Cover cropping strategies for year-round weed control on mixed vegetable farms in southern New England

Cover cropping strategies for year-round weed control on mixed vegetable farms in southern New England

Summary

The four cover crop/tillage regimes were repeated on the same plots, vegetables were planted, and a second year of data was collected on yields and labor requirements for each regime. In addition data was collected on the number and types of weeds in each regime. Soil health was assessed in April, and soil moisture, nitrogen, and microbial activity were tracked throughout the growing season. The first winter workshop was held February 17; 29 farmers and service providers attended. The spring twilight meeting on April 12 included a tour of cover crops; 57 people attended. An on-farm twilight meeting in June featured zone tillage and was attended by 23 people. The cover crop/tillage research was a highlight of the September 1 twilight meeting, attended by 35 people. Nine URI students interested in careers in agriculture participated in the cover crop/tillage research project as student employees and 16 students learned about the project through the vegetable production class.

Objectives/Performance Targets

Performance Target: Twenty vegetable producers (10% of Rhode Island total) will adopt a combination of cover crops and reduced tillage to control weeds and improve soil quality on a total of 500 acres (25% of RI vegetable acreage). Quarterly twilight meetings and workshops will attract 200 growers over three years; participants will learn about new vegetable varieties and production methods they can adopt on their farms. Fifty University of Rhode Island students pursuing careers in agriculture will receive hands-on learning opportunities by assisting with cover crop trials as part of the vegetable production class or as summer interns.
Milestones
• 20-30 growers will attend each Twilight Meeting at the URI research farm. This milestone will be met repeatedly in years 1-3.
o 40 farmers, 11 service providers, and 6 agriculture students attended the April Twilight meeting. Only 15 farmers attended the June twilight meeting; low attendance was attributed to the unseasonably cold, wet weather. The September twilight meeting was attended by 18 farmers.
• At least 50 growers will attend each winter workshop. This milestone will be met repeatedly in years 1-3.
o The first winter workshop, held February 17, 2011, was attended by 20 farmers, mostly from Rhode Island. Attendance was well below expectations due to failures in advertising the workshop to growers in Massachusetts and Connecticut, and a lack of communication that resulted in a cover crops workshop being held in Connecticut the previous week The second workshop has been scheduled for February 16, 2012, and is already being advertised in all three states.
• 15 URI undergraduate students will participate in the cover crop research each year as part of the vegetable production class.
o We exceeded our expectations with 16 students in this year’s class. In addition 2 graduate students and 7 undergraduate students participated in the project as members of the farm crew.
• By the end of the second year 50 growers will have contacted us for more information on cover crops/reduced tillage and individual assistance in implementing these practices on their farms.
o Seven growers have already contacted us for more information and individual assistance at the end of the first growing season. At least two growers have borrowed our zone tiller to attempt zone tillage on their farms. Data for the second growing season is not yet available.
• The field research will generate new information on the relative efficacy of the four cover crop + tillage treatments for improving soil quality, controlling weeds, and maintaining profits.
o A second year of data was collected on crop yields and labor inputs. Soil was sampled biweekly to track nitrogen levels and microbial activity. Data was collected on the types and number of weeds associated with each treatment.

Accomplishments/Milestones

Research
2011 was the second growing season for the project. We got off to a better start than in 2010, in that the field and all necessary equipment were in place prior to the beginning of the growing season. Wet spring weather prevented us from establishing a spring lettuce crop, but the summer crops were established on time. In addition to data on crop yields and input costs (including labor) we monitored weed populations and soil nitrogen levels throughout the growing season. The vegetable crops were altered slightly for 2011 in that we grew cucumbers as well as melons, and the broccoli was replaced with cabbage. All plots were fertilized through the irrigation system with liquid fish emulsion. The recommended rate was sufficient in the conventional tillage treatment, but we encountered problems with nutrient deficiency in the other treatments.
Treatment A: Conventional Tillage
Use of both walk behind and tractor mounted tillers improved our weeding efficiency. The ability to till several times controlled weeds both in the rows and in the walkways. This improved yield for all crops, especially the cabbage.
Treatment B: Zone Tillage
We rolled and crimped the winter rye in the beginning of June at anthesis. Our biomass was very low due to problems with stand establishment and right away we knew we were going to not have enough of a mulch layer to compete with the summer weeds. The mulch was enough to suppress the weeds until the second week in July, after which the plots became a thick mat of weeds, primarily large crabgrass. Mowing was utilized the remainder of the summer in an attempt to control weed height and maturity. Planted rows were weeded by hand although large crabgrass continued to be a problem. The zone builder created a furrow making crop establishment, especially for fine seeded crops (salad, carrots, cabbage) difficult. Crop yield was impeded by weed pressure in all crops but tomatoes. We have been unable to find a way to combine zone tillage and plastic mulch, which negatively impacts cucurbit yields.
Treatment C: Raised beds and Perennial Mulch
Raised bed construction was challenging, as the perennial mulch limited our ability to bring soil in from the alleys. Some of the perennial mulch was lost to errors in row placement, and weed levels were higher in the newly-seeded mulch. Competition with weeds continued to be a problem in beds without plastic mulch. Between the beds the weeds, perennial rye and white clover were mowed to limit height and promote spreading of the clover. Overall the treatment yields were similar to that of the conventional treatment for the tomatoes, melons, and cucumbers but weed problems stunted the cabbage.
Treatment D: Intercropped Crimson Clover
Weeds were controlled by hand or with tractor mounted tiller until the cabbage had emerged and had two true leaves, at that time the crimson clover was seeded. Our weeding efforts were hampered when the large crabgrass reestablished and continued to compete with the crimson clover. Similar to treatments B and C we utilized mowing to keep the weeds in check and encourage branching of the crimson clover. While the crimson clover did not suppress the weeds, we were able to establish a nice cover crop and experienced a noticeable yield increase in the tomatoes. The crimson clover also resulted in the highest marketable yields in both melons and cucumbers. The cabbage crop was off to a good start but the weeds and clover started crowding it out eventually leading to a very small harvest.
Tomatoes
A wide variety of determinant slicing tomatoes were planted with a small sub plot of Celebrity plants randomly placed in each treatment. The mix of varieties was larger than intended as sparrows destroyed the first crop of tomato seedlings in the transplant greenhouse and we had to use remanat seed from previous years. The plots were staked this year keeping the majority of the plants upright until late in the season when the trellis could not hold the plant weight and started to sag or break. The trellising raised the quality substantially as the tomatoes were no longer touching the ground. We saw a large difference in the marketable yields between the treatments. Total marketable yields (provided) and total yields show a large treatment effect, A 176 lbs., B 64 lbs., C 140 lbs., and D 300 lbs. Differences in yields were primarily due to nutrient deficiencies in some plots, but were also impacted by disease. Both powdery mildew and early blight were problematic.

Melons and Cucumbers
This year we planted a single variety of melon, ‘Diplomat’, which is a powdery mildew resistant Galia type. All treatments utilized BioTelo biodegradable black plastic except for treatment B. This improved yield but also caused some damage on the bottoms of the fruit, as the weight of the fruit caused the mulch to degrade. While we were able to get a decent harvest from the melons gummy stem blight damaged the crop half way through the growing season. This disease skewed our marketable yield by delaying maturity and distorting several fruits. The overall marketable yields for melon were as follows: A 272lbs., B 0 lbs., C 314lbs., D 322lbs. We also planted a powdery mildew resistant slicing cucumber. Cucumber yields were: A 209lbs., B 21 lbs, C 203lbs., and D 258lbs.
Cabbage
The cabbage was seeded in two rows side by side in the bed. Direct seeding turned out to be a poor choice for this crop in reduced-tillage treatments. While we were able to control the weeds in treatment A all other treatments were heavily impacted by weeds. We were able to knock back the weeds in Treatments C and D enough to produce a small late harvest, but nothing materialized in treatment B.
Salad and Carrots
Weed pressure made carrot and salad establishment very difficult this season. The first seeding quickly became full of weeds in all treatments. Subsequent plantings were eaten by mice and voles. After our third seeding attempt, the seeding was terminated and our focus directed back to the other crops. Incorporation of flaming into our weeding regime should help to create better seed beds for these crops next season. We are also thinking of growing head lettuce instead of salad mix, that way we could use transplants to keep the mice and voles from eating all the salad seeds and seedlings.
Soil Analysis with Solvita
In 2011 we incorporated several tools to help us measure various features of the soil. The Solvita test is a rapid way to measure soil microbial activity and potentially available nitrogen. We sampled all 48 individual plots every 2 weeks from April 22 through October 17. While we are still analyzing the data, initial results indicate that the soil microbial activity differed between tillage/cover treatments from May 21 through August 2. The perennial living mulch had the highest microbial activity during this period and the conventional tillage treatment had the lowest. We also monitored soil moisture and collected soil samples for nitrate analysis.
Lessons Learned and plans for 2012
Weeds continue to be a major issue, and none of the reduced tillage methods are resulting in satisfactory weed control. This is partially due to a high soil weed seed bank in our field. Crab grass is a particularly severe problem. We are still struggling to make the zone tillage work for us. Our zone builder is creating a poor seed bed that forms a furrow below soil level making the planting bed very difficult to weed and creating difficult growing conditions for the crop. We will be making a few changes to our zone builder this winter such as adding an elevated duck foot on the ripper shank to build the bed up above the soil. This fall we doubled our winter rye seeding rate for treatment B and are hoping the extra biomass will have greater effect on controlling weeds. In 2012 we also plan to switch to a 3 foot wide traditional plastic mulch for the melon/cucumber rows. The narrower width will permit us to lay the mulch flat on the ground, avoiding the problems with disturbing the perennial living mulch when creating raised beds. The traditional plastic also is more effective at protecting melon fruit from bottom rot. We are also considering transplanting our cabbage and lettuce crops to help with weed control.

In 2011 we held three twilight meetings and a winter workshop. The Spring twilight meeting set an attendance record, and also provided an opportunity for URI students to interact with growers. The June twilight meeting was held on a grower’s farm. Interest in cover crops remains strong among attendees at twilight meetings. Tillage reduction has attracted less attention, perhaps due to equipment limitations among the growers.

• Jeff Pieper presenting results of cover crop/tillage research at twilight meeting Sept. 1
• mowing the living mulch in treatment C
• Living mulch treatment in mid-July
• soil microbial activity in cover crop/tillage treatments as measured by Solvita test
• zone-tilled treatment in mid-July

Impacts and Contributions/Outcomes

The research is still not to a place where it is resulting in contributions or outcomes to report. Data is still be analyzed on the impacts of the extension component. However, it is clear that the increased research and extension effort in vegetable production financed by this project is having a significant impact on the attitude of the university administration regarding extension to food production agriculture, and regarding our research farm. In addition, the agriculture community is once again viewing URI as a source of relevant information and expertise.

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