Chapter 6
Calcium and Magnesium
S. C. Hodges, G. J. Gascho, and G. Kidder
The unique fruiting habit of the peanut plant and the importance
of calcium (Ca) in pod development make Ca a primary feature
of any peanut fertility program. For over 50 years, the role
of Ca and the means of ensuring adequate supplies have occupied
the thoughts of scientists and growers alike. While few will
debate the major principles involved in Ca nutrition, there have
been disagreements on the soil test levels needed to maintain
maximum production and the means of supplying these levels.
While magnesium (Mg) has demanded much less attention in peanut
production than Ca, deficiencies have been reported on sandy
soils of the Coastal Plain (Adams and Hartzog 1980, Walker et
al. 1989). Peanut requirements for Mg are quite low, but Mg must
be considered for its role in peanut production, and as part
of the total cropping system.
Current Calibration
Soil test ratings for Mehlich-1 extractable Ca and Mg vary
considerably among states (Table
1). Alabama, Florida, and Georgia rate peanuts separately
from other crops. In the remaining Coastal Plain states, where
virginia market types predominate, Ca ratings are essentially
the same for all crops, perhaps reflecting the fact that all
peanuts will automatically receive application of gypsum. Georgia
is the only state that bases its rating on samples taken from
the fruiting zone after plants emerge.
Supplemental Ca recommendations also vary, primarily based on
the market type of peanut grown. All states except Alabama recommend
gypsum applications for virginia market types and seed peanuts
regardless of soil test Ca (Table
2). Alabama is the only state that currently recommends reduced
rates of gypsum as soil test Ca increases. Since guaranteed analysis
of products sold in the state currently range from 15 to 21%
Ca, Georgia recommends application rate be based on the Ca content
of gypsum. Although not mentioned in the reference by Cope et
al. (1981), Alabama growers are advised to add lime after deep
turning to concentrate the lime near the soil surface. Additional
gypsum is recommended following this practice only where soil
Ca levels are “low” (Hartzog and Adams 1988).
Florida recommends Mg at both “low” and “medium”
ratings, while Alabama does not recommend treatment other than
the use of dolomitic lime where soil tests indicate a need for
lime (Table 2). Other states recommend Mg at rates ranging from
10 to 35 pounds Mg per acre when soils are rated “low.”
Calcium
Research Review
The unusual interest in Ca nutrition of peanuts results from
the striking and well-documented effects of Ca deficiency on
peanut yields, grades, disease resistance, and seed germination.
Peanuts are very efficient in obtaining other nutrients, but
because of their unusual fruiting habit, developing pods must
obtain their Ca directly from the soil solution. This results
in unusually high soil requirements relative to other crops that
are able to supply Ca to developing fruit through xylem transport.
These features of Ca nutrition of peanuts were extensively reviewed
by Cox et al. (1982). This review will concentrate on the assessment
of residual Ca levels and corrective treatments to ensure adequate
Ca in the fruiting zone during fruit development.
Critical Soil Calcium Levels
From a practical standpoint, the farmer must ensure an adequate
supply of Ca in the fruiting zone during pod development. This
can be accomplished in a number of ways. Residual soil levels
may be adequate, and the grower simply needs to confirm this
through a reliable soil testing procedure. Otherwise, supplemental
Ca can be added as lime or gypsum. Cox et al. (1982) concluded
that Mehlich-1 Ca levels of 125 mg kg-1 were adequate
for runner and spanish market types, while 250 mg kg-1
were required for virginia market types. Several states have
since studied the levels of soil Ca required to achieve maximum
yields.
Alabama
A long-term, on-farm testing program with gypsum and lime has
been used to establish and confirm soil Ca requirements of peanuts
for soils of the Coastal Plain of Alabama (Hartzog and Adams
1973, Adams and Hartzog 1980, Hartzog and Adams 1988). These
tests generally consisted of comparisons of gypsum and no gypsum
in fields planted to a single variety, or to combinations of
gypsum and liming materials. Several runner and virginia type
cultivars were tested.
Test sites were selected which were likely to respond to Ca
applications based on farmers’ soil samples submitted to
the Auburn Soil Testing Laboratory (Adams and Hartzog 1980).
