Burley Tobacco Production Research Articles

No-tillage culture and nitrogen fertilizer management for burley tobacco production

SUMMARYFew studies have investigated nitrogen (N) fertilizer management in no-tillage (NT) tobacco (Nicotiana tobacumL.) production systems, even though N fertilization is known to influence tobacco cured leaf yield and quality. The present study evaluated how tillage practice and N fertilizer rate affected burley tobacco agronomic performance, plant available nitrogen (PAN) supply, and leaf chemical constituents. In 2012 and 2013, three N fertilizer rates (0, 140 and 280 kg N/ha) were introduced as split-plots within a long-term NT and conventional tillage (CT) (mouldboard plough) comparison study. Results (2007–2013) showed that the effect of tillage on tobacco yield depended on seasonal weather; NT tobacco appeared to have lower yield than CT tobacco in seasons with <450 mm growing season rainfall, but similar yields when rainfall was >500 mm. In 2012 (432 mm rainfall; 84% of the long-term seasonal mean), leaf SPAD reading, leaf nitrate concentration, total nitrogen concentration at the topping day (i.e. removal of flowers/buds at the tops of the plants) and cured leaf nicotine and alkaloid content suggested that N deficiency was more pronounced in NT than CT at the lowest N fertilizer rate. The PAN supply, as measured by a modifiedin situresin core method, was similar in 2012 between NT and CT, suggesting that plant factors may have had a role in N uptake efficiency. This scenario did not repeat in 2013 (706 mm rainfall; 137% of the long-term seasonal mean). Even though N fertilization rates were identical for both tillage practices in 2012 and 2013, PAN was lower, on average, in 2012. Because N uptake is largely the result of mass flow, the impact of reduced root density in NT tobacco would be expected to be more pronounced in a season such as 2012, when water was limited. Banding N close to the tobacco root system and/or side-dressing some portion of N may be recommended strategies to improve N use efficiency in NT burley tobacco production.

Conservation Practices in Tobacco Production Increase Large Aggregates and Associated Carbon and Nitrogen

Burley tobacco (Nicotiana tobacum L.) production in Kentucky is typically tillage intensive and is often mono-cropped. Intensive tillage has been reported to degrade soil structure and deplete soil organic carbon (SOC) and total soil nitrogen (TSN) stocks. This study assessed the effect of tillage, crop rotation, and N fertilizer application on soil structure, water-stable aggregation, and aggregate-associated SOC and TSN concentrations and stocks for rotations including burley tobacco. Four burley tobacco production systems (main plots) were established in 2007 on a Bluegrass-Maury (fine, mixed, active, mesic Typic Paleudalf) silt loam soil including: (i) no-tillage continuous tobacco (NT-Tobacco); (ii) conventional tillage continuous tobacco (CT-Tobacco); (iii) 2-yr sod (Festuca arundinacea Schreb.) 1-yr no-tillage tobacco (NT-Rotation); (iv) 2-yr sod and 1-yr conventional tillage tobacco (CT-Rotation). In 2012, two N rates (0 and 280 kg N ha-1) were applied to split plots. Soil samples were taken in Spring 2013 to determine water-stable aggregate-size distributions and associated SOC and TSN concentrations and stocks. Compared with conventional tillage and tobacco monoculture, no-tillage and rotation with sod significantly increased macroaggregate fractions (>250 μm), and associated SOC and TSN stocks at the expense of the silt-clay size class (<53 μm) and associated SOC and TSN stocks. Although previous fertilizer N application had no significant effect on whole-soil SOC and TSN stocks, a significant interaction with crop rotation on macroaggregate distribution and macroaggregate-associated SOC and TSN stocks was observed. Using NT and/or rotation practices in burley tobacco production maintains desirable soil physical and chemical properties via macroaggregate stabilization, which leads to the conservation of SOC and TSN stocks.

REDUCTION IN LABOR REQUIREMENTS FOR BURLEY TOBACCO PRODUCTION, PART 1: PROGRESS SINCE THE 1970s

The high labor requirements of burley tobacco production have prompted considerable mechanization interest and efforts over the years. Significant progress has been made in reducing the amount of manual labor required. Major labor reductions of the 1972–2007 era for several practices having widespread adoption and the economic effects those reductions had for burley producers are analyzed in this article, the first in a two-part series. Major mechanization developments of the era considered in the analysis include the adoption of small-bale packaging, the transition from plant beds to float-bed systems, the use of outside field-curing structures, the use of stripping wheels and similar stripping aids, and the adoption of big-bale packaging. Total labor requirements at the beginning of the era were reported at more than 300 worker-hr/acre, but were reduced a total of 157 worker-hr/acre by 2007, or more than 50%, considering the widely adopted methods. Most of the adopted practices resulted in net savings t...

