This is a brief summary of a research project by Dr. Amy Turnbull, A&L Biologicals Agroecology Research Services Centre, London, Ontario. It looked at the impact of sulphur on tomato root disease and vine decline symptoms. Root and soil samples for the study were taken from processing tomato fields in Essex and Chatham-Kent.
Six tomato fields were visited in 2011. Healthy and diseased plants were pulled from three fields, while only healthy plants were taken from two fields and only diseased plants from one field. The soil surrounding the roots was analysed for nutrients. A higher concentration of sulphur was observed in healthy soil compared to diseased soil when comparing between plants pulled from the same field.
Sulfate was then tested in growth room studies. Sulfate sources were magnesium sulphate, ammonium sulphate and ferrous sulphate. Controls were magnesium chloride, ammonium chloride, and ferric chloride. Chemicals were added to 50 ppm and 500 ppm to naturally infested soil collected from a field with tomato vine decline symptoms. No difference in disease severity was noted in sulphate-treated plants using the amount of lesions on the roots or shoot biomass as indicators of disease. These trials were repeated twice with five plants per treatment.
Report from Dr. Amy Turnbull, A & L Biologicals Agroecology Research Services Centre, London, ON.
I used potassium sulphate this year at fairly high levels for the first time (usually just use KCl) and have the most uniform plots I have had in about 5 years. I am doing a few other things too such as rotating after a full season with pearl millet. Nematodes were not a problem last year, and my nematode levels are below thresholds in general. I believe that I have had a significant root rot problem because of my practice of growing tomatoes every other year. Soil test levels for S were ok last fall, but if you read the data from western Canada on sampling for S on canola, it is very easy to get erroneous S data from soil samples due to the high variability within a field. My growth in previous years was also highly variable, with some excellent areas and some very poor ones. The fact that this difference has virtually disappeared in one year is very suspicious. Despite the lack of support in Amy’s growth chamber tests for a S connection, the artificial conditions used and the small number of plants grown does not necessarily constitute a robust test of the hypothesis. I would keep an open mind to the possibility of S being one potential factor in the root decline problem, at least until a field trial is run. In this year’s field, I pulled out one plant to see what the roots were like and got a full 18″ of clean root (without using a shovel).