This sample was recently sent in.
The root system was poor and they were suspecting a root rot. However, there were no pathogens in the sample.
The symptoms (pale leaves) looked somewhat like a nutrient deficiency, but the brown roots made me think nutrient excess.
We did a quick electroconductivity test using this machine:
The overall salt content was extremely high, definitely in the damaging range. In the first photo, SME stands for saturated media extract, and the 9.0 represents 9.0 mmohs/cm, which is a measure of salt content. (9 mmohs = 9 dS/m)
My colleague Kim Williams recently did a podcast about salt toxicity and you can check that out here:
http://www.greenhousegrower.com/ggtv/?vid=511
I talked to Kim about this sample, and she pointed out that when temperatures are really high, slow-release fertilizers can release faster than they otherwise would. That may be part of the problem in this case.
Here are some of the fertilizer prills:
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