AGR-49 
LIMING AND FERTILIZING BURLEY TOBACCO
ISSUED: 3-76
REVISED: 10-85
J.L. Sims and K.L. Wells

Burley tobacco is a billion-dollar crop in Kentucky. One of every 14 jobs in Kentucky, directly or indirectly, exists because of tobacco. The effect of the more than $200 million in taxes generated annually in Kentucky by the tobacco industry is felt throughout the Commonwealth.
The dry matter removed by a burley tobacco crop can put a lot of stress on soil to provide the necessary nutrients for such intensive production during the 85-95 day growing period in the field. A good crop of burley can remove about 200 lb nitrogen, 35 lb phosphate, and 240 lb potash/acre while producing 2.5 to 3 tons of dry matter during this relatively short growing period.
Figure 1 shows the rate at which growth (dry matter accumulation) and nutrient uptake occurs during the season. These data, from University of Kentucky research, show graphically that only about a third of the dry matter and nutrient uptake takes place during the first half the season. To ensure that fertilizer is unlimiting, Kentucky burley producers have traditionally used a ton or more of mixed fertilizer (usually a 1-2-3 ratio) and 500 to 900 lb of ammonium nitrate/acre, all broadcast and plowed under or disked in before transplanting.
Continual use of such heavy fertilization has often led to early season growth problems which result in reduced yields, particularly for producers not routinely liming their fields. Good fertilizer management practices should ensure that by mid-season plants will be sound, healthy, and fast-growing, capable of maximizing yield and nutrient uptake during the last half of the season when about two-thirds of growth and nutrient uptake occurs.
During recent years another concern has been the crop's production costs, of which fertilizer makes up 15-20%. Many producers, attempting to cut total production costs, try to provide only the minimum amounts of lime and fertilizer necessary to produce a good crop. This approach is often workable because many tobacco fields have very high soil test levels of phosphate and potash having been over-fertilized in the past. In fact, soil test results often indicate no need for phosphate and/or potash to produce a high yielding burley crop. About two-thirds of the tobacco field soil samples sent to UK's Soil Testing Laboratory indicate no need for phosphate, one-third need no potash, but about half need lime to adjust soil pH to desirable levels.

Determining Lime and Fertilizer Requirements
Determining lime and fertilizer needs for burley in a particular field requires knowledge of that field's fertility status. Analysis of a representative soil sample taken from the field is the best way to get this information. Because of the high crop value and because pH levels and nutrient content can change following each production year, soil samples should be taken from tobacco fields every 1-2 years. The best time to take soil samples is immediately following harvest. This schedule allows enough time to get the results back from the testing laboratory so that when lime, phosphate or potash is needed, it can be broadcast and disked into the soil prior to seeding the cover crop. The amount of lime, phosphate and potash needed is dependent on the soil's residual status as determined by a good soil test.
UK does not offer a soil test for nitrogen since seasonal nitrogen availability is so difficult to estimate. Instead, nitrogen recommendations reflect the influence of past cropping history on the amount of residual soil nitrogen available for plant uptake.
Additionally, internal drainage characteristics of the soil, that is, how fast water percolates through the rooting zone, and data from field experiments testing nitrogen rates are incorporated into nitrogen fertilizer recommendations.

Lime and Fertilizer Recommendations
Lime
Limestone should be applied in the fail and thoroughly mixed with the soil. While applying agricultural limestone several months before transplanting tobacco is preferable, it can be applied in the spring if it can be thoroughly mixed into the plow layer by turning about 1/2 under with the cover crop and disking 1/2 into the surface when smoothing the field before transplanting.
Rates--If a soil buffer test has been made (soil buffer pH), use the amount of limestone indicated to raise soil pH to 6.6 (see Table 1). If a soil buffer test is unavailable, follow the rates shown in Table 2.

