From the August 26, 2009 issue of PestMinder, a weekly publication of the Cornell Cooperative Extension Vegetable Program:
Greenhouse/High Tunnel Crops: Disturbing greenhouse tomato foliar tests came in this week that showed low levels of zinc, manganese and potassium. Soil tests indicated these nutrients were at adequate levels.
So what was the problem?
A soil pH of nearly 8.0 made these nutrients unavailable to the plant.
Any solution will have to be drastic: massive leaching or soil removal. Switching to pots or hydroponic production is another option. An ounce of prevention is worth a pound of cure. Acid injection, soil rotation and annual leaching with clear water will help prevent the pH from climbing in soil-based tomato greenhouses.