These sites were predominately located in non-irrigated fields
containing loam or sandy loam soils. Farmers were responsible
for all phases of production except for application of lime or
gypsum. Yields were often not as high as well-managed research
plots, but exceeded state average yields and provided comparisons
of the treatments under numerous field conditions. Soil Ca levels
for calibration were determined in plow depth samples (6 in)
collected in the untreated check plots at the end of the growing
season.
.
Hartzog and Adams (1973) summarized the results of experiments
from 1967 to 1972 with the following statement:
The results are clear and consistent: (1)
no soil with a soil-test Ca above M80 (100 mg kg-1)
needed gypsum; (2) all soils with a soil-test Ca below L70 (87.5
mg kg-1) needed gypsum; (3) the variety had no influence
on whether gypsum was needed or not.
The lack of response to gypsum by virginia-type cultivars
did not agree with earlier reports (Cox et al. 1982). Further
on-farm tests conducted between 1973 and 1986 (Hartzog and Adams
1988) showed significant yield increases for runner types in
12 of 17 cases when the Mehlich-1 Ca was less than 100 mg kg-1,
and no yield increases in 27 cases where Ca was above this level.
Similar results were obtained in 15 studies with virginia-type
peanuts. Grade was significantly increased by gypsum for Florunner
in two cases where Mehlich-1 Ca was 110 and 120 mg kg-1,
and in one case for GK-3 (a virginia market type) at 230 mg kg-1.
On a Dothan fine sandy loam that had not been limed in 52 years,
Cope et al. (1984) reported a 21% reduction in peanut yields
relative to limed treatments. Soil Ca concentrations were 140
mg kg-1 in the unlimed soil (pH of 5.1), and 490 mg
kg-1 in the limed soil.
Adams and Hartzog (1991) recently reported increases in germination
and seedling survival of seed peanuts at soil Ca levels greater
than 120 mg kg-1, although yield and grade were not
affected.
Florida
Gypsum and liming tests in Marianna (E. B. Whitty, Univ. of Florida,
unpublished data, 1981) showed substantial differences in yield
response between Florunner and Early Giant. At a soil Ca level
of 370 mg kg-1, Ca treatments did not affect yields
and grades of Florunner, but significantly increased yields of
Early Giant. Pod rot in Early Giant was also substantially reduced
by gypsum. application. Samples taken before and after the season
showed that Ca levels dropped from 370 to 290 mg kg-1
during the season on this sandy site. Whitty et al. (1986) found
that seed germination was the most sensitive measure of Ca fertilization.
Yields in five sites were not affected by gypsum application
because of high Ca levels in the unfertilized plots (Mehlich-1
values not reported). They also reported that gypsum applications
counteracted the effects of excess K in the pegging zone.
Georgia
Calibration work in Georgia has been conducted in numerous environments,
but predominately on experiment station sites and usually under
irrigated conditions. At least 45 tests on runner market types
and 20 tests on virginia peanuts have been conducted in Georgia
since 1980 (Walker and Csinos 1980; Gaines et al. 1989, 1991;
Gascho et al. 1989, 1991; Alva et al. 1989, 1990a, 1990b; Hodges
et al. 1989). Mehlich-1 Ca levels in these studies were determined
in plow-layer samples taken before the season or fruiting zone
samples taken 10 to 14 days after planting. Soils have varied
widely, ranging from excessively well-drained Quartzipsamments
and well-drained, loamy Rhodic Kandiudults to somewhat poorly
drained Kandiaquults.
In the Georgia tests, gypsum significantly increased runner type
peanut yield in three of four cases with soil test levels less
than 100 mg Ca kg-1, in zero of three cases in the
range of 100 to 150 mg Ca kg-1, in three of eight
cases in the range of 150 to 200 mg Ca kg-1, in two
of six cases in the range of 200 to 250 mg Ca kg-1,
and in zero of 24 cases with greater than 250 mg Ca kg-1.
Most of the responses occurred on soils classified as sands,
and many have arenic horizons (greater than 20 in to the argillic
horizon).
In sandy soils, large seeded virginia market type cultivars have
consistently required higher Ca levels than runner and spanish
market types (Walker 1975, Walker and Csinos 1980, Walker et
al. 1976). Gaines et al. (1989) recently reported significant
yield increases in seven of seven experiments with virginia-type
peanuts even though Mehlich-1 Ca levels ranged as high as 700
mg kg-1. Where studies were conducted on a Rhodic
Kandiudult (Greenville sandy loam) containing from 250 to 365
mg Ca kg-1, gypsum applications did not improve yields
of either runner- or virginia-type cultivars (Walker and Csinos
1980, Walker et al. 1979, Walker and Keisling 1978). Gaines et
al. (1989) concluded that soil texture influences peanut response
to gypsum at different soil Ca levels.
