Canopy Cover Provides Practical Clue to Plants' Thirst

Published in the May 2009 Issue Published online: May 03, 2009 Irrigation
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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.