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Mehmet Ali Çullu 1 Ahmet Almaca 1, Yüksel Şahin 2, Salih Aydemir 1 1 Harran University, Faculty of Agriculture, Department of Soil Science, Şanlurfa, Turkey 2 Regional Directory of Agricultural Reform, Şanlıurfa, Turkey Abstract The Harran Plain as the biggest plain of Southeastern Anatolia Project (GAP) has 152000 ha irrigable area. The plain is under the semiarid climate regime and it is dominated by clay-textured soils. Due to excess irrigation with a minor control, salinization problems are becoming prevailed in the plain. Salinization maps were prepared in GIS by using the salinity values of 1987, 1997 and 2000 to determine changes and distribution over the study area (36167 ha). The study investigated an increasing trend of salinization in 13 years. Especially the increase was almost doubled after beginning of the surface irrigation in the plain. Results showed that total salinized area was 5550 ha in 1987, 7498 ha in 1997 and 11403 ha in 2000, respectively. It was observed that capillary movement of shallow saline ground water with very high evapotranspiration to the upper horizons or soil surface results in accumulation of salt in the system. To bring the salinity accumulation to a reasonable level, amount and type of the water application and removing of the excess water needs to be considered for sustainable agriculture in the plain. Introduction Salinized soils are a major constrains for agricultural production in the irrigated arid and semiarid regions. Periodic monitoring salt-affected areas are essential for developing reclamation and management strategies. The most important factors effecting soil productivity are soil salinity, alkalinity and shallow ground water levels. Movement of salty water to topsoil and excess evapotranspiration can cause salt accumulation at the different soil horizons ( Mehanni, 1998; Çullu et al., 2000; Aydemir, 2001). Soil salinity and alkalinity are mainly caused by natural and cultural factors. While climate, natural drainage, topographic properties, geological structure, parent material, distance to the sea are the natural factors; unsuitable irrigation methods and water quality, insufficient drainage, poor land management are agricultural factors (Mehanni, 1998; Özcan and Çetin, 1998). The selection of an irrigation method for applying water to the soil is related to salinity. The method that is best adapted in any particular case depends upon a number of conditions: the crop to be grown, topography, soil characteristics, availability of water, soluble-salt content of the water, and salinity status of the soils (US Salinity Lab. 1954). Understanding the changes of salt in the soil profile is a perquisite for devising appropriate management strategies to improve land productivity of salinized regions. In the Harran Plain slight decrease was observed in structure stability and aggregation indexes after irrigation, however decrease in hydraulic conductivity was significant. Moreover, salinity was significantly increased in soils and there were no changes in clay mineral contents (Çullu et al., 2000). There is a clear need for the development of cost-effective, quantitative salinity monitoring techniques. The initial diagnosis of the soil salinity conditions within a field typically represents just the first step in a long-term reclamation project or salinity management process (Lesch et al., 1998). Geographic Information System (GIS) helps to provide solutions and particularly management solutions for the problems. Data stored in GIS, therefore be rapidly manipulated, reconfigured, updated, compared, displayed and mapped in a suitable scale format (Chagar and Plunkeft, 1993). The objective of this study was to monitor soil salinity changes of the Harran Plain between 1987 and 2000 years using GIS techniques. Material and Methods The study area (36167 ha) was located in the Southeast part of the Harran Plain, in Şanlıurfa (Figure 1). The Harran Plain has a semiarid climate with practically no precipitation takes place between June and September. Generally, salty ground water level remains close to the soil surface during the year. At the most part of the plain cotton is the major crop produced. It has been proved that when Sahara originated dusts are put in cultured environment in certain conditions an extraordinary amount of fungi colonies appear and it has been detected by satellite images that the dust from Sahara spreads over Anatolia in different dates (Saydam and Şenyuva, 2000; Şenyuva, 2001). In this study, detailed soil map prepared in 1987 by Dinç et al. (1988) was digitized and based on the salinity data determined in three different years 1987, 1997 and 2000, salinity classes and their distributions applied to the map using GIS, ArcView software to monitor and compare the salinity changes between 1987 and 2000 (Çullu et al., 2000).  