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 will study nitrogen uptake rates in 2 southern highbush blueberry varieties, ‘Sentinel’ and ‘Arcadia’. Plants (50 ‘Sentinel’ and 50 ‘Avanti’) will be 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 will be 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 will be applied through drip tape. To measure nitrogen uptake efficiency, we will apply 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 will consist of applying 10% 15N labeled ammonium sulfate fertilizer at three points in the season: 1) during the fall root flush, 2) outside of the root flush (in spring), 3) during winter dormancy. Since blueberry is grown as evergreen and deciduous crop in the southeast, we will measure both dormant and non-dormant plants during time-point 3. At each treatment application, 12 plants (6‘Sentinel’ and 6 ‘Avanti’) will be fertilized with 0.57 g 15N/plant, the equivalent of 125 lbs of N/A/year. 15N ammonium sulfate fertilizer will be dissolved in water and applied manually. Two weeks after application, plants will be destructively harvested by removing the entire plant including roots up to 30 cm deep. Roots will be carefully washed to remove soil material while maintaining structure. Plant tissue will be separated into root and shoot, measured by weight, and oven dried to prepare for further sampling. Dried tissue will be 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 will calculate nutrient uptake efficiency as the ratio of recovered N divided by provided N in each sampling period. We will measure root abundance at each point in the season using root observation boxes and a RBG cameras, which are part of my 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.

I will write and publish 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 with me. We will also record and publish an instructional video detailing the results of this research intended for growers and industry professionals. Professional video recording and editing support will be contracted with UF IFAS Communications. Finally, we will record and publish a series of videos within our lab, focused on at home 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, TikTok, and Instagram) to reach interested parties by targeting a different demographic than the extension article.