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ARS scientists are exploring the idea that canopy cover measurements can determine how much water plants have recently used and how much they'll need at the next irrigation. Photo courtesy of Thomas Trout, ARS

Perfect peppers: How much water do they need?   Quenching plants' thirst--below ground   Research aims to improve fertigation for farmers

Canopy Cover Provides Practical Clue to Plants' Thirst

By Marcia Wood
January 23, 2009

When plants in your garden burst forth with lush new growth this spring, they may begin to shade and cover patches that just a few months earlier were simply bare ground. When scientists describe the amount of space that plants shade or actually cover, they use the term "canopy cover." The term applies to all kinds of plants, from a ground-hugging tomato plant to a tall cornstalk.

Agricultural Research Service (ARS) scientists are exploring the idea of using canopy cover measurements in a calculation to determine how much water plants have recently used, and how much they'll need at the next irrigation.

Knowing plants' precise water needs helps reduce risk of applying too much water. Excessive irrigating can lead to leaching of fertilizer and other potential pollutants into underground water supplies.

According to agricultural engineer Thomas Trout, leader of the ARS Water Management Research Unit in Fort Collins, Colo., satellite imagery of farmers' fields could be analyzed by computers to estimate crop canopy cover. Growers could visit a website to get those measurements for their fields. The figure, along with a few other pieces of information—such as locally relevant weather—could then be added to a standard equation to calculate the amount of water used and the amount now needed for each field.

The calculation could indicate, for example, that bell pepper plants in a field that has a canopy cover of 40 percent may have used one inch of water in one week, the amount the grower may choose to replenish at the next irrigation.

Trout and co-investigators Dong Wang, a soil scientist and research leader at the ARS San Joaquin Valley Agricultural Sciences Center near Parlier, Calif., and Lee Johnson, a satellite imagery expert with the National Aeronautics and Space Administration, are exploring this futuristic use of canopy cover measurements to save water and satisfy plants' thirst.

Read more about this research in the January 2009 issue of Agricultural Research magazine.

ARS is a scientific research agency of the U.S. Department of Agriculture.