The purpose of this project is 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. Currently, maintenance of a bare orchard floor is the common practice and erosion and nutrient leaching are major concerns during the wet winter season. Harvesting under wet conditions can also be extremely problematic, and while growers try to avoid this scenario, at times they are forced to harvest under inclement weather. Cover crops could potentially mitigate the uptake of mud into harvesters by holding wet soil in place with a well-developed root system. We have used this project to develop collaborations with a number of organizations with interest in soil conservation or promoting benefits of cover crops.
Our initial experience has taught us that establishing a cover crop in a hazelnut system after a fall harvest is very challenging. Hazelnut harvest is typically finished by mid-October to early November depending on the variety. By this time, soils are cool and light intensity is low, resulting in slow germination and seedling growth. Young seedlings are vulnerable to low temperatures, falling leaves, and slugs. In 2016, fall rains came early and were unrelenting, giving us very few opportunities to seed cover crops into cooperator orchards. We were able to seed the plots, but seed germination and establishment was very poor. The 2016 hazelnut crop suffered serious quality issues because of nuts dropping onto muddy orchard floors and growers being unable to get into the orchards to harvest them. The longer the finished nuts come into contact with water, the greater the incidence of mold, a serious defect. However, the disastrous 2016 harvest has also stimulated industry interest in the potential use of cover crops as a harvest surface and as an aid in improving water infiltration and drainage in the orchard at harvest.
Given the difficulties in establishing postharvest winter cover crops in hazelnuts in 2016, we tested preharvest seeding into dry ground before harvest for 2017. However, we found this was not possible because the drill we have access to cannot penetrate the hard soil after the dry growing season and the orchards floor has been prepared for harvest by dragging. There is also risk that if the rains come early, the seeds may germinate and interfere with harvest, and harvest equipment would kill many of the young seedlings.
To summarize, we have had limited success with fall seeded cover crops as we had originally planned to evaluate and our objectives have changed in response. For 2018 we are looking at spring establishment of perennial and annual cover crops that can hold up to a season of orchard management and be terminated in time for harvest and also reestablish themselves after harvest. We are also taking a closer look at grasses that can be maintained as permanent cover. These will be evaluated for compatibility with machine harvest of nuts.
- Select candidate cover crop species using producer input.
- Lay out cover crop research plots in mature orchards.
- Collect historic and current baseline data on test plots for yield history, soil quality, erosion and canopy cover.
- Coordinate seed purchase and seed drill rental.
- 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.
- Evaluate fall seeded winter cover crop germination and establishment and for green manure crops, evaluate the amount of N added to the soil.
- Evaluate spring seeded cover crops for resiliency and harvest facilitation.
Objective 1. Select candidate cover crops with producer input.
In selecting our candidate cover crops we reached out to multiple specialty seed producers in the Willamette Valley to solicit opinions and knowledge. We also met with the USDA-NRCS Plant Materials Center in Corvallis, OR and attended their field days.
We held a cover crop workshop and grower panel at the Oregon State University North Willamette Research and Extension Center (NWREC) in Aurora on June 2, 2016 (Fig. 1). The workshop attracted approximately 35 growers. In the workshop we had presentations from representatives of both the Clackamas and Yamhill County Soil and Water Conservation Districts, who discussed cover crop options for hazelnut orchards and how cover crop plantings could fit in with NRCS conservation incentive programs (EQIP). We also had a grower panel where growers discussed their experience with different cover crops in orchards.
In 2016, the final cover crop selections were determined at a separate planning meeting with the producers cooperating on this grant. We utilized the knowledge that came out of the workshop to make preliminary cover crop selections. Based on grower input, we selected the following cover crops for the first year: subterranean clover (28 lbs/acre), white clover (15 lbs/acre), creeping red fescue (35 lbs/acre), and an annual mix consisting of phacelia (15%), vetch (15%) and triticale (50%; 83 lbs/acre). All cover crops were locally sourced. The untreated control blocks were not seeded but volunteer cover crops may be present (mainly Poa spp.).
In 2017, we consulted with various cover crop and turf seed growers, and the OSU turfgrass Extension specialist to identify additional crops and varieties that may be suitable for an orchard system. Cover crops that were trialed in postharvest and spring seeded plots in 2017 included several varieties of hard fescue, bentgrass, and Kentucky bluegrass, and balansa, berseem, and strawberry clovers. We plan to evaluate mechanized harvest of nuts over grasses and we will evaluate resiliency of other crops to grow back after orchard floors are prepped for harvest.
Objective 2. Coordinate seed purchase and seed drill rental.
Yamhill County Soil and Water Conservation District (SWCD) has become a partner in our project as a way to promote conservation practices. Hazelnuts are one of the top agricultural industries in Yamhill County. Our project precipitated the purchase of a Land Pride 606 NT seed drill (http://www.landpride.com/products/73/606nt-compact-drills )(Fig. 2) by Yamhill SWCD. This seeder was made available for us and for growers to rent. Sam Sweeny, Gordon Cook and Marie Vicksta were key cooperators from the Yamhill County SWCD. Gordon Cook has helped us seed our plots and has invested considerable time in the project.