A recent study in Georgia indicated that limestone, incorporated
into sandy soil with a pH less than 6.2 and a Mehlich-1 Ca less
than 200 mg kg-1 to a depth of 2 to 3 inches following
turning and prior to planting, was effective for reducing pod
rot and for increasing pod yield, grade, and value of both runner-
and virginia-type peanuts (Gascho et al. 1993). However, the
least pod rot and the greatest yield, grade, and value per acre
for the virginia type was only attained when gypsum was applied
at early bloom, regardless of limestone application. Incorporation
of gypsum prior to planting was not effective.
North Carolina and Virginia
Gypsum applied at a rate of 200 lb acre-1 in a 12-inch
band increased yields of Florigiant peanuts on a soil containing
305 mg Ca kg-1 (Cox 1972). Gypsum applications of
400 and 800 lb acre-1 did not result in additional
yield increases. No response to gypsum was found at three other
sites with soil Ca levels of 190, 360, and 440 mg kg-1.
Hallock and Allison (1981) reported yield increases for virginia
market type peanuts in 28 of 43 sites on a range of Hapludults
and Paleudults. Although soil type affected Ca uptake by seed,
yield and grade responses were not strongly correlated with Mehlich-1
Ca levels. Similar results have been reported by Coffelt and
Hallock (1986), Hallock and Allison (1980), Sullivan et al. (1974),
and Cox et al. (1976).
Corrective Treatments
If soil levels are low, supplemental Ca may be added in the
form of lime or gypsum. The lack of consistent yield increases
with lime in early studies led most growers to rely on gypsum
for supplemental Ca. Failure to integrate the concepts of critical
Ca levels, pegging zone Ca management, application timing, and
cultivar differences has until recently slowed progress in this
area.
Lime as a Ca Source
Liming has a long history of improving peanut yields in the soils
of the Coastal Plain. Reed and Brady (1948) reported that dolomitic
lime top dressed at seedling emergence was as effective as gypsum
applied at bloom in two of three cases. Cox et al. (1982) cite
two examples from sandy soils where limed plots out yielded gypsum-treated
plots under leaching conditions. Lime can improve soil conditions
for peanut growth through reducing Al, Mn, and Zn toxicity, or
through increases in soil Ca and Mg levels.
The limited solubility of lime led some to believe that it could
not supply available Ca to the fruiting zone as effectively as
gypsum. This was reinforced by studies showing limited responses
to lime. Lime application in the seed furrow at planting (Colwell
and Brady 1945) or applications in the fall prior to moldboard
plowing (Sullivan et al. 1974) were ineffective in supplying
sufficient Ca to virginia-type peanuts, not only because of their
greater Ca requirement, but also because of spatial unavailability.
Timing of applications is also important. Applications at bloom
are not effective, since the lime has insufficient time to react
with the soil before the critical uptake period (Hartzog and
Adams 1988). In many cases, results from virginia market types
were erroneously extended to smaller seeded cultivars.
Numerous studies conclusively show that lime can provide adequate
Ca for maximum yield of runner-type peanuts when applied and
incorporated into the pegging zone after moldboard plowing prior
to planting (Hartzog and Adams 1973; Adams and Hartzog 1980;
Gascho et al. 1991, 1993). Where recommended to correct low pH,
lime incorporated in the surface after moldboard plowing can
also supply Ca (at a lower cost) and eliminate a trip across
the field before bloom. Lime applied in the spring is less subject
to leaching than gypsum, and the possibility of missing a needed
gypsum application because of wet fields or scheduling problems
is averted.
Lime is not the most appropriate supplemental Ca source in all
cases. Applying lime on freshly plowed soil is difficult, increases
maintenance costs for spreader trucks, and can lead to undesirable
compaction. High flotation equipment is better suited to this
task, but very few of these expensive units are available. Many
dealers have tractor-pulled spreaders available for farmer use,
but timing can become a problem for growers with large acreage.
They must turn the land, lime, and apply herbicides before incorporation.
Overliming can become a serious problem in some areas. If poorly
drained sands of the Atlantic Coast (Aquults) are overlimed,
Mn deficiencies are frequently observed. Parker and Walker (1986)
found greatly reduced pod yield at pH 6.8 in comparison to pH
6.0 due to Mn deficiency. For this reason, excessive use of limestone
as a Ca source should be avoided. In Georgia, North Carolina,
South Carolina, and Virginia, growers are advised to keep pH
below 6.3 in susceptible soils.
In addition, other factors such as market type, contractual requirements,
soil K levels, climatic conditions, and disease problems may
influence a grower’s decision to use gypsum rather than
lime. These are discussed in more detail below (See Other Considerations).
Gypsum as a Ca Source
Although liming can improve yields of large-seeded peanuts, additional
responses to gypsum are frequently observed on limed plots (Gascho
et al. 1991, 1993).
Gypsum is a relatively soluble source of Ca compared to lime,
and generally is one and one-half to three times more expensive
than lime per unit weight. It is especially useful for supplementing
available Ca near critical uptake periods. Although nutritional
responses to sulfur (S) are seldom reported on peanuts in the
region (Cox et al. 1982), the use of gypsum also ensures adequate
S levels. While mined deposits have historically been the primary
source of gypsum, by-products from phosphorus fertilizer manufacture,
industrial acid neutralization processes, and scrubbing operations
in coal-fired power generation are becoming more important gypsum
sources.
Leaching
The solubility of gypsum leaves Ca from this source more subject
to leaching, especially in deep sands, than Ca derived from lime
(Adams and Hartzog 1980). Leaching from the pegging zone can
occur (Walker 1975, Alva et al. 1990b, Alva and Gascho 1991),
but the extent of the problem in the field is variable
Rates
Gypsum is recommended at rates ranging from 250 to 500 lb
acre-1 applied in 12- to 18-inch bands (equivalent
to 500 to 1,500 lb acre-1 broadcast) for runner peanuts,
and 600 to 800 lb acre-1 applied in bands (equivalent
to 1,200 to 1,600 lb acre-1 broadcast) for virginia
types (Table 2). There have been very few gypsum rate studies,
and in these studies yield and grade responses are seldom improved
beyond the lowest application rate. Thus, little information
is available on optimum rates of gypsum required for response.
Three experiments with large responses to gypsum indicated that
a rate of 250 lb acre-1 (12-inch band, equivalent
to 750 lb acre-1 broadcast) was as good as 500 lb
acre-1 banded (Hartzog and Adams 1988). Yields of
Florigiant peanuts were maximized on a soil containing 305 mg
Ca kg-1 (Cox 1972) by 200 lb acre-1 of
gypsum (12-inch band). In essentially all other calibration and
gypsum response studies over the last 20 years, regardless of
the market type, the lowest application rates reported have been
500 lb acre-1 (12- to 20-inch bands) or 900 to 1,500
lb acre-1 (broadcast). Additional work is needed in
this area.
Other Considerations
The decision to add supplemental Ca is not always based on
the soil Ca level or the market type grown. Various site-specific
and external factors in a given year may affect the decision.
These may include rotational effects, the potential for economic
returns, contractual obligations for seed peanuts, climatic conditions,
and other soil-based factors.
Rotational Effects
Crop rotation, or the lack of rotation, can influence the levels
of both residual nutrients and pathogens. In many irrigated fields,
it is increasingly common to see two and even three consecutive
years of peanuts, resulting in ever-growing pest and disease
problems. When following crops such as corn or cotton, the soil
K levels can be very high. In recent years, there is a disturbing
increase in some areas for growers to make direct applications
of K to peanuts, either to maintain high K levels for other crops
in the rotation or to account for K removal where peanut hay
is removed at the end of the season. As cited by Cox et al. (1982),
several studies have demonstrated the negative effects of excess
K or Mg in the fruiting zone on Ca uptake and utilization. Although
fungal pathogens are the primary cause of pod rot (Filonow et
al. 1988), gypsum has increased seed Ca contents and reduced
the incidence of pod rot in numerous studies where K or Mg is
excessive (Hallock and Garren 1968, Walker and Csinos 1980, Csinos
and Gaines 1986). Less K fertilization is a long-term remedy,
but where levels are already high, additional Ca in the form
of gypsum can enhance leaching of excess K from the fruiting
zone, and increase yield and grade (Cox et al. 1982, Sullivan
et al. 1974, Alva et al. 1990b). Georgia currently recommends
the use of gypsum where the Ca:K ratio is less than 3:1. This
recommendation was apparently based on numerous unreported observations
and field demonstrations (McGill 1981), but has not been documented.
