ARS | Publication request: Viable Alternative Substrate Components for Use in Nursery and Greenhouse Production

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 1, 2010
Publication Date: February 25, 2010
Citation: Witcher, A.L., Fain, G.B., Blythe, E.K., Spiers, J.M. 2010. Viable Alternative Substrate Components for Use in Nursery and Greenhouse Production. Meeting Proceedings. 26:57-59.

Interpretive Summary: Peat moss is the predominant component of most substrates used for greenhouse crop propagation and production. Future environmental policies, adverse weather conditions, and rising transportation costs can contribute to a limited peat moss supply and drive up the cost of peat moss for American growers. Processed whole pine trees (WPT) have been identified as a replacement for peat. Whole pine tree substrates require additional fertilizer compared with traditional substrates and the application of additional fertilizer may lead to new production problems, such as an adverse affect on substrate pH or increased concentrations of nutrients in runoff. Separate experiments were conducted at the Southern Horticultural Laboratory in Poplarville, MS to evaluate WPT substrates. The objective of the first experiment was to evaluate the effects of substrate and irrigation volume on substrate pH and Boston fern growth. We demonstrated WPT substrates could be substituted for a peat-lite substrate to produce a quality Boston fern crop with little to no change in irrigation volume. The objective of the second experiment was to evaluate the effects of nitrogen form and concentration on substrate pH and petunia growth. We concluded that nitrogen form affects substrate pH similarly in WPT and peat-lite substrates, yet to a greater degree in a WPT substrate. Results from these experiments will be used by scientists evaluating alternative substrates, extension agents, and growers interested in using wood-based substrates.

Technical Abstract: Peat-based container substrates are widely used for greenhouse crop production. A variety of alternative materials have been evaluated due to uncertainty over the cost and availability of Canadian peat moss. Processed whole pine trees (WPT) have been identified as a replacement for peat due to the widespread availability and proximity to greenhouse producers in the Southeastern United States. Investigators of previous experiments have demonstrated that WPT substrates require additional fertilizer compared with traditional substrates. The application of additional fertilizer may adversely affect substrate pH or increase the nutrient content of irrigation runoff. Separate experiments were conducted at the Southern Horticultural Laboratory in Poplarville, MS to evaluate WPT substrates. In the first experiment, three WPT substrates and a peat-lite (PL) substrate were irrigated with either a high or low irrigation volume. Plant growth was similar among all substrates within a specified irrigation volume, high or low. Substrate pH was significantly lower in the WPT substrate compared with the PL substrate at project termination, although no adverse effects on plant growth were visible. We demonstrated WPT substrates could be substituted for PL substrates with little to no change in irrigation volume. In the second experiment, petunia plants in a WPT substrate or PL substrate were fertigated with one of five nutrient solutions composed of ammonium and nitrate at varying proportions. Substrate pH was affected to a greater degree by nitrogen form in the WPT substrate (pH 5.2 to 7.7) compared with the PL substrate (pH 5.0 to 5.9). We concluded that the buffering capacity of the WPT substrate should be increased to reduce changes in pH.