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

Progress report for LS19-309

Project Type: Research and Education
Funds awarded in 2019: $297,119.00
Projected End Date: 03/31/2022
Grant Recipient: University of Georgia -- Griffin
Region: Southern
State: Georgia
Principal Investigator:
Mussie Habteselassie
University of Georgia-Griffin Campus
Expand All

Project Information

Abstract:

The word biostimulant is used to describe a collection of products that contain ‘effective’ microorganisms (informally called bugs in a jug) and/or plant or animal derived constituents that are alleged to stimulate plant growth and improve crop yield and soil health. They are marketed as being more sustainable alternative and/or supplements to conventional agrochemicals. The biostimulant market in the USA is growing rapidly but there has been limited research to test their efficacy. We are proposing to address this gap in research. Biostimulants are often used in blueberry production, which is one of the fastest growing agricultural sectors in the Southeast, and Georgia is one of the leading growers.

Our project fits in the blueberry production system, with a focus on the response of soil microorganisms to application of biostimulants and how that in turn affects the growth of blueberries. Microorganisms drive soil processes that are essential for the sustainability of the system. As such, the soil biological health is a crucial component of the overall sustainability of the blueberry production system. The use of inputs that promote the soil biological health will therefore strengthen the system by contributing to its overall sustainability.

Our project is highly relevant to sustainable agriculture. Biostimulants often contain bacterial and fungal inoculants that have the potential to enhance plant nutrient availability and prevent diseases. The supply of labile sources of organic matter from biostimulants has also the potential to enhance the beneficial services of the indigenous soil microorganisms. As such, the availability and use of effective biostimulants may decrease the reliance on some traditional agrochemicals. It can also address the lack of alternative products for organic farming and play an important role in recycle wastes that often are the sources of ingredients for biostimulants. Our proposal employs systems approach as it addresses multiple components of the system — blueberry, soil health and growers. It also includes multiple stakeholders and experts to address several components of the system.

Project Objectives:

The project objectives are:

  • Characterize Georgia blueberry growers’ experience and expertise in using biostimulants.
  • Determine the impact of biostimulants on blueberry growth and postharvest fruit quality characteristics in greenhouse and field studies.
  • Determine the impact of biostimulants on soil biological health and relationship between soil biological health and blueberry plant growth and postharvest fruit quality characteristics.
  • Develop educational materials on selection, use and evaluation of biostimulants for growers.

Cooperators

Click linked name(s) to expand
  • Camilla Drocco (Researcher)
  • Joel Kirksey (Researcher)

Research

Materials and methods:

This report covers some of the work done under Objectives 1 and parts of objectives 2 and 3. Objective 1 was to characterize Georgia blueberry growers’ experience and expertise in using biostimulants. Parts of Objectives 2 & 3 were to determine the impact of biostimulants on blueberry growth and soil biological growth in a greenhouse study.

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

  • To understand key issues of importance to Georgia blueberry growers and to develop an initial understanding of how growers talk about biostimulants, 35 to 40 hrs of participant observations were made in eight in-person and virtual blueberry networking and education events early in the project period.
  • Survey of Georgia blueberry growers (n=41, representing 8% of GA blueberry acreage) was developed following Scherm et al. (2001) after participant observations. The survey was distributed to approximately 500 individuals through an online UGA Extension listserv of blueberry industry stakeholders, as well as in-person and virtual education events. This survey served multiple purposes of providing background information about the practices of GA blueberry growers, their research priorities, and to identify growers willing to participate in one-to-one interview. We are in the process of analyzing the survey data using the program Statistical Package for the Social Sciences. Descriptive analysis will be used on both quantitative and categorical variables.
  • Semi-structured interviews (n=10) were also conducted. Due to COVID-19, we were not able to conduct walking interviews with growers; rather, we conducted telephone interviews (approx. 30-60 minutes) to explore growers’ perceptions, experience, and expertise using biostimulants in blueberry production. Interviews are being analyzed using a Framework Analysis approach to detect, categorize, and define key themes related to the research subject.

