Buckwheat Cover Crops on Wisconsin Vegetable Farms: Grower Perspective, Genetic Variation, and a Weed Supression Study Using Tartary Buckwheat

View the project final report

• 2011 annual report

Commodities

• Vegetables: cabbages

Practices

• Crop Production: conservation tillage
• Education and Training: focus group, on-farm/ranch research
• Pest Management: allelopathy, mulches - killed, smother crops, weed ecology
• Production Systems: agroecosystems, holistic management, organic agriculture
• Soil Management: green manures, organic matter

Common buckwheat (Fagopyrum esculentum) is a widely used summer cover crop on Wisconsin fresh market vegetable farms. Buckwheat cover crops are believed to provide environmental and farm production benefits including improving soil quality and fertility, weed suppression, beneficial insect habitat, and erosion prevention. Despite its utility, the relative importance to growers of different functions of buckwheat cover crops is not well understood. We used a web-based survey instrument and interviews to identify common grower practices and questions. Survey results were shared with participants. Farmer input was used to design a series of on-farm and on-station studies on buckwheat cover crops, including a weed suppression study, a comparison of reduced-tillage killing methods, and a late-summer planted, overwintered residue study. The weed suppression experiment included a novel comparison with a cultivated relative of common buckwheat, tartary buckwheat, which has been shown to contain possibly allelopathic substances. This project provided farmers with information about their peers’ practices, and promotes discussion and better management for buckwheat and other cover crops. Both cover crops effectively suppressed weeds, but there were no differences observed between common and tartary buckwheat, and neither cover crop improved cabbage yields in comparison with a fallow check. Reduced tillage management proved ineffective compared to conventional tillage. Oats outperformed both buckwheats in production of late-season biomass and persistence of overwintered residue.

Introduction:

Systematic assessment of novel crops and management techniques are practical objectives of agricultural field research. This study sought to expand the cover cropping toolkit available to WI farmers with a series of on-station experiments using buckwheat (Fagopyrum spp).
Cover crops provide many benefits to farms and the environment, including improving soil quality and fertility, weed suppression, beneficial insect habitat, and erosion prevention. Summer cover crops have not been widely studied in Wisconsin because a relatively short growing season tends to limit their use on commercial grain farms. However, many organic vegetable growers use summer cover crops as part of complex, diverse rotations. In a survey conducted in 2006 of 70 Wisconsin and Illinois vegetable growers, 78% reported using common buckwheat (F. esculentum) cover crops, with over a third of respondents using it every year.
Common buckwheat (CBW) is known for its ease of establishment, thick canopy, profuse flowers and rapid decomposition. Previous research has detailed the positive effects of buckwheat cover crops on soil tilth, weed suppression, phosphorus availability, and promoting beneficial insect populations. WI vegetable growers value these benefits to varying degrees, and are open to more research and information that would improve the efficacy of buckwheat cover cropping.

Tartary buckwheat, a novel cover crop

Our study evaluated the cover cropping potential in southern WI of tartary buckwheat (F. tataricum), a related species to CBW. Tartary buckwheat (TBW) is primarily grown as a subsistence grain at high altitudes in the Himalayas, and its unique nutritional profile has spurred development as a functional food. It is self-pollinating, relatively frost tolerant, and has a similar growth habit and phenology to common buckwheat. TBW has been reported to grow more vigorously than CBW in cold climates, which may fill a unique niche for vegetable farmers in the Upper Midwest. Tartary buckwheat also contains high levels of potentially allelopathic phytochemicals in the vegetation and seeds.

Weed suppression

TBW and CBW were compared for effectiveness in weed suppression both during the cover cropping phase and after cover crop termination. This study takes a detailed look at weed emergence and growth in an early-sown buckwheat cover crop, and tracks the season-long effects of buckwheat on weeds and yield of a cabbage test crop (Brassica oleracea).

Reduced tillage

Development of reduced tillage systems is an active area of cover crop research. Tillage reduction using cover crop mulches in agricultural systems can improve soil conservation, suppress weeds, and provide habitat for beneficial organisms. Tillage tends to stimulate weed seed germination, which can increase weed pressure in crop fields. Tillage is also associated with greater costs in terms of labor, equipment, and soil quality. This study includes a test of a reduced-tillage management system using buckwheat cover crops.

Overwintered crop residue

Planting a fall cover crop provides erosion protection and is a source of soil organic matter. Many WI vegetable farmers plant fall cover crops that do not survive the winter, to allow for easy incorporation and earlier spring planting dates. The most commonly planted winterkilled cover crop in this region is oats (Avena sativa), which has relatively good growth into the fall. Yet because of high lignin content, "stringy" oat residue can be difficult to work with in the spring and get caught in machinery. Some interviewed farmers reported planting buckwheat in this cover cropping window, because the brittle residues are easy to incorporate in a single pass. We compared both buckwheat species with oats for fall biomass production and persistence of overwintered residues in an on-farm and on-station study.

• Survey WI vegetable growers about their buckwheat cover cropping practices and disseminate the results to participants, which will allow them to compare their own practices to those of other growers.
• Compare cover-cropping qualities of common buckwheat to a related species, tartary buckwheat, which shows promise in cold hardiness and allelopathy.
• Compare reduced-tillage management techniques for killing a buckwheat cover crop, and evaluate the ability of a buckwheat mulch layer to suppress mid-summer weeds.
• Characterize weed growth and emergence in an early summer buckwheat cover crop in order to better understand the mechanisms by which buckwheat suppresses weeds.
• Compare late-planted common and tartary buckwheat to oats for fall biomass production and persistence of overwintered crop residues.