Can't search in a certain field using solR

Question

Hi,

I'm setting up an environment using Nutch 1.0 + solR 1.4. In Nutch I configured the subcollection plugin which seems to work nicely. If I search as normal adding fl=* I can see the subcollection field is filled as intented. (something like <str name="subcollection">mysite.com</str>).
My problem is, I would like to be able to search only in one or more given subcollections, but whenever my searchquery is something like q=subcollection:mysite.com it won't work. I've also tried to add a fl=* or searched in mysite* instead but I never get any results. Obviously solR "knows" the subcollection field, as it doesn't result with an error but simply with an empty result.

I'd be glad for any help