Seasonal Variation in Mineral Nutrient Concentration of Primocane and Floricane Leaves in Trailing Blackberry Cultivars Produced in an Organic System

The impact of floricane-fruiting trailing blackberry ( RubusL. subgenus Rubus, Watson) cultivar (‘Black Diamond’, ‘Marion’, ‘Obsidian’, and ‘Onyx’) and leaf sampling time during the growing season were studied for 2 years in an organic production system to evaluate impacts on leaf nutrient concentration in primocane and floricane leaves. Primocane leaves were sampled every 2 weeks from late May through early October, whereas leaves on fruiting laterals (floricane) were sampled every 2 weeks from bloom (early May) through fruit harvest (late July) and were analyzed to determine concentration of macro- and micronutrients. Sampling date through the season, cultivar, and year had an effect on the concentration of all nutrients in the primocane leaves, though patterns of change were similar between years and cultivars. Primocane leaf N, S, and Cu concentration generally declined over the season while P, K, and Zn generally increased. Primocane leaf Mg, Ca, B, Fe, Mn, and Al concentrations peaked during the harvest season. The concentration of nutrients in floricane leaves generally decreased (N, P, K), remained steady (Mg, S, Cu), or increased (Ca, B, Fe, Mn, Zn, Al) from bloom through fruit harvest. ‘Black Diamond’ tended to have lower primocane but higher floricane leaf nutrient concentrations than the other cultivars. ‘Obsidian’ tended to have among the highest concentrations in both primocane and floricane leaves for many nutrients. Our results confirm the need to sample cultivars separately. The primocane leaf nutrient concentrations measured in this study were below the published recommended sufficiency levels for N (in ‘Black Diamond’), Mg (in 2014), K (in ‘Onyx’), Ca, and B, indicating the sufficiency levels for these nutrients and cultivars may need to be revised for this region.