NFT Ponding Problem
I'm growing lettuce in an NFT system. As the roots grow bigger, the nutrient solution gets more than 1-2 mm. deep. Today I observed that at some places it is at least 6-8 mm. thick.
Note that before planting the seedlings, I set the slope of the channels as high as possible. If I set them any steeper, the solution did not spread and cover the bottom of the gully, flowing more thin line following either side of the gully. That would be a problem because roots of the seedlings would not be wetted.
Anyway the roots seem to be ok. No browning or rotting, all white. Though the growth is definitely slowed down. EC, pH etc. are ok. No disease symptoms that I could observe.
I'm thinking, this ponding problem may be the cause. Even there is enough oxygenation to let the roots stay alive, It may not be enough for the plants to grow properly. But of course this is just a guess.
Do you have any experience/ideas about this problem?