Optimizing Planting Density to Increase the Sustainability of Blueberry Farms

Progress report for GS23-290

Project Type: Graduate Student
Funds awarded in 2023: $16,417.00
Projected End Date: 08/31/2025
Grant Recipient: University of Florida
Region: Southern
State: Florida
Graduate Student:
Major Professor:
Dr. Gerardo Nunez
University of Florida
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Project Information


Blueberry farms in the southeastern United States have a high potential for water and nutrient leaching. In other crops, increasing planting densities improve water and nutrient uptake efficiency and reduces nutrient losses. This project aims to improve the sustainability of blueberry farms by determining the optimum number of plants per unit area to optimize water and fertilizer use efficiency. We will evaluate the nutrient use efficiency (NUE) and water use efficiency (WUE) in two southern highbush blueberry varieties (‘Optimus’ and ‘Meadowlark’, which align with the canopy charcateristics criteria we established for this assessment.) grown at low- (1,383 plants/acre), standard- (1,936 plants/acre), and high-planting density (3,227 plants/acre) in an experimental field at the UF Plant Science Research and Education Unit in Citra, FL. Canopy volume, light interception, yield, fruit quality, NUE, and WUE will be measured and compared between density treatments for two seasons. We will disseminate our results through standard (extension publications), and non-standard outlets (social media). This study will generate informational tools about the planting density that brings about greater WUE and NUE for growers to make informed decisions that improve the sustainability of blueberry production.

Project Objectives:

The goal of this project is to improve the sustainability of blueberry farms by determining the ideal planting density that results in the optimization of water and fertilizer use efficiency. Specific objectives are:

Objective 1: Evaluate nutrient use efficiency (NUE) and water use efficiency (WUE) in blueberry plants grown at different planting densities.

Activity 1.1: Research trial was planted on March 4th 2024 using two blueberry varieties ('Optimus' and 'Meadowlark') spaced 18 inches, 30 inches, and 42 inches apart.

Activity 1.2: Measure WUE, NUE, canopy volume, canopy light penetration, and marketable fruit for two consecutive seasons.


Objective 2: Disseminate research findings among growers, extension educators, and scientists.

Activity 2.1: Publish two articles in trade journals such as The Blueberry News (Aug of 2024 and 2025) and one extension publication in English and Spanish (December 2025).

Activity 2.2: Share brief updates and media (photos and videos) in social media like Twitter (social media update for Q2 2024: https://twitter.com/MartinZapien6/status/1765472437230022712). Scientists and young people with and without a horticulture background will be the target audience for these media.

Activity 2.3: Organize a field day to showcase plant performance during the production period (March 2025).


Materials and methods:

We will evaluate two southern highbush blueberry varieties (‘Optimus’ and ‘Meadowlark’) at three different planting densities. The proposed varieties in this study represent different canopy characteristics (e.g., spreading, and compact) that can be found in blueberry farms in the region.

Objective 1: Evaluate nutrient use efficiency (NUE) and water use efficiency (WUE) in blueberry plants grown at different planting densities.

This study is located at the Plant Science Research and Education Center (lat. 29°24′300″N, long. 82°8′521″W) in Citra, FL. One-quart blueberry plants were obtained from a commercial nursery and planted (03-04-24) in a field into raised beds made with pine bark and native soil (Arredondo soil series Ultisol). Blueberry plants were established at three different planting spacings as follows:


In-row plant spacing (in)

Between rows spacing (in)

No. plants/Acre

Low density




Standard density




High density




The experiment follows a split-plot design with four 7-plant replications (main plot= variety; split-plot= density treatment). Plants are managed in a deciduous growing system under open-air field conditions, the prevalent production system in the southeastern region. Fertilization and irrigation practices are provided according to industry practices. Data will be collected from five central plants in each plot. We will measure the following parameters:

Vegetative stage (April-August). Canopy volume will be estimated monthly using the ellipsoid equation by Kovaleski et al., 2015. Also, we will use the Line Quantum Sensor (LI-191R; LI-COR Biosciences, Lincoln, NE) to measure incident photosynthetic active radiation (PAR) in the canopy at 2 and 4 ft above the ground level.

Production stage (February-May). We will measure yield efficiency (lb. of fruit/canopy volume), water use efficiency (lb. of fruit / gallon of irrigation water), total yield, and fruit quality (Brix, titratable acidity, berry weight).

During the Q3 of each year (starting in 2024), two plants within each plot will be randomly selected and destructively sampled by removing the entire plant including roots. These plants will be dissected to separate the leaves, roots, stems, and fruits. Separate plant organs will be dried (65 ℃ for 72 h), ground (20 mesh), and placed in paper bags for further determination of nutrient content. NUE will be computed as the ratio between nutrient content in plant organ and total nutrient applied in the season. Destroyed plants will be replaced to continue field evaluation in the second year. Irrigation volume will be measured with a flow meter. WUE will be computed as the ratio between pounds of harvested blueberries to gallons of irrigation water applied. Evaluate nutrient use efficiency (NUE) and water use efficiency (WUE) in blueberry plants grown at different planting densities.


Objective 2: Disseminate research findings among growers, extension educators, and scientists.

To secure the transfer of information to growers, collaborators, stakeholders, etc., we will present our research results in technical events including the Florida Blueberry Growers Association spring field day (Q1 of 2025).

For our results to reach growers and industry stakeholders, we will write extension publications at UF/IFAS EDIS (1 article written in English and Spanish, Q4 of 2024) and trade magazines (1 article per year of study in The Blueberry News, Q3 of 2024 and Q3 of 2025). To secure continuous and timely updates about this project reach growers and other stakeholders, we will also use other non-standard outlets such as social media posts (Twitter, once in the second and third quarters of both 2024 and 2025).


Research results and discussion:

The nursery did not supply the planting material until the end of 2023, therefore we had to push the planting date to March aiming to avoid the potential for frost damage throughout January and February. Prior to planting, we prepared raised pine bark beds and marked the field according to the treatment map. In March 2024, we planted 168 one-qt blueberry plants selecting varieties 'Optimus' and 'Meadowlark' for this purpose.

In April 2024, we will start collecting the phenotypic data associated to canopy volume and canopy light interception. 

Young blueberry plants in their first month of growth in field conditions
Young blueberry plants (photo taken on 03-25-24)
Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

We will potentially start with these activities at the Q3 of 2024 once we have the first collection of data.  

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.