The rather small percentage of fields most susceptible to pod
rot are typically on sandy soils low in Ca (Gascho et al. 1993)
or sites without adequate crop rotation. At present, it seems
that good Ca and K management practices will effectively reduce
the incidence of pod rot in all but a few problem fields.
Seed Germination
Seed germination is strongly affected by Ca concentration in
the seed, and therefore by soil Ca levels in the fruiting zone.
Cox et al. (1982) reported acceptable germination of virginia-type
peanuts when seed Ca concentrations were in the range of 420
to 680 mg kg-1. Adams and Hartzog (1991) found that
gypsum increased germination and seedling survival at extractable
soil Ca levels below 400 mg kg-1, while yield and
percent sound mature kernals (SMK) were not increased at soil
Ca levels of 136 mg kg-1. In a more recent study,
Adams et al. (1993) found critical seed Ca levels ranging from
381 to 414 mg kg-1 for four runner-type peanut cultivars.
They calculated that maximum germination for the various cultivars
occurred at soil Ca levels ranging from 235 to 252 mg kg-1,
but indicated that only a few soils with high extractable Ca
were included in the study, and the fact that only SMK were included
in the germination tests could well affect these critical levels.
Addition of gypsum is commonly recommended for seed peanuts (Table
2). From a pragmatic standpoint, most seedsmen require contract
growers to apply gypsum, regardless of soil Ca levels.
Soil Sampling Procedure
Various sampling methods have been used to determine soil
Ca for calibration studies. In Alabama, soil samples were taken
from the upper 6 in of the untreated check plots at the end of
the season. Preliminary studies have shown insignificant changes
in soil Ca levels throughout the season (J.F. Adams, Auburn University,
personal communication.,1991; Adams and Hartzog 1991). This sampling
method could overestimate the Ca-supplying capacity of a soil
where leaching could produce large changes within the sampling
zone. In sandy soils, such changes in Ca levels can occur following
moldboard plowing, and even during the season. Whitty (E. B.
Whitty, Univ. of Florida, unpublished data, 1981) reported a
70 mg kg-1 drop in Mehlich-1 Ca during the growing
season at Marianna, Florida. Walker (1975) mentions similar reductions
in fruiting zone Ca in Georgia, and similar declines have recently
been documented following gypsum applications (Alva et al. 1990).
To compensate for potential losses, Georgia research soil samples
were typically taken from the upper 6-inch depth upon initiation
of the experiments. Since 1984, most studies have included samples
from the upper 3 inches of the fruiting zone taken 10 to 14 days
after planting.
Hodges and Gascho (1992, and unpublished data) compared pegging
zone samples with samples taken before moldboard plowing. In
48 sites with Mehlich-1 extractable soil Ca levels less than
250 mg kg-1, two-thirds had less Ca in pegging zone
samples than in the plowed samples. One-third had more. There
was a linear relationship between the two sampling methods:
pegging zone Ca = 8.9 + 0.83 (plow-layer Ca)
r2 = 0.72; std. dev. = 34 mg Ca kg-1
A slope less than 1 indicates a potential for soil samples
taken before moldboard plowing to overestimate the pegging zone
Ca levels.
Correlation between Ca levels in pegging zone samples and Ca
levels in harvest samples was greater even though fluctuations
were still large (maximum decreases of 100 mg kg-1
and increases of 76 mg kg-1):
pegging zone Ca = -10.1 + 1.01 (harvest Ca)
r2 = 0.87; std. dev. = 25.8 mg Ca kg-1
Calcium levels decreased in 28 samples (average of 49.9 mg
Ca kg-1) and increased in 20 samples (average of 39.9
mg kg-1). In four of 16 sites with harvest Ca levels
less than 125 mg kg-1, the pegging zone Ca levels
were above 125 mg kg-1. By comparison, 10 sites with
less than 125 mg Ca kg-1 by the pegging zone test
were found to have higher Ca when samples were taken before moldboard
plowing.
