Name: Jerry
Status: Other
Grade: Other
Location: CA
Country: United States
Date: Spring 2010
Question:
Is rainwater falling on the soil from above any more
nutritious for plants than irrigation water pumped from the ground?
Replies:
Jerry,
Rain water normally is more nutritious than ground water.
Rainwater contains nitrogen-bearing molecules, partially
a result of air pollutants scavenged from the air by
raindrops, but more often a result of nitrogen oxides
produced by lightning. Nitrogen is an important natural
fertilizer for the soil. Therefore, rain from thunderstorms
tends to be the most nutritious rain.
Soil tends to strip nitrogen and other "chemicals" from
rainwater as it percolates through the soil. Thus, the water
that accumulates in the ground as groundwater can vary from
being somewhat to mostly depleted of nutrition.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
I am not sure I would be happy with the word nutritious in answering
this question. Water has no 'nutritional' value to the plant
Water is essential to all plants as a medium in which the plant can
dissolve the minerals it needs from the soil, as well as the sugars it
manufactures as food, and the carbon dioxide it makes as a waste
product.
The problem with underground water for irrigation is that if often
contains dissolved salts which can interfere with the plants ability
to dissolve the stuff it needs. For instance if the ground water has
too much calcium (from limestone) the plant will have difficulty in
dissolving the iron and magnesium it needs to make chlorophyll.
I live in a desert region of Australia which relies almost entirely on
ground water. The change in the colour of many plants after a shower
of rain is very noticeable. Even lawns which have been tended
carefully become greener after rain. We say that an inch of rain is
worth five of tap. The reason for this is the large amount of
dissolved calcium in our groundwater. There is also the bonus to the
plant that the rain water falling through the air dissolves a small
amount of Nitrogen from the air - and nitrogen is a nutrient for the
plant. It is the main ingredient in most fertilisers, and is essential
in the formation of plant proteins.
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