Morphological and molecular characterization of Phytophthora glovera sp. nov. from tobacco in Brazil

A root rot disease of cultivated tobacco called yellow stunt has been observed in the burley tobacco production areas of Brazil since the early 1990s. Root infecting fungi and straminipiles were isolated from the roots of diseased tobacco plants, including a semi-papillate, homothallic, slow growing Phytophthora species. Pathogenicity trials confirmed that Phytophthora sp. caused root rot and stunting of burley and flue-cured tobaccos. Morphological characteristics of the asexual and sexual stages of this organism did not match any reported Phytophthora species and were very different from the widely known tobacco black shank pathogen P. nicotianae. Phylogenetic analysis based on sequences of the internal transcribed spacer rDNA, β-tubulin and translation elongation factor 1-α regions indicated that this organism represents a previously unreported Phytophthora species that is significantly supported in clade 2 and most closely related to P. capsici. However P. glovera differs from P. capsici in a number of morphological characters, most significantly P. glovera is homothallic and produces both paragynous and amphigynous antheridia while P. capsici is heterothallic and produces only amphigynous antheridia. In this paper we confirmed pathogenicity of this species on tobacco and describe the morphological and molecular characteristics of Phytophthora glovera sp. nov.

Improved Nitrogen Management for Burley Tobacco Production in the United States

Burley tobacco (Nicotiana tabacumL.) has historically been fertilized with nitrogen rates ranging from 150 to 250 kg N/ha. The objectives of the this study were to: (i) evaluate the response of burley tobacco to N fertilization; (ii) determine if split N applications increase burley tobacco yields; and (iii) evaluate a modified pre-sidedress soil nitrate test (PSNT) as a tool for N management in burley tobacco. Nitrogen rates included: 0, 67, 135, 202, and 270 kg N/ha preplant in combination with 0 and 67 kg/ha N sidedress. In 2008, the 270 kg N/ha rate was dropped and the variety TN 90LC was added to the study. Modified pre-sidedress nitrate test (PSNT) samples were taken to a depth of 15 cm prior to sidedress N applications. Analysis of variance was used to analyze burley tobacco yield response to preplant and sidedress N applications and polynomial regression was used to analyze PSNT levels and preplant N rates. Optimal yields were reached with 135 kg N/ha. Pre-sidedress nitrate test levels in 2008 predicted yields more precisely than in 2007 due to higher precipitation at experimental sites. The information from the study indicates that burley tobacco yields were maintained at lower N rates than traditional N applications rates.

Surface Water Quality Impacts of Conservation Tillage Practices on Burley Tobacco Production Systems in Southwest Virginia

Surface Water Quality Impacts of Conservation Tillage Practices on Burley Tobacco Production Systems in Southwest Virginia

Surface Water Quality Impacts of Conservation Tillage Practices on Burley Tobacco Production Systems in Southwest Virginia

A plot-scale, rainfall-simulation study measured edge-of-field pollutant losses from conventional-till, strip-till, and no-till treatments in a burley tobacco production system. The field experiment results show that the conventional-till treatment yielded more total runoff than strip- and no-till treatments. Compared to the conventional-till treatment, both no-till and strip-till reduced the total mass losses of total suspended solids (TSS), total nitrogen (TN), total Kjeldahl nitrogen (TKN), nitrate (NO-N), ammonia (NH3-N), total phosphorus (TP), orthophosphate (PO4-P), and the insecticide chlorpyrifos in runoff. Although statistical analyses indicated that there was no significant difference between the no-till and strip-till practices, the no-till practice consistently yielded less edge-of-field pollutant loss than the strip-till practice. This research reinforces the body of knowledge documenting the effectiveness of conservation-tillage practices in reducing edge-of-field pollutant losses.

