PHYSICAL-PROPERTIES OF 2-COMPONENT GROWTH MEDIA BASED ON SPHAGNUM PEAT AND THEIR IMPLICATIONS FOR PLANT-AVAILABLE WATER AND AERATION

The physical properties, in particular the water retention characteristics, of two-component growth media based on low-humified Sphagnum peat were studied. The high water retention of pure peat, which is further increased by shrinkage of the medium at desorption, yielded low air-filled porosity at high matric potentials (greater than or equal to -1 kPa). The addition of coarse perlite to peat decreased the shrinkage markedly and also tended to increase the low saturated hydraulic conductivity of peat, which had initially been rather low. In all media studied, the amount of water that is easily available to plants (water content retained between -1 and -10 kPa matric potential) was relatively high. In peat that contained half repellent rockwool or hydrogel, this water retention was, however, markedly lower. Between -10 and -50 kPa matric potential, water retention was rather low in all media (< 10%). Within the lowest matric potential range studied (-50 to -1500 kPa), water retention was considerably elevated in peat that contained half hydrogel. The implications of the physical properties of the media for plant-available water and aeration in the media are discussed.