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Kezban Şahin 1 , Zeki Alagöz 2 1 Toprak ve Gübre Araştırma Enstitüsü, Ankara,Turkey 2 Akdeniz Üniversitesi, Ziraat Fakültesi, Toprak Böl.,Antalya,Turkey ABSTRACT The experiments were carried out to determine relationships between water erosion and some physical properties of Terra Rossa (Red Mediterranean Soil/Alfisol) and Brown Forest Soils (Inceptisol) in the Antalya region under the simulated rainfall conditions. For this purpose, soil samples taken from the two different regions were brought to the study area and sieved through an 0.8 cm mesh and placed in the flume to form a layer of 10 cm deep over the gravel layer which was placed in 5 cm thickness on the base of the flume. A flume with a diameter of 500x80 cm and a longitudinal gradient of 8 % was designed. Two rainfall simulators with multiple nozzles producing 3.4 mm. average raindrop in diameter, 51 mm/hour rainfall intensity and 0.55 ton-m/4m2 total kinetic energy were used. A total of 60 minutes rainfall, 30 min + 10 min break + 30 min, was applied on the soil, and runoff and soil losses were determined. The results of the study showed that both soils are susceptible to soil erosion, whereas Brown Forest Soil is more prone to erosion than Terra Rossa Soil. INTRODUCTION Today soil erosion is a major problem in Turkey and all over the World. It causes degradation of soils and the environmental pollution. About 75 % of soils in Turkey have been affected by water erosion in different intensities. In the Antalya region it appears as a serious problem due to harsh conditions and high amount of precipitation that fall mainly in winter season (57 %). 551767 ha (32.4 %) area of the land in this region is influenced by the water erosion due to destruction of the natural plant cover and/or agricultural practices applied on very steep slopes. Severely eroded areas of 800283 ha (47.1 %) are mainly used as pasture, natural plant cover which was forest and dry agricultural lands before degradation. It is a thought that simulated rainfall studies is a useful tool to predict the properties of soils that should be considered in the conservation practices to combat soil erosion. Few studies carried out in the region to determine the relationship between soil properties and erosion. Hence, increases in researches about soil erosion is very important in terms of soil conservation studies. Soils properties are important factors governing the susceptibility of soils to erosion. Olson and Wischmeier (1963) stated that responses of soils to water erosion depend on their composition. Because of differences in their inherent properties, soils exhibit different degrees of susceptibility to the forces generated by erosion agents. All other forces remaining the same, differences in erosion up to 30- fold have been observed due to differences in soil properties. In a study of Bhatia et all (1985) it was found that erosion ratio and dispersion ratio were significantly positively correlated alluvial soils of the Budelkhand and Vindhjan regions of Utter Pradeshi. Plot studies at the Hilton experimental site, Shropshire (U.K), showed that small reductions in soil organic matter content markedly increased erodibility and erosion rates (Fullen, 1991). Sanroque et all. (1991), studied that the relationships between soil erodibility and chemical properties were studied in 12 soils from Valencia (Spain) using a laboratory rainfall simulator. Organic matter content and structural stability were the two properties most correlated with soil erodibility. Scjonning and Rickson (1994), carried out some experimental studies about susceptibility of some Danish soils to water erosion under simulated rainfall, and found that surface runoff and soil loss were greatest for sandy soils but they were reduced by clay content and soil porosity. The main goal of this study was to determine the relationships between some physical properties of two great soil groups, Red Mediterranean Soil and Brown Forest Soil in the region, and water erosion under the simulated rainfall. Results obtained from the study will be a tool to use in soil conservation practices. 2.MATERIALS & METHODS 2.1. Soils and erosion indices In the study two great soil groups, Terra Rossa Soil (Red Mediterranean Soil/Alfisol) which covers 26 % (5473332 ha.) of the catchment and the other is Brown Forest Soil (Inceptisol) which occupies 15.9 % (326246 ha) of the catchment, were chosen considering the covered area and agricultural importance. Disturbed soil samples taken from the surface of the both soils on the flume were used to perform the analyses of Organic Matter, CEC, Exchangeable Cations, CaCO3 equivalent and pH as described in Kacar (1995). After determination of the texture of the samples (Uzunoğlu, 1992), some erosion indices were calculated such as Clay Ratio (CR) (Bouyoucos, 1935), Silt Ratio (SR), % of Aggregates Smaller than 50mm (Taysun, 1977), Dispersion Ratio (DR) (Lal,1990), Structure Stability Index (SSI) (Tüzüner, 1990), Erosion Ratio (ER) (Özden, 1992), K Factor (Wischmeier &Smith,1978). 2.2. Experimental study Disturbed soil samples taken were sieved through an 0.8 cm mesh. After some gravels were placed on the flume in 5 cm. depth, the soils were placed on the gravel layer as a 10 cm thick layer and then watered to obtain field capacity after 48 hours waiting time. Before the study, surface of the soil layer was disturbed in a 3-4 cm depth and then soil samples were taken to use in some physical and chemical analyses. A flume with a diameter of 500x80 cm and a longitudinal gradient of 8 % was designed. Two rainfall simulators with multiple nozzles (Gardena Polo 280) producing 3.4 mm. average raindrop in diameter (Laws,1941), 51 mm/hour rainfall intensity and 0.55 ton-m/ 4m2/ hour total kinetic energy (Doğan &Gücer), were placed on the both side of the flume. A rainfall intensity of 51 mm/h was chosen, considering the rainfall intensity in the region. A total of 60 minutes rainfall (30 min +10 min break + 30 min) was applied on the flume and runoff and soil losses were determined. Transported soil materials were deposited in the collector in the bottom of the flume, while sediment in suspension was collected in buckets which were placed under the collector. 