ROLE OF FREEZE-THAW CYCLES IN AVAILABLE Fe LEVELS OF SOME HIGHLAND SOIL ORDERS

Frequency and efficiency of freeze-thaw cycles (FTTCs - freezing and thawing treated cycles) are increasing over soils of cold regions or high altitudes as a natural outcome of global warming. Such cases result in significant changes in available macro and micro nutrient contents of soils. Very little information is available about the effects freeze-thaw cycles have on the availability of soil micronutrients. Therefore, the present study was conducted to determine the effects of frequency of freeze-thaw cycles on available micro nutrient contents of Pellustert, Argiustoll, Haplustept, Fluvaquent and Calciorthid large soil orders of Northern Turkey. Results revealed significant effects of freeze-thaw cycles on available micro nutrient contents of soils mostly based on soil characteristics. The highest Fe content was observed in step 3 of Pellustert soil order (Step 3; each soil was kept at -10, -15, and -20 degrees C for a month, at -10 degrees C for 15 days, -5 degrees C for 15 days, 0 degrees C for 15 days, then thawed at +2.5, +5, +7.5 and 10.0 degrees C for 18 hours. This freeze-thaw cycle was repeated 3, 6, and 9 times). It was concluded that the effects of freeze-thaw cycles on Fe availability varied mainly based on soil characteristics and increased frequency of freeze-thaw cycles increased Fe-fixation to soil.