2018 ASHS Annual Conference

Stability of substrate pH is a crucial factor in managing nutrition of container-grown crops. Substrate pH is one of the chemical parameters that influences nutrient availability but may change rapidly under some cultivation practices. Fluctuating pH can cause problems with managing nutrition in the crop. High pH buffering capacity of substrates is needed to prevent rapid changes that may lead to losses in quality and quantity of cultivated plants. Soil buffering capacity is well known and depends mainly on the clay and organic matter content, but in organic soilless growing media factors influencing this parameter are not well understood. To assess the pH buffering capacity of pine bark in comparison to peat moss, four pine bark substrates with different size particles ranging from fine to coarse (< 0.3 cm, < 0.6 cm, < 1.3 cm, and < 1.6 cm), were collected from a pine bark supplier. Three replications of each bark substrate and peatmoss with weights equivalent to 100mL were placed in 250mL jars and filled with 100mL of and acid or base solution. Acid and base solutions were prepared with HCl and NaOH, respectively, at concentrations ranging from 0 to 50 meq^.L^-1 in 10 meq^.L^-1increments using deionized water (18 MΩ). Jars were fitted with lids and stirred for 10 minutes. Stirring was repeated after 24 hours and pH was measured immediately to prepare pH buffering curves for each substrate. Peatmoss had the highest buffering capacity. Pine bark substrates differed slightly among each other but showed lower pH buffering capacity compared to peatmoss. Moreover, all pine bark substrates tended to have higher buffering capacity for bases than acids. These data can be used to better understand how substrate type and particle size affect changes in pH over time during plant cultivation.