Cover Crops as Living Mulch under Organic Vegetables

View the project final report

• 2015 annual report

Commodities

• Agronomic: clovers
• Vegetables: brussel sprouts, cucurbits

Practices

• Crop Production: cover crops
• Education and Training: on-farm/ranch research, participatory research

Incorporating long-standing leguminous cover crops into vegetable rotations is commonly known to improve soil quality and increase nitrogen availability to subsequent crops.  Small-scale, organic vegetable growers, however, struggle to include season-long covers on limited land.  Further, it can be difficult for growers to establish winter covers after harvest of late season crops like winter squash and Brussels sprouts.  Using cover crops as living mulches under vegetable crops could address both of these issues if vegetable yield is still comparable to clean cultivated controls.

In the 2015 we established two living mulch treatments under acorn squash and Brussels sprouts on four cooperating organic farms in south central Wisconsin.  The living mulches were Dutch white clover and medium red clover.  In 2016 we tilled 24” planting strips into the established clovers and planted the same vegetable crops in reversed locations.  We also applied marsh hay mulch in half of each plot to completely cover the planting strip.  In both years these treatments were compared to a clean cultivated control. To measure the effect of the living mulches, we collected weed density and biomass, cover crop density and biomass, labor time per treatment, and cash crop yield.

Key Findings:

• Using living clover mulch under Brussels sprouts can achieve an N credit without significant yield loss when planting into an established clover stand.
• Acorn squash yield was negatively impacted by living mulch, especially when planted into an established clover. Also, although we did not measure survivorship specifically, we anecdotally noted that many squash plants died in the marsh hay mulch.
• Dutch white and medium red clover performed equally as living mulches. Neither had an impact on weed density or biomass in year 1 (the year they were established).  Both dramatically decreased weed density and biomass in year 2.  There was no difference in their effect on vegetable crop yield.
• In the clean cultivated control, Brussels sprouts mulched with marsh hay outperformed those left open by over a half pound in yield per plant and were well worth the time and money to mulch them.

Objective 1:  Build on existing research to further develop a living mulch system that will maintain vegetable yields as compared to clean cultivated controls.

Previous research with living mulches has shown some decrease in vegetable yield (SARE Project# LNE 10-293), likely due to water and nutrient competition between the mulch and vegetable crop.  The following innovations in this project were designed to reduce weeds and minimize nutrient and water competition in order to maintain vegetable yields:

• Establishing vegetables and weeding twice prior to planting living mulches in year 1
• Tilling a 24” vegetable planting strip in year 2
• Using marsh hay mulch in the planting strip in year 2

Objective 2:  Gather information on how two vegetable crops perform in year 1 and year 2 of a living mulch system.

To measure the effect of the living mulches, we collected weed density and biomass, cover crop density and biomass, labor time per treatment, and cash crop yield.  Data were analyzed separately for the establishment year and the second year of the trials.  An analysis of variance (ANOVA) was conducted using the R package lme4 (Bates et al 2015).  Means and 90% confidence intervals for each treatment were calculated with the R package lsmeans (Lenth 2016).  A confidence level of 90% was used, meaning that for each comparison that is statistically significant, we are 90% confident that the difference is due to the treatments and not to chance variation.

Objective 3:  Share information with growers at two field days (2015 & 2016).

We held a field day at High Meadow Farm on 9/15/15 for organic vegetable growers.  The 20 attendees toured the trial plots, received a handout with the results to date, and discussed pros and cons of clover living mulch.  We held a second field day at Roots and Shoots on 9/21/16.  Severe storms came up right before the event time and kept many who had RSVP’d from attending.  In the end, only 4 growers attended the event.  We toured the plots, distributed a handout with second year results, and discussed next steps for living mulch.

2015 Living Mulch Field Day Handout

2016 Living Mulch Field Day Handout

Objective 4:  Write up project findings and recommendations in an illustrated bulletin to be posted on the FairShare website and disseminated through the FairShare listserv, the CRAFT listserv, and the Midwest Cover Crops Council listserv (over 1000 listserv recipients, combined.)

The Living Mulch under Organic Acorn Squash and Brussels Sprouts bulletin was completed and distributed in May 2017.

References:

Bates, Douglas, Martin Maechler, Ben Bolker, Steve Walker (2015). Fitting Linear Mixed-Effects Models Using lme4. Journal of Statistical Software, 67(1), 1-48. doi:10.18637/jss.v067.i01.

Lenth, Russell V. (2016). Least-Squares Means: The R Package lsmeans. Journal of Statistical Software, 69(1), 1-33.  doi:10.18637/jss.v069.i01