Foliar Testing and Visual Assessment of Nutrient Status in Berry Crops

Topic #5: Foliar Testing and Visual Assessment of Nutrient Status in Berry Crops – [Dec. 2, 2011] Dr. Marvin Pritts, Cornell University, Professor & Chair, Dept of Horticulture (with a concentration in Small Fruit Production); Online Profile

This was part of a 12-part “Soil and Nutrient Management for Berry Crops” webinar series, a project that was funded by NE SARE (Northeast Sustainable Research and Education Program), and which was organized by Marvin Pritts (Professor of Horticulture at Cornell Univ.) and Cathy Heidenreich (Extension Berry Specialist at Cornell Univ.).

Key Points:

Determining what the plant itself has taken up is a more accurate assessment of nutrient status than estimating availability from a chemical extractant (i.e. tissue test better than a soil test). Soil extractants attempt to ‘mimic’ what a plant root does. Also, a tissue test can identify a potential problem before it results in visible symptoms or reduced growth and yield, and a tissue test can help you diagnose what may be wrong in a problem location/area of your crop.
Foliar testing is especially relevant for perennial plants that accumulate nutrients over a time span of years.
Tissue analysis standards are the same from lab to lab; not as extraction-dependent as soil tests are. The standards are derived from healthy plants (not derived from detailed experimentation), and the standards are based upon samples taken during a time of the year when leaf nutrient values are relatively stable (NOT when plants are growing rapidly, and NOT when fruits are expanding). Best time for cranberries is end of August through early September.
Two exceptions to uniformity from lab to lab: Nitrogen and Sulfur, because there are several different methods a lab can use to measure nitrogen and sulfur in leaves. But, the values obtained from the different methods are fairly closely correlated or similar to one another.

Shortcomings of Foliar Testing:

Provides total amount of an element, but not the amount of it that is biologically active (iron is one example of this limitation).
Sampling time may not be ideal for all
Requires a soil test to be meaningful, especially because of the importance of your soil pH in how that effects nutrient uptake (adding more of a nutrient may not solve a ‘lacking’ situation if your pH isn’t right).

Functions of Nutrients in Plants:

Nitrogen (N): amino acids; cation-anion balance; osmoregulation
Phosphorus (P): DNA/RNA structure; energy transfer; metabolism
Potassium (K): osmoregulation; metabolism; enzyme activation (50+); Pn
Calcium (C): cell walls, cell extension; enzyme modulation; vacuole pH
Magnesium (Mg): chlorophyll; protein synthesis; enzyme activation; vacuole pH
Iron (Fe): chloroplast development; redox systems; protein synthesis
Manganese (Mn): oxygen evolution; enzyme activation
Copper (Cu): strongly bound; lignifcation; enzyme activation; pollen formation
Zinc (Zn): root cell elongation; pollen germination
Molybdenum (Mo): enzyme activation
Boron (B): cell elongation, lignification; xylem differentiation; auxin activity

Note: Lignin or lignen is a complex chemical compound that is an integral part of the secondary cell walls of plants and some algae. Lignification has an important role in host defense against pathogen invasion.

Visual Symptoms of Deficiencies:

Certain nutrients are extremely mobile in the plant, and because of that fact, visual symptoms can help us to diagnose some problems we might see.
N, P, K, Mg, and S are the most mobile.
Mobile nutrients tend to move to actively-growing points through the phloem; therefore, older leaves exhibit deficiencies first. Calcium is just the opposite (not very mobile, so deficiencies of calcium will be noticed first in the newer-growth parts of the plant).
Sulfur deficiency: mimics Nitrogen deficiency, visually (yellowing of leaves) because both N and S are components of amino acids, and when amino acids are in short supply, yellowing occurs. But sulfur deficiency is rare.
Phosphorus deficiency: dark red coloration on leaf margins (older leaves first) (P deficiency also not very common, at least not in the northeast); sometimes confused with the dormant color of blueberry and cranberry leaves in the Spring, which is simply due to a lack of chlorophyll which warmer temperatures and sunlight, of course, takes care of.
Potassium (K) deficiency (see this sometimes): browning where the leaves attach to the petiole, and eventually marginal leaf burning (older leaves first since it is one of the elements that is very mobile).
Calcium deficiency: growing points turning brown because calcium isn’t very mobile, so it affects actively-growing areas first because there is not enough calcium moving out to the tips; hence, the older leaves will look fine.
Magnesium deficiency: Mg is more mobile than calcium is, so older leaves may show it some as well as newer leaves; Shows a very distinctive symptom (color between the leaf veins will be red, and the veins themselves are green – commonly referred to as a Christmas tree pattern because of the red and green colors)
Iron chlorosis: very common when blueberries are planted in high pH soils.
Manganese deficiency: rare, but more likely when the soil pH is too high; younger leaves first; yellowing between the leaf veins;
Boron deficiency: Can run into this situation in the Northeast, especially in blueberries and it’s possible in cranberries but rare (STRONGLY resembles winter-kill, at least with blueberries); stubby root tips (poor auxin activity); another symptom is asymmetrical leaves, and/or deformed fruit from the auxin levels being low as a result of the low boron.
Watch out for Herbicide injury!! (often mimics nutrient deficiency; look for patterns, and with herbicide injury, the symptoms often show up quickly, whereas they ‘should be’ much more gradual with nutrient problems)

Take-home messages:

Visual symptoms of nutrient deficiencies are difficult to diagnose and can be confused with other things.
One should try to address nutritional problems before visual symptoms occur.
A foliar elemental analysis is the best technology we have for assessing plant nutrient status.