Growers are increasingly impacted by and/or interested in learning how to prevent declines in the health, quality, or productivity of soils in their high tunnels. More are experiencing or aware that various biotic and abiotic issues threaten crop yield and quality and farm income. As some have learned, increases in nematode populations, disease inoculum, salinity, nutrient deficiencies/excesses/imbalances, and/or compaction or reductions in soil structure can be troublesome. Thankfully, a comprehensive effort is underway to help understand and address soil health/productivity-related challenges in high tunnel production. Sponsored by the USDA Specialty Crops Research Initiative and coordinated by Dr. Krista Jacobsen of the University of Kentucky, researchers with different expertise and extension specialists are documenting grower concerns and practices and charting a path leading to greater grower success. The OSU and five other universities are also currently involved. Team members recently hosted a focus group of eight growers from the Great Lakes (including Ohio) and will hear from more in other regions soon. Growers in the recent focus group represented a range of experience, size of operation, crops grown, typical number of annual production seasons (1-4), and overall farming approach (conventional, organic). Collectively, they shared concerns with issues referenced earlier and gave special attention to others such as the effects of high tunnel soils going extremely dry fall-to-spring unless watered (with or without also being cropped). Interestingly, this observation and concern lines up with the view shared by Dr. Bruce Hoskins of the University of Maine that high tunnel production is like “irrigated desert production in the west and southwest,” and that “failing to realize or take steps to address potential problems because of this” can be detrimental (see VegNet article Feb. 20, 2021). In any case, the recent conversation with growers was a reminder of: (1) potential causes of declines in (high tunnel) soil productivity (examples are listed below), (2) innovative steps growers and researchers are taking to limit the problem, and (3) benefits of addressing the complex problem through partnerships. It also prompted me to ask myself what I am doing to maintain the productivity of soils in my high tunnels. Maybe it will do the same for you!

The health-quality-productivity of soils used in vegetable production, including in high tunnels, can decline for many reasons. Some major ones are listed below in no particular order.

1. Repeated or excessive use of a potentially narrow range of fertilizers, various chemicals, and other soil amendments.
2. Vegetable plants often having relatively small and shallow root systems (compared to other annual crops) and crops returning relatively little residue to the soil.
3. Short rotations with few crops.
4. Placing frequent pressure on and aggressively disturbing soil, especially when it is wet.
5. In high tunnels, relatively unique and potentially extreme temperature and moisture profiles.

Installing a stationary high tunnel (HT) is a significant, long-term commitment to the parcel of soil beneath it, especially if the crops will grow directly in that soil. Maintaining, and preferably enhancing, the health, quality, or productivity of that soil for as long as possible should be a high priority beginning at HT installation.

Soils in HTs are less well understood than uncovered soils in “open sky”/open field production. However, the HT farming, extension-research, and industry communities are aware that HT soils are prone to specific issues and require specific care to remain commercially viable. These issues and preventative or reclamation tactics are the subject of much research and extension. Therefore, HT growers are encouraged to stay tuned for more information, including on how they can participate directly in identifying concerns and developing solutions. Examples of concerns and working solutions were summarized in a recent presentation (https://www.youtube.com/watch?v=XpUl0IwaDFI). Choosing one concern, in a summary of a presentation given at the 2013 New England Fruit and Vegetable Conference (https://newenglandvfc.org/sites/newenglandvfc.org/files/content/proceedings2013/Hoskins%20High%20Tunnel.pdf), Bruce Hoskins of the University of Maine’s Analytical Lab and Soil Testing Service mentions that the buildup of nutrient salts over time is “one of the most common problems in a continuously covered HT system,” that HT soil management can be similar to “irrigated desert production in the west and southwest,” and that growers familiar with open-field production can “fail to realize this potential problem or take steps to remediate it.” He also mentions that nitrate may carryover from one HT crop cycle to the next more readily than in open field production.

We heard from Bruce Hoskins and John Spargo during recent conversations about HT soil management. They direct soil testing and analytical labs at the University of Maine (https://umaine.edu/soiltestinglab/) and Penn State University (https://agsci.psu.edu/aasl), respectively. Each of these labs receives soil samples from hundreds of HT growers (conventional, organic) each year and have been actively helping improve soil management recommendations and cropping outcomes for HT growers. They have been joined in that work by others, including farmers, across the Northeast and Mid-Atlantic regions for years.

Take-aways from these recent conversations include that routine soil testing is essential, along with accounting for potential nutrient salt buildup when collecting soil samples. Normally, samplers: 1) use a soil probe or spade to retrieve a column of soil about twelve inches deep, 2) drop the soil in a bucket, 3) repeat the process one or more times from other areas, 4) mix the soil in the bucket, and 5) submit a portion of it for analysis. Listening to testing and other experts, the best approach appears to include “stratified” sampling; that is, submitting samples taken from 0-4 inches deep (upper layer of the rooting zone) separately from samples taken from four inches and deeper (lower layer of the rooting zone). Salts tend to accumulate in upper layers, especially if soil is heavy-textured and irrigation is frequent but brief. So, standard “mixed” samples may either: (a) underestimate salt levels in upper layers of soil experienced by roots of transplants and more mature plants or (b) overestimate salt levels if samples include only the upper level. Stratified sampling, mindful that soil characteristics can change with depth, equips growers and others with information to better manage HT soils. Regarding the costs of soil testing, especially of stratified samples, input from soil testing labs suggests that few of the growers they work with mention it as a significant concern. Instead, most growers appear to have done their math and concluded that soil analysis offers a significant return on investment, given that its cost is more than offset by gains in crop yield and quality in the current and subsequent years.

Grafting creates physical hybrids between seedlings of at least two varieties. The rootstock variety is used for its root system and traits and the scion variety is used for its shoot and fruit traits. Grafting is providing growers with an expanding list of key plant traits more rapidly and in different combinations than standard hybrid variety development. These traits include resistance to specific soilborne diseases (e.g., Fusarium, Verticillium) and the ability to overcome various abiotic stresses (e.g., salinity, drought, low fertility). Plant growth at low soil temperatures, improved fruit quality, and/or greater fruit holding ability on the vine may also be possible in specific cases. Among grafted crops, field and high tunnel acreage of tomato and watermelon are greatest, although interest in and acreage of grafted pepper, eggplant, cucumber, and melon are also rising.

Resources to help growers make the best use of grafting are also increasing and improving. The most important resource is growers who have experimented with grafted plants and share their experiences and views. Online resources (e.g., http://www.vegetablegrafting.org/) can also be useful. For example, one site (http://graftingtool.ifas.ufl.edu/) helps growers “run the numbers” on grafting’s potential impact on their bottom-line. That decision-support tool improves as information from farm-level tests of grafting is added.

Growers also ask how they can obtain grafted plants. The number of operations supplying Ohio and the U.S. (http://www.vegetablegrafting.org/resources/suppliers/) is rising. I have personal experience with the three suppliers listed below in alphabetical order. Contact them soon if you are interested in receiving grafted plants for use in 2021.

1. Banner Greenhouses (Nebo, NC; ph. 828-659-3335; https://www.bannergreenhouses.com/).
2. Re-Divined (Bainbridge, PA; ph. 717.286.7658; grafted@redivined.net; https://redivined.weebly.com/).
3. Tri-Hishtil (Mills River, NC; ph. 828.891.6004/828.620.5020 – Chris Furman; sales@Tri-Hishtil.com; http://www.trihishtil.com/).

Grafted plants can also be prepared by the same person or farm that uses them in the field or high tunnel. Many guides describing how to graft vegetables are available. The following are a small number of examples.

1. https://u.osu.edu/vegprolab/grafting-guide/ and other resources at https://u.osu.edu/vegprolab/research-areas/grafting-2/.
2. http://www.vegetablegrafting.org/resources/grafting-manual/.

Please contact me if you need additional information.

Researchers representing the USDA and six universities are spearheading an effort to improve both soil-less rooting media used in specialty crop and transplant production and peoples’ success using soil-less media. Their research focuses on grower concerns and their extension/outreach will include a North American Soilless Substrate Summit. The team’s work is supported by the USDA Specialty Crop Research Initiative  (Grant # 2020-02629). Learn more about it by contacting Dr. James Owen in Wooster, OH (jim.owen@usda.gov; 757-374-8153) or Dr. Jeb Fields (jsfields@agcenter.lsu.edu; 985-543-4125). Just as important, help steer the team’s research by completing a 5-minute survey at https://bit.ly/2ZLNIkn.