Table 1. -- Rates of Agricultural Limestone Needed to Raise Soil Water pH to 6.6 as Influenced by Soil Buffer pH.
Soil Buffer pH Reading1 Agricultural Limestone Needed (tons/A)
6.7 2.0
6.6 2.0
6.5 2.0
6.4 2.5
6.3 3.0
6.2 3.0
6.1 3.0
6.0 3.5
5.9 4.0
5.8 4.5
5.7 5.0
5.6 5.5
5.5 6.0
1 Soil buffer pH is measured in the UK Soil Testing Laboratory only when soil water pH is less than 6.0. If soil water pH is 6.0 to 6.6, apply 1-2 T Agricultural Limestone/acre.
 

Table 2. -- Rate of Aglime When Buffer pH is not Available.
Soil-Water pH Tons Limestone/A
Above 6.4-6.6 1
6.4- 5.8 1-3
5.8- 5.2 3-5
Below 5.2 5

Nitrogen
Rates -- Nitrogen fertilization rates depend primarily on the field cropping history and the type of soil. Since losses of fertilizer nitrogen may occur on sandy soils or on soils with poor internal drainage, splitting nitrogen applications on these soils is helpful. Apply 1/3 to 1/2 of the nitrogen before transplanting and the remaining nitrogen 2 to 3 weeks after transplanting.

For soil with low N levels (problem soils as mentioned above, or the first year of tobacco following a poor sod crop), use 250-300 lb of N/A.
For soil with medium N levels (first year of tobacco following a good grass or grass-legume sod), use 200-250 lb of N/A.
For soil with high N levels (first year of tobacco following a good legume sod or legume cover crop), use 150-200 lb or N/A.
For continuous tobacco, add 50 lb of N/A to the amount shown above.

Time and Method -- Currently, most nitrogen fertilizer is broadcast within 4 weeks of transplanting with some side-dressed 4 to 5 weeks after transplanting. Since Kentucky usually has large rainfall amounts during April and May, applying the broadcast nitrogen as near to transplanting (10 days to 2 weeks before) as possible will significantly lessen the chances for losses of applied nitrogen. Apply the nitrogen after plowing and disc into the surface soil.
Further efficiencies in nitrogen use, decreased manganese toxicity and increased early growth may be obtained by banding all the nitrogen (sidedress) after transplanting. These bands should be applied 10 to 12 in. to the side of the row in either 1 or 2 bands, and at depths of 4 to 5 in. The nitrogen should be banded all within 10 days after transplanting or in 2 applications, 1/2 within 10 days and 1/2 at 4 or 5 weeks after transplanting.

Phosphate and Potash
Rates -- Phosphorus and potassium fertilizer additions should be determined by soil tests. Based on these tests, apply the amounts shown in Table 3.

Table 3. -- Rates of Phosphate and Potash at Different Soil Test Levels.
Soil Test Level
Lb/A to Apply Burley
P2O5 K2O
Very high (above 80 P, 450 K)  0 0
High (80-60 P, 300-450 K) 0-100 0-200
Medium (60-30 P, 200-300 K) 100-140 200-300
Low (below 30 P, 200 K) 150-200 300-400

Secondary and Micronutrients
Sulfur -- Sufficient sulfur is available in soils from atmospheric fallout and from sulfate of potash used for tobacco. No additional sulfur fertilizer is needed.
Calcium -- Residual levels of available calcium in Kentucky soils, even when acid, are high enough for good burley production. Application of calcium solely for use as a plant nutrient is not recommended.
Magnesium -- Levels in Kentucky soils range from very high (chiefly the loess-derived soils), to somewhat low (primarily some of the sandstone-derived soils). Soil test levels are rarely low enough to justify use of magnesium as a fertilizer. UK soil test levels and the recommended amounts, are shown in Table 4.

Table 4. -- Rates of Magnesium at Different Soil Test levels.
Soil Test Level Lb Mg/A
Low (below 40) 25-50 1
Medium (41-80) 25-0 1
High (above 81) 0
1 These rates may be applied when no lime is
needed or where dolomitic lime cannot be
obtained. When lime and magnesium are needed,
the addition of dolomitic lime is preferred.

