|Abstract or Summary
- The study was conducted in an organic trailing blackberry (Rubus L. subgenus Rubus, Watson) planting established at the North Willamette Research and Extension Center in Aurora, OR on 26 May 2010. Three weed management systems were compared for 'Marion' and 'Black Diamond': 1) non-weeded; 2) hand-hoed two to three times per year (hand weed); and 3) black landscape fabric mulch (weed mat). The planting was certified organic in May 2012, the first fruiting year. Aboveground weed dry weight (DW) increased from 2010 through 2012 in the non-weeded plots. Findings suggest that nitrogen (N) was the major nutrient affecting blackberry cane growth and fruit development. Other nutrients were considered sufficient as evidenced by soil and plant tissue testing, with the exception of calcium (Ca) and boron, which were at the low end of the sufficiency range in some soil and tissue samples. Soil nutrients fluctuated a small amount by distance and location relative to the emitter and sampling depth. However overall nutrient concentrations were adequate for good blackberry growth. Given some of the observed nutrient trends, soil sampling should be completed in-row, under the drip emitters where fertilizer is applied, at a 0.15 cm depth, to ensure proper long-term soil management. Total aboveground plant biomass increased from 0.3 and 2.0 t·ha⁻¹ in the non-fruiting years (2010 and 2011, respectively) to 3.4 t·ha⁻¹ in the fruiting year (2012). Primocane number and plant DW were not affected by cultivar or weed management in 2010. In 2011, 'Black Diamond' had shorter primocanes and less biomass and macro- and micro-nutrient accumulation than 'Marion'. Plants grown without weed control produced fewer but longer primocanes with less biomass and lower nutrient content. In 2012, floricane biomass removed at pruning was greater for ‘Marion’ plants and was least for plants in non-weeded plots, and greatest for plants in weed mat plots. Floricanes had greater macro- and micronutrient concentrations than the primocanes, but less than when the floricane leaves were sampled in July, indicating nutrient loss to the fruit and possibly remobilization of some nutrients during cane senescence. Ultimately, floricanes were also a sink for nutrients, reducing primocane biomass in 2012. During the first harvest year (2012), the cultivars did not differ in the DW yield, however, 'Black Diamond' had a greater fresh yield than 'Marion' (6.0 kg·plant⁻¹ and 5.2 kg·plant⁻¹, respectively). The proportion of above-ground DW biomass allocated to fruit in weed controlled plots averaged 40% in 'Marion' and 56% in 'Black Diamond', suggesting a greater yield efficiency of 'Black Diamond' plants. Non-weeded plots produced approx. half the fresh yield (3.65 kg·plant-1), 39% of the fruit DW biomass as weed mat plots, and the treatment had fruit with lower moisture content, higher percent soluble solids, and lower Ca concentrations, than the other treatments. Net gain of N averaged 41 kg·ha⁻¹ with weed control compared to 25 kg·ha⁻¹ without weed control. Both cultivars accumulated large quantities of N, potassium, and Ca for growth and yield. Nutrient gains may have exceeded fertilizer nutrients available in the fruit production year. Overall, cultivar and weed management strategies had inconsistent effects on tissue and soil nutrient status during the study, with the exception of N. 'Black Diamond' and 'Marion' performed similarly across all three weed management strategies and appeared well suited to organic production for high-value processed markets. Weed mat appeared best suited for organic systems, reducing labor required for weed control, enhancing nutrient uptake by plants, and producing the greatest amount of plant growth and yield. Weed management strategies affected nutrient accumulation and loss, indicating fertilization may need to be adjusted depending on the strategy used.