Chapter 7
Micronutrient Deficiencies and Toxicities
J. G. Davis and F. M. Rhoads
Current Recommendations
Micronutrients are required by plants in small amounts, but
are no less essential than macronutrients. Micronutrients for
crop production include B, Cu, Fe, Mn, Mo, Zn, and Cl. Micronutrient
removal by peanuts is estimated to be 1.0, 0.04, 0.04, 0.30,
and 0.25 lb acre-1 of Cl, B, Cu, Fe, and Mn, respectively,
for 3,000 lb nuts acre-1. If the vines (5,000 lb acre-1)
are also removed, the nutrient removal increases to 2.0, 0.06,
0.06, 0.50, and 0.40 lb acre-1 of Cl, B, Cu, Fe, and
Mn, respectively.
All peanut growing states in the Coastal Plain recommend B application
to peanuts (Table 1). Some states recommend 0.3-0.5 lb B acre-1
(Alabama, South Carolina) and others recommend 0.5 lb B acre-1
(Georgia, North Carolina). Only one state presents a condition
for B recommendation; Georgia recommends that if (hot-water soluble)
B >0.5 mg kg-1 then no B should be applied (Table
1).
In addition to B, North Carolina and Virginia recommend Mn and
Florida recommends Cu and Zn when soil levels are rated low.
No other micronutrients are recommended for peanut production
in the Southeast. Most states recommend that farmers maintain
soil pH at about 6.0 to prevent most micronutrient deficiencies
or toxicities. In addition, it is recognized that micronutrient
applications to the rotation crop will provide additional micronutrients
to peanuts.
Table 1. Micronutrient Recommendations for
Peanuts in the Atlantic
and Gulf Coastal Plain |
|
Boron |
|
Alabama1 |
0.3 - 0.5 lb acre-l |
|
Florida2 |
0.75 lb acre-l in fertilizer or 0.5 lb acre -l
foliar |
|
Georgia3 |
0.5 lb acre-l on all peanut soils, unless soil B >0.5
mg kg-l |
|
N. Carolina4 |
0.5 lb acre-l |
|
S. Carolina5 |
0.3 - 0.5 lb acre-l |
|
Copper |
|
Florida2 |
3 - 5 lb acre-l if M-1 soil Cu <0.1 mg kg-l
(pH 5.5-6.0), <0.3 mg kg-l (pH 6.0-6.5), or <0.5
mg kg-l (pH 6.5-7.0) |
|
Manganese |
|
N. Carolina4 |
10 lb acre-l if [101.2 + 3.75 mg M3 Mn dm-3
- 15.2 pH] is less than 25 |
|
Florida2 |
8-10 lb acre-l if M-1 soil Mn <3 mg kg-l
(pH 5.5-6.0), <5 mg kg-l (pH 6.0-6.5), or <7
mg kg-l (pH 6.5-7.0) |
|
Zinc |
|
Florida2 |
5-10 lb acre-l if M-1 soil Zn <0.5 mg kg-l
(pH 5.5-6.5) or <1.0 mg kg-l (pH 6.5-7.0) |
|
1Cope et al. 1981. 2Hanlon et al. 1990
(These are general recommendations; they are not specific for
peanuts). 3Plank 1989. 4Tucker and Rhodes
1987. 5Clemson Univ. 1982. |
Boron
Boron (B) is the only micronutrient generally applied to peanuts
on Coastal Plain soils. Peanut is a crop with a medium B requirement,
requiring 0.1-0.5 mg kg-l available B (water extraction)
in the soil (Berger 1949). Perry (1971) recommended 0.5 lb B
acre-l for sandy soils and 1 lb acre-l
for clay soils, but warned against over application due to potential
B toxicity.
Deficiency
Early research in Florida indicated that B deficiency resulted
in hollow-heart, compacted branch terminals, and cracks on pods
(Harris and Gilman 1957). Application of 0.15 lb B acre-l
as H3BO3 increased peanut yield and grade
in the greenhouse, but B deficiency was not detected in field
studies. Harris (1968) stated that B application of 0.4 lb acre-l
was beneficial in greenhouse tests.
Research in North Carolina showed that 0.5 lb B acre-l
decreased hollow-heart in a field study (Cox and Reid 1964).