Fig. 2 Land Pride 606 NT seed drill being pulled by OSU faculty research assistant Aaron Heinrich at one of the farmer cooperator sites.
Objective 3. Establish replicated research plots at each cooperating producer orchard.
We used a randomized complete block design with three replicates to plant cover crop blocks at each orchard. Orchards had tree and alley spacings from 9 ´18 ft (double density) to 20 ´ 20 ft (single density), and each plot was 100 x 6 ft. In all cases we planted the treatments on both sides of the trees (two alleys), and left two unplanted rows between adjacent treatments as a buffer (Fig. 3).
In the fall of 2017, we had much more favorable conditions. All four commercial orchards were seeded between 10/25 and 11/1. Based on cover crop performance in 2016-17 and grower input, subclover and the annual mix were excluded from replicated trials. The treatments in the 2017-18 replicated trials included creeping red fescue (35 lb/acre), highland bentgrass (20 lb/acre), and white clover (25 lb/acre). To avoid the issue of weed competition as experienced the previous year, we sprayed out the plots with glyphosate before seeding. At one site, we also seeded a single, unreplicated 600-ft strip of various cover crops. If these cover crops establish, we will evaluate how they affect hazelnut harvest. This will be done with a GPS enabled harvester weigh wagon. Based on visual observations, germination has been good, but growth has been slow, and many of the seedlings are covered by leaves.
Objective 4. Monitor cover crop growth and influence on soil health, insect diversity, erosion, and nut harvest.
In 2016 and 2017, cover crop plots were assessed for germination and percent cover every six weeks following planting. Percent cover was assessed within a 1/2m quadrat that was randomly placed within each of the test plots.
In 2017, we collected biomass and N uptake data for the annual cover crop mix (triticale, vetch and phacelia).
The fall/winter of 2016-17 was a challenging year for establishing winter cover crops throughout the Willamette Valley. We planned on seeding cover crops immediately after harvest but the weather was not cooperative. October was the second wettest in history, with 10-11 inches of measured precipitation at locations near the producer orchards. Wet and muddy conditions delayed planting of cover crops until mid-November. Due to wet, cold soil conditions and low light intensity, germination and growth was poor for all cover crops. In early January of 2017, we experienced several weeks below freezing temperatures with significant snow accumulation in some locations.
Germination of treatments was successful at most sites, but following an extremely cold spell in January, many plants died. In the winter, the cover crop was too small to effectively minimize erosion, but by the spring would be effective (Fig. 5). At several sites, the seedlings that were not killed by the cold were killed by slugs. Also, significant weed competition at some sites hindered establishment and growth. The relatively large seed size of the annual mix compared to the perennial crops tested likely helped the annual cover crop establish. At the final check in May 2017, the flowering annual mix was performing extremely well (Fig. 6). All previously seeded cover crop plots are followed in subsequent years. The annual mix was allowed to reach maximum standing crop in 2017 (Fig. 7), and we have noted that the vetch successfully reseeded itself for 2018.
No cover crops seeded postharvest provided adequate cover on the orchard floor during the winter (Fig. 8). Early in the growing season the amount of cover increased, but this was too late to contribute to a reduction in erosion (Fig. 9).
The annual mix represented our most successful treatment from 2017 and it produced enough biomass during the growing season to make a substantial contribution to the N budget of the orchard (Fig. 10). At three of the sites, N uptake was approximately 20 lbs/acre, but at Site 1, it was 60 lb/acre. At Site 1, N uptake was high enough to offset spring fertilizer applications, which are typically around 200 lb N per acre (Fig. 11). This assumes that the cover crop is flailed and sufficient moisture is available to break down plant residues and release the nutrients to the hazelnut trees.
Due to poor establishment in the winter of 2016-17, we were unable to measure cover crop influence on soil health, effects on erosion, and nut harvest. Because conditions in the fall of 2017 were much more conducive to cover crop establishment, and we have seeded plots in spring of 2018, we are confident that we will be able to collect the necessary data in 2018/2019. Also, in 2017, we seeded large strips in the orchard that will allow us to determine if the presence of a cover crops impedes nut harvest, and if harvest takes place under wet conditions we will also look at the uptake of mud and debris by a hazelnut harvester across the different treatments.
Educational & Outreach Activities
Improved knowledge of cover crop applications in hazelnuts.
Improved knowledge of challenges for establishing cover crops in hazelnut orchards.
A number of productive collaborations have been initiated with this project. These collaborations include conservation agencies such as Yamhill and Clackamas SWCDs, USDA-NRCS Corvallis Plant Materials Center, various specialty seed producers and seed distribution companies. Rogue Farms Corps was present at one of the seeding days and they featured our cover crop seeding in a video called “Preserving Oregon’s Farmland”. At the cover crop workshop, we provided growers with a document summarizing information for cover crops that we were considering planting. This document summarized our background research (largely from SARE resources) on the most applicable cover crops for our environment (Willamette Valley, Oregon) and the hazelnut farming system. Growers interested in cover crops were also exposed to experienced hazelnut growers that had been experimenting with winter cover crops as they gave their thoughts during the grower panel at the workshop. We have featured our WSARE cover crop project on our hazelnut extension Facebook page.