Determining Fertilizer requirements for Pecans
Procedures for Leaf and Soil
Sampling
Summary
Accurate and economical lime and fertilizer
applications needed for optimum production in your pecan orchard can be
determined if you follow the procedures outlined, and
1)
Send in a leaf sample annually
to determine levels of Nitrogen (N), Phosphorus (P), Potassium (K), Magnesium
(Mg), Calcium (Ca), and zinc present in leaves. Your soil test results
reflect nutrients levels in soil while foliar analysis specifically indicates
what the tree is able to absorb from the soil.
2)
Soil Test,
preferably annually, to determine soil group, soil pH, and soil levels of
available P, K, Mg, and Ca.
3)
Observe and keep careful
records of past soil and leaf
analysis results, of fertilizer applications, and of condition and yields of
trees.
Consistent
production of high yields of good quality pecans is not possible on Alabama
soils without fertilization. Not only maintaining adequate levels, but
also maintaining proper balance of nutrients is important. Of the 15 or so
elements necessary for growth and production of pecans, only six must commonly
be bought and applied to soil or as foliar sprays in Alabama. These six
are nitrogen, phosphorus, potassium, magnesium, calcium, and zinc. Other
elements, with rare exceptions, are provided in sufficient quantities from soil,
air, and water.
WHY IS A
SOIL TEST NECESSARY?
Since we know the nutrients pecans
usually need in Alabama, why can’t we make a standard recommendation of what to
apply and avoid the trouble and expense of a soil test?
One major
reason is that past fertilization practices often have greatly changed the
fertility levels of soils. Nutrients, such as phosphorus for example, may
have built up to high or very high levels so that additional applications may
not only be wasteful and unnecessary, but also could be detrimental. A
soil test will determine if phosphorus and several other nutrients are actually
needed.
Another common
effect of past cultivation and fertilization practices is a lowering of soil pH.
Pecans are pH sensitive, and require a pH between 6.5 and 7.0 for best growth.
A soil test is essential to determine the pH level of the soil, and to determine
the amount of lime required to bring the pH to the desired range. In
addition to determining soil pH and soil levels of phosphorus, a soil test will
also give an indication of the amounts of potassium, magnesium, and calcium in
the sample.
Since the soil
type and cation exchange capacity affect the level of nutrients required, the
soil test classifies the soil into a certain group. Finally,
recommendations are made which consider the soil group, the soil nutrients
levels, the soil pH, and the needs for the crop specified. A rule-of-thumb
recommendation does not take these into account, and may be a poor
recommendation in many situations.
WHY IS A
LEAF ANALYSIS NECESSARY?
Even though soil testing is essential
to determine soil group, pH and soil levels of several nutrients, a soil test
alone leaves some important questions unanswered. One of these questions
is, “Are the nutrients I’ve applied to the soil being taken up in adequate
amounts by the roots and moved to the leaves?” and “Do I need foliar sprays of
zinc?”
A leaf
analysis detects “hidden hunger”, which is a level of nutrition where deficiency
symptoms are not apparent but yields are reduced. Leaf samples can reveal
shortages or excesses in time to correct them before serious damage and crop
loss occur. A leaf analysis also will provide a index for determining
whether nutrients are present in the proper balance. Among the important
nutrients measured by leaf analysis are N, P, K, Ca, Mg, and Zn.
WHY
ARE OBSERVATIONS AND RECORDS IMPORTANT?
Keeping close records of soil and
leaf levels of nutrients gives a indication of trends developing in your
orchard. For example, if you routinely apply phosphorus or zinc,
eventually levels can build up and cause problems. Writing down your soil
and leaf sample records over a number of years along with applications made will
give you a good indication of the effects of additional applications.
Comparing records with yields and condition of trees over a number of years will
provide you with index for measuring the effectiveness of your fertilization
program. Careful observations for weak trees, deficiency symptoms, etc.,
can help you pinpoint problem areas in your orchard, which may need special
attention. Keep in mind when making observations that pecans are slow in
responding to fertilization. Improvements in growth and yield may not be
apparent for several years after a good fertility program is begun.
Remember that returns from fertilizer applications may not be realized if
disease and insect pests, inadequate water, poor drainage, poor pollination, or
other factors are limiting production.
1.
Obtain soil sample boxes, shipping cartons, and forms (Soil Testing Form A) from
your county Extension office
 2.
Sampling every year is suggested for high value crops like pecans. Samples
can be taken at any time. A late fall or winter sample will allow you to
plan you February fertilizer applications accordingly. Or, you can
conveniently soil sample in July, which is the suggested time for leaf sampling,
so that your soil and leaf sample are considered together.
3.
A sample should represent a uniform area. Soils which differ in
appearance, crop growth, or past treatment should be sampled separately.
4.
A single sample should consist of just over a pint of soil. This pint of
soil should be a mixture of 15 to 20 subsamples collected over a large area
which accurately represents conditions over the orchard.
(Figure 1).
5.
Use a soil tube, soil auger, or spade to take soil samples to uniform
depth.
Figure 2). Sample to a depth of 8 inches. For new orchards, which
should be deep-plowed before planting, sample to the depth of the
plowed layer.
Since recommendations are based on a 8-inch layer, you
will need to increase the
recommendation by 1/8 for each inch deeper
that 8 inches that you plow.
For example, if you plow to 12 inches and 2
tons per acre of lime are
recommended, apply at least 3 tons per acre.
6.
Complete your soil test forms and send them along with the test fee and your
soil sample to the soil lab or you county Extension office, whichever is
recommended for your area. You should receive your results within ten days
to two weeks.
PROCEDURE FOR COLLECTING PECAN LEAF
SAMPLES
1. Collect leaf
samples during the month of July.
2. Take a
sample of at least 100 leaflets from at least eight trees. The trees should be
representative of trees in the area sampled. The sample area should be
reasonably uniform regarding tree performance, past fertility practices, and
soil.
3. Collect
the middle pair of leaflets from leaves in the middle of the current season’s
shoot, or growth (See figure at right). Collect leaflets from all sides of the
tree that are exposed to sunlight and can be easily reached from the ground.
Choose leaves that are free of damage from insects or disease and that have not
collected an excessive amount of dust. Do not collect leaves in galvanized
containers, since these may contain zinc which could affect results.
4. Place the
leaflets in a perforated paper bag and air-dry them at room temperature.
5. It is
suggested to take a soil sample at the same time and from the same area where
the leaf sample was collected. If you do not soil sample at the same time, be
sure and write in on Form B the results of your last soil sample of the areas
where leaves were collected. This information will aid in analyzing your
situation and in making a correct recommendation.
6. Complete
Form B, Pecan Grower’s Information Sheet, as accurately as possible for each
leaf and soil sample submitted. Information concerning past treatments, and
leaf and soil nutrients is necessary to make the best recommendations.
7. Put the dry
leaf samples in paper bags (not plastic), identify bags by sample number or
orchard name, close the bag with tape (not metal staples), and pack in shipping
carton or large envelope. Do not allow soil from soil sample to contaminate
leaf samples. Separate shipping boxes are best.
8. Enclose the
testing fee and send the samples to your testing lab or county Extension agent,
whichever is recommended for your area.
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