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48th TWC, Tob. Work. Conf., 2018, abstr. 20

Screening of acidifying chemicals for use in the production of organic tobacco seedlings

(1) North Carolina State University, Raleigh NC USA; (2) North Carolina Department of Agriculture and Consumer Services, Raleigh NC USA

Float water bicarbonate concentration in excess of 2.0 meq/L (100 ppm) can result in stunted, unusable seedlings unless float water is acidified. In conventional greenhouse systems, sulfuric acid is used for this purpose; however, that chemical is not currently approved for use in organic production. Research was conducted in 2017 to evaluate the following organic acidifying compounds: 30% acetic acid, 50% liquid citric acid, 45% B-Hydroxytricarballylic acid, and 99.5% granular citric acid. One additional treatment included continuous float water aeration, which has been documented as a long-term option for bicarbonate reduction. A non-treated control (no acidification) was included as a negative control treatment. Sulfuric acid (35%) was included as a conventional grower standard. Float water samples were collected at five days intervals after seeding and titrated to quantify bicarbonate concentration. Following titration, acidifying materials were added to each bed at rates determined by titration results. Twenty-four hours after acidification, float water samples were again collected to measure the effects of each material. Preliminary results indicate that acetic, B-Hydroxytricarballylic, and sulfuric acid can rapidly neutralize bicarbonates to an acceptable concentration. Alternatively, the effects of both citric acid sources are not sufficient for suitable bicarbonate adjustments, thus indicating that application rates should likely exceed those evaluated in this study. Lastly, results from aerated treatments indicate that oxygen supplementation could produce a long-term reduction in bicarbonate concentration that is also complimented by an increase in nitrate-nitrogen concentration and seedling vigor. (Reprinted with permission)