Progress report for LNC15-369

Project Type: Research and Education
Funds awarded in 2015: $195,968.00
Projected End Date: 09/30/2019
Grant Recipient: Kansas State University
Region: North Central
State: Kansas
Project Coordinator:
Dr. Jason Griffin
Kansas State University
Expand All

Project Information

Summary:

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.

2018 Update

In summer 2018 we continued our work examining best management practices for post harvest treatment of sweetpotato slips and the impacts on yield. Sweetpotato slips, cultivar ‘Orleans’, were harvested at the John C. Pair Horticultural Center (Haysville, Kansas, USA) and transported to the Postharvest Physiology Laboratory at Kansas State University Olathe (Olathe, Kansas, USA). Upon arrival 50 slips were placed into small waxed cardboard boxes (12” x 4” x 4”) with or without nylon-film liner. Boxes were stored in environmental chambers at three different temperatures: 16°C, 22°C, 30° at 65% relative humidity. An overall quality rating scale was developed to evaluate the visual quality of the slips with ratings from 1 to 9 (1- completely senesced to 9- field fresh slip). Changes in slip quality were evaluated throughout storage by measuring overall visual quality, water loss, chlorophyll fluorescence, respiration, color, and chlorophyll content. Slips stored at 16°C had the longest shelf life maintaining marketable quality for just over 10 days, followed by 7.5-8 days for 22°C and 6.5 days for 30°C. After 4 days of storage, slips stored with the addition of a liner had significantly lower water loss. After 4 days of storage, slips stored with the addition of a liner had significantly lower rates of water loss. Slips stored at 16°C with a liner lost 3.6 percent water weight compared to 13.3 percent for slips stored without a liner (p= 0.0020). Slips stored at 22°C with a liner lost 1.7 percent water weight compared to 14 percent for slips stored without a liner (p= 0.0031). Slips stored at 30°C with a liner lost 6.4 percent water weight compared to 19 percent for slips stored without a liner (p= 0.0304). The results of this work show that temperature and the addition of a liner play a critical role in maintaining quality and freshness of sweetpotato slips. Information from this study increases the postharvest handling knowledge of sweetpotato slips with hopes to aid in creating new standardized shipping practices. Ultimately, leading to increased availability of quality planting material for sweetpotato producers in the Northern and Central regions of the United States. In our second experiment slips planted the same day they were harvested (quality 9) established the quickest after transplant according to various parameters. However, slips that were stored for 6 days (quality 5), often out performed slips stored for 3 days (quality 7) in establishment and growth measurements. Slips planted at a quality 9 (1.81 lb/plant) and quality 5 (1.68 lb/plant) had significantly higher bulk yields than slips planted at a quality 1 (0.76 lb/plant) with p-value of 0.0020 and 0.0052 respectively. The results of this work indicate that storing slips for more than 6 days could have a detrimental effect on early vine growth as well as, storage root yield.

Project Objectives:

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.

2018 Update

We are still on target with our objectives. One graduate student has graduated while the second graduate student is continuing on with the postharvest studies mentioned above. 

Cooperators

Click linked name(s) to expand
  • Dr. Eleni Pliakoni
  • Dr. Cary Rivard
  • Dr. Mykel Taylor

Research

Hypothesis:

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.

Materials and methods:

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.

2018 Update

In 2018 we continued our post-harvest studies on sweetpotato slips and their effects on yield.

Slips were harvested from commercial slip production beds on three separate dates: August 1, 2017, September 1, 2017, June 4, 2018, June 26, 2018, July 16, 2018, and August 20, 2018. Slips were cut to 8-10” and placed (50 each) into waxed cardboard boxes, dimensions 12”x 4”x 4”. Half of the boxes were packed with slips wrapped inside a perforated liner. The liner-wrapped sample was subsequently placed into a box and closed. The sample boxes (both liner and no-liner) were stored at three different temperatures: 16°C, 22°C, or 30°C, all at 65% relative humidity. Changes in slip quality were evaluated throughout storage by monitoring overall visual quality, water loss, chlorophyll fluorescence, respiration, color, and chlorophyll content.

