Organic Production of Tobacco Transplants: The Nitrogen Dilemma Bob Pearce University of Kentucky
Organic Tobacco Small but growing niche market for tobacco growers. Requirements for organic production frequently change Different rules in each country Confusion over what is or is not allowed Growers still want to use float system for transplants
The nitrogen dilemma Tobacco plants grow best with nitrate-n Will utilized ammonium to limited extent Organic forms of N must be mineralized and then nitrified to produce nitrate Float environment is not conducive to nitrogen transformations Soilless system Microbial population imbalances Saturated root zone Low oxygen levels in water
Nitrogen fertilizer problem in float beds mid 1990s JCC 20-10-20 Mostly urea-n Pro Sol 20-10-20 Mostly nitrate-n
Impact of urea N on nitrite-n accumulation in the root zone of tobacco float plants Transient nitrite accumulation Nitrite increased as proportion of N supplied by urea increased Root tips negatively impacted by as little as 5 to 10 ppm nitrite- N Pearce et al. 1998
Lab Incubation Study of Nitrogen Transformation in Nutrient Solution Fertilizer Source Nature Safe 5-6-6 Added at rate of 125 ppm Total N Treatments Check (water + fertilizer) Soil inoculant Compost inoculant Aquarium nitrifier inoculant
Lab Incubation Study
60.00 Accumulation of Ammonium check soil compost nitrifier 50.00 Ammonium (ppm) 40.00 30.00 20.00 10.00 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 days
Accumulation of Nitrate Nitrate-N (ppm) 25.00 20.00 15.00 10.00 check soil compost nitrifier 5.00 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 days
Inoculation of Water?? Results were inconsistent Many factors impacted activity of nitrifiers ph of the solution Availability of other nutrients Viability of inoculant Temperature of water Oxygen status of water Not enough information yet for grower recommendations
Organic Tobacco Transplants Grower Farms 2015 Two growers with similar problem growing transplants for organic production system Fertilized with organic fertilizer 5-6-6 Added Sodium Nitrate at 5 weeks Plant still not responding at 6 weeks
Grower Water Test Reports
There is something eating the roots off my plants Rat-tailed maggots Larvae of the drone fly Thrive in low oxygen organic rich environment tail is actually a breathing tube
Organic fertilizer float test research greenhouse Spring 2015 5-6-6 Organic ph: 7.7 Alk: 314 ppm Nitrate-N: 1 ppm 20-10-20 Inorganic ph: 7.1 Alk: 67 ppm Nitrate-N: 32 ppm 5-6-6 Organic + 15-0-1 Organic ph: 7.6 Alk: 496 ppm Nitrate-N: 2 ppm
Denitrification in Fresh Water Systems Typically carried out by facultative anaerobic bacteria under low oxygen conditions. 2NO 3- + 12 H + + 10 e - = N 2 + 6 H 2 O Increases alkalinity by 3.57 mg CaCO 3 per mg Nitrate-N Presence of RT Maggots low Oxygen Lack of Nitrate-N High alkalinity levels
Research greenhouse test fall 2015 Organic soilless media 4 Fertility treatments 20-10-20 water soluble fertilizer 5-6-6 plus 15-0-1 in float water 5-6-6 plus 15-0-1 in media 5-6-6 plus 15-0-1 ½ rate in media Fertilizer incubated with media 1 week prior to seeding Aerated vs Non-aerated
15-0-1 Foaming in Water
Media Saturation Extract (1 week incubation with fertilizer) No added fertilizer 5-6-6 (14g/L) 15-0-1 (4.7g/L) 5-6-6 (7g/L) 15-0-1 (2.4g/L) ph 6.2 7.7 7.7 Conductivity (mmho/cm) 1.28 10.54 5.75 Nitrate-N (ppm) 40 5 3 Phosphorus (ppm) 34 10 19 Potassium (ppm) 54 1031 454
Inorganic Nitrogen in Media (2 weeks after seeding) 600 Nitrate Nitrite Amonium 500 Nitrogen (ppm) 400 300 200 100 0 20-10-20 Organic (water) Organic (media) Organic (1/2 media)
Leaf injury on Non-aerated Organic Fertilizer in Water
Alkalinity in Float Water (6 weeks after seeding) Alkalinity (ppm) 700 600 500 400 300 200 Aerated Non-aerated 100 0 20-10-20 Organic (water) Organic (media) Organic (1/2 media)
Nitrate in Float Water (6 weeks after seeding) Aerated Non-aerated 45 40 Nitrate-N (ppm) 35 30 25 20 15 10 5 0 20-10-20 Organic (water) Organic (media) Organic (1/2 media)
Float Water Appearance with Organic Fertilizer in Water Non-aerated Aerated
Dry Weight of Plants (7 weeks after seeding) Aerated Non-aerated Dry weight (g/10 plants) 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 20-10-20 Organic (water) Organic (media) Organic (1/2 media)
Growth of Transplants at 6 Weeks
Growth with Organic Fertilizer Added to Water Aerated Non-aerated
Conclusions Aeration improved nitrogen transformations of organic fertilizer in tobacco float system. Aeration improved growth of tobacco transplants in tobacco float systems fertilized with organic based fertilizer. Best growth may be achieved with combination of organic fertilizer in media supplemented with additional applications to float water.