988. The Influence of Depth and Salinity of Watertables on the Salt Levels in the Duplex Red-Brown Earths of Goulburn Valley of Victoria. Australian-Journal of Experimental-Agriculture. V. 28(5), p.593-597. Australia. Nunns, F.K., 1956. Work Plans For Soil Survey of the Seyhan Delta Area. TA Project 77-149, USOM/TURKEY. Özcan, H.; Çetin, M., 1995. Aşağı Seyhan Ovasında Sulama ve Drenaja Yönelik Problemler ve Çözüm Önerileri. Türkiye Toprak İlmi Derneği, İlhan Akalın Toprak ve Çevre Sempozyumu, Ankara. Özcan, H.; Çetin, M., 1996. Land Degradation Induced By High Groundwater Level and Soil Salinity In The IV. Stage Project Area of Yüreğir Plain: A Case Study. 1ST International Conference on Land Degradation. Proceedings, p. 93-99, 10-14 June, Adana, Turkey. Özcan, H.; Çetin, M., 1998. The Relationship Between Groundwater and Soil Salinity in the Eastren Mediterranean Coastal Region, Turkey. Şefik Yeşilsoy International Symposium on Arid Region Soils. 21-23 September, Izmir-Turkey. Özgül, Ş., 1974. Tuzluluk ve Sodiklik. Uluslararası Sulama ve Drenaj Komisyonu Türk Milli Komitesi. Teknik Rehber, 04.02-02. Ankara. Smedema, L.K.; Rycroft, D.W., 1983. Land Drainage. Batsford Academic and Educational Ltd. London. 376 pp. TGAE, 1959. Yüreğir Ovası arazi Tasnif Raporu. Toprak Etüğd Raporları No:1. Ankara. Yüzgeç, A., 1985. Çukurova Bölgesi Tuzlu ve Alkali Topraklarının Oluşumu, Dağılımı ve Özellikleri. Ç.Ü. Fen Bilimleri Enstitüsü. (Master Tezi). Adana. |