Understanding the best methods for applying hardwood chips for soil quality improvement while avoiding crop nutrient deficiencies is the key. Hardwood chips from large trees may have a carbon to nitrogen ratio approaching 200:1. A typical healthy soil has a carbon to nitrogen ratio of about 10 or 12:1. Spread and tilled into soil, without following the recommendations below, will result in crops with nutrient deficiencies due to microbial immobilization of soil nitrogen.
The benefits and methods of hardwood chip application to fields were reviewed by our colleague, Brian Caldwell. Brian summarized findings from 15 years of field studies conducted in NY State and Canada as well as offering his own farm experience in this area.
In Caldwell's review, he writes that better results came from:
- Topdressing the hardwood chips on the soil surface between rows after planting, rather than from soil incorporation between crops.
- Testing hardwood chips on small plots. Twenty pounds of hardwood chips applied post-planting on a 15’ x 3’ strip of row, equals about 10 tons/acre. Make several test strips. If test plot plants are yellow and yields lower, nitrogen-tieup was likely.
- Applying supplemental nitrogen at a rate of about 10 lb. N for every one ton of chips to avoid crop deficiency symptoms.
- Spreading hardwood chips at a maximum rate per year of about 10 tons/acre moist weight (equal to about 7 tons/acre dry weight), in combination with cover crop rotations.
- Avoiding the use of hardwood chips that heat up and partially decompose, as they produce volatile organic compounds that inhibit seed germination and plant growth. These chips should either be used fresh, or windrowed and used after they cool down.
- Using chips from the smallest diameter trees and limbs when offered a choice, as they have more plant nutrient value.
- Adding 10 tons/acre of wood chips each year did more to maintain soil quality than adding grass cover crops alone, or resting the soil with harvested alfalfa sod hay crops.
Don't forget:
South Jersey farmers who receive truckloads of wood chips for spreading on cropland application need to file a simple one-page NJDEP Recycling Exemption Form (required under N.J.A.C. 7:26A) with their municipal health department.
Here is an excerpt from Brian Caldwell's review, Wood Chips in Vegetable Production, which is worth reading in its entirety.
From 1951-1965, a remarkable experiment was carried out on a Soil Conservation Service research farm in Marcellus, NY. The project is written up in a 1971 Cornell bulletin called, “Soil Management for Vegetable Production on HoneoyeSoil with Special Reference to the Use of Hardwood Chips” by G. R. Free. This 15-year study used a 5-year vegetable rotation of sweet corn, beans, tomatoes, cabbage, and peas. It compared 14 different treatments, including several in which 10 tons per acre moist weight (7 tons dry weight) of wood chips were added each year. Other treatments looked at using overwintered ryegrass or bromegrass cover crops, and more extensive rotations in which legume sod hay crops were substituted for the beans and tomatoes. The hay crops were harvested and removed, not simply plowed under. Crops were fertilized with chemical fertilizers and (as seems likely) probably sprayed for pests and weeds. Crops were also cultivated for weed control.-Jack Rabin
