PineTreeSubstrat

Pine Tree Substrate: A Promising Alternative to Peat Moss and Pine Bark



Robert D. Wright and Brian E. Jackson

Virginia Tech University, Dept. of Horticulture, Blacksburg, Virginia 24061

Email:**************

INTRODUCTION

Afterfour years of research and development at Virginia Tech, pine tree substrate (PTS) shows

excellent promise as analternativeand renewable container substrate for nursery and greenhouse

crop production (Wright and Browder, 2005; Wright et al., 2006; Wright et al., 2008). PTS is

competitively priced, locally available, and of consistent high quality. This is a totally different

approach to container substrate production in that a new material is created for use as a container

substrate rather than mining peat (P) (a non-renewableresource) or using pine bark (PB)or some

other industry by-product. The development of a new substrate for container-grown nursery

crops is very timely since the availability of PB is currently unpredictable due to reduced forestry

production and its increased use as fuel and landscape mulch (Lu et al., 2006). Further, the cost

of peat substrates continues to rise due to transportation and growing environmental concerns

over the mining of P bogs in Canada and paper reports the currentstatus of our

research including the manufacturing process, physical properties, cost, growth trials, wood

toxicity, fertility management, and post-transplant landscape evaluation.

Producing tree substrate is produced by chipping freshly harvested pine logs (Pinus

taeda)to produce chips that are approximately 2.4 cm x 2.4 cm x 0.6 cm (1 inch x 1 inch x ¼

inch). These chips are further ground in a hammermill to produce a substrate of a given particle

size range designed to meet specific substrate requirements (porosity, water holding capacity,

etc.)for a wide variety of plant genera and plant sizes (Saunders et al., 2006).No composting of

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PTS is necessary, and the trees can be literally harvested one day and used to pot plants the next

day after grinding and amending. Loblolly pine treesare native to the southeastern U.S., but have

a distribution and potential planting range across much of the U.S. (Fig. 1). The large potential

growing area for loblolly pine means that trees can be grown in close proximity to greenhouse

and nursery operationsacross a large portion of the country, saving on shipping costs of raw

products needed for manufacturing and deliveries of substrates to the growers. Also the harvest

of pine trees is less weather dependent than peat harvest, pine trees are renewable and pose fewer

environmental concerns associated with harvest, and substrates produced from pine trees appear

to be of consistent quality over time. As well, the production of PTS interfaces an already

existing industry related to the paper industry where large volumes of pine wood chips are

already being produced for paper production.

Cost of Pine Tree chips produced for the paper industry or for fuel can be

purchased for $5 to $6 per cu. yd. After adding the costs of grinding and fertilizer, one could

conceivably produce a substrate for under $15 per cu. yd. compared to $40 plus for traditional P

substrates and $15 plus for aged PB. Since PTS is ground to the correct particle size to provide

the desired aeration and water holding capacity, there is no cost associated with adding

aggregates such as perlite and vermiculate as required for P substrates.

Growth have successfully produced a wide range of nursery and greenhouse crops

in PTS including 30 genera of woody plants, 3 genera of greenhouse crops, 14 genera of bedding

plants, and 7 genera of herbaceous perennials.

Post-transplant evaluation of PTS grown plants. No differences in appearance or growth

index have been observed two years after transplanting into the landscape for twelve species of

woody plants including maples (Acer rubrum) and pin oaks (Quercuspalustris) planted from 15

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gallon containers. The landscape performance of four annual species and five perennial species

also shows no differences in visible appearance or growth index. Evaluations indicate that plants

grown in PTS establish and perform just as well as plants grown in P or PB.

Toxicity freshly harvested trees are ground and immediately used to plant 14-day

old plugs of marigold and tomato seedlings, there can be somereduction in seedling growth.

The degree of toxicity was determined for 12 species of various hardwoods and softwoods, and

loblolly pine was the least toxic (Rau et al. 2006). Growth inhibition was related to the level of

polyphenollics in the wood. The toxicity to seedlings in PTS can be reduced by leaching the

substrate with water, and some of our research indicates that aging of logs before grinding and

aging of PTS after grinding can reduce the extent of toxicity. Regardless, our research has shown

that by the end of production periods of more than four weeks, with proper attention to mineral

nutrition, there is little if any difference in plant growth between PTS and traditional substrates.

