This is a raised bed and I bought good vegetable gardening soil from a local nursery.  I add new store or nursery bought compost each year.  I do not put food scraps in the soil or make my own compost.  And when I add compost, I mix it in thoroughly.

I first noticed this white stuff a couple of years ago.  It was in big pockets around the bottom of my carrots which I let winter over.  The carrots were ruined.  I have tried not to plant root vegetables in any of the beds where I have seen the white stuff.  It seems to be multiplying and spreading to the other beds, so this year I'm thinking I'll use that soil as fill dirt and get fresh soil for my garden beds.  This picture is from my backyard bed.  It's never had this in it before and this is the only spot of it in the bed.  This is also the first and only time I've ever seen this brown layer beneath the white or anywhere else.  Usually it's just pockets of white in the super dark soil.

I am hoping to find out what it is, how I came to get it, whether it's ok to grow in, and how to get rid of it.

Please let me know if you need any more clarification or pictures.

Thanks! Calina