Progress report for LNE22-451R
Project Information
This project is investigating best management practices associated with planting cover crops into standing, late season vegetables. Based on our findings, we are underway with educate farmer audiences and promoting ecologically, logistically, and economically sound practices of advancing soil health for vegetable operations in Maine and the Northeast. This three year project has included two years of replicated field trials, along with farmer outreach in years 2 and 3 of the project.
Jason Lilley from the University of Maine Cooperative Extension is providing overall leadership for research and outreach aspects of the project. Dr. Rachel Schattman of the University of Maine School of Food and Agriculture is providing leadership on hiring and advising a PhD level graduate student. She will also be responsible for data analysis. Lilley, Schattman, and the graduate student will share final results for farmers, agricultural service providers, and academic audiences. A grower advisory committee has been providing project input and guidance based on past experiences with cover crop species selection, timing of seeding, and planting methods in various vegetable crops. The input of the advisory committee will also be used to ensure that research findings are applied to real-world contexts in a way that is meaningful for the farming community.
Results from a 2021 survey about cover cropping practices on Maine farms (n= 27), showed that 77.8% of respondents (n=21) are limited in their ability to plant cover crops due to “late season cash crops coming out too late”. 74.1% of respondents (n= 20) stated that research- based data about interseeding in the Northeast would help them with decision making about late season cover cropping.
We hypothesize that 1) Interseeding at an appropriate growth stage of sweet corn and fall cabbage will result in high cover crop biomass and with no negative effects to the crops; 2) incorporation of cover crop seed into the soil at interseeding will result in the best cover crop germination, biomass, and weed control; and 3) that utilizing lower biomass cover crops such as annual ryegrass and crimson clover will minimize nutrient and water competition.
Findings from this research will be shared at four regional grower meetings/ conferences including the Northeast Regional Cover Crop Conference, the Maine Fruit and Vegetable School, the Vermont Vegetable and Berry Association Annual Conference, and the Maine Organic Farmers and Gardeners Association’s Farmer to Farmer conference. Project outcomes will include a graduate thesis, one or more peer-reviewed publications, and Extension publications. Anticipated benefits include that farmers will be able to identify equipment and strategies for interseeding that will fit their existing production systems. This will result in the total vegetable acreage planted to overwintered cover crops being significantly increased by the use of interseeding.
This project will develop recommendations for interseeding cover crops into late season vegetables in the Northeast to improve overwintered soil coverage. The goals of the proposed research are to investigate key management considerations including: timing of planting the cover crop in relation to the cash crop, methods of seeding, and how these factors affect crop nutrient availability, pests, and yields. We will also investigate cover crop species performance. By sharing these research results with conventional and organic vegetable farmers, we will support farmers with the information they need to protect more acres overwinter with cover crops.
A 2021 survey, conduced by our team, of Maine vegetable farmers who use cover crops found that 78% (n= 21) of Maine affirmed that “late season cash crops coming out too late for establishment of a cover crop” was the primary barrier to planting more cover crops. These fields left bare over winter are susceptible to soil erosion, nutrient leaching, and winter-annual-weed seed production (Pimentel et al. 1995; Sainju and Singh 1997; Sarrantonio and Gallandt, 2003; Williams et al. 1998). Climate change forecasts relevant to the northeast suggest that our region is likely to experience longer spring wet periods in coming decades, making bare spring soils increasingly vulnerable (Wolfe et al. 2018).
Interseeding cover crops in standing grain crops has proven successful in warmer regions, like the Mid-Atlantic (Curran et al. 2018; Caswell et al. 2019). However, investigations of interseeding in vegetable crops suggest timing, species selection, and cover crop placement are all key variables for avoiding weed growth and water and nutrient competition in the system (Brainard et al. 2004; Pfeiffer et al. 2015; Brainard and Bellinder 2004; Vanek et al. 2005).
