There is alot of things that impact crops, but never had any issues with straw in all my yearsThere have been posts here at BYC of birds who got very sick and/or died from sour crop. There's also info on the internet. Here's a good write-up on what causes an impacted/sour crop: http://www.tillysnest.com/2012/01/crop-issues.html
My little Light Brahma (named Drama) isn't the brightest bird in the bunch. She ended up with a pretty bad impacted crop because she preferred to eat sand and pine shavings over food. She free-ranges a lot now, so she's a little better. When I put straw out there in the coop, I noticed she was eating a lot of straw that had blown out of the coop in the wind instead of grass or food. I decided to not take a chance with her. I've nursed her back to health once in her short 10 weeks, didn't really feel like going there again.Yesterday I replaced the straw with pine chips, and now the dumb bird nibbles on the pine chips that blew out. But, at least the pine chips pieces are smaller than the straw pieces she was sucking down.
I did like the straw better in the coop though. It was really easy to clean the poop out of the coop. Plus, I didn't have to wear a respirator just to breath with the straw, like I do with the pine chips.
That said, I have had issues with crop impaction from grapes and cherry tomatoes, and small stone fruit such as cherries.
They just roll around in the crop as a chicken cannot chew, nor do they have stomach acid to mush up these small hard round items.
Lost a beautiful Blue Copper marans hen from a single green grape.
And man do they love grapes !
If you feed grapes, please cut each one up in quarters.