First of all please do not repeat posts!!

Bagagge allowance is based on destination, check it here

http://www.qatarairways.com/global/en/baggage.html

As per excess lugagge read the following statement

"Excess baggage will be subject to additional fees, to be collected at the airport. For excess baggage rates please contact your nearest Qatar Airways Office"

So in the end contact tha airline for details on costs; & cargo availability for extra "weight".

Regards!!