The efficient use of nutrients, including those in the soil naturally
or as a result of previous fertilization and management practices,
can help reduce fertilizer costs and environmental concerns without
reducing yield or quality. This requires a well-planned fertilization
program based on soil testing, wise selection of nutrient sources
based on needs and costs, and proper application. Overfertilization
is expensive, wastes natural resources, and increases the potential
for contamination of water resources.
Soil testing is the first step in planning an economical and environmentally
sound fertilization program and is provided as a free service by
the Agronomic Division of the North Carolina Department of Agriculture
and Consumer Services. It analyzes each soil sample to determine
pH and the available levels of most major nutrients, such as phosphorus
(P205), potassium (K2O), calcium
(Ca), magnesium (Mg), and sulfur (S). It also determines soil levels
of several micronutrients, such as manganese (Mn), copper (Cu),
and zinc (Zn). The soil test report suggests application rates for
lime and for each nutrient that should meet crop needs under good
The nutrient rates suggested on the soil test report reflect only
what is found in the sample. Therefore, each sample should be taken
properly so it adequately represents the field where the crop is
to be grown. Take samples every three years (coastal plain) or four
years (piedmont) from fields tended regularly by the same grower.
Sample unfamiliar fields or those out of tobacco production for
several years several months before the first tobacco crop. Submitting
samples in the fall rather than winter or spring will enable you
to receive soil test reports quickly and allow more time for planning
fertilization programs. Soil boxes and instructions for taking samples
can be obtained at your county Cooperative Extension center.
The information below, along with your experience and a soil test,
will help determine reasonable application rates for most nutrients.
Nitrogen has a greater effect on tobacco yield and quality than
any other nutrient. Too little nitrogen reduces yield and results
in pale, slick cured leaf. Too much nitrogen may increase yield
slightly but may also make mechanical harvesting and curing more
difficult, delay maturity, extend curing time, and result in more
unripe cured leaf. Excessive nitrogen also stimulates sucker growth,
which can lead to excessive use of maleic hydrazide (MH) and increase
problems with hornworms and aphids. Nitrogen is also very
leachable, and overapplication may contribute to groundwater contamination
in deep, sandy soils.
Soil analysis is not used to estimate the nitrogen rate
needed for a specific tobacco field in North Carolina.
Rather, the 50- to 80-pound-per-acre range shown on the soil test
report is based on information from numerous field tests conducted
across the state. In these tests, a base nitrogen rate of 50 to
80 pounds per acre has given consistently good results on most soils
in most seasons. This is the total amount of nitrogen supplied by
normal applications of the N-P-K fertilizer and the sidedresser
but does not include additional nitrogen sometimes needed for leaching
adjustments. The lower portion of the range is suggested
for fine-textured, fertile soils, especially where legumes such
as soybeans or peanuts were grown the previous year. The higher
portion of the range is suggested for coarse-textured soils with
topsoils deeper than 15 inches to clay.
Suggested nitrogen rates for several average topsoil depths are
shown in Table 5-1.
Determine your portion of the nitrogen rate range primarily by topsoil
depth, or depth to clay. Fields with deeper, sandier topsoils usually
are more leachable and contain less nitrogen as humic matter than
those with shallower, more heavily textured topsoils. Generally,
you should reduce the nitrogen rates shown by about 5 to 10 pounds
per acre if the previous crop was a legume or the variety to be
planted is known to mature late or cure poorly when overfertilized
with nitrogen. Even greater nitrogen rate reductions may be needed
on dark soils with 1 percent or more humic matter. Also, when tobacco
follows a heavily fertilized but poor corn crop (less than 75 bushels
per acre), the residual nitrogen available for the tobacco may be
as high as that left by soybeans or peanuts.
Only 15 pounds of extra nitrogen may reduce leaf quality, particularly
in dry seasons. Both drought and excess nitrogen delay maturity
and increase the amount of unripe tobacco. The first step to increasing
the amount of ripe tobacco is to use a reasonable base nitrogen
rate (particularly if irrigation is not available and mechanical
harvesting is used), depending on topsoil depth, previous crop,
variety to be grown, and experience. Also, be cautious and conservative
with leaching adjustments for nitrogen. (See next section.) The
second step is to delay harvest, if necessary, and make three or
more primings so that each priming will have a high percentage of
ripe leaves. The rate of ripening primarily depends on the
amount and distribution of water, nitrogen rate, soil type, and
variety, so base your harvest rate on these factors, not on the
calendar date or how fast your neighbor's tobacco is being harvested.
Table 5-1. Base Nitrogen Rates for Tobacco in Relation
to Topsoil Depth
|aDoes not include leaching
The normal ripening process is caused by partial nitrogen
starvation, which should begin about topping time. This means
that nitrogen in the soil should be near depletion by that time. Overapplication
of nitrogen and/or prolonged drought extends nitrogen uptake beyond
topping time and therefore delays ripening because the crop is still
absorbing nitrogen. Leaves harvested when they are high in nitrogen
are more difficult to cure and often turn dark at the end of yellowing
and into the leaf-drying stage. This problem is increased by dry,
hot conditions, which cause the leaves to appear riper than they really
Leaching. Leaching is the movement of certain
nutrients below normal rooting depth due to excessive water moving
(percolating) through the root zone of deep, sandy soils. Leaching
of nitrogen is more likely to reduce yield and quality than leaching
of other nutrients. Although leaching losses of sulfur, magnesium,
and potassium sometimes occur, their effects on yield and quality
are relatively small.
More than 50 to 80 pounds of nitrogen per acre may be needed if
leaching occurs, but determining the correct amount to replace is
one of the most difficult and risky tasks in tobacco production.
A general guide for making leaching adjustments for nitrogen is
shown in Table 5-2.
The amount of nitrogen to replace is expressed as a percentage of
the suggested base rate that was applied before leaching occurred.
If you used excess nitrogen before leaching occurred, subtract the
number of excess pounds from the number of replacement pounds calculated.
This guide is based on three major factors that influence the amount
- topsoil depth to clay,
- the age of the crop when leaching occurs, and
- the estimated inches of water that move through the fertilized
Topsoil depth is used in the guide because water usually moves
more freely and in larger quantities through deeper topsoils. Since
the mass of tobacco roots normally occurs in the upper 12 to 14
inches of soil, the deeper the clay below rooting depth, the more
likely nitrogen is to leach below the root mass.
Crop age is included in the guide because plants absorb more of
the needed nutrients as they get older, and the amounts left in
the soil and subject to leaching decrease as the crop grows. Too,
as the plants get larger, their leaves form a canopy that sheds
some of the water to the row middles, reducing the amount of water
passing through the fertilized zone.
A reasonable estimate of the amount of water that enters
the soil and ultimately percolates through the root zone is necessary
for the adjustment procedure to be reliable. Amount of
rainfall alone usually is not a good indication of how much leaching
has occurred. Factors such as soil texture and slope, crust formation,
duration of rainfall, and the amount of moisture already in the
soil also are important.
Unfortunately, a practical method that includes these many percolation
factors has not been developed, but growers who have experienced
similar rainfall on their land in past years can make reasonable
estimates. An invaluable tool in making leaching adjustments
is an up-to-date record of daily rains and estimates of how much
of each rain soaked into the soil.
Because phosphorus leaches very little in our soils, it is expensive
to use phosphorus-containing fertilizers, such as 3-9-9 or 6-6-18,
to make leaching adjustments. Some growers do this, however, to
supply additional sulfur (S), magnesium (Mg), or both along with
nitrogen for adjustments on deep, sandy soils. These nutrients can
be supplied at lower cost by using 13-0-14 or an 8-0-24 that guarantees
sulfur and magnesium, which is less expensive and just as effective
as using any phosphorus-containing fertilizer for leaching adjustments.
Another alternative is to mix equal amounts of Sul-Po-Mag (K-Mag)
and one of the 1:0:0-ratio sidedressers. For example, an equal mixture
of 16-0-0 fertilizer and Sul-Po-Mag gives an 8-0-11 N-P-K analysis,
which also provides 5 percent magnesium and 11 percent sulfur. (If
additional nitrogen is not needed, about 100 to 150 pounds of Sul-Po-Mag
per acre usually will supply adequate sulfur and magnesium.)
Drowning. Distinguishing between drowning and
leaching is often confusing because excess water causes both problems.
Leaching is usually not a serious problem on soils that have clay
within 10 to 12 inches of the surface because percolation through
the root zone is restricted. If the soil becomes saturated, oxygen
starvation and then root decay will begin unless the saturated condition
is alleviated within about 24 hours. Usually, the plants yellow
and partially or completely wilt. Wilting is a symptom of
drowning and indicates that leaching losses are minimal because
water remains in the root zone rather than moving through it.
Although some nitrogen may be moved down to the clay, causing a
temporary deficiency, it will be absorbed later as root growth resumes.
Table 5-2. Nitrogen Adjustments for Leaching
(inches to clay)
Percolated through Soil
|Weeks after Transplanting
|(% of applied N to replace)a
|Less than 10
3 or more
|10 to 16
3 or more
|17 or more
3 or more
|aApply about 1 pound of
potassium (K20) for each pound of nitrogen used as
a leaching adjustment if the topsoil is deeper than 10 inches.
Adding 10 to 15 pounds of extra nitrogen in most drowning situations
usually benefits the crop if it was not overfertilized with nitrogen
before drowning. However, using the leaching adjustment procedure
on a drowned crop often overestimates the amount of nitrogen to replace
and results in overapplication.
Fertilizer Additions on Partially Drowned Tobacco. Heavy
and frequent rains may cause drowning (i.e., root injury). Deep
rooting is limited as long as the soil remains saturated, confining
root development to the upper 6 to 10 inches. Many growers make
at least one application of dry or liquid fertilizer following drowning
in an attempt to reduce losses in yield and quality. Experiments
were conducted on research stations near Kinston and Clayton in
1995 to evaluate the effects of soil-applied fertilizer materials
on yield and quality of partially drowned tobacco; the term "partially
drowned" is used because the tobacco remained wilted for only several
days and then recovered. The fertilizers used are shown in Table 5-3;
the results are averages of two nitrogen rates at Kinston (15 and
30 lb/a) and one nitrogen rate at Clayton (20 lb/a). All fertilizer
treatments, made in one application on June 20, improved yield and
value per acre compared to the nonfertilized control; the 16-0-0
and 30 percent liquid nitrogen fertilizers increased yield and value
about 10 percent, while the 15-0-14 and 8-0-11 fertilizers increased
yield and value about 15 percent. This indicates that the potassium
supplied by the 15-0-14 and 8-0-11 fertilizers may have improved
yield more than the 16-0-0 and 30 percent liquid nitrogen fertilizers
that supplied only nitrogen. Compared to the control, none of the
fertilizers improved grade index or average market price.
