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

Four cover crop/tillage regimes were established, vegetable crops were planted, and first-year data was collected on yields and labor requirements for each regime. An equipment twilight meeting in June featured the cover crops roller and zone builder; 19 farmers and 2 service providers attended. As a result of that meeting one farmer arranged to have us zone-till her pumpkin field. A second twilight meeting on September 1 featured the research plots themselves and the variety trials; 17 farmers attended. A winter workshop scheduled for February will feature the first year’s research results and speakers on managing cover crops and estimating effects on potential soil nitrogen. Five URI students considering careers in agriculture were employed as summer interns and 18 students assisted with the variety trials and cover crop/tillage trials as part of the vegetable production class.

Objectives/Performance Targets

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.

• 20-30 growers will attend each Twilight Meeting at the URI research farm. This milestone will be met repeatedly in years 1-3. o 19 farmers attended the June Twilight meeting and 17 attended the September meeting. This was slightly below expectations, but only 5 growers attended both meetings. We have already scheduled and announced the twilight meetings for 2011, which should increase attendance.
• At least 50 growers will attend each winter workshop. This milestone will be met repeatedly in years 1-3. o The first winter workshop is scheduled for February 17, 2011.
• 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 18 students in this year’s class.
• 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.
• 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 Data was collected on the labor required to implement and maintain each cover crop + tillage treatment and on the effects on crop yield. Initial soil health evaluation was conducted.

Accomplishments/Milestones

The 2010 growing season was a real learning experience for us. In March we learned that the university had decided to put a new road through the field we had intended to use for this project. We were able to move the project to another field but the new field is stonier and much weedier than the field we had planned to use. The new field is also outside the deer fence and beyond the reach of the sprinkler irrigation system; we did have drip irrigation in the field. The field had been seeded to a mixture of winter rye, vetch, and white clover rather than to the straight winter rye we had planned to use.

We established four cover crop + tillage treatments in late May. This was later than we had planned on due to delays in obtaining the crop roller and difficulties in building the zone tillage unit. None of our tractors could handle the “off the shelf” units available from Unverfirth, so we constructed our own from a donated subsoiler unit and zone builders purchased from Unverfirth. The vegetable crops were seeded or transplanted the first two weeks of June. Because of the late planting date we planted half a plot each of lettuce and carrots, rather than using a succession planting. The trial was maintained and harvested through October; data was collected on yield and all inputs. In October treatments A and B were tilled and seeded to winter rye. Crop residue and large weeds were cleared from treatments C and D by hand; the treatments were not tilled.

Treatment A: Conventional Tillage
This treatment did relatively well, but even with tillage we were unable to keep the weeds entirely controlled. One difficulty was the stoniness of the field, which made it difficult to use our cultivating tractor.

Treatment B: Zone Tillage
This treatment had the poorest results. The abundant white clover was not killed by the roller-crimper, even with three passes, and became a major weed problem. The rye stand was not sufficient to prevent weeds from penetrating the killed cover crop mulch, but was sufficient to impeded cultivation. The zone builder was not able to prepare a seedbed sufficiently fine for the direct seeded lettuce, carrots, and broccoli although it was sufficient for the transplanted melons and tomatoes. We abandoned the lettuce and carrots in treatment B due to weeds and poor establishment.

Treatment C: Raised beds and perennial mulch
Treatment C did relatively well, partly because both the tomatoes and the melons had black plastic. The perennial mulch of ryegrass and white clover was slow to establish due to no rain, and did not effectively prevent weeds. However, the same mulch seeded two weeks earlier in another trial was very effective. The stones and the narrow space between raised beds made it impossible to mow the weeds in the perennial mulch, so a weed whacker was used to keep the vegetation at 4 inches.

Treatment D: Intercropped crimson clover
The late planting dates and lack of rain in June and July caused major problems in establishing the crimson clover. By the end of the season we had decent cover in the tomato and melon rows, but the clover was never seeded in the broccoli and carrot/lettuce rows because the weeds were too thick by the time the vegetable seedlings had established sufficiently for undercropping. The clover did not effectively suppress weeds even in the tomatoes and melons.

