What happens to irrigation water in Wisconsin's Central Sands?

David Tenenbaum
Lynn and Justin Isherwood, along with their son Isaac and Justin’s brother Gary, plant more than 1,200 acres of corn, sweet peas, soybeans and potatoes southeast of Plover, Wisconsin.

MADISON - More than 14,000 years ago, receding glaciers left a broad, deep swath of sand and gravel across central Wisconsin. Today, the Central Sands region hosts a thriving agricultural economy, but the sandy soil renