Erosion is the action of exogenic processes which remove soil and rock from one location on the Earth's crust, then transport it to another location where it is deposited.
Procedure: Put soil in a erosion tray and make it a slope. Use a liter sized cup with a hole on a bottom suspended above the soil slope. Put water on the cup and observe how much material which is eroded. Scoop up the eroded material and weigh it. Repeat procedure with rocks on the top of the soil of the soil. Do it again with the mulch and then again with plants (or fake plants).