I have over 30 pecan trees in my yard and ya, you-betcha you can add pecan shells to the compost. If it's just the hulls, they make an attractive mulch to your garden beds too, that will break down over about 18 months into nitrogen-rich compost. When we rake up last years pecans in the Spring we add them directly to the compost bins and let the microbes do the rest. Takes a little longer than the rest of the stuff, but it's worth it.
I have one acre that is made up of mostly soil that has washed down the hill where the pecan trees are growing. These are old pecans, some of them probably over 100 years. In the course of all those years and seasons of pecans all that material has built up a layer of what I like to call "pecan soil" because of the color and texture. It's rich, black, loose and fertile. If we let the weeds grow up in it, they get 4' tall. I planted some fruit trees down ther a couple years ago and the "pecan soil" is about 2' deep. The fruit on the trees has to be thinned so it doesn't break the limb it's growing on.
Pecans are good stuff for the compost, the soil and the plants it will support. Crushed hulls will break down fairly quickly.
Cheryl
