Something New in the Mix

Growing Knowledge

Something new in the mix

Researchers evaluate alternative substrates for ornamental crop production in the Pacific Northwest OSU Owen-Altl a nd-St o ven

ability, consistency, and meeting the increased interest in providing “sustainable” products. Soilless substrate produced from readily available regional biomass can potentially provide a sustainable, peat-free, reproducible and cost-effective alternative.

Testing the options Figure 1. These rhododendrons were grown in a substrate consisting of either Douglas fir slash or culled Christmas trees. Each substrate was fortified with nitrogen — either 0, 1.5, 3 or 6 pounds per Regionally available biomass cubic yard. Researchers then evaluated the results. options have undergone screening in greenhouse trials at OSU North Willamette Research and Extension Center. The objective was to investi- By Jim Owen, Heather Stoven and gate the physiochemical properties of James Altland the substrate and ensure no biomass Douglas fir bark availability and is phytotoxic to ornamental crops. cost was an increasing concern dur- Alternative substrate options evaluated ing the nursery industry boom of the include biomass from culled, unsold last decade. However, in recent years, or recycled Christmas trees, Douglas

growers have remained attentive to ▲ alternative substrate components 34 because of potential issues with avail-

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Oregon State University 50 ▲ in partnership with OAN DECEMBER 2012 ▲ DIGGER 33 ▲ Something new in the mix

fir slash, culled shade trees, grass seed 3) determine nitrogen removal of vary- straw, and poplar, as well as a poten- ing alternative substrates and subse- tial Pacific Northwest biomass producer quent effect of crop growth. such as bamboo. Physical properties — Substrate Culled shade trees and grass seed physical properties were determined straw warrant continued research as a using a 3-inch aluminum core in con- soilless substrate alternative, since they junction with the NCSU Poromoter™. are currently abundant in the Northern Physical properties obtained from Willamette Valley and pose a possible this lab procedure provide a relative disposal issue now and in the future. measure of air space to water holding Pine slash and hybrid poplar capacity as a function of total porosity sawdust or chips also show promise. (all void space between the particles). OSU Owen-Altl a nd-St o ven However, concerns remain regarding In addition, bulk density (dry cost feasibility due to the distance mate- weight per unit of volume) was calcu- rial needs to be shipped. lated for each of the substrates investi- Lastly, bamboo as a substrate could gated. Furthermore, an experiment to be feasible. Use remains uncertain, evaluate the effect alternative substrate however, due to lack of understanding particle size has on physical properties of bamboo cane production, biomass and how this impacts plant growth was yield, and overall cost feasibility. initiated using Rhododendron ‘PJM’. These preliminary results show This plant species was chosen due to its Figure 2. Researchers evaluated the use of Douglas fir slash and culled Christmas sensitivity having “wet feet” as a func- hammer-milled Douglas fir (left) and culled trees have the greatest promise as an tion to substrate porosity. Christmas trees (right) in soilless substrates. alternative substrate due to ease of To produce substrate mixes with integration into existing production various physical properties, both OSU Owen-Altl a nd-St o ven practices, increased availability due to Christmas tree and Douglas fir slash Oregon burning law revisions and local- were hammer-milled into either coarse ity of biomass from nursery producers or fine particles. Varying proportions minimizing transportation costs. of each were combined with proportions of horticultural peat and/or pum- A further examination ice. Irrigation was maintained monthly Preliminary screening of the afore- by monitoring leaching fractions and mentioned substrate alternatives has been chemical properties were observed via completed to ensure each alternative is pour-throughs. not phytotoxic, as well as estimating sta- To evaluate the effect of the sub- bility (how much it shrinks). However, strates with different particle sizes, Figure 3. These rhododendrons were grown further in-depth examination of the effect rhododendron shoots were harvested, in soilless substrates comprised of varying of physiochemical properties on produc- dried and weighed at the end of the combinations of Douglas fir slash, sphagnum peat and pumice. tion practices in woody ornamentals was growing season. done only on the most promising two Increasing the percent Christmas components, Douglas fir slash and culled tree or Douglas fir slash in a bark based Christmas trees (Figure 2). substrate resulted in decreased water The objectives of the project were holding capacity and increased air to identify cost effective, readily avail- space, as seen in Table 1. We hypoth- able biomass products and engineer esize this is a result of an increased alternative soilless substrates to extend amount of medium to fine particles with or replace Douglas fir bark within an irregular shape, which creates larger the Willamette Valley as follows: 1) pores with fewer micro-pores, thus investigate the effect of organic and holding less water and more air. non-organic amendment on substrate Previous research has found Douglas physical properties; 2) investigate pH fir slash to be the more stable of the two dynamics of alternative substrates and alternative components due to a higher Douglas fir bark or peat mixtures; and wood content. Therefore, the physical