These same fertilizers were applied at two nitrogen rates at the
Kinston station. The results in Table 5-4
indicate that using them at rates to provide 30 pounds of nitrogen
per acre was no more effective than using them at rates to provide
15 pounds of nitrogen per acre. In addition, the nitrogen rate did
not affect grade index or average market price. The plant roots
in these tests never regained normal development and/or function
following the extended drowned period. Therefore, the crops did
not respond fully to the applied nutrients. Unfortunately,
the results of these tests indicate that much of the extra fertilizers
applied to drowned crops does not benefit them. Observations
on farms in 1995 indicated that the more severe the drowning (i.e.,
root injury), the less likely the crops were to recover, regardless
of the kinds or rates of fertilizers used.
Foliar spray treatments with 30 percent liquid nitrogen were also
evaluated in these and other tests in 1995, but the results probably
are not reliable due to frequent showers within several hours after
application. In addition, several close observations later in the
season did not reveal any greater visual response to the foliar
spray treatments than to the fertilizers shown in Table 5-3.
Foliar Sprays to Supply Extra Nitrogen. When excessive
rain falls between lay-by and topping, the crop may turn yellow
when the plants are too tall to band-apply dry fertilizers with
tractor-mounted applicators. Consequently, some growers consider
applying foliar sprays or dry materials overtop to supply extra
nitrogen. Research has shown foliar sprays on tobacco to be of questionable
value because most contain so little nitrogen that several applications
are needed to be beneficial (10 to 15 pounds per acre). Also, substantial
leaf injury may occur on tender crops if high rates are used to
reduce the number of applications. Other possible disadvantages
for some foliar products include (1) the cost is high per unit of
nutrient and (2) a major portion of the nitrogen may be in the ammonium
form. Results from recent tests indicate that 16-0-0 fertilizer
applied overtop or 30 percent liquid nitrogen applied as a wide
band in the row middles is as or more effective than foliar sprays,
and all of the needed nitrogen can be applied in one application
without injuring leaves.
Table 5-3. Effects of Fertilizer Additions on Yield
and Value of Partially Drowned Tobacco, 1995a
|aAverage results of tests
conducted at research stations near Clayton and Kinston; N rates
for each fertilizer were 15 and 30 lb/a at Kinston and 20 lb/a
at Clayton. Adjustments were applied on 6/20/95; BC-OT = broadcast
overtop of plants and WB-RM = wide band sprayed in row middle.
Table 5-4. Effects of Nitrogen Rate Adjustments
on Yield and Value of Partially Drowned Tobacco, 1995
|aResults averaged over
16-0-0, 30 percent liquid N, 15-0-14, and 8-0-11 fertilizers
for each N rate. Test conducted at Lower Coastal Plain Research
Station near Kinston.
and Potassium (K20)
Phosphorus is not very leachable, even in sandy soils, and a good
tobacco crop only removes about 15 pounds per acre (as P205).
However, many times this amount has been applied annually or biennially
to most tobacco fields over the years, resulting in at least "high"
levels of available phosphorus in about 85 percent of the fields
used for tobacco.
Potassium is leachable, especially in deep, sandy soils, and a
good crop removes about 90 pounds per acre (as K20).
However, about 60 percent of our tobacco soils contain at least
"high" levels of available potassium because of more abundant soil
sources and excessive application. Also, subsoils in tobacco fields
often contain substantial amounts of potassium and other leachable
nutrients that are seldom measured by soil tests because only topsoils
are usually sampled (Table 5-5).
Table 5-5. Average Soil Test Levels of Several
Nutrients in Topsoils and Subsoils of 13 Flue-Cured Tobacco Fields,
||(% of CEC)
|a 0-10 = very low; 11-25
= low; 26-50 = medium; 51-100 = high; 100+ = very high
These results represent primarily coastal plain soils and should be
considered as preliminary at this point, but do provide additional
evidence that application of several leachable nutrients above soil
test recommendations usually does not improve tobacco yield and quality,
but does increase production costs. In addition, overapplication
increases the potential for these nutrients to reach our ponds and
streams by soil and water movement.
Selecting the N-P-K Fertilizer
Growers with access to fertilizer blend plants can save money by having
their N-P-K fertilizers blended according to specific soil test suggestions.
However, standard-grade tobacco fertilizers are still predominantly
used in North Carolina. Most contain three times more potassium than
nitrogen but varying amounts of phosphorus relative to nitrogen and
potassium. This is called the N:P:K ratio (Table 5-6).
For example, analyses such as 6-6-18 and 8-8-24 are 1:1:3 ratios because
they contain 1 pound of phosphorus and 3 pounds of potassium for each
pound of nitrogen. An 8-0-24 analysis has a 1:0:3 ratio because it
does not contain phosphorus. So the primary difference among ratios
is that they supply different amounts of phosphorus for each pound
of nitrogen applied. Therefore, if you select the proper ratio
and application rate, you can obtain phosphorus rates very close to
the soil test suggestion without altering the rates of nitrogen and
Generally, the N-P-K fertilizer should supply all of the
suggested phosphorus, and possibly potassium, but no more than 40
pounds of nitrogen per acre; this is true for most soil types and
rainfall conditions. Therefore, the amount of phosphorus suggested
on the soil test report should determine which fertilizer ratio
is selected from Table 5-6.
For example, if a phosphorus rate between 0 and 40 pounds per acre
is suggested, use 667 pounds of 6-6-18 or 500 pounds of 8-8-24 fertilizer
Table 5-6. Selection of Standard-Grade N-P-K Fertilizer
Ratio, Analysis, and Rate Based on Soil Test Suggestions for Phosphorus
|P205 Suggested on
Soil Test (lb/a)
|N-P-K Fert. Selection
|Between 80 & 120
|Between 40 & 80
|Between 0 & 40
|a Based on 2000 average
costs of N-P-K fertilizers from surveys conducted by 21 county
Extension service agents across North Carolina; prices are primarily
for manufactured, bagged products.
b Analyses most commonly available; other suitable
analyses of the appropriate ratio may be available in some areas.
c Each rate will supply 40 pounds of nitrogen and
120 pounds of potassium per acre and the highest rate of phosphorus
listed to the left of each ratio.
