The bed with the green peppers is a two year old bed, but the bed with the yellow ones is a one year old bed--so it's fresher bagged compost (which isn't well finished). So I think your right that those woodchips are locking up the nitrogen.

I fed both beds with epson salt and general purpose fertilizer slow-release pellets but that was at least a month ago and the heavy rain probably washed it out.

Epson salts do NOTHING to help your plants, and in fact may even be harming them as it can lower PH as well as excess Magnesium, it is not recommended by any accredited source around the world.

hit the yellow peppers with a water soluble fertilizer with a high N%.

Please see the link below for the benefits of Epsom Salts.

http://www.garden.org/articles/articles.php?q=show&id=68

Also the other articles in the following link:

https://www.google.com/search?q=epsom+salts+and+plants&ie=utf-8&oe=utf-8

<Epson salts do NOTHING to help your plants, and in fact may even be harming them >

That's a rather broad statement and I would have to disagree with it. True ES is not any sort of magical cure but it can play a beneficial role in certain circumstances. MG deficiency is a chronic problem in some soils and ES is often recommended by many accredited sources as a quick and easy method of correcting for it. Like anything it can be toxic if used in extreme or when it isn't needed but that doesn't mean it has no benefit for the plants.

Dave

When I mix my fertilizer in a 5 gallon bucket I always throw a handful of Epson salt with it.

Provide me an .edu site recommending amending with Epson Salts I will happily eat crow. Unless there is a major deficiency in the soil, adding these salts just to add them is not a good idea, and I stubbornly stand by my broad statement. ;)