United Kingdom 
i have 9 raised beds last autumn i spread horse manure on them all and covered them with black plastic this spring i duly uncovered them worked the soil a little and planted everything is growing well and healthy except one bed which has now had three lots of carrot seeds sown in it and none has germinated strangely there isnt a single weed growing in it either it is completely sterile base soil is clay but every year i put well rotted horse manure and my own garden compost on the beds i hope you can shed some light on this problem for me thanking you in hope of an answer jan davis
14 Jun, 2014
Answers
I'm not a veggie grower either, but I do know that root crops like carrots and parsnips don't like manure, so that may be why you're having trouble with your carrots.
14 Jun, 2014
My carrots never germinate either. Maddening isn't it?
14 Jun, 2014
Also I wouldn't cover the beds over the winter - let the weather get at them. See if you can borrow a book on veg growing from the library, so you can see what veg like manure, and which crops are good to follow on from which others. They don't all like the same treatment.
14 Jun, 2014
Welcome to GoY....
I'm not a veggie grower but I'd be looking at the depth of the raised bed before hitting the clay level and whether there is any drainage above the clay. I've just discovered solid clay about three inches below the surface in my new garden - which explains the rather nasty raised beds there which are also sterile because there is just no drainage.
If the raised bed is a suitable depth for carrots then maybe you need to improve the drainage - mix in coarse material such as grit and/or drill through the walls of the raised bed just above ground level and/or take out the compost, place in a layer or coarse grit, refill with fresh compost/soil.
14 Jun, 2014