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S. Şahan 1 , E. Akça 1 , S. Kapur 1 , R. Kanber 2 1 University of Çukurova, Department of Soil Science, Adana, Turkey 2 University of Çukurova, Department of Agricultural Infrastructure and Irrigation ABSTRACT Physical and micromorphological analyses were conducted on soil samples collected from surge flow and continuos furrow experimental plots of the widely distributed Harran Soil Series in Southeastern Anatolia for the determination of the suitable irrigation method. The surge flow method is determined to be more appropriate than the continuos irrigation by reducing irrigation water losses and improving irrigation performances. The generally increasing patterns of pore area classes in the surge flow profiles and the generally decreasing and variable patterns of the pore areas in the continuos furrow profiles from Ap to Ad/A2 may also be attributed to an advantage in the water use of plants as well as less water losses of the former irrigation method which is also a merit in increasing the already decreased physical quality of soils by the excess use of water. INTRODUCTION Soil structure may be defined either in terms of the shape, size and spatial arrangement of individual soil particles and clusters of particles (aggregates), or in terms of porosity and pore size distribution (Bullock et al. 1985). The quantification of soil porosity is essential to evaluate soil structure conditions and to correlate soil porosity with root growth and water movement, which is a quality indicator of soil physical conditions (Eswaran et al. 1998). Rapid and accurate quantitative characterisation of porosity in thin sections of soils was carried out using image analysis with Quantimet 720 (Jongerius et al. 1972). The aim of this study is to compare the effects of surge flow and continuos furrow irrigation methods on the physical quality of soils in an area highly prone to land degradation, by determining the probable changes in pores, i.e microstructural and physical properties following each irrigation treatment in the widely distributed Harran Soil of SE Anatolia. MATERIALS AND METHODS Surge flow was compared with conventional continuous flow applications in a furrow irrigation on cotton. The field experiment was conducted in 1991 and 1992 on the Harran soil series (Calcic Xerosol-FAO/UNESCO (1974); Vertic Xerochrept-USDA 1996) located at the Koruklu Research Station of the Harran plain, Şanlıurfa, in the GAP (Figure 1). The soil profile is uniformly clayey rich in smectite with blocky subsoil structure to a depth of 85 to 135 cm. The soil contains 15 to 20% calcium carbonate which increases with depth. The average available soil water capacity is 15% by volume for a profile available capacity of 174 mm for 1.2 m. The probable changes in the porosities were determined at surge flow (S) and continuous furrow (C) experiments conducted on 160m long and 0.7m spaced forrows of 0.14% slope, following each field test, comprising furrow and infiltration tests. A total of 26 undisturbed soil samples were taken for preparing polished blocks for image analysis (FitzPatrick, 1994) from selected sites. Treatments of (a) surge irrigation with two inflow rates of 0.05 m3.min.-1 (q1) and 0.12 m3.min-1 (q2) and two different cycle ratios of 0.5 (CR1) and 0.3 (CR2) were compared with (b) two conventional steady flow applications with the same inflow rates in surge, C1 (q1) and C2 (q2). In 1992, the cycle ratio of 0.3 was changed to 0.33. The on-time was 30 minutes for all surge treatments. Surge treatments were made by the combination of the inflow rates and cycle ratios. These will be referred to as S21 (q2CR1); and S22 (q2CR2), respectively. The irrigation treatments were distributed in a randomized fashion. Three adjacent furrows were employed in each treatment. The advance, tail runoff, soil water and yield data were collected from one of the three furrows identically managed for surge and continuous flow field strips. The stations along the furrows were located at 20m intervals for monitoring the advance phase. The flow advance in the furrows was measured up to 130 m in C1, and 160 m in S21, S22 and C2 treatments. The porosity measurements and water retention characteristic curves were determined as specified in Vomocil (1965) and Hillel (1980). Undisturbed and disturbed soil samples for physical analyses were also collected, once before irrigation and three times after irrigation treatments from the field experiments. The pore classes varying between 0-1500 mm2 areas -PA (Pore Area Classes)- were measured (quantified) at 4 different plots on polished surfaces of the soil blocks by image analysis-Quantimet 520. All 4 plots were approximately chosen from similar morphologies at the microscope i.e. by attempting to take almost the same amounts of planar voids-channels at each field of view. For correlation of physical data (esp. porosity %), the quantimet measurements were calculated as sq. microns versus counts. Therefore the area classes were determined by accepting the maximum length or area for the smallest area class of a planar void-pore as 100 mm or 100x1mm2 respectively and irregular and so-called rounded pores with varying dimensions between 0-100 mm2. The classifications and/or sorting of the dominant pore classes were also fitted to the pore classification produced by Bullock et al. (1985). The upper boundary of the smallest