Increasing adoption of reduced tillage strategies on organic vegetable farms in the maritime
Grower interest in reduced tillage techniques stems from concern over soil quality and energy use. Tillage decimates large-bodied soil organisms, reduces soil carbon storage and weakens the stability of aggregates. Yet, organic vegetable growers in the Pacific Northwest currently pass over their fields 10 to 20 times annually to incorporate cover crops and amendments, prepare the soil for planting, and manage weeds. In response to the interest in tillage reduction, our syndicate of growers, researchers, and Extension educators has worked collaboratively to develop and test reduced tillage strategies for organic vegetable production in the Pacific Northwest since 2009. Incorporating reduced tillage into organic vegetable cropping systems requires careful integration of cover crops with equipment. Cover crops for reduced tillage systems must be winter hardy, produce sufficient biomass to smother weeds, mature early, and preferably add nitrogen to the system. Tools must effectively kill the cover crop without tillage and also prepare the soil to receive a transplant or seed.
Our goal is to increase organic farmer economic and environmental sustainability through soil conservation and reduced tillage. Through SARE Project SW11-072 we have carried out four on-farm experiments, cover crop variety trials, and initiated a long-term systems experiment. This project will continue our systems-based work to develop and implement reduced tillage strategies for organic vegetable cropping in the maritime Northwest and other northern climates. Our future focus is to reduce risk for early adopters of reduced tillage by sharing successes and failures. We will also encourage more wide-spread adoption of reduced tillage by building on our previous experience to address specific obstacles and remaining questions, including:
- Which implements and strategies are most effective to manage residue in zone-tilled ground? (Objective 1)
- How does reduced tillage affect nutrient cycling and fertility management? (Objective 2)
- Which cover crops, mixes, and termination strategies perform best? (Objective 3)
- What specific challenges and opportunities do continuous reduced-tillage present? (Objective 4)
We will address these questions and extend our outreach (Objective 5) by:
- Facilitating research with seven commercial organic vegetable producers. We will improve residue management and compare cover crop termination strategies through on-farm trials and demonstrations. (Objectives 1, 3, and 5)
- Continuing an on-station long-term reduced tillage cropping systems experiment with three cash crops in rotation and adaptive management to include new cover crops and equipment improvements. Specifically, we will implement more aggressive zone tillage. (Objectives 1, 2, and 4)
- Executing 6 cover crop variety trials at two different research stations. (Objective 3)
- Reaching out to producers through field days, farm walks, articles, a video, and presentations to state-wide, regional, and national audiences. (Objective 5)
- Develop and analyze best strategies for cover crop residue management in zone tilled organic agriculture systems: Zone tillage has thus far provided the most interest among cooperating growers. Our current zone till treatment will be modified to provide more aggressive in-row tillage and a second zone tiller will extend our ability to reach more farms. We will measure the success of zone tillage by comparing soil temperature and crop yield in zone-tilled and full-tilled treatments in on-farm trials and in our long-term reduced tillage systems trial. We will also measure zone tillage success by comparing the density of volunteer cover crops and weed management in the inter-row for the two cover crop termination methods.
- Evaluate nitrogen cycling dynamics in reduced tillage organic systems: Through our previous cover crop trials we have been able to identify a successful legume cover crop (Purple Bounty vetch) for inclusion in our long-term reduced tillage trial. We will focus our evaluation of nutrient cycling dynamics in tilled and reduced tillage treatments following vetch by measuring cover crop N at termination, cover crop decomposition rate dynamics, soil nitrate and plant uptake by broccoli through the season each year.
- Select cover crops and termination strategies for reduced tillage organic agriculture: Successful cover cropping is essential to reducing risk in adopting reduced tillage organic vegetable production. The cover crop must produce enough biomass to effectively suppress weeds and also reach a late developmental stage to mechanically terminate while accommodating a relatively short growing season. One of the largest barriers to successful organic reduced tillage is termination of the cover crop. We will perform cover crop trials at two research stations (WSU Puyallup and WSU Mount Vernon) during each year of the grant. We will measure above-ground biomass and carbon to nitrogen ratios of different varieties and mixtures, and will also consider timing for termination and compare termination methods (roller/crimper vs. flail mower) for grain cover crops.
