Evaluating the Impact of Biostimulants on Blueberry Growth and Soil Biological Health

Objective 1: Characterize Georgia blueberry growers’ experience and expertise in using biostimulants

• We received a total of 68 surveys, of which 37 were usable responses (based on completion rate of at least 70% and removal of duplicate farms).
• Farm size of survey participants ranged from approximately 1 hectare (2 acres) to more than 256 hectares (635 acres), with an average farm size of approximately 49 hectares (~121 acres) (Table 1).
  

  

• The completed surveys represent approximately 1,661 bearing hectares (4,105 acres), and 1,811 hectares (4,475 acres) in total planted area, an estimated 16% of blueberry production area in Georgia at the time of the survey.
• Farms in Bacon, Appling, and Clinch counties accounted for 58% of the survey responses and 61% of the total planted area in the survey, with most being from Bacon County (45% and 50%, respectively) (Figure 3). Farms in Brantley and Coffee counties also accounted for a significant amount of survey responses (13%) and total 34 planted area (30%). Other counties from across the state with producers represented in this survey include Baker, Burke, Candler, Colquitt, Jeff Davis, Meriwether, Mitchell, Tift, Ware, and Wilcox counties.
  

  

• The most common rabbiteye varieties reported by producers were ‘Brightwell’ (n=26) and ‘Premier’ (n=11), both of which are unpatented and the products of early blueberry cultivar development.
• Analysis of survey data indicates that plant biostimulant use among Georgia blueberry growers is not widely adopted and may be more prevalent among organic producers. Among survey participants in the present study, 27% percent reported currently using plant biostimulants in their production.
• When asked if their knowledge of plant biostimulants has changed at all within the last year, the majority (67%) reported no change in their level of understanding. Most participants (80%) reported the cost of plant biostimulants as “very much” or “somewhat” impacting their decision to use them.
• Analysis of interviews indicates that growers’ familiarity with plant biostimulants is highly variable. Growers are interested in researchers providing clarity regarding plant biostimulants: They want an unequivocal definition of what biostimulants are and how they work, as well as an impartial review of biostimulant products on the market and which benefits they can provide to the growers' production systems.
• Additionally, results indicate that there is still quite a bit of uncertainty among growers regarding plant biostimulants. Specifically, they are unsure as to where reliable sources of information can be found about biostimulants outside of university sources, and that some sources like chemical suppliers may be untrustworthy.

Objectives 2 &3: Determine the impact of biostimulants on blueberry growth and soil biological growth in a greenhouse and field studies.

Greenhouse Study Results

• From mixed model analysis, biostimulants did not significantly influence any of the plant growth and biomass parameters over the study period. Treatment effect was observed only on foliar pigment content indicators (chlorophyll, flavonols and anthocyanin) and differed by cultivar and time.
• For all the blueberry cultivars, no significant difference was detected in chlorophyl content between the Control and the biostimulants, except with the Brightwell cultivar. The biostimulant Terra grow resulted in significant higher chlorophyll content than Control in Brightwell in February, suggesting a potentially positive effect on the process of photosynthesis. Another exception was with the Legacy cultivar in which the Control had significantly higher chlorophyll content than the biostimulant Fertiactyl GZ in May.
• Terra grow was the only biostimulant that resulted in significantly higher anthocyanin content than the Control with the Legacy cultivar in June. For flavonols, the only cultivar in which significant difference between the biostimulants and the Control was observed was Brightwell in July. The biostimulant Fertiactyl GZ resulted in significantly lower flavonols content than the Control. Anthocyanin and flavonols contents are indicators of plant response to stress.
• Overall, the data indicate that most of the biostimulants did not significant affect the growth of the blueberry plants or their ability to respond to stress. Those biostimulants that affected any aspect of the plant growth did so in a manner that was not consistent over time or cultivar.
• In regard to the soil biological health indicators, no significant treatment effect was detected on soil respiration, urease and phosphatase activities. The biostimulant Fertiactyl GZ resulted in significantly higher FDA activity than the biostimulant Micron Nutrients but not against the Control with the Legacy cultivar.
• With AOA and AOB abundance, the biostimulants Inocucor, Huma Gro, Terra Grow and Micron Nutrients resulted in significantly higher abundance than Control in Farthing and Premier cultivars. This suggests these biostimulants might have stimulated growth of the microorganisms, potentially impacting the fate of nitrogen in the system. However, the results were not consistent across cultivars and biostimulants, and it was not easy to link the change to ingredients in the product. However, these are based on preliminary analysis, and we still have additional analysis to conduct on soil microbial community.

