Date of Award
Doctor of Philosophy
Sustainable Agriculture; Horticulture
Ajay . Nair
Tomatoes and peppers are two of the most popular vegetable crops within the state of Iowa. Both solanaceous crops benefit from high tunnel production which allows for earlier planting and fruit production, improved yields and fruit quality, and an extended growing season. While tomatoes and peppers are two of the most economically beneficial crops to grow within high tunnels, growers struggle to optimize yields and manage the environment inside high tunnels, primarily heat and light. In the case of tomato, the use of vigorous, disease-resistant tomato rootstocks has become a sought-after production tool for increasing yields and productivity, although results are often tied to scion x rootstock x environment interactions. Additionally, adoption of tomato grafting is on the rise across the country, and growers are eager for information on how to successfully produce grafted plants. One of the main challenges that exist in grafting is the healing of the grafted plants immediately after grafting in order to optimize plant survival. Healing chambers can be either locally constructed or bought but it adds to the overall cost of producing a grafted plant. Growers are interested in learning about low-input alternative healing systems that are less expensive, yet efficient, in producing a successful graft union. While pepper production can also be improved through grafting, a more immediate concern for Iowa growers is the management of high temperatures and solar radiation within high tunnels which can contribute to increased flower abortion, decreased fruit set, and decreased yield due to losses from both abiotic and biotic disorders. High tunnels are an excellent resource for season extension in early spring and late fall, however, they can capture and hold excessive heat during peak summer months.
The overarching goal of this research was to test and improve the use of grafting and shade cloth placement to improve tomato and pepper production in Midwest high tunnels. We began with a study of grafted and nongrafted hybrid and heirloom tomatoes which showed minimal yield increases with the rootstock used. Further research using seven additional rootstocks grafted to a commonly used hybrid tomato showed that five of the commercially available rootstocks increased marketable yields, and this research will be the first published study on yield performance for two high-performing rootstocks. In order to aid small-scale producers in successful post-grafting management of tomato transplants on farm, we conducted a study to examine the role of heat and light management in low-cost healing chambers. Our results demonstrated that healing chambers constructed from minimal materials placed in ambient greenhouse conditions, without light reduction, can still result in a high percentage of plant survival. Finally, to improve colored bell pepper production, we examined the use of 30 and 50% shade cloths placed on high tunnels. Our hypothesis was that shade cloth would affect yield, quality, and growth of colored bell pepper cultivars. Our findings indicated that the use of shade cloth above 30% should be avoided, and future work should examine lower levels of light reduction (10 and 20%) or alternative heat management methods. In summary, we demonstrated the potential of several tomato rootstocks to improve production while proposing a low-input method for production of on-farm grafted plants, and we were able to provide localized research-based recommendations for heat management within Midwest high tunnels. This collective body of work provides practical science-based strategies that will allow high tunnel growers to improve their production systems.
Lang, Kristine, "Optimizing high tunnel vegetable crop production through grafting, cultivar selection, and microclimate modification" (2019). Graduate Theses and Dissertations. 17725.