Alignment between University Nutrient Guidelines and Grower Practices for Blackberry and Red and Black Raspberry in Oregon

Abstract

Information was gathered from 13 caneberry (blackberry and red and black raspberry; Rubusspp.) growers in Oregon’s Willamette Valley in 2018 to learn which nutrient management tools growers were using and to determine relationships between plant (leaf and fruit) and soil nutrient status and planting performance for various cultivars. The floricane-fruiting caneberry cultivars studied were ‘Meeker’ red raspberry, ‘Munger’ black raspberry; ‘Black Diamond’, ‘Columbia Star’, ‘Marion’, and ‘Obsidian’ trailing blackberry; and ‘Triple Crown’ semi-erect blackberry. Our goal was to understand key challenges and questions that remain after many years of nutrient management research and extension outreach. Considerable variation in fertilization practices among grower sites was found. Several growers were applying fertilizer within the recommended rates and had good plant growth and yield, but many sites in this study included fields that were not performing to their full potential. Key problems identified that may have reduced plant performance and yield included soil pH lower than the recommended range of 5.6–6.5, likely reducing nutrient availability; in the study, 28% had a soil pH below 5.6 and some had a pH as low as 4.6. Soil levels of P, K, and Mg were generally high across grower sites indicating no fertilizer was needed, yet many growers fertilized with P and K regardless. Many growers applied excessive rates of N fertilizer from sources that would exacerbate low pH, and timed applications improperly based upon existing extension recommendations. Site or grower management impacted the concentration of almost all leaf nutrients within cultivars, with deficient levels for N, P, K, and Ca at many sites. Site had a significant impact on the concentration of many fruit nutrients. Fruit %P, K, Ca, Mg, and S were positively correlated with their respective leaf concentrations. Percent moisture content of fruit ranged from 72–86% and was affected by grower management for ‘Black Diamond’, ‘Munger’, ‘Obsidian’, and ‘Triple Crown’. Despite adequate to high N fertilizer rates being applied, leaf %N was low or just sufficient, supporting the hypothesis that management practices were limiting fertilizer uptake. Some growers applied granular product while drip irrigating, likely reducing availability of nutrients during periods of demand. Insufficient irrigation at key times of the season or stages of plant development may have limited plant uptake of N and K. While current recommendations are to collect soil samples every few years and leaf tissue samples annually to assess nutrient management programs, many growers were not doing so. Growers most frequently relied on fertilizer company field representatives regarding best nutrient management practices rather than using free extension resources for sampling and fertilization methods. Improved outreach to company representatives and revising nutrient management publications to incorporate new research-based information will be key in helping the industry better monitor soil and leaf nutrient status and manage fertilizer requirements in their caneberry crops.