Nitrogen Status of Cranberry Plants Can Be Evaluated Based on Vegetative Growth, Plant Greenness, or Tissue Nitrogen

Abstract

A standard value of 0.9% to 1.1% N in tissue has been established as the normal range for cranberry shoot tip samples collected late in the season. Recently, a survey (30 sites, four cultivars, mid-month in June, July, August) was conducted over a 4-year period comparing tissue N, SPAD Meter readings, length of new upright growth, yield, and fertilizer use. Length of new growth (from the point of budbreak on the old tissue) could be used as an indicator Of cranberry N status in the month of June up until early bloom. Length at this developmental stage was positively correlated with subsequent yield. From hook stage through early bloom, recommended standard lengths were as follows: `Early Black', 50 to 60 mm; `Howes', 45 to 55 mm; `Stevens', 60 to 70 mm; `Ben Lear', 55 to 65 mm. The SPAD Meter proved to be a viable alternative to in-season monitoring of cranberry tissue N. Readings below proposed standard values indicated the need for N fertilizer if vegetative growth was normal. SPAD Meter readings could be used to determine if tissue N was in the normal range by reading old or new leaves in June and July. However, in August, only diagnostic readings on new leaves were recommended. High readings in old leaves in August were associated with poor crops the following year. DeMoranville: e-mail carolynd@umext.umass.edu; phone (508) 295-2212 ext. 25.