These studies indicate that the potential for changes in soil
Ca following moldboard plowing, and for leaching during the season
is significant in some cases. This has become increasingly important
with the increasing use of switch-type plows that are able to
turn the soil more deeply and invert the plow layer with less
mixing. This increases the potential for bringing unsampled soil
to the surface. Such soil is usually more acid and contains less
Ca.
Synthesis
There are obvious points of agreement and disagreement on
the issue of Ca nutrition for peanuts. In an attempt to resolve
these problems, we have attempted to collect all information
possible for comparative analysis, and to analyze factors that
could account for differences. From the preceding discussion,
the primary issue to be resolved is the critical Ca level for
optimum yield. Data from numerous sources for relative yield
(untreated yield divided by gypsum-treated yield) as a function
of untreated soil Ca levels are summarized in figure 1 for runner
market types and in figure 2 for virginia market types using
the quadratic plateau technique.
Figure 1. Runner peanut yield
vs. soil Ca using a quadratic-plateau relationship. Dashed lines
indicate 95% confidence interval.
 |
Studies were initially segregated into groups of sands or loams
as well as by market type, but there were no significant differences
in the fit of curves for the different textural groups. This
does not imply that texture has no effect on ability of the soil
to supply Ca. The sands in the data set were mostly irrigated
research station plots. Irrigation alone is known to improve
Ca uptake, and this could be reflected in the combined data sets.
In addition, soil Ca levels for these plots were determined primarily
by the pegging zone method, which on these soils tends to give
higher values than are present at harvest (Hodges and Gascho
1992). It should be noted that several “outliers” indicative
of large responses to applied Ca are found above the 200 mg Ca
kg-1 level. These represent recent results from irrigated
sands conducted in relatively dry years, and cannot be easily
dismissed.
Depending on the curve-fitting method used, these data can be
used to justify a critical Ml extractable soil Ca value for runner-type
peanuts from around 125 mg kg-1 (linear plateau) to
over 300 mg kg-1. Using the regression coefficient
as the basis of comparison, an exponential equation (r2=0
.55) resulted in the best fit of the data. At current prices,
the expense of gypsum could be justified for quota peanuts when
yields fall below the 97% relative yield level. Within the lower
arm of the 95% confidence interval (figure 1), this corresponds
to a soil Ca level of 200 mg kg-1.
Figure 2. Virginia peanut
yield vs. soil Ca. Dashed lines indicate 95% confidence interval.
 |
For large-seeded peanuts, notable responses occur even above
600 mg kg-1, particularly on sandy soils (figure 2).
In this case, Ml extractable Ca does not appear to be a suitable
test method for correlating soil Ca with response to applied
Ca. The pragmatic solution is to recommend gypsum until better
testing methods are developed or until we are able to improve
our interpretation of results through inclusion of other factors.
In developing the following recommendations, we have considered
only the current state of factual knowledge. In summary, Mehlich-1
extractable Ca provides an adequate and convenient measure of
available Ca for runner-type peanuts, but not for virginia-type
peanuts. A critical level of 200 mg kg-1 appears economically
and agronomically justifiable. Limestone can provide sufficient
Ca if applied in sufficient quantities at the proper time and
in the proper manner. Further work appears justified on the best
sampling methods to assess Ca status. Until we know more about
the nature of change in soil Ca during tillage and within the
season, logic dictates that Ca is best assessed by a pegging
zone test in sandy soils. Further work is also needed to define
the effects of K and Mg on Ca availability, disease incidence,
and responses to gypsum.
Recommendations
Runner Market Types
If fall soil test results do not indicate the need for lime
and Mehlich-1 Ca is less than 200 mg kg-1, indicate
that Ca level is “low” and recommend spring sampling
in the pegging zone. If pegging zone Ca test is less than 200
mg kg-1, recommend gypsum at a rate of 250 lb acre-1
(50 lb Ca acre-1) in a 12-inch band or 750 lb (150
lb Ca acre-1) broadcast. Apply gypsum at early bloom.
If fall soil test results indicate the need for lime, apply recommended
rate of lime to the surface after moldboard plowing to ensure
the applied lime remains in the pegging zone. Incorporate to
a depth of 2 to 3 inches to increase reaction of lime with the
soil. Gypsum is not required since lime should supply adequate
Ca.