- Develop and analyze strategies for long-term continuous reduced tillage in organic agriculture: To date we have not experimented with continuous reduced tillage methods in northwest Washington. We implement annual fall tillage to prepare the ground for winter cover crop seeding. However, we see the ability to eliminate fall tillage as an important next step to soil quality improvement which has been shown to occur over the long-term. We will measure soil quality indices (e.g. penetrometer, bulk density, chemical properties, and soil fauna) and weed populations in this treatment and the other 5 treatments in the long-term reduced tillage experiment.
- Provide essential support to 15 western Washington organic producers implementing reduced tillage techniques on their farms. Our surveys show 25-30% of respondents have tried some form of reduced tillage, but only 2 or 3 farmers in our stakeholder base have adopted the techniques we have studied. We will increase the number of commercial farms adopting these techniques through farmer recruitment at our events, and allowing farmers the use of our equipment.
We continued a long-term experiment on reduced-tillage organic agriculture that was initiated in fall 2011 at the WSU Puyallup Research and Extension Center. The experiment originally included 6 treatments that varied in cover crop termination and ground preparation strategies. Beginning in summer and fall 2014 we transitioned one of the treatments to continuous organic reduced-tillage.
Specific accomplishments under each of our objectives include:
Develop and analyze best strategies for cover crop residue management in zone tilled organic agriculture systems:
A more aggressive zone tillage system was introduced in 2015 with the use of a modified walk-behind tiller. With this strip tiller, soil temperature was different than the no-till treatment for some of the growing season (Figure 1). In 2016, a PTO-powered strip tiller was designed, built and implemented in the experiment (Figures 2 and 3).
Figure 1. Mean daily temperature by tillage treatment type at WSU Puyallup, 2015. Thickness of bands indicate standard error. Statistical significance of contrasts between treatments on each day is indicated by * for P < 0.05 and + for P < 0.1. Top row represents contrasts between Full Till and both reduced till treatments (No Till and Strip Till) and bottom row represents contrasts among reduced tillage treatments (No Till and Strip Till).
Figure 2. PTO-powered strip tiller designed and built at the WSU Puyallup Research and Extension Center.
Across 2015 and 2016, treatment significantly affected squash yields (treatment P value =0.01, year P value = 0.1; treatment X year P value = 0.6) (Figure 3). The Full Till treatment was significantly different than the lowest yielding treatment (Roll + NoTill), but not different than other treatments. Among reduced tillage treatments and across 2015 and 2016, type of termination had a notable effect on yield (P value = 0.075) with flail mowing yielding more squash (Figure 4). Type of tillage was not significantly different (P value = 0.12) (Figure 5).
Figure 3. Squash yield by treatment for 2015 and 2016 combined.
Figure 4. Squash yield for 2015 and 2016 by cover crop termination type for reduced tillage treatments (P value = 0.075) .
Figure 5. Squash yield for 2015 and 2016 by soil preparation type for reduced tillage treatments (P value = 0.12).
In 2015 there was no significant treatment effect for broccoli (P value = 0.361) or beans (P value = 0.875). In 2016, the continuous reduced tillage treatment yielded significantly greater broccoli than full till or other reduced tillage treatments (P value < 0.0001) (Figure 6). Bean yields were significantly higher with Full Till and Flail + Strip treatments than other treatments (P value = 0.025) (Figure 7). Broccoli is grown following vetch and vetch is not terminated with rolling, so no evaluation of effect of termination type was considered. For beans, however, it was clear that Strip Till resulted in significantly higher yields (Figure 8) (P value = 0.016).
Figure 6. Broccoli yield by treatment in 2015 and 2016 at WSU Puyallup Research and Extension Center
Figure 7. Bean yield by treatment in 2015 and 2016 at WSU Puyallup Research and Extension Center
Figure 8. Bean yield by tillage type for reduced tillage treatments in 2016 at WSU Puayllup Research and Extension Center
Evaluate nitrogen cycling dynamics in reduced tillage organic systems:
Nitrogen cycling and cover crop decomposition dynamics in vetch cover crop were examined with residue bags in both 2015 and 2016. Fertilizer was withheld from ½ of each plot in this experiment to better distinguish nitrogen contribution from cover crop. In the full tillage and strip tillage treatments residue bags were buried at 10 cm and in the no-till treatment bags were left on the soil surface. Bags were recovered at 5 times throughout the growing season and weighed. A subsample of the residue was ashed to account for soil contamination in the residue bags. Soils were sampled for nitrate testing each time bags were removed.