Molybdenum is recommended for use on burley tobacco either as a broadcast soil application or as a mixture in transplant setter water when the soil pH is less than 6.4. Recent research and field trials have shown that setter water applications are as effective as broadcast applications for supplying molybdenum to the crop. Molybdenum may be purchased in dry solid form or as a liquid. Either source is satisfactory when molybdenum is needed and may be applied either broadcast or in the setter water.

1. Soil Broadcast -- Apply one lb of sodium molybdate (6.4 oz of molybdenum)/acre. Dissolve this amount of dry sodium molybdate (or 2 gal of 2.5% Mo liquid product) in 20 to 40 gallons of water and spray uniformly over each acre. Apply prior to transplanting and disc into the soil. Since sodium molybdate is compatible with many herbicides used on tobacco, it may be mixed with herbicides normally applied as a spray in water to save application costs since only one trip over the field is necessary. It is recommended that not more than 2 lb of sodium molybdate (12.8 oz of molybdenum)/acre be used during a 5-year period.

2. Setter Water -- Use 1/4 to 1/2 pound sodium molybdate (1.6 to 3.2 oz of molybdenum)/acre. If dry sodium molybdate is used, divide the total recommended amount (1/4 to 1/2 lb/A) equally among the number of 52 gal barrels of water used/acre. For example, if 8 barrels of water/acre are used, add 1/8 (0.2 to 0.4 oz sodium molybdate) of the total recommended amount to each barrel and fill the barrel with water. Adding the dry material prior to filling the barrel will help it dissolve and mix. If a 2.5% liquid source of molybdenum is used with 8 barrels of setter water/acre, add 1/2 to 1 pt (1 to 2 cups) of the liquid product/barrel prior to filling the barrel with water.

Iron, Copper, Zinc, Manganese, Boron -No need for these micronutrients has been found for burley production in Kentucky.

Selecting Lime and Fertilizer Materials
Lime
Agricultural limestone is the most economical source of lime. If it meets the minimum requirements of the Kentucky Lime Law, its purity will be no less than 80% (calcium carbonate equivalent); would pass a 10-mesh screen; and at least 35% would pass a 50-mesh screen. Such a product will have a relative neutralizing value of 50%. UK lime rate recommendations are based on use of agricultural limestone with a relative neutralizing value of 67%. County agricultural agents have up-to-date information on the relative neutralizing value of agricultural limestone produced by quarries in the state, most of which exceed the minimum requirements.
Finely ground limestone, commonly sold at farm supply stores throughout Kentucky's burley growing area, can be broadcast and disked in just before transplanting. Pelleted lime is another fast reacting product manufactured by granulating very fine lime to make it more easily handled. Both bagged, fine lime and pelleted lime will be considerably more expensive than regular agricultural limestone. Their best use is for situations where a relatively rapid neutralization of soil acidity is desired. Both of these fast-acting lime sources can also be used in "rescue" procedures to alleviate manganese toxicity after transplanting. A broadcast application of about 1000 lb/A, followed by a cultivation to work it into the soil, sometimes relieves manganese toxicity symptoms of growing plants.

Commercial Fertilizers
To supply the needs for good burley production based on soil test results, some combination of straight materials (those guaranteeing only one nutrient such as ammonium nitrate, triple superphosphate, or sulfate of potash) and/or mixed materials (those containing more than one nutrient such as a 5-10-15 or 10-20-20 grade) will be required. Although many burley growers commonly use mixed fertilizer of a 1-2-3 ratio, there is no agronomic basis for a 1-2-3 ratio of N:P2O5:K2O being best suited for burley production. If mixed fertilizer is needed as determined by a soil test, the ratio of the grade purchased should reflect the amount of fertilizer recommended. With the high levels of fertility currently existing in many burley fields, grades of a 1-2-3 ratio many times do not supply phosphate and potash in the ratio really needed.

1. Straight Materials
Nitrogen Sources -- All commonly available N sources can be used satisfactorily on tobacco, particularly on well-drained soils where a good liming program is followed and soil pH is maintained in the range of 6.0 to 6.5. Table 5 compares the effect of acid-forming and non acid-forming nitrogen fertilizers on soil pH.

