Abstract

Wood-based substrates are potential alternatives or amendments to traditional peat-based and pine bark substrates. Undesirable changes in substrate pH may result from the application of supplemental fertilizer required by some crops grown in wood-based substrates. Experiments were conducted to evaluate petunia growth and substrate pH in response to nitrogen (N) treatments applied as a nutrient solution to whole pine tree (WPT) and peat-lite (PL) substrates. Nitrogen treatments were applied as 100% ammonium (NH₄⁺ N), 100% nitrate (NO₃⁻N), or a combination of both in various proportions. The pH range of WPT substrate widened considerably over time among the N treatments, while a change in substrate pH was minimal for PL substrate during the same period. Generally, 100% NO₃⁻N and 100% NH₄⁺ N resulted in the highest and lowest substrate pH, respectively, regardless of substrate. Greater shoot dry mass was obtained in PL substrates compared with WPT substrates. Maximum shoot dry mass and flower count with ‘Celebrity Rose’ petunia were obtained with the mixed N-form treatments in both substrates. Greater substrate air space and total porosity was associated with WPT substrates compared with PL substrates, the latter having greater container capacity.