3. RESULTS & DISCUSSION Analyses results showed that major differences in the soils in terms of physical and chemical properties were organic matter content and texture (Table 1 and 2.)   Sand fraction was dominant in the Brown Forest Soil, whereas clay was more than others in the Terra Rossa Soil which had affected the erosion indices determined (Table 3.) Both of the soils were in the susceptible category for soil erosion in terms of clay ratio (CR), silt ratio (SR), structure stability index (SSI), aggregate percentage of less than 50 mm, erosion ratio (ER) and the factor of K. However, as there have also been some differences between the soils in terms of indices of CR, SR, SSI, ER and K factor, Brown Forest Soil was more susceptible to soil erosion than Terra Rossa Soil. Especially ER value of Terra Rossa Soil was half of that of Brown Forest Soil, and percent of aggregate less than 50 mm for Terra Rossa Soil was more than that of Brown Forest Soil. Therefore, it is found that the previous soil is more resistant than the latter one in terms of transportation of particles by surface runoff. This is consistent with the study of Meyer and Harmon (1984) which showed that poorly aggregated high-silt soils were most erodible and the high-clay soils were least erodible.  The results obtained showed that total soil loss from Terra Rossa Soil was less than Brown Forest Soil. The rate of surface runoff formed in Terra Rossa Soil was 96 lt / 4m2 which is 47 % of the total application of 204 l/4m2 of rainfall, causing a total of 1249 g/ 4m2soil loss, whereas in Brown Forest Soils, runoff occurred as 138 lt/4m2 which is 68 % of the total rainfall of 204 l/4m2 applied and the total soil loss was 2144 g/ 4m2. It can be seen from these figures that Terra Rossa Soil was more resistance to soil erosion than Brown Forest Soil (Table4). These results are consistent with the results obtained by Taysun (1977) and Dokumacı (1987). They showed that Terra Rossa Soil, a great soil group, is fairly resistant to water erosion, whereas Brown Forest Soil is not so). As can be seen from the study, it is that the mainly textural and structural properties enable Terra Rossa Soil to be resistant against water erosion. Consequently, it is possible to conclude from the results that physical properties of soils, especially texture and degree of aggregation and their stability, and indices obtained using physical properties are important parameters to explain strengths of soils against water erosion.  4. REFERENCES Bhatia K. S., Narain B. and Nath J. (1985). Erodibility of some Utter Pradesh soils in relation to their nutrional behaviour. Indian Forester. (111): 610-614. Bouyoucos G. J. (1935). The clay ratio as a criterion of susceptibility of soil to erosion. J.Am.Soc. Agron. Madison. 27: 738-741. Doğan D. ve Güçer C. (1976). Su erozyonunun nedenleri oluşumu ve üniversal denklem ile toprak kayıplarının saptanması. Topraksu Genel Müdürlüğü, Merkez Topraksu Araştırma Enstitüsü Müdürlüğü yayınları. Genel Yayın No:21, Teknik Yayın No:24. ANKARA. Dokumacı T. (1987). İzmir ili ve çevresinde bulunan bazı Terra-Rossa topraklarının önemli fiziksel özellikleri ve bunun erozyon ile olan ilişkileri üzerinde bir araştırma. Yüksek lisans tezi. Bornova-İZMİR. Fullen M. A. (1991). Soil organic matter and erosion processes on arable loamy sand soils in The West Midlands Of England. Soil Technology. 4:19-31. Lal R. (1990). Soil properties and erodibility. Soil Erosion In Tropics; Principles and Management. pp.60-99. Laws J.O. (1941). Measurements of the fall velocity of water drops and raindrops. Papers, Hydrology. 709-721. Meyer L.D. and Harmon W.C. (1984). Susceptibility of agricultural soils to interrill erosion. Soil Science Society Of America Journal, 48:1152-1157. Olson O.C. and Wischmeier W. H. (1963). Soil erodibility evaluations for soils on the runoff and erosion stations. Soil. Sci. Soc. Am. Proc. 27:590-592. Özden Ş. (1992). Doğu Anadolu Bölgesinde yaygın bazı büyük toprak gruplarının aşınıma duyarlılığı üzerine bir araştırma. Atatürk Üniversitesi Fen Bilimleri Enstitüsü Toprak Anablilim Dalı. Yüksek lisans tezi. ERZURUM Sanroque P., Rubio J. L. and Izquierdo, L. A. (1991). Relationship of soil erodibility with other soil physical and chemical properties determined by a laboratory simulator in soils from Valencia, Spain. Revue-D'ecologie-Et-De-Biologie-Du-Sol 27(2):135- 146. Schjonning P. and Rickson J. (1994). Soil erodibility in relation to soil physical properties. Conserving soil resources: European perspectives. Selected Papers From The First International Congress of The European Society For Soil Conservation. 78-86. Taysun A. (1977). Bornova ve civarında mevcut büyük toprak gruplarının bazı fiziksel özellikleri ile bunların erozyonla olan ilişkileri üzerinde araştırmalar. Doktora Tezi. Bornova- İZMİR. Tüzüner A. (1990). Toprak ve Su Analiz Laboratuvarları El Kitabı. T.C Tarım ve Köy İşleri Bakanlığı Köy Hizmetleri Genel Müdürlüğü. ANKARA. Uzunoğlu, S. (1992). Toprak Bünyesi ve Analiz metodları. T.C. Tarım ve Köy İşleri Bakanlığı, Köy Hizmetleri Genel Müdürlüğü, Toprak ve Gübre Araştırma Enstitüsü Müdürlüğü Yayınları, genel yayın No: 184, Teknik yayın No: T-64. ANKARA Wischmeier W. H. and Smith D. D. (1978). Predicting rainfall erosion losses. A Guide To Conservation Planning U.S.D.A. Agriculture Handbook. No: 537. |