The goal of this research project was to investigate the impact of plant spacing on yield performance of sweetpotato varieties in an organic management system in Tennessee and to share our findings with farmers, researchers and stakeholders. The sweetpotato crop is increasing in popularity because of its nutritional value, wide range of flesh-color types being introduced from all over the world, low cost of production, ability to grow well on marginal lands with little amounts of water and its sweet taste. The sweetpotato fresh markets and processing industries are enlarging due to the development of new and improved value-added products. Sweetpotato production in Tennessee, however, is believed to have declined since 1980 and currently certified organic sweetpotato production is below consumer demand. A preliminary trial was conducted in the fall of 2017 on the certified organic research farm at Tennessee State University, Nashville, Tennessee. The effect of 12” in row plant to plant spacing on the yield performance of cv. Beauregard, Centennial and Covington was measured. A randomized block design was implemented using 36” wide beds with 72” spacing between rows and cultivars. Cultivars were grown with strict adherence to the rules of the national organic standards board (NOSB). Data was collected on the root number, sizes and yields of sweetpotato. Marketable yields were highest in the Covington followed by the Beauregard and Centennial varieties respectively. Of the three varieties, Covington also had the highest U.S. no 1 and least number of U.S. no 2, Meanwhile jumbo-sized roots were observed only in Beauregard cultivar. In the summer of 2018 the effects of 8”, 14” and 18” row plant spacing on the yield performance of cv. Beauregard, Centennial and Covington will be measured and compared. The findings from this study would provide sweetpotato growers with desired information on yield performance of the crop in organic farming systems to adequately measure market value and hence profitability. It would also contribute to and help fill in existing knowledge gaps on how yield production of various sweetpotato cultivars in sustainable farming systems are affected differential plant spacing. Information gathered will be shared with farmers, researchers and stakeholders during small farm expo, field day and conference presentation.
1. Determine the impact of the plant spacing pattern (12” in-row) on yield, number and sizes of three sweetpotato varieties grown in an organic management system.
2. Access the effect of three other plant spacing patterns (18”, 14” and 18” in-row) on yield, number and sizes of three sweetpotato varieties grown in an organic management system.
3. To disseminate information of project findings with researchers, Tennessee’s small and minority growers through TSU’s Cooperative Extension Agents, Small Farm Expo, field demonstrations, fact sheets, and social media videos.
- Materials and supplies were ordered and literature relevant to project work gathered in preparation for the second field trial.
- Hiring of project personnel was made to assist with project logistics and data collection
- Field plot of first field trial was set up in the summer of 2017 and maintained as needed (weeding, irrigation, harvesting etc..) and data was collected at the end of growing period after harvesting
- Field plot was maintained after harvest and soil sample was sent for analysis at soil science laboratory from field areas.
- Sweetpotato slips from first trial were raised in green house within pots in October 2017. Animal manure, vermi-compost and cover crop planting was done on the field after first cycle to prepare land during fallow period.
Variety trial/first cycle 2017
- Cover crops such as buckwheat and clover (Johnny’s selected seeds Winslow, ME) was applied in late fall each year proceeding planting to stifle weed germination and improve organic matter content in the soil.
- Land was cultivated, ploughed and prepared for planting using a bush hug, a tractor roto-tiller on 5/23/17. Ridger and bed maker was used to make furrows on 5/25/17. The soil was tilled and raised beds were formed.
- Labels depicting treatment and variety were prepared.
- Slips of Beauregard, Covington and Centennial were transplanted from readily available raised slips from the preceding years growing season in greenhouse pots and then transferred to field in summer/2017.
- A randomized was employed of 10 plants in each cultivar spaced 12” apart in-row. Each sweetpotato bed was 36” wide with 108” spacing in-between the beds or rows. A 108” spacing was placed between each variety and row
- Drip irrigation system was set up and wheat straw mulch cover laid.
- Weeding by hand in between plants and with the tractor in between the beds at intervals throughout the growing season
- Field was observed for incidences of pest and disease in growing season
- Shortly before harvest, sweetpotato vines were trimmed, and roots harvested with potato digger on 10/9/17and placed into labelled boxes
- Data collection commenced after sorting and grading roots as per USDA standards into different groups in the marketable and cull category.
- Curing of sweetpotato roots will be for 7 days immediately after harvest at 85 F, 80–90% relative humidity before storage.
