610 Evaluation of Sawmill Residue as a Component of Nursery Potting Mix

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The standard mix used by most nurseries consist of a 9 pine bark: 1 sand. With the ever-increasing cost of bark, nurseries are looking for an alternative. Sawmill residue may hold potential utility as part of a potting mix. Although sawmill residue is highly variable, it can serve as soil bulk as well as an organic medium. The purpose of this study was to determine if old sawmill residue not treated by pathogen-free requirement procedures could be used “as is” as part of a nursery soil mix. For this study, a sample, a typical conglomerate of undetermined wood chips, bark, and soil particles, was obtained from an “old pile” (just how old is not known) of sawmill residue. To determine how this sample would function in a nursery bark/sand mix, tests were run on its physical properties of pore space and water-holding capacity. The sawmill residue had the following characteristics: a mean 44.2% porosity capacity, 23.4% air space, and 20.8% water holding capacity. A standard fertilizer and lime amendment package was added to the sawmill residue in the same rates as a regular nursery mix. The sawmill residue and the standard nursery mix were then blended according to the treatment percentages. The treatments were sawmill residue/standard nursery mix 0/100, 10/90, 30/70, 60/40, and 100/0. The Ilex crenata `Compacta' liners were planted into standard 1-gallon nursery pots filling to just below the rim. The pots were randomly placed on a well-drained rock surface in full sun. No additional fertilizer was used and watering was done as needed. Plants were grown for 1 year. Visual assessments were made throughout the growing period and at harvest. There was no visible difference in any of the treatments as far as overall growth was discerned. The plants were of uniform height and width showing consistent, even growth and good leaf color. Root system growth and development were evaluated visually and over all treatments were uniformly good. No root problems were noted. There was not any plant loss in any treatment over the entire study. Each plant was cut at the soil line and dried for 24 hours at 1150 °C. Dry weights were taken after the plant material had cooled for 4 hours. Results were based on four plants per treatment times four replications for a total of 16 plants per treatment. There was not any measurable growth difference in dry weight among treatments 1, 2, 3, and 4 [sawmill residue/standard nursery mix 0/100 (41.03 g dry weight), 10/90 (39.83 g dry weight), 30/70 (38.98 g dry weight), 60/40 (37.42 g dry weight)]. However, treatment 5 [100/0 (31.03 g dry weight)] was significantly lower when compared to the remaining four treatments. The lower dry weight may be attributed to the 100% sawmill residue being too heavy and not well-drained enough. However, the roots did not show any damage from being too wet. Further work is being done with the sawmill residue.