At the Kansas State Agronomy field day, kids were able to see the mini-rainfall simulator in action.  Real rainfall is highly variable, and results from simulators shouldn't be directly compared to actual rainfall.  But the principles of erosion and lessons for controlling erosion can be shown using these tools.

Soil erosion begins with the first raindrop.  The collision of the raindrop with the aggregates at the soil surface starts the erosion process.  Raindrops travel at about 20 mph.  When they hit the soil, the aggregates (soil particles tied together) are broken apart, and reduced to the sand, silt, and clay particles that make up the soil.  At first, water moves down into the rest of the soil, carrying these finer particles along.  But soon the fine soil particles begin to clog up the pore space, and water infiltration rates (water movement into soil) are reduced.

Smaller particles, especially the silt and clay fractions, are suspended in the water creating puddles on the soil surface.  When the infiltration rate is less than the rainfall rate, runoff begins to occur.  Crop residue on the soil surface plays an important role in protecting the soil from erosion, and in maintaining higher infiltration rates.  For soil conservation purposes, a minimum of 30% of the soil surface should be covered with crop residue.  From a soil erosion point of view, more residue is better.

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