It has been encouraging to see the attention that Ramial Chipped Wood (RCW – chips of deciduous tree branches that are smaller than 7 cm in diameter) is getting in The Maine Organic Farmer & Gardener. I first read about RCW in this paper in an article written by Tom Roberts of Snakeroot Organic Farm (see www.snakeroot.net/farm/index.html). While searching for more information, I read a paper by Céline Caron and Gilles Lemieux of Laval University in Quebec. I contacted Lemieux and asked about using alder to produce RCW, as I have an abundance of alder on my land. He stated that he had not used alder in his research, but could see no reason why it could not be used. In 2004, I received a SARE grant to study the use of RCW in my fruit tree nursery. The research will be posted at www.sare.org/reporting/report_viewer.asp?pn=FNE04-507&ry=2004&rf=0.
The farm where the research took place is OxBow Herbs and Heirlooms in northern Maine. With a mixed stand woodlot and 20 acres of cleared fields, the farm was out of production for 40 years. It now produces a diversity of greenhouse seedlings, perennial plants and ornamentals, vegetables and nursery trees (apple and pear trees, mostly). The nursery bed is in a sandy loam soil that is low in organic matter and in fertility. Soil improvement has been the greatest challenge for raising nursery stock. With the availability of wood chips on the farm, using RCW could be a sustainable solution to soil fertility problems.
In the spring of 2004, soil samples were taken in the area to be used for research. To meet University of Maine Soil Testing Lab recommendations, I applied 50 bushels of three-year-old, composted horse manure (with wood shavings for bedding) and 75 pounds of rock phosphate to the 2,700-square-foot plot. Additional nitrogen was supplied to some individual test plots by sidedressing with bloodmeal as noted below.
In the fall of 2004, after the leaves had dropped, alder and poplar saplings not exceeding 7 cm in diameter were harvested from an abandoned gravel pit on the farm. The reason for waiting for leaf drop is that leaf tissue tends to be broken down more by bacteria, and wood chips by Basidiomycetes. Breakdown by fungi releases nutrients from wood, and I wanted to limit bacterial competition with these fungi.
With a rented chipper, we produced several cubic yards of wood chips. The RCW was spread 2 inches thick in the experimental area, excluding the control area. With a PTO driven tiller behind a tractor, the RCW was incorporated into the top 4 to 5 inches of soil. Surplus RCW was piled for use as mulch around trees in some treatments in the spring.
In March of 2005, 250 dormant “Antanovka” apple rootstocks were delivered to the farm for grafting. Scionwood for ‘Cortland’ and ‘McIntosh’ was obtained from the University of Maine Experimental Orchard in Monmouth. We completed grafting scions onto rootstocks in March, and the resulting trees were held in cold storage until conditions were suitable for outdoor planting.
During the last week in April 2005, dormant nursery trees were moved from cold storage to the prepared area. Each of the two varieties received four treatments:
Control: 25 trees planted 1 foot apart. These trees received no RCW but were sidedressed with bloodmeal.
RCW + blood meal: 25 trees planted 1 foot apart with bloodmeal sidedressing and with RCW tilled into the soil.
RCW + mulch: 25 trees planted 1 foot apart with no bloodmeal; with RCW tilled into the soil; and with 2 inches of RCW mulch around the base of each tree.
RCW + mulch + blood meal: 25 trees planted 1 foot apart with bloodmeal sidedressing and with RCW tilled into the soil and with 2 inches of RCW mulch around the base of each tree.
We added bloodmeal because RCW may draw nitrogen from the soil as it begins to break down, and young trees cannot tolerate nitrogen deficiency.
From June to September of 2005, no more amendments were added to the soil in the treatment area. Trees were monitored for good graft unions and insect problems that may affect the results. Some graft unions were not successful, so the number of trees per treatment area was not always 25 as planned.
In September 2005, soil samples were taken from each treatment for testing. (See Table 2.) Shoot growth was measured in all treatments; means are reported in Table 1.
In spring 2006, treatments were repeated as in the previous spring.
In June 2006, weeds were removed by hand. Trees were monitored for insect problems and winter damage.
