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İrfan Oğuz, Ö. Faruk Noyan Rural Services Tokat Research Institute PO Box : 256 Tokat/Turkiye ABSTRACT In this research, changes in the physical and chemical properties and erodibility of the soil, along a certain slope, have been studied by making statistical comparisons of different analysis realized in a homogeneous sloped field. Soil samples have been taken from different depths (0 - 20 and 20 - 40 cm). It was observed that, with the increase of the distance to the upper slope; while salt, clay, potassium oxide and wilting point contents were increasing; sand, pH and CaCO3 contents of the soil were decreasing. While the soil erodibility was high in the upper slope, it was decreasing towards the lower slope. Main identifying characteristic of soil erodibility was the soil texture. No statistical link was found between the organic matter, bulk density, specific gravity, aggregate stability, macropore, field capacity and the distance with the upper slope. INTRODUCTION Soil properties may not only vary from one field to another, but also vary in the different parts of the same field. One of the reasons for physical and chemical changes in the soil was soil erosion. This study has been realized at Ugrak Catchment, which is a seven square km area, and 16 km from Tokat. The purpose of the study was to find out the changes in the soil characteristics in a sloped field along the slope. Basin's 74.7 % is farmland, 15.8 % pasture, 6.3 % forest, 3.2 % scrub. Wheat - fallow system has been applied where dry farming took place. Grain, sugar beet, clover and leguminous vegetables were planted where irrigated farming was applied. Wheat - fallow planting system has been applied in the field, which was a dry farming field, the research was run. The field's productivity is very low with a wheat productivity of 1490 kg/ha, because the climate conditions which are not optimal, as well as traditional farming applications. MATERIALS & METHODS The research area has a 6 % homogenous slope towards southwest. The field has a thin granular structure between 0 - 20 cm depth, and thick cornered block structure between 20 - 40 cm depth. . The research area has a clay texture, has slightly alkali reactions, has a few organic matter, has very little phosphorous content, has more potassium, has little CaCO3 content and has no salt. The hydraulic permeability was found very high among the identified physical properties. The bulk density of the soil varied between 0.97 g/cm3 and 1.52 g/cm3. The average specific gravity has been found as 2.64 g/ cm3. Aggregate stability has been changed between 0.03 mm and 0.07 mm. The field capacity and wilting point varied between 30.37 %- 33.43 %, and 21.63 % and 25.05 % respectively. The soil erodibility of the field has been calculated with the help of a statistical equation developed by Wischmeier and his friends (Erodibility Equation), and by adjusting the "K" factor in order to find the protection effect of the particulars bigger than 2 mm, the actual "K" factor has been found (Anonymous, 1983). According to this finding the field's average K factor value is 0.075 as a very little erodible soil. The annual potential soil loss calculated with USLE is 1.35 ton m/ha, which is in the acceptable soil loss range. Soil samples have been taken and sent to the laboratory for further analysis, with 10 m distance intervals, from 0 - 20 cm and 20 - 40 cm depth, beginning from top to lower parts in the same slope. Salt content, pH, CaCO3, phosphorous, potassium, organic matter, texture, hydraulic permeability, bulk density, specific gravity, aggregate stability, field capacity and wilting point have been determined (Tuzuner 1990). DISCUSSION In order to find out the change in different soil specifications subject to the slope, Minitab Statistics Software has been used and the simple correlation coefficients found out by the statistical analysis are listed in Table 1 below.  According to the Table 1, the highest correlation was found for CaCO3. This has been followed by clay, one of the soil's textural parameters.  The research field's CaCO3 content varied between 1.8 % and 6.1 %. When comparing the soil samples taken from 0 - 20 cm and 20 - 40 cm depths, for the CaCO3 content, it was found that in the upper parts the CaCO3 content was less in the deep soil compared to the surface of the soil. However in the lower parts of the field the content of CaCO3 content was higher in the deep soil compared to the surface of the soil. This can be related to the runoff in different parts of the field and the water infiltrated in to the soil. The rainfall, which can not be infiltrated upper slope, moves towards the lower slope. In the lower parts of the field water is accumulated and infiltrated. While the evaporation in the upper parts of the field, which contained less humidity, and the CaCO3 was increasing, the leaching was efficient in the lower parts, where the humidity was higher. The CaCO3 content in the sloped field, depending on the slope distance, has significantly changed and decreased with the distance to the upper slope. While going down from the upper slope of the field towards lower slope, the reason of the significant decrease in the CaCO3 content was the decrease in the soil thickness in the upper parts with the effect of previous erosion and the soil was gathered in the lower parts. This caused the thickness in the lower parts, and with this effect the main material containing CaCO3 was left in the deeper segments.  