528 Use of Cultivar and Plant Characteristics as the Basis for Fertilizer Nitrogen Applications in Cranberry (Vaccinium macrocarpon Ait.)

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  • 1 University of Massachusetts Cranberry Experiment Station, E. Wareham, MA 02538
  • | 2 Department of Crop and Soil Science, Washington State University, Prosser, WA 99350

The relationship between yield and applied N in cranberry has been investigated. Cultivar was important in determining optimum seasonal N rate. Sustained production for the hybrid `Stevens' required an annual seasonal total of N at up to 67 kg·ha–1, higher than was optimal for native selections `Early Black' and `Howes'. High N rates were associated with increased fruit rot and vine overgrowth. Optimum N rate varied within cultivar, likely due to variation in soil conditions, but soil N test results have not correlated well with subsequent yield in cranberry. Soil organic matter content can predict potential N release, but plant response must also be taken into account. To refine N rate recommendations, plant characteristics that might predict N requirements/status of cranberry were investigated. A standard of 0.9% to 1.1% N in August tissue has been established for cranberry. To find characteristics that could be used earlier, we surveyed 30 sites for percentage of N in tissue, length of new growth, SPAD chlorophyll meter ratings, fertilizer N use, and yield. Length of new growth could be used as an indicator of cranberry N status from June until bloom, being positively correlated with subsequent yield. The SPAD meter proved to be a viable alternative to in-season monitoring of tissue N during June and July. Readings below proposed standard values indicated the need for N fertilizer if vegetative growth was in the standard range. Thus, the easily determined factors of upright length and SPAD rating could be used to refine fertilizer rates during the active growing season, while tissue testing for percentage of N could be used as a “report card” on the fertilizer program at the end of the season.

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