Can we modify the field to restrict it to a particular crop or project?

No, the BiOS license and all BiOS-compliant MTAs will not be   restricted to a particular use.  In an open source license such as   this, one significant incentive allowing the technology to grow in   value is that each licensee is agreeing, in exchange for the right to   use the technology both for research and commercialisation royalty- free, that all improvements will be shared with all other licensees.    Since the license grant is for any agricultural use, the licensee   will benefit from improvements that others are making on many other   plant species,  and it's not appropriate that (s)he agrees to receive   all those but put back into the growing pool only improvements   relative to a self-limited field.