Peat shrinkage during drying according to particle size

S. Durand, P. Boivin, J.-C. Michel
For non-rigid porous materials like many soils and growing media, the ability to shrink during drying should be considered because it modifies the total pore volume and pore size distribution, and then leads to changes in water and air properties. Many studies have shown that the physical properties of growing media depend in part on their particle size. However, no study has been focused on the relationships between shrinkage and particle size for growing media so far. A milled peat (H3 – H6) was fractionated by wet sieving into six particle size fractions, on which shrinkage curves using Hyprop systems coupled to Linear Variable Displacement Transducer (LVDT) were performed for simultaneously measuring water content, water potential, and total volume during a drying process. The results were expressed in void and water ratios as a function of water potential. The shrinkage curves suggested two types of physical behavior, differentiated by the presence or not of an initial shrinkage in the range of higher water potentials (from saturation to a maximum of -100 hPa). The initial shrinkage only concerned the finest particle size fractions, and was characterized by little or no air entry in the porosity. It progressively decreased with increasing particle size and was not reported for >2 mm particle size fractions. Once the finest particle size fractions consolidated, but also for the other coarser particle size fractions, drying was accompanied by the absence or a very low shrinkage up to water potentials around -200 to -300 hPa. These previous drying phases refer to the drainage of interparticle porosity, whereas a last phase of shrinkage corresponding to that of intraparticle porosity was observed for lower water potentials. This study thus revealed a significant shrinkage for fine particle size distribution materials over the range in water potentials of interest with regard to irrigation management, confirming the importance to assess shrinkage as one of the relevant indicators of physical properties.
Durand, S., Boivin, P. and Michel, J.-C. (2024). Peat shrinkage during drying according to particle size. Acta Hortic. 1389, 27-32
DOI: 10.17660/ActaHortic.2024.1389.3
pore volume, structure, horticultural substrate, growing media

Acta Horticulturae