To address the suitability of interseeding cover crops in late season vegetables in Northern New England, our team has conducted two seasons of field trials investigating the timing of seeding cover crops in relation to cash crops and the method of seeding (broadcasting, vs. drilling, vs. broadcasting and incorporating). In other field trials we are investigating cover crop species selection for interseeding. To date, we have completed two years of trials on timing and seeding methods in cabbage, one year of trials on timing and seeding method in sweet corn, two years of cover crop species selection trials in sweet corn, and one year of species selection in cabbage crops. Due to production and plot layout issues, we were unable to complete the cabbage species trial in 2022, and the corn timing trial in 2023. We plan to complete this research (one more field season of timing in sweet corn, and species selection in cabbage) in 2024, using additionally leveraged funds. In addition to providing another field season, those leveraged funds will support a graduate student to complete a sociological investigation of Northeast farmers' perceptions of and experiences with interseeding in vegetable crops. We will also enhance the outreach component of our original proposal with support of these funds.
Additionally, we have worked with our farmer advisory committee to trial this practice on their working farms. Those trials have shown great promise for this practice, as well as some approaches that should be avoided. While one cooperating farmer has implemented this practice by hand on their smaller scale farm, 3 others have spent time and money modifying equipment to make interseeding efficient on their operations. Our team is documenting those experiences to be published in an interseeding in vegetable crops guide and compilation of case studies.
Cooperators
Research
This proposal includes two distinct experimental trials, referred to in the following sections as Trials A and B.
Trial A:
Research plot treatments: Late season plantings of sweet corn and fall cabbage were tested in separate sub-trials in 2022. This was year one of these two year trials. Treatments were be the same for both: (a) timing of seeding (main-plot treatment), and (b) cover crop seed incorporation method (sub-plot treatment). Past research on interseeding and weed management in brassica crops has utilized a days-after-transplanting (DAT) approach for determining the timing of seeding (Brainard and Bellinder 2001; Brainard et al, 2004; Weaver, 1984). Based on the literature, our timing treatment for interseeding the mix of annual ryegrass and crimson clover cover crops in the cabbage trials were intended to be 14, 21, and 30 DAT and post-harvest as a control. Due to weather and staffing issues the planted dates ended up being 17, 23, and 31 DAT, and post harvest. Past field corn trials rely upon crop maturity stage for initiating cover crop seeding (Caswell et al., 2019; Curran et al., 2018). Based on this, our timing treatments for planting the above cover crop mix in the sweet corn trials were v3, v5, and v8, using a post-harvest cover crop planting date as our control. These timing treatments were testing planting dates that are earlier, later, and at a hypothesized optimal planting date that has been informed by published literature from other regions.
Subplot treatments tested the effects of different interseed planting methods in Trial A. While broadcasting seed is the easiest method for distributing seed for an interseeding a cover crop, there is significant evidence that incorporation of the seed will significantly decrease time to germination and increase germination rate (Baker and Griffis, 2009; Barnett and Comeau, 1980; Brennan and Leap, 2014). Therefore, we will test; broadcasting by hand, broadcasting by hand and incorporation, and drilling the seed between crop rows with an earthway seeder, calibrated to use the "beet/ swiss chard/ okra" plate. We hypothesized that drilled seed will result in the optimal time to germination, cover crop stand density, and long term cover crop biomass.
Trial B:
There is minimal data available about what cover crop species will work best for this practice in northern New England. To address this question, the two trials of Trial B tested cover crop species planted at the hypothesized optimal seeding time (v5 for sweet corn, and 30 DAT for cabbage). In 2022 we only conducted the corn species trial due to production and pest issues with the cabbage transplants. We completed the second year of the corn species trial, and first cabbage year for this trial in 2023. We will conduct the final year of the cabbage species trail in 2024. The species treatments included oats and peas mixed, cereal rye and vetch mixed, and annual ryegrass and crimson clover mixed, and a control treatment (bare ground), all broadcasted and incorporated.
Methods:
Trial A:
A replicated split plot design was used to evaluate timing of the cover crop planting and planting method in both the cabbage and sweet corn trials. In the cabbage trial, each replicated block consisted of four beds from which we collect data, with a buffer bed between each data plot (9 total crop beds wide). The cabbage was spaced 18" in row 18" between rows on bed centers (2 rows per bed) with beds 5.5' on center. Cover crop treatments (timing and planting method) were planted in between bed zones, flanking the crop rows in the data plots. Each main plot treatment (timing) was planted in the between bed zones along 45 bed feet, with subplots (seeding method) being 15’ long within that. Those blocks were randomized and replicated four times. The full cabbage trial field was 225 bed feet, by 54’ wide (9 beds).
