SažetakGranulometrijski sastav tla (GST) jedan je od najvažnijih parametara fizičkih značajki tla. Određivanje GST najčešće se temelji na kombinaciji mokrog prosijavanja i pipetiranja, a razlike između pojedinih metoda temelje se na različitim tretmanima uzoraka u pripremi suspenzije za mokro prosijavanje i pipetiranje. Kako je do sada u mnogim laboratorijima korištena metoda pripreme suspenzije s Na-pirofosfatom (i još se uvijek koristi), opravdana je upitnost usporedivosti rezultata s rezultatima normirane metode (norma ISO 11277). S obzirom na specifičnosti dviju metoda, postavljena je hipoteza o postojanju razlika između istih, bilo na razini granulometrijskog sastava ili teksturne interpretacije. U svezi s navedenim, cilj rada je testirati razlike između dviju navedenih metoda.Istraživanje je provedeno na 67 uzoraka šumskog tla, od čega je 15 uzoraka iz njegovog površinskog dijela. Dobiveni rezultati istraživanja pokazali su da nema statistički značajne razlike između metoda za sve uzorke, kako iz mineralnog i iz površinskog dijela tla. Utvrđena je visoka korelacija između udjela svih istovrsnih frakcija određenih po različitim metodama.U interpretaciji teksturnih oznaka na temelju teksturnog trokuta utvrđena je značajna razlika između frakcije pijeska i frakcije praha, dok kod frakcija gline nije bilo statistički značajne razlike. Veći udjel frakcije pijeska utvrđen je interpretcijom na temelju teksturnih klasa po staroj metodi, dok je za prah obrnut slučaj.The purpose of this research was to comparison of two sieving and sedimentation methods for determination of particle size distribution (PSD). Until 2009, PSD was determined at the Faculty of Forestry in Zagreb by a sieve and pipette method after soil preparation using Na-pyrophosphate according to the Pedological manual (old method) (Škorić, 1965). Since the opening of the ecological-pedological laboratory at the Forestry Faculty in 2009, PSD determination has been performed according to the ISO 11277 (2009) Standard. The most important difference between the two methods is that according to the ISO 11227 Standard, pre-treatment is accomplished with hydrogen peroxide which oxidizes the organic matter, so that PSD is determined only in mineral soil particles, while according to the old method, the organic matter was not removed at PSD determination.The purpose of this research was to establish whether there was a difference in the results of PSD determination between the old method and the ISO 11277 Standard in the overall number of samples and particularly in the topsoil. Another goal was to test the difference in the textural interpretation of PSD results obtained by these two methods.For the needs of the analysis, 67 forest soil samples were taken from two areas in Croatia. The two methods were compared in order to determine whether there was a statistically significant difference in the total number of the samples. A comparison was also made to determine whether there was a statistically significant difference between the samples taken from the topsoil layer, since according to ISO 11277 the organic matter largely found in the surface soil part oxidizes.Statistical analysis and t-test revealed no statistically significant difference in any single fraction from the topsoil layer between the old method and ISO 11277. A high correlation was found in the topsoil layer for all the measured fractions (r = 0.98 for coarse sand, r = 0.96 fine sand, r = 0.94 coarse silt, r = 0.84 fine silt and r = 0.97 clay) as well as in the all established samples (r = 0.99 for coarse sand, r = 0.97 fine sand, r = 0.89 coarse silt, r = 0.88 fine silt and r = 0.97 clay).Based on the classification into three main fractions (sand, silt and clay) a higher percentage of sand and a lower percentage of silt was established by the old method compared with ISO 11277. This difference is directly reflected on textural interpretation. No statistically significant difference between the two methods was found for the clay fraction