The highest analysis available in a ratio will supply
the nutrients at the lowest cost when used at the rates suggested
in Table 5-6.
For some soils, particularly in the coastal plain, available phosphorus
is so high that the soil test report does not suggest applying it.
In these instances, applying 500 pounds of 8-0-24 fertilizer per
acre will provide 40 pounds of nitrogen, no phosphorus, and 120
pounds of potassium per acre, plus some secondary nutrients. The
zero phosphorus suggestion has caused some concern among growers.
However, the results from many field tests conducted on soils with
high to very high levels of soil test phosphorus do not reveal any
reduction in yield and quality when 1:0:3-ratio fertilizers are
used (i.e., when no phosphorus is applied). Remember, however, that
phosphorus suggestions are made on the assumption that soil pH is
maintained in the desirable 5.8 to 6.0 range. Therefore,
failure to apply phosphorus on acid soils may reduce early growth
and delay maturity, particularly when early root growth is reduced
by unusually cool, wet conditions. These unfavorable soil and weather
conditions are more likely to occur in the piedmont than the coastal
Some growers use N-P-K fertilizers at rates higher than those shown
in Table 5-6.
This is not recommended because it increases costs and supplies
excessive rates of phosphorus and potassium. Also, numerous field
tests have shown that using the N-P-K fertilizer to supply more
than 40 pounds of nitrogen per acre does not improve yield and quality
(see Table 8 on page 41 of 1991 Tobacco Information).
Additional nitrogen (and potassium if needed) can be obtained
more economically from sidedress materials than from N-P-K fertilizers.
For example, a pound of nitrogen from 6-6-18 fertilizer costs about
$1.96, while a pound of nitrogen from 16-0-0 fertilizer costs only
about 77 cents (based on average costs per ton in Tables 5-6
Use of 3-9-9 fertilizer declined from 36 percent of the acreage
in 1979 to 5 percent in 2000, while use of 6-6-18 fertilizer increased
from 3 percent to 50 percent during the same period (Table 5-7).
The combined use of 1:1:3 and 1:0:3 ratios increased from 5 percent
of the acreage in 1979 to 69 percent in 2000. These changes occurred
because many growers with high-phosphorus soils recognized the money
they could save by using low-phosphorus, high-analysis fertilizers
to meet soil test suggestions for phosphorus and other nutrients.
The reduction in phosphorus application of approximately
45 percent since 1981 has also lowered the potential for phosphorus
movement into ponds and streams without reducing tobacco yield and
After choosing the fertilizer ratio based on the rate of
phosphorus needed, the next step is to select a high-analysis grade
of that ratio. Although high-analysis grades cost more
per ton, they are less expensive per acre because much lower rates
are needed to provide the same amounts of nitrogen and potassium
Also, less fertilizer has to be transported, stored, and applied.
These advantages may explain the trend in recent years toward greater
use of the 8-8-24 analysis, with declining use of 4-8-12 and 6-12-18
analyses (Table 5-7).
Initially, some growers experienced curing problems with high-analysis
fertilizers because they used them at higher than suggested rates
without reducing the rage of sidedress nitrogen accordingly. Fortunately,
this problem has been largely corrected by most growers. But fertilizer
calibration information, if needed, is available at your county
Cooperative Extension center.
Table 5-7. N-P-K Fertilizer Use Estimated by County
|Percentage of Acres
Dry Versus Liquid N-P-K Fertilizers. Tests have been
conducted to compare the same analysis (6-4-10) of dry-blended and
liquid fertilizers on tobacco yield and quality. Each fertilizer was
applied broadcast, in two deep bands (about 5 inches deep and 4 to
5 inches to each side of the row), or in two shallow bands (about
0.5 to 1 inch deep and 4 to 5 inches to each side of the row). The
broadcast applications were made about one week before planting and
the band applications about one week after planting. The application
rate (670 pounds per acre) was the same for both fertilizers and for
each method of application, and all plots received the same rate of
sidedresser about three weeks after planting.
The type of fertilizer (dry or liquid) did not affect yield, market
price, grade index, or value per acre. However, deep fertilizer
placement produced higher yields than shallow placement of both
fertilizers when little rainfall occurred during the first six weeks
after planting. When the early season was unusually wet, however,
broadcast application reduced market price, grade index, and value
per acre because of a higher proportion of pale, immature tobacco.
These results indicate the following:
Fertilizer placement and time of application are more important
than whether the fertilizer is dry or liquid.
- Dry and liquid fertilizers should perform equally well if they
have similar nutrient contents and are applied at the same time
and by the same method.
- Deep band application (4 to 5 inches) should produce good yields
and quality more consistently than broadcast or shallow band application
(such as that obtained with rolling cultivators), regardless of
the fertilizer type.
The specific yield and quality data for these tests are on page
45 of 1994 Flue-cured Tobacco Information. Contact
your county Cooperative Extension Service agent for more information.
