When salary requirements are requested, you have a little more flexibility. One option is to state that your salary requirements are negotiable based upon the position and the overall total compensation package, including benefits. Another alternative is to include a range, based on the salary research you've done, i.e. my salary requirement is in the $35,000 - $45,000 range.
Either way, note that your salary requirements are flexible. That may help keep you in the running for the position and will give you some flexibility when negotiating compensation later on.