52 BULLETIN AMERICAN METEOROLOGICAL SOCIETY Weather and the Production of Burley Tobacco JAMES M. BEALL U. S. Weather Bureau ABSTRACT Tobacco is an economically important crop in the United States. It is grown under a variety of climatic conditions each imposing its particular microclimatological and micro- meteorological effects. The curing of burley tobacco depends particularly on the proper con- trol of relative humidity. A humidity forecasting project started in 1954 in Kentucky by the Weather Bureau with the cooperation of the University of Kentucky has resulted in that some farmers using the service have received up to 7 cents a pound more than parity for their tobacco. Consequently the Weather Bureau has decided that the service is well worth while. OBACCO as an economically important ley is the number one cash crop in the State. The crop in the United States goes back to number of acres of tobacco cultivated during re- T the early colonial days in Virginia. The cent years has been reduced because of govern- use of tobacco was first recorded by Columbus in ment controls, but because of better agronomic Cuba in 1492 when he saw it being smoked by the practices the yields have steadily increased. Even American aborigines. The use of tobacco was with this technological advance tobacco is still made popular in the French Court by Jean Nicot, virtually unmechanized. Each tobacco plant is French Ambassador to Portugal. The drug nico- handled at least six times from seed to market. tine derived its name from this proponent of its The fact that it is still a crop of hand labor is il- use. Sir Walter Raleigh made tobacco popular in lustrated by examination of the statistics which the Court of St. James in the sixteenth century. show that only three percent of the arable land of Since then its use has spread world-wide. Kentucky is planted in tobacco yet this crop uti- Tobacco is a weed of the nightshade family. lizes about twenty-seven per cent of the available Other members of this indigenous American plant farm labor force in the State. family are tomato, potato, egg plant and green That weather accounts for more than fifty per- pepper. The distinguishing feature of tobacco is cent of the variability in the yields of the cereal the habit forming nicotine content of the leaf. crops is a fact that has been long recognized. We Because environment is not a critical factor in know subjectively that weather is an important growth its culture has spread to many soil types factor in the production of high quality even and climates from Canada and Scandinavia in the though we know of no work that has correlated sub-arctic to Cuba and Sumatra in the tropics. weather and yield or quality of tobacco. The This spread of its culture has resulted in several proper utilization of weather forecasts in farm distinct varieties. The best cigar wrappers come management decisions will pay increased divi- from Cuba in the Tropics. The best oriental or dends to the farmers of Kentucky. Turkish tobacco comes from Macedonia in the First we will discuss the life cycle of the to- Balkans. The best bright leaf comes from the bacco plant from seed to the sale of the leaf, and Carolinas. The best burley comes from the Blue then we will discuss how weather affects each Grass area of Kentucky. The present discussion phase of production. The seed is extremely small. will be limited to burley. Three hundred thousand to three hundred fifty The trend in the sale of finished tobacco to the thousand are needed to make one ounce. They consumer has been a phenomenal rise in the use of are not planted directly in the field since the seed- cigarettes. In the last 30 years cigarette sales lings are subject to injury from cold, insects, dis- have soared 500 per cent. Associated with this eases and weed competition. Tobacco in Ken- development has been the increase in the use of tucky is planted in seed beds six to nine feet wide burley tobacco which is blended with other to- and sometimes in excess of a hundred feet long baccos to give the desired qualities which the early in the spring. Between May 20 and June 10 cigarette manufacturers extol. the seedlings are transplanted into the fields. The Over seventy percent of the burley grown in the plants are cultivated several times during the sum- USA is produced in the State of Kentucky. Bur- mer to keep down the weed competition for food Unauthenticated | Downloaded 09/25/21 10:08 PM UTC VOL. 38, No. 2, FEBRUARY, 1957 53 and water. Harvesting begins in late August or mum protection. A tight fence, farm buildings, the first of September. The plants are then placed dense woodland, or a bamboo hedge can all serve in tobacco barns to begin the curing process which to break up the wind. takes from six weeks to two months. In the late The heat loss in advective situations is a func- fall and early winter the stalks are taken down and tion of the wind velocity. The purpose of the wind the leaves stripped off, sorted and made ready for break is to reduce the wind velocity and therefore the market. During December and January the decrease the advective heat loss. tobacco leaves are sold at auction in the ware- The plants are transplanted into the fields about houses. The care and culture of tobacco is vir- the last week of May. The ideal sequence in tually a year-round operation. spring weather as far as tobacco is concerned is for Seed bed preparation begins in the fall. It is the weather to be fairly dry long enough for the necessary to sterilize the soil in order to eliminate farmer to prepare the field followed by a slow soil-borne diseases, insects and weeds. Alternate steady rain to moisten at least the first six inches freezing and thawing aids in the sterilization of the soil just prior to transplanting. As soon process. The traditional method is by burning as the plants are in another short rain is needed wood on the bed for at least half an hour. Later to get the new root system established. Field steam was introduced as a method of sterilization. cultivation starts about two weeks after trans- Chemical sterilization of seed beds is now be- planting and it should be dry for several days for coming more widespread. this field operation. During the summer the soil Seeds should not be planted until the soil tem- should never become so dry as to place stresses peratures have reached an average daily value of on the plants. 50 degrees Fahrenheit. Greenhouse experiments The tobacco plant, being essentially a weed, is have shown the lower threshold of germination of able to withstand periods of more adverse weather tobacco seeds to be 45°F; the upper limit above than some of the other kinds of field crops with- which they will not germinate to be 95 °F and the out appreciable differences in yield. However, optimum germination temperature to be 78°F. the nicotine content of the tobacco is markedly The micro-meteorological aspect of seed bed higher if the plants have withstood periods of location becomes important largely from the stand- drought than if they have an adequate moisture point of reducing the frost hazard and securing supply to insure steady growth. Physiologists the maximum heating. Location on a south slope have shown that a plant experiencing continuous will insure faster germination and a larger per- growth has a different chemical makeup than one centage of usable plants. An effective wind break that has had severe stresses placed on it. In ad- will decrease the losses due to advective freezes. dition other factors of quality are adversely af- Some phenomenal differences between the cli- fected in the drought periods such as the thicken- mate of the southern slope versus the northern ing of the leaf, smaller leaf size and smaller total slope of a small hill have been reported by Geiger number of leaves. and others. The reasoning is quite simple. Con- Harvesting is a process that requires dry sider the heat received on a unit area normal to weather for at least two successive days. The the direct rays of the spring sun. As the projec- tobacco stalk is cut near the ground and impaled tion of this unit area is rotated the amount of heat on a stick about four and a half feet long. Six received per unit area on the projection is re- plants are usually arranged on each stick. The duced as a function of the cosine of the angle be- plants are left overnight in the fields to wilt. The tween the plane normal to the sun's rays and its wilting serves two purposes; first it reduces the projection. Carr [1] has shown experimentally moisture carried into the barn and second, it makes in 1943 in Georgia that under similar conditions the leaves easier to handle without danger of in- a five per cent slope to the south yielded twice as jury. The sticks of tobacco are then hung in the many tobacco plants as a five per cent northerly barn to begin the curing process. Eighty percent slope. Plants on east and west slopes produced of the green weight of the tobacco must be lost intermediate results. in the curing process. For each five thousand The micro-meteorology of temperatures in the pounds of newly housed tobacco two tons of water lee of shelter belts is important since freezing must be lost before the curing process is complete.