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45th TWC, Tob. Work. Conf., 2012, abstr. 26

Evaluation of the impact of growing season moisture on burley crop quality

BRIDGES T.C.; WALTON L.R.
Biosystems and Agricultural Engineering Dept., University of Kentucky, Lexington, KY 40546-0276 USA

The yearly grade index was calculated and used as a measure of burley quality for the years of 1959 - 2000. Grade index is a numerical standard that provides an overall measure of crop quality based on approximately 110 grades established by the U. S. government grading system. The numerical grades were divided into 3 major color groups: a tan or buff group containing XL, XF, CL, CF, BF and TF grades; a red or tannish red group containing the BFR, BR, TFR, TR and MFR grades and a green group containing grades with V, VF, VR, G, GF and GR designations. Color group correlations with grade index found the tan group to be significantly positive (<.0001); the red group was positive but not significant, and the green group was significantly negative (<.0001). Green color is detrimental to overall crop quality and is generally thought to occur when curing conditions are less than ideal. However, a previous study used an available moisture index (precipitation minus evapotranspiration) to identify a critical moisture interval (CMI) during the growing season that had a significantly negative correlation (.0045) with the yearly per cent of green burley tobacco. For Lexington, KY this CMI begins day 34 of the growing season (or approximately 5 weeks into the season) and lasts for 25 days (approximately 3.5 weeks). The CMI statistics showed a 42 year average precipitation of 3.63 inches while the evapotranspiration average was 4.35 inches, for almost a 0.75 inch moisture deficit. Such a deficit may set up conditions contributing to additional green color. Prediction statistics showed the amount of green leaf as a function of available moisture yielded an r2 value of 0.1845 indicating that the moisture deficit was responsible for approximately 18 – 20 per cent of yearly green color. (Reprinted with Permission)