Organic wastes for improving soil physical properties and enhancing plant growth in container substrates

Increasing rates (5, 10, 25 and 40% v/v) of 6 sources of organic wastes were substituted for peat to assess changes in the physical properties of peat-perlite substrates and investigate the relationship between plant response and these properties. Wastes were either fresh or composted bio-filter sludge (FBF and CBF), sewage sludge (FSS and CSS), and de-inked paper sludge (FDP and CDP). Geranium plants (Pelagornium x hortorum 'Orbit Hot Pink') were grown in the substrates. Growing substrates' saturated hydraulic conductivity (K_s), airfilled porosity (f_a), pore tortuosity (τ), and relative gas diffusivity (D_s/D_o) all increased linearly (p = 0.0001) as the rate of organic wastes increased. Geranium plant height (PHT), shoot dry mass (SDM) and root dry mass (RDM) were either linearly or quadratically decreased (p = 0.0001) as the amount of waste increased in the substrates. During both growing seasons, Geranium SDM and RDM were either linearly or quadratically correlated with D_s/D_o and τ. Organic waste types and their rate of application strongly affected the aeration status of the substrates. D_s/D_o and τ better expressed the relationship between plant growth and the physical conditions of the root zone.