They also showed that liming increased soil extractable B, but
did not increase B content in peanut kernels.
Prior to 1964, B was not recommended for peanuts in Georgia (Giddens
1964). Results had been inconclusive with some positive and some
negative responses to B application. By 1966, B was recommended
in Georgia at 0.5 lb acre-l for sandy soils, but not
for clayey soils (McGill and Bergeaux 1966). Walker (1967) stated
that 0.5 lb B acre-l applied as a foliar spray increased
peanut yields in Georgia on sandy Ruston and Tifton soils, but
not on Greenville soil (a clayey soil).
In Alabama, Hartzog and Adams (1968) determined that topdressing
1 lb B acre-l had no effect on yield, and increased
grade in only one out of five experiments. Hartzog and Adams
(1971) reported that in eight experiments with hot-water-extractable
soil B <0.07 mg kg-l, hollow-heart did not develop,
and yield and grade were unaffected by B fertilization. Hartzog
and Adams (1973) again reported no yield or grade effect of B
fertilization.
In Virginia, hollow-heart symptoms were noted in 1958, but the
symptoms were not identified with B deficiency until 1965 (Anonymous
1965). Research showed that 1 lb B acre-l decreased
damage to seed kernels, but that 2 lb acre-l could
be toxic. Hallock (1966) obtained a marked decrease in hollow-heart
by B application, but found that rates of 1 to 2 lb B acre-l
did have phytotoxic impacts. He also notes that B deficiency
is more common in sandy, droughty soils than in finer-textured
soils. Allison (1966, 1980) recommended 0.5 lb B acre-l
foliar application at early bloom.
Hill and Morrill (1974) found B deficiency in 50% of field locations,
but reported that B application did not affect yield or grade.
They stated that hollow-heart was related to soil B (hot-water-soluble)
<0.15 mg kg-l. Hill and Morrill (1975) found that
B application did improve peanut grade, except in soils high
in potassium. Morrill et al. (1977) suggested that peanut soils
with B  0.15 mg kg-l (hot-water-soluble)
require B fertilization at a rate of 0.5 lb acre-l.
We recommend 0.5 lb B acre-1 when soil B <0.2
mg kg-1 (hot-water-soluble).
Toxicity
Boron can be toxic to peanuts; therefore, B should be applied
at the recommended rate only. McGill and Bergeaux (1966) warned
of exceeding 0.5 lb B acre-l applications in Georgia.
Morrill et al. (1977) stated that 1.0-1.5 lb B acre-l
caused toxicity and reduced yields in Oklahoma. Boron application
>6 lb Borax acre-l (0.6 lb B acre-l)
had an adverse yield effect (Asokan and Raj 1974), and 5 lb Borax
acre-l (0.5 lb B acre-l) resulted in toxicity
symptoms (Reddy and Patil 1980).
In conclusion, care should be taken not to overapply B
to peanuts. A soil critical level of 0.2 mg kg-1 hot-water-soluble
B should be included in B recommendations.
Chloride
Chloride (Cl) toxicity has been described for soybeans in
Georgia (Parker et al. 1983), but has not been found in peanuts.
Athough Cl is an essential element for plant production, Cl deficiency
has not been described for peanuts.
Chloride effects on Florunner peanuts were studied in the greenhouse
and field in Georgia (M.B. Parker, Univ. of Georgia, personal
communication, 1984). Addition of Cl to an Ocilla sand increased
Cl concentration in peanut leaves, but there was no significant
effect on dry matter production (greenhouse) or pod yield (field).
Chloride application rates which caused toxicity in soybeans
had no effect on peanuts.
There are no data that would warrant fertilizer Cl recommendations
for peanuts.
