C. de Kreij, S.S. de Bes
Several methods for determination of dry bulk density, wetness ratio, volume fraction water and air, are compared in order to get an impression of their differences and possibilities. The methods differ in the way the cylinder is filled - with or without compaction - and in the way the substrate is wetted; water is sucked up or the substrate is flooded from beneath. Although the mean values differ, very high correlation coefficients are found, except for the 1:1.5-volume method, which was not developed for physical analysis, and a method, in which the substrate is dried before filling a cylinder, and the wetness ratio is calculated from the dry bulk density.

When extremely wet substrates are filled in a cylinder and compressed, the wetness influences the later in that cylinder found volume air content at a certain pressure head. The higher the wetness the lower the volume air content.

The densities of peat substrates occuring in pots for pot plant production and packs for bedding plants are approximately 1.2 respectively 1.5 times lower than in a cylinder, which is filled, compacted by several times a free fall and pressed twice with 10 kPa. So, to imitate physical circumstances in potplant and bedding plant production, the substrate should not be compressed so much.

A good method is filling a cylinder without artificial pressure and achieve a natural assesment by flooding from beneath.

de Kreij, C. and de Bes, S.S. (1989). COMPARISON OF PHYSICAL ANALYSIS OF PEAT SUBSTRATES.. Acta Hortic. 238, 23-36
DOI: 10.17660/ActaHortic.1989.238.2

Acta Horticulturae