Peatmoss, a commonly used substrate component, is facing numerous challenges to remain a sustainable option for horticultural production. Due to mounting factors such as weather-limited harvesting, increasing transport costs, waning public acceptance, and now potential international tariffs, many are searching for alternative materials to replace some of the peatmoss in their operations. Biochar is one such alternative that may present numerous benefits as a peat alternative in container production. Biochar is the product of the pyrolysis of biomass (commonly agricultural residues) in an oxygen limited environment, resulting in a product that has increased porosity, increased water and nutrient retention, and can be produced regionally from a number of sources. Incorporating biochar into container production can reduce peat use and improve nutrient retention. However holistically blending can prove costly and alter the substrate physical properties, requiring major changes to production practices, an obstacle that can be considered a barrier. The use of stratification has been shown to successfully reduce peat use while maintaining highly productive growing conditions. With stratification, growers can incorporate alternative materials strategically in the container while limiting the associated costs. Therefore, this study was designed to evaluate the effect of sugarcane bagasse biochar on nutrient retention in both stratified and non-stratified peat-based container systems. Nine peat-based substrate treatments were utilized in this study, with either the entire container filled with peat-based substrate or stratified above a pine bark or hammermilled wood fiber. Within each substrate, sugarcane bagasse biochar was amended at 0 (control) or 10% of the container volume, by either blending throughout the container or blending at 20% upper strata only (equivalent to 10% by vol. overall). Petunia plugs were planted into 3.8 L containers filled with each of these different substrate treatments. The plants were placed on two different fertilizer regimes, with plants receiving either 100 ppm or 300 ppm fertilizer once a week. Leachate was collected biweekly to assess the impact on nutrient retention. Plant growth and nutrition were assessed. The incorporation of biochar has not significantly impacted plant growth; however, it has improved nutrient retention. Biochar improved nutrient retention in the plants stratified with wood fiber in both the high and low fertilizer regimes, while improving nutrient retention in stratified bark in the high fertilizer regime. The results indicate that strategic inclusion of biochar may reduce fertilizer application frequency.
