2018 ASHS Annual Conference

Soilless substrates were initially developed with high porosity to balance air to water ratio and ensure good drainage. As a result, researchers and allied suppliers tend to rely heavily upon “static” physical properties (water holding capacity and air filled porosity) to prescribe substrate recommendations which may be unachievable physical states in production such as saturation. Due to the reliance upon these minima and maxima values, conventional soilless substrates used by the nursery industry may not be efficient in regards to water resource management. Our research manipulated the hydrology of pine bark-based soilless substrates through fractioning by particle size or blending with fibrous materials (Sphagnum peat and coir) to yield varying substrate dynamic, hydrological parameters while maintaining static physical properties. We were successfully able to alter the unsaturated hydraulic conductivity of the soilless substrates while holding static physical properties similar. Containerized crops were then grown in pine bark-based substrates with altered hydraulic properties at optimal (Hibiscus rosa-sinensis ‘Fort Myers’) and sub-optimal (Hydrangea arborescens ‘Anabelle’) substrate water potentials. The increased substrate hydraulic conductivity allowed for added hibiscus growth and vigor, as well as increased water use at optimal substrate water potentials (-50 to -100 hPa). At suboptimal substrate water potentials (-100 to -300 hPa), increased substrate hydraulic conductivity allowed for salable hydrangea crops to be produced with < 6.5 L water which resulted in poor crop performance in conventional pine bark substrates. It was also determined that fiber type recommendations should be influenced by growing irrigation parameters. Peat addition yielded the greatest increase in hydraulic conductivity at optimal water potentials and coir yielded the greatest increase in hydraulic conductivity at sub-optimal substrate water potentials. No observable relationship existed between saturated hydraulic conductivity and production hydraulic conductivity indicating the easily measured saturated hydraulic conductivity is not a good indicator of crop water relations in soilless systems. Thus, a shift to utilization of dynamic substrate hydraulic properties can provide beneficial information to researchers and allied suppliers by enabling more informed recommendations based upon water flux that mimics actual production conditions. Moreover, optimizing the hydrology of pine bark-based substrates resulted in the water efficient production of ornamental container crops under both optimal and sub-optimal irrigation regimes. Aside from benefits associated with increased water resource management, and potential reduction in costs associated with subsequent fertility requirements, production time was reduced.