Using organic fertilizers for hydroponic lettuce production

From Hort Americas corporate blog:

With the increased interest in organic produce by growers, retailers and consumers, researchers at Kansas State University looked at the production of hydroponically-grown lettuce using organic fertilizers. Jason Nelson, who received his Master’s degree this year, said the purpose of the research was to study overall plant performance with organic and inorganic fertilizers. Another aspect of the research was to study the effects of commercial microbial inoculants that are marketed to promote plant growth.

‘Rex’ butterhead lettuce was grown in nutrient film technique troughs. The nitrogen sources of the complete inorganic fertilizer were ammonium nitrate and ammonium phosphate. The organic fertilizers consisted of four Kimitec products for hydroponic production, including Bombardier (8-0-0), Caos (10.5 percent calcium), Espartan (2.7-3.0-2.6) and Tundamix NOP (micronutrients), plus KMS (potassium magnesium sulfate) from a different supplier. The microbial inoculants included SubCulture-B bacterial root inoculant and SubCulture-M mycorrhizal root inoculant.

“Nitrogen in organic fertilizers is primarily found in proteins and other complex molecules that break down to ammonium,” Nelson said. “The ammonium levels could be considered comparable between the two types of fertilizer systems, although the level was slightly higher with the inorganic fertilizer. The biggest difference was in the nitrate nitrogen. Starting out, the inorganic fertilizer contained 75 parts per million nitrate. With the organic fertilizer there was no nitrate at all. For the other nutrients, including phosphorus, potassium, calcium and sulfur, using all of Kimitec products except Katon, which is a potassium source, those were all comparable with the inorganic fertilizer.”

Nelson said the purpose of incorporating the microbial inoculants was to learn if they had any impact on the plants grown with either of the fertilizers.

“Growers have had some trouble getting the same amount of growth using organic fertilizers compared to inorganic fertilizers,” he said. “These microbial inoculants are advertised as being able to boost plant growth. One purpose of the study was to determine if the inoculants would boost growth in an organic hydroponic system so that it would be comparable to plant growth with inorganic fertilizers.”

Read the rest of this blog here.