Answer: While tomatoes are known to be "heavy feeders" too much of a good thing can also be a problem. Unfortunately it is impossible to tell you how much fertilizer to use wothout running some basic soil tests to find out what kind of shape your soil is in to begin with. Your County Extension (421-6430) can help you with the tests as well as with interpreting the results.
Yellowing lower leaves would not normally be a symptom of needing fertilizer. It can however be an early sign of fusarium wilt or possibly verticillium wilt, or even a sign of overwatering or overfertilizing. You might want to take a sample to your County Extension and see if they can help you determine the cause.
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