Response of Blackberry Cultivars to Fertilizer Source during Establishment in an Organic Fresh Market Production System

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by American Society for Horticultural Science and can be found at: http://horttech.ashspublications.org/Blackberry (Rubus ssp. Rubus) cultivars, three trailing types (Marion,\ud Black Diamond, and Obsidian) and one semierect type (Triple Crown), were\ud studied for their response to different types of fertilizer from 2011–12, at a certified\ud organic, grower collaborator site located in Jefferson, OR. Plants were fertilized at\ud a target rate of 50 lb/acre nitrogen (N) each spring using three different sources: 1)\ud a liquid fish and molasses blend (4N–0P–1.7K); 2) pelletized soy (Glycine max)\ud meal (8N–0.4P–1.7K); and 3) pelletized, processed poultry litter (4N–1.3P–2.5K).\ud Plants were drip irrigated, and weeds were managed using a polypropylene,\ud permeable landscape fabric (weed mat). Plant responses were greatly affected by\ud cultivar, whereas the effects of fertilizer type were relatively minor. ‘Triple Crown’\ud produced the greatest yield in both years, whereas ‘Black Diamond’ and ‘Marion’\ud had the lowest yield in 2011 and 2012, respectively. ‘Triple Crown’ fruit had the\ud highest percent soluble solids and were the least firm in 2011, whereas ‘Marion’\ud fruit were the least firm in 2012. Harvest date, within year, affected the fruit quality\ud variables measured in all cultivars. Most soil nutrient levels were within the\ud recommended range for all fertilizer treatments, except for boron (B), which\ud declined to deficient levels in the second year. Fertilizer type had no effect on soil\ud nutrient levels other than fertilization with the fish and molasses blend product\ud increased soil potassium and sodium. Soil nutrient levels were affected by cultivar\ud but varied by year for many nutrients. Primocane leaf tissue nutrient concentrations\ud were above or within recommended standards for most nutrients, except for\ud magnesium (Mg), calcium (Ca), and B, which, depending on the cultivar, were\ud below standards. Over the 2-year study, the blackberry cultivars responded similarly\ud to the three types of organic fertilizer. However, the cost of N varied from $8.16/lb\ud for the liquid fish and molasses blend, $5.35/lb for the pelletized soy meal, and\ud $2.54/lb for the pelletized, processed poultry litter. Supplemental fertilization\ud with B, Mg, and Ca would be required with each fertilizer studied to maintain\ud recommended soil fertility levels