Coming Together to Combat Tobacco's Tragic Health Consequences

together is a beginning; keeping together is progress; working together is success. - Henry Ford (1863–1947), Auto Manufacturer Scientists and health care professionals from around the world will come together in Louisville, Kentucky, U.S., in October for the Third Annual Conference of the International Society for the Prevention of Tobacco Induced Diseases. The meeting is a further step in keeping together the effort begun by PTID founding president the late Dr. Ed Nelson in 2000. Proceedings at the meeting will help to further the Society's mission to foster scientific medical studies, health education and other efforts to prevent diseases caused by tobacco abuse, addiction, and involuntary exposure to tobacco smoke. Louisville, located on the Ohio River in the heartland of the United States, is a historically significant city. Named for King Louis XVI of France, in recognition of his assistance during the United States' Revolutionary War, the city was founded by George Rogers Clark in 1778 – just two years after the nation declared its independence in 1776. Louisville has been home to the United States' 12th President Zachary Taylor, inventor Thomas Edison, naturalist and artist John James Audubon, and heavyweight boxing champion Muhammad Ali, among other notables. The city boasts 11 institutions of higher learning, including the University of Louisville. With more than 21,000 students on three campuses, this university receives more than $100 million annually in grants and contracts for research. The 155-year-old University of Louisville School of Medicine is one of the oldest medical schools west of the Allegheny Mountains, and is a leader in medical research. University of Louisville surgeons, working at Jewish Hospital, successfully implanted the world's first self-contained artificial heart in 2001. In addition to the School of Medicine, the university's Health Sciences Center includes schools of Dentistry, Nursing, and Public Health and Information Sciences. The selection of Louisville as the site for this year's PTID conference is particularly significant in light of Kentucky's prominence as a major producer of tobacco. In the U.S., Kentucky is second only to North Carolina in total production of tobacco, and leads the nation in production of burley tobacco. Tobacco accounted for 16% of Kentucky's total agricultural cash receipts in 2001. [1] Burley tobacco, used primarily in cigarettes, is grown in 117 of Kentucky's 120 counties and accounts for 85% of the state's total tobacco production, with 220,500,000 pounds produced annually. The state also produces dark fire-cured and dark air-cured tobaccos, used in products such as snuff, chewing, and pipe tobacco. Sales of tobacco generated $566.3 million (U.S. dollars) for Kentucky farmers in 2001. [1] But along with the economic benefits, Kentuckians have reaped the tragic health consequences that follow in tobacco's path. More than 8,000 Kentuckians die each year from illnesses caused by tobacco use. [2] More than $1.2 billion in tax dollars, through the government's Medicaid and Medicare health care programs, is spent each year to treat Kentuckians for illnesses caused or made worse by the use of tobacco products. [2] According to the Kentucky Tobacco Prevention and Cessation Program, 32 percent of Kentucky's adults smoke; 34% of the state's high school students use cigarettes, and 15% of the state's middle school students smoke. It is estimated that 23 percent of women in Kentucky smoke during their pregnancies. [2] In an effort to combat the negative impact of tobacco on the health of the state's residents, the Tobacco Prevention and Cessation Program has adopted four goals established by the U.S. Centers for Disease Control: preventing the initiation of tobacco use among young people; promoting cessation among young people and adults; eliminating non-smokers' exposure to environmental tobacco smoke; and identifying and eliminating disparities related to tobacco and its effects on different population groups. [2] The presence of PTID scientists and health care professionals in Louisville will be an encouragement to Kentuckians who are working to address the problem of tobacco-induced diseases in their state. Dates for the PTID annual conference are October 29–November 1, 2004. The conference will be held at the Seelbach Hilton in Louisville. More information is available on the conference website, http://www.dental.louisville.edu/research/ptid_conference.htm. If you have not yet made plans to attend this conference, we encourage you to do so. Coming together, keeping together, and working together, we can make a difference for millions of adults and young people who are at risk for tobacco-induced disease and death.

Injuries to Tobacco Farmers in Kentucky

Like all types of farming, raising tobacco has many hazards that may lead to injury, disability, or death. Burley tobacco farming is a multistep process that is not highly mechanized. An 8-year emergency department surveillance system in Kentucky identified 674 injury cases related to the production of burley tobacco. Most of the injuries were a result of a fall, cutting and piercing instruments, or sprains and strains. More than 90% of the injured patients were treated as outpatients, and the average charge for emergency room services was $402 (range, $0 to $14,729). One quarter of the patients were uninsured. Injuries to Hispanic workers increased over the 8-year period. Estimated hospital charge per acre of tobacco produced ranged from $1.28 to $1.74. Low-cost interventions such as gloves and chaps could reduce the injuries incurred in burley tobacco farming.

