Rainwater Harvesting: A Better System
From MOTHER EARTH NEWS
By Cheryl Long
Harvesting rainwater to use for growing vegetables makes a great deal of sense. Unfortunately, the most common method of rainwater harvesting isn’t the most effective. Typically, gardeners invest in a rain barrel - which holds only 50 or 60 gallons of water - and then dole out the captured water to plants as needed, hopefully emptying the barrel before the next storm.
But 50 gallons is only a small fraction of the water you could be harvesting each time it rains. During a 1-inch shower, more than 900 gallons of water flow off the roof of a 30-by-50-foot house or barn. Instead of catching just a little bit of it in a rain barrel, why not capture it all?
How Soil Stores Water
Except in areas with consistently high rainfall, your garden soil’s moisture level will seldom be at “field capacity.” That’s the term scientists use to describe the maximum amount of water a soil can hold. When it rains or when we irrigate, gravity pulls the water down into the soil. After a heavy rain, some of the water may move all the way down to the water table or the bedrock, but a large amount of it is held by capillary forces that cause water to coat each soil particle and partially fill the spaces between particles. (An example of capillary action is the way a paper towel absorbs liquid.) That capillary water is what your crops use as they grow.
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