AVAILABLE AMMONIUM AND NITRATE LEVELS OF HIGHLAND SOIL ORDERS IN TURKEY AT DIFFERENT FREEZE-THAW CYCLES

Turkey has diverse climate zones and therefore, number of the freeze-thaw process (FTCS) varies from one region to another. The number is increasing especially in high shear and cold regions and such cycles have significant impacts on available nutrients for plants. The present study was carry out with 5 major soil groups (Vertisol, Chernozem, Andosol, Leptosol and Calcisol) under field conditions to determine the effects of repeated freeze-thaw processes on available nitrogen (ammonium and nitrate) (NH4-N and NO3-N) levels of the soils. Five different nitrogen doses (0, 100, 200, 300 and 400 mg kg(-1)) were applied to 5 major soil groups in three replications. While the first freeze-thaw process usually increased the ammonium and nitrate nitrogen, the second and further freeze-thaw processes usually reduced available N contents of soils for plants. Current findings revealed that available NH4-N and NO3-N levels greatly depended on number of freeze-thaw cycles and increasing number of cycles decreased available soil nitrogen levels for plants, thus required higher nitrogen fertilizer levels to supply sufficient nitrogen during the plant-growth periods.