Selecting the Sidedress Fertilizer
The soil test suggestion for potassium is useful in selecting the
proper ratio of the sidedress material. When the soil test suggests
applying less than 120 pounds of potassium per acre, a 1:0:0 ratio
sidedresser such as 16-0-0 (soda), 15.5-0-0 (calcium nitrate), 34-0-0
(ammonium nitrate), or one of several liquid nitrogen sources can
be used to supply the nitrogen needed in addition to the 40 pounds
obtained from the N-P-K fertilizer. If the soil test suggestion is
greater than 120 pounds of potassium per acre or if severe leaching
occurs after the N-P-K fertilizer application, some potassium, in
addition to nitrogen, may be needed in the sidedresser. In these instances,
1:0:1 ratio sidedressers such as 15-0-14 or 13-0-14 will usually supply
all the extra potassium needed in addition to the 120 pounds obtained
from the N-P-K fertilizer. In rare instances on deep, sandy soils,
available potassium may be low enough to require use of a 1:0:3-ratio
sidedresser such as 8-0-24 or 13-0-44. However, topsoil analyses and
field tests indicate that less than 10 percent of the tobacco soils
in North Carolina are low enough in potassium to require the l:0:3
ratio as a sidedresser if 100 to 120 pounds of potassium per acre
are supplied by the N-P-K fertilizer. In addition, the accumulation
of available potassium in the subsoils of many tobacco fields (Table 5-5)
indicates that only 1:0:0 ratio sidedress fertilizers are needed in
many instances, even when topsoil analysis suggests adding more than
120 pounds per acre of potassium.
The per-acre costs of several sidedressers and the amounts required
to supply 30 pounds of nitrogen per acre are shown in Table 5-8.
At present, the least expensive dry source of sidedress nitrogen
is 34-0-0 fertilizer. However, take care to apply no more
than half as much 34-0-0 fertilizer per acre as 16-0-0 or 15.5-0-0.
Applying excessive rates of 34-0-0 fertilizer will drastically increase
nitrogen application and reduce curability and quality of cured
leaves. The most expensive sidedresser is 8-0-24 and should
be used only when the soil test suggestion for potassium cannot
be met with the 1:0:1-ratio sidedressers. An alternative and less
expensive 1:0:3-ratio sidedresser is 13-0-44 fertilizer, which should
be available at most blend plants.
Table 5-8. Average Costs of Sidedress Fertilizers
in 2000 Based on Surveys by 22 County Extension Agents
|Rates and Costs
for 30 lb N
30% N Liq.
The average performance of the most commonly used dry sidedressers
in 11 tests conducted in 1991 through 1994 is shown in Table 5-9.
The surface soils contained medium levels of available potassium in
five tests, low levels in three tests, and high levels in three tests.
All plots received 670 pounds per acre of 6-6-18 or 6-12-18 fertilizer
(120 pounds of potassium per acre) banded five to seven days after
transplanting. The sidedressers were banded about two weeks later
at equal rates of nitrogen. The results indicate that:
- Yield and quality were similar for all sidedressers even though
rainfall was relatively high at most sites in 1992 and 1994. Tobacco
topsoils often test low to moderate in available potassium, but
sidedressers containing potassium seldom increase yield or quality
because adequate potassium is usually contained in subsoils of
many tobacco fields that have clay within 10 to 12 inches of the
- Using a phosphorus-containing fertilizer, such as 6-6-18 or
6-12-18, as the sidedress fertilizer did not improve yield and
quality compared to using one of the less-expensive sidedresser
Table 5-9. Agronomic Performance of Dry Sidedress
Materials in 11 Tests, 1991 - 94
|a Initial fertilizer was
670 lb/a of 6-6-18 or 6-12-18 banded five to seven days after
transplanting; all sidedressers were banded about two weeks
later at equivalent rates of N.
Based on estimates by 26 county Extension agents, use of sidedress
materials (expressed as a percentage of acreage) in 2000 was 16-0-0,
44 percent; 15-0-14, 21 percent; 15.5-0-0, 8 percent; 30 percent liquid
nitrogen and 24 or 25 percent liquid nitrogen (+ sulfur), 7 percent;
13-0-14, 6 percent; 8-0-24, 4 percent; 34-0-0, 3 percent; and various
other local analyses, 3 percent. Unfortunately, about 4 percent of
the acreage was sidedressed with N-P-K fertilizers, the most expensive
choice, which do not improve yield or quality (Table 5-9).
This costly practice occurred in both the piedmont and coastal plain
Liquid Nitrogen Sidedress Fertilizers. Some growers
who usually need only nitrogen in their sidedress fertilizer want
less expensive nitrogen sources that can be applied faster than
dry materials. In 13 tests conducted in the 1996 through 1999 seasons,
30 percent liquid nitrogen and 24 or 25 percent liquid nitrogen
(+ sulfur) were evaluated as sidedress fertilizers against more
traditional dry sidedressers such as 16-0-0. All plots were fertilized
with an N-P-K fertilizer such as 6-6-18 several days after transplanting,
and the nitrogen sidedressers shown in Table
5-10 were applied two to three weeks later. Each sidedresser
was applied at the same nitrogen rate in each test, ranging from
20 to 40 pounds of nitrogen per acre, depending on local soil and
early rainfall conditions. The liquids were not diluted
with water, and rates ranged from about 7 to 14 gallons
per acre over the sites. All sidedressers were banded in furrows
5 to 6 inches from each side of the plants and 4 to 5 inches deep;
they were covered with soil immediately after application to guard
against possible volatilization of the urea nitrogen contained in
both liquid fertilizers.
No noticeable growth and maturity differences were observed among
the sidedressers in any test. Further, yield and grade index values
were similar for the sidedressers in all tests (Table 5-10).
While the yield for the 24 or 25 percent nitrogen sidedresser appears
to be slightly higher than that for the 30 percent liquid nitrogen
or 16-0-0, the differences were not statistically significant in
any of the 13 tests, indicating that factors other than the sidedress
fertilizer were most likely responsible for the yield differences
shown. Since these tests were conducted over a wide range of soil
and climatic conditions, growers who use these sources of sidedress
nitrogen should not experience adverse effects on maturity, yield,
and quality if the nitrogen rate is in the normal range for a given
field and if the liquid fertilizers are strained and properly banded
and covered with soil as recommended.
