Evaluating cover crops for mature hazelnut orchards in the Willamette Valley, Oregon

Project Overview

Project Type: Professional + Producer
Funds awarded in 2016: $49,997.00
Projected End Date: 01/15/2019
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Principal Investigator:
Dr. Nik Wiman
Oregon State University

Annual Reports


  • Nuts: hazelnuts


  • Crop Production: cover crops, nutrient cycling, organic fertilizers, tissue analysis
  • Education and Training: decision support system, demonstration, extension, focus group, on-farm/ranch research, participatory research
  • Pest Management: biological control, integrated pest management
  • Production Systems: agroecosystems
  • Soil Management: soil analysis, soil microbiology, organic matter, soil quality/health
  • Sustainable Communities: sustainability measures


    The purpose of this project was to examine potential benefits of cover crops for mature hazelnut orchards in the Willamette Valley, Oregon where 99% of the US hazelnut crop is produced. Summers are dry but winters are characterized by intense precipitation and are very wet (40-50 in precipitation annually). Currently, maintenance of a bare orchard floor is the common practice to facilitate efficient mechanical harvest of nuts from the orchard floor where the nuts drop naturally when they are mature. Erosion and nutrient leaching are major concerns during the wet winter season in bare ground orchards with any kind of slope. Harvesting from the bare soil surface under wet conditions can be very problematic, and while growers try to avoid this scenario, at times they are forced to harvest under inclement weather when the alternative is to lose the crop to defects like mold. Mechanical harvest on wet ground causes damage to the orchard floor and a results in dirty crop, and increased cleaning fees from the nut receiving station where the product is washed and dried. Nut quality and economic returns decline rapidly as the crop rests on wet ground. Maintaining permanent cover crops that are compatible with harvest has potential to improve economic returns for hazelnut growers by mitigating the uptake of contaminants into harvesters, improving drainage of surface water, providing a drier vegetative surface for the nuts to rest on (may reduce mold defects), and allowing equipment to access orchards that would otherwise be too slippery to harvest. Cover crops that can be seeded or regenerated from a spring seeding after being terminated for harvest from a bare orchard floor to protect soil during winter also have value. This project also explored potential for N-fixing cover crops to not only mitigate erosion, but also provide nitrogen to the hazelnut trees. Finding affordable off-farm sources of N for organic growers can be prohibitive and use of N-fixing cover crops could provide a less expensive, more sustainable source of N. Food safety concerns for a crop that is harvested from the ground limit feasibility of using cheap off-farm sources of N such as manures.

    In preparation for harvest, hazelnuts are first "windrowed" by a sweeper after they drop from the trees.
    A harvester immediately behind the tractor mechanically picks up windrows of hazelnuts, de-husks them, and transfers nuts to the harvest cart that is towed behind the harvester.
    Some debris (sticks, dirt clods, rocks etc.) must always be cleaned from the nuts even under ideal conditions, but a wet harvest can substantially increase contaminants. Uneven orchard floors inhibit harvest efficiency and nuts can be lost in cracks or imperfections in soil. Thatch or other debris from a cover crop could negatively affect nut cleaning costs, making growers resistant to changing the practice of maintaining smooth, bare orchard floors.


    Project objectives:

    1. Select candidate cover crop species with producer input.
    2. Lay out cover crop research plots in mature orchards.
    3. Coordinate seed purchase and seed drill rental.
    4. Seed 1 acre of each of 4 seed treatments and controls (unseeded, bare ground) into replicated test plots in randomized block design at each cooperating producer orchard.
    5. Evaluate fall seeded winter cover crop germination and establishment and for green manure crops, evaluate the amount of plant available N (PAN) produced.
    6. Evaluate biomass production and percent cover produced by seeding cover crops in spring vs. summer.
    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.