Improving Blueberry Farming Sustainability Through Better Fertilizer Timing

Previous research in our lab has identified a large blueberry root flush period in between August and November (Nunez et al. In preparation). Fang et al. (2018) showed that nitrogen uptake rates peak between August and October. The overlap of root flushes and peak nitrogen uptake suggests there is a relationship between the two, which we aim to explore further.

Objective 1: Evaluate nitrogen uptake rates during and outside root flush periods in Southern Highbush Blueberry.

We studied nitrogen uptake rates in 2 southern highbush blueberry varieties, ‘Sentinel’ and ‘Arcadia’ grown at the UF Plant Science Research and Education Unit (lat. 29°24′300″N, long. 82°8′521″W) in Citra, Florida. Plant spacing is 2.5 ft in row with 9.5 ft between rows (1936 plants/acre) in pine bark beds. The soil is classified as Arrendondo sand. Nitrogen-free fertigation was applied through drip tape. To measure nitrogen uptake efficiency, we applied isotopic nitrogen (15N) according to the method outlined by Fang et al. (2018). Isotopes are naturally occurring versions of an atom that can be measured separately due to their different weights. 15N is a stable isotope that represents 0.336% of all nitrogen in the planet (Mariotti, 1983). Due to its safety and stability, 15N is widely used in agricultural and ecological studies.

Treatments consisted of applying 10% 15N labeled ammonium sulfate fertilizer at two points in the season: 1) during the fall root flush and 2) outside of the root flush (in spring). At each treatment application, 8 plants (4 ‘Sentinel’ and 4 ‘Avanti’) were fertilized with 0.57 g 15N/plant, the equivalent of 125 lbs of N/A/year. 15N ammonium sulfate fertilizer was dissolved in water and applied manually. Two weeks after application, plants were destructively harvested by removing the entire plant including roots up to 30 cm deep. Roots were carefully washed to remove soil material while minimizing tissue losses. Plant tissues were separated into root and shoot, measured by weight, and oven dried. Dried tissue was ground and loaded into scintillation vials for testing at the Light Stable Isotope Mass Spectrometry Lab (University of Florida) for total 15N and N. We calculated nutrient uptake efficiency as the ratio of recovered N divided by provided N in each sampling period. We also measured root abundance at each point in the season using root observation boxes and a RBG cameras, which are part of Ms. Goldsby's ongoing MSc. research (Figure 1).

Objective 2: Disseminate research results to inform growers, citizens, and young adults.

To inform farming practices, the research results must reach growers and make an impact on them. Sharing research outcomes at no cost and through diverse media broadens access to the research and increases its potential impact on grower practices.

Ms. Goldsby will write an extension article focused on fertilizer timing using results from this research. Current blueberry growers are the intended audience for this article. Dr. Nunez will co-author this article. the article will be submitted for review before the end of the gran period.

We recorded an instructional video detailing the results of this research. The audience for this video is growers and industry professionals. Professional video recording and editing support was provided by UF IFAS Communications. The video is in the post-production stage now. We expect the video to be published in the next month.

Finally, we will record and publish a series of videos focused on backyard blueberry production and the basics of sustainable fertilization practices. The videos are intended for young adults not familiar with growing blueberries and home gardeners. Videos will be posted on social media platforms (Twitter, Facebook, and Instagram) to reach interested parties by targeting a different demographic than the extension article.