Can't say for certain in general, but I can give you some advice from my (one) personal experience.

If you are composting with wood products (mine came with what looked like wood mulch mixed in) the decomposing wood will actually rob you of nitrogen.

My garden struggled for over a month until I figured this out and added some chicken poop to the soil around each of the plants. I did a broadcast of chicken poop across the whole garden this fall after everything died off to help pick things up for next year.

Composted manure can be good. Soil too rich? Maybe they meant soil high in nitrogen? If that's the case then I would agree. Nitrogen causes vegetative growth and in abundance with nitrogen rich soil, which can be bad for peppers in the sense more leafy growth and less pod production. Also manure is a slow release type of fertilizer so if you use it, I would recommend not using any other fertilizer to add more nitrogen or one that contains it while adding the other necessary nutrients P-K and the other micronutrients.

Mark

Following my intuition worked well for me ('tho it would drive the purists crazy). I didn't understand why until I read the above posts.

I started with my usual potting mixture when potting up(basically peat, leaf compost, pine fines and a little lime) then added 10 to 20 percent well-composted manure. And for the first few weeks I also watered with some of that blue liquid to get the plants off to a quick start.

Those plants were very happy and productive. Whenever I'm trying out a new potting mix, I only use it on a few (5-10) plants. Next year I'm going to do something similar with the main crop.
Rick

That's a great, if not obvious tip, there, Rick! When trying something new, whenever possible, test on only a part of your garden / plants. I feel like I should have known better, but, I tried different mix for my potted peppers last year (all but 2 of them) and I struggled through most of the season. If I had only tried on a few, I could have worked out the problems on the few while the others would have been fine.

I grew my peppers with 5 gallons of compost per plant this year. I had the best production I've ever seen. Caveat that it was NOT wood fiber based which as noted above can rob soil of nitrogen.

DarJones

Heehee, dung heap in progress.

I knew about the potential nitrogen robbing problem with wood. Sawdust makes an excellent bedding/litter for animals on that account because it soaks up the nitrigen rich urine.

I've got to cut this post short, company just drove in, be back later... :-)

I'll be 'building' a pile of horse manure in layers and wetting it down to bring it 'in heat' and compost for the 2013 gardenSome observations here: 1) Addition of nitrogen-diluting materials to manures (sawdust, pine straw, etc.) lowers the concentration of total N in the mix, so more of the stuff needs to be accumulated to acquire the same total N mass of a manure more concentrated in N. 2) Manures with initial lower total N concentrations will not lose more N than those with relatively greater N concentrations but may lose more mass over time because of greater amounts of C losses. 3) A significant problem with most horse manures is the presence of a goodly amount of weed seed, which is hard for the townie gardener to "compost" away because the heating requirements for such are difficult to attain.
So for the average gardener using the horse, I suggest that it be gathered and stored in a heap as compact in size as practical, if accumulating it for future use. For "garden time" application, fresh horse should preferably be worked into existing soil if possible to minimize fugitive losses of N (mostly NH3).
Reggie

"...A significant problem with most horse manures is the presence of a goodly amount of weed seed, which is hard for the townie gardener to "compost" away because the heating requirements for such are difficult to attain.
So for the average gardener using the horse, I suggest that it be gathered and stored in a heap as compact in size as practical...."

Right on Reggie. Years ago I used horse and rabbit manure almost exclusively in my garden as fertilizer and soil builder; I did supplement with a commercial phosphate and potash from the wood burner.

Many years ago my very first experience was with a load of very old cow manure from an abandoned dairy barn which I just broadcast over the garden and tilled it in, and, oh my oh my, I might as well had hand sown the weed seed, it was a nightmare. There were weeds that I still don't know what they were, but it was a lesson learned.

About that time Rodale published their 'Guide To Composting', which I promptly bought, and the knowledge I gained from there was invaluable. I learned all about manures, and it just so happened that just down the road less than a mile away from me was a very large horse barn (est 80 stalls) that rented stables to the public - read an inexhaustable supply of horse poop for lil' ol' me! (at that time)

Horse manure taken directly from the stall and built in layers into a compact pile as you say, and thoroughly soaked with water as you go along and then covered with plastic will indeed heat up (I've never had a failure even in Winter) and kill the weed seed.

This is a strictly anaerobic composting method which is described in Rodale's book under, well, Anaerobic Composting. I believe horse manure was taylor made for this method of composting.

It takes 3-5 weeks and it's ready to use. I prefer to stretch it out by spot using it in the hills with individual plants.

Here's the completed 'dung heap'. It's funny, we had snow the other night and I peeked out the window and the covered straw pile had a coating of snow, the covered mulch pile had a coating of snow, BUT NO SNOW ON THE MANURE, it's hot already, and I even used very cold water from the rain trough to wet it down.