AIR-FILLED POROSITY, GAS RELATIVE DIFFUSIVITY, AND TORTUOSITY - INDEXES OF PRUNUS X CISTENA SP GROWTH IN FEAT SUBSTRATES

A 2-year experiment with Prunus x cistena sp. was conducted in pots us ing seven substrates composed of various proportions of primarily peat , compost and bark. Feat substrates significantly affected root and sh oot dry weight. Water desorption characteristics and saturated hydraul ic conductivity were measured in situ to estimate the pore tortuosity factor and the relative gas diffusion coefficient. The pH, electrical conductivity, C/N ratio, total and hydrolyzable N, as well as NO3--N a nd NH4+-N in solution were also measured, Estimates of the physical pr operties suggest that a lack of aeration limited plant growth. Plant g rowth was significantly correlated with both the gas relative diffusiv ity and the pore tortuosity factor. Among the chemical factors, pH and soil nitrate level were also correlated with plant growth. No signifi cant correlation was found between plant growth and air-filled porosit y or any other measured chemical properties. This study indicates that an index of gas-exchange dynamics could be a useful complementary dia gnostic tool to guide substrate manufacturing.