In the field study, slips were harvested by hand, every 3 days over a 12-day and period. All slips, except for those harvested the day of transplant were stored in an environmental chamber at 22°C and 65% relative humidity. The slips were held in storage for various lengths of time to artificially influence their quality at time of transplant. Slip quality was determined using a visual quality scale previously developed (1=low quality, 9=freshly harvested). The first sample of slips harvested represented a visual quality of 1 (lowest quality) and were held in storage for 12 days. The second group of slips harvested 3 days later, represented a visual quality rating of 3 and were held in storage for 9 days. This process was repeated two more times to achieve slips quality ratings 5 and 7 which were held in storage for 6 days and 3 days, respectively. Slips representing quality 9 were harvested the day of transplant.

The slips were planted on July 10, 2018. The plots were irrigated with an overhead system as needed to prevent stress but not fertilized. Transplant establishment and growth data was collected 10, 14, 21, 28, and 35 days after transplant. Data included survival rate, stem diameter, vine length, leaf area, shoot biomass, and root biomass. Storage roots were harvested on October 11, 2019 (93 days after transplant).  The harvested storage roots were cured for one week at 30°C and 90% relative humidity and then cleaned to remove excess dirt. The storage roots were then sorted into two groups: marketable and cull. Marketable grades consisted of U.S. #1 (5.1 to 8.9 cm in diameter and 7.6 to 22.9 cm long), 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). Storage roots were also counted and weighed (lbs/plant).

Research results and discussion:

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.

2018 Update

Slips stored at 16°C had the longest shelf life maintaining marketable quality for just over 10 days, followed by 7.5-8 days for 22°C and 6.5 days for 30°C. After 4 days of storage, slips stored with the addition of a liner had significantly lower water loss. After 4 days of storage, slips stored with the addition of a liner had significantly lower rates of water loss. Slips stored at 16°C with a liner lost 3.6 percent water weight compared to 13.3 percent for slips stored without a liner (p= 0.0020). Slips stored at 22°C with a liner lost 1.7 percent water weight compared to 14 percent for slips stored without a liner (p= 0.0031). Slips stored at 30°C with a liner lost 6.4 percent water weight compared to 19 percent for slips stored without a liner (p= 0.0304). The results of this work show that temperature and the addition of a liner play a critical role in maintaining quality and freshness of sweetpotato slips. Information from this study increases the postharvest handling knowledge of sweetpotato slips with hopes to aid in creating new standardized shipping practices. Ultimately, leading to increased availability of quality planting material for sweetpotato producers in the Northern and Central regions of the United States.

The results of the transplant study show that slips transplanted the same day they were harvested (quality 9) established the quickest after transplant.  However, slips that were stored for 6 days (quality 5), often out performed slips stored for 3 days (quality 7) in establishment. Slips planted at a quality 9 (1.81lb/plant) and quality 5 (1.68lb/plant) had significantly higher bulk yields than slips planted at a quality 1 (0.76lb/plant) with p-value of 0.0020 and 0.0052 respectively. The results of this work indicate that storing slips for more than 6 days could have a detrimental effect on storage root yields.

Research conclusions:

Impacts

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).

Accomplishments

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.

Participation Summary

Education

Educational approach:

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.

Project Activities

OHREC Field Day
Great Plains Growers Conference
2017 ASHS Annual Meeting
2018 OHREC Field Day
2018 Annual ASHS Conference
Great Plains Growers Conference

Educational & Outreach Activities

70 Consultations
2 Journal articles
10 Tours
16 Webinars / talks / presentations
6 Workshop field days

Participation Summary

55 Farmers
25 Ag professionals participated
Education/outreach description:

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. 

Learning Outcomes

32 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
4 Service providers reported changes in knowledge, attitudes, skills and/or awareness as a result of project outreach
4 Agricultural service providers reported changes in knowledge, skills, and/or attitudes as a result of their participation
Key areas taught:
  • General slip production, handling, and post planting care.

Project Outcomes

23 Farmers changed or adopted a practice
Key practices changed:
  • Have added or expanded sweetpotatoes in their operation.

12 New working collaborations
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.