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Name: Jerry
Status: Other
Grade: Other
Location: CA
Country: United States
Date: Spring 2010

Is rainwater falling on the soil from above any more nutritious for plants than irrigation water pumped from the ground?


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
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.

Nigel Skelton
Tennant Creek High School

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