The sweet corn trial treatment plots encompassed 2 rows of corn planted 30” apart, with 2 buffer rows between each data-collection plot. Treatment plot lengths were the same as the cabbage trial, with 2 rows of corn taking the place of one bed. The cover crop treatments were planted in the 3 between row zones; between and on either side of the 2 corn rows (7.5’ wide).
At designated DAT and crop maturity stages, weeded with hand cultivation tools immediately prior to seeding 25 lb per acre of the ryegrass and crimson clover mix (60%:40%) (calculated based on specific seeding zone). Both broadcasted and broadcast-and-incorporate treatments were spread by hand prevent seeding into adjacent plots. The broadcast-and-incorporate treatment was worked in using a landscape rake to mimic the shallow soil disturbance of cultivation tools. Drilled plots were planted with an Earthway Seeder (beet/ swiss chard/ okra plate), spaced at 7.5” between rows.
Trial B:
Cover crop species were tested in a sweet corn trial. All treatments (cover crop species mixes) were planted at the v5 maturity stage. All treatments were broadcasted and incorporated using the methods described in Trial A. In this replicated complete block trail, treatments was replicated 4 times. All plots were 15’ long with 4 treatments, creating 60’ blocks. Corn plots were comprised of 2 x 15’ rows of corn which were 30” apart. The cover crop treatments were planted to cover a 7.5’ wide swath (30" on either side of the corn data rows and in between the rows). Both trials will include buffer crop rows on either side of all plots to reduce edge effects.
Data Collection and Analysis:
Trial A:
Soil nitrate testing (Vanek et al., 2005) occured at the first cover crop planting date, and again at crop harvest. All soil tests were analyzed at the UMaine Soil Analytical Services Lab. Soil moisture data was collected hourly starting at cover crop planting, with centralized Irrometer Watermark soil moisture sensors. Weed biomass was collected and separated from the cover crop at harvest. Cabbage yields was assessed at harvest by counting the number of heads per plot, weight and diameter per head, marketable vs. diseased or damaged yields, and total plot yield. Sweet corn yields were assessed at harvest by counting the number of ears, and length/weight of ears per plot. Cover crop biomass yields were collected by harvesting and separating above ground biomass from 0.25m sq. quadrants on November 17, just prior to the first major snow fall. Following both crops will include an early May weed survey.
Trial B:
Data collected in trial B mirrored that of trial A with the exception of the frequency of collecting soil moisture levels. Soil moisture data was collected in each plot weekly starting at cover crop planting, with Watermark soil moisture sensors and a handheld meter. We collected this data using a different system than Trial A for cost efficiency, and due to the relative lower level of complexity in this trial.
Statistical Design and Analysis. For both Trial A experiments and years, a split-plot factorial design is being used, with seeding timing being the whole plot treatment and seeding method being the subplot treatment. Independent variables of yields, soil moisture, soil nitrate, weed density, and cover crop biomass will be analyzed using the R Core Team (2020). For Trial B, statistical design for the cover crop species comparison will be a randomized complete block design, to analyze the same variables as Trial A. To analyze data collected in both trials, we will use repeated measurement regression models (MANOVAs) to examine the effects of variables that change through the season (e.g. soil moisture), and chi square or ANOVA tests when working with data averaged over the growing season.
ON-FARM RESEARCH
We collaborated with 4 commercial farms to install small plots of these treatments. This included 2 organic, and 2 conventional production farms. We worked with each farm individually in year 1, to determine the timing, cover crop species, and equipment that would fit into their systems. The farmers helped with seeding, and joined our research team for a field walk at least once prior to harvest. In these plots, we were mostly focused on assessing and reporting on logistical considerations and hurdles to adoption from farmers' perspectives. Additionally, we collected photo based canopy densities to assess cover crop coverage using the Canopeo app. Qualitative assessments of pest damage, weed densities, and differences in water movement in the fields were recorded.