In July 2006, leaves from each treatment were analyzed.
In September 2006, we measured tree height, and stem circumference 9 inches above the graft union (Table 1), and took soil samples (Table 2).
Table 1. Tree Growth, 2005-2006
|Treatment||Tree Height (in.)||Trunk Circumference (in.)||Tree Height (in.)||Trunk Circumference (in.)|
|RCW + blood meal||18.6||1.4||22.1||1.6|
|RCW + mulch||24.3||2.2||26.0||1.5|
|RCW + mulch + blood meal||27.3||1.6||28.8||1.9|
This was a preliminary study and was not designed for statistical analysis, so differences in mean tree height and circumference only suggest trends. Adding RCW both to the soil and as mulch seemed to increase tree height but had little or no effect on tree circumference. Within mulched treatments, trees seemed taller when bloodmeal was used as a sidedressing. Trees growing with RCW but without mulch seemed shorter than trees in other treatments and the controls. The combination of RCW, mulch and blood meal generally seems to have given the best growth.
Table 2 shows the mean increase or decrease in soil properties from 2005 to 2006 for each treatment, with numbers from the two varieties combined.
Table 2. Change in soil properties from 2005-2006
|lbs. per acre||lbs. per acre||lbs. per acre||lbs. per acre||lbs. per acre||lbs. per acre||lbs. per acre|
|P||K||Mg||Ca||CEC||% Organic matter||pH|
|RCW + blood meal||19||62||19||226||1.3||0.05||0.05|
|RCW + mulch||42||78||36||150||2.5||0.3||-.10|
|RCW + mulch + blood meal||61||77||52||45||1.2||0.2||-0.2|
Organic matter appears to have increased where RCW was used as a mulch. The Cation Exchange Capacity seems to have increased in all RCW treatments. The pH seems to have decreased with RCW mulch treatments.
The high concentrations of P and Ca in the control plots may be due to sampling more rock phosphate-amended soil than RCW and RCW mulch in these plots. With 2 to 4 inches of RCW in treatment plots, the wood chips themselves may have displaced soil in the sample and confounded the results. Soil tests taken over several years should show different results.
Results from the leaf tissue analysis were roughly the same in all the treatments and are included in the final report on the SARE Web site.
Conclusions and Recommendations
Trees seemed to grow tallest and soil organic matter increased most when RCW was used both as a mulch and was incorporated into the soil. The increase in organic matter is most encouraging. This sandy loam has been extremely low in organic matter, and cover cropping, adding manure and compost have not changed the organic matter as much as two years of RWC applications did. Lime may have to be applied where RCW is used as a mulch, because the application seems to lower the pH of the soil.
The most labor intensive part of this research, cutting and chipping the trees, may not be practical on a large scale with equipment currently available. Further research should study the application of RCW over a longer period, possibly combining RCW with cover crops and compost; and the economics of RCW use.
It is amazing how populated the chips became with fungi. In late August, mulched treatments were covered with mycelium. Given the difficulty of improving the structure of a sandy loam, this visual effect may suggest the most promising aspect of my study. A large population of mycelium should help hold soil particles together, improving water and nutrient retention, and building an environment more amenable to soil life.
Caron, Céline, G. Lemieux, Lionel Lachance, “Building Soils with Ramial Chipped Wood,” The Maine Organic Farmer & Gardener, Dec. 1998/Feb. 1999
Caron, Céline, “Pedogenesis: The Importance of Deciduous Trees in Forest Ecosystems,” The Maine Organic Farmer & Gardener, Dec. 1999/Feb. 2000.
Caron, Céline, “Oak Trees from Seed to Seed,” The Maine Organic Farmer & Gardener, March/May 2000
Caron, Céline, “What is a Forest,” The Maine Organic Farmer & Gardener, Sept./Nov. 2000
Caron, Céline, “Connecting with the Terrestrial Ecosphere,” The Maine Organic Farmer & Gardener, March/May 2006
Grubinger, Vern, “Wood Chips as a Soil Amendment?” GROWING, Aug. 2006.