Copper
Copper is a micronutrient which is rarely applied to agronomic
crops as a nutrient, but is commonly applied in the form of pesticides,
particularly fungicides. Bledsoe and Harris (1947, 1948, 1949)
reported that application of 5 lbs Cu acre-l as CuCl2
increased the proportion of sound to shriveled nuts for runner
peanuts in experiments done in Florida. Three years after application,
the residual effect of Cu on peanut quality was maintained. Harris
(1952) described Cu deficiency symptoms as affecting the bud
area in particular, as well as causing small, irregular leaflets
with marginal necrosis and mild chlorosis and small yellow-white
spots on the foliage. Harris (1952) stated that spanish-type
peanuts were more sensitive to Cu deficiency than runner peanuts,
but that yields for all three varieties studied (two runner types
and one spanish-type) were increased more than 300% by applying
5 lb Cu acre-l as CuCl2, to an Arredondo
loamy fine sand (pH 5.7). Copper application also decreased seed
shriveling and increased the percentage of sound, plump nuts
(SMKs). The residual effect of soil Cu application (10 lb acre-l)
to oats, wheat, rye, or cotton in rotation with peanuts was found
to be equally effective as peanut foliar applications (0.1 lb
Cu acre-l as CuCl2). However, Harris (1952)
concluded that, in general, peanut yields in Florida had not
been increased by Cu applications (though yields were increased
on the Gainesville experimental farm), and, therefore, Cu application
was not recommended.
Boswell (1964) stated that in Georgia research no definite relationship
was found between Cu application and peanut yields.
No Cu recommendation for peanuts is warranted.
Iron
Iron (Fe) deficiency in peanuts can be a serious problem in
calcareous soils (Hartzock et al. 1971). Most Gulf and Atlantic
Coastal Plain soils are acidic, and Fe deficiency has never been
reported for peanuts grown in this region. Perkins (1964) stated
that the total Fe content of most Georgia soils is greater than
10,000 mg kg-l; therefore, he concluded that Fe is
available in Georgia soils in sufficient amounts for agronomic
crop production. Iron deficiency in peanuts results in interveinal
chlorosis (starting in the youngest leaves), followed by chlorosis
of the entire leaf (whitish-yellow) and brown spots leading to
marginal necrosis (Lachover and Ebercon 1972b).
Lachover and Ebercon (1972b) showed that yield response to Fe
application in Israel was related to % CaCO3, in the
soil. Papastylianou (1989) surveyed 35 peanut fields in Cyprus
and determined that plants were chlorotic when % CaCO3
>20-25% and Fe content <2.5 mg kg-l (DTPA extractable).
Lachover et al. (1970) applied an Fe chelate (FeEDDHA) to a soil
in Israel with pH 7.9 and 15% CaCO3 and measured a
50% increase in pod yield and a 40% increase in hay yield. Lachover
and Ebercon (1971) showed that Fe chelate applied to a soil of
pH 7.9 and 11% CaCO3 caused leaves to green up and
increased yield. Yields were increased 359% by application of
10 lb Fe acre-l (as FeEDDHA) to a loamy clay with
pH 7.9 and 31% CaCO3 (Lachover and Ebercon 1972a).
Reddy and Patil (1980) applied FeSO4 spray to spanish-type
peanuts grown on an Indian soil with pH 7.5 (2.5% CaCO3
and 9 mg kg-l orthophenonthroline extractable Fe)
and measured no yield increase. Hillock (1964) applied Fe chelates
to peanuts grown in Virginia (acid soils) and found no yield
effect. Schneider and Anderson (1972) did measure yield response
to FeEDDHA in Texas, where calcareous soils occur. Patil et al.
(1979) determined that foliar application of FeSO4
produced higher yields than soil-applied FeSO4 on
a black clay soil with pH 7.7 (2.5% CaCO3 and 1.26
mg kg-l orthophenonthroline extractable Fe). Iron
deficiency could be a problem in peanuts grown in Texas, Oklahoma,
and New,Mexico, where calcareous soils are widespread. The estimated
critical level is <2.5 mg kg-l (DTPA extractable)
Fe in soil.
Iron deficiency in peanuts is very unlikely in the Coastal
Plain, and no recommendation is made for peanuts in this region.
Manganese
Deficiency
Only North Carolina (Tucker and Rhodes 1987) and Virginia
(Donohue and Hawkins 1980) recommend manganese (Mn) application
to peanuts, although recent research in Georgia (Parker and Walker
1986) has illustrated the importance of Mn applications to peanuts
grown on high pH soils.