Table 5. -- Effect of Liming an Acid Soil Prior to Use of Acid Forming
(Urea) and Non-Acid Forming (Sodium Nitrate) Sources of Fertilizer Nitrogen.
Rate of Lime Tons/A N1/Source Yield Lb/A
Leaf Characteristics
Soil pH2
Manganese Ppm Molybdenum Ppm
0 Sodium Nitrate 2612 170 0.22 5.3
0 Urea 2358 673 0.14 4.7
5.0 Sodium Nitrate 2765 116 0.50 5.8
5.0 Urea 2647 101 0.41 5.7
7.5 Sodium Nitrate 2772 108  0.60 6.3
7.5 Urea 2750 107 0.58 6.0
1 Both N sources applied at 225 lb N/A pre-plant.
2 Soil pH (water) measured at midseason of each year. Soil pH before liming was 5.4.

The greatest difference in yield occurred when no lime was used. In that case, soil pH dropped to 4.7 during the growing season where urea was used, but hardly changed where the non-acid forming all-nitrate N source was used. When the soil was limed to offset the acid-forming potential of urea, no significant difference between N sources existed. These data also show that leaf concentration of manganese (Mn) was greatly increased when urea was used without liming the initially acid (pH 5.4) soil. Leaf concentration of molybdenum (already deficient) correspondingly dropped to even lower levels. But with use of lime, urea performed agronomically as well as the nitrate source of N. If soil pH is moderately to strongly acid (pH 6.0 or below) and no lime is applied, using a non-acid forming source of N (sodium nitrate, calcium nitrate or nitrate of soda-potash) will lower the risk of manganese toxicity. Use these sources (or ammonium nitrate or potassium nitrate) for side-dressing since nitrate is more mobile in soil than ammonium nitrogen. If tobacco is grown on sandy soils or soils which tend to waterlog, regardless of pH, using ammonium sources (urea, ammonium nitrate, ammoniated phosphates, ammonium sulfate, nitrogen solutions) will lower the risk of leaching and denitrification losses. Nitrogen content of sources commonly used for burley in Kentucky is shown in Table 6.

Table 6. -- Nitrogen Concentration of N Fertilizer Sources.
Nitrogen Material % Total N LB/N per Ton Material (approximate)
Urea 45 to 46 900
Ammonium nitrate 33.5 to 34.5 670
Nitrogen solution 28 to 30 560
Ammonium sulfate 20 to 21 400
Calcium nitrate 15 to 16 300
Sodium nitrate 16 320
Nitrate of soda-potash 15 300

Phosphate Sources -- Triple superphosphate is the most commonly used straight phosphate material. It contains 44 to 46% available phosphate and has no agronomic limitations. Other sources sometimes used are ordinary superphosphate (20% available P2O5) and ground, raw rock phosphate. Although ground rock phosphate has a relatively high content of total P2O5 (27-41%), its availability to plants is quite low. Phosphate fertilizers can safely be applied in the fall by disking in just before seeding the winter cover crop.

Potash Sources -- Because a large price difference has recently developed between the preferred source of potash for tobacco (sulfate of potash) and the other widely available source (muriate of potash), there has been great interest in the cheaper source (muriate of potash). Recent research at the University of Kentucky has shown that spring applications of chloride- containing fertilizers, such as muriate of potash (KCI), above 50 lb of chloride/ acre, leads to excessive levels of chloride in the cured leaf of burley tobacco, increased curing and storage problems, decreased combustibility of leaf and ultimately greatly reduced quality and usability of cured leaf.
Although several field experiments have shown a yield increase to spring applications of muriate of potash, chloride content of the leaf lamina, particularly at the higher rates of application, is increased. Such increased chloride levels are usually associated with lower leaf grades. Table 7 shows the effect of fail and spring application of muriate of potash on leaf concentration of chloride. Consequently, sulfate of potash (K2SO4) should be the major source of potassium if applied in the spring. Because animal manures contain chlorine, applications of manure should not exceed 10 tons/acre and should not be applied with potash fertilizer other than sulfate of potash in the spring.
Fall application of chloride-containing fertilizers (prior to January 1 of the production year) will greatly minimize increases in chloride concentration of cured leaf but may lead to somewhat higher levels than spring applied sulfate of potash. Neither source of potassium (KCI or K2SO4) should be applied in the fall on sandy soils since the potassium will leach out of the soil over the winter. Research to date indicates potassium does not leach appreciably during winter and spring when applied in the fall to silt loam or other fine textured soils in Kentucky.

