Mehanički sastav tla (MST) je postotni maseni udio primarnih čestica tla (pijeska, praha i gline). Jedna je od najvažnijih značajki tla, a laboratorijski se određuje nakon disperzije strukturnih agregata tla, i to najčešće različitim kemijskim sredstvima, a ponekad destiliranom vodom. Određen je MST 20 uzoraka (modioficiranom metodom HRN ISO 11277:2011), s tim da se svaki uzorak analizirao zasebno nakon dezagregacije Na–heksametafosfatom (Na–H) i Na–pirofosfatom (Na–P). Cilj je bio utvrditi postoje li značajne razlike u rezultatima analize, obzirom na izbor sredstva za dezagregaciju. Zaključeno je da Na–H i Na–P ne djeluju sasvim jednako na dezagregaciju, što u nekim slučajevima može utjecati na izmjereni udio pojedinih frakcija (rjeđe i na teksturnu oznaku tla). Daljnjim istraživanjima treba ispitati utjecaj ovih, ali i drugih, disperzivnih sredstava na rezultate analize MST, i tona uzorcima različite teksture, te različitih sadržaja humusa, Ca-karbonata i seskvioksida.

Soil particle size distribution (PSD) is the weight percentage of primary soil particles (sand, silt, clay).As one of the key soil features, it is determined in the laboratory after dispersing soil aggregatesusing mostly various chemical agents and sometimes distilled water.PSD of 20 soil samples was determined by modified HRN ISO 11277:2011, with each sample analyzed separately after using Na-hexametaphosphate (Na-H) and Na-pyrophosphate (Na-P). The aim was to testif there are significant differences in the results of the analysis, regarding the use of different dispersants. It is concluded that the effect of Na-H and Na-P on soil dispersion isnot completely equal. In certain cases, this can affect the measured weight percentage of some soil fractions (more rarely, also the soil textural name). Further studies should test the impact of these and other dispersants on PSD analysis, on soils with different texture, and varying contents of humus, Ca-carbonate and sesquioxides.