Bumbleroot Organic Farm-
At this farm the cabbage plots are planted very dense with 3 rows per bed with plants spaced 12" in-row. In 2022 we trialed 25' bed length plots of the following treatments; 1) annual ryegrass and crimson clover (60%:40%) seeded at 25lb/A broadcasted and incorporated over the entire beds, 2) annual ryegrass and crimson clover (60%:40%) seeded at 25lb/A broadcasted and incorporated just in the walkways, 3) and oats and peas broadcasted full width and incorporated at 100lb/A 50%:50%). All treatments were planted 30 days after transplanting. In 2023, we seeded either annual ryegrass and crimson clover, dutch white clover, or medium red clover in a variety of brassica crops at 21 days after transplanting.
Belanger's Farm-
In 2022, Belanger's Farm trialed annual ryegrass and crimson clover, as well as winter rye, either drilled with an Earthway Seeder, or broadcast and incoorporated over bare soil cabbage an in a plasticulture cauliflower field. In 2023, they trialed broadcasted annual ryegrass and crimson clover in bare soil cabbage. The seed was incorporated with their Kult Kress finger weeder system at last cultivation. The annual ryegrass and crimson clover showed no visible damage. Broadcast and incorporated plots showed the most uniform and thickest coverage. There was significant deer damage in the bare soil cabbage field. The growers are concerned that the clover may be more of a draw to their already very troublesome deer pressure.
This farm has a Gandy Orbit Air fertilizer sidedress unit, which they have retrofitted to deliver cover crop seed to deflection plates to distribute seed over 6 rows of corn when the corn is at knee height. The seeder has attached liliston cultivators for weed management and to work the seed into the soil. Separately, the farm has a tool bar with 2 12" wide rotovators, intended for renovating strawberries. This piece of equipment works well for incorporating cover crop seed over beds, including over plastic mulch.
Goranson Farm-
One of the farm managers at Goranson Farm collaborated closely with our team to install large scale plantings of annual ryegrass and crimson clover (60%:40%) seeded at 25lb/A broadcasted and incorporated over whole blocks of sweet corn in 2022. The seed was spread with a human powered chest spin spreader, just prior to final cultivation in the corn at the V5 stage.
We also trialed interseeding in their bare soil cabbage fields with beds 6' on center, with two rows of cabbage planted 18" between rows and 18" in rows. 25' bed length plots were installed to, 1) annual ryegrass and crimson clover (60%:40%) seeded at 25lb/A broadcasted and incorporated just in the walkways, 2) and oats and peas broadcasted and incorporated at 100lb/A 50%:50%) and 3) annual ryegrass and crimson clover (60%:40%) drilled at 25lb/A with an Earthway seeder.
Additionally, Goranson Farm used a chest spin spreader to broadcast medium red clover, and crimson clover seed over their winter squash fields, just prior to vine run.
In 2023 the farm interseeded annual ryegrass and crimson clover (60%:40%) seeded at 25lb/A over sweet corn at the v5 stage, and a block of late storage cabbage. Additionally they seeded medium red clover over winter squash at vine run again.
Jordan Farm-
Their 2022 sweet corn field was selected for broadcasting annual ryegrass and crimson clover (60%:40%) seeded at 25lb/A over a block of their corn while sidedressing with urea. The seed was mixed into the 3-point hitch tractor mounted spin spreader with the fertilizer. A final cultivation happened after spreading the seed to control weeds and to work in the seed.
That same cover crop mix and rate was applied between plastic in a pepper field early in the season, at planting of the peppers. A narrow mulching riding mower (blocked discharge shoot) was used to keep the cover crop and weeds low throughout the season.
In 2023, interseeding was used on a large portion of the 25 acre farm. Crops including onions, peppers, brassicas, and sweet corn all had annual ryegrass and crimson clover planted, or dutch white clover. In 2023 the farm mostly used a Gandy box gear driven sidedress hopper for calibrating and precisely distributing the seed between rows of crops.
Statewide, the weather of 2022 was very different than 2023, with drought conditions and high heat being the norm in our first year of trials (2022), and 2023 being the 3rd wettest June-July-August on record. These two extremes showed vastly different outcomes of what the practice of interseeding. In dry conditions, we observed a slower cover crop germination and growth rate, meaning that seeding the cover crop soon after the cash crop did not result in crop competition. There was also relatively little weed pressure due to the dry conditions. In 2023, the wet conditions made it difficult to access field for seeding on the dates that we had planned for. When seeding was able to happen, the availability of water resulted in quick germination and fast cover crop growth rates. In this season, seeding early (21 days after transplanted and earlier) resulted in apparent crop competition at all of our research and demonstration sites. While the demonstration sites did not show visible yield reduction, the cover crop was taller than the brassica crops at harvest. The wet conditions had high potential to create favorable conditions for disease development. The leaching of soil nutrients due to the excessive rains, paired with the potential competition for nutrients of the cover crop was also a concern in these early seeding dates. Lastly, early seeding dates meant that weed management could not be accomplished after the cover crop seeding date. In addition to excessive cover crop biomass, the weeds were allowed to go to seed in the early seeded plots. These observations were significantly lower in the 30 days after transplanted cover crop seeding dates.
Research trial data is currently being analyzed.
ON-FARM RESEARCH
We collaborated with 4 commercial farms to install small plots of these treatments.
Bumbleroot Organic Farm-
Due to the very tight plant spacing in 2022, the crop closed in and covered the soil shortly after seeding. These resulted in next to no cover crop biomass being present at harvest. In 2023 we planted earlier (21 DAT) and focused on the walk rows. Given the extra time to establish prior to canopy closure, the farm collaborators reported an ease of access into these plots and cleaner crops as the cover crop reduced the mud in the trial plot areas.
Belanger's Farm-
In the 2022 bare soil cabbage field, the winter rye experienced very poor germination and had apparent herbicide damage. We are currently looking into the spray records to identify what materials had been applied to that field prior to planting that may have had carry over to negatively effect that seeding. The annual ryegrass and crimson clover showed no visible damage. Broadcast and incorporated plots showed the most uniform and thickest coverage. There was significant deer damage in the bare soil cabbage field. The growers are concerned that the clover may be more of a draw to their already very troublesome deer pressure. We are consulting with the farmers to identify a cover crop mix that might work as a deer "trap crop" to draw the deer away from their crop fields.
This farm has a Gandy Orbit Air fertilizer sidedress unit, which they have retrofitted to deliver cover crop seed to deflection plates to distribute seed over 6 rows of corn when the corn is at knee height. The seeder has attached liliston cultivators for weed management and to work the seed into the soil. Separately, the farm has a tool bar with 2 - 12" wide rotovators, intended for renovating strawberries. This piece of equipment works well for incorporating cover crop seed over beds, including over plastic mulch.
In 2023, the bare soil cabbage had annual ryegrass and crimson clover seed incorporated with finger weeders at last cultivation (21 DAT). The seed germinated quickly and out competed the weeds very effectively. At the same time, the cover crop grew quickly and was as tall as the cabbage crop at harvest. There was some minor purpling of the outer leaves observed in the interseeded plots at a higher rate than the control, however, no difference in yield or incidence of disease was observed.
Goranson Farm-
The 2022 block of annual ryegrass and crimson clover (60%:40%) seeded at 25lb/A broadcasted and incorporated over whole blocks of sweet corn was very successful. The other half of that succession of corn was not cover cropped until after harvest. Winter Rye was seeded on that half of the field until October 20th, and was barely germinated (about 1" of growth) before winter dormancy. The interseeded half had a lush stand of mostly crimson clover with some annual ryegrass.
The cabbage trial at this farm had mixed results. Due to the size of the cabbage at harvest, and the amount of crop residue left on the soil surface at harvest, the cover crop was largely smothered going into the winter. Any exposed areas were well covered by cover crop, however that was a small percent of the total area in that field.
Additionally, Goranson Farm used a chest spin spreader to broadcast medium red clover, and crimson clover seed over their winter squash fields, just prior to vine run. The field was left as very uniform mat of clover as coverage going into the winter, post-harvest. A pass with a mower set high after harvest would have cut back escaped weeds.
Jordan Farm-
This 2022 sweet corn field had excellent germination. After a heavy rainfall event, we observed significantly less erosion late season, prior to harvest, in the interseeded blocks as compared to the neighboring bare soil plots.
In the full season mowed cover crop in the plasticulture peppers, there was no observed negative effects to the crop, and better access into the field for harvest.
In 2023, the Gandy sidedress hopper was used widely to distribute seed on many crops across the farm. Doing this at final cultivation took no additional time, but had great benefit for improving harvest access in a very wet season.
