- Vegetables: sweet potatoes
- Production Systems: general crop production
- Soil Management: green manures, organic matter
Sweetpotato production is an important part of North Carolina’s economy, but less than three percent of sweetpotato acreage is certified organic. Despite the demand for organic produce, few production recommendations exist for organic fresh market vegetables from land grant universities. This study was conducted to explore management options for conventional growers interested in producing organically managed sweetpotatoes. Local conventional growers were consulted prior to the initiation of this project to identify specific research needs and concerns related to the adoption of organic systems. Specific management protocols in organic systems and the conventionally managed system are representative of organic sweetpotato growers in our area and best management practices, respectively. A three-year field study on the effect of management of a cover crop mixture of hairy vetch and ‘Wrens Abruzzi’ rye in organically managed sweetpotato was compared to a conventional control using a systems approach. The organic systems included 1) no cover crop, 2) cover crop incorporated prior to transplanting, and 3) reduced tillage. All three years, experiments were conducted at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC. We examined weed suppression, nutrient management, wireworm larvae insect density, insect feeding damage to sweetpotato roots and costs and returns of each system
North Carolina has produced the majority of the nation’s sweetpotatoes since 1971 (USDA ERS, 2003). In 2004, North Carolina supplied 46% of the nations’ market and generated 79 million dollars for the state (NCDA & CS, 2005). Although there were over 16,000 ha in production that year (NCDA &CS, 2005), only 405 ha were managed according to federal organic standards (K. Hardison, personal communication).
Growers implementing best management practices for sweetpotato in North Carolina typically employ multiple tillage events including subsoiling, discing, field leveling, hilling, and cultivation. Due to heavy pest infestations typical of the warm and humid seasonal climate of southeastern NC, pest control is largely preventative rather than curative and includes soil fumigation prior to planting and multiple applications of preplant and postemergent herbicides and insecticides. According to a 1996 survey of North Carolina sweetpotato growers, 66% of respondents reported they used insecticides, 70% use herbicides, and 97% used cultivation to manage weeds (Toth et al., 1997). Soil-dwelling insect larvae of wireworm (Melanotus communis Gyllenhal and Conoderus spp.) pose the greatest risk to growers. Despite repeated applications, conventional insecticides post emergence dicot weed control are only marginally effective. Additionally, some of the insecticidal materials are currently being reviewed under the Food Quality Protection Act because of their potential for environmental harm.
In conventionally managed systems, nutrients are supplied with high analysis fertilizers. Although the actual amount supplied depends on preseason soil test results, producers typically apply 62 kg NO3-N, 112-168 kg K, 112 kg P, and 0.56 kg B ha-1 for control of blister. Common rotational crops include tobacco, cotton, soybean, and mixed vegetables. Although the soil in our area has low organic matter, few producers incorporate organic matter via cover crops or compost prior to planting. The extensive tillage and high number of vehicle passes required to manage sweetpotato as well as its associated rotational crops can lead to a loss of organic matter, decline in soil structure, and erosion.
Organic soil amendments such as compost and cover crops are an integral component of organic management systems. Hairy vetch and rye are species that establish easily, overwinter successfully, produce sufficient biomass, and are easily killed in the spring by mechanical methods (Creamer et al., 1997). Integration of this cover crop mixture in cropping systems has been shown to reduce nitrate leaching and carbon losses (Drinkwater et al., 1998; Rannells and Wagger, 1997), improve nutrient use efficiency (Staver and Brinsfield, 1998), increase the nitrogen fixation rate of legume species (Rannells and Wagger, 1997), increase water retention (Teasdale and Mohler, 1993) and decrease soil bulk density (Jackson et al., 2004). Cover crop residues that remain on the surface can inhibit weed seed germination due to a reduction of light penetration to the soil surface (Teasdale and Mohler, 1993) as well as physical interference (Creamer et al., 1996; Hutchinson and McGiffen, 2000). Chemical interference of weed germination has been demonstrated for a number of cover crop species including rye (Creamer et al., 1996; Reburg-Horton et al., 2005), members of the Cruciferae family (Blum et al., 1997) and crimson clover (Creamer et al., 1996).
There are few published reports on the effects of cover crops on sweetpotato. Growers implementing conventional and organic sweetpotato systems will benefit from research on the effects of cover crops on weeds, insects and nutrient management.
- Identify the organically managed system with the best weed and insect suppression.
To confirm yield was not limited by nutrient availability among systems.
To investigate the impact of organically managed systems on crop productivity including foliar biomass, sweetpotato quality and yield.
Evaluate the economics of conventional verses organically managed sweetpotato production in terms of cost effectiveness and product return.
To participate in outreach and education events for growers and extension agents.