The Effect of Spring Seeded Annual Medic, Genus Medicago, on Weed Management and Soil Quality in Corn Production

Project Overview

LNC95-079
Project Type: Research and Education
Funds awarded in 1995: $73,000.00
Projected End Date: 12/31/1998
Matching Federal Funds: $10,000.00
Matching Non-Federal Funds: $59,600.00
Region: North Central
State: South Dakota
Project Coordinator:
Sharon Clay
Dept of Agronomy, Horticulture, and Plant Science, South Dakota State University

Annual Reports

Commodities

  • Agronomic: corn

Practices

  • Crop Production: cover crops, nutrient cycling, application rate management
  • Education and Training: demonstration, on-farm/ranch research
  • Farm Business Management: new enterprise development, budgets/cost and returns
  • Pest Management: allelopathy, biological control, competition, weed ecology
  • Production Systems: general crop production
  • Soil Management: green manures, organic matter, soil analysis, nutrient mineralization, soil quality/health

    Abstract:

    Production management systems that incorporate smother crops to control weeds and/or supply plant nutrients may reduce the transport of agrichemicals to surface and ground waters. Alternatives to agrichemicals will be adopted by producers when they effectively replace those chemicals without reducing crop yield, disrupting management practices, and diminishing farm profitability. This project investigated if annual medics, used as a living smother crop, would control weeds, not adversely effect corn productivity, supply N to corn, increase soil quality, and be similar in cost to synthetic chemical application.

    Field experiments were conducted in South Dakota and Iowa using three species of annual medic (barrel medic, Medicago trunculata; burr medic, Medicago polymorpha; and snail medic, Medicago scutellata). The first of several experiments evaluated the effect of medic planting date and rate on corn production and weed control.

    Medics were planted at two planting dates (about 2 weeks before average planting date for the area and at corn planting) and two broadcast planting rates (15 and 30 lb seed per acre). The crop year in 1995 was cool and wet, and medic grew aggressively except in drainage areas. The 1996 growing season was warmer and drier and medic biomass was about 70% less than in 1995. Medic planted early had more biomass and ground cover than medic planted at the same time as corn but all medic senesced by mid to late July. Medic reduced total weed biomass (predominant grass weeds were yellow and green foxtail, predominant broadleaf weed was common lambsquarters) in both 1995 and 1996. Corn yield was very poor in 1995 at both Brookings and Sioux Center sites and was reduced by medic. In 1996, the barrel medic broadcast at high rates reduced corn yield by about 30% compared to the weed-free control. However, when medic was banded into the interrow areas and alachlor was banded in the row, yields were similar to areas where only herbicide was applied.

    In a second experiment, the effect of medic on soil quality and N cycling were evaluated. Medic increased water infiltration from about 1.5 inches per minute (bare soil) to about 6 inches per minute (medic planted at 30 lb per acre). Nitrogen mineralization measured from mid-July to mid-August increased by about 50% in medic plots compared to areas without medic. However, nitrogen credit from medic the following year was minimal. Corn yield was not influenced in this study.

    In economic analyses using enterprise budgets, results were similar (within 5%) when comparint the cost to produce a bushel of corn (assuming no N credit for the medic) using broadcast methods for medic alone or alachlor alone, or a band combination of medic (interrow) and alachlor (row). It is important to note that banding would reduce herbicide application by 50% compared to a broadcast application.

    The information gained in this research indicates that annual medics may have a very important niche in achieving more sustainable, environmentally benign crop production systems. Early in the growing season, medic was competitive with corn for soil N. However, after the medic senesced, this N was subsequently mineralized and made available for plant uptake. When using medic, enough N must be present in the soil so corn does not become N deficient. In addition, using medic in conjunction with other agrichemicals, especially in sensitive areas such as acres coming from CRP, would benefit the soil water profile, reduce soil erosion, and reduce N losses in agronomic systems.

    Introduction:

    Production management systems that incorporate smother crops to control weeds and/or supply plant nutrients may reduce herbicide and fertilizer applications, chemicals that often pollute both surface and ground water in environmentally sensitive areas. Alternative input systems for agrichemicals will only be adopted by producers if crop productivity can be maintained, fits within current management practices (or management that is considered feasible by the producer), controls weeds or has other beneficial aspects, and is cost effective. The testable hypotheses for this SARE research grant were that annual medics, when used as a living smother crop, would control weeds, do not adversely effect corn productivity, supply nutrients (primarily nitrogen) to corn (Zea mays L.), increase soil quality, and be similar in cost to synthetic chemical application.

    Three species of annual medic (barrel medic, Medicago trunculata; burr medic, M. polymorpha; and snail medic, M. scutellata) were evaluated in field trials on experimental and producer farms in South Dakota and Iowa. In the first set of studies, medics were planted at two planting dates (about 2 weeks before average planting date for the area and at corn planting) and at two broadcast planting rates (15 and 30 lb seed per acre). The crop year in 1995 was cool and wet and medic grew aggressively except in drainage areas. The 1996 growing season was warmer and drier and medic biomass was about 70% less than in 1995. Medic planted early had more biomass and ground cover than medic planted at the same time as corn, and all medic senesced by mid to late July. Medic reduced total weed biomass [predominant grass weeds were yellow and green foxtail (Setaria glauca (L) Beauv. and S. viridis (L.) Beauv.), predominant broadleaf weed was common lambsquarters (Chenopodium album L.)] in both 1995 and 1996. Corn yield was very poor in 1995 at both Brookings and Sioux Center sites and medic reduced yield even further. In 1996, the barrel medic broadcast at high rates reduced corn yield by about 30% compared to the weed-free control. However, when medic was banded into the interrow areas and alachlor was banded in the row, yields were similar to areas where only herbicide was applied.

    The effect of snail medic on soil quality (water infiltration and N cycling) was evaluated. Medic increased water infiltration from about 1.5 inches per minute (bare soil) to about 6 inches per minute (medic planted at 30 lb per acre). Nitrogen mineralization measured from mid-July to mid-August increased by about 50% in medic plots compared to areas without medic. However, nitrogen credit from medic the following year was minimal. Corn yield was not influenced by medic in this study.

    In economic analyses using enterprise budgets, the results were similar (within 5%) when the cost to produce a bushel of corn (assuming no N credit for the medic) using broadcast methods was compared to medic alone or alachlor alone, or a band combination of medic (interrow) and alachlor (row). Banding would reduce herbicide application by at least 50% compared to a broadcast application.

    The information gained in this research indicates that annual medics may have a very important niche in achieving a more sustainable, environmentally benign crop production system. Planting medic as a cover crop may be very appropriate in sensitive areas such as land coming out of CRP because it can reduce soil erosion, change N cycling so that the N available when the crop requires it, and reduce herbicide applications through banding.

    Project objectives:

    1. Quantify weed suppression by three annual medic species.
    2. Measure corn productivity in medic-corn production systems.
    3. Determine the impact of medic on soil quality parameters and N contribution to soil.
    4. Compare the economics of corn production in conventional and annual medic-based systems.

    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.