2018 ASHS Annual Conference

Pine bark is the dominant component of soilless substrates in the eastern U.S. for producers or woody ornamental crops. The low pH of the unbuffered pine bark substrate is commonly adjusted with a lime material in order to promote proper nutrient uptake and ensure general plant health to avoid abiotic disorders. Our objective was to evaluate the long-term effect of pulverized dolomitic, pulverized calcitic, ground dolomitic, and granular calcitic lime at rates of 0, 0.5, 2.5, 4.5 and 6.4 kg·m^-3 on pH of a < 15.9 mm aged pine bark substrates over 267 d. Each substrate was also amended with 5.5 kg·m^-3of an 8-9 month 18N-2.2P-10K coated, controlled-release fertilizer. All substrates were used to pot Ilex crenata `Bennett’s Compacta´ into 2.8 L containers. The main effect of lime material on substrate pour-through pH was not significant; however, the significance of sampling time x rate x material indicates the interaction of the three factors may provide opportunities for growers to have increased control over substrate pH. Increasing incorporation rate of lime from ≈ 4.0 to 6.4 kg·m^-3, regardless of lime material used, resulted in a > 2 pH unit sigmoidal increase. All lime materials applied at less than 4.5 kg·m^-3 failed to maintain the desired pH (5.2 to 6.5) for ornamental crop production after ≈ 50 DAI. kg·m^-3, regardless of lime type, pH range of 5.2 to 6.5 currently recommended for general healthy plant growth. However, it remains uncertain if lime rates > 5.0 kg·m^-3 would have a significant impact on increasing pH further since effectiveness of lime decreases with increasing rate beyond a critical point. Ground dolomitic lime had the least effect on increasing the substrate pH and provided no greater longevity than pulverized materials applied at rates > 4.5 kg·m^-3. These data, along with past research, will aid producers in using the proper lime material and rate to maintain their desired pH during an 8-9 month production period.