Rich (1956) stated that Mn deficiency had long been recognized
as a problem for peanuts in Virginia. He reported that Mn concentration
in the plant was inversely related to soil pH, Ca, and Mg levels,
in a study using 32 Coastal Plain soils. However, Mn deficiency
in peanuts has been observed on soils with pH values as low as
5.8 in Virginia. Anderson (1964) reported that research in Georgia
showed no yield effect of Mn additions (4 to 18 lb Mn acre-l
as MnSO4) to a Tifton loamy sand with pH 6.5, a Norfolk
sandy loam, or a Greenville clay loam. Hickey et al. (1974) recorded
significant yield increase for peanuts grown on a Lakeland sand
(pH 6.3, M1 extractable Mn 0.67 mg kg-l due to addition
of 40 lb Mn acre-l (MnCl2). The 1980 Virginia
Peanut Production Guide stated that foliar Mn should be applied
at a rate of 0.75-1.0 lb acre-l in each of up to three
applications, when interveinal chlorosis, which is symptomatic
of Mn deficiency, is evident (Allison 1980).
In Virginia, Hallock (1979) reported increased yields due to
foliar Mn application to peanut grown in soils with pH values
of 6.7 and 6.4. Parker and Walker (1986) studied the interaction
of Mn response with soil pH on a Pelham sand in Georgia. Manganese
deficiency occurred only on plots with pH levels near 6.8 (M1
extractable Mn = 3.7 mg kg-l), not in plots with pH
levels of 5.2 (Ml extractable Mn = 2.3 mg kg-l) or
6.0 (Ml extractable Mn = 2.8 mg kg-l). At pH 6.8,
soil application of Mn at 0, 10, 20, and 40 lb acre-l
resulted in yields of 3410, 5400, 5730, and 6370 lb acre-l,
respectively. Parker and Walker (1986) concluded that maintaining
a soil pH near 6.0 was optimal for peanut production. In Georgia,
regardless of soil pH levels, the only Mn deficient area is in
the Atlantic Coast Flatwoods soils with pH levels >6.2. Whitty
(1991) stated that Mn deficiency can occur in Florida when soil
pH exceeds 6.3.
Soil Mn applications can be used to prevent Mn deficiency
when the soil pH is known to be >6.0. Foliar Mn applications
can correct Mn deficiency, diagnosed through foliar symptoms
(interveinal chlorosis) and plant analysis, more rapidly than
soil Mn applications and can be applied with fungicide in the
tank mixture, thus eliminating the need for additional trips
across the field.
Toxicity
Manganese toxicity can be a problem in low pH soils. Boyd
(1971) described Mn toxicity symptoms for peanuts in greenhouse
studies as interveinal leaf chlorosis followed by marginal leaf
necrosis. He found that soil Mn (NH4OAc extractable)
was correlated with leaf necrosis. Severe symptoms occurred when
soil Mn was greater than 10 mg kg-l (NH4OAc
extractable).
More research is needed in the area of Mn toxicity in peanuts.
However, if soil pH is maintained above 5.5, Mn toxicity is highly
unlikely in Coastal Plain soils.
Molybdenum
Molybdenum (Mo) is essential for N fixation, and is therefore
recommended for some legumes (e.g., soybeans, alfalfa). However,
it is currently not recommended for peanuts. Harris (1959) stated
that Mo application caused peanut foliage to be a darker green
and frequently increased the size of the foliage, but it has
never caused a significant increase in peanut yield in research
in Florida.
Rao et al. (1960) reported that a 0.12 lb Mo acre-l
application in India increased pod yield. Walker (1967) found
that 0.2 lb Mo acre-l soil application increased yield
by 200 lbs on a Tifton soil, but had no effect on yield on a
Greenville soil. Welch and Anderson (1962) found that Mo availability
was increased by liming and that Mo application increased Mo
concentration in peanut leaves, but deficiency symptoms were
not evident in areas which received no Mo. They stated that peanut
seed Mo concentration may be high enough to provide the plant’s
Mo requirement even in a low Mo soil. Sellschop (1967) stated
that Mo deficiency in South Africa is best corrected by liming,
since increasing the soil pH increases Mo availability. Parker
(1964) reported that in 15 Georgia experiments, Mo only had a
yield response in one experiment. He concluded that Mo had a
color response in many experiments, but that this was seldom
reflected in yield. In Georgia, Boswell et al. (1967) showed
that peanut yield was not well correlated with leaf or soil Mo
content, and that Mo addition increased N content of peanut folinge.