Table 5-10. Effects of Liquid Nitrogen Sidedresser
Fertilizers on Tobacco Yield and Grade Index in 13 Tests, 1996-99a
|30% Liquid N
|24 or 25% Liquid N + S
|aTests conducted on research
stations near Whiteville, Kinston, and Oxford.
As an example, for each 10 pounds of nitrogen needed per acre from
these fertilizers, only 3.1 gallons of 30 percent liquid nitrogen
or 3.9 gallons of 24 percent liquid nitrogen would be required per
acre. The liquid nitrogen sources will need to be diluted with water
if the liquid application equipment will not uniformly apply the 7
to 14 gallons per acre that most fields would need. However, because
no adverse stand or growth effects were observed with the undiluted
liquids, it should be sufficient to use only enough water to ensure
uniform application. If 10 gallons of volume per acre were used, for
example, a 200-gallon liquid applicator would sidedress about 20 acres
of tobacco between refills. The disadvantages of using liquid nitrogen
fertilizers compared to traditional dry sidedress fertilizers are
the requirement for liquid banding equipment and a slight reduction
in soil pH in the row (0.1 to 0.2 units in 1997 tests). However, a
number of growers have constructed their own inexpensive liquid applicators
in the last year or two, and the cost of the extra dolomitic lime
needed to correct the pH reduction is only about one dollar per acre.
Another possible advantage of liquid nitrogen sidedressers is that
they might be tank mixed with certain soil pesticides and both applied
in one trip over the field. Numerous tests conducted on research
stations have shown no adverse effects on early growth, yield, or
quality from adding 1 pint per acre of Ridomil-Gold EC with the
liquid nitrogen sources. In two additional on-farm tests conducted
in cooperation with NC State plant pathologist Tom Melton, tank
mixing Ridomil-Gold EC with 30 percent liquid nitrogen did not reduce
black shank control. In most of these tests, a compatibility agent
was included because Ridomil-Gold EC tended to float on the water,
particularly when mixed with the sulfur-containing liquid nitrogen
sources. Therefore, a "jar" test is suggested to evaluate
compatibility before tank mixing Ridomil-Gold EC with any liquid
nitrogen source. Growers are also reminded that tank mixing Ridomil-Gold
EC with liquid fertilizers is not specified on the Ridomil-Gold
EC label, so Syngenta may not assume responsibility for poor black
shank control if its product is used in this manner.
Cooperative research with NC State entomologist Clyde Sorenson
is also underway to evaluate tank mixing of Admire 2F or Platinum
2SC (a Syngenta insecticide likely to be approved for 2001) with
the liquid nitrogen sources. While agronomic and aphid control results
obtained in 2000 were encouraging, tank mixing these products with
liquid nitrogen sources is not yet labeled for grower use.
The secondary nutrients of concern for tobacco are calcium (Ca), magnesium
(Mg), and sulfur (S). These nutrients are called secondary because
they are usually needed by most crops in smaller amounts than the
primary nutrients. However, they must be available in adequate amounts
for good yields and quality.
Calcium and Magnesium (Dolomitic Lime)
If soil pH is kept within the desirable range of 5.8 to 6.0 with dolomitic
limestone, the available levels of calcium and magnesium
will usually be high enough to meet the needs of the crop. Otherwise,
40 to 50 pounds of calcium (Ca) and 15 to 20 pounds of magnesium (Mg)
per acre are needed from the N-P-K fertilizer. Even with proper liming,
some magnesium deficiency may occur on deep, sandy soils (more than
15 inches to clay) under severe leaching conditions. In these instances,
supplying 15 to 20 pounds of magnesium per acre in the fertilizer
may be desirable in the second and third seasons after lime application.
However, using N-P-K fertilizers containing calcium and magnesium
will not substitute for using dolomitic lime if soil pH is too low.
Growers should be especially aware of low soil pH. The state's latest
soil test summaries show that 29 percent of the tobacco fields tested
in 2000 had a pH lower than 5.5, and piedmont soils generally were
more acid than those in the coastal plain.
Low pH causes greater solubility of soil aluminum (and manganese
in some piedmont soils), which reduces root growth and development.
Therefore, liming to promote healthy root systems improves drought
tolerance and nutrient absorption, sometimes resulting in better
yields (see Table 5-11).
In this test, limed plots produced higher yields than nonlimed plots
regardless of nitrogen rate. Also, note that the yield of nonlimed
plots that received 15 pounds per acre of extra nitrogen was no
higher than that of limed plots that received 15 pounds per acre
less than suggested nitrogen. These data indicate:
- Extra nitrogen cannot overcome the adverse effects of low soil
- Lower nitrogen rates are possible when acid soils are limed
according to soil test suggestions.
Table 5-11. Effects of Lime and Nitrogen on Tobacco
|Suggested - 15
Sulfur deficiencies are most likely on deep, sandy soils (over
15 inches to clay) that are low in humic matter (less than 0.5 percent).
Because sulfur leaches, deficiencies are more likely in these soils
following heavy rainfall in the winter and spring, especially if
sulfur is omitted from the fertilizer of the next tobacco crop.
Symptoms of sulfur deficiency are very similar to and often mistaken
for those of nitrogen deficiency. When a plant is low in nitrogen,
the lower leaves are paler than the upper leaves and "burn up" prematurely.
