Actually, there is no scientific definition of organic food. The National Organic Program (NOP) is a marketing program that certifies that the crop has been produced using a specific set of legally defined methods and products approved by that program.
There are standards that must be followed in organic production. These standards allow for the use of program-approved herbicides and pesticides, required certain agricultural practices be followed and require completion of a formal certification process to verify that the standards are followed. You can see these at the website:
In the United States, no food can be labeled "organic" unless it complies with the requirements of the NOP. Qualified products can bear the "USDA Organic" seal. It is a certification program only; there is nothing that you can measure to verify that it is organic.