Farming with drip irrigation consumes more water

It's the opposite of conventional wisdom: When farmers use drip irrigation on their crops, they wind up consuming more water than if they used less efficient irrigation techniques. At least that's what water resources professor Frank A. Ward concludes in a new study.

Ward, who is on the faculty of New Mexico State University, used computer models to analyze farm water use in the upper Rio Grande River basin.

While drip irrigation can require half the water that flood irrigation does, plants absorb more water with drip, crop yield increases and more water is lost to evapotranspiration. Because drip is more efficient, there is also less overflow to seep back into aquifers or wash into nearby streams or rivers.

That means less water for downstream users and future generations dependent on the aquifers. "Higher consumption comes from someplace -- someone else's use," Ward said. Drip, he added, has its benefits. "It's just not a water conserving thing."

To get a true picture of water use and more equitably administer water rights, Ward suggests it should be measured according to how much is depleted from a basin, not by how much comes out of an irrigation pump.

The study, published this week by the Proceedings of the National Academy of Sciences, was co-written by Manuel Pulido-Velazquez of the Polytechnic University of Valencia in Spain.

-- Bettina Boxall

Photo: Lowell Weeks in his Coachella Valley lemon grove, which uses drip irrigation. Credit: Gina Ferazzi / Los Angeles Times

Comments

[Ronnie Cohen]

Wasting water isn't the answer.

http://switchboard.nrdc.org/blogs/rcohen/wasting_water_isnt_the_answer.html

[Justin Finch]

Why would we WANT agricultural overflow into the rivers? Pretty sure the salmon don't like drinking our pesticide/fertilizer soaked leftovers.

[In Tucson]

That is illogical. It is stated that drip uses half the water. If the water saved is not kept in the river or groundwater, then that needs to be stated as the follow up to the logic. Is there nothing set up so that water saved stays in the environment instead of being sold to another user? Future generations are therefore not harmed by water conservation but lack of protections and planning. Is Frank Ward trying to point out the loop hole, where he would rather see water used, or that he does not prefer productive crops for less water? Something is missing in this story.

[Tom Reynolds in AZ]

Mr. Ward is absolutely correct that irrigation designers need to design drip irrigation system for more evapotranspiration per week. The crop is in full-photosynthesis production every daylight hour, rather than in shock and suffocation from total root-zone water saturation/oxygen depletion. So he is correct that yields are enhanced with well-managed (precision irrigation and fertigation). He left out that labor and tractor diesal and herbicides are reduced, and all the energy used to get the water to the field is reduced, because the total deliveries per acre are generally still less. However, all pressurized systems carry their own carbon foot-print e.g. energy to pressurize filters and laterals.
The most obvious fact I think Dr. Ward has left out of his discussion is the definition of Water Use Efficiency. Only farmers can define the boundaries of that analysis. Dr. Ward's day when local farmers become liable for another farmer's water supply 10's or hundreds of miles away, and thus he is compulsed to deep percolate water for return flows for this distant farmer, will be the day pigs fly.