Potential of coppiced alder as an on-farm source of fertility for vegetable production

Project Overview

Project Type: Partnership
Funds awarded in 2013: $14,896.00
Projected End Date: 12/31/2016
Region: Northeast
State: Maine
Project Leader:
Dr. Suzanne Morse
College of the Atlantic

Annual Reports


  • Vegetables: tomatoes


  • Crop Production: forestry
  • Education and Training: farmer to farmer, participatory research
  • Natural Resources/Environment: hedges - woody
  • Production Systems: general crop production
  • Soil Management: green manures, soil quality/health

    Proposal abstract:

    Building and maintaining soil organic matter is central to the productivity of vegetable farms. One of the challenges for stockless vegetable farms is the need to offset losses of soil organic matter and nutrients attendant with tillage and the selling of produce. To date, many vegetable growers import compost from off-farm sources as their reliable source of additional soil organic matter. The use of woody species from woodlots and forest edges has the potential to save farmers money and time while also managing their boundaries between field and forest. The use of chipped branches of these hardwoods has shown great promise for soil building yet has been little explored in vegetable production, particularly within the US. This partnership project will be done in collaboration with two farms and will test the effects of ramial wood chips (RWC) derived from alder, a nitrogen fixing species, on tomato yield and health, and measure the short and longer term effects of either incorporation of RWC or mulching with alder RWC on soil bulk density, pH, mineral content, and organic matter. During the experiment, we also will measure growth of the on-farm alder subsequent to coppicing, and the time and costs associated with this alternative practice. Outreach will include articles for the MOFGA newsletter and for Biological Agriculture and Horticulture, a field day hosted on both farms, and a presentation at the Maine Ag Trade show.

    Project objectives from proposal:

    The primary focus of this study will be to measure effects of alder RWC on tomato growth, health, yield and indicators of soil quality. Although there is great potential to use alder from areas to be clear-cut, in this study we will use shrubs on site and assess their regrowth for two seasons after cutting. The time and cost implications of this alternative approach to organic matter production and use will also be documented.
    Objective 1: Assess changes in tomato growth and health that occur as the result of the application of alder woodchips as an amendment to current grower practices and as a substitute for off-farm compost.

    Objective 2: Provide farmers guidelines for coppicing alders and other hardwoods on the edge of their farm properties
    Coppicing of hardwood species has a long tradition in the UK (Harmer 1995) and once again is being developed throughout Europe for biofuels (Jørgensen et al. 2005), wildlife management (Fuller and Warren 1993), and wood from crafts such as thatching and basket making (Harmer 1995). Coppicing of shrubs found on farm pasture and woodlots might be one innovative solution for New England farmers to establish a perpetual regimen of carbon and nutrient harvesting that can be used to fuel soil formation and to transfer mineral nutrients from surrounding woody edges into agricultural production areas. Historically, this kind of nutrient transfer was mediated through the nighttime collection of manure from animals that browse in forest during the day. This proposal is a stockless form where coppicing and chipping are mechanical replacement for mouths with grinding teeth, and has the potential advantage of transferring more organic carbon and nutrients directly to the soil faunal and microbial decomposer communities.
    In this project we will examine whether Maine farmers might cost effectively add energy and plant nutrients, and build soil organic matter for vegetable production through the use of currently underutilized on-farm resources of ramial wood (small branches of hardwood species of < 3 inches in diameter) from forests, woodlots, and pasture edges. This study will focus on the chipping of the nitrogen-fixing alder for ramial wood chips (RWC). In Maine, alder (Alnus spp) is often perceived as an invasive species of pasture or a trash tree in forestry. Alder and its ability to regenerate from cutting, however, has been utilized in habitat management for the woodcock (Williamson 2010). The twenty-year rotations for bird habitat management in Maine suggest that the local species are amenable to coppicing. European studies conducted on Alnus incana (one of our local species) suggest that coppicing on a 3 to 5 year cycle would produce a resilient and healthy stand that could be used by farmers on a long term basis (Uri et al 2011).
    Previous studies on traditional farming systems in China (GIAHS 2012) , Nepal(Pulamte 2009), India (Rathore et al. 2010) and Mexico (CEDICAM 2012) have demonstrated the importance of alder biomass for the building and maintenance of long term fertility of agricultural systems (Tarrant and Trappe 1971, Brown 2012). Tissue analyses indicate that leafy twigs and small branches contain approximately 1.5 % nitrogen and have a C/N ratio of 25:1 (Uri et al 2003, Tarrant and Trappe 1971). Studies also have demonstrated that alder easily decomposes and, due to lignin forms in young leaves and branches, tends to form relatively stable humus (Seo et al. , Sharma 1993 ). In Maine, use of alder ramial wood chips has been documented only in fruit tree orchards (Currier 2007) and not used for vegetable production despite impressive findings in a fifteen-year study in New York (Free 1971), in Canada (Lemieux 1996), and more recently in Senegal (2002).
    In this project, we focus on alder because of its abundance and often weedy nature on farms, its favorable C:N ratio (which may solve the typical tie-up problem seen with other woody tissues), its rapid decomposition, and its potential as a local, renewable source of energy for the soil decomposer communities and of soil carbon and nitrogen. Coppicing and chipping also are an easy way to move other minerals from the forest and forest edge into the more nutrient-demanding cropping areas. All of these contribute the sustainability of the farm by decreasing the dependence on off-farm inputs and instead using local, almost entirely renewable resources.
    Approximately 2 cubic yards of alder RWC (from branches less than 3 “ diameter) will be generated with a winter harvest from stands on Peggy Rockefeller Farm. Brush piles will be chipped at the time of tomato crop establishment in the spring of 2013. Average nutrient content of RWC will be calculated for three samples from the spring wood chip pile. Cut individuals will be marked and re-growth of ten different individuals will be measured in terms of number and length of stems over the subsequent two-year period (Harmer 1995, Jørgensen et al. 2005).
    These field experiments will be conducted on the two farms owned by College of the Atlantic. These on-farm studies will examine the effect of alder chips on tomato production and the subsequent year’s rotation into greens. There will be 3 replicate beds (10 ft by 2.5 ft) for each treatment.
    On Daybreak Farm, three replicates of treatments 1 and 2 (see explanation below) will be followed through the entire growing season. All five treatments will be followed at Peggy Rockefeller Farm and are designed to look at the effects of alder chips as a substitute for compost, as a substitute for compost in combination with mulch, and in combination with added crab meal and compost. The control for all treatments is the current management practice used on COA’s vegetable farm (Beech Hill Farm).
    Control: compost, crab meal
    Treatment 1: compost, crab meal, alder mulch
    Treatment 2: alder chip, crab meal
    Treatment 3: alder chip, crab meal, alder mulch
    Treatment 4: alder chip, alder mulch
    Treatment 5: spring alder chip with leaves, alder mulch
    Three plants from each replicate will be followed throughout the season for a total of 27 individuals on Daybreak and 54 individuals on PRF.
    For each individual, disease frequency, nutrient deficiency symptoms (due to possible N immobilization) time of flowering, leaf nutrient concentrations at time of transplanting, flowering, and fruiting, and total yield (number and weight) will be measured.
    For each replicate strip with an alder treatment, twenty pounds of chips will first be inoculated with half oz. forest duff (Caron 1998) in order to increase fungal abundance, and then incorporated into the top 2 to 3 inches. Mulch treatments will receive an additional 20 lbs of inoculated chips. These application rates are following methods used by Free (1971). Each control plot with compost and crab meal also will receive the forest duff inoculant.
    The tomato varieties to be used will be determined by the farmer and may include Orange Blossom, Defiant and Speckled Roman. Tomatoes will be trellised and grown at 1.5-ft spacing, with approximately 7 plants per ten ft strip. To avoid edge effects, 3 randomly selected plants from center of each replicate will be marked and followed throughout the growing season.
    Replicate strips will be randomized across treatments. During July, August and September, fruit from the 3 designated individuals within treatment blocks will be collected and weighed two to three times a week on both farms.
    In addition to yields, the variation in weed species and biomass will be measured biweekly. The time and cost of harvesting, chipping, application and weeding will be estimated throughout the growing season.
    Solvita soil tests prior to the experiment, at selected times during the growing season, and the following spring will be used to assess short-term effects on selected soil quality parameters (Brinton 2011, Breland and Eltun 1999). We expect that inclusion of alder chips that rapidly decompose will increase microbial activity and biomass, which are early indicators of increasing soil organic carbon content and are correlated with improved soil structure. As indicator of microbial activity at semi-natural conditions, we will measure CO2-evolution rate at controlled temperature and moisture from soil where larger pieces of RWC have been separated from bulk soil with natural moisture by sieving through a 4 mm mesh. As an indicator of microbial biomass and microbial residues, we will measure flush in CO2 evolution at controlled temperature and moisture in soil after it has been air-dried, forced through a 1-mm mesh and rewetted. Soil bulk density and plant nutrient concentrations will be measured in the sampled soil, and soil moisture and temperature will be measured in the field. Possible relationships between these parameters and tomato growth and disease resistance will be investigated. The continued decomposition of the alder supplement through the fall may influence the growth of the following crops, which will be measured in terms of yield of lettuce and kale established in spring of 2014.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.