Effects of soil pH and nitrogen fertility on the population dynamics of Thielaviopsis basicola

Black root rot of tobacco, caused by Thielaviopsis basicola, is generally severe at soil pH values >5.6 and suppressed under more acidic conditions (pH < 5.2). Soil acidifying fertilizers containing NH4–N are generally recommended for burley tobacco production in North Carolina, but the effects of N form and application rate on development of black root rot and on the population dynamics of T. basicola have not been determined. Greenhouse and laboratory studies were conducted to evaluate the effects of N form (NH4+ or NO3−) and rate on pathogen and disease parameters at several initial soil pH levels. A moderately-conducive field soil, initial pH 4.7, was adjusted to a pH of 5.5 or 6.5 by the addition of CaOH2, then amended with the desired nitrogen form and rate. Pathogen populations were determined over time. In addition, spore production in extracts of roots from plants grown in the various nitrogen and pH treatments was determined. Finally, because tobacco responds to acidic soil conditions and exposure to NH4–N by accumulating high concentrations of the polyamine putrescine, the toxicity of putrescine on vegetative growth and reproduction of T. basicola was investigated. Low soil pH and high levels of NH4–N suppressed reproduction of T. basicola in soil and in root extract, while use of NO3–N and depletion of NH4–N resulted in rapid increases in populations of T. basicola. At 20 mM, putrescine inhibited hyphal growth by 60% and aleuriospore production by 98%. Fertilizers that reduced soil pH also reduced reproduction by T. basicola, and thus have potential for management of black root rot by suppressing populations of T. basicola over multiple years of crop production. The suppression of T. basicola and black root rot observed with NH4–N amendments may partially be due to development of an inhibitory environment in the root and not solely to changes in rhizosphere pH.

Smoking Zucchini—Introducing Commercial Vegetable in Tobacco Country

“We are a tobacco state” is frequently heard among farmers and agricultural leaders in Kentucky; the state's farm economy has always revolved around burley tobacco production. Tobacco, grown in Kentucky for nearly two centuries, remains the most valuable crop earning approximately $694 million in 1995. Even our unusual terminology of “alternative,” “supplemental,” or “opportunity” crops denotes the prime position of tobacco and attitudes toward vegetable crop production. This long tradition and attitudes associated with it contribute to a serious lack of confidence and low expectations when it comes to diversification with vegetable crops. These low expectations and the consequent circular pattern of experience with vegetable production were revealed in a multidisciplinary, 5-year research project designed to determine opportunities for and constraints to vegetable production in the state. The study showed that nearly half of Kentucky's commercial vegetable growers also were tobacco growers and that there were no fundamental incompatibilities in tobacco–vegetable cropping systems. Although farmers considered lack of markets a major constraint, economic research revealed that growers were often unwilling to use and take the risks associated with existing market structures and channels. As a result of these findings, a major on-farm demonstration program was implemented to raise expectations and break the “circular syndrome”. More recently, new partnerships and collaborative relationships have been established between university horticulture and marketing specialists and the Burley Tobacco Growers Cooperative Association for the promotion of “supplemental crops” among Kentucky's tobacco growers.

Tobacco Aphid Control on Burley Tobacco with Transplant Water and Foliar Treatments, 1995

Abstract This experiment was conducted at the VPI &amp; SU Southern Piedmont Agricultural Research and Extension Center, Blackstone, VA, to evaluate various insecticides applied as foliar and transplant water (TPW) treatments for control of TA on burley tobacco. Tobacco ‘Tennessee 90’ was transplanted into experimental plots on 23 May. Nine treatments and an untreated control were established in a RCB design with 4 replications. Plots, 4 X 40 ft (1 row X 24 plants), were separated by single untreated guard rows. Transplant water treatments were applied around each plant at 4 fl oz solution/plant (204 gal/acre) using a measuring cup and bucket. Foliar treatments were applied with a CO2-pressurized backpack sprayer that delivered 28 gal/acre at 60 psi through 3 TX-12 nozzles/row on 3 Jul. Temperatures ranged from 85-88 °F during application. TA counts were made on the upper 4 leaves of 10 plants per plot before treatment and at 3, 7, 14 and 21 DAT. Except for insect control, burley tobacco production methods including transplanting, fertilization, topping, sucker control, and herbicide and fungicide applications followed recommendations by the Virginia Cooperative Extension Service. Data were analyzed by ANOVA and significantly different means were separated WD test (K-ratio = 100). TA count data were transformed to Log10(X+l) before analysis. Actual means are presented in the table.