However, the yield effect of Mo was inconsistent.
In recent research in India, Reddy and Patil (1980) found that
1 lb acre-l ammonium molybdate increased yield of
Spanish peanuts. The soil test level was 0.5 mg kg-l
extractable Mo, and pH was 7.5. The authors suggested that this
beneficial effect may be due to increased N availability which
resulted in increased protein in peanut kernels. Kene et al.
(1988) found that Mo increased modulation and nodule N content
for peanuts in India.
Most of the literature agrees that Mo increases greenness
and nitrogen content of peanut leaves, but yield increases due
to Mo application are rare. No Mo recommendation is warranted
for peanuts.
Zinc
Deficiency
Carter (1964) summarized Georgia research and showed that
sometimes zinc (Zn) fertilization tended to increase yield and
sometimes it tended to decrease yield, but the differences were
not significant. Sellschop (1967) stated that Zn insufficiency
was less conspicuous in peanuts than in maize in South Africa,
and recommended 15 to 20 lb Zn acre-l where the problem
is common. Schneider and Anderson (1972) found that a Zn application
of 0.1 lb Zn acre-l gave a positive yield response
for spanish-type peanuts in Texas. In a calcareous soil in India
with <0.3 mg kg-l extractable Zn, applications
of 24 lb Zn acre-l as ZnSO4 had no significant
yield effect (Lakshminarasimhan et al. 1977).
Phosphorus application can show antagonistic effects on Zn uptake
(Chahal and Ahluwalia 1977). Zinc deficiency is associated with
high soil pH and high available P levels (Graham 1979). Patil
et al. (1979) found no yield response to either soil or foliar
applications of ZnSO4 on chlorotic peanuts in India,
although the chlorosis was attributed to high soil pH and heavy
P fertilization.
Reddy and Patil (1980) stated that 0.5 mg Zn kg-l
(DTPA extractable) was the critical level for Zn deficiency in
peanuts in India. Rhoads et al. (1989) applied Zn to soil in
a greenhouse study in Florida and determined that Southern Runner
was more sensitive to Zn deficiency than Sunrunner. They suggested
a critical M1 soil Zn level of 2.5 mg kg-l when soil
Ca >400 mg kg-l.
Bell et al. (1990) described Zn deficiency symptoms in peanuts
as decreased internode length and restricted development of new
leaves. They also found that Zn deficient plants accumulated
reddish pigments in stems, petioles, and leaf veins.
Zinc deficiency is also related to high soil pH, high soil
Ca, and high soil P. Foliar application is probably the best
way to correct Zn deficiency.
Toxicity
Zinc toxicity was first reported in Texas by Quintana (1972)
who noted that application of 90 lb Zn acre-l as ZnSO4
decreased yields. Keisling et al. (1977) described Zn toxicity
symptoms as chlorosis, stunting, purple coloration of the main
stem and petioles, usually a lesion at the base of the plant
(stem splitting), and premature necrosis. The tentative Zn toxicity
critical value reported by Keisling et al. (1977) was 12 mg kg-l
soil (M1) for Georgia Coastal Plain soils. Liming reduced Zn
uptake and eliminated toxicity symptoms but did not change the
Ml level of Zn in soil. Davis-Carter et al. (1990) showed that
leaf chlorosis and stem purpling were not well correlated with
leaf Zn levels in a greenhouse study in Georgia and described
Zn toxicity symptoms of horizontal leaf growth and leaf closure.
Rhoads et al. (1989) stated that peanut response to Zn appeared
to be more dependent on soil Ca level than on soil pH in Florida.
Up to 10.3 mg Zn kg-l (Ml extractable) did not adversely
affect plant growth when soil Ca >400 mg kg-l and
soil pH was 6.5-6.8, but 3.6 rng Zn kg-l (Ml extractable)
reduced plant growth when soil Ca ranged from 150 to 200 mg kg-l
and pH was  6.6. Cox (1990) and Davis-Carter
et al. (1991b) stated that since Ml extraction of Zn from soil
is not pH sensitive, it is necessary to include soil pH with
Ml extractable Zn in any regressions predicting leaf Zn. Davis-Carter
et al. (1991b) used such equations to calculate the probabilities
for the development of Zn toxicity symptoms in peanuts as a function
of soil pH and soil Zn. Georgia recently adopted a sliding scale
which recommends minimum pH levels for peanuts as a function
of soil Zn concentration (Table 2). According to this scale,
if soil pH is 6.0, extractable soil Zn concentration above 10
mg kg-l could cause Zn toxicity in peanuts.
