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Gökhan Çaycı 1, Abdullah Baran 1, Cihat Kütük 1, Yener Ataman 1, Hüseyin Öztekin 2, Orhan Dengiz 1 1 University of Ankara, Faculty of Agriculture, Department of Soil Science 2 University of Selçuk, Faculty of Agriculture, Department of Soil Science ABSTRACT Aim of this study was to determine physical properties of Bolu-Yeniçağa peat and improve its physical properties as plant growing medium. For this idea, five organic soil profiles were excavated. Then, those profiles were described, and some physical and physicochemical properties of organic soil samples taken from each horizon were determined. While some soil characteristics were ascertained in 0-2.00 mm fraction, moisture characteristic values of samples were determined in 0-4.00 mm and 0-6.35 mm fractions. Air capacity, easily available water and water buffering capacity values indicating air-water balance of growing medium were obtained in two different fractions. When air capacities of the samples take into consideration, eleven of 56 samples were found at optimum air capacity. A great part of the samples was found insufficient with respect to air capacity. As we consider air capacity and easily available water together, eleven samples were found in optimum ranges in all the soil samples. However, it was observed that unsuitable samples with regard to air-water balance can be improved by using of different particle sizes in mixtures. INTRODUCTION In last decades, soilless culture and growing media have drawn attention in Turkey as all over the world. Several materials are used for this idea in Turkey. Peat, perlite and pumice are used the most common materials as growing medium or a component of the medium in Turkey. The desired principal properties in growing medium can be pointed out as follow; firstly the growing medium should have a good air-water balance, and then should not comprise toxic elements or compounds to plant growth. In addition to those basic properties, cheapness, availability and regional customs are effectual factors to prefer the growing medium (Ataman, 1988). Peatlands in Turkey include approximately 240 km² area (Çaycı et al. 1989). When we compare the peatlands in Turkey, Bolu-Yeniçağa peatland has better physical and chemical properties than the others. Besides, this area is close to big municipalities. These advantages make it the most favoured peatland in Turkey. Nevertheless, Yeniçağa peatland has some unfavourable properties resulting from its eutrophic formation, the changes in groundwater composition and seasonal fluctuanation of groundwater level in peatland. While the basic properties of commercial peat such as water and air capacity, CEC and amounts of nutrients are well-known and standartized in Europe, there is no any standard of commercial peat sold in Turkey as growing medium. Further, the native peat producers can not benefit from some physical and chemical amendments to improve the quality of peat because of a lack of knowledge. The aim of this study was to determine the properties of Bolu-Yeniçağa peat, to evaluate its properties as growing medium and suggest some recommendations in order to improve its unfavourable physical properties. MATERIAL AND METHODS Lake Yeniçağa, peatland was occurred around it, is located in a depressional area between Bolu Plain and Gerede Town. Lake Yeniçağa is not only tectonic but also affected from karstic occurrences. At first, organic soils around the lake were checked with random grid method and auger examinations based on land observations. Afterwards, five profiles representing the peatland were excavated. Soil samples taken from each horizon were dried to workable moisture content in laboratory conditions, then, they were sieved and fractured as 0-4 mm and 0-6.35 mm for physical analysis. Physicochemical analyse were carried out on 0-2.00 mm fraction. Moreover, undistributed soil samples were taken from the each of horizon in order to determine bulk density of soils in situ. In peat samples, fiber content was determined by (Soil Survey Staff, 1975) bulk density (U.S. Salinity Lab. Staff, 1954), moisture-tension values (De Boodt et al. 1973), mechanical analysis was done within the mineral part after combustion of organic fraction by hidrometer (Bouyoucos, 1951) and pipette methods (U.S.Salinity Lab. Staff, 1954), pH was measured in saturated medium and EC was determined in saturated medium extract (Kirven, 1986), organic matter was determined by (DIN, 1978). DISCUSSIONS Organic soils in the study area were formed on a flat land. Their formation result from the accumulation of decomposed organic residues in an anarobik conditions and decrease in water level within the time related to mineral sedimentation and organic matter accumulation. Therefore, organic soils in the region have an eutrophic (nutrient rich) character and they are classified as basin organic