Rhizosheaths are coatings of soil particles that cling to plant roots. They are a sign of biological/microbial activity in the rhizosphere (root zone). Roots are brown, not white. Soil particles are bound to the roots by biotic glues, secreted by microorganisms. This is aggregation in action and therefore the start of forming good soil structure.
Do this test at the same time as the spade test/VESS test.