However, sulfur deficiency begins as yellowing in the buds; the
leaves gradually pale from top to bottom, and the lower leaves do
not "burn up" prematurely unless nitrogen is also deficient. Because
sulfur is required for nitrogen use in the plant, adding high rates
of nitrogen to sulfur-deficient crops will not turn the crops green,
and can, in fact, reduce leaf quality. Therefore, accurate diagnosis
of the deficiency is very important and often requires tissue analysis.
Soil tests for sulfur are sometimes unreliable. Therefore,
to reduce the chance of sulfur deficiency on deep, sandy soils,
add 20 to 30 pounds of sulfur (S) per acre from the N-P-K fertilizer
every year. Sulfur deficiency occurring before lay-by can
be corrected by banding 100 to 150 pounds of Sul-Po-Mag or potassium
sulfate (0-0-50) as soon after the deficiency is identified as possible.
However, sulfur deficiency on soils less than about 12 inches to
clay is often temporary, even when no extra sulfur is applied, because
adequate sulfur is usually contained in subsoils (Table 5-5)
and will be absorbed as roots reach this depth.
Minor Nutrients (Micronutrients)
The soil test report for tobacco shows a $ symbol in the "Suggested
Treatment" block for copper (Cu) and zinc (Zn), and a $pH symbol for
manganese (Mn) if the availability index for one of these micronutrients
is low. The $ symbol indicates that corrective treatment may be beneficial,
but it is uncertain that tobacco will respond to application of copper
or zinc. The $pH symbol appears on the report when soil pH is greater
than 6.1 and the manganese availability index is less than 26 (low
or very low). The symbols also call attention to an enclosed note,
also identified by a $ symbol, that provides information on suggested
rates, sources, and application methods for these three micronutrients.
Crops differ in their response to micronutrients, and tobacco is
considered less sensitive to low soil levels than crops such as
corn, soybeans, and small grains. Micronutrients are also somewhat
expensive, depending on kind and source. Therefore, their application
for tobacco is not likely to be beneficial unless indicated by soil
or tissue analyses. When in question, tissue analysis or strip testing
on several rows may be needed to confirm a micronutrient need.
Copper (Cu) and Zinc (Zn)
Known deficiencies of copper or zinc are extremely rare for tobacco.
Rates suggested on the soil test report will be sufficient for several
years, and the time and need for reapplication should be based on
Manganese deficiency begins on the lower leaves as flecks very
similar to those caused by high ozone concentrations in the air
(commonly called weather fleck). While weather fleck can
occur anywhere in the state, manganese deficiency occurs primarily
on low-manganese, overlimed soils in the coastal plain. Using too
much lime causes soil pH to increase, which reduces manganese availability
to plant roots. Most tobacco crops that develop confirmed manganese
deficiency are grown on soils with a pH of 6.2 or higher and low
levels of soil-test manganese (availability index less than 26).
Tobacco performs well when soil pH stays in the 5.8 to 6.0 range.
Other major crops, such as soybeans, corn, and small grains, also
perform well in this pH range if soil phosphorus is high. Therefore,
when these crops are in rotation with tobacco, they usually should
not be limed at rates higher than those suggested by the soil test
Tissue analysis of flecked leaves, along with a soil test, is the
best way to distinguish between manganese deficiency and weather
fleck. However, it is important to submit leaf and soil samples
as soon as flecking occurs because several days are required to
complete analyses. If the problem is manganese deficiency, a corrective
treatment should be made as soon as possible. If it is weather fleck,
only cooler, drier weather will help.
Manganese deficiency can be corrected by soil or foliar application
of several manganese sources. Manganese sulfate is a relatively
soluble, inexpensive source that can be used for soil or foliar
treatment. The more expensive chelated sources generally perform
satisfactorily as foliar sprays but are not superior to sulfates
when applied to the soil. For soil applications, mixing the manganese
source with acid-forming fertilizers increases its effectiveness,
and banding is usually better than broadcasting. Do not apply manganese
broadcast on soils with a pH greater than 6.1 because it will be
converted to a less available form. For band application, special
blends may be required because premium fertilizers usually do not
contain enough manganese to correct a deficiency. General recommendations
for manganese application in North Carolina are about 3 pounds per
acre banded, 10 pounds per acre broadcast, or 0.5 pound per acre
as a foliar spray. Foliar application of manganese is an efficient
way of correcting an unexpected deficiency because lower rates are
often as effective as much higher rates of soil-applied manganese.
There is no suitable soil test for chloride, but this nutrient
is included in most N-P-K tobacco fertilizers. You will apply sufficient
chloride when you use N-P-K fertilizers guaranteeing chloride at
rates suggested in Table 5-6.
Suggested rates of most fumigants also supply adequate amounts of
chloride; when Telone C-17 or Chlor-o-Pic is used, it is not necessary
that the N-P-K fertilizer contain chloride. Otherwise, sufficient
chloride should be included in the fertilizer to provide a maximum
of 20 to 30 pounds per acre. Higher rates will not improve yield
but can reduce quality. Chloride may not be included in some fertilizers,
particularly blends or liquids, unless requested by the grower.
Excessive rates or improper application of some micronutrients
can cause toxicity. Contact your county Cooperative Extension agent
if you suspect you had a micronutrient problem in 2000 or if your
soil test indicates that a problem might occur in 2001. Your agent
can help you decide whether treatment is advisable and, if so, which
sources, rates, and application methods are most effective.
Other Economic Considerations
- Premium fertilizers with small amounts of several micronutrients
and 20 to 30 percent water-insoluble nitrogen usually cost $10
to $20 more per ton than regular-grade fertilizers, but the yield
or quality increases sometimes claimed for premium fertilizers
cannot be confirmed in field tests.
