For every 2.3 feet in elevation, one pound per square inch of pressure is gained. The 16-foot tower produces enough water pressure to run a standard drip irrigation system. The four-foot tower only produces enough pressure to run a special drip tape, which is reusable.

To get water to the tower is a challenge. There are two options for sites with no electricity. The first is a solar-powered pump and the second is a peddle pump that is much like a bicycle — both could be used in Afghanistan.

Steve Rimar, who works with John Deere Water and has been a part of the Edisto project since its inception, says the gravity flow system is not really feasible for most U.S. growers, because virtually everyone has access to electricity. However, for small resource farmers, or those in areas where electricity isn’t cost effective, these systems may be valuable where natural elevation changes occur or where runoff from rooftops or other water catchment systems can be easily fed to the gravity flow systems.

Clemson area Extension agent Tony Melton says he helped one farmer in upstate South Carolina build a gravity flow system to irrigate tomatoes. “This farmer couldn’t run a pump because of a lack of water pressure. He had a big tank, and we lifted it up off the ground and got enough elevation to get water to his tomatoes,” Melton says.

In Afghanistan the quarter-acre system being tested at the Edisto Station would be ideal for typical-size vegetable operations. It would take 16 refills of the 400 gallon tank per week to provide an inch of water to the quarter acre field.

In Afghanistan the biggest challenge to growing vegetables is getting water to these crops. Rimar says keeping clean water is a big challenge when using one of these gravity flow systems. The four-foot elevation in particular would require near constant management to keep clean water flowing, he says.