In eastern North Carolina, as strawberry fertilization begins, the clock is ticking for growers to begin their tissue sampling program.
The North Carolina Department of Agriculture and Consumer Services recommends tissue sampling begin about two weeks after fertilization is initiated, usually the first week of March. It should continue at two-week intervals throughout the growing season.
Tissue analysis enables strawberry growers to accurately monitor the nutritional status of their crop. It provides the information needed to make timely and accurate adjustments to fertilizer applications. Growers who are not familiar with tissue testing and want to initiate a sampling program should contact their NCDA&CS regional agronomist for guidance.
David Dycus, an NCDA&CS regional agronomist based in Sanford, believes growers must have an overall understanding of fertilization strategy to use tissue analysis effectively.
“The ratio of nitrogen to potassium is important,” Dycus said. “Berries tend to be firmer and sweeter when fertilized with twice as much potash as nitrogen. For this reason, a fertilizer such as potassium nitrate is often recommended for strawberries.”
Later in the season, tissue analysis often indicates a need for calcium and/or sulfur. If so, calcium nitrate and potassium sulfate are good sources. Rates of these fertilizers can be adjusted to keep the nitrogen-to-potassium ratio in balance. Alternatively, sulfur can be supplied by applying Epsom salt at a rate of 10 pounds per acre in conjunction with potassium nitrate.
“It is not wise — economically or agronomically — to use fertilizers containing micronutrients on a routine basis,” Dycus said. “Doing so usually means spending too much money as well as jeopardizing the health of the crop. A preplant soil test or an in-season tissue analysis is the only reliable indicator of the need for micronutrients. They should not be applied unless recommended by an agronomic test.”
To collect a tissue sample from strawberry plants, select the most recently mature, trifoliate leaves (MRMLs). Those leaves are full-sized and green and consist of one petiole or leaf stalk with three leaflets. MRMLs are usually located three to five leaves back from the growing point. Avoid collecting older, dull leaves and damaged tissue. Detach the petioles from the leaves as you collect them, but submit them together as one sample.
Each sample should include leaves and petioles from 20 to 25 plants within a uniform area. For example, all of the plant material in a single sample should be the same variety, growing on the same soil type, planted at the same time and having the same management history. This is known as a representative sample.
When submitting tissue samples, be sure to fill out the NCDA&CS Plant Sample Information form completely, including fertilization history and environmental conditions. It is particularly important to provide the name of the strawberry variety being grown as well as its stage of growth at the time of sampling. Stage of growth refers to week of bloom and can be coded B1 through B12 (first through 12th week of bloom). Accurate management recommendations depend on this information.
Strawberry tissue analysis costs $7 per sample for North Carolina growers and $27 for out-of-state growers. It requires both leaflets and petioles. Analysis of leaflets reveals nutrient deficiencies or excesses. Analysis of petioles gives a good indication of the amount of soil nitrogen currently available for crop growth and development. When test results show nutrient levels to be out of the optimal ranges, the plant analysis report provides recommendations for corrective action.
A guide to collecting and submitting strawberry tissue samples is available online at www.ncagr.gov/agronomi/pictorial.htm.
NCDA&CS regional agronomists are also available throughout the state to offer guidance and answer question about sampling and fertilization. For contact information, visit www.ncagr.gov/agronomi/rahome.htm, or call Kent Messick at (919) 733-2655.