Potential of coppiced alder as an on-farm source of fertility for vegetable production
The primary problem addressed in this project is how to develop new on-farm sources of organic material for New England vegetable farmers that are cost-effective, stimulate soil biological activity, supply plant-available nutrients, and build soil organic matter. In this study we examine the potential use of alder chips as a soil conditioner in intensive vegetable production systems. In the first year of a three-year rotation, we examined the growth and yield of two tomato varieties grown with ramial wood chips either incorporated into the soil or as mulch, in addition a treatment with incorporated chips made from spring harvested, leafy branches. In the second year of the three-year rotation, we examined the growth and yield of Brussels sprouts on the same plots receiving a new application of the chip treatments.
Prior to the third growing season, soil samples pulled at the conclusion of the 2014 experiment were sent in for analysis. Alder branches less than 3” in diameter harvested in the previous year and fresh, spring alder with leaves were coarsely chip one week prior to the direct sowing of black beans. Based on the soil analyses, all treatments except for the compost control received sul-po-mag as a side dress in order to compensate for the decline in potassium availability. Over the 2015 growing season, we collected data on soils, density of plots, height, in row weed biomass, and yield per plant. Re-growth estimates of alder initially cut at the beginning of the study in 2013 were measured in mid-December.
The third year work plan focused on measuring cumulative impact of alder chip treatments on Peggy Rockefeller Farm. Experimental plots locations remained the same. The tomato and Brussels sprout rotation was completed with dry beans (var. Midnight Black Turtle). Plant height and density was recorded once during the growing season. Inter-row weed biomass and diversity were sampled in late July and September. Final harvest for yield component analysis and yield per row foot was completed in November.
Soil samples for a soil food web analysis were pulled in 20 September and for the final soils analyses were pulled on 24 November 2015.
Chipping of leafy alder
Field preparation, incorporation of alder chips, and compost (Morse and Walke)
Direct seeding on 15 June (Walke)
Sul-po-mag side-dressed and drip irrigation installed (Walke)
Mulch for mulched treatments applied post-emergence (Morse)
Plant heights and density measured (Morse and Liam Torrey)
Weed sampling (Morse)
Cutworm damage assessed (Morse)
Weed sampling and harvest (with Ian Medeiros)
Soils collected for Soil Food Web Analysis
October – November
Five individuals per treatment harvested for estimates of yield components
Five row-feet harvested for total yield estimates (to be completed)
Final soil sampling
Measurement of alder regrowth from original stands harvested in winter 2013
Impacts and Contributions/Outcomes
Overall, drilling into the chipped treatments was more challenging and led to uneven densities across treatments. Germination and establishment of plants in the fresh spring chip was slower than the other treatments and final senescence was delayed by nearly a month. The chip treatments along with the individuals within fresh chip treatment had the most pods per plant and highest bean yield (both number and mass) per plant. The two mulch treatments had the lowest bean yield per individual.
Soil biological activity in September remained high (Solvita CO2 burst test) across all treatments. There were no significant differences except for the higher rates in the treatments receiving two bushels of chips (chip incorporated plus mulch).
In row weed biomass patterns were similar across all three years. Both mulched treatments consistently had a low weed biomass as compared to the controls and the chip incorporated. Variation in total biomass across years corresponds to the competitive ability of the crop, lowest biomass with beans, intermediate with tomatoes and highest biomass with Brussels sprouts. The fresh chip treatments were either equal to or lower than the mulch treatments, suggesting that the fresh material had an allelopathic effect on weeds and also for the beans, the one direct seeded crop in this study.
Alder regrowth was measured for 11 individuals along a 150-foot transect that ran north/south along a hayfield/pasture fence line. The northern half of the transect was shaded by mixed forest to the west and received only morning sun. The southern end of the transect, in contrast, received full sun for the majority of the day.
Of the eleven individuals surveyed, the average cut stump diameter was 65 millimeters, with a range of 41 to 118 mm. The number of primary stump sprouts was similar for each individual along the transect, ranging between 6 to 9 primary stump sprouts. Amount of growth of each primary stump sprout differed significantly, with the diameter of those in the shade on average was 8 mm in on contrast to those to the south of 14 mm.
All of five individuals on the southernmost part of the transect had on average 15 more secondary sprouts associated with the primary sprouts. Three of these five individuals also were in flower in the third year after the initial harvest.
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