High tunnel hydroponic systems are increasingly adopted to extend the growing season and improve fruit quality in red raspberry (Rubus idaeus) production. While nutrient management guidelines exist for northern climates, they are often not suited to Lower Midwestern systems especially those using soilless substrates such as coconut coir. In these cooler climates, nitrogen uptake is limited by low root zone temperatures and reduced microbial activity, often resulting in unchecked vegetative growth that shades developing fruit and reduces yield and quality. In contrast, warmer Lower Midwestern high tunnels promote faster nitrogen uptake due to elevated root temperatures and increased plant metabolic rates. While this enhances nutrient absorption, it also encourages overly vigorous vegetative growth when fertility is not carefully managed, limiting light penetration and shifting resources away from fruit development. These challenges highlight the need for region specific nitrogen thresholds that optimize fruit yield without promoting excessive shoot growth. Without region-specific fertility strategies, nutrient applications often exceed crop demand, reducing efficiency and productivity. This project aims to develop optimized nutrient management strategies tailored to soilless raspberry production in Lower Midwestern high tunnels. A completely randomized split-plot experiment was conducted in a high tunnel located in southern Illinois. Three nitrogen fertigation rates (low, medium, high) were assigned to main plots, and five foliar nutrient treatments to split plots. Raspberries were grown in coconut coir, and each of the 15 treatment combinations was replicated four times (n = 60 plots), with five plants per plot and two fruiting canes per plant. Measured variables included shoot length, leaf number, total fruit yield, average berry weight, and foliar nutrient concentrations. These metrics were used to evaluate treatment effects on nutrient efficiency and overall plant performance. Results showed a 222.5% increase in potential fruit yield between the lowest and highest producing plots per 9 × 27-meter-high tunnels. However, this yield gain was accompanied by a 5.9% decrease in average berry size, indicating a trade-off in which higher yields are associated with smaller berries, while lower yields produce larger fruit. This research provides practical, science-based fertility recommendations to growers for improvement of fruit quality and yield, reduced fertilizer waste, and enhanced sustainability and profitability of raspberry production in Lower Midwestern high tunnels.
Funding Source This work was supported by a grant from the SIU Advanced Energy Institute, which gratefully acknowledges funding awarded through the Advanced Energy Resource Board.
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