Table 7. -- Effect of Rate of Muriate of Potash and Date of Application on Chloride Concentration of Cured Leaf Lamina.
Rate of KCI lb/A Date Applied
Leaf Position on Stalk
Tip Mid-Upper Mid-Lower Flyings
% Cl
200 October 0.54  0.51 0.53 0.57
April 0.57 0.53 0.73 0.75
400 October 0.50 0.52 0.49 0.57
April 0.64 0.68 0.89 0.92
800 October 0.86 0.65 0.92 0.80
April 1.89 1.72 1.66 2.35

2. Mixed Materials
Liquid vs. Dry Fertilizer -- Fluid fertilizers in various forms (clear liquids or suspensions), grades and ratios are an important segment of fertilizer usage in Kentucky. They represented 15% of total fertilizer tonnage used in 1981-82 and 10% of total fertilizer tonnage used in 1982-83. However, most of this fluid tonnage is nitrogenous material (anhydrous ammonia and UAN solutions). About 4% of the total mixed fertilizer tonnage used during 1981-82 and 1982-83 was in fluid form. Solid fertilizers are currently the most commonly available form in Kentucky, either as materials or mixtures. However, fluid mixtures are available in some Kentucky localities, and fluid materials are generally available statewide.
Fluid mixed fertilizers have been shown in numerous field and laboratory tests to be equivalent to dry mixed fertilizers. For this reason, agronomists generally have no basis to predict any difference between the agronomic effectiveness of fluids or solids when applied in the same manner at the same rate of actual nutrients. A producer should determine whether or not to use fluid or solid mixed fertilizer by considering only such factors as convenience, how it fits into his program, cost, and flexibility.
To determine the plant food content of some volume of fluid fertilizer, the weight of that volume must first be determined. Generally speaking, fluid fertilizers weigh 10-12 lb/gallon, depending on the product. Once gallons are converted to pounds, plant food content is calculated just as with dry fertilizers since the guaranteed fertilizer analysis is on a percent-by-weight basis.

Organic Sources of Nutrients -- Many growers apply animal manures, tobacco stalks or tobacco stems to fields. Such practices add nutrients to the soil and fertilizer rates should be reduced accordingly as shown in Table 8.

Table 8. -- Nutrient Content of Organic Sources.
Material Applied For each ton/A of material applied, reduce fertilizer rates (lb/A) as follows:
N P2O5 K2O
Animal manure 1
Dairy cattle (80% water)
11 5 12
Hogs (75% water) 10 6 9
Poultry (55% water) 31 18 8
Horses (60% water) 14 5 14
Sheep (65% water) 28 10 24
Tobacco stalks 30  10 70
Tobacco stems 30 10 140
1For tobacco production, do not apply more than 10 T/A of animal manure because of high chlorine content.

Transplant-Water Fertilization -- Although somewhat unclear, research on N-P2O5-K2O fertilizer in the transplant water finds the practice questionable when N-P2O5-K2O fertilizer has been broadcast and disked in before transplanting. Best results are likely to result when this practice is combined with a post-transplant band application of fertilizer, because small transplants need only a small amount of nutrients in the transplant water. The slight decline of soil pH around the roots will not suppress root development until roots are able to reach the post-applied band application of N-P2O5-K2O. It is generally agreed that transplant water fertilizer should contain a much higher proportion of phosphate than nitrogen and potash. Some UK research has shown that 3 gal/acre of a 7-14-7 grade liquid fertilizer mixed with the transplant water is effective for transplant water fertilization.
As discussed under micronutrients, molybdenum in transplant water is an efficient way of applying it when needed (soil pH below 6.4).
Foliar Fertilization -- University of Kentucky research has shown no value to foliar application of fertilizer at topping.

