Selecting management practices and cover crops for reducing tillage, enhancing soil quality, and managing weeds in western WA

Project Overview

Project Type: Research and Education
Funds awarded in 2011: $196,626.00
Projected End Date: 12/31/2014
Region: Western
State: Washington
Principal Investigator:

Annual Reports


  • Vegetables: broccoli, cucurbits


  • Crop Production: conservation tillage
  • Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research, participatory research, workshop
  • Energy: energy use
  • Farm Business Management: budgets/cost and returns
  • Natural Resources/Environment: carbon sequestration
  • Pest Management: cultural control, mulches - killed, weed ecology
  • Production Systems: agroecosystems, organic agriculture
  • Soil Management: earthworms, organic matter, soil analysis, soil microbiology, soil chemistry, soil physics


    In response to organic grower desires to improve soil quality through tillage reduction, while maintaining adequate weed control, we formed a research and producer group to plan research and extension activities matched to the unique climate, soil properties, and topography of western Washington. A summary of activities and findings under each of three project goals includes:

    1) Identify production methods that effectively integrate cover crops and reduced tillage technologies to improve soil quality while reducing in-season weed pressure and seed bank populations on western WA organic farms.

    Between 2012 and 2014 we initiated a multi-year reduced tillage cropping systems experiment and collaborated with organic producers to execute six on-farm experiments, one on-farm demonstration, and two cover crop selection trials.

    The reduced tillage technologies evaluated to prepare soil for planting or transplanting included zone tillage (12-inch wide swath with a ground-driven strip tiller) and a no-till planting aid (disturbs a 2-inch swath of soil). Relative to complete tillage we found that soil at 5-10 cm in reduced tillage treatments was more compact and moist, and temperatures at 10 cm were 1.7 to 2.8 C cooler. Broccoli yields in research plots did not differ by tillage treatment in any of the three years, indicating no effect of reduction in tillage on broccoli yield. Squash yields were higher in full-tilled plots in 2012 and 2014. On-farm trials also indicated reduced squash yields with zone tillage relative to conventional tillage, especially in heavier-textured soils. However, broccoli planted to zone-tilled vetch performed as well as the farmer’s standard practice in two successive years with less equipment passes, but more time spent hand weeding.

    In the fall of 2011 and 2012, cover crops were planted to evaluate variety, termination type, and termination time. Cover crops (five grains, five vetches, and seven mixes) were terminated at two different maturity stages: 60% and 100% flowering for vetches and late anthesis and early milk for grains. Cover crops were terminated with either flail mowing or a roller/crimper. The roller/crimper method was ineffective for vetches irrespective of termination date. Termination time influenced the effectiveness of rolling in grains; “early” was less effective than “late.” Termination time also influenced the percent weed cover (in 2013 only): “early” had fewer weeds than “late.” Rolled grains had lower weed percentage cover than did flailed grains. Termination by rolling was more effective for rye than barley. Vetches contained between 117 and 179 kg ha -1 N.

    2) Evaluate profitability and greenhouse gas impacts of reduced tillage cropping systems on these farms.

    Insitu soil respiration was consistently higher in the full-tillage treatment than in the reduced tillage treatment for the first seven days after tillage. The effect was most dramatic five hours after tillage when the spader treatment generated CO2 at a rate 1.5 to 2.2 times the rate in untilled areas. In both 2013 and 2014, tillage was significant on days 1, 3, and 7, with CO2 emissions higher in fully tilled plots than in the no-till plots. Emissions were highest on Day 0. CO2 emissions in both zones (In-Row and Out of Row) were similar within the full till treatment. The In-row zone occasionally produced higher emissions but was not consistently different, in the no-till treatment.

    From an economic perspective, there was no significant difference among treatments in broccoli. Yield and time spent weeding were not significantly different in any of the three years studied. Both tractor-labor and fuel usage were greater in the spader treatment than in the reduced tillage treatments. Treatments utilizing the roller/crimper utilized about 0.5 hours less labor per acre than treatments utilizing the flail mower. Treatments utilizing the planting aid used about two gallons per acre less fuel than treatments using the strip tiller. For squash, there seems to be more yield potential in the spader treatment, as long as weeds are adequately controlled. Hand weeding times, the largest labor requirement in squash, were greater in the spader treatment in July 2012 and July 2013, but tractor cultivation done in June 2014 reduced the effort required for controlling weeds by hand in that year in the spader treatment.

