Reports from multiple sources are indicating that the availability of potassium sulfate (sulfate of potash, 0-0-50) for the upcoming tobacco growing season will be limited. At the current time it is not known what factors have contributed to the fertilizer shortage or how long it will last.
But tobacco producers, fertilizer dealers and crop consultants are being advised to make other arrangements when sourcing or making recommendations for potassium (K) fertilizer applications in tobacco production.
When considering K sources for tobacco production, chlorine (Cl) content is the primary concern due to the toxic effect it can have on the plant when applied at rates greater than 30 pounds per acre. Chlorine toxicity is a result of excessive chloride (Cl-) accumulation and will result in a decrease in leaf yield and quality as well as very poor smoke flavor.
Complete tobacco grade fertilizers, such as 6-6-18 and 8-8-24, will contain no more than 2 percent Cl or no more than one-half the total amount of nitrogen when nitrogen is greater than 4 percent. Homogenized fertilizers will typically blend various sources of K to meet crop-based nutritional requirements.
Additionally, non-homogenized K fertilizers such as sulfate of potash and K-Mag will contain somewhere between 1 and 2 percent Cl. Ultimately, both fertilizer sources (homogenized and non-homogenized) will not oversupply Cl when used at recommended rates.
Since state law limits chloride levels in tobacco fertilizers, issues with excessive Cl content in fertilizers occur when non-tobacco grade sources are used in substitution for fertilizers formulated for tobacco.
The most commonly used K fertilizer, worldwide, is muriate of potash (potassium chloride, 0-0-60) because of its high K analysis and relatively low cost. Muriate of potash is not recommended as the sole K source for tobacco production, regardless of tobacco type, due to its high Cl content (45 to 47 percent).
An example of the problem with using only murate for potassium needs is as follows: 100 pounds of muriate of potash applied per acre will only supply about 50 pounds of K+ but will supply around 46 pounds per acre of Cl-. The end result of this application is that K is in short supply, while Cl is applied at too high of a rate for tobacco.
The fertilizer K issue is further compounded when soil fumigants are used to suppress soil borne diseases and nematodes. The two most commonly used soil fumigants in tobacco production (Telone and Chloropicrin) both have active ingredients comprised of chlorine-based compounds. It is safe to assume that these products will provide 10 to 15 pounds of Cl- per acre when used at recommended rates, which only furthers the need to give serious consideration to fertilizer source. So to be safe apply no more than 30 pounds per acre from the fertilizer.
Alternatives to sulfate of potash
Alternatives to sulfate of potash do exist for tobacco producers if you are having difficulty in sourcing the product. These alternatives are as follows:
•Do not over-apply K for soil building purposes; rather only apply the recommended amount based on a recent soil test. Over 60 percent of the tobacco producing soils in North Carolina have a high to very high K-index; therefore, soil reserves of K can be utilized to supplement nutritional needs beyond what is applied through fertilizer.
•K-Mag (Sul-Po-Mag, 0-0-22): K-Mag is an excellent source of K and also provides sufficient amounts of magnesium (11 percent) and sulfur (22 percent); additionally, the Cl content of K-Mag is also very low (less than 2.5 percent) so it is not a significant concern. The price of K-Mag is typically higher than sulfate of potash; however, price may not be a strong consideration if 0-0-50 cannot be sourced.
•14-0-44 (potassium nitrate), 13-0-14 (sodium nitrate), 15-0-14: These fertilizers have long been used as nutrient sources for tobacco production. However, they are often more expensive than other sources of K. Producers should consider the economics of these products and the need for nitrogen prior to purchase.
•6-6-18 & 8-8-24: Many producers continue to utilize complete fertilizers in tobacco production. These fertilizers used in tobacco contain trace amounts of Cl and are suitable for tobacco production. However, producers must consider the economics of these products because they contain nutrients (such as phosphorus) that may not be needed.
•Muriate of Potash (potassium chloride, 0-0-60): Muriate of Potash can be blended with other potassium fertilizers so long as the delivered Cl is no more than 30 pounds per acre. It is critical that blenders and producers use appropriate blending ratios and techniques to ensure that Cl does not become highly concentrated. Sixty-five pounds of Muriate of Potash will supply about 30 pounds of Cl, and it is recommended that blending rates do not exceed this threshold.
•It is critical that growers are aware of this issue and that they inquire about the source of K used in their blended fertilizers. Assuming that the source is the same as in previous years can lead to a number of production-related issues.