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Index : Watering
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- 33. When it Comes to Rain - Top
- I can't help anticipating the rains that hopefully will come soon, and the beneficial effects they have on the desert, our gardens and landscapes.
Have you ever noticed how plants always look greener after it rains. If it seems this "greening up" is more pronounced after an active thunderstorm, your right! Lightening is a potent fertilizing agent. Every time it strikes nitrogen in the atmosphere is combined with hydrogen to form an ammonium form of nitrogen. This form is readily washed to the ground with rainfall, and utilized by plants.
Physicists estimate that roughly 250,000 tons of nitrogen are produced by about 1,800 thunderstorms that occur on Earth every day. Our summer thunderstorms can release significant amounts of nitrogen for plant growth here in Tucson. That can cause part of the greening.
In theory, rain water is pure. It is formed from evaporation of moisture largely from the ocean, but also from inland bodies of water, the soil, plants, and even animals. Condensation returns it to earth; but not before it picks up some hitch-hikers. Sulfur is one of these. It is possible for rain to provide as much as 40 pounds of sulfur per acre per year. Less in our desert environment, but still when the rains come so to does the sulfur. Sulfur is an important constituent in the formation of plant amino acids.
Dust is something we have no shortage of here in the Southwest, but dust although a nuisance indoors can be beneficial. Dust can be carried thousands of miles on the upper air currents, and come down to earth during rain storms. Dust carries with it a number of mineral nutrients and beneficial micro organisms. These solubilized nutrients can quickly influence the color of foliage.
The level of soil benefiting elements is related to the origin of such dust. Ashes from forest fires contain potash, an essential plant nutrient. Debris from volcanos, which can travel world-wide contains a wealth of essential minerals for plant growth.
Most importantly, rain provides the kind of even and thorough wetting that irrigation can provide. In practice, drip irrigation is one of the least uniform types of irrigation possible. This is because not enough drip emitters are used around plants. Even most large trees are lucky to have more than a couple of drip emitters placed near the trunk. These emitters are watering only a fraction of the rooting area of a tree. Shrubs too, suffer the same fate.
Considering that plant roots grow well beyond the edge of their branches, A few drip emitters just don't do the job. Rains however places water over the entire root system. And even if the rains come down too fast, at least the top layer of soil is thoroughly soaked. It's in the top layers were a majority of the roots are.
You can trap and store rainwater by attaching rain barrels to down spouts from roof gutters. Large plastic garbage cans work well. Use a dark color to keep the light out, and keep the lid on. This will prevent algae from growing in the water. Cut a hole in the lid, large enough to put the downspout through. A valved exit pipe at the bottom of the barrel allows you to attach a drip system or hose for irrigating plants. If you want, you can connect several rain barrels to collect more water. PVC piping from the top of one barrel to another will allow water to overflow from the first barrel into the next. You can connect a number of barrels this way. Barrels can be screened with shrubs if appearance is a priority.
Rainwater does have real benefits for plants. So, if after the next thunderstorm you notice everything looks greener. It's not your imagination. It's just mother nature working her special magic.
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Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona 626-5161.
Material originally appeared in Arizona Daily Star gardening column, on June 29, 1997
- Updated: June 29, 1997
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