Growers, consultants, seed company representatives, and others have questions about watermelon management protocols, especially when grafted plants are used. The three panels below provide background on and summarize preliminary findings from two experiments on this topic completed in Wooster in 2020.

Please contact me at kleinhenz.1@osu.edu or 330.263.3810 for more information.

Data collection on fruit taken from two “grafted watermelon” experiments being completed at the OARDC in Wooster,OH has started. These experiments were outlined in VegNet posts on June 6 and July 11 and they are described in the image below, too.

Harvest 1 occurred on 8/19/20 with ‘Jade Star’ fruit harvest and analysis. The first harvest of ‘Fascination’ will be the week of 8/24 and a second harvest of each variety from both experiments is also planned. We assess the maturity of each fruit and its readiness for harvest using these criteria: a) yellow belly, b) dry vine tendril, c) developing longitudinal ridges, and d) white stripes brightening and widening (‘Fascination’). Occasionally, fruit weighing less than 8 lb meet one or more of these criteria, so they are harvested and photographed along with all other fruit from the same plot. Fruit weighing less than 8 lb are later separated from the group of fruit weighing more than 8 lb (marketable). In all pictures below, fruit are shown on a blue tarp slightly larger than 7 ft wide x 4 ft tall.

Pictures below are representative of what was observed in replicates 1-3 but conclusions should not be drawn from them. Data from Harvest 2 are needed to complete the picture and all data from 2020 must be analyzed along with data from previous years of the research (2018, 2019). On 8/19/20, in the “density” study, we observed that all four plots containing grafted plants produced a total of 12 fewer fruit than the four plots containing grafted plants at an in-row plant spacing of four feet. However, the situation was reversed at an in-row plant spacing of five feet since the four plots containing grafted plants produced a total of thirty-five more fruit than the four plots containing ungrafted plants at the same spacing.

The last planned fertilizer application (fertigation) in the “fertility” study was completed on 8/21/20. Two days before, the number of fruit taken from all twelve plots containing grafted plants was greater than the number of fruit taken from the twelve plots with ungrafted plants, regardless of seasonal nitrogen (N) rate. The difference in fruit number was greatest, moderate, and least at 75%, 100%, and 50% of the normal N rate, respectively. The pictures below are an example of the difference in fruit number at the standard N rate developed for watermelon production using ungrafted plants.

The experiments are being completed with USDA-SCRI program support and we look forward to sharing the results when the work is complete. In the meantime, please contact us (kleinhenz.1@osu.edu; 330.263.3810) for more information.

Growers, seed, grafted plant, and fertilizer suppliers, extension-research personnel, and others are interested in identifying if, where, and how grafted plants may fit in vegetable production toolboxes. Those questions can be answered reliably only after the performance of grafted plants is documented under a range of management schemes because it is possible that standard production practices may need to be altered to account for the influence of rootstocks. Plant spacing (i.e., population density per acre) and fertilizer application rates (e.g., total seasonal nitrogen applied) are two variables likely to influence (grafted) plant performance; therefore, they have many peoples’ attention, including ours.

With USDA-SCRI program support, we began studying these variables at a preliminary level in 2018 and more thoroughly in 2019. Experiments started in 2019 are being repeated in 2020.

Data collection begins with tracking crop development and concludes with laboratory analyses of fruit quality. The experiments provide an opportunity to analyze fruit yield and quality as influenced by grafting, scion, spacing, and N level. In 2019, soilborne disease did not appear to be a factor and grand mean total cumulative fruit yield (ton/acre) values were: a) 32.5 (ungrafted ‘Fascination’), b) 25.0 (ungrafted ‘Jade Star’), c) 42.6 (grafted ‘Fascination’), and d) 47.7 (grafted ‘Jade Star’); these values include data for all density and N rate treatments. Analyzing data collected in both study years more thoroughly will provide a more reliable assessment of the influence of grafting, in-row spacing (4 or 5 ft), and total seasonal N application (100, 120, or 142 lb/acre) on watermelon fruit yield and quality.