- Blended fertilizers generally cost several dollars less per
ton than manufactured fertilizers of the same grade; they also
perform as well as manufactured fertilizers of similar nutrient
content if properly blended.
- You can save an additional several dollars per ton if you use
bulk rather than bagged fertilizers.
- Prescription blends and liquids prepared according to soil test
specifications are often less expensive than dry, standard-grade
fertilizers, but they may not be the best choice if broadcast
application is the only option (see "Dry
Versus Liquid N-P-K Fertilizers" discussed previously in this
chapter and "Time
and Method of Application" below). Also, growers with deep,
sandy soils should make sure that the liquid or blended fertilizer
purchased will supply sulfur and possibly chloride at rates suggested
Time and Method of Application
Proper placement and timing of fertilizer application provide maximum
return for each dollar spent on fertilizers. Fertilizers should
be applied at the proper time and with the proper method to maximize
nutrient use by the crop while minimizing leaching losses and fertilizer
salts injury to roots. Four methods of fertilizer application have
been evaluated in on-farm tests under a wide range of soil and climatic
conditions. Results varied among locations, primarily because of
differences in soil moisture at and following transplanting:
- If soil moisture was adequate but not excessive, the "bands
at transplanting" and "bands within 10 days after transplanting"
methods yielded moderately better than the "broadcast" or "one
band deep" methods.
- If early leaching conditions occurred, best results were obtained
with the "bands within 10 days after transplanting" method, with
"bands at transplanting" being a close second, and the "broadcast"
method giving the poorest results.
- When the soil was dry, which contributed to fertilizer injury,
the "bands within 10 days after transplanting" method gave the
best results, and the "one band deep" method the poorest results.
- Overall, the "bands at transplanting" and "bands within
10 days after transplanting" methods produced better yields more
consistently than the "broadcast" and "one band deep" methods.
These methods are also more environmentally sound than pretransplant
methods because nutrient uptake is more efficient and leaching
losses are reduced.
The "broadcast" and "one band deep" methods may contribute to fertilizer
salts injury, particularly on sandy soils in dry seasons. Also,
because the fertilizer is sometimes applied several weeks before
transplanting with these methods, there is more time for leaching
to occur. The "bands at transplanting" and "bands within 10 days
after transplanting" methods virtually eliminate fertilizer injury,
resulting in a more uniform crop, and they may reduce leaching losses
because the fertilizer is exposed to leaching conditions for a shorter
time early in the season when leaching is most likely to occur.
A problem with the "bands within 10 days after transplanting" method
is that prolonged rains after transplanting may delay fertilizer
application for more than 10 to 14 days. Because this delay may
reduce early growth and possibly yields, many growers apply the
N-P-K fertilizer as soon as the plants regain turgor or they apply
some nitrogen (and sometimes potassium) at transplanting with equipment
("Soda-Flo") attached to the rear of the transplanter. This latter
practice may be especially beneficial on poorly drained fields when
the "bands within 10 days after transplanting" application method
is planned for the N-P-K fertilizer. However, you should reduce
the rate of regular sidedress nitrogen accordingly, if more nitrogen
is needed at all, to prevent ripening and curing problems due to
excess nitrogen. On soils where leaching is not a problem, some
growers use "Soda-Flo" as the only sidedress application, regardless
of how the N-P-K fertilizer is applied. This eliminates a trip over
the field or reduces the time and labor needed later for normal
- Have a soil sample tested to determine nutrient and lime needs.
Use dolomitic lime, if needed, to adjust pH and
supply magnesium as well as calcium. Do not overlime!
- Use a base nitrogen rate of 50 to 80 pounds per acre (total
nitrogen from N-P-K and sidedress fertilizers); your portion of
the rate range will depend on topsoil depth and texture, previous
crop grown, variety to be grown, and personal experience.
- Select a high-analysis ratio of N-P-K fertilizer that will supply
all the phosphorus suggested by the soil test when used at a rate
that will supply no more than 40 pounds of nitrogen per acre.
For many tobacco soils in North Carolina, this rate of a 1:1:3
or 1:0:3 ratio fertilizer will also supply adequate potassium.
- Consider applying 20 pounds of sulfur per acre or possibly chloride
on deep, sandy soils. There are no suitable soil tests for these
nutrients, and some fertilizers do not contain them in adequate
- Select a sidedress nitrogen fertilizer that contains potassium
only if the N-P-K fertilizer in step 3 will not supply all the
potassium suggested by the soil test. Only nitrogen from 1:0:0-ratio
sidedressers will be sufficient for many soils. Additional potassium,
if needed, can be obtained economically from 1:0:1-ratio sidedressers.
Potassium levels in North Carolina tobacco soils are rarely low
enough to require a 1:0:3-ratio sidedresser if 100 to 120 pounds
of potassium per acre are applied from the N-P-K fertilizer. In
addition, recent soil test results indicate that available potassium
in subsoils of many tobacco fields is high enough that only 1:0:0
ratio sidedress fertilizers are needed in many instances, even
when topsoil analyses suggest more than 120 pounds per acre of
potassium. However, application of a sidedress fertilizer containing
both nitrogen and potassium on partially drowned tobacco may be
- Determine and make leaching adjustments for nitrogen losses
with caution only after leaching has occurred, not on the assumption
that it will. Using the leaching adjustment procedure on drowned
tobacco often results in overapplication of nitrogen.
- Use a method of N-P-K fertilizer application that maximizes
nutrient uptake efficiency but minimizes fertilizer salts injury
and early-season leaching losses, such as the "bands at transplanting"
or "bands within 10 days after transplanting" methods. The latter
method is more risky on poorly drained soils because frequent
rains after transplanting could delay fertilizer application for
more than 10 days.