ARS | Publication request: Factors affecting early seedling development in whole pine tree substrates

Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: December 11, 2011
Publication Date: N/A

Interpretive Summary: Wood-based substrates can be successfully used in nursery and greenhouse crop production, yet have not been extensively evaluated for seed or cutting propagation. Wood-based materials, such as processed whole pine trees (WPTs), contain organic compounds that can be phytotoxic to sensitive species and inhibit seedling root growth. A Phytotoxkit™ test and a seedling growth test were conducted to determine their effectiveness for identifying potential phytotoxicity in WPT. In our study, seed germination and early root development in sensitive species were inhibited by fresh pine needles, but no such inhibition was observed in aged or fresh WPT. However, a disparity in seedling root development between WPT and a peat-lite (PL) substrate suggests factors other than phytotoxicity are involved. Further investigation into the affects of substrate physical properties and root development is required before making production recommendations for growers. Researchers can use this information when evaluating WPT or other wood-based substrates for seedling production.

Technical Abstract: Wood-based materials derived from pine trees, such as processed whole pine tree (WPT), can be a viable option for producers looking to offset pine bark or peatmoss usage in container substrates. Reduced root development of stem cuttings rooted in WPT compared with pine bark (PB) has been observed, but the factors involved must be identified in order to develop corrective measures. Two experiments (Phytotoxkit™ and seedling growth test) were conducted for identifying phytotoxicity in WPT, a potential contributing factor to reduced root development. Substrates evaluated in the Phytotoxkit™ included a reference soil (RS), aged (WPTA) and fresh (WPTF) whole pine tree, aged (PNA) and fresh (PNF) pine needles, PB, peatmoss (PM), and saline pine bark (SPB). Substrates evaluated in the seedling growth test included WPTA, WPTF, PL (3 peatmoss : 1 perlite : 1 vermiculite by vol.), and PB. The Phytotoxkit™ did not reveal any significant concerns regarding phytotoxicity resulting from organic compounds present in WPT (aged or fresh), yet PNF can be phytotoxic to sensitive plant species. In the seedling growth test, greater root development occurred in PL, which had the greatest container capacity and lowest air space. The goal of future research will be to evaluate the relationship among substrate physical properties, water availability, and root development in WPT.