2026/01/22 by Amanda M. Lay-Walters, Renee T. Threlfall, Ryan W. Dickson +2 · 1 voice
Agricultural and Biological Sciences · #Berry genetics and cultivation research #Horticultural and Viticultural Research #Plant Physiology and Cultivation Studies
paper · doi:10.21273/hortsci19078-25
openalex publication_date 2026/01/22 · openalex created_date 2026/01/23 · openalex updated_date 2026/06/11
The current nitrogen (N) fertilizer rate recommendation (56–90 kg N·ha −1 ) for all blackberry types grown in the United States was developed based on research of trailing blackberries grown in the Pacific Northwest, where the majority of US blackberry production occurs. In the southeastern United States, blackberry production has grown rapidly over the past two decades. Because of this expansion and regional differences in cultural practices, climate, growth habit, and cultivars, it is necessary to verify whether the current N fertilizer rate recommendation is appropriate for the southeastern United States. A planting of mature erect ‘Ouachita’ floricane-fruiting blackberry was fertilized with six annual rates of ammonium-nitrate (0, 34, 67, 101, 135, and 168 kg N·ha −1 ) each year over 3 years. During the growing season, leaf tissue nutrient samples were collected from primocanes and floricanes every 2 weeks to assess leaf tissue nutrient concentration. During each season, blackberry yield and fruit quality were assessed and recorded. After each season, physiological characteristics of blackberry plant growth and development were recorded. Generally, higher rates of N fertilizer resulted in higher leaf N concentrations in both blackberry primocanes and floricanes. However, blackberry yield and fruit size did not respond to increased rates of N fertilizer. The baseline soil N concentration was high at the experimental site, which most likely contributed to 0 kg N·ha −1 and other lower N rates showing no signs of N deficiency. Higher rates of N also had no impact on fruit characteristics, including chemistry (pH, titratable acidity, and soluble solids), firmness, red drupelet reversion, and white drupelet occurrence, or weight loss in fruit 7 days postharvest. However, higher rates of N fertilizer resulted in higher blackberry fruit decay 7 days after storage and increased winter pruning weights for blackberry plants. Based on these results, higher rates of N fertilizer could cost growers more in fertilizer and labor costs and product loss in storage or after shipping. Our results indicated that no benefits were obtained from higher rates of N for ‘Ouachita’ blackberry, and this cultivar likely has a low N requirement for optimal production. The current N fertilizer rate recommendation of 56 to 90 kg N·ha −1 supported growth without negative effects on production, but our results indicate that lower rates may also be adequate for southeastern blackberry production. Because of the high soil N concentration throughout the trial, further research must be conducted to quantify the lower N rate optimal for southeastern erect blackberry production. Based on these results, we recommend that southeastern US blackberry growers should use soil and leaf tissue nutrient sampling to fine-tune N rates for their sites.