Excerpt from the
Agronomy Department, Florida Cooperative Extension Service
Institute of Food
and Agricultural Sciences, University of Florida
Peanut Fertilization
Soil tests from soil samples taken
immediately after harvest of crops in the fall can be used to determine
lime as well as fertility requirements for crops for the coming year.
If soil pH needs adjusting, fall is a good time of the year to apply
needed lime since it may take as long as six months for full reaction.
However, some reaction does occur soon after application. Bacteria,
which fix nitrogen in relation to the peanut plant, do better and form
more nodules with an adequate calcium (Ca) level and with pH around 6.0
or higher. If the crop that precedes peanuts is well-fertilized, there
may be enough residual nutrients in the soil to make direct
fertilization unnecessary. The analysis and report of the soil sample
will also indicate which nutrients are needed on a particular field.
Calcium and magnesium (Mg) may be supplied by limestone. If no lime is
needed, Ca can be supplied by gypsum, and Mg can be included in the
fertilizer. If phosphorus (P) is low, add P according to soil tests.
The
same is true for potassium (K) and other nutrients needed by peanuts.
Boron (B) and manganese (Mn) are normally the most deficient
micronutrients on sandy soils. Therefore, if peanuts are to be planted
on a sandy soil, it would be advisable to use B at the rate of 0.5–0.75
lb of elemental B per acre. Higher rates of B can be toxic to the
plants. Applications of B should be split since it is a highly
leacheable, mobile nutrient. High application rates of other nutrients
can make B deficiency more pronounced.
The deficiency that we
most often associate with B deficiency is internal fruit damage called
“hollow heart”, which reduces the quality and value of the crop.
However, in more severe cases, B deficiency can result in split stems
and roots, on the lower part of the stem with shortened internodes,
terminal death, and extensive secondary branching. Leaves may be dark
green and mottled with few or no peanuts developing on stubbed pegs.
Some fields have been observed with these symptoms recently and this is
a reminder that there is a reason to apply B even if few visual
observations of deficiencies are seen. B may be applied early with
herbicides or with fungicides to avoid making additional trips across
the field. The crop may take up less than a tenth of a pound per acre
but it is still important for crop production.
Peanuts with a
yellow cast during the growing season can have several causes including
poor nodulation, micronutrient deficiencies, water logged soils, or
herbicide damage. Some fields are yellow due to being water logged
which results in poor nodulation and nitrogen fixation. Plants usually
grow out of this as soils dry out. Iron and other micronutrients may be
limiting in water logged soils too, which will grow out of it as soils
dry out.
Manganese deficiencies often occur in soils that have
been limed for years and have a pH above 6.3. These symptoms can be
seen as a light green to yellow cast to the peanut canopy and are
usually more prevalent late in the season and on sandier sites.
Manganese applications can be made to the crop or a base application
may be made at planting. It is possible to lower the pH through acid
forming fertilizers such as ammonium sulfate; however, applications of
a few pounds of micronutrient may be more cost effective and the
response will be quicker than changing the pH.
Calcium, Liming, pH, and Gypsum
Lime
should be added if the soil pH is below 5.8, with the target pH being
6.2–6.5. If lime is needed, both a dolomitic or calcitic lime can be
used and additional Ca as gypsum may be needed on larger seed
varieties. In addition to reducing soil acidity, calcitic lime supplies
the plant nutrient Ca while dolomitic lime supplies both Ca and Mg.
Peanut responds very little to direct fertilization of most nutrients.
However, Ca is needed in high levels by peanut for developing a viable
seed.
High levels of Ca are not necessary to grow a healthy
plant. The amount of Ca taken up by the plant is dependent on the
concentration in soil solution and on the amount of water moving into
the plant. Calcium deficiency results in high incidence of pod rot and
unfilled pods called “pops”. These peanuts also have lower germination
if saved for seed.
Georgia research has shown that Ca applied as
lime should not be turned under and that turned under lime had yields
similar to no lime. Even though peanut has a lower Ca requirement than
soybean or cowpea, peanut does have an exceptional need for Ca for seed
maturation and quality.
