Southeastern U.S. Vegetable Crop Handbook - 2021 - 17

tional 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 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 macro- and
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. The best indicator
samples have been identified for most economically important
vegetable crops. In turn this has provided the basis for developing
data for which we can compare values from our analysis to those of
established, recognized values. These are called Sufficiency Ranges
or Critical Values. For those crops such as tomatoes which receive
the greatest research support, indicator samples have been identified
by stage of growth. In tomato we have sufficiency ranges established
for plant tissue samples taken at mid-bloom of the first, second,
third, fourth, fifth, and sixth flower clusters.
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.
2021 Vegetable Crop Handbook for Southeastern United States
Method for Collecting Leaf Tissue Samples
for Analysis
* Each vegetable crop has a specific corresponding plant part
that is collected and used to determine foliar nutrient levels.
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
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.
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.
High phosphorus fertilizers are often referred to as 'pop-up' fertilizers
because of their positive effect during early growth when soil
temperatures in early spring can be very low. 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 particles and very little is subject to loss
via leaching. When the soil test level exceeds crop needs, growers
can benefit economically by withholding P fertilizers.
17
http://http:// http://www.ncagr.gov/agronomi/saaesd/scsb394.pdf
Southeastern U.S. Vegetable Crop Handbook - 2021

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