Final report for LS22-370
Project Information
There are over 28,000 acres of blueberry farms in the southeast. Something all these farms have in common is the extensive use of soil inputs. Growers use pine bark, large amounts of fertilizers, and large volumes of irrigation water to support agricultural production. These inputs increase blueberry establishment and production costs, reducing farm profitability and limiting who can grow blueberries in the southeast. Soil inputs also increase the likelihood of soil degradation, nutrient percolation, and water pollution. Reducing or eliminating the need for soil inputs is a critical step to increase the sustainability of blueberry farming systems in the southeast. Grafting blueberry on resilient rootstocks is an avenue to reduce the need for soil inputs, reduce establishment and production costs in blueberry farms, and broaden participation of underrepresented farmers in blueberry production. Previously, we have shown that commercial blueberry production targets can be attained with blueberry grafted on sparkleberry rootstocks. This project investigated creating a reduced input blueberry production system that leverages the strengths of sparkleberry rootstocks to reduce water, pine bark, and fertilizer use in blueberry farms in the southeast. We documented that sparkleberry rootstocks have deep root systems that allow grafted blueberry plants to grown in minimally amended soils and withstand drought periods longer than a week. The deep root systems might also help grafted plants access leached nitrogen. We used this information in combination with growers' knowledge, experiences, and perspectives to design a reduced input blueberry production system adapted to the farming practices in Florida and Gorgia. We identified adoption gaps and information interests among growers. This informed the design and delivery of educational materials and activities including multi-media products (social media posts, videos, and magazine articles), hands-on learning (field days for growers), and train-the-trainer workshops (regional workshop for growers and extension agents). Ultimately, this project has moved blueberry farming systems towards systems towards environmental, economic, and social sustainability by 1) identifying resilient rootstocks that can reduce reliance on practices that compromise soil health and water quality, 2) developing grafting methods that can reduce establishment and production costs in blueberry farms, and 3) remove barriers for the participation of underrepresented groups in blueberry farming.
Our overall goal is to increase the sustainability of blueberry farming systems in the southeastern United States by leveraging the resilience of grafted blueberry plants. Specific goals include:
Objective 1: Develop input reduction thresholds for blueberry production
Objective 2: Design a reduced input production system that uses grafted blueberry plants
Objective 3: Evaluate reduced input blueberry production using agronomic productivity, environmental, and economic sustainability metrics
Objective 4: Increase adoption of the reduced input blueberry production system
Cooperators
Research
We constructed microcosms that imitate the blueberry production system in the southeastern U.S. (Figure 1). Microcosms consisted of a 70 cm by 40 cm container. The lower half of the container was filled with a well-drained Arendondo series soil collected from a blueberry farm. The top half of the container was filled fine pine bark. This stratification of the soil column represents the prevalent blueberry farming system in the region, where growers plant in raised beds made of pine bark that sit on top of native soil. We equipped is microcosm with drip irrigation according to commercial farming practices.
We planted grafted and own-rooted blueberry plants in these mesocosms. One year-old sparkleberry plants were side-grafted with scions of southern highbush blueberry cultivar ‘Sentinel’. One year-old ‘Sentinel’ plants were used as controls. ‘Sentinel’ is a new highbush blueberry variety that enjoys wide popularity among growers. Grower advisory board members Bert Sheffield and Kyle Straughn concurred with the cultivar selection.
We grew plants in the microcosms for 12 months. We used root observation tubes and a minirhizotron scanner to monitor root growth. We also used soil moisture, soil water potential, photosynthetically active radiation, temperature, and air relative humidity sensors to measure environmental conditions in the microcosms. We used RGB cameras and quantum sensors to measure plant size.
We validated mesocosm results in a field planting of grafted and own-rooted blueberry. This field is managed with a reduced-input approach. Mature grafted and own-rooted 'Patrecia' southern highbush blueberry plants were connected to stem psychrometers, infrared gas analyzers, and soil moisture sensors. A polyethylene rain shelter and a Tyvek soil moisture barrier were installed above and beneath the plants to isolate them from any precipitation (Figure 2). Then, data collection began. Plant responses to water deficit were observed before (acclimation period), during, and after (rehydration period) stress. Irrigation was lapsed for 3 days during the fall of 2023. This experiment was repeated with a 9-day lapse in irrigation in the spring of 2024.
We connected with growers from Georgia and Florida. They indicated that 'Farthing' and 'Sentinel' southern highbush blueberry scions would be attractive for the field plantings in their farms. We grafted these scions onto clonal sparkleberry rootstocks during the fall of 2023. Then, we pruned and trained these plants in preparation for planting. We planted replicated fields in commercial farms in Archer, FL in October 2024 and Alma, GA in December 2024 (Figure 3). We communicated with the growers and established input reduction goals (less water, less pine bark, and less nitrogen fertilization). The most feasible way to accomplish this was to reduce the number of drip lines in the bed from 2 to 1 (in Florida) or to increase the emitter spacing in the drip line from one emitter every 12 inches to one emitter every 18 inches (in Georgia). We collected soil health data before and after planting in both locations.
Additionally, we set up a hydroponic experiment with grafted and own-rooted ‘Sentinel’ plants. Plants were transplanted to individual hydroponic solution reservoirs (2 L) supplied with a complete nutrient solution and continuous aeration (Figure 3). Nitrate was the only form of nitrogen provided in the nutrient solution. We measured nitrate uptake, nitrate assimilation in the roots, and plant biomass gain using previously established methods (Imler et al. 2019; Poonnachit and Darnell 2004). We used hydroponics as a method to isolate plant nutrient uptake from soil heterogeneity and nitrification.
Edaphic and environmental conditions in the microcosms closely resembled blueberry farms and promoted vigorous plant growth. Own-rooted plants exhibited larger canopies than grafted plants (Figure 5A). This is consistent with the long establishment period of grafted plants in field conditions (Heller et al. 2023). Own-rooted plants also exhibited larger root systems (Figure 5B). However, there were notable differences in root distribution between grafted and own-rooted plants. Own-rooted plants exhibited higher root length than grafted plants in the first 22 cm of the soil profile (Figure 6A). There were no differences at depths between 22 cm and 44 cm (Figure 6B). Grafted plants exhibited higher root length than own-rooted plants at depths higher than 44 cm (Figure 6C). These results confirm field observations that suggested there could be contrasting root architecture between sparkleberry and blueberry (Lyrene 1997). Deeper roots in grafted plants might be an asset to promote reductions in irrigation and fertilizer use.
We found additional evidence of the resilience of grafted blueberry plants in the field validation experiment. When subjected to water deficit, six-year old grafted plants maintained their midday photosynthetic rates. In contrast, own rooted plants exhibited declining photosynthetic rates when challenged with water deficit. Grafted plant net photosynthesis was greater than 5 μmol/m2/s during the stress period, whereas own-rooted plants were as low as zero μmol/m2/s. Resilience was also documented during rehydration. Grafted plants maintained their photosynthetic rates, but own-rooted plants did not recover up to 3 days after rehydration. Similar patterns were observed when we repeated this experiment with a longer drought period.
Stem water potential data helped put gas exchange results in context. Stem water potentials are negative magnitudes that measure the water status of the plant (the more negative a number the worse the hydration status of the plant). Midday stem water potentials of grafted plants were higher than those of own-rooted plants during the acclimation, water deficit, and rehydration periods. Grafted plants did not exhibit abnormal stem water potential patterns during the drought period (Figure 7). In contrast, own-rooted plants exhibited increasing drought stress symptoms. Altogether, these results indicate that grafted blueberry plants avoid water deficit stress -likely due to their deep root systems.
