Tillage reduction and cover cropping for enhanced soil quality and weed management in western Washington organic vegetable farms (OREI)

Organic vegetable growers in western Washington pass over their fields 10 to 20 times annually with tillage equipment ranging from spring tooth harrows to mold board plows. Soil preparation activities such as plowing, rototilling, and even spading pulverize large‐bodied soil organisms and reduce soil carbon storage and aggregates. Successful reduced tillage in organic agriculture relies on cover crops to produce a weed controlling mulch layer. We evaluated four cover crop varieties for their potential success in an organically‐certified reduced tillage system. Using the two most successful varieties, we then evaluated soil quality parameters, weed population dynamics, and yield under two methods of cover crop termination (flailing and roller/crimper) and three methods of soil preparation (no‐till planting aid, strip tillage, and conventional tillage) at both the WSU Puyallup and Mount Vernon research centers.

At Puyallup, ‘Delicata’ squash yield was higher under ‘Lana’ vetch (11.1 tons/acre) than ‘Strider’ barley (2.2 tons/acre). The increased yield following ‘Lana’ was likely due to increased nitrogen (N) availability in soil from the legume cover crop. ‘Lana’ vetch produced 2.5 and 3.1 tons/acre at Puyallup and Mount Vernon respectively, with 3.1% N content at both sites. ‘Strider’ barley produced 4.5 and 3.7 tons/acre at Puyallup and Mount Vernon with 0.93 and 0.95% N content. Mid‐season soil nitrate averaged 26 ppm under vetch and 7.3 ppm under barley. Cover crop termination and tillage treatment combinations did not significantly affect yield at Puyallup (p=0.16) or plant biomass at Mount Vernon (p=0.17). Bulk density was lower in the flail + till treatment (p=0.001) at both sites, but not different between planting aid and strip tillage. Infiltration was not different between treatments. Endogeic earthworms were negatively affected by both strip tillage and full tillage (p=0.001) and the nematode structure index (an indication of a soil ecosystem with more complex food web linkages) was decreased by full tillage compared to strip tillage (p=0.03). Weed populations were significantly reduced at both sites at all assessment dates in all reduced tillage treatments when compared to conventionally tilled plots (p=0.001). Average daily light penetration remained near zero below the mulch layer created by both flailing and roller/crimping throughout the season in ‘Strider’ at both sites, but flailed ‘Lana’ did not block light better than the tilled treatment in late August. Weed biomass was significantly higher in ‘Lana’ vetch compared to ‘Strider’ barley at Puyallup (p=0.0035), but not between any of the other treatments in zones that were not hand‐weeded. In zones where hand‐weeding occurred, biomass was only significantly lower at the Puyallup site in reduced treatments of ‘Strider’ barley. No differences existed in weed biomass between cover crop termination and tillage treatments at Mount Vernon.

There was a treatment X site difference in hand‐weeding times such that at Puyallup hand‐weeding was faster with reduced till methods, but at Mount Vernon there was no difference.

Two field days were held in 2011 to highlight on‐going research in organic no‐till vegetable production. A total of 47 people attended the two field days. A “virtual field day” was produced and posted on‐line and was watched 300 times in 6 months. We evaluated the no‐till field days with a participatory evaluation; questions were asked of the entire group and results were recorded. Participants were encouraged by early progress, though questions remain about successful and complete integration of reduced tillage technologies into a diversified vegetable farm.

Grant Information

  • Project ID: 086
  • Project Status: Complete


  • Principal Investigator(s): Collins, D.
  • Investigator(s): Bary, A., Benedict, C., Burrows, C., Cogger, C., Corbin, A.
  • Grant Amount: $20,000


Wayman, S., C. Cogger, D. Collins, C. Benedict, I. Burke, and A. Bary.  2014.  The influence of cover crop variety, termination timing, and termination method on mulch, weed cover, and soil nitrate in organic reduced-tillage.  Renewable Agriculture and Food Systems. FirstView: 1-11. http://dx.doi.org/10.1017/S1742170514000246

Additional Funds Leveraged

This BIOAg – funded project has already leveraged grants totaling $942,118. Another $1,550,000 grant is in preparation.  See below.

2011‐2014. Collins, D, A. Corbin, C. Cogger, C. Benedict, A. Bary. Selecting management practices and cover crops for reducing tillage, enhancing soil quality, and managing weeds in western WA organic vegetable farms. Western SARE. $196,624. Awarded.

2012‐2014. Fortuna A., D. Collins, R. Turco, C. Cogger, A. Stone, A. Bary. Greenhouse Gas Emissions and Soil Quality in Long‐term Integrated and Transitional Reduced Tillage Organic Systems. USDA Organic Transitions. $745,494. Awarded

2012‐2013. Cogger, C., S. Wayman, C. Benedict, A. Bary, and A. Corbin. Choosing and managing cover crops to improve weed management in reduced tillage organic vegetable production. WSU BIOAg. $39,838. Submitted.

2014-2016:  Collins, D, C. Benedict, A. Corbin, A. Bary, and C. Cogger.  Increasing adoption of reduced tillage strategies on organic vegetable farms in the maritime Northwest.  Western SARE.  $249,919.  Competitive.