Float water alkalinity adjustment in organic seedling production
Float water bicarbonate (HCO3-) concentration in excess of 2.0 meq/L (100 ppm) can result in stunted, unusable seedlings unless neutralized. In conventional greenhouse systems, sulfuric acid is used for this purpose; however, it is not currently approved for use in organic production. Research was conducted to evaluate the following organic acidifying compounds: 30 % acetic acid, 50 % liquid citric acid, 45 % ß-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-day 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. Results indicate that acetic, ß-Hydroxytricarballylic, and sulfuric acid can rapidly neutralize bicarbonates to an acceptable concentration and that re-application may be required as soon as five days later for neutralization. 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 complemented by an increase in nitrate-nitrogen concentration and seedling vigor.