pores in the classification used in this study relates to the upper boundary of the resolvable pores-voids with optical microscope, but not clearly visible to the naked eye and covers the micro and the fine mesopores of Bullock et al. (1985). The remaining area classes may be partly related to meso and macropores. The macropores, as stated earlier in the materials and methods, are >10mm according to limits given by Hillel (1980) and Vomocil (1965). This does not seem to fit into Bullock et al's. (1985) classification of pore classes. However, the smallest area class used in this study may relate to an average 10 mm2. RESULTS AND DISCUSSIONS Soil Water Retention Characteristics and Micromorphological Properties versus Cumulative Infiltration (Z) : Results reveal an increase in the water content of the Ad/A2 horizons at saturated conditions of 0, 1S22, 1C1, 2S21, 2S22, 2C1, 2C2, 3C1, 3S22 and 3C2 profiles (the numbers in front of treatment symbols refer to the evaluated irrigation events and zero shows the conditions before starting irrigation). This may well document a higher total porosity in the Ad/A2, whereas, the water contents at saturated conditions decreased with depth in profiles 1S21, 1C2 and 3S21 revealing a probable gradual decrease in total porosity. Field capacities decreased with depth in profiles 0 and 2C2, decreased in the Ad/A2 of 1S22, 2S21 and increased in the Ad/A2 of 1C1, 1C2, 2C1, 3S22 and 3C2 whereas profiles 1S21, 2S22, 3S21 and 3C1 showed an increase with depth. Permanent wilting points increased with depth in the profiles 1S21, 2C1 and 2C2 and decreased with depth in 3S22. There was an increase in the Ad/A2's of 1S22, 2S21, 2S22. Available water was found high in the surface horizons of 1S21, 1S22, 2S21 and 3S21 irrigated with surge flow. Inversely values showed a decrease in continuous furrow profiles 1C1, 1C2, 2C1 and 3C2 at the surface which is regarded a disadvantage for the continuous furrow method. Higher water contents are related to high clay contents and micropore volumes, whereas some of the low values of water contents indicate the layers of compaction, in spite of the higher number of pores obtained in Ad/A2 than the Ap horizons of the untreated -blank- experimental plot. Image analysis data revealed presence of dominant 0-100 µm2 PAs in all Ap and Ad/A2 horizons studied. The dominant decreasing trends in the PAs of the Ap horizons following the 2nd irrigation treatment of the S21 and S22 plots are most probably indications of clogging of the pores -an advantage for the water surge-. Conversely the increase of the PAs after the 2nd irrigation in the C1 and C2 plots of the Ap horizons and C1 plot in Ad/A2 should be considered a disadvantage causing an increase in infiltration, thus loss of irrigation water. Similarly, the step wise increasing trends of PAs in the Ad/A2 horizons of the S22 and C2 plots seem to be a disadvantage in the course of irrigation treatments for water loss. However, increase of water availability, due to increasing porosity, synchronous to deeply penetrating roots in the course of crop growth may be an advantage. The cumulative infiltration values (Z) support the data mentioned above showing similar trends to the PA in S21, S22 (Ap horizons) and C1 (Ad/A2 horizons) plots. CONCLUSIONS Conventional irrigation systems, such as surface irrigation, practised on the clayey soils of SE Anatolia have been accelerating soil physical degradation in the recent years. However, methods of drip irrigation with the optimal water use are not profitable in the GAP area due to the high investment requirements of the extensive arable lands. Thus, this study aimed to resolve the sustainable use of water with lesser damage on the soil physical qualities by comparing the surge and continuos furrow methods that are both economically irreplaceable in the area. Surge irrigation was found to accelerate water advance rates in this 2 year study as seen in the decreasing porosities after the 2nd and 3rd irrigations of the S21 and S22 treatments. Hence, surge irrigation appears to be a promising alternative for decreasing drainage volumes in the Harran Plain, where the soils have high infiltration capacities when using the existing surface irrigation systems and increasing loss of water. Consequently, surge irrigation seems to cause less damage on the soil physical quality than the continuos furrow irrigation method. REFERENCES Bullock, P, Fedoroff, N., Jongerius A, Stoops, G., Tursina, T., 1985. A Handbook for Soil Thin Section Description. Waine Research Publications. The Netherlands. p150. FAO/UNESCO., 1974. Soil Map of the World 1/5.000.000. Vol 1, Legend. UNESCO Paris Working Group on Land Use Planning. Rome. p 121 FitzPatrick, E.A., 1994. Soil microscopy and micromorphology. John Wiley and Sons. New York. p 304. Eswaran, H., Kapur, S., Reich, P., Akça, E., Şenol, S., Dinç, U. 1998. Impact of Global Climate Change on Soil Resources Conditions: A Study of Turkey. In: M. Şefik Yeşilsoy International Symposium on Arid Region Soil, 21-24 September 1998, Menemen, Turkey. pp. 1-14. Hillel, D., 1980. Fundamentals of soil physics. Academic Press, New York. p 487 Vomocil, J.A., 1965. Porosity. In: Methods of Soil Analysis, Part 1, (Eds. C. A. Black et al.), No.9, ASA Inc. Pub. Madison, Wisconsin. p 299-314. USDA, 1996. Keys to soil taxonomy. USDA, Natural Resources Conservation Service. 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