Evaluation of Cover Crops and Conservation Tillage for Conventional and Organic Sweetpotato (Ipomoea batatas) Production in North Carolina

2002 Annual Report for GS00-006

Project Type: Graduate Student
Funds awarded in 2000: $9,927.00
Projected End Date: 12/31/2004
Region: Southern
State: North Carolina
Graduate Student:
Major Professor:
Dr. Nancy Creamer
North Carolina State University

Evaluation of Cover Crops and Conservation Tillage for Conventional and Organic Sweetpotato (Ipomoea batatas) Production in North Carolina


The effect of hairy vetch and rye cover crop management on organic sweetpotato was compared to a conventional check using a systems approach. The organic systems include 1) no cover crop, 2) cover crop incorporated prior to transplanting, and 3) reduced tillage. Both years, weed biomass interfered with crop biomass in the reduced tillage treatment. Except for a reduction in yield in the reduced tillage treatment the second year, yields of organic treatments were the same as conventional yields both years. To assess marketability, roots were examined for insect damage. In 2001, yield quality of No.1's was dramatically improved in reduced tillage (76% marketable) verses conventional (49%) treatments.

Objectives/Performance Targets

Sweetpotato is one of the most economically important crops in North Carolina. In 2002, N.C. supplied 37% of the nations' market and generated over 64 million dollars for the state. There are 37,000 acres in production in N.C., and over 98% are managed conventionally. Sweetpotato has a variety of insect, weed and plant pathogen pests that reduce quality and yield. Soil-dwelling insects such as wireworm (Melanotus communis Gyllenhal and Conoderus spp.) pose the greatest threat. Despite repeated applications, conventional insecticides are only marginally effective; as evidenced by the fact that 30-40% of harvested yield suffers extensive root damage and is not suitable for sale. These insecticidal materials are currently being reviewed under the Food Quality Protection Act because of their potential for environmental harm. Additionally, growers have few chemical options for weed control. Little research has been conducted to provide growers with innovative alternative practices that will preserve or improve environmental health while maintaining economic viability. Therefore, the objectives of this trial as follows:

1. To examine differences in soil dwelling insects, soil physical properties, crop growth parameters, and weed competition on crop yield in organic and conventional sweetpotato production.

2. To investigate the impact of conservation tillage on sweetpotato quality and yield.

3. Evaluate the economics of conventional verses organic sweetpotato production in terms of cost effectiveness and product return to serve as a guide for growers who are interested in producing organic sweetpotatoes.

4. To participate in outreach and education events for growers, buyers and extension agents.


Sweetpotatoes 'Beauregard' were transplanted July 2001 and June 2002, and harvested October 2001 and September 2002. The third year of the trial was postponed until the 2004 growing season due to maternity leave. Soil nitrogen, soil moisture, seasonal wireworm larval densities, weed densities throughout the season, weed and crop biomass at harvest, plant tissue nutrient analysis, and yield quantity and quality were measured. Further data analysis will explore relationships among soil physical properties, wireworm densities and root damage. Preliminary results indicate a weak positive correlation between soil moisture and wireworm densities, yet further exploration is needed. Therefore, laboratory trials will be conducted on wireworm larvae to identify feeding stimuli as well as to determine effects of soil properties on feeding activity. An understanding of this pest’s biology will guide future management decisions. A second replicated field trial was conducted in 2002 to examine the influence of other cover crop species and methods of kill on weed control and yield in reduced tillage sweetpotatoes. Data indicate hairy vetch and rye mixture rolled with a coultipacker was most effective in early season weed control.

Impacts and Contributions/Outcomes

Preliminary results were disseminated to growers and university personnel at the National Sweetpotato Collaborator's Meeting in Mobile, Al. on February 1, 2003 and at Southern Region American Society for Horticultural Science in Mobile, Al. on February 2, 2003. Results were also presented at the Research and Extension Committee Meetings of the N.C. Agricultural, Dairy, and Tobacco Foundations in Raleigh, N.C. on April 10, 2003.