Soluble calcium fertilizer effects on early growth and nutrition of burley tobacco

Abstract During production of burley tobacco (Nicotiana tabacum L.), initial soil pH needs to be 6.6 in order to maintain pH at midseason in the range of 5.8 to 6.2 to control manganese (Mn) toxicity, molybdenum (Mo) deficiency, and to enhance overall nutrient availability in soil. A field experiment was conducted at Lexington, Kentucky, during 2 years to determine the effects of rate of soluble calcium (Ca) (as gypsum‐CaSO4) on early growth and chemical composition of burley tobacco. On Maury silt loam soil (Typic Paleudalf; pH 6.6), plant dry weight and concentrations of potassium (K), Ca, and magnesium (Mg) 40 days after transplanting increased with rate of Ca fertilization up to 380 kg Ca/ha. Further increases in Ca fertilization decreased dry weight and K but had no effect on plant Ca or Mg concentrations. Generally, the effect of Ca on growth and nutrient accumulation was greatest in the presence of supplemental irrigation, K fertilization, and use of a nitrate (NO3) source of N. Plant Ca concentrat...

A Field Curing Structure and Mechanized Housing System for Burley Tobacco

Two deterrents to expanded production of burley tobacco are a lack of barns located conveniently to the tobacco fields and a lack of hired labor for harvesting and housing. The objective was to meet these needs by developing a mechanized housing system and a one-tier field curing structure that would accommodate the mechanized housing system and provide an economical alternative to the conventional curing barn. The mechanical housing system for the field curing structure requires only 39% of the labor required to load, transport, and house burley tobacco in the conventional barn. The mechanical housing system for the field curing structure requires two workers compared to three or four for conventional barns. Using Net Present Value as a means of comparing capital investment decisions showed the field curing structure with mechanized housing system to be a better investment than the conventional and tiered field curing structure systems for land areas of and above 0.7 ha (1.6 acre) and 6 ha (15 acre), respectively.

Genetic Variation for Agronomic Characters in a Burley Tobacco Synthetic Following Recurrent Selection for Increased Black Shank Resistance

AbstractBlack shank, a fuagal disease caused by Phytophthora parasitica var. nicotianae, is a major hazard in the production of burley tobacco (Nicotiutta tubacum L.). Moderate levels of resistance have been bred into cultivars, but little success has been achieved in utilizing high levels of resistance found in the cigar line. Beinhart 1000‐1. Beinhirt 1000‐1 and seven burley cultivars were combined into a synthetic population and three cycles of selection for increased black slunk resistance were conducted. The objectives of this study were (i) t0 estimate genetic variability for agronomic traits in the original base population (Co) and die three selection cycles and (ii) to characterize the effects of selection for black shank resistance on the agronomic traits. Fifty selfed lines From the base population and each of three selection cycles were evaluated in replicated field trials at Lexington and Princeton, KY. Differences among cycle means for six agronomic traits were not statistically significant. Genetic variation for the six traits among lines within cycles was highly significant and did not change during selection. The results indicated that previously assumed associations between black shank resistance in Beinhart 1000‐1 and undesirable agronomic traits were due to chromosomal linkages which were apparently broken by intercrossing. The C3 population would be a useful base population for selection to improve agronomic performance in black shank resistant genotypes.