When evaluated in a hydroponic experiment where nitrate concentrations were stable and homogeneous in the rhizosphere, own-rooted and grafted plants did not exhibit differences in their ability to take up or assimilate nitrate. Nitrate uptake ranged between 25 mg N plant-1 week-1 and 35 mg N plant-1 week-1 in both kinds of plants. Nitrate reductase activity ranged between 200 μmol g-1 h-1 and 1,500 μmol g-1 h-1. Both kinds of plant exhibited a tendency to increase their nitrate reductase activity as the experiment went on. These results contrast with previous studies (Poonnachit and Darnell 2004) were own rooted sparkleberry outpaced the nitrate uptake and assimilation of southern highbush blueberry, suggesting that nitrate uptake and assimilation in this genus is related to nitrogen use in the canopy and not root-level limitations. Additionally, these results suggest that if there are differences in nutrient uptake between grafted and own-rooted plants, these differences are likely a consequence of root distribution patterns and soil heterogeneity.
Educational & Outreach Activities
Participation summary:
Results from this project have been disseminated in a variety of venues and using multiple media formats.
Grower education
We hosted groups of growers, extension educators, and industry professionals as part of the 2023, 2024, and 2025 Spring Field Days of the Florida Blueberry Growers Association. These meetings were held at the UF Plant Science Research and Education Unit in Citra, FL. We started with a brief presentation in the conference room, and then we followed with a field tour to showcase ongoing experiments. Additionally, we hosted a workshop at the 2025 Southeast Regional Fruit and Vegetable Conference in Savannah, GA. This conference has over 5,000 growers in attendance from across the southeast. The workshop has 37 registered participants, 14 of which where agricultural service providers.
Multimedia products
We made short videos in English, Portuguese, and Spanish where we disseminated findings from the first peer-reviewed article produced from the project. These videos were publishes in social media platform X, and they have accrued 2,218 (English), 732 (Spanish), and 350 (Portuguese) views to date. Additionally, we recorded an instructional video about grafting techniques for blueberry liner production with the assistance of the UF/IFAS Communications office. The video was published in social media platform YouTube under the UF/IFAS Extension channel, and it has accrued 1,200 views to date. Finally, we published a grower article in The Blueberry News. This is a magazine that reaches all members of the Florida Blueberry Growers Association and all county extension offices in Florida.
- The Feasibility of Grafting Blueberry Plants - UF/IFAS (link)
- Blueberry Grafting Comes of Age - Nunez et al. (link)
Scientific Communications
Results from this project were presented at the 2022 and 2023 Annual Meeting of the American Society for Horticultural Science. This is the flagship scientific meeting of the horticulture industry. Conference participation led to two published abstracts.
- Heller, C. R., Williamson, J. G., Sapes, G., Hammond, W. M., & Nunez, G. H. (2023). Exploring the impact of deep-rooted rootstocks on water stress resistance in blueberries. HortScience, 58(9), S77.
- Heller, C. R., Williamson, J. G., & Nunez, G. H. (2022). Grafting onto sparkleberry rootstocks increases
rooting depth in southern highbush blueberry. HortScience, 57(9), S89.
Additionally, two peer-reviewed scientific articles have been published to date. A third article is currently undergoing peer-review.
- Heller, C. R.G, Williamson, J. G., & Nunez, G. H. (2025). Impact of rootstocks on water stress in blueberries. Acta Horticulturae, 1440, 357-362. doi.org/10.17660/ActaHortic.2025.1440.49
- Heller, C.H.G, G. H. Nunez, J.G. Williamson. (2023). Effects of Vaccinium arboreum rootstocks on yield and fruit quality of ‘Patrecia’ southern highbush blueberry grown with minimum soil amendment. Journal of the American Pomological Society, 77(2): 103-109.
Learning Outcomes
Project Outcomes
The graduate student working on this project was awarded the 2022 Grant A. Harris fellowship ($10,000 in instrumentation) to augment her work in the microcosm experiment.