chelation in the nitrogen cycle

You move quick Sandra! The diagram in question is in lecture 23 (slide 5) and also on Soilweb 200 (http://soilweb200.landfood.ubc.ca/soil-biology/nutrient-cycles/4-nitrogen-n/).

Metalo-organic complexes are indeed chelates
Since both organic compounds and clay particles are charged, they can interact with each other, forming complexes of organo-clay complexes. We did not cover this in our course, but this is something that does happen often in soils.