Primocane-Fruiting Blackberry: Optimum N-Fertilization

This study was conducted in 2011 at the University of Arkansas, Fayetteville to determine the optimum rate and time of nitrogen (N) application for `Prime-Ark® 45\u27 primocane-fruiting (PF) blackberries under high tunnel conditions. There were four N treatments: Control (0), 10, 10-split, and 20 kg*ha-1 (Treatments 1, 2, 3, 4, respectively). In a randomized complete block (RCB) design, the following variables were compared: total and marketable yield, fresh weight of plant above ground, and cane diameter. Total fruit yields for Treatments 2 and 3 (2.5 and 2.5 kg, respectively) were highest and significantly different from the other treatments (p\u3c 0.05). Marketable yield had a similar trend as total fruit yield, although not significantly different. Cane diameter and plant fresh weight were not significantly affected by fertilizer treatments. There were not significant differences in N content in leaves among treatments. Results indicated that either a single or split N application of 10 kgN*ha-1 could result in better yields. Four experiments were conducted to determine the most stable period in foliar elemental concentration, in order to identify the best time for foliar fertilizer applications in `Prime-Ark® 45\u27 PF blackberry cultivar. The four experiments were conducted in five separate locations. In North Carolina (N.C.), `Prime-Ark® 45\u27 leaf samples were collected at three commercial farms; in Clarksville, Arkansas (Ark.), three cultivars `Prime-Ark® 45\u27, `Prime-Jan®\u27, and `Ouachita\u27 were sampled; and in Fayetteville, Ark., `Prime-Ark® 45\u27 blackberry plants were sampled from plantings managed under two cultural methods (high tunnel and ambient ). For N fertilization trials, 0, 10, 10-split, and 20 kg.ha-1 N rates were compared under high tunnel conditions. Rates were compared for cultural practices (mown, mown + tipped, and not pruned) under ambient conditions. Leaf samples were collected and analyzed every two weeks from June to Aug. 2011. Sampling dates revealed variations in foliar elemental nutrient concentrations. In Fayetteville, Ark., in one-year-old `Prime-Ark® 45\u27 blackberry plants, under high tunnel conditions, the period with the highest level of elemental stability was between 11 July and 25 July. Under ambient conditions, the most stable period was from 7 July to 25 July. In Clarksville, Ark., the period of most stability in foliar nutrient concentration was from 30 June to 12 July. In N.C., the proper period with most stability in leaf nutrient content was between 5 July and 22 July. Also in N.C., the logarithm of variance means analysis indicated that the least variance in foliar elemental concentration occurred from 5 July and 22 July 2011