Potassium is a critical nutrient for the growth and quality of flue-cured tobacco (Sims 1985), playing a key role in various plant functions. The tobacco plant, however, is a luxury consumer of potassium, often accumulating more than it requires for optimal growth (Raper and McCants 1967; Vann et al. 2012). Potassium accumulation is significantly higher than for any other nutrient, often reaching levels twice that of nitrogen (Raper and McCants 1967).

While tobacco plants can accumulate substantial amounts of potassium, healthy crops need only about 90 pounds of potassium fertilizer (K₂O) per acre (Vann et al. 2024). In the past, growers have applied two to three times this amount to prevent visual symptoms of potassium deficiency (Sims 1985) (Figure 1, Figure 2, and Figure 3). With rising fertilizer prices and the risks associated with nutrient loss to the environment, however, such practices should be reevaluated. According to North Carolina Department of Agricultural & Consumer Services (NCDA&CS) soil test reports, about 60% of North Carolina's tobacco soils already contain "high" potassium levels (≥213 lb K₂O/acre) due to previous seasons' applications and nutrient accumulation (Vann et al. 2024); these levels often are sufficient to meet the crop's nutritional needs.

Potassium is leachable, particularly in coarse soils, whereas finer soils and those with shallower depths to clay tend to retain more potassium in the root zone. Although rainfall can cause leaching of potassium from the effective rooting zone, potassium can also be bound in clay subsoils (Vann et al. 2013), which can supply the plant with some of the needed potassium if the depth to clay is less than 18 inches. Producers are advised to remember this unique point about potassium in contrast with nitrogen, which is assumed to be at negligible residual levels from year to year and thus requires replenishment each season. In addition, the plant uptake of potassium depends on soil moisture levels—while excessive rainfall may cause leaching, drought can reduce the plant's ability to absorb potassium. Consequently, mild potassium deficiency symptoms may appear even in fields with high residual potassium levels if moisture is insufficient (Figure 1). Mild potassium deficiencies, often observed during droughts or periods of excessive moisture, typically occur at about the flowering stage of crop development.

Severe potassium deficiency symptoms (Figure 2 and Figure 3) include interveinal chlorosis of leaf tips and margins, which can spread to upper leaves and lead to yellowing, browning, and leaf drop if uncorrected. In extreme cases, such deficiencies can significantly impact yield and quality, although these severe instances are rare and usually occur only in deep, sandy soils with low residual potassium.

Figure 1. Mild potassium deficiency symptoms (chlorotic leaf tips) in flue-cured tobacco near the flowering stage of growth.

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Figure 1. Mild potassium deficiency symptoms (chlorotic leaf tips) in flue-cured tobacco near the flowering stage of growth.

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Figure 2. Severe potassium deficiency in flue-cured tobacco research trials. Plants in the photograph were not fertilized with potassium.

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Figure 2. Severe potassium deficiency in flue-cured tobacco research trials. Plants in the photograph were not fertilized with potassium.

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Figure 3. Severe potassium deficiency in flue-cured tobacco.

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Figure 3. Severe potassium deficiency in flue-cured tobacco.

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In the current agricultural landscape, where input costs are a significant concern, traditional potassium fertilization practices should be reconsidered. According to NCDA&CS soil test reports, 85% of tobacco soils have "high" phosphorus (P) levels, making it more common for growers to apply nitrogen (N) and potassium (K) separately, rather than using a traditional N-P-K fertilizer blend. While higher potassium rates may alleviate deficiency symptoms, excessive fertilization can be costly and lead to nutrient loss.

Research suggests that fields with abundant residual potassium in the topsoil and subsoil do not benefit from potassium applications above the recommended levels. Recent studies have shown that potassium rates as low as 75 pounds per acre can yield satisfactory results on medium- to high-potassium soils with fine textures, and this rate may even be further reduced under certain conditions. For example, a study at four sites in North Carolina found no significant differences in yield or quality when potassium application rates ranged from 0 to 225 pounds per acre (Table 1), likely due to the high residual potassium in these fields and the moderate rainfall during the growing season (Vann et al. 2012).

