What's killing my Orange tree?

I just just giving out what I personally used. Sorry they are no use to you.

I use a hoe and/or hand trowel. No desire to add the chemicals in table salt or vinegar to my soil.

Those two are completely different. Vinegar is essentially a water solution of acetic acid, CH3COOH, which disintegrates very fast into basic compounds (H2O and CO2), so it does not have any long-term effect. It’s a weak herbicide though. On the other hand, salt is a strong herbicide, but sodium and chlorine ions will stay in the soil for a very long time (until leached away by rains over many years) and will be harmful to any plant in the area.

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The by-product of acetic acid mixed with my soil is clay.