General Use of Foliar Analysis
for Tropical and Subtropical Crops
 My main goal today is to discuss the feasibility of using foliar
analysis to diagnose nutritional problems of tropical crops.
However, I have conducted only a minor portion of my research
under a tropical environment. Therefore, my knowledge of many
of your conditions is very limited. Hopefully, a discussion of
foliar analysis fundamentals, regardless of the crops used, will be
of value to you.
 Extensive nutritional studies have been conducted on several
important tropical and subtropical crops such as bananas, pineap-
ple, citrus, oil palm and sugarcane. A review of the literature ap-
pears to indicate that foliar analysis data is available. However,
there are many additional horticultural crops of lesser importance
that have received only minor attention. Assuming that your in-
stitution wanted to set up a diagnostic service program as soon as
possible, how easy would it be to develop a database for some of
these crops? Personal experience, as well as a review of the
literature on foliar analysis, shows that at least two procedures can
be effectively used:
 1. Conduct a routine foliar analysis survey of the crops under
 consideration.
 2. Conduct some field experiments either concurrent with or
 following the survey.
 Through the first procedure, general levels can be established,
 such as those presented in Table 1. If this information is combin-
 ed with visual symptoms, growth ratings, quality evaluations and
 indications of general plant condition, then much usable data can
 be obtained quite rapidly. Some of the obvious errors created by
 this procedure are that if soils do not provide an adequate cross-
 section of nutritional conditions, i.e., mostly deficient or ex-
 cessive amounts of certain elements (copper, boron, zinc, etc.)
 are present, then adequate nutritional levels cannot be sampled.
 However, in most areas there is an adequate range of condi-
tions, and foliar nutrient levels can readily be related to yield and
quality. Visual deficiency or excess symptoms can also help in-
dicate minimum levels.
 Once approximate levels have been established by the survey
data, then field experiments should be conducted. Plantings
thought to be low or deficient in certain nutrients can be utilized
as effective experimental sites and corrective measures applied.
The results of your survey data can thus be verified and refined.
 Without any previous history on a crop, what can be learned
from a foliar analysis? One of the very desirable associations that
can be used effectively is to compare plants growing in a satisfac-
tory vigorous condition with plants not growing well or those that
exhibit visual symptoms and those that do not. Some of the pit-
falls to be avoided here are: (1) do not take samples from ob-
viously diseased or physically injured plants; and (2) avoid plants
with known herbicide or chemical damage. Under either condi-
tion, nutrient concentrations will be obtained that are mean-
ingless because the primary cause of poor growth, etc., is not due
to nutrition, but to the injured or diseased condition. Drought,
salinity, poor drainage, and saturated soil conditions also offer
pitfalls that will lead to false interpretations of the foliar analysis
data.
 Thus, even though little or nothing is known about the re-
quired nutrient level of a crop, if comparisons are made using
healthy plants as your base, then some fundamental deductions
can be made. It has been the author's experience that within
reasonable limits somewhat typical levels of nitrogen,
phosphorus, potassium and other nutrients can be expected in
the average leaf or petiole of a plant (Table 1). There are notable
exceptions to this, but they become readily apparent with normal
sampling procedures for a given crop.


TABLE 1. Foliar nutrient levels associated with dry weight of some fruit crops.
 --------------------------------------- -------------------ppn------------
 Crop N P K Ca Mg Mn Fe B Cu Zn
 Mango 1.4/2.0 .14/2.0 .7/1.1 1.8/2.6 .25/.35 30/150 70/120 35/100 5/15 25/50
 (M. indica)
 Guava 1.5/2.4 .15/3.0 .7/1.1 1.8/2.6 .25/.40 30/150 50/120 35/100 5/15 25/50
 (P. guajava)
 Litchi 1.9/2.6 .14/2.0 1.0/1.5 2.0/3.0 .30/.55 30/150 50/130 35/100 5/15 20/50
 (L. chinensis)
 Fig 1.8/2.0 .12/.18 1.0/1.5 3.0/5.5 .40/.70 25/50 50/120 35/100 5/15 25/50
 (F.carica)
 Orange 2.0/2.6 .12/.18 1.2/1.7 3.0/5.5 .26/.60 25/50 50/120 35/100 5/10 25/50
 (C.sinensis)
 Mandarin 2.8/3.0 .15/.26 .9/1.1 3.0/5.5 .26/.60 25/50 50/120 30/100 5/10 25/50
 (C.reticulta)
 Grapefruit 1.5/2.2 .15/.26 .6/1.5 3.0/5.5 .26/.60 25/50 50/120 35/100 5/10 25/50
 (C.paradisi)

 Three basic criteria should be combined when establishing a
foliar analysis procedure. They include: (1) a sample taken from a
leaf, petiole, or other easily identified tissue; (2) the position on
the plant should be equally easy to identify (first fully mature leaf
on current season's growth or mid-shoot leaf on the spring flush
of growth, etc.; (3) the tissue (leaf or petiole) should be in an 'ac-
tive' position on the plant (a leaf well exposed to ambient
sunlight on a fruiting shoot, etc.); (4) the time of sampling
should be a well-defined phenological period (mid-season or at a
specified number of days following bloom, veraison, etc.).

Relative Importance of Nutrient Elements
 As a general rule the element of greatest concern in nutrition
studies is obviously nitrogen because it relates so strongly to yield
and quality. Most of our cultivated crops require additions of
nitrogen in one form or another in order to produce satisfactory
yield. Legumes are the major exception. The second element of
major concern would probably be potassium, especially in our
higher rainfall soils. Phosphorus, although very necessary for
plant growth, is generally not of major concern for fruit crops,
although for vegetables it frequently is in second position in
general fertilizer recommendations. Around the world, deficien-
cies or excesses of minor elements such as boron, zinc, and copper
play an important role in developing adequate yield and quality.

Development of a Grower Foliar Analysis Program
 Ohio has had a grower service program since 1964. During this
period many thousands of samples have been sent to the
laboratory for analysis and the results returned to the growers
with recommendations. Some comments relating to this ex-
perience may be appropriate at this time.

Development of a Questionnaire. In most programs, the nutri-
tional specialist for a laboratory takes the sample, analyzes it and
completes the service by returning the information to the grower
with his recommendations. In Ohio, we have allowed the grower
to fill out a questionnaire (Fig. 1), take his own samples, and
send them to the laboratory.
 With the development of computers, it seems as though much
of our information must be in abbreviated form. Thus, the use of
the information questionnaire, such as the one shown (Fig. 1),
has been reduced to the bare essentials. The original question-
naire developed for fruit crops in Ohio allowed the grower to in-
dicate conditions he saw in his plantings, but not interpret the
problem (nutritional or otherwise).
 Kits are distributed to all county or district offices and depart-
ments. Only when the grower uses the kit and sends in the sam-
ple is he charged a fee. Thus, the kits are available in quantity at
a number of locations. Instructions for their use are attached. At
least 60 units (leaves, petioles, etc.) are requested per sample.
This is an attempt to make the grower get a good cross-sectional
sample of his planting. Turn-around time in the Ohio program
generally takes about 3-5 days. By the time the samples arrive on
my desk, five days have generally passed. For sample analyses on
which growers rapidly need the information, transmittal of
results may be by telephone. It must be recognized that in many


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