We are in the process of analyzing data.
Education & Outreach Activities and Participation Summary
Educational activities:
Participation Summary:
To date, we have been presenting on preliminary data in addition to previously published findings related to interseeding and cover cropping more generally. We have completed the following outreach activities;
- Field Tour/Workshop at the UMaine Roger's Research Farm, Old Town, ME. 11/4/22. At this program we described the project and allowed farmer attendees to walk through the fields to observe the cover crops stands of our various treatments. We also discussed soil health more generally, and highlighted other research taking place at Roger's Farm including late season W. Rye seeding assessments.
- Presentation- MOFGA's Farmer to Farmer Conference in Belfast, ME. 11/6/22. In this presentation, we highlighted Innovative Cover Cropping Systems. This included a detailed explanation of the role of cover cropping in nutrient and fertility management, and an overview of preliminary findings of the Cover Ground, interseeding trials. We also discussed cover crop mixes.
- Presentation- The New England Fruit and Vegetable Conference in Manchester, NH. 12/13/22. Graduate student Gladys Adu Asieduwaa presented on this trial. She presented on the justification and theory behind interseeding, our approach to our research trials, preliminary cover crop and weed biomass data and yields data. She also highlighted the logistical approaches that our farmer collaborators utilized to make this practice feasible on their operations, and the few hurdles that farmers ran into.
- Presentation- The Mid-Atlantic Fruit and Vegetable Conference in Hershey, PA. 2/1/23. Our team presented on this trial. We presented on the justification and theory behind interseeding, our approach to our research trials, preliminary cover crop and weed biomass data and yields data. We also highlighted the logistical approaches that our farmer collaborators utilized to make this practice feasible on their operations, and the few hurdles that farmers ran into.
MidAtlanticFVC- Lilley Organic- Yr1 Interseeding in Late Season Veg- Presentation
- Presentation- Northeast Cover Crop Council Conference in Portland, ME. 2/16/23. Our team presented on this trial. We presented on the justification and theory behind interseeding, our approach to our research trials, preliminary cover crop and weed biomass data and yields data. We also highlighted the logistical approaches that our farmer collaborators utilized to make this practice feasible on their operations, and the few hurdles that farmers ran into.
- Field Day- University of Maine Roger's Farm Field Day in Old Town, ME. 7/26/23. This field day to highlight the various research projects happening at the research farm was attended by farmers, service providers, and university administrators. Attendees had the opportunity to see the cash crops planted for the trial, see the trial layout, learn about project objectives, and hear about first year findings.
- Presentation- Common Ground Country Fair in Unity, ME. 9/23/23. Innovative Cover Cropping Approaches. This talk was targeted towards smaller scale farmers and gardeners and highlighted several considerations and approaches to cover cropping, including the concept and practical considerations for interseeding.
Learning Outcomes
Farmers have expressed a knowledge gain related to interseeding in the following areas:
- Understanding of benefits and drawbacks of interseeding.
- Understanding optimal timing for interseeding.
- This includes the realization that the optimal timing often aligns with final cultivation, or sidedressing of crops.
- Farmer participants have been seeding cover crops in the same pass as fertilizer sidedressing applications, resulting in added soil health benefits with no additional labor.
- Understanding of the benefit of seed incorporation for interseeding success related to germination rate and weed competition.
- This has resulted in 4 farmers making equipment modifications to improve outcomes of this practice.
Project Outcomes
One of our farm collaborators from Southern Maine has always struggled to get fall cover crops planted on more than 60% of their land. They produce a wide diversity of crops including a lot of late season brassicas. Between those late harvests, much of the farm being on wet soils that stay wet after harvest, and the business of the harvest season, cover cropping in time to get germination was often not feasible. After trialing interseeding on one sweet corn succession in 2023, the farmers spent the winter retooling fertilizer spin spreaders and drop spreaders to make distribution of cover crop seed more efficient. They also ensured that the size of hoppers was sufficient to carry fertilizer and cover crop seed. This allowed for them to distribute cover crop seed and fertilizer at the same time, costing them no extra time beyond the labor of sidedressing. In 2024, they interseeded 85% of their land and were able to traditionally plant cover crops on the majority of the remaining open ground.