We completed year one of a three year project. We established field plots and plots within high tunnels for the production of sweetpotato slips. We investigated the effects of high tunnels on slip morphological characteristics and found a greater number of marketable slips were produced in the high tunnels. However, slips from outside plot had greater compactness (dry weight/length). We also explored seed root planting density and its effects on slip production. Not surprisingly, increasing seed root density also increased slip number per area. However, the benefit appears to be reduced above 65 seed roots per square meter. Slips from high tunnels and open field were planted out to determine any influence on root yield. First year data suggests no significant different in yield per plant based on slip origin. In the lab we established a visual rating scale for slip quality to determine when a slip would be considered unmarketable. We also obtained preliminary data suggesting a shipping container lining can increase water content of slips during storage. However, there may be negative implications of increased humidity during shipping.
We completed year two of a three year project. Similar to 2016, we established field plots and plots within high tunnels for the production of sweetpotato slips at two locations within the state of Kansas. For the second year, we investigated the effects of high tunnels on slip morphological characteristics. Unlike the previous year we found no difference in the number of marketable slips between high tunnel and open field plots on the first harvest. Similarly, there was no difference in the fresh weight of the entire plot harvest between high tunnel and open field plots. At the John C. Pair Horticultural Center there was no difference in compactness (dry weight/length) of slips, however, slips produced in the open field at the Olathe Horticulture Research and Extension Center were more compact than slips from high tunnels. We also explored seed root planting density and its effects on slip production. In 2017 there was no difference in the number of slips produced from three different planting densities (45, 65, and 85 seed roots/m2). Slips from high tunnels and open field were field planted to determine if root yield was influenced. At both field locations there was no statistical difference in root yield from slips produced in either high tunnel or open field. In general, there was a 20% increase in root yield from slips produced in open field, however, that difference was not statistically significant. In the lab we established a visual rating scale for slip quality to determine when a slip would be considered unmarketable. We also continued our investigations into post-harvest handling. Not surprisingly, cooler storage temperatures and a shipping package liner maintained overall quality and total slip water content longer than higher temperatures and no liner. Likewise increasing temperature rapidly increased the rate of respiration, which ultimately leads to slip decline. We also measured chlorophyll fluorescence as a measure of plant stress and found a storage temperature of 30C dramatically reduced Fv/Fm compared to a storage temperature of 16C or 22C.
We are on target with our objectives. We have conducted first and second year research station trials to evaluate the efficiency of producing sweetpotato slips in high tunnels. We have also conducted first and second year experiments on postharvest physiology of slips in simulated storage and shipping conditions including a visual rating scale of harvested slips. We have physiological data from those slips in various storage conditions. We have two graduate students (Masters) who are incorporating this work into their degree programs. One student will be graduating in May 2018 and the other is completing his first year in the program. A grower survey was conducted at the Great Plains Growers Conference to establish baseline data regarding acceptance and willingness to explore growing sweetpotatoes.
It can be economically feasible to produce sweetpotato slips in a high tunnel system without a significant loss in production volume or quality and the resulting sweetpotato crop will be comparable to conventional slip production. The shelf-life of sweetpotato slips can be extended through proper control of temperature and relative humidity during storage and shipping.
Trials were conducted in 2016 and 2017 at two research stations operated by Kansas State University: the Olathe Horticulture Research and Extension Center (OHREC) in Olathe, Kansas and the John C. Pair Horticultural Center (JCPHC) in Haysville, KS. In both years, seed roots were planted in high tunnels (HT) and open field (OF) at 45, 65, and 85 seed roots/m² density and covered with soil and plastic mulch. Plastic mulch was removed when shoot emergence was observed. Slips were harvested when slip canopy reached approximately 30 cm in length. To determine if slips from HT and OF are comparable in quantity and quality, data from the 65 seed roots/m² density plot was collected and included: total slip number, marketable slip number, slip length, stem diameter, number of nodes, leaf area, fresh weight, and dry weight. To determine if planting density influenced slip production, similar data was collected from the three density plots.
