Investigating the Incorporation of Microbial Probiotics in Hydroponic Lettuce Production in Ohio

Soilless controlled environment vegetable production is designed to tailor growing environments and nutrient delivery to enhance both crop yield and quality. Typically crop nutrients are provided through a nutrient solution, which for leafy crop production is either flowing in channels or contained within ponds or deep water systems. To achieve accurate and consistent supply of plant nutrients, the majority of hydroponic nutrient solutions are formulated with inorganic fertilizers. This method of nutrient delivery is less reliant on the biological activity critical in nutrient cycles in soil systems. While much is known about crop nutrition in hydroponic production, the potential managed incorporation of microorganisms and their products is incompletely understood. Soilless production of vegetables stands to benefit from increased utilization of biological materials, if applied and managed correctly. Therefore, this work was carried out to evaluate the performance of a microbial product (BiOWiSH^TM) in hydroponic lettuce production during Summer and Fall 2012 in Wooster, OH. Three commercial cultivars (‘Fidel’, ‘Multy’, and  ‘Ferrari’) were grown using nutrient film technique (NFT) with solutions maintained at 1.8 mS/cm EC and 5.8 pH. Greenhouse aerial temperature, relative humidity, and solar radiation in addition to nutrient solution pH, EC, and temperature were continuously monitored. Seeds were germinated in rockwool cubes (2.5 x 2.5 x 3.8 cm), transplanted to NFT channels after 2 weeks, and harvested after about an additional 4 weeks. Shoot weight was measured on all plants and elemental composition was evaluated on a subset of plants. Experiments one (13 June–20 July) and two (22 August–3 October) compared a control solution with three experimental treatments incorporating BiOWiSH^TM formulations at either 10.0 or 3.3 ppm. Significant cultivar differences were present in both experiments (P ≤ 0.0001). ‘Fidel’ consistently yielded highest. In experiment one, completed under summer conditions, biomass was significantly different among the control and BiOWiSH^TM treatments (P = 0.0046). BiOWiSH^TM treatments one and two were both significantly higher than the control. Experiment two, conducted in the early fall, showed similar trends but differences were not significant between the control and BiOWiSH^TM treatments (P = 0.83). These two experiments indicate opportunities for microbiological products to impact crop yield in leafy hydroponic systems in northern U.S. climates, but also indicates that environmental conditions and management will likely be important in incorporating biological or microbial products in soilless leafy crop production systems.