Manganese (Mn) toxicity of burley tobacco is viewed by tobacco specialists in Kentucky as the greatest single factor which reduces yields. Estimates are that this problem adds 30 to 50 million dollars to the cost of burley production because of the greater acreage (and all associated costs) required by growers to produce their allotment. And, even though the cause and cure of Mn toxicity has been known for about 50 years, many growers are caught each year at transplanting time with no knowledge as to whether Mn toxicity may be a problem in their fields. The solution to Mn toxicity is to keep soil pH in the rooting zone from dropping below 5.5-5.8 during the growing season. To accomplish this requires starting the season with a soil pH of about 6,4, If soil pH is near this level before fertilizer is applied and the green manure crop decomposes, there is a much better chance that root zone pH will not drop below 5.5-5.8 after transplanting.
Wells, Kenneth L. and Sims, J. L., "Control Measures for Manganese Toxicity of Burley at Transplating Time" (1987). Soil Science News and Views. 138.