The salt content of the research field has varied between 0.026 % - 0.044 %. Though there was not a significant relation in the 0 - 20 cm soil depth, the salt content of the field has increased, towards the lower slope, according to the statistical relation faund for 20 - 40 cm soil depth. However this had no effect on agricultural production. The salt leaching with the rainfall, from the upper parts of the field towards the lower parts, caused high salt content.  The pH of the research area has changed between 7.67 and 8.02. Correlation for the 0 - 20 depth soil was not found, however for the 20 - 40 cm soil depth a negative relation was found from the upper slope towards the lower slope. The low pH value in the lower parts of the field compared to the upper slope was related to the CaCO3 content and increasing clay content adsorbing active hydrogen ions (Sezen, 1991). In the lower slopes the decrease in CaCO3 content led to the decrease in pH value. In the upper parts where the CaCO3 content was higher, higher pH values, caused by CaCO3 were observed. In the texture of soil samples taken, sand, clay, and silt were found. According to this, sand content varied between 32.64% - 41.52 %, clay content varied between 39.17 % - 49.95 %, and silt content varied between 12.93 % - 25.86 %. Through the slope no relation for silt was found, however between 20 - 40 cm depth for sand negative, between 0-20 and 20 - 40 cm depth for clay positive correlation was found.  Sand content increased through the slope, for 20 - 40 cm depth, towards the upper slope Though the change was very small, this significantly decrease for 20 - 40 cm depth was caused by the soil's gained richness in sand with the loss of thin material in this sloped field by the past erosion. The clay content has been increased for both study depths while going away from the higher slope. The clay content of the deep soil (20 - 40 cm) compared to the higher soil (0 - 20 cm) was higher. The increase in the clay content with respect to the distance to the upper slope was caused by the thin material, which was carried and gathered towards the lower parts of the field. In the soil samples taken to determine the changes between the distance to the upper slope and the productivity, in the field the study was made, phosporus, potassium and organic material contents were found. The phosphorous content of the field varied between 18.3 and 93.9 kg/ha. No important relation was found between the P2O5 content and the distance to the upper slope. We think that, this resulted from the fertilizer containing phosphorous, which was widely used in the past years.  The potassium content varied between 408.8 and 773.6 kg/ha. In both soil depths the K2O increased with the distance to the upper slope. The K2O content of the upper soil was higher, compared to the deeper soil. The K2O carried with the eroded soil caused the K2O content to increase in the lower parts of the soil. Organic matter content varied between 0.84 % and 1.69 %. No important relation was found between the organic matter and the distance to the upper slope.  The wilting point values of the field varied between 21.63 % and 25.05 %. The wilting point has increased when the distance between the upper slope and the wilting point has increased. This increase was parallel to the clay increase seen in the lower slope. The wilting point value has increased with respect to the clay quantity increase in the lower slope. No statistical relation was found between the other physical properties of the soil; i.e. bulk density, specific gravity, aggregate stability, makropore, field capacity and the distance to the upper slope.  In order to determine the soil erodibility along the slope, simple regression analysis have been realised. To define the important elements the stepwise equations are shown in Table 2 and 3 below. The soil erodibility has varied between 0.03 - 0.16, for both soil depths, along the slope. The soil erodibility has decreased for both soil depths with respect to the increase in distance to the upper slope. The soil erodibility of the top soil was less than the lower soil. While the slope's upper parts were easily erodible, the lower parts were more resistant to erodibility. According to the stepwise regression analysis made for the two soil depths, clay content determines the soil erodibility 76 %. The erodibility was less in lower slope where the clay content was high, and the erodibility was high where the in the upper slope where the clay content was less.   REFERENCES Anonymous (1978). Predicting rainfall erosion losses. Agr. Handbook No 537,Washington Anonymous (1983). USDA Soil Conservation Service National Soils Handbook. Demiralay I. (1977). Toprak fiziği ders notları. Atatürk Üniversitesi Ziraat Fakültesi (Teksir), Erzurum Martz L.W. (1992). The variation of soil erodibility with slope position in a cultivated Canadian Praire landscape. Earth Surface Process and Landforms, 17:6, p 543-556, Canada Minitab (1996). Release 11 for windows Minitab inc, USA Lal R. (1998). Soil erosion research methods. Soil and Water Conservation Society, Iowa Oguz I., Durak O. (1998). Çekerek havzası büyük toprak gruplarının bazı özellikleri ile su erozyonu ilişkileri ve havza topraklarının erozyon duyarlılık değerlendirmesi. Toprak ve su kaynakları araştırma yıllığı 1997. Yayın no:106. Ankara Sezen Y. (1991). Toprak kimyası. Atatürk Üniversitesi Ziraat Fak. Yayınları No 127, Erzurum Troeh F.R., Hobbs J.A., Donahue, R.L. (1999). Soil and water conservation. Prentice Hall , New Jersey Tüzüner A. ( 1990). Toprak ve su analiz laboratuvarları el kitabı. Köy Hizmetleri Genel Müdürlüğü Yayınları, Ankara Williams R.D., Naney J.W., Ahuja L.R. (1985). Soil properties and productivity changes along a slope. ASAE Publication 8-85, Michigan |