||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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