Agriculture Reference
In-Depth Information
Analyzing Your Soil's Water Characteristics
Soil has three important characteristics pertaining to water:
infiltration, percolation and available water-holding capacity.
Infiltration is a measure of how quickly water is absorbed into
the soil. Quicker infiltration means less water is either lost or
runs off. Percolation is how quickly water that is in excess of
what the soil can hold leaves the soil. Available water-holding
capacity is how much water the soil can hold. In practice, if
you can get the infiltration and percolation rates within
reasonable ranges, your water holding capacity will take care
of itself.
Analyze percolation rate by digging a hole 1' deep and 6"-8"
in diameter, and keep it topped off with water for at least four
hours on the day before you test. The day you test, adjust the
water level in the hole to 6" from the bottom (use a plastic
ruler). Next, set a timer for ten minutes. At the end of ten
minutes, use a ruler to measure how many inches the water
fell. Bring the water level back up to 6", repeat the process,
and average the two distances. The percolation rate in minutes
per inch (MPI) is: MPI = 10/Distance. You want an MPI of
between 60 and 30. If it is greater than 30, use raised beds to
prevent waterlogging. If it is less than 6, increase the level of
compost you would add based on biological activity by 50
percent. Do this with each compost addition until you have an
MPI of 6 or greater.
Infiltration rate is tested two days after a thorough (e.g.
equivalent to 1" of rain) watering. It is measured using a
"double ring infiltrometer". This fancy sounding gadget is two
pieces of PVC pipe, each 8" long, one being 4" in diameter
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