Broadcast vs. Band Fertilizer
Generally, research has shown that only 1/2 to 2/3 as much fertilizer is required to produce maximum crop yields when properly banded as when it is broadcast. However, the magnitude of plant response to banding compared to broadcast applications varies widely with soil nutrient levels, soil temperature, soil pH, and the mobility of the nutrient being applied. Greatest benefits from banding result from (a) applications to soils having low or very low soil test levels of the nutrient in question, (b) applications to crops grown in cool soil, (c) applications to either acid or alkaline soils, and (d) applications of nutrients designated as being immobile in soil. In contrast, broadcast and band applications have about equal efficiencies on soils with medium to high soil test levels, neutral pH, high temperatures, and when the nutrient is considered to be a mobile nutrient in soil. Because of the potential for greater efficiency from banded fertilizers, banding may be one way to lower fertilizer costs under certain conditions.
In addition to banding's potential for more efficient nutrient use, recent University of Kentucky research has suggested other advantages including less manganese toxicity, improved early growth, fewer days to maturity and increased cured leaf yields (Table 9). These advantages occur primarily because the fertilizers are placed between the rows allowing transplants to become established before roots permeate the fertilized soil zone. High rates of commercial fertilizers applied to tobacco soils through commonly used broadcast methods greatly increase the salt concentration of the soil solution and decrease soil pH 0.5 to 1.0 pH unit. Such changes in the soil may result in damage to plant roots, cause nutrient toxicities or deficiencies and adversely affect plant growth and yield. Banding of the fertilizer appears to alleviate many of these problems. Research on the best system for banding continues to proceed along several avenues.

Table 9. -- Effect of Broadcasting and Banding Fertilizer on Burley Tobacco.
Crop Characteristic
Location
Frankfort
Lexington
Broadcast Band 1 Broadcast Band 1
Leaf Manganese (ppm) 45 days after transplanting 153 114 111 73
Early season growth dry wt (g/plant) of all above-ground portion of
plant 45 days after transplanting
50 62 29 35
Days from transplanting to flowering -- -- 71 69
Cured leaf yield (lb/A) 2790 2950 2992 3260
1 Fertilizer was placed in a band 12 in. from the row, 4 to 5 in. deep, 5 days after transplanting.

Steps in Developing a Good Fertilizer Program For Growing Burley Tobacco
1.Soil test each year immediately after harvesting so that any needed lime, phosphate and potash can be spread onto fields before they are disked and seeded with a cover crop.

2.Seed a cover crop after harvest each year to prevent erosion and conserve soil nutrients.

3.Minimize the likelihood of manganese toxicity by liming burley fields to pH 6.6 (this will prevent the normally occurring pH drop after fertilization and plowing from getting low enough to release large amounts of soil manganese).

4.Use only the amount of phosphate and potash indicated by soil test results. Application of needed kinds and amounts is much more important than using a specific fertilizer grade.

5.Time nitrogen application to soil type. All nitrogen on well drained soils can be broadcast and disked-in just ahead of transplanting. For soils which waterlog or percolate water slowly, apply no more than 1/3 to 1/2 the total N ahead of transplanting and sidedress the remainder (this minimizes fertilizer nitrogen losses from such soils). Do not apply nitrogen fertilizer in the fall in Kentucky.

6.Apply molybdenum in the transplant water on soils testing less than pH 6.4

7.Do not use muriate of potash on tobacco fields after January 1 since it will result in elevated leaf chloride levels and can lower quality.

8.Rotate tobacco with a sod crop (clover-grass mixture) every two years if possible. This will help maintain good physical condition of the soil.

9.Do not plow or disk fields when they are too wet.