Pine wood chip aggregates for greenhouse substrates: Effect of age on plant growth

Recent work has shown the potential for pine wood (Pinus taeda L.) to be a suitable and cost-effective organic alternative to perlite in horticultural substrates in the United States. The objective of this research was to determine the effect of pine wood chip (PWC) aggregate age on young plant growth. Pine trees were harvested and chipped in a wood chipper which created coarse wood chips (1 L × .2 W × .9 H – cm). Wood chips were then hammer-milled through a 6.35 mm screen to produce PWC (0.11 L × 0.4 W × 0.2 H – cm). Phytotoxicity germination bioassays were used to determine the potential presence and effect of phytotoxins released from substrates amended with fresh or aged PWC and the effect on growth of cucumber (Cucumis sativus L. ‘Muncer’), tomato (Solanum lycopersicum L. ‘Ace 55’), and radish (Raphanus sativus L. ‘Easter Egg’). Germination count and seedling dry mass were similar among peat-based substrates formulated with 20, 30, or 40% fresh or aged PWC. Growth trials of three popular bedding plants including: celosia (Celosia plumose L. ‘Fresh Look Mix’), impatiens (Impatiens walleriana Hook f. ‘Super Elfin Bright Orange’), and African marigold (Tagetes erecta L. ‘Moonsong Deep Orange’ were conducted in substrates amended with 20% perlite (v/v) or 20, 30, or 40% fresh, or 4-monthed aged PWC aggregates. Results from germination bioassays conclude no visual or detrimental effects on seedling emergence, growth, or substrate chemical properties. In plant growth trials, the plant response was varied (by species and by aggregate type and percent) but the overall trends indicated in most cases as the percent PWC increases, pH increases and EC decreases. Plant shoot growth was often as large in fresh PWC-grown plants compared to aged.