Physical and Hydraulic Properties of Commercial Pine-bark Substrate Products Used in Production of Containerized Crops

Abstract

Additional index words. aged bark, air space, dynamic physical properties, evaporative method, fresh bark, particle size, Pinus taeda, porometer, sand, static physical properties, water holding capacity Abstract. Pine bark is the primary constituent of nursery container media (i.e., soilless substrate) in the eastern United States. Pine bark physical and hydraulic properties vary depending on the supplier due to source (e.g., lumber mill type) or methods of additional processing or aging. Pine bark can be processed via hammer milling or grinding before or after being aged from £1 month (fresh) to ‡6 month (aged). Additionally, bark is commonly amended with sand to alter physical properties and increase bulk density (D b ). Information is limited on physical or hydraulic differences of bark between varying sources or the effect of sand amendments. Pine bark physical and hydraulic properties from six commercial sources were compared as a function of age and amendment with sand. Aging bark, alone, had little effect on total porosity (TP), which remained at ' '80.5% (by volume). However, aging pine bark from £1 to ‡6 months shifted particle size from the coarse (>2 mm) to fine fraction (<0.5 mm), which increased container capacity (CC) 21.4% and decreased air space (AS) by 17.2% (by volume) regardless of source. The addition of sand to the substrate had a similar effect on particle size distribution to that of aging, increasing CC and D b while decreasing AS. Total porosity decreased with the addition of sand. The magnitude of change in TP, AS, CC, and D b from a nonamended pine bark substrate was greater with fine vs. coarse sand and varied by bark source. When comparing hydrological properties across three pine bark sources, readily available water content was unaffected; however, moisture characteristic curves (MCC) differed due to particle size distribution affecting the residual water content and subsequent shift from gravitational to either capillary or hygroscopic water. Similarly, hydraulic conductivity (i.e., ability to transfer water within the container) decreased with increasing particle size.

Container Type and Substrate Affect Root Zone Temperature and Growth of ‘Green Giant’ Arborvitae

“…The PB and PM for each study were obtained from different sources which led to slight differences in physical properties for each study. Pine bark physical properties can vary due to a number of factors including source, age, and processing method [11]. Nevertheless, the addition of PM provided PB:PM with more plant-available water resulting in overall improved plant growth at both locations.…”

“…Pine bark typically has a high proportion of drainable air space, whereas PM has greater water holding capacity. Nevertheless, PB physical properties can vary by region and source due to processing methods and aging which could affect crop growth [11]. The combination of PM with PB would increase substrate water holding capacity and possibly reduce RZT.…”

Container Color and Compost Substrate Affect Root Zone Temperature and Growth of “Green Giant” Arborvitae

“…Bachman and Metzger [23] reported vermicompost had varied physical and chemical properties based on the type of parent material used. The physical properties of PB can also vary due to source, processing method, and age [2]. Substrate components typically have a range of particle sizes and when combined with another component the resulting substrate will have different physical properties due to nesting of smaller particles within the larger particles [2,23].…”

“…The physical properties of PB can also vary due to source, processing method, and age [2]. Substrate components typically have a range of particle sizes and when combined with another component the resulting substrate will have different physical properties due to nesting of smaller particles within the larger particles [2,23]. When considering compost-amended substrates, nursery producers should conduct small-scale evaluations to determine optimum compost proportions and amendment rates (fertilizer, lime, etc.)…”

“…Nevertheless, PB has become a relatively universal substrate for producing a wide range of nursery crop species. Pine bark is acquired from different local or regional sources, thus the age and physical structure of PB can vary greatly depending on how long the material has been stored and how it has been processed [2]. These variations will result in substrates and crops with different irrigation demands and may result in over or underwatering if not managed properly, leading to crop stress and nutrient leaching.…”