34 DECEMBER 2012 ▲ DIGGER properties should remain relatively consis- Douglas fir bark to Christmas tree were relationship between Christmas tree and tent through the production cycle. used from 33–100 percent (by volume). Douglas fir slash alternative substrates Abundant needles in the In addition to the four ratios of alter- and nitrogen rates on plant growth for Christmas-tree-based substrate result native substrate, three rates of lime were herbaceous and woody ornamental crops. in partial composting during storage incorporated. Bi-monthly pour-throughs Azaleas shown in Figure 1 were chosen or potting, if not blended with large (substrate solution extract) were complet- to represent the woody crop due to the amounts of Douglas fir bark. The ed to observe the effect of lime rates on visibility of foliar deficiency symptoms in resulting decomposition could cause substrate pH. Both alternative substrates past experiments. Marigolds were chosen a decrease in air space throughout have a liming effect when incorporated for the herbaceous crop due to grower production when compared to bark. into bark-based substrate, resulting in recommendations as an indicator of sub- Therefore, it may be advantageous to increased pH. strate nitrogen availability. use this substrate at low incorporation Table 2 shows that 3 pounds of For both experiments, four fertiliz- rates, or add an inorganic component dolomitic lime was able to maintain a er rates were applied to three substrate such as pumice, to ensure adequate air pH between 5.5–6.5 for short-term crops types (Douglas fir bark, Christmas tree, space remains throughout medium to when using an alternative substrate. When and Douglas fir slash). To evaluate the long production cycles. using either alternative substrate material, effect the alternative substrates had on pH Adjustment — To evaluate how the lime or dolomite lime rate will be sub- nitrogen availability, shoots were rated, the pH of alternative substrates affect plant strate specific and should be adjusted to tissue samples were collected and ana- growth, an experiment was initiated using meet crop specific pH requirements. lyzed for nutrient content and shoot Cotoneaster ‘Coral Beauty’. Varying ratios Nitrogen Dynamics — Two stud- dry weight was determined and com-

of Douglas fir bark to Douglas fir slash or ies were undertaken to investigate the ▲ 36

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Table 1. Physical properties of soilless substrates.

Alternative Water Air Total Water at Bulk substrate holding space porosity container density capacity capacity pared across treatments. Nitrogen drawdown, the con- percent volume lb / yd3 sumption of nitrogen by the substrate, percent volume Douglas fir bark lb / yd3 appeared to impact plant performance Control (100) 32 46 77 944 421 potentially indicating a need for addi- Douglas fir slash tional nitrogen when using large percent of an alternative substrate. However, it 33 40 47 87 994 320 remains difficult to separate the impact 66 38 51 89 927 287 of nitrogen from the effect of physical 100 32 54 86 843 320 properties even when like particle sizes Culled Christmas tree were used in all substrates. A nitrogen application of 3 pounds 33 39 51 90 927 270 per cubic yard appeared to be adequate 66 38 54 91 876 236 to overcome any reduction of applied 100 32 61 93 742 202 nitrogen when using an alternative substrate (Figure 2).

Table 2. pH of soilless substrates comprised of varying ratios of alternative components and Summary Douglas fir bark when amended with 0 to 6 lb/yd of lime. Crops produced in Douglas fir slash outperformed crops grown in culled Alternative Lime Date substrate rate Christmas trees. In addition, Douglas fir % volume lb/yd 27-Jun 25-Jul 18-Aug 15-Sep slash was used to make successful sub- Douglas fir bark strates with desirable physical properties when blending with peat and pumice Control (100) 0 6.54 4.59 5.39 4.20 (Table 3, Figure 3). Therefore, Douglas Douglas fir slash fir slash could be a possible bark extend- 33 3 6.62 6.37 5.71 6.14 er with little change in cultural practices. 6 7.10 6.72 6.14 6.51 Douglas fir slash could also potentially 66 3 7.22 6.62 6.05 6.82 serve as a bark replacement if pH and nutrition are properly managed. 6 7.04 7.18 6.41 6.66 100 3 7.20 7.03 6.30 6.68 Acknowledgment 6 7.66 7.53 6.85 7.09 Research was funded by Oregon Culled Christmas tree Department of Agriculture/Oregon Association of Nurseries, Floriculture 33 3 6.59 6.67 6.30 6.21 Nursery Research Initiative and Oregon 0 6 6.85 7.26 6.31 6.60 Agricultural Research Foundation. 66 3 7.21 7.11 6.42 6.36 6 7.31 7.32 6.43 6.66 Jim Owen is an assistant professor 100 3 7.35 7.60 6.75 6.71 of nursery crops at Virginia Tech in 6 7.50 7.92 6.77 7.11 Hampton Roads, Va. He can be reached at 757-363-3904 or [email protected]. James Altland is a research horticultur- alist at the USDA Agricultural Research Table 3. Plant response of rhododendron grown in soilless substrates comprised of Sphagnum peat, pumice and varying ratios of Douglas fir slash at different particle sizes. Service in Wooster, Ohio. He can be reached at 330-263-3870 or Particle size of Douglas fir slash Sphagnum Screened Avg. Shoot [email protected]. Heather Coarse Fine peat pumice weight Stoven is a faculty research assistant Percent volume grams with Oregon State University, stationed 40 30 30 0 13.3 at the North Willamette Research and Extension Center. She can be reached at 40 45 15 0 14.1 503-678-1264 ext 136 or 40 30 15 15 16.6 [email protected].

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