ARS | Publication request: Assessing phytotoxicity in fresh and aged whole pine tree substrates

Submitted to: Plant Propagators Society Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 1, 2011
Publication Date: N/A

Interpretive Summary: Whole pine tree (WPT) substrates can be used for horticulture crop propagation and production, although optimum plant growth may require using increased fertilizer rates and/or storing substrates for a period of time before use. Reduced plant growth in wood-based substrates has been attributed to a variety of factors, including phytotoxity. A detailed method for evaluating the phytotoxic potential of wood-based substrates has not been identified. A Phytotoxkit™ and seedling growth test were conducted to determine their effectiveness for identifying potential phytotoxicity in WPT. This study demonstrated fresh pine needles negatively affected seed germination and initial root growth of sensitive plant species compared with aged pine needles, while such detrimental effects were less pronounced between aged and fresh WPT. The Phytotoxkit™ and seedling growth test could be useful tools for testing substrates in a laboratory setting when reproducible tests are required, while the seedling growth test could be conducted by producers wanting to evaluate potential substrates.

Technical Abstract: Reduced plant growth in wood-based substrates has been attributed to a variety of factors, including phytotoxity. A detailed method for evaluating the phytotoxic potential of wood-based substrates has not been identified. Two biological assays (Phytotoxkit™ and seedling growth test) were conducted for identifying phytotoxicity in WPT, while examining the potential of such methods for testing other alternative substrates. 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, pine bark (PB), peat moss (PM), and a saline pine bark (SPB) substrate. Substrates evaluated in the seedling growth test included WPTA, WPTF, PB, and a peat-lite (PL) substrate. The Phytotoxkit™ revealed some plant species may be sensitive to compounds present in PNF. The greatest germination/emergence rate and root length varied by species in regard to WPTA and WPTF; therefore, factors other than phytotoxicity affected seedling development in WPT. In the seedling growth test, total root length was greatest in the PL substrate for all three species, while substrate air space was lowest in the PL substrate.