Select cover crops and termination strategies for reduced tillage organic agriculture:
A cover crop variety and termination timing experiment was performed with Kale as a cash crop. Terminating cover crops with organic methods generally requires waiting relatively late in the spring for cover crops to mature. The purpose of this experiment was to examine opportunities for pushing the termination earlier to increase the growing season for cash crops. The experiment was repeated at two sites in 2015 and included 3 cover crop selections (common vetch, Aroostook rye, and rye-vetch mix), 3 termination dates (mid-April, early May, mid-May), and 2 tillage types (full-till and strip till). The experiment was also repeated in 2016 at 2 sites, though excessive soil wetness resulted in a loss of the vetch crop at one of the sites. The same experiment has been planted again for summer 2017 at 1 site.
We investigated spatial-explicit cover cropping as another cover cropping strategy for strip tillage in 2016. Six different cover crops were planted in the strip-till zone with and without rye in the remaining plot. The presence of rye significantly reduced cover crop growth across all six cover crop types (Figure 9).
Figure 9. Cover crop biomass in the strip-till zone when planted with and without rye in the non-strip-till zone.
Develop and analyze strategies for long-term continuous reduced tillage in organic agriculture:
In summer 2014 we transitioned one of our 6 original treatments in the long-term trial to a continuous organic reduced tillage treatment. Plots were planted to a summer cover crop of Sorghum X Sudan grass and we used a seed drill to plan winter cover crops through this cover crop. This worked well for rye, but vetch did not establish successfully.
We followed the rye cover crop with beans and squash. Despite the poor vetch establishment we still proceeded with planting broccoli in these plots. We were successful in growing beans, squash, and broccoli in the continuous reduced-tillage plots.
In summer 2015 we acquired a minimum till drill and used this to seed cover crops in fall 2015. The continuously reduced tillage treatment was seeded into the previous season’s cash crop after flail mowing and undercutting. Rye established well in this treatment and rye biomass was significantly greater than the full till treatment in 2016 (Figure 10). Vetch did not produce as well without tillage and vetch biomass was significantly lower in the continuous reduced tillage treatment (Figure 11).
Figure 10. Rye cover crop biomass in 2015 and 2016 at WSU Puyallup Research and Extension Center.
Figure 11. Vetch cover crop biomass in 2015 and 2016 at WSU Puyallup Research and Extension Center.
Earthworm populations were higher in spring 2015 and spring 2016 in both the continuous reduced tillage and rotational reduced tillage treatments (Figure 12).
Figure 12. Earthworm biomass in 2015 and 2016 at WSU Puyallup Research and Extension Center.
Provide essential support to 15 western Washington organic producers implementing reduced tillage techniques on their farms.
- One on-farm research trial and two on-farm demonstrations were supported in 2016. In the on-farm trial at Oxbow Farm strip tillage resulted in significantly less yield of summer squash than full tillage.
Impacts and Contributions/Outcomes
A listserve of past participants in field days and symposia grew from 160 in 2015 to 212 in 2016. Two field were held at WSU Puyallup in 2016 (101 attendees). 45% of the attendees were farmers, and 30% of attendees were certified organic farmers.
Most field day attendees indicated that their primary interests in reduced tillage in organic agriculture were improving soil quality (95%, n=82), reducing weed pressure (54%, n=46), and reducing greenhouse gas emissions (42%, n=36). Fewer attendees cited improved produce quality (36%, n=31) and reduced fuel usage (33%, n=28). 92% of Participants (n=35) of the second field day stated they had a somewhat to great increase in their knowledge of reduced-tillage equipment, cover crop nitrogen, soil moisture monitoring, long-term weed management, or transitioning to reduced-tillage systems.
When queried about barriers to adoption, producers consistently point to access to equipment. Largely because of this project, Conservation Districts in King and Pierce counties recently purchased no-till drills and project results are being used to shape lending programs and recommendations for adoption. Through the project, a powered strip tiller was developed to strip till in heavy cover crop residue. This equipment development generated great excitement and in 2016, thirty-two of the 101 attendees at field days indicated they were interested in hosting on-farm experiments. Seventy-five percent (75%) of farmers (n=12) at a field day in 2016 indicated they intended to implement changes to transition to reduced tillage.
Field day participants were asked about their future management plans in regards to reduced tillage and soil moisture management. Farmers that attended the second field day (n=12) indicated that they intended to make changes in long-term weed management (100%) and implement changes to transition to reduced tillage (75%). Additionally, 68% of all participants said they would change their soil moisture monitoring practices after the second field day (n=36).
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