Root growth of annual and woody plants grown in PTS is equal, and most often better, than root

growth of the same plants in P or PB.

Fertilizer Requirements. In most studies additional fertilizer is required for PTS compared to

commercial P or PB substrates. Research has concluded that it takes about 100 ppm more N from

a 20-10-20 soluble fertilizer to produce comparable growth of bedding plants,poinsettia, and

chrysanthemums in PTS compared to P substrates (Wright et al., 2008). Theaddition of 25%P

or 5% calcined clay to PTS has been shown to improve plantgrowth, especially at lower

fertilizer rates. This is likely because P and clay increase the retention of nutrients available for

plant uptake by increasing the cation exchange capacity (CEC) of the PTS. For woody plants it

has been shown that an additional 1.2 to 2.4 kg•m

3

(2 to 4 lbs•yd

3

)controlled release fertilizer is

required (depending on species, PTS particle size, irrigation regime, etc.) for optimal plant

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growth in PTS compared to PB. Our research has shown that higher N requirements are due in

part to more nutrient leaching from PTS since the CEC is very low compared to P and PB, and

more microbial immobilization of N with PTS due to the high C:N ratio of the non-composted

though there is evidence of microbial activity, it does not result in substrate

shrinkage of PTS over a two to three month plant production cycle for greenhouse crops. Even

after two years in larger containers with woody nursery crops, no visible degradation or

shrinkage has occurred with the PTS substrate compared to PB. The lack of shrinkage in the face

of N immobilization and some decay of PTS is likely due toincreased root volume which fills

the void left by the decaying PTS.

Our research has also shown that low lime additions may be required, no more than 0.9 kg•m

3

(1.5 lbs•yd

3

), for optimal growth of marigold (Fig. 2).For woody nursery plants a large number

of genera have been grown without lime additions with comparable growth to those grown in

pine bark which requires lime depending upon the species grown. Also, an addition of sulfur is

required for PTS compared to peat moss and pine bark for the growth of marigold (Fig. 3).

Sulfur can be supplied as elemental sulfur, Micromax, FeSO

4

, MgSO

4

, or CaSO

4

at the rate of

0.9 kg•m

3

(1.5 lbs•yd

3

).

LITERATURE CITED:

Gilman, E.F. and D.G. Watson. taeda, Loblolly pine. Fact Sheet ST-478 Forest

Service, Dept. of Ag.

Lu, W., J.L. Sibley, C.H. Gilliam, J.S. Bannon, and Y. Zhang. 2006. Estimation of U.S. bark

generation and implications for horticultural industries. J. Environ. Hort. 24:29-34.

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Rau, B., B.E. Jackson, J.F. Browder, and R.D. Wright. 2006. Wood substrates derived from a

variety of tree species affect plant growth. Proc. Southern Nursery Assoc. Research

Conf. 51:43-45.

Saunders, T., J.F. Browder, B.E. Jackson, and R.D. Wright. 2006. Particle size of a pine

chips substrate affects plant growth. Proc. Southern Nursery Assoc. Research Conf.

51:46-48.

Wright, R.D. and J.F. Browder. 2005. Chipped pine logs: A potential substrate for greenhouse

and nursery crops. HortScience 40:1513-1515.

Wright, R.D., J.F. Browder, and B.E. Jackson. 2006. Ground pine chips as a substrate for

container-grown wood nursery crops. J. Environ. Hort. 24:181-184.

Wright, R.D., B.E. Jackson, J.F. Browder, and J. Latimer. 2008. Growth of Chrysanthemum

in ground pine trees requires additional fertilizer. HortTechnology (in press).

Figure 1. Potential planting range for loblolly pine trees in the United States (Gilman, 1994).

Figure 2. Shoot dry weights of marigolds grown in peat-lite (PL) and pine tree substrate (PTS)

when amended with five rates of lime; values followed by a different letter are significantly

different.

Figure 3. Shoot dry weight of marigolds grown in peat-lite (PL) and pine tree substrate (PTS)

with various sources and rates of sulfur (S) amendments; values followed by a different letter are

significantly different.