soils. Some physical and physicochemical properties of the soil samples taken from each horizon are given Table 3.1. The soil properties significantly change on account of profiles (Table 3.1). Organic matter ranges from 12.5 % to 91.5 %, fiber content ranges from 4.3 % to 91.5 %, bulk density changes from 0.09 to 0.78 g cm-3, pH and EC values ranges 5.38 to 7.92 and 0.50 to 3.80 dSm-1, respectively in Bolu-Yeniçağa samples. As we consider mineral matter content of organic soils after combustion, sand, silt and clay contents of soil samples range between 0.73 % - 3.92 %, 40.70 %, - 74.77 % and 24.15 % - 57.30 %, respectively. These substantial differences among the organic soil samples result from eutrophic occurance, botanical origin, decomposition degree, topography, differences in groundwater composition and land use management.  As we take into account peat samples as growing medium, some physical properties such as air capacity, easily available water (EAW) and water buffering capacity (WBC) with related to air-water balance have a great of importance. Those physical properties are affected from mainly particle size distribution of material (Çaycı et al., 1994). For this reason, those properties of peat samples as growing medium were determined in 0-4.00 mm and 0-6.35 mm fractions. Air capacity, easily available water and water buffering capacity values of the peat samples are given Table 3.2.  Verdonck (1984) classified growing media in five groups according to their air volume and easily available water content (Table 3.3). As we take into consideration this classification, the most suitable medium to plant growth is the third class. Eleven samples of totally 56 samples are included in this group. The ratio of this group to all samples is only 19.6 %. Fifteen samples are included in the second class according to Verdonck's Classification. The ratio of the samples in the second class to the all samples is 26.8 %. The rest of the samples are not suitable especially because of their low air capacities.  The most suitable peat samples can not show differences according to fraction size while relatively suitable samples are mainly included in 0-6.35 mm fraction. Other peat samples, unsuitable with respect to air-water balance, can be improved by mixing of different particle sizes. For example, as we examine the Table 3.2, 0-6.35 mm fraction of 4/4 sample, easily available water content is very high, can be mixed with 0-6.35 mm fraction of 2/6 sample having low easily available water, nearly at the rate of 50 %. The peat samples having low air capacities, also can be improved with application of various materials having high air capacity such as pumice and perlite. The second important property with respect to air-water balance is water buffering capacity. This value is desired almost 5-7 %. As we consider buffering capacities of the samples, it can be seen that a great part of samples has lower values than optimum values. It means that growing medium requires more frequent irrigation. As it can be seen from the results, the physical properties of Bolu-Yeniçağa peat as growing medium change significantly dependent on locations and depths. The regional producers, excavating peat from Bolu-Yeniçağa peatland, do not realize or consider those differences. The producers should take into consideration the properties of Bolu-Yeniçağa peat to evaluate it properly and produce a good quality commercial peat as growing medium. REFERENCES Ataman Y. (1988). Saksı kompostlarının bazı önemli fiziksel ve kimyasal özellikleri. Ankara Üniversitesi Zir. Fak. Yayınları No:82. Bouyoucos G.D. (1951). A recalibration of the hydrometer method for making mechanical analysis of the soil. Agronomy Journal, 43, 434-438. Çaycı G., Ataman Y., Ünver İ., Munsuz N. (1989). Distribution and horticultural values of the peats in Anatolia. Acta Horticulturae, 238, 189-196. Çaycı G., Baran A., Özkan İ. (1994). Tane büyüklüğünün peatin bazı fiziksel özellikleri üzerine etkisi. Ankara Üniversitesi Zir. Fak. Yıllığı, 44(1, 2):131-139. De Boodt M., Verdonck O., Cappaert I. (1973). Method for measuring the water release curve of organic substrates. Proceeding Symposium Artificial Media in Horticulture. 2054-2062. DIN, 11542. Torf für Gartenbau und Landwirtshaft. Kirven D.M. (1986). An industry viewpoint: Horticultural testing-is our language confusing. Hort. Sci., 215-217. Munsuz N., Ünver İ., Çaycı G. (1999). Türkiye suları. Ankara Üniversitesi Zir.Fak. Yayınları No:1505. Soil Survey Staff (1975). Soil Taxonomy. A basic system of soil classification for making and interpreting soil surveys. USDA. Agriculture Handbook No 436. Washington D.C. U.S. Salinity Lab. Staff (1954). Diagnosis and improvement of saline and alkali soils. USDA Agricultural Handbook, No.60, 160 s. Verdonck, O. 1984. New developments in the use of graded perlite in horticultural substrates. Acta Horticulture. 150. 575-581. |