The term "substrate for plants" refers to the growth medium used in cultivation in containers, often resulting from the mixture of materials. The final quality depends on the physical and chemical attributes of each component and the interaction among them, which need to be characterized. Although the reference works are unanimous including volumetric density for substrate characterization, the interpretation of reports from different laboratories is difficult, because they use different methods or variations of the same method. In addition to the differences between methods, there might be other causes of variation in the achievement of results from a single sample. This work aims to demonstrate two of the causes of variation in the determination of density by volume: 1) the method of analysis [method of double ring (CEN), the method used by the industry (IND) and method of auto compact (AUTO) of substrate dust] of coconut, washed sand of river, peat brown in natura and Plantmax® for horticulture; 2) and the initial level of humidity (0.62, 0.69 and 0.72 g/g) in in natura samples of peat brown. The density values, determined by the AUTO, represented about 20% more than the values determined by IND; relations between the AUTO and CEN methods as well as CEN and IND were not uniform, depending on the material. Initial moisture of the sample also represents the cause of variation in the results.
self-compacting; double ring
