Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
In last week’s Weekly Crop Update, I gave some recommendations for petiole sap nitrate and potassium levels in plasticulture strawberries. This is based on sampling leaf petioles from the most recently expanded leaves from plants in the field, extracting the sap, and using portable nitrate and potassium meters. The procedure can be found at this website http://edis.ifas.ufl.edu/cv004, along with recommended levels for different growth stages.
While this is a quick way to monitor nutrient levels, growers are also encouraged to take petiole and leaf samples for laboratory analysis. The recommended levels for petiole nitrate and leaf tissue contents from laboratory analyses can be found at this publication from North Carolina: http://www.ncagr.gov/agronomi/pdffiles/sberrypta.pdf. A description of how to sample is also given. We do now have a lab on Delmarva that can run tissue samples. Leaf tissue nitrogen levels should be maintained as follows: N (%) 3–4, P (%) 0.2–0.4, K (%) 1.1–2.5, Ca (%) 0.5–1.5, Mg (%) 0.25–0.45. Petiole nitrate content until the end of the month should be around 4000 ppm (3000 ppm is low and 5000 ppm is high).