Field Study Results:

•  As in the greenhouse study, we did not see any consistent effect of any of the biostimulants tested in the field on plant growth and soil biological health indicators. However, there were some trends. For example, anthocyanin levels were higher in plants with Terra Grow and Fertiactyle treatments in the organic farm (Table 2). Soil respiration was higher in plots that received Inocucor, Terra Grow and Huma Gro in both systems. Urease activity was elevated by Inocucor and Terra Grow. Some of these differences were not significant due to large variation among replications and hence the need to repeat this study for a second year. The field study was done only once during the project period because of COVID-related delays. We will continue the field study for the second year with support from other sources. Multiple year field study will provide better insight on the effect of the biostimulants on blueberry growth and soil biological health.

Presentations/Publications

• Preliminary survey results were presented at a UGA Extension virtual workshop with the purpose of sharing of information and recruitment for subsequent grower interviews on October 15, 2020 by graduate student Joel Kirksey who is part of the project.
• Renee Holland (project co-investigator) presented partial results of the survey to growers for sharing and recruitment on October 23, 2020 during Fruit Quality Workshop Update (virtual) hosted by UGA Extension.
• Kirksey, J. and Thompson, J. 2021. Understanding Growers’ Perceptions of Plant Biostimulants in Blueberry Production and Soil Biological Health. University of Georgia graduate seminar course, March 17, 2021, Athens, GA.
• Kirksey, J, JJ Thompson. 2021. Navigating Emergent Technologies and Scientific Uncertainty with Biostimulants in Georgia Blueberry Production. 2021 Joint Annual Conference. Association for the Study of Food and Society, Agriculture, Food and Human Values Society, Canadian Association for Food Studies, and The Society for the Anthropology of Food and Nutrition. (Virtual)
• Kirsey, J. 2021. Understanding Grower Perceptions of Plant Biostimulants in Georgia Blueberry Production. MS Thesis. University of Georgia.
• Kirksey, J and JJ Thompson. 2021. Understanding Grower Perceptions of Plant Biostimulants in Georgia Blueberry Production. ASA-CSSA-SSSA International Annual Meeting. Salt Lake City, UT.
• Kirksey, J. 2021. Understanding Grower Perceptions of Plant Biostimulants in Georgia Blueberry Production. MS Thesis. University of Georgia.
• Drocco, C. 2021. Evaluating the Impact of Biostimulants on Blueberry Growth and Soil Biological Health in a Greenhouse Study. MS Thesis. University of Georgia.

References

Mobley H.L. and Hausinger R.P. 1989. Microbial ureases: Significance, regulation, and molecular characterization. Microbiol. Rev. 53: 85-108

Mundepi et al. 2017. Ammonia oxidizers in grazing land with a history of poultry litter application. J. Environmental Quality 46:994-1002.

Scherm et al. 2001. A survey of horticultural and pest management practices of the Georgia blueberry industry. Small Fruits Review 1(4):17-28.

Tabatabai, M.A. 1994. Soil enzymes. In Methods of Soil Analysis, Part 2 – Microbiological and Biochemical Properties. R.W. Weaver, J.S. Angle and P.S. Bottomley (eds.) Soil Science Society of America, Inc. Madison, WI. pp. 775–834.

Zibilske, L.M. 1994. Carbon mineralization. In Methods of Soil Analysis, Part 2 – Microbiological and Biochemical Properties. R.W. Weaver, J.S. Angle and P.S. Bottomley (eds.) Soil Science Society of America, Inc. Madison, WI. pp. 835–906.