This research was conducted in the southeast part of the Harran Plain that has shallow groundwater and potential salinity problem. Some selected chemical data of five common soil series are given for 2000 in Table 1. Data in the table reveal that soils sampled form 0-30 cm depth reflect calcareous characteristics (pH 7.6-8.3); series especially Akçakale, Cepkenli and Gürgelen showed wide range with high EC of soil extract and ground water and ESP values. Ground water depth from the surface fluctuate (80 cm to 2 m) between seasons, May and August period gives the lowest depth (e.g. 80 cm in Akçakale) indicating shallow ground water with intensive irrigation. Results and Conclusions In order to delineate salinity changes of the study area, salinity maps were established using integrated GIS approach for 1987, 1997 and 2000 (Figure 2). Figure 2 shows significant increase on salt accumulation during 13 year period. Especially after 1995 when the flood irrigation was began, the soils build up about 1/3 more salt in 5 years. Figure 2 reveals that salinization showed a trend from none to strong between three different years. Mostly soils showed an alteration of salinization as from none to slight, slight to moderate and moderate to strong. Particularly, strongly saline soils was located at the north part of the study area in 1987, but same kind of soils was also appeared in the middle and south part in 1997 and almost all strongly salinized soils are located at the south part close to Akçakale in 2000.  When salinity changes are compared as percent base between three different years, figure 3 indicates very clear and significant results to show the increase of the Arial percentage of saline soils and decrease of none-saline soils. While the none-saline soils was about 90 % in 1987, the percentage decreased about 75 % in 2000. Levels of the saline soils from slight to strong also showed significant increase during the years. Especially strongly saline soils increased from 1 % to 8 % and increase was about 6 % for slightly saline soils in 13 years. Akçakale series is the one that is most effected with salinization resulted from the location of the soils which are at the lowest elevated part (about 350 m from sea level) in the study area. This results in shallow saline ground water and accumulation of salt at the most level due to the capillary movement of the water with the great evaporation from the soil surface (Figure 2 and Table 1) The use of temporal soil analysis results for determination of salinity on agricultural lands has always been thought of as a fast and cost-effective method to monitor salt problems affecting crop yields. So, the use of GIS for monitoring salinity has proved feasible in large areas where salinity already a serious problem. Overall it can be concluded that soils of the southeast part of the Harran Plain especially after beginning of the irrigation show a significant salinity increase trend due to increase of groundwater level (range about 50-100 cm) in particularly south part of the study area. To bring the salinity accumulation to a reasonable level the excess of water needs to be removed from the system by selection of a proper drainage method and applied most efficient water with a proper irrigation method as well, and salinity level also needs to be monitored in certain times for sustainable agriculture in the area.   References . Aydemir, S. 2001. Palygorskite-influenced Vertisols and Vertic like soils in the Harran . Plain in the Southeastern Turkey. PhD. Thesis, Texas A&M University, Soil and Crop Sciences Department, College Station, TX 77843, USA. . Chagar L. P. and G. W. Plunkeft, 1993. Mapping Applications for low-cost Remote Sensing and Geographic Information Systems. Int. J. Remote Sensing,Vol. 14, No 17, p:3181-3190. . Çullu, M. A., İ. Çelik, A. Almaca. Degradation of The Harran Plain Soils Due To Irrigation. Proceedings of International Symposium on Desertification. Konya-Turkey. (2000), 193-197. . Çullu, M. A., Almaca A, Öztürkmen A. R., Ağca N., İnce F., Derici M. R. Harran Ovası Topraklarında Tuzluluğun Yayılma Olasılığının Belirlenmesi. T. C. Başbakanlık GAP Bölge Kalkınma İdaresi Başkanlığı (2000) (In Turkish) . Dinç, U., S. Şenol, M. Sayın, S. Kapur, N. Güzel, R. Derici, M. Ş. Yeşilsoy, İ. Yeğingil, M. Sarı, Z. Kaya, M. Aydın, F. Kettaş, A. Berkman, A. K. Çolak, K. Yılmaz, B. Tunçgöğüs, V. Çavuşgil, H. Özbek, K. Y. Gülüt, C. Karaman, O. Dinç, N. Öztürk, E. E. Kara. Güneydoğu Anadolu Bölgesi Toprakları (GAT) 1. Harran Ovası. TUBİTAK Tarım ve Ormancılık Grubu Güdümlü Araştırma Projesi Kesin Sonuç Raporu. Proje No:TOAG-534, (1988) (In Turkish) . Lesch, S. M. J. Herrero, J. D. Rhoades. Monitoring for Temporal Changes In Soil Salinity Using Electromagnetic Induction Techniques. Soil Sci. Soc. Am. J. 62 pp. 232-242, (1998). . Mehanni, A. H. The Influence of Depth on Salinity of Water Table on the Salt Levels in The Duplex Red-Brown Earths of the Goulburn Valley of Victoria. Australian J. of Experim. Agr., 28 (5), 593-597, (1998). . Özcan, H. M. Çetin. The Relationship Between Groundwater and Soil Salinity In The Eastern Mediterranean Costal Region, Turkey. M. Şefik Yeşilsoy Int. Syposium on Arid Region Soil. İzmir-Turkey, (1998), 370-373. . U.S. Salinity Laboratory Staff. 1954. Diagnosis and Improvement of Saline and Alkali Soils. p. 7-33. In L.A. Richards (ed.) USDA Handbook No. 60, U.S. Gov.Print. Office, Washingt |