No abstract

Wettability is a major factor in determining whether a material can be effectively and efficiently used as a component in greenhouse substrates. Poor wettability can lead to poor plant growth and development as well as water use inefficiency. This research was designed to test the wettability and hydration efficiency of both traditional and alternative components of substrates under different initial moisture contents (MCs) and wetting agent levels. Peatmoss, perlite, coconut coir, pine bark, and two differently manufactured pine tree substrate components (pine wood chips and shredded pine wood) were tested at 50% and 25% initial MC (by weight). The objective of this research was to determine the effects of initial MC and wetting agent rates on the wettability and hydration efficiency of these substrate components. Each component received four wetting agent treatments: high (348 mL·m−3), medium (232 mL·m−3), low (116 mL·m−3), and none (0 mL·m−3). Hydration efficiency was influenced by initial MC, wetting agent rate, and inherent hydrophobic properties of the materials. Wetting agents did increase the hydration efficiencies of the substrate components, although not always enough to overcome all cases of hydrophobicity.

Nurseries rely on soilless substrates to provide suitable growing media for container grown crops. These soilless substrates have been developed to readily drain water to prevent issues with waterlogging and associated soil-borne disease. A negative consequence of high porosity and subsequent drainage throughout the container profile is the required high or frequent irrigation rates with poor retention of applied nutrients. Substrates with relatively high levels of moisture and nutrient retention placed on top of a coarse and freely draining substrate could further optimize water and nutrient retention, while allowing for needed gas exchange for plant establishment and growth. Containerized Red Drift® rose (Rosa ‘Meigalpio’ PP17877) plants were grown under 16 mm or 12 mm daily irrigation, utilizing a traditional pine bark substrate or stratified substrates with either a conventional bark, bark fines, or a bark–peat mixture on top of a coarse bark within a container. The stratified substrates received 20% less controlled-release fertilizer; however, the fertilizer in the stratified treatments was concentrated in the upper strata only. During the first growing phase or season, plants grown in stratified substrates outperformed those grown in conventional, non-stratified bark substrates under normal irrigation. The stratified substrates did not reduce growth under reduced irrigation regimes. Overall, crop growth was equal or superior for stratified substrates when compared to the non-stratified controls, even with a 20% reduction of fertilizer. This research suggests that stratified substrate systems can be used to reduce fertilizer and irrigation rates while producing crops of similar or superior quality to conventionally grown containerized crops.

Many soilless substrates are inefficient with regard to water (i.e., high porosity and low water holding capacity), which provides an excellent opportunity to increase water efficiency in containerized production. We suggest that increasing hydraulic conductivity in the dry range of substrate moisture content occurring during production can increase water availability, reduce irrigation volume, and produce high quality, marketable crops. Three substrates were engineered using screened pine bark (PB) and amending with either Sphagnum peatmoss or coir to have higher unsaturated hydraulic conductivity between water potentials of −100 and −300 hPa. There was no correlation between substrate unsaturated hydraulic conductivity and saturated hydraulic conductivity (r = 0.04, P = 0.8985). Established Hydrangea arborescens (L.) ‘Annabelle’ plants were grown in the three engineered and a conventional (control) PB substrates exposed to suboptimal irrigation levels (i.e., held at substrate water potentials between −100 and −300 hPa) for 32 days. The plants in the engineered substrates outperformed the control in every growth and morphological metric measured, as well as exhibiting fewer (or no) physiological drought stress indicators (i.e., vigor, growth, plant development, etc.) compared with the control. We observed increased vigor measures in plants grown in substrates with higher unsaturated hydraulic conductivity, as well as greater plant water uptake. The coir increased unsaturated hydraulic conductivity and provided an increased air space when incorporated into coarse bark vs. if peat was incorporated into bark at the same ratio by volume. Increasing PB hydraulic conductivity, through screening bark or amending bark with fibrous materials, in concert with low irrigations can produce marketable, vigorous crops while reducing water consumed and minimizing water wasted in ornamental container production.

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.