Date of Graduation

12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Agricultural, Food and Life Sciences (PhD)

Degree Level

Graduate

Department

Horticulture

Advisor/Mentor

McWhirt, Amanda

Committee Member

Threlfall, Renee

Second Committee Member

Dickson, Ryan

Third Committee Member

Roberts, Trenton

Keywords

berry; Fertilizer; isotope; leaf sample; Rubus; small fruit

Abstract

Current blackberry (Rubus subgenus Rubus) research on nutrient needs, monitoring practices, and dynamics in the United States has primarily been conducted on cultivars popularly grown in the Pacific Northwest. Thus, regional research is required to understand the needs of blackberry cultivars grown in the southeastern U.S., with southeastern U.S. production practices. In 2022 and 2023, 12 cultivars of blackberry, across seven states, were leaf tissue sampled across multiple phenological stages for nutrient analysis. In Clarksville, AR from 2022 to 2024, six rates of N were applied to established ‘Ouachita’ blackberry plants. During the trial, plant yield, post-harvest fruit quality, fruit chemistry, leaf tissue nutrient concentrations, and growth were evaluated. In 2023, an established planting of ‘Prime-Ark® Traveler’, primocane-fruiting blackberries, in Clarksville, AR were fertilized with 135 kg N·ha-1 of 15N-enriched fertilizer. Destructive whole plant samples were collected at nine phenological stages from 2023 to 2024 to determine total N and 15N content of individual organs and removed plant tissues such as pruning and fruit. From these studies, updated recommendations of existing blackberry nutrient sufficiency ranges for N and S were established, and phenological stages were identified for in-season leaf tissue nutrient sampling. Additionally, it was observed that ‘Ouachita’ blackberry, and possibly other cultivars, may require less N fertilizer than previously recommended (56-90 kg N·ha-1). Previous understandings of blackberry N dynamics indicated that in-season applied N is primarily allocated to the primocanes. In primocane-fruiting blackberries N was allocated to new growth, which is predominantly primocanes, however similar concentrations of 15N were found in both floricane and primocane fruit in 2023. Additionally, this research indicated that blackberry fertilizer needs may require factoring growth habit and plant size, as biomass accumulation and total N accumulation were closely related. With these findings the U.S. southeastern blackberry industry now has a foundation for blackberry nutrient management for their modern cultivars and production practices. From these works, continuing research will improve the production of southeastern blackberry and support the expansion of the industry in the region.

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