Variety trial/second cycle 2018
2018 field experiment will be conducted at Tennessee State University Certified organic research farm to determine the ideal plant spacing for three varieties Covington, Centennial and Beauregard. All three varieties are commercially grown in southern region for the fresh market and processing industries. The effect of three plant spacing (8”, 14” and 18”) on yields, number of roots and sizes of the three varieties stated above would be evaluated. Field plots will be marked out on a different side of the field plot from last growing season (crop rotation), land prepared and sweetpotato slips will be purchased from certified vendors. Plastic mulch covering will be laid mechanically by a mulcher, with drip tape underneath to mat down firmly to the soil on the research field plot. A randomized complete block with three treatments and three replications would be employed. Weeding would be done by hand and hoeing in between plants and with the tractor in between the beds when required at intervals throughout the growing season. Field plots would be maintained in organic management practices as per standards of National Organic Program throughout the planting season (Anonymous, 2015). At 120 days after transplanting (DAT), roots will be harvested with a potato digger (Spedo Inc., Castagnaro, Italy). After data collection, analysis of variance (ANOVA) would be measured using PROC GLM procedure in SAS (ver. 9.4, SAS, Inc., Cary, NC) to determine significant influences of variety, and spacing on yields, number and root size.
Objective 1: For the 2017 variety trial, soil sample analysis was made. Roots were counted, sorted, weighed with digital scales (Berry hill supplier, TN) and graded as per United States Department of Agriculture (USDA) standards. A general review (regardless of plant spacing, or location) was made to find out what the yields were of cultivars (Beauregard, Centennial and Covington) cultivated using conventional management practices in literature and to compare them with our results in organic production system. The average marketable root yield of sweetpotato (12” plant to plant spacing) from the TSU, Organic Farm Nashville, TN was then compared to conventionally produced sweetpotato available in literature regardless of plant spacing and location.
On analysis, the average soil pH of our field plot was determined to be 6.1. Soil organic matter was 2.33%. Supply of the nutrients phosphorous (534 lbs./acre) and potassium (376 lbs./acre) was very high in the soil and further application of the nutrients was not recommended, since further additions may have created nutrient imbalances. The availability of the secondary/micro nutrients i.e. Calcium (3211 lbs./acre), Magnesium (225 lbs./acre), Zinc (8.3 lbs./acre), Iron (22 lbs./acre) and Manganese (31 lbs./acre) were found to be sufficient and in an adequate supply for plant utilization.
Our results showed that average marketable yields of sweetpotato in organic management systems was highest in Covington (35864.4 lbs./acre) followed closely by Beauregard (35428.8 lbs./acre). When compared with the conventional yields accessed from literature, yields of Beauregard (29924.19lbs./acre) sweetpotato were however higher than in Covington (28402.38 lbs./acre). In both organic and conventional production systems, Beauregard and Covington yields were significantly higher than the Centennial cultivar (organic-24829.2 lbs./acre; conventional-12037.66 lbs./acre). Overall, our results showed that the average marketable yields of sweetpotato yields produced on the organic farm (using a 12” plant to plant spacing) at Tennessee State University were on the average higher than yields of similar cultivars produced in conventional farming systems where spacing and location was not considered.
Furthermore, in this present study, sweetpotato roots were also sorted into the cull or unmarketable roots category. Of the three cultivars tested, the least quantity of unmarketable roots was observed in Beauregard at only 7% while in Centennial it was recorded 36% of the harvested roots was unmarketable. Centennial was followed closely by Covington where 25% of its total yield were culls. According to USDA standards, sweetpotato cultivars were sorted into different groups. Covington had no Jumbo-(9438 lbs./acre) sized roots, Covington had the least quantity of US no 2 (871.2lbs./acre) root sizes and the highest amount of US no 1 petite (13213 lbs./acre) and US no 1 (21780 lbs./acre) sized roots when compared to the two other cultivars. Only the Beauregard cultivar contained Jumbo (9438 lbs./acre) sized roots. The highest quantity of US no 2 (4792 lbs./acre) sized roots, including the least amount of US no 1 petite (6824 lbs./acre) and US no 1 (8712 lbs./acre) roots amongst all three cultivars tested was observed in the Beauregard cultivar. A second trial would commence in the summer of 2018 to evaluate the impact of 8, 14 and 18 in row spacing on organic sweetpotato yields.
Educational & Outreach Activities
A tour of the organic sweetpotato field and variety trial was held shortly before harvest in the Fall of 2017. Participants included growers, researchers and stakeholders. In July of 2018, we plan on preparing Sweetpotato workshop fliers, factsheets, and survey forms for distribution at the Tennessee State University summer farm expo that would gather small-farm producers, students and researchers from Tennessee and other parts of the United States for seminars and field trips. We plan to share our findings at the 2018 SARE conference in April at St. Louis MO. A Sweetpotato field day would be organized a few weeks before sweetpotato harvest and findings will be shared with growers and stakeholders. Feedback from attendees will be gathered through survey forms so as to make improvements and note concerns or other interests. Fact sheets based on findings from this study would be published through Tennessee State University Cooperative Extension and made available to the public. At the end of the research study, a final report will be put together and results from this study will be presented orally at the annual meeting of the National Sweetpotato Collaborators conference in the Spring of 2019. In addition, we expect several regular on-farm visits and field days for students, growers and individuals with a general interest on organic sweetpotato cultivation and production.
None. Outcomes will be reported in final report.
None. Outcomes will be reported in final report.