Phosphorus Mobilization and Weed Suppression by Buckwheat.

Project Overview

Project Type: Research and Education
Funds awarded in 2000: $50,000.00
Projected End Date: 12/31/2005
Region: North Central
State: Minnesota
Project Coordinator:
Jim Stordahl
University of Minnesota Extension Service

Annual Reports


  • Agronomic: oats, sorghum (milo), soybeans


  • Crop Production: cover crops, fallow, nutrient cycling, organic fertilizers, tissue analysis
  • Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research
  • Farm Business Management: whole farm planning, risk management
  • Natural Resources/Environment: biodiversity, soil stabilization
  • Pest Management: biological control, field monitoring/scouting, integrated pest management, mulches - killed, mulches - living, smother crops
  • Production Systems: holistic management
  • Soil Management: organic matter, soil analysis, nutrient mineralization, soil quality/health


    This project looks at the uses of buckwheat as a cover crop in the Red River Valley area of North Dakota and Minnesota. A variety of results were obtained from the experiments, many of them creating additional questions in the process.


    In the Red River Valley of Minnesota/North Dakota all the major crops have become problematic due to a serious disease or insect problem: scab (Fusarium head blight) in barley and wheat, white mold and midge in sunflowers, and numerous diseases in sugar beets. Furthermore, incompatibilities between these crops and various alternative crops in rotation with them have left many farmers with fallowing their land as the only alternative to high pesticide inputs. Besides helping with diseases, a black fallow with frequent disking reduces the weed seed bank. This has traditionally become a standard weed control practice for the area's organic farmers. However, fallowing has problems of its own: the frequent tillage burns off soil organic matter and leaves the soil vulnerable to wind and water erosion, no residues are returned to the soil to maintain the soil's microbial life or to hold on to soil nutrients, and it requires large amounts of fossil fuels to run the tractors, not to mention the long hours the farmer must spend in the field away from family and civic life. If summer cover crops suitable to the Red River Valley could be identified that do not harbor the same pests as the cash crops, protect the soil from erosion, build organic matter, maintain or improve soil fertility, and help control weeds, insects and diseases, they would add some much-needed diversity to the farming system of the Red River Valley.

    Buckwheat (Fagopyrum esculentum) is one such candidate for a green manure crop. In "Managing Cover Crops Profitably" (SAN, 1998) buckwheat is lauded as an outstanding smother crop for its ability to mobilize soil P, especially from calcareous soils such as are found in the Red River Valley. Anecdotal information from Minnesota farmers supports this: many have remarked on the absence of weeds in a healthy buckwheat stand, and some have observed increases in soil test P following buckwheat plow down. However, there is little scientific research to translate this into practical recommendations. For example, although the ability of buckwheat to scavenge phosphorus from extremely low-P soils has been well documented, we need to know how well this translates into increased availability of P to subsequent crops. This would be valuable because livestock production is rare in the Valley and therefore organic farmers are currently supplying P by importing large quantities of manure from elsewhere, at great cost both monetarily and energetically.

    Likewise, we do not know how well buckwheat's smother crop capabilities carry over to better weed control in subsequent years. There are other questions: many farmers appreciate the way buckwheat mellows the soil, making it easier to work; however there are concerns that, because it returns relatively little residue to the soil, this may actually increase the erosivity of the soil, unless it is followed by another cover crop that protects the soil over the following winter.

    Project objectives:

    To assess the value of buckwheat as alternatives to black fallow in the crop rotations of the Red River Valley to verify their value for 1) mobilizing soil P and other nutrients, 2) suppressing weeds, and 3) providing habitat to beneficial insects.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.