Native Cover Cropping in Hazelnut Orchards

Research objective 1) Develop self-sustaining, native seed mixes for two types of hazelnut orchards (entering production and max production) and evaluate their compatibility with orchard management goals:

We will develop native seed mixes based on orchard management goals like compatibility to hazelnut life-cycle, disturbance-resistance, and competitiveness against agricultural weeds. To test compatibility, will measure the seed mix population’s response to mechanical treatments, performance in each orchard type, and ability to suppress/compete with orchard weeds over the duration of the project. We hypothesize that 1) newly designed native cover crop mixes will be compatible with their selected orchard types (‘entering-production’ and ‘max-production’) and 2) the mechanical treatments associated with hazelnut orchard management. We hypothesize that these seeded populations 3) will support self-regenerating cover crop communities that 4) suppress agricultural weed populations for the duration of the study. 5) We also hypothesize that these new seed mixes will be as vigorous in establishment and persistence as the seed mix established in the Lane-Massee’s ‘multi-generational’ orchard in 2021 (see Figure 1).

Methods:

We developed seed mixes based on the listed criteria: compatibility to hazelnut life-cycle, disturbance-resistance, competitiveness, plant height, and price. In September of 2023, we purchased local biotypes of all native cover species from Heritage Seedlings & Liners in Salem, Oregon. Each orchard type  received a seed mix catered to its canopy density, with the ‘entering production’ orchard receiving a full/part-sun seed mix  and the ‘max-production’ orchard receiving a full-shade seed mix (see seed mix table).

Each project site was seeded with a two acre block of native cover at one corner of the orchard, placement determined by farmer preference. After hazelnut harvest in 2023, we prepared our sites for the project. To prepare the sites, we removed leaves from the seeding area using a Flory sweeper. We then broadcast sprayed a 6% concentration of glyphosate to kill any vegetation present. We waited fourteen days for the vegetation to die off and the herbicides to break down before seeding. After removing any additional fallen leaves, the seed mixes were then roughly spread at a rate of 60g/6m using a hand-held broadcast seed spreader, with the seed ratios being calculated by seed weight and mature plant size.

Our mechanical treatments will take place May through July and consist of summer flailing and scraping,  both to be determined by farmer preference for adequate orchard floor texture to fulfill hazelnut harvest requirements. After these processes take place, a final flail will happen to crush up any blank nuts that have fallen. A month later, after the majority of nuts have fallen, the project sites will be harvested using each farmer’s personal harvesting equipment. During harvest, we will collect nut-entanglement data to ensure our cover crops do not interfere with the harvesting process by entangling nuts in vegetation. To collect this data, we will wait until the harvester has picked through our flailed plots and a section of the non-cover cropped (control) orchard. We will lay a 1m x 1m quadrat in the center of orchard alleys which have been picked (20 cover and 20 control) and collect the leftover nuts. We will then compare the cover crop entanglement rate with the control entanglement rate. We will then continually evaluate each species and seed mix for their regenerative, reseeding, and weed suppression capabilities throughout the following fall, winter, and spring using the methods discussed below.

To test each of our hypotheses, we have embedded data collection plots inside of the larger two-acre blocks. Each plot is one 6m x 6m  tree block that is not in the presence of a seed mix block edge. Plots are replicated five times per seed mix / orchard type.

To test hypotheses 1-3, we are measuring each species and seed mix community’s disturbance response. We will measure species and seed mix growth throughout the years by their responses to mechanical treatments, their ability to produce viable seed prior to timed treatments, and ability to produce regrowth and/or establish a new generation after the conclusion of mechanical treatments. We will survey these variables every 2-4 weeks, depending on outdoor ambient temperatures and weather patterns, surveying in shorter intervals during the height of the spring and summer months. Our hypotheses will be supported if each annual species reaches maturity and each perennial species reaches maturity in a two-year window, if each seed mix/perennial species regrows after harvest, and if each species produces viable seeds prior to the allotted flailing window. 

To test hypothesis 4, agricultural weed exclusion, we will measure percent cover of seeded species vs non-seeded species every 2-4 weeks inside of these plots. We will factor in bare-ground, debris, and disturbance as part of the percentages. Our hypothesis will be supported if our seed mixes retain ≥75% of ground coverage during their height of growth (June/July) and weed species occupy ≤ 25% cover by that time frame. 

To test hypothesis 5, establishment vigor and persistence, we will compare data across the 2022-2023 growing season for the ‘multi-generational’ orchard to the new plantings and their data in the 2023-2024 growing season. We will continue to collect data for all three cover crop types every year to determine that each hazelnut orchard is meeting the hypothesis criteria for cover crop success. Our hypothesis will be supported if  the ‘multi-generational’, ‘entering-production’, and ‘max-production’ cover crop seed mixes have similar disturbance-response and weed-suppression data. We will quantify efficacy by comparing seed mix types by disturbance-response and weed-suppression ratios.

Research objective 2) Evaluate the economic impacts of both native cover cropping and conventional, bare-ground orchard management practices. Compare production expenses across both management regimes. We will evaluate each orchard management strategy for total labor, flailing and scraping, herbicide, and other cover-cropping related management costs. We hypothesize that 1a) native seed mixes will require less labor hours, number of flailing and scraping treatments, and quantity of herbicide treatments to manage, compared to conventional management practices. Overall, we hypothesize that 1b) native cover cropping in Willamette Valley hazelnut orchards can reduce overall operational costs for farmers.

Methods: 

To test our hypotheses, we will test each variable on a two-acre scale, comparing these management blocks’ (cover cropped vs. conventional) inputs (monetary, labor, and mechanical). We will (1a) measure labor (hours), the number of times flailing and scraping treatments are performed, and the quantity (gal/acre) of herbicide, surfactant, and water used in relation to orchard floor management. To calculate the labor input, we will measure the number of hours that are invested into each management block for orchard floor treatment (herbicide spraying, flailing, scraping, and harvesting). To measure flailing and scraping inputs, we will evaluate the number of treatments each management block receives. For example, one flailing treatment will be measured by the completion of flailing the entire management block one direction (North-South or East-West). 

To collect and record data, we will use online spreadsheets to enter data, with each farmer having access to their individual spreadsheets. Both farming operations will enter their data after the completion of the treatment, with data being a combination of quantitative and qualitative data. Both farming groups are technologically equipped and knowledgeable, making online processes smoother for all parties than paper data collection. 

We will evaluate hypothesis (1b) at the end of the data collection period, by analyzing the time spent and costs of each activity, and summarizing our findings and comparisons between the two management strategies (cover cropped vs. conventional). We will compare the differences of economic input by management strategy on a two-acre scale, and scale up our data for the final report and website (see Educational Objective 2b) at 2, 5, 10, and 50 acres. Because the two farms will be receiving different seed mixes based on orchard light availability, each seed mix will likely require slightly different management strategies, so this will also be taken into account and recorded. The ‘entering-production’ orchard will likely be mowed earlier in the growing season compared to the ‘max-production’ orchard. Our hypotheses will be supported if each seed mix type can reduce farmer monetary, labor, and time inputs by statistically significant margins.

Here is data available from the 'multi-generational orchard' regarding chemical and mechanical input passes. We will replicate this analysis with new data from the trial here after the Summer of 2024.