Date of Award

Summer 2019

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Anissa Poleatewich

Second Advisor

Rebecca Sideman

Third Advisor

Ryan Dickson

Abstract

Sphagnum peat moss is the most commonly used soilless substrate component to produce containerized greenhouse bedding plants. Perlite is often blended with peat to achieve desirable physical properties. Increasing transportation costs and occasional shortages of peat and perlite have increased the need for alternative substrate components. Wood fiber materials produced from the extensive secondary processing of pine wood chips are a potential partial alternative to peat and perlite. Incorporating wood materials into soilless substrates may result in nitrogen immobilization, increasing the amount of fertilizer nitrogen needed during production. Wood materials also have a naturally higher pH compared to peat, requiring less limestone to adjust initial pH and leaving unknown effects on the substrate’s ability to buffer against pH changes. The objectives of this research were to evaluate the effects of wood fiber soilless substrates on plant performance, nitrogen requirements, and pH buffering capacity. Sphagnum peat-based substrates amended with 30% (by volume) coconut coir, pine tree materials or a commercial wood fiber material were compared for their effects on plant performance of container-grown petunia (Petunia × hybrida Mill.). There was a slight reduction in shoot growth of plants grown in pine tree substrates and wood fiber compared to plants grown in peat alone; however, plant performance was not significantly affected. In a second study, plants grown in substrates made up of sphagnum peat:pine tree materials (50:50) or sphagnum peat and a commercial wood fiber product (50:50) were evaluated for their nitrogen requirements compared to a 100% sphagnum peat control. Plants grown in 50:50 peat wood fiber did not reach comparable growth to plants grown in peat alone, even when fertilized with increased (400-ppmN) nitrogen concentrations. Finally, substrates made up of sphagnum peat and wood fiber (80:20, 60:40, 40:60, 20:80) were compared to substrates made up of sphagnum peat alone and a peat and perlite control for effects on pH buffering and nutrient management with container-grown impatiens (Impatiens walleriana). This work shows the feasibility of amending soilless substrate with ~20-40% wood fiber (by volume) without drastic effects on plant performance or the need to change any cultural practices. Results from this work show that surpassing ~40% incorporation rate affects plant performance where it starts to suffer. This is potentially the result of physical properties, pH buffering or the presence of phytotoxic compounds present in the material.

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