Southeastern U.S. Vegetable Crop Handbook - 2023 - 4

system. When these nitrogen reduction scenarios arise, an additional
application of nitrogen is warranted. Leaf tissue testing is
the best option when deciding if and how much more nitrogen is
needed to meet expected yields and is described below. Leaf tissue
testing can help identify any " hidden hunger " that might exist
in the crop. A " hidden hunger " develops when a crop needs
more of a given nutrient but has shown no visual deficiency
symptoms. With most nutrients on most crops, responses can be
obtained even though no recognizable symptoms have appeared.
Evaluating the Effectiveness of Your Fertility Program-Using
Plant Analysis/Leaf Tissue Testing. Plant analysis is the chemical
evaluation of essential element concentrations in plant tissue.
Essential elements include those that are required to complete the
life cycle of a plant. The elements carbon (C), oxygen (O), and
hydrogen (H) are supplied by the atmosphere and water and generally
are not considered limiting. Scientists place most emphases
on essential elements supplied by soil or feeding solutions.
Macronutrients - nitrogen (N), phosphorus (P), potassium (K),
calcium (Ca), magnesium (Mg), and sulfur (S) - are required
in greatest quantities. Micronutrients - iron (Fe), manganese
(Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), and
chlorine (Cl) - are required in very small quantities. Toxicities
of micronutrients are equally important and yield limiting as deficiencies.
Plant analysis is also effective in diagnosing toxicities
of micronutrients. The interpretation of plant analysis results is
based on the scientific principle that healthy plants contain predictable
concentrations of essential elements.
State and private soil testing laboratories can provide nitrogen
concentrations as well as those of the other essential macroand
micronutrients to aid in mid-season fertilizer application decisions.
A program of periodic leaf tissue sampling and analysis
will help you optimize your fertility program and often can allow
you to correct deficiencies before symptoms become apparent.
Sufficiency Ranges or Critical Values have been established for
most economically important vegetable crops.
Critical values have been defined as the concentration at which
there is a 5-10% yield reduction. The use of critical values for
practical interpretation has limited value. It is best suited to diagnose
severe deficiencies and has little application in identifying
hidden hunger. Symptoms are generally visibly evident when
nutrient concentrations decrease below the critical value. Critical
values play an important role in establishing lower limits of sufficiency
ranges.
Sufficiency range interpretation offers significant advantages
over the use of critical values. First, hidden hunger in plants
can be identified since the beginning of the sufficiency range is
clearly above the critical value. Sufficiency ranges also have upper
limits, which provide some indication of the concentration at
which the element may be in excess.
Method for Collecting Leaf Tissue Samples
for Analysis
* It is best to send in two samples. One sample from the
problem area and another from an area that is growing
well. This will allow comparison for your particular situation.
4
*
Each vegetable crop has a specific corresponding plant
part that is collected and used to determine foliar nutrient
concentrations. Often this corresponds to sampling the
most recently matured or fully expanded leaves. Careful
sampling ensures the effectiveness of plant analysis as a
diagnostic tool. For major crops, best indicator samples
have been identified by stage of growth. For young seedlings,
the entire plant is sampled 1 inch (2.5 cm) above the
soil level. For larger plants, the most recent fully expanded
or mature leaf is the best indicator of nutritional status.
As some crops, including corn, approach flowering and
fruiting, the best indicator of nutritional status is the leaf
adjacent to the uppermost fruit (ear leaf). When unfamiliar
with sampling protocol for a specific crop, it is generally
acceptable to select the most recent mature leaf as the
best indicator of nutritional status. Detailed information
for sampling most vegetable crops can be found at http://
www.ncagr.gov/agronomi/saaesd/scsb394.pdf.
* Sample from 20 to 30 plants.
* Sample across the field, from different rows, and avoid
problem areas (low spots, ridges, washed out areas, etc.)
unless you are trying to diagnose a problem in one of
these areas.
* Sample when the plants are actively growing (typically
between 9 a.m. and 4 p.m.).
* Do not collect samples from water stressed plants.
* Send samples to a laboratory in a paper bag. DO NOT
SEND SAMPLES IN A PLASTIC BAG. Plastic bags will
cause your samples to spoil and will impact results. Contact
your local Extension office for information on how to
submit leaf tissue samples to your state diagnostic labs.
Phosphorus Management. Crops are very likely to respond to
P fertilization when the soil test indicates that P is deficient-
very low or low. A soil testing deficient-medium will sometimes
respond to P fertilization and will sometimes not. Soils testing
optimum or exceeds crops needs are unlikely to respond to P fertilizer,
but P may be applied to maintain the fertility level in the
optimum range. Crops are more likely to respond to P fertilizer
when growing conditions are favorable for high yields. Some
crops, such as tomato and potato, benefit from crop removal
amounts of starter P fertilizer even if the soil is testing optimum
or very high. Consult your local Extension office for more information.
It
is often recommended that a band of P fertilizer be placed
near the seed as a starter fertilizer regardless of the P fertility level.
Banded P is especially helpful at low soil test levels. Even at P
soil test levels that exceed crop needs, a small amount of banded
P may benefit crop establishment. When the soil test level is deficient,
P should generally be applied as a combination of broadcast
and banded methods. When the level exceeds crop needs,
only a small amount of P should be applied as a band. Many soils
exceed crop needs category for P due to previous fertilizer and
manure applications. When applied in excess of crop removal, P
accumulates in the soil. Phosphorus is strongly adsorbed to soil
2023 Vegetable Crop Handbook for Southeastern United States
http://www.ncagr.gov/agronomi/saaesd/scsb394.pdf http://www.ncagr.gov/agronomi/saaesd/scsb394.pdf
Southeastern U.S. Vegetable Crop Handbook - 2023

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