Cranberry Tissue Testing

Tissue testing is regarded as an integral part of a cranberry grower’s fertilizer decision-making process, but there is unfortunately no ‘cookbook’ type of recipe for fertilizing cranberry beds based on one’s test results.  This holds true for soil testing as well.  One source of the uncertainty surrounding tissue test results, and the question of how much fertilizer might be needed in the soil, is that nutrient availability changes with soil pH.  Another reason is that tissue test nitrogen concentration will vary depending on the length of an upright.  Also, nitrogen concentration in the tissue does not correlate well with added nitrogen.  In spite of these sources of variation, however, both soil and tissue test analyses can be beneficial as a long-term record of changes in a cranberry bed, and are particularly helpful and useful when comparing one sample to another (assuming the different samples are taken on the same day).

When–And How Often–To Test:
Tissue samples are best collected anytime during mid-August to mid-September, which is a period when the nutrient levels in the cranberry tissues are most stable (at other times, levels fluctuate too much).  Also, the standard values you see in the table below were developed based on samples collected during that same time period.  Massachusetts researchers currently suggest sampling every 2-4 years for tissue (every 3-5 years for soil). A soil test alone offers no real value in determining a fertilizer protocol, whereas with a tissue test, one can at least develop a ‘target’ fertilizer range. Use periodic soil testing primarily to monitor changes in soil pH.  Compare your results over time against your bed management and performance indicators (growth and yield) to aid in making your fertilizer decisions.

How to Test (UMaine’s Submission Form and Plant Tissue Price List):
A good cranberry sample consists of current-season growth from both fruiting and non-fruiting uprights, being sure to get only current-season growth. For fruiting uprights, clip the uprights just above the fruit; for non-fruiting uprights, clip just above the bud-break location. The standard recommended practice is to collect about 20 tips from about 10 different locations within a bed, with the intention of getting a representative sample.  Thus, each sample you take will consist of about 200 uprights or about 1 to 1-and-a-half cups of tissue.  If you are bothered by the thought of removing 200 tips from your bed, especially if it is your only bed and is small in size, our UMaine Analytical Laboratory and Soil Testing Service has hinted that half that number of tips should still be adequate for their testing needs.  If taking only 100 tips instead of 200 tips appeals to you, then it is probably best to still visit 10 or more different locations within the bed, but simply reduce by half the number of tips you would otherwise collect from each location (i.e. 10 tips each from 10 different locations instead of 20 tips each from 10 different locations).  Don’t collect all the samples from one corner or along one edge, unless you are interested in only those areas–for comparing with other areas in a bed, for example. But if you want to capture an overall snapshot of your entire cranberry bed’s nutrient tissue levels, then it is suggested that you walk a zigzag pattern throughout the bed, or walk from one corner to the opposite corner collecting samples along the way.  Do not wash or rinse the uprights. Washing will remove soluble nutrients and give you an inaccurate test.  Also, do not separate the leaves and stems.  Allow the sample to dry overnight before mailing. Use paper bags or envelopes to mail the samples, ensuring that they remain dry. Don’t use plastic bags or cellophane, which hold in moisture. Be sure to label each sample with a bed number or other identification code that makes sense to you. Submit the samples promptly to a reputable laboratory.  Your county Extension office can help you locate a suitable lab.  If the lab is ASCS-certified you can be sure of reliable results.  The report you get back will not tell you how much fertilizer to apply next season, but it will allow you to monitor the efficacy of your current program and point out potential concerns to watch out for later. If you plot the results of your tissue testing over time you might begin to see patterns of nutrient changes that could help you to prevent deficiencies or excesses in subsequent seasons.

Tissue Standards (Aug. 10 to Sept. 15 collection time) These standards were developed in conjunction with researchers throughout the cranberry-growing areas of the United States.
Nutrient Normal Concentration*
Nitrogen (N) 0.9-1.1%
Phosphorus (P) 0.1-0.2%
Potassium (K) 0.4-0.75%
Calcium (Ca) 0.3-0.8%
Magnesium (Mg) 0.15-0.25%
Sulfur (S) 0.08-0.25%
Boron (B) 15-60 ppm
Iron (Fe)** >20 ppm
Manganese (Mn)** >10 ppm (if greater than 500-600 ppm, check your drainage)
Zinc (Zn) 15-30 ppm
Copper (Cu) 4-10 ppm
* Normal levels are based on samples taken between August 15 and Sept. 15. If your sample is taken at any other time of the season, do not compare the results with these standards. But samples taken at other times of the season can still be beneficial for comparative purposes (in other words, comparing one sample to another sample–assuming they are collected on the same day).

** Cranberry researchers have not found a normal range for Fe and Mn.

See also: