Sweetpotato is an economically important crop for North Carolina growers. Current sweetpotato production systems rely heavily on cultivation. The lack of chemical and non-chemical weed control methods further increases reliance on cultivation. Excessive cultivation is detrimental to soil health. Reduced tillage cover crop systems have the potential to reduce reliance on cultivation and herbicides by providing an alternative weed control method. These systems also increase soil organic matter content and soil structure. A study is being conducted to evaluate the effect of a reduced tillage rye cover crop system on soil, crop growth, and yield. Another study will be conducted to evaluate conventional and organic weed control programs in this system. At the conclusion of these studies, the knowledge gained will be disseminated to growers and the broader research community.
- Determine how a reduced-tillage and strip-tillage production system influence sweetpotato growth compared to a conventional tillage system.
- Develop weed management programs in reduced and strip-tillage systems. Determine how a reduced- and strip-tillage system respond under intense weed pressure with and without herbicides.
- Disseminate lessons learned and recommendations through grower meetings, extension articles, and refereed journal publications.
The first objective is evaluating how a reduced-tillage rye cover crop sweetpotato production system influences crop growth compared to a conventional tillage system. Studies were initiated at the Horticultural Crops Research Station in Clinton, NC and the Cunningham Research Station in Kinston, NC. For the reduced tillage system, rye was broadcast seeded at 135 kg ha-1 across raised beds in October 2018. After seeding the studies were irrigated to facilitate seed germination. Nitrogen was applied to the rye in December (2018) (33.6 kg ha-1) and February (2019) [67.3 kg ha-1] to increase biomass. In May 2019, sweetpotato (non-rooted cuttings) will be directly transplanted through the standing rye onto the raised beds using a commercial mechanical transplanter. A conventional production system will be included for comparison.
Within each production system multiple cultivars with varying canopy architectures will be tested for performance. ‘Covington’ and ‘Averre’ have low-growing sprawling architectures. ‘NC04-0531’ and ‘NC15-0650’ were bred for organic production and have upright architectures. The study is a split-plot design with tillage system as the whole-plot factor and cultivar as the split-plot factor. The split-plots will be 4 rows each 15 meters long. The first and fourth row will be nontreated border rows. The second and third will be a treated data rows. Each whole-plot will be replicated 4 times. This study will be repeated next year.
Data collected will include cover crop biomass measured at sweetpotato transplanting. In addition, sweetpotato canopy height, light interception, time to canopy closure, storage root yield and quality, and soil moisture and bulk density will be measured. Soil bulk density will be collected at sweetpotato transplanting, canopy closure, and harvest. Soil moisture and crop canopy height and light interception will be measured weekly. Storage root yield will be collected at harvest. Storage roots will be graded by hand into jumbo (> 8.9 cm in diameter), no. 1 (> 4.4 cm but < 8.9 cm diameter), and canner (> 2.5 cm but < 4.4 cm diameter) (USDA 2005). Marketable yield will be calculated as the sum of jumbo and no. 1 grades. Storage root shape and volume will be measured using a laser grader. Data will be subjected to analysis of variance using PROC MIXED (SAS 9.4, SAS Institute, Inc. Cary, NC).
The second objective is to develop weed management programs in the reduced-tillage system. This study is in a field with a history of severe Palmer amaranth infestation (50 to 100 plants per m2). The rye cover crop will be evaluated to see how well it control weeds with and without the use of herbicides. Herbicides that will be included are flumioxazin, fomesafen, S-metolachlor, linuron, and d-limonene (citric acid). Flumioxazin and S-metolachlor are industry standards. Fomesafen and linuron are in the process of being registered for use in sweetpotato through the IR-4 program. D-limonene is an organic herbicide that has been shown to control amaranth species. A nontreated weed-free (hand-weeded) and weedy check will be included for comparison. A conventional production system will be included for comparison. The study is a split-plot design with tillage system as the whole-plot factor and weed management program as the split-plot factor. The split-plots will be 4 rows each 15 meters long. The first and fourth row will be non-treated border rows. The second and third will be treated data rows. Each whole-plot is replicated 4 times. This study will also be repeated the following year.
Data collected will include cover crop biomass, weed density, soil moisture, soil bulk density, and storage root yield. Data will be subjected to analysis of variance using PROC MIXED (SAS 9.4, SAS Institute, Inc. Cary, NC).
The last objective of this project is to disseminate the knowledge gained. The results will be presented at grower field days, local sweetpotato meetings, regional grower meetings including the Organic Production Field Day, Southeast Vegetable & Fruit Expo, and Southeast Regional Fruit and Vegetable Conference; and at scientific conferences. Extension and refereed journal articles will be used to disseminate results to the broader grower and scientific community.
Because the cover crop was planted in the fall preceding sweetpotato planting, no results have been obtained yet. Data collection will begin once sweetpotato are planted in May of this year.
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