The quality and chemical composition of flue-cured tobacco is determined by the interaction of nitrogen, sugar, and soil moisture. Ideally, nitrogen should be depleted about the time flowering occurs. As nitrogen is depleted, sugar accumulation begins. Dry spells 30-60 days after transplanting have pronounced effects on yield and quality of flue-cured tobacco, as nitrogen uptake and metabolism is limited. Normal nitrogen-sugar metabolism is delayed, thus preventing normal ripening of the tobacco. When cured, this tobacco has less than desirable physical and chemical characteristics.
Factors that may improve soil moisture availability include in-row subsoiling and supplemental irrigation. Irrigation of tobacco would improve quality and yield and promote a normal maturing crop. Tobacco grown on Coastal Plain soils usually responds less to irrigation than that of the Sandhills, but surveys in neighboring states indicate, in an average year, yield and value/lb could improve 10-15%. In a severe drought, like 2002, yield and price/lb might improve 25% or more with irrigation. Irrigation allows timely maturity and thus helps keep sucker control, harvesting, curing and marketing on schedule. North Carolina data indicates it costs $11.45/A to irrigate tobacco one time. In addition, the fixed cost based on a 72 acre traveling gun system would be $67/A.
For irrigation of tobacco, a dependable supply of clean water is a must. The water can come from ponds, streams, or wells and should be free of plant disease organisms and high levels of chemicals, such as sulfur and chloride. Water should be tested prior to use.
A practical irrigation system for South Carolina producers is some type of traveling gun. At transplanting and the layby to flower stage are the most critical periods of drought stress for tobacco. A light irrigation (about .5 inch) usually proves beneficial at transplanting. In the knee high to bloom stage, a drought can drastically affect yield and quality of the crop, and tobacco will need about 1 inch of water per week. Begin irrigation when 50% of the available soil moisture is depleted during this stage. Irrigate at the after transplant to knee high and after flowering stage only when severe drought and wilting occur. Irrigation of tobacco would have been of tremendous benefit in 1980, 1986, 1990, 1993, 1998, 1999, 2002, and 2007 in South Carolina. Approximately 6.0% of South Carolina's tobacco crop was irrigated in 2009.