Lime should be applied to fields well in
advance of planting and may be applied to strip tilled fields as a
surface application. For those growers who use minimum tillage and
strip tillage, surface applications are acceptable. We have long term
plots that have not been turned or had lime incorporated for 35 years
that are still producing good crop yields.
A high Ca and P layer
can develop in the top two to three inches after many years of surface
applications of fertilizer and lime. Calcium is routinely applied as
gypsum at pegging on sandy soils for rapid replenishment of soil
solution Ca. This is not as necessary on heavier soils or fields with
irrigation that have higher diffusion gradients toward the pods. Since
peanuts are often grown on sandy soils, which are drought prone, there
is a limited ability of these soils to replenish the soil solution Ca.
Heavier soils and irrigated soils are better able to supply needed Ca
for proper uptake. The Ca needs are primarily for pod and seed
development and not for growing a healthy plant. Test soils and apply
needed amounts of Ca for good yields and quality.
The critical
period for Ca absorption begins about 20 days after pegs start entering
into the soil and may extend for an additional 60 days. However, some
researchers have reported that 69% of total Ca uptake occurred between
day 20 and 30 after pegging begins. It is then a necessity that proper
amounts of Ca are supplied for the first 30 days after pegging begins.
The
problem occurs when limited soil moisture coincides with the high Ca
need period and there is no moisture for Ca to be in solution for
uptake by peanut. Sandy soils in the peanut region have low moisture
retention capacity which leads to moisture induced Ca deficiency.
Much
of the irrigation installed in the Southeast was due to corn in
rotation with peanuts. High levels of K and Mg in the soil can inhibit
uptake of Ca and therefore peanuts are often not fertilized and “high
cal” lime is used instead of dolomite. Soil test levels of about 450
lb/A of Ca result in maximum yields of runner type peanuts while levels
almost double this are necessary for maximum yield of Virginia type
peanut as noted from research by S. Hodges at the University of Georgia.
The
larger peanuts have a smaller surface-to-weight ratio and require a
higher concentration of soil solution Ca in order to provide adequate
Ca to the pod. Therefore, if soil samples show only Ca to be low, then
calcitic lime would be satisfactory. However, if both Ca and Mg are
low, then dolomitic limestone should be selected.
Lime should be
applied three to six months before planting peanuts, but can be applied
up to time of planting. Lime should be applied in the fall to allow
time to react with the soil.
If Mg soil test is not low, use
calcitic lime so that Mg will not compete with Ca for uptake by
peanuts. Gypsum is often applied to peanuts at pegging time so that
peanuts will have an adequate Ca supply.
Rates of 250 lb/A of
dry gypsum in a band to 1000 lb/A of wet gypsum are often applied to
peanuts that are to be saved for seed or when the soil test shows a
need. Recent research from Alabama over several SE locations has shown
that non-irrigated peanuts may have proportional yield increases with
gypsum applications up to 1500 lbs/A.
Inoculating Peanuts
Peanuts
may not always respond to rhizobium inoculation. The main reason for
this is that there is an indigenous population of rhizobium called
cowpea miscellany that is common to many native plants. These organisms
are potentially able to nodulate a crop of peanuts grown for the first
time in a field. Peanuts are only moderately efficient in fixing and
translocating atmospheric nitrogen (N). With soybean, as much as 80% of
the plant N comes from the atmosphere while about 55% of the plant N
needs of peanut are from N fixation.
Calcium is important to
nodulation, and maximum peanut root growth occurs at a pH of about 7.3
while shoot growth, nodulation, and N fixation is best at a pH range of
5.9 to 6.3. An application of lime can improve the availability of Ca,
Mg, and P and decrease aluminum toxicity.
Inoculants may be
applied to soils that have not had peanuts grown on them for several
years or at all. In some cases inoculation can increase nodulation and
in others little response may be noted. However, inoculants are cheap
insurance in providing needed N for plant growth. Nitrogen fertilizer
will not normally increase yields unless the N-fixing bacteria that
live in nodules on the peanut roots are not present. If needed, a
commercial inoculant can be applied in the seed furrow at planting to
provide the needed bacteria.
Back to
Peanut Page
|