Evaluation of Wood Fibers Derived from Different Tree Species and Processing Methods on Crop Growth and Microbial Activity in Soilless Substrates

Soilless culture use is expanding as arable land and viable fumigants have decreased in availability. This has subsequently increased the demand for soilless substrates for container crop production. The primary component in most soilless substrates is Sphagnum peat moss, which is considered unsustainable due to the extensive time it takes to produce and the release of large amounts of carbon into the atmosphere during harvesting. Research into viable peat moss amendments to reduce reliance on this relatively non-renewable material has become a necessity. The most promising amendment that has been accepted in the horticulture industry as a viable amendment is wood fiber. However, there is still concern surrounding characteristics of wood fiber, such as nitrogen immobilization. Nitrogen immobilization is when microorganisms will breakdown wood fiber by consuming carbon and utilizing nitrogen, which can cause plant nutrient deficiencies. This process can be influenced by many factors, including moisture, temperature, the processing method used for the wood material, and the tree species in which the wood fiber was derived from. To expand the research on wood fibers and how these different factors impact the biological stability of wood fiber substrates, the following thesis was conducted. Three projects were formulated to test wood fibers derived from six different tree species (Abies concolor, Calocedrus decurrens, Pinus lambertiana, Psuedotsuga menziesii, Pinus ponderosa, and Pinus taeda) and two different processing methods (disc-refining and hammermilling) under different moisture and temperature levels. The biological stability of the substrates was tested by assessing CO2 respiration rates and microbial community abundance, and growth trials were conducted to evaluate plant health and development. It was concluded that tree species, moisture level, temperature, and wood fiber processing influence biological stability of substrates and crop health. A commercial 85:15 peat:perlite substrate amended with x 30% (vol.) hammermilled Calocedrus decurrens and Abies concolor wood fibers produced comparable crops to a 100% peat:perlite control substrate, and crops grown in a hammermilled wood-amended substrate at low root zone temperatures performed better than crops grown in a disc-refined wood fiber-amended substrate at high root zone temperatures. The results from this thesis gave insight into how the biological stability of different tree species and processing methods of wood fibers may influence crop performance in a greenhouse and outdoor nursery environment.