    3) Facilitate adoption of reduced tillage technologies and ideas to a wide audience.

    Interest in incorporating cover crops and reducing tillage to improve soil quality is high among organic growers in Washington. Over the three year project we have directly reached 210 producers and professionals in six field-based events. Evaluations at each field day have helped us determine the degree to which our research has influenced growers' adoption of reduced tillage techniques and what remaining challenges exist. Agricultural professionals also attended the field days to increase their knowledge on the subject and better serve their clientele.

    Weed management is an impediment to further adoption at cooperating farms in this study and presumably other diversified vegetable farms. We have learned that despite cover crop biomass as high as 7 Mg ha-1 and small percentages of weeds prior to termination, weeds will find their way through the mulch created by the terminated cover crop. When this happens, managing them is difficult. Also from our evaluations we hear consistently about barriers to adoption of reduced tillage organic practices. The barriers most often cited are: lack of access to specialized equipment, lack of a successful example that can be emulated, and worry about increased weed and pest pressure. Yet, the interest in reduced tillage organic agriculture continues to be high and we see potential for further adoption as new strategies are developed and equipment becomes more available.

    Project objectives:

    Objective 1: Identify production methods that effectively integrate cover crops and reduced tillage technologies to improve soil quality while reducing in-season weed pressure and seed bank populations on western WA organic farms.

    Performance targets:

    1. Through rigorous evaluation we will identify reduced organic no-till systems that are the most practical, economical, and beneficial to soil quality for Pacific NW vegetable producers.
    2. Weeds are a challenge when tillage and cultivation - the most common weed management tools for organic farmers – are removed or reduced. An important performance target will be to find cover crop species, cover crop management techniques, and cover crop termination strategies that combine to suppress weeds to the same degree as cultivation and tillage.
    3. Find cover crop varieties that mature early enough to be terminated and still plant or transplant a variety of cash crops. They must also produce sufficient biomass to cover the soil with a weed-suppressive mulch.
    4. Introduce leguminous cover crops into organic no-till rotation either alone or in combination with a grain cover crop to provide a nitrogen source while still serving a weed-suppressive function.

    Objective 2: Evaluate profitability and greenhouse gas impacts of reduced tillage cropping systems on these farms.

    Performance targets:

    1. Farm businesses that adapt new techniques must remain profitable to remain viable. To provide farmers with a broad analysis of reduced tillage cropping systems, we will compare relative profitability of these systems to their conventional counterparts. This will allow us to more fully address the viability of systems and also be extremely important in outreach.
    2. Provide regionally relevant information to growers for reduced till organic vegetable production.
    3. Consumers are increasingly aware of the environmental impacts of agriculture. Another performance target for our project will be to increase our understanding of greenhouse gas impacts from potential increased carbon storage and reduced fuel use and convey this information to growers and the public.

    Objective 3: Facilitate adoption of reduced tillage technologies and ideas to a wide audience and identify tools and strategies most effective at encouraging behavior change.

    Performance targets:

    1. Since our 2009 symposium and planning meeting, we have seen increased interest in reduced tillage in organic vegetable production. One of our “light house” farmers and cooperators, who already uses cover crops extensively, experimented this year with strip tillage (imposed with a walk-behind tiller) to grow winter squash surrounded by a mat of cover crop. Enabling, enhancing, learning from, and broadcasting this kind of experimentation and behavior change is an important performance target for our project.
    2. We will survey farmers throughout our field days and workshops to monitor their interest in adopting and willingness to try new soil conservation strategies such as reduced tillage. We will also survey and interview farmers to see what challenges they perceive to changing behavior around soil tillage. Identifying the top three or four strategies likely to result in behavior change will be another performance target.
    3. Facilitating farmers to overcome the obstacles to adopting reduced tillage will be another performance target. Equipment is likely to be one of these challenges, and working with local agencies such as conservation districts and NRCS personnel to help acquire appropriate technologies for use by interested farmers will be another performance target.

    Research objectives 1 and 2 will be addressed by project researchers and producers by evaluating reduced-till cropping systems and cover crop varieties in the maritime NW through experiment station and on-farm trials. Outreach objective 3 will be addressed through evaluations and surveys of producers that participate in research and outreach events.

    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.