Runner Market Types for Seed Production
Apply gypsum at early bloom at a rate of 250 lb per acre-1
(50 lb Ca acre-1 in a 12-inch band) or 750 lb acre-1
(150 lb Ca acre-1) broadcast.
If fall soil test results indicate a need for lime, apply
recommended rate of lime to the surface after moldboard plowing
to ensure the applied Ca remains in the pegging zone. Incorporate
to a depth of 2 to 3 inches to increase reaction of lime with
the soil. Apply gypsum as recommended.
All Virginia Market Types
Apply gypsum at early bloom at a rate of 500 to 600 lb acre-1
(100 to 120 lb actual Ca acre-1) in a 12-inch band
or 1,500 to 1,800 lb acre-1 (300 to 600 lb actual
Ca acre-1) broadcast.
If fall soil test results indicate a need for lime, apply recommended
rate of lime to the surface after moldboard plowing to ensure
the applied Ca reamins in the pegging zone. Incorporate to a
depth of 2 to 3 inches to increase reaction of lime with the
soil. Apply gypsum as recommended.
Magnesium
Research Review
Magnesium deficiency can occur at low soil test levels, and
is most likely on deep, excessively drained sands. Brady and
Colwell (1945) found no response to Ma on a soil with an extractable
Mg content of 32 mg kg-1. Hartzog and Adams (1988)
reported no response to addition of MgSO4 on a McLaurin
loamy sand even though the Mehlich-1 Mg level was 3.5 mg kg-1.
In a comparison of calcitic and dolomitic limestone, Adams and
Hartzog (1980) found two cases where plots treated with dolomitic
lime clearly out-yielded plots treated with calcitic lime or
gypsum. The soils, a Troup and a Bonifay, had Mehlich-1 Mg levels
of 3.5 and 4 mg kg-1. They concluded that responses
could be expected at Mehlich-1 Mg levels of 3 to 10 mg kg-1
in the surface soil.
Cope et al. (1984) found no response to Mg from dolomitic lime
(vs. calcitic lime) at Mehlich-1 Mg levels of 20 mg kg-1.
They found that Mg levels in this soil increased with depth,
even on unlimed plots. Adams and Hartzog (1980) concluded that
accumulation of Mg in the subsoil may prevent accurate prediction
of Mg availability when testing only surface soil samples.
Application of Mg to Fuquay and Lakeland soils with Mehlich-1
Mg levels of 7 and 4 mg kg-1, respectively resulted
in a significant yield response on a Lakeland soil (Walker et
al. 1989). Their results over a five-year period indicated no
response should be expected when Mehlich-1 Mg levels were greater
than 11 mg kg-1. These conclusions were based on the
upper 12 inches of soil.
Schmidt and Cox (1992) reported no response attributable to Mg
on a Wagram soil with Mehlich-3 extractable levels ranging from
2 to 30 mg kg-1. With no response to Mg, critical
soil Mg levels could not be determined from yield response curves.
Based on soil and leaf Mg data and assuming a Mg sufficiency
level of 2 g kg-1 in the leaf, as currently recommended
by the North Carolina Department of Agriculture for virginia-type
peanuts, they concluded the soil Mg sufficiency level was 7 mg
kg-1 or less. Unlike previous studies, they found
that including data on Mg levels below the 20 cm depth only slightly
improved the correlation between soil and leaf Mg levels. They
concluded that evaluation of surface soil Mg appears adequate
in establishing criteria for critical soil Mg levels.
Davis-Carter et al., (1993) reported on a three-year study on
a Lakeland sand (22.5 mg kg-1 of Ml extractable Mg)
and found that excessive Mg application (50 to 100 lb Mg acre-1)
can result in reduced yields of both runner-type and virginia-type
peanuts. Therefore, Mg recommendations should not be exceeded.
Recommendations
If Mehlich-1 extractable Mg is less than 10 mg kg-1,
indicate the soil Mg level is “low”.
If lime is needed to correct soil pH, recommend dolomitic
lime.
Where no lime is needed and soil Mg is low, recommend 15 to
30 lb Mg acre-1 be applied.
Document Prepared by:
Leigh H. Stribling, lstribli@acesag.auburn.edu
Alabama Agricultural Experiment Station
Auburn University |