|
Table 2. Minimum Soil pH to Avoid Zn Toxicity in
Peanutsl |
|
Mehlich 1 - extractable Soil Zn |
Minimum Soil pH |
|
mg kg-l |
|
|
<0.5 |
5.7 |
|
0.5 - 2 |
5.8 |
|
3 - 5 |
5.9 |
|
6 - 10 |
6.0 |
|
11 - 15 |
6.1 |
|
16 - 20 |
6.2 |
|
21 - 25 |
6.3 |
|
26 - 30 |
6.4 |
|
31 - 35 |
6.5 |
|
lFrom Davis-Carter et al. (1993). |
Rhoads et al. (1991) also noted varietal differences in tolerance
to Zn toxicity. Southern Runner had greater dry matter yield
and lower plant Zn concentration than Sunrunner at the same soil
Zn level. Davis-Carter et al. (1990, 1991a) illustrated the influence
of soil texture on critical levels. Peanuts grown on clayey soils
required lower soil pH and higher soil Zn levels to develop Zn
toxicity symptoms than peanuts grown on sandy soils.
Conclusions and Recommendations
1. Maintaining soil pH between 5.7 and 6.0 is the key to good
micronutrient nutrition for peanuts. Lower soil pH values can
lead to toxicities (e.g., Mn or Zn) or Mo deficiency, and very
high soil pH (>6.5) can result in micronutrient deficiencies
(e.g., Mn or Zn).
2. Apply 0.5 lb B acre-l when soil B <0.2 mg
kg-l (hot-water-soluble). It is important to give
an upper limit for soil B to minimize potential for B toxicity,
particularly for fine-textured soils since B buildup in sandy
soils is unlikely.
3. No Cl recommendation is warranted for peanuts.
4. No Cu recommendation should be made.
5. No Fe recommendation is necessary for peanuts grown in
the Coastal Plain, since Fe deficiency has only been reported
on calcareous soils.
6. On soils where Mn deficiency has been documented, soil
Mn application of 20 lb acre-l is recommended just
prior to planting if soil pH >6.2. If interveinal chlorosis
is evident and Mn deficiency is confirmed by plant analysis,
foliar application of 1 lb acre-l is recommended.
Repeated foliar applications may be required. Critical level
for Mn toxicity is estimated to be 10 mg kg-l (M1
extractable) in soil although the critical level is pH dependent.
Maintaining soil pH at about 6.0 will prevent most cases of Mn
toxicity or deficiency.
7. No Mo recommendation is warranted for peanuts. Increasing
the soil pH by liming usually increases available Mo to the extent
that Mo is not needed.
8. Soil critical levels for Zn deficiency and toxicity are
pH and Ca dependent, as well as being related to soil texture.
If soil Zn <2.5 mg kg-l (M1 extractable) and soil
pH 6.0, soil or foliar application
will correct Zn deficiency. If soil pH is< 6.0, soil Zn concentrations
above 10 mg kg-l (M1 extractable) could cause Zn toxicity
in peanuts.
|
Appendix 1. Sufficiency Ranges for Micronutrients
in Peanut Leaves in Coastal Plain Soils |
|
|
B |
Cu |
Fe |
Mn |
Mo |
Zn |
|
|
mg kg-l |
|
Alabama |
20-60 |
5-30 |
50-300 |
15-200 |
-- |
20-70 |
|
Georgial |
20-60 |
5-30 |
50-300 |
20-600 |
0.1-5 |
20-602 |
|
N. Carolina |
20-*3 |
5-* |
-- |
20-* |
-- |
20-* |
|
N. Carolina |
20-60 |
-- |
50-300 |
50-350 |
-- |
20-60 |
lPlank 1989.
2Cz:Zn ratio <50:1 (Parker et al. 1990).
3* = no upper limit or toxicity level designated. |
Document Prepared by:
Leigh H. Stribling, lstribli@acesag.auburn.edu
Alabama Agricultural Experiment Station
Auburn University |