To further evaluate the effect of the HT system on sweetpotato propagation beds, slips produced in the HT and OF systems at both sites were planted at each trial location to determine treatment effect on transplant performance. These trials were planted in a randomized complete block design. Each plot was 25 ft long and had 25 slips, which were transplanted by hand at 12 inch in-row spacing and a planting depth of ~3 nodes. Transplant establishment data was collected by taking plant growth measurements at 3, 4, 5, 6, 7 weeks after transplanting (WAT) from three random subsamples within each treatment and replication. Transplants were maintained according to normal organic best management practices and sweetpotatoes were harvested 94 -100 days after planting. Harvested roots from both sites were cleaned to remove excess soil and sorted as either marketable or cull. Roots were culled if they were damaged, diseased, irregular shape, malformed, and/or not meeting size requirements of marketable grades. Marketable grades consisted of U.S. #1 (5.1 to 8.9 cm in diameter and 7.6 to 22.9 cm long), medium or “canner” (2.5 to 5.1 cm in diameter and 5.1 to 17.8 cm long), and jumbo (larger diameter and/or length but not less than U.S. #1).
In another study we investigated the post-harvest longevity of slips. Following harvest, slips were weighed and packed in waxed boxes either with or without a perforated nylon film (liner). Boxes were then placed in growth chambers with temperature set to 16, 22, or 30 C and 65% humidity. A sample of slips was removed every-other day and data collected. Data included a visual rating, water loss, color, respiration, and chlorophyll fluorescence.
In 2016, the HT plots produced more slips than in the OF, and the overall average slip number was 226.7 in the HT and 147.8 in the OF across both years. Slips grown in HT were on average 12% less compact (slip dry wt/cm length) with fewer nodes then their OF counterparts in 2016. Nonetheless, neither vine length, stem diameter nor total marketable root yield post-transplant was influenced by HT or OF treatments (1.7 and 2.1 lbs/plant, respectively). Similarly, the number of marketable roots was not affected by the HT or OF treatments (3.4 and 3.8 roots/plant, respectively). Increased planting density treatment corresponded with greater average slip yield across all harvests, but were only statistically significant during 1st harvest of 2016. The positive correlation between slip yield and planting densities plateaued between 65 and 85 seed roots/m2.
The results of these trials suggest that slip production in HTs may provide growers in the Central and Northern regions of the U.S. a viable technology for developing their own sweetpotato propagation schedule, without compromising plant yield or root production.
Data analysis for the post-harvest longevity is incomplete with only preliminary results thus far.
We made significant progress in 2016 and 2017 and used several opportunities to make various interest groups aware of our work. Budgets and comparison models and methods for an economic feasibility study with collaboration from the Department of Agricultural Economics is nearing completion. Data was presented at the Great Plains Growers Conference, American Society for Horticultural Science Annual Meeting, and the K-State Department of Horticulture and Natural Resources Seminar Series. Presentations and field plot tours at the Olathe Horticulture Research and Extension Center were conducted during a public open house in July (2016 & 2017) and to commercial growers and apprentices of the Growing Growers program in August (2016 & 2017).
We have demonstrated that sweetpotato slips can be successfully produced in high tunnels and then field planted to produce a marketable crop. We were able to establish baseline data from slips produced in high tunnels and those produced in open field. Data we collected included total marketable number and weight and cull weight. We also collected morphological data including fresh and dry weight, leaf area, stem diameter, length, and number of nodes. We also calculated slip ‘compactness’ (dry weight/length). Seed root planting density was investigated to determine how it influenced slip characteristics. Roots were planted at 45, 65, or 85 roots/square meter. We determined that increasing seed root density increase slip number per unit area, but there is likely a limit to the benefits of increasing density. Slips that were produced in high tunnel or open field produced a similar yield when field planted and grown out. In the lab we were able to establish a 9 point visual scale for rating sweetpotato slips. This simple, but effective, tool for communicating slip condition previously did not exist. We also established some baseline preliminary data for postharvest physiology of slips. We measured water loss and CO2 production from slips in storage over time and different temperatures. We also measured electrolyte leakage from leaf discs. Leaf color and chlorophyll content were documented as well. Preliminary data showed water loss from slips was greatly reduced when stored in wax-lined boxes. However, CO2 production was increased and slip quality rapidly declined in the wax-lined boxes. Electrolyte leakage was also hastened in the wax-lined boxes.
Currently this project is using traditional research and extension methods to disseminate information. Data has been presented in formal educational settings such as conferences and meetings. Field days and open houses have been used to demonstrate our activities.
Educational & Outreach Activities
Education and outreach for this project has thus far been traditional research and extension methods. Data has been presented and grower and research conferences. The project has been highlighted at several field day and workshop events throughout the year. Many informal educational opportunities have occurred through consultations over the phone, via farm visits, or growers stopping by the center to discuss sweetpotato production.
- General slip production, handling, and post planting care.