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

  • A nine-month greenhouse study (January to September 2020) was conducted to evaluate the impacts of eight biostimulants on blueberry growth and soil biological health.
  • Four blueberry cultivars (Brightwell, Premier, Legacy and Farthing) that belong to two different blueberry types (Rabbiteye and Southern highbush) were included in the study. The choice of the cultivars was based on the state’s blueberry acreage that is planted with the cultivars. Blueberry plants of 17-18 months old were obtained in December 2019 from blueberry farms in Alma, Georgia and were transferred to three-gallon pots that contained growth medium with a 75% pine bark and 25% sand mixture (Figure).
  • Based on input from Georgia’s blueberry growers, eight biostimulants were chosen for the study. The list included the following with company’s name in bracket: Fertiactyl GZ (Alltech), Huma Gro ZAP (Huma Gro), Inocucor (Inocucor Technologies), Micron Nutrients (Suntton International, Inc), Quantum Organic Total (Ecological Laboratories), Radiate (Loveland Products), Soil Set (Alltech Crop Science) and Terra Grow (BioSafe Systems). The products were applied according to instructions on the labels. If there were any doubts about the instructions on the labels, we reached out to company representatives for more information or clarification.
  • The experimental design was a randomized complete block design, with nine treatments (8 biostimulants and 1 control), 4 blueberry cultivars and 5 replications per combination. The plants were put in five benches (blocks) in the greenhouse where they were maintained according to standard horticultural practices for blueberries during the study period. Each bench had a dimension of 1.52 m width and 3.01 m length. Each bench had 36 plants organized in 9 rows, with each row having 4 plants, following treatment and cultivar randomization process. The pots were evenly spread on each bench (Figure). The treatment schedule included application of some products biweekly and others monthly according to instructions on the product labels.

Figure: Blueberry plants in the greenhouse study

  • Every month, measurement of plant growth and biomass parameters (height, width, volume, leaf area, cane number and diameter, biomass) and foliar pigment content indicators (chlorophyll, flavonols and anthocyanin contents) were taken following standard protocols. Tissues and root samples are being processed for nutrient analysis. Instruments used include ruler (height & width), electronic caliper (cane number and diameter), Licor 3100 area meter (leaf area), balance (biomass) and Dualex ForceA (pigment analysis).
  • At the end of the study, rhizosphere soil samples were obtained from each blueberry plant with destructive sampling to carryout analysis on soil biological health indicators for microbial activity and abundance. The parameters included soil respiration (Zibilske, 1994), urease activity (Mobley and Hausinger, 1989), phosphatase activity (Tabatabai, 1994), fluorescein diacetate hydrolysis activity (FDA) and abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) (Mundepi et al., 2017). Additional analysis of microbial community from extracted soil genomic DNA is ongoing.
  • Plant and soil data were statistically analyzed (analysis of variance) to test for the significance of biostimulants on plant growth and soil biological health parameters.
Research results and discussion:

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

  • Data analysis on this part of the project is still ongoing.
  • Preliminary 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.
  • Preliminary 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, preliminary 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 untrust worthy.

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

  • 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. However, these results are based on preliminary analysis, and there are still remaining analyses to carryout (tissue and root nutrient analysis; additional statistical analysis).
  • 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.
  • One way by which biostimulants are often described as being capable of influencing plant growth is through their impact on soil biological health. It is stated that their positive impact on soil microbial activity and function will lead to improved nutrient availability and stress tolerance in plants. As such, the presence of any relationship between the plant and soil biological health parameters will be further explored with statistical analysis such as correlation or multivariate analysis once all the data are gathered.
  • We are planning on conducting field study with growers with select biostimulants in Spring 2022 after the data collection and analysis from the greenhouse study is completed.

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. 

 

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.

Participation Summary

Education

Educational approach:

None

Educational & Outreach Activities

2 Webinars / talks / presentations

Participation Summary

41 Farmers
18 Ag professionals participated
Education/outreach description:
  • 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.

Project Outcomes

Project outcomes:

N/A at this time. 

Recommendations:

N/A at this time. 

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.