Effects of soil ph, nitrogen source, phosphorus, and molybdenum on early growth and mineral nutrition of burley tobacco

Abstract Previous research has indicated that P application may influence plant Mo nutrition, and that both P and Mo are influenced by soil pH. This is of interest, since Mo is deficient in some soils and because large quantities of acidifying nitrogenous fertilizers are commonly applied in production of burley tobacco (Nicotiana tabacum L.). Burley tobacco was grown in two experiments using Maury silt loam soil (Typic Paleudalfs) to determine the influence of soil acidity, form of N applied, and P application on plant growth and mineral nutrition. The studies were conducted in the greenhouse so that high root densities would develop and the data primarily reflect rhizosphere effects. Ammonium application depressed rhizosphere pH 0.4 to 0.6 pH units. Nitrate nutrition raised soil pH less than 0.1 pH unit. Plants supplied NH4 exhibited slower early growth than plants supplied NO3. Several significant interactions involving soil pH, N source, P, and Mo occurred. In the first experiment, plant P was not affected by form of N applied, while in the second experiment NH4 application resulted in higher plant P concentration, both in presence and absence of applied P. Application of NH4 also increased plant weight in the second experiment. Plant P concentration was influenced by pH, being greatest at pH 6.2 and decreasing as pH levels decreased or increased. Plant Mo concentration did not differ among forms of N at pH 5.4, but at pH 7.2 was three times greater in the presence of NO3. When Mo was applied, P addition enhanced plant Mo concentration, but when Mo was not applied, P addition did not increase Mo concentration. This effect of P on Mo occurred only in the presence of N and was greater in the presence of NH4 than NO3. These observations suggest that enhancement of plant Mo nutrition by P application may be dependent on adequate levels of N being present.

Production of Burley Tobacco Using No-Tillage and Conventional Tillage

Production of Burley Tobacco Using No-Tillage and Conventional Tillage

Soil and Plant Factors Influencing Accumulation of Dry Matter in Burley Tobacco Growing in Soil Made Acid by Fertilizer1

AbstractA field experiment was conducted to elucidate factors influencing dry matter accumulation in tobacco (Nicotiana tabacum L. cv. ‘Burley 21’) growing in soil whose acidity was increased by fertilizer. Relatively large amounts of commercial fertilizers commonly are added to soil in burley tobacco production and knowledge of the effects of such additions on dry matter accumulation may lead to increased yields of cured leaf and improved usability of cigarette smoke. Samples of soil and plant material were obtained at varying dates during the growing season and were chemically analyzed. Varying soil pH levels were obtained from applications of N as ammonium nitrate at rates of 0, 90, 180, and 360 kg N/ha.The addition of N fertilizer to Maury silt loam soil with an initial pH of 6.2 significantly increased exchangeable Mn and decreased soil pH, exchangeable Ca, and concentrations of available MoO4−2 and H2PO4−. Exchangeable Mg and K were little affected by N fertilizer at any sampling date. Much of the decrease in exchangeable Ca may be attributed to leaching with NO3− by excessive rainfall early in the season. Evidence indicated some delay of nitrification of NH4+ in plots fertilized at the 360 kg N rate.Nitrogen fertilization of tobacco increased concentrations of Mn in leaves, but levels were not judged to be excessive for normal growth. A tendency existed for concentrations of Ca and Mg to be decreased by N at 40 days after transplanting and concentrations were near deficiency levels for Ca at this date, although exchangeable soil Ca levels exceeded 1500 ppm. In contrast, at 77 days and at harvest, N fertilizer significantly increased plant concentrations of Ca and Mg. Molybdenum concentrations in leaves from high N plots were only 20 to 50% of those in plots unfertilized with N. Concentrations of MoO4−2 in leaves from fertilized plots were near deficiency levels for most of the growing season. The data suggested interaction of MoO4−2 and Mn, and of Mn with Ca and Mg within the plant.Correlation and regression analyses revealed significant relationships of soil measurements near transplanting and dry matter at 40 days and of plant constituents and dry matter at all dates. Results indicated the depression of dry weight by N fertilizer noted previously during early growth was the direct or indirect result of fertilizer‐induced soil acidity.

The Optimum Geographical Location of Burley Tobacco Production within the Burley Belt

Burley tobacco is a major crash crop in Kentucky, middle and eastern Tennessee, and Southwestern Virginia. Burley tobacco acreages and the farm acreage distributions of burley tobacco have been determined by the United States Department of Agriculture since 1933. In 1966, approximately 250,000 acres of burley tobacco was alloted to farmers in the United States.The purpose of burley acreage allotments has been to equate the supply and demand for burley tobacco at a price considerably higher than that which a free market would establish.

Nitrogen‐Irrigation Interactions in Burley Tobacco Production1

Nitrogen‐Irrigation Interactions in Burley Tobacco Production¹