Abstract
Optimizing nitrogen (N) fertilizer rates maintains good red raspberry (Rubus idaeus L.) production while alleviating environmental risks. Although raspberry growers in Washington are using the caneberry nutrient management guides derived from western Oregon, these guides may not be appropriate for other production regions given the differences in climate, soil type, and crop productivity. However, limited research has been conducted to observe the impact of the N fertilizer rate on floricane red raspberry growth, yield, and fruit quality in Washington. The aim of this study is to evaluate the response of “Meeker” floricane red raspberries grown in northwest Washington, USA, to different N fertilizer rates in order to provide information for future local nutrient management guides. Treatments of urea (46% nitrogen (N)) were surface-applied to raised beds of established ‘Meeker’ raspberry plots at controls, low, medium, and high rates (0, 34, 67, and 101 kg N ha−1, respectively) in 2019 and 2020. The experiment was arranged in a randomized complete block with three replications. Fruit yield and quality, plant growth and leaf tissue nutrient concentrations, and soil characteristics were evaluated. There were no N fertilizer rate treatment effects for the yield, fruit quality, plant growth, leaf tissue nutrient concentrations, and soil characteristics, except for fruit titratable acidity and soil ammonium (NH4-N) concentrations. The lack of a plant response may be due to nutrients mineralized from soil organic matter (3.81–4.0%) and the utilization of plant nutrient reserves. Based on the results, the soil organic matter level and plant nutrient reserves should be considered when making nutrient management suggestions. Fertilizer costs as well as the potential for environmental pollution from excess fertilizers could be reduced through utilizing these two potential sources of nutrients. Furthermore, longer periods of research is warranted to understand how to adjust N fertilizer rates based on plant and soil characteristics while sustaining yields.
Highlights
Red raspberry (Rubus idaeus L.) is a globally important crop, with the Pacific Northwest (PNW) region of the United States of America (USA) leading in the raspberry processing market [1]
The fruit quality was minimally impacted by the N fertilizer rate, with only TA being responsive to N fertilizer rate adjustments
Soil organic matter and plant nutrient reserves likely contributed to sufficient N to meet plant demand, which may obscure the effects of the N fertilizer rate
Summary
Red raspberry (Rubus idaeus L.) is a globally important crop, with the Pacific Northwest (PNW) region of the United States of America (USA) leading in the raspberry processing market [1]. The processed market primarily uses floricane (“floricane-fruiting” or “summerbearing”) red raspberry with biennial canes that are vegetative one year and fruiting the following. Growers rely on regional caneberry nutrient management guides that may require adaptation to local conditions. These guides recommend applying N fertilizer based on annual plant tissue tests and periodic soil analyses, as well as observations of annual cane growth and yield to ensure optimal plant growth and productivity. The current regional nutrient management guides recommend 34 to 56 kg N ha−1 during the establishment year and 56 to 90 kg N ha−1year−1 after establishment [4,6] This application strategy should maintain current season yields, good primocane growth for season’s crop, and replenish N lost through pruning, leaf senescence, and harvest
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