It is recommended that 75 pounds per acre of K₂O be applied to tobacco when soil tests indicate sufficient residual potassium. While growers may be tempted to reduce the rate below this threshold, doing so could deplete the soil’s potassium reserves.

Adapted from Vann et al. 2012

^[a]Potassium applied as 0-0-22 (sulfate of potash magnesia). Nitrogen applied from liquid 32% UAN. ↲

^[b]Potassium supplied from base applications of 6-6-18 or 8-8-24. ↲

^[c]Grade index is a measure of tobacco quality on a ranking scale from 1 to 100, with 100 representing the highest quality. ↲

Several methods exist for applying potassium, each with its own timing recommendations and benefits. One of the advantages of separate potassium applications is the ability to adjust the timing based on specific needs.

• Broadcast application (100% applied prior to transplanting): Potassium can be broadcast and incorporated into the soil before transplanting. This method is best for soils with medium to fine textures and shallow depths to clay, as it minimizes the risk of leaching prior to transplanting.

• Sidedress application (100% applied at transplanting): This approach places potassium directly in the effective root zone, improving uptake efficiency. The fertilizer is applied about 4 inches from base of the plant and 4 inches deep. Sidedressing reduces salt injury to roots and enhances nutrient absorption.

• Split application (50% applied at transplanting; 50% applied at layby): This method is beneficial in coarser soils with deeper clay layers (≥20 inches). Split application reduces early-season leaching risks and ensures late-season potassium availability, helping to prevent deficiency symptoms later in the growing season.

Potassium is prone to leaching, particularly in fields with coarse texture and deeper clay layers (>10 inches of topsoil). In such conditions, a 1:1 potassium-to-nitrogen ratio is recommended to optimize potassium availability in the root zone. This application rate takes into consideration the shallow-rooted nature of the tobacco plant and the low cation exchange capacity of sandy soils. Sidedress applications are preferred over broadcast applications, as they place potassium closer to the roots and improve uptake.

Selecting the right potassium fertilizer source is crucial. The most common sources for tobacco are sulfate of potash (0-0-50) and sulfate of potash magnesia (KMag, 0-0-22). Both of these formulations provide sulfur, which is necessary for tobacco growth. KMag also offers magnesium—important for soils lacking in this nutrient. Avoid potassium chloride (muriate of potash) due to its high chloride content, which at excessive levels can harm tobacco quality and combustion properties (Tiecher et al. 2022).

Potassium is critical for producing high-quality tobacco, but many producers have been overapplying potassium for years. Reducing potassium inputs may not only lower costs but also help protect the environment. Growers should consider alternative application methods and take into account their specific soil conditions, including texture, residual potassium levels, and depth to clay. Moreover, using potassium sources that are free from chloride should be prioritized to protect the crop's quality.

Raper, C. D., and C. B. McCants. 1967. "Nutrient Accumulation in Flue-Cured Tobacco." Tobacco Science 10: 109. ↲

Sims, J. L. 1985. "Potassium Nutrition of Tobacco." In Potassium in Agriculture, edited by R. D. Munson. American Society of Agronomy. ↲

Tiecher, T., C. R. Pace, L. C. Gatiboni, M. Vann, D. Hardy, and L. Fisher. 2022. "Flue-Cured Tobacco and Cl Rates: Implications on Yield, Quality, and Nutrient Concentrations." Agronomy Journal 115 (2): 896–908. ↲

Vann, M. C., L. R. Fisher, D. L. Jordan, D. H. Hardy, W. D. Smith, and A. M. Stewart. 2012. "The Effect of Potassium Rate on the Yield and Quality of Flue-Cured Tobacco." Tobacco Science 49: 14–20. ↲

Vann, M. C., L. R. Fisher, D. L. Jordan, W. D. Smith, D. H. Hardy, and A. M. Stewart. 2013. "Potassium Rate Application Effect on Flue-Cured Tobacco." Agronomy Journal 105 (2): 304–310. ↲

Vann, M. C., L. Gatiboni, M. James, and L. R. Fisher. 2024. "Managing Nutrients." In 2024 Flue-Cured Tobacco Guide. NC State Extension. ↲