Investigating impacts of Electrical Conductivity in Nutrient Solutions
Lettuce and Brassica winter production in NFT systems in Ohio
By: Dr. Natalie Bumgarner
Seeding was done by hand into pre-moistened 1” x 1” x 1 ½” cubes. Seeds were germinated in 9” nursery channels that were receiving a continuous flow of nutrient solutions set at experimental levels. After 15 to 17 days, seedlings were transplanted to the production NFT channels at a spacing of 8” on centers. After transplanting, plants were grown in 4 ¾” channels until harvest. The nutrient solution was automatically and continually adjusted to maintain a target pH of 6.0. Electrical conductivity was maintained by hand additions of nutrient concentrate as
needed based on daily measurements of EC. These trials were carried out in a system designed to pull from four different 40 gallon nutrient tanks so that differing solution could be tested in a randomized block design. At harvest, shoot fresh weight was recorded individually for each head.
Timing and Conditions
Biomass Yield by EC Treatment
EC x Cultivar Biomass Yield
As discussed earlier, both of these trials were carried out in low light, winter conditions. It is quite likely that when light is less limiting that more nutrition impacts will be present. Likewise, quality impacts (tipburn) may be more of a factor in summer trials.
In most of our recirculating systems, our goal is to manage solutions to prevent nutrients from becoming limiting. Tank changes at specific intervals are often how we accomplish this goal (without purchasing specific ion probes). Only through nutrient testing and trials will we know for sure what the optimum EC and intervals between solution changes will be. While it stands to reason that tank changes may need to be less frequent at higher EC levels and/or higher light conditions, we need data to back up our practices and theories.