ISHS Acta Horticulturae 481: International Symposium on Growing Media and Hydroponics
EFFECT OF THE PACKING DENSITY ON THE MECHANICAL IMPEDANCE OF ROOT MEDIA |
| Authors: | A. N. Kämpf, P. Allen Hammer, T. Kirk |
| Keywords: | physical properties of substrates, compaction, penetrometer, sand, perlite, Sphagnum peat, coir, Fafard Mixture 2P® |
| Abstract:
The force applied to fill containers with growing media in greenhouses results in varying packing densities. The physical properties of the medium also vary with packing densities. The influence of the packing density on the penetrability of five media (sand, perlite, Sphagnum peat, coir and a commercial mixture Fafard 2P ® (60% S. peat + perlite) was studied. Four levels of compaction were applied: 1. loose (no compaction); 2. firmed (the bulk density determined in lab); 3. compacted (middle point between levels 2 and 4); 4. “maximal” compaction that could be obtained by hand. The substrates were analyzed at the moisture content as received and at container capacity. The pressure needed to penetrate a pointed metal probe of 6.5 mm diameter vertically 3.5 cm into the medium was measured by a penetrometer. The mechanical impedance significantly increased for all substrates with increasing packing density. A significant interaction between the moisture level and the applied packing density was observed. Loosely packed samples showed higher mechanical impedance when the moisture content was at container capacity as compared with the drier samples, with exception of Fafard 2P®; maximal compacted samples showed higher mechanical impedance at the lower moisture content. | |
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