Tomatoes
We planted determinate slicing tomatoes, mostly Celebrity but also some other varieties. The plants were never staked, as we ran out of time, so many fruits were damaged by contact with the soil. Fruit was harvested from all treatments. Treatment B had the lowest yields but the greatest percentage of marketable fruit as the killed rye mulch effectively kept the fruit from contacting the soil. Treatment C had the highest yield, with 1212 pounds. This was the only treatment where black mulch was used on the tomatoes. The other three treatments had similar yields, with 666, 607, and 763 pounds harvested from A, B and D respectively.

Melons
We planted four varieties of melons. The plants best in treatments A and C where we used black BioTelo degradable mulch and raised beds. Total yields were 1509 pounds for treatment A and 1518 pounds for treatment C. Treatment D yielded 625 pounds with effective weed control but no but bare soil. Weed pressure reduced yields in treatment B to only 87 pounds. The biggest problems with the melons were coyotes and powdery mildew. The coyotes ate the ripe fruit, and the mildew killed the foliage so that only the first flush of fruit had acceptable quality.

Broccoli
Our Earthway seeder was not an effective tool for seeding the broccoli, as it seeded much too heavily. Most of the third replication failed to establish, and most of treatment B was abandoned due to weeds and poor establishment. The other plots produced a good yield, although we had problems with cross-striped cabbageworm in September. Yields were 66, 71, ad 80 pounds for treatments A, C and D respectively; the variation between replications masked any treatment effects.

Carrots and Lettuce
The initial planting of carrots failed to establish, and the lettuce was significantly impacted by weeds. The lettuce/carrot plots in treatment B were abandoned. The plots in the other treatments were retilled and reseeded in late July for a fall planting. The fall planting did quite well in reps 1 and 2, which were weeded and thinned on schedule. Plots in rep 3 were weeded and thinned late or not at all, which reduced yields and quality but did not eliminate the crop. Total carrot yields were 190 pounds for treatment A, 134 pounds for treatment C, and 218 pounds for treatment D. Total lettuce yields were 102 pounds for treatment B, 119 pounds for treatment C, and 92 pounds for treatment D.

We are modifying our zone tillage unit to improve seedbed preparation and are investigating either using a Jahn CleanSeeder or modifying our Earthway seeder to improve establishment of the direct seeded crops. We are changing the treatments slightly to eliminate raised beds, which should make it easier to cultivate. The BioTelo black mulch will be laid on flat beds instead. For 2011 we plan to use powdery mildew resistant melons and to install electric fencing around the field to eliminate the coyote problem. We are hoping that earlier planting and better planning will permit us to keep up with the weeds.

In addition to data on yields and inputs, in 2011 we plan to conduct weed counts, monitor soil temperature, and monitor soil microbial activity. Soil temperature will be monitored using an iButton temperature logger installed in each plot and correlated to an iButton and a soil temperature probe installed at the weather station. Soil microbial activity will be monitored using Solvita CO2 kits with sampling to be conducted monthly beginning one week after spring tillage.

We conducted two twilight meetings and have three twilight meetings and a winter workshop scheduled for 2011. Attendance at the twilight meetings was good considering that announcements were sent to growers only a few weeks before the meetings. Many growers expressed interest in the reduced tillage techniques, especially zone tillage. We have recruited a number of farmers for on-farm trials in 2011. We also had a surprising amount of interest in cover crops, especially from our sod producers who are converting large acreages back to annual crops such as corn and potatoes. We have had a lot of interest from URI students who become involved in the project through the Vegetable Crops class or summer internships. We hope to increase student involvement and foster connections between students and growers through our spring twilight meeting, which is scheduled for March 31.

• A C treatment plot in mid-July
• A D treatment plot in mid-July
• weeding lettuce in plot 1A
• the zone builder in action

Impacts and Contributions/Outcomes

As this was the first year of the project, we do not really have any impacts or outcomes to report. However, we have had strong interest from our target audiences, and this project has been leveraged to increase URI support of research and extension efforts in food production agriculture, including significant investments in new equipment and staff for the Agronomy Farm.

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