|DIXON, EMILY - Oregon State University
|STRIK, BERNADINE - Oregon State University
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2015
Publication Date: 2/1/2016
Citation: Dixon, E.K., Strik, B.C., Bryla, D.R. 2016. Weed management, training, and irrigation practices for organic production of trailing blackberry: III. Accumulation and removal of aboveground biomass, carbon, and nutrients. HortScience. 51(1):51-66.
Interpretive Summary: The objective of this study was to examine the effects of cultivar (‘Black Diamond’ and ‘Marion), postharvest irrigation, weed management (weed mat, hand-weeding, and no weeding), and primocane training time (August and February) on aboveground gains and losses of biomass, carbon (C), and nutrients in a mature planting of organic trailing blackberry. Biomass production was negatively affected by weeds and often by training the primocanes in August. The aboveground C stock of the planting in winter reached a maximum of 0.5 ton per acre and was negatively impacted by weeds, postharvest irrigation, and February training. While this C stock is relatively low compared to what has been reported in some other crops, this value does not include the roots or crowns. Nutrient content gains and losses in the aboveground portions of the plants were directly related to biomass accumulation. The use of weed mat led to a particularly high fruit nutrient content, even when compared with hand weeding. ‘Black Diamond’ had lower floricane nutrient content than ‘Marion’, but a similar primocane nutrient content. The nutrient deficiencies found in ‘Black Diamond’ primocane leaf N concentrations may have reflected only a difference in allocation between the two cultivars, not a true plant deficiency in N. The current caneberry nutrient standards may need to be revised for cultivars other than ‘Marion’. The organic fertilizer applied to the planting often contained less nutrients than what was removed from the planting in floricane prunings and fruit. Although, since the floricanes were left in the field, true losses in the fruit were lower than the fertilizers applied. Fertilization rates may also need to be adjusted for some of these organic production systems, and it is unknown if other less mobile nutrients would be as readily available to plants as N is in the floricane prunings.
Technical Abstract: The effects of various production practices on biomass, C, and nutrient content, accumulation, and loss were assessed over 2 years in a mature organic trailing blackberry (Rubus L. subgenus Rubus, Watson) production system. Treatments included two irrigation options (no irrigation after harvest and continuous summer irrigation), three weed management strategies (weed mat, hand-weeded, and non-weeded), and two primocane training times (August and February) in two cultivars (‘Black Diamond’ and ‘Marion’). Floricanes comprised an average of 45% of the total aboveground plant biomass, while primocanes and fruit comprised 30% and 25%, respectively. Depending on the treatment, the total aboveground biomass gain over the course of the season was 5.0–6.5 t/ha per year, while C stock of the planting was an estimated 0.4–1.1 t/ha in late winter. Carbon accounted for approximately 50% of the dry weight of each aboveground plant part. Weed management had the largest impact on plant biomass and nutrient content. No weed control reduced aboveground biomass, the content of nutrients in the primocanes, floricanes, and fruit, whereas use of weed mat resulted in the most biomass and nutrient content. Nutrient accumulation was similar between the cultivars, although February-trained ‘Marion’ plants had a greater loss of most nutrients in 2014 than the year prior. Plots with weed mat tended to lose the most nutrients through harvested fruit in both years. In 2014, August-trained ‘Marion’ lost 5 kg/ha N less than the other training time and cultivar combinations. Plants that were irrigated throughout the summer gained more biomass, N, K, Mg, S, B, and Cu in one or both years than those that received no irrigation after fruit harvest. The irrigation treatment had inconsistent effects on nutrient content of each individual plant part between the two years. Nutrient losses were often higher than what was applied through fertilization, especially for N, K, and B, which would eventually lead to depletion of those nutrients in the planting.