Ponzu is one sauce I see completely bastardized all over the Internet and in Japanese cookbooks. Traditionally, it was made from the juice of daidai (a bitter orange similar to Seville orange), not yuzu or vinegar (as many recipes say). Ponzu also usually has some dashi splashed in, but farmers are most likely skip that unless they happen to have some handy. Farmers also like a strong salty flavor, since they work hard in the fields before sitting down to dinner.
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*Note: The ratio of soy sauce to citrus juice should be 1:1.
Mix the soy sauce and daidai in a small bowl. Sprinkle in some chopped chives, if you like. Use within a day or so, but store in the refrigerator.