Laboratory Bioassay and Greenhouse Evaluation of a Pine Tree Sub- strate Used as a Container Substrate

Bioassays with tomato and lettuce seeds and three plant experiments with marigold (Tagetes erecta L.) ‘Inca Gold’ were conducted in the laboratory and greenhouse, respectively, in order to investigate possibilities of determining and mitigating the effects of phytotoxins in pine tree substrate (PTS). PTS is produced by grinding loblolly pine tree (Pinus taeda L.) logs, and using as horticultural growing substrate. PTS extracts obtained with cold and hot water reduced the germination rate and radicle growth of tomato and lettuce. After the washing, an improvement was monitored for radicle length of both species. The germination index supported the data of radicle length showing a better performance after the substrate washing. Radicle growth of tomato in extracts from PTS used in a plant growth experiment was improved after leaching PTS six times. The performance of marigold plants was similar to bioassays with tomatoes and lettuce. Marigold growth was improved by pretreatments of PTS. Some of these pretreatments could be recommended for use in the manufacturing process for PTS or from growers before planting. However, the best results were shown in a commercial peat-lite substrate.