The difference between the two boards will show the value of plant cover for erosion protection. All the soil sticking to the board would theoretically wash down the stream until it reached a collection point such as a lake or stream. The hard one that is low in organic matter will dissolve first. The plant roots and the organic matter hold the soft one together. Engineers put steel in concrete to hold it together.
Plant roots do the same thing, they hold the soil together.
The jar under the lamp chimney with high organic soil should fill first. The high organic soil will allow water to soak through it faster recharging underground water supplies or stream systems. Measure how far the water went into the ground. In lakes and streams. Other Activities Create an earthworm farm using inverted two-liter soft drink containers.