Are you presently on probation for another crime and question whether doing your business in public will violate it? It could but probably won't. Pay the fine and hope.
This appears to be a continuation of the question I previously answered under http://www.avvo.com/legal-answers/if-public-urination-is-a-violation-and-no-record---83019.html
As I said there, I do not believe that you are going to get maxed out here. On the other hand, there may be some exposure.
One of the issues that you need to review are the standard terms of probation that you received when you were placed on probation. In many States, these list arrested for another offense / charged with another offense as a basis to violate you. It also may depend on whether your State defines the terms arrested and charged as being the same thing. Some States do.
This information is offered for educational purposes only. It is not intended as legal advice and you should not rely upon it to decide how to resolve this issue. No Attorney-Client relationship is intended or established by this response. You are faced with a situation where you need to consult with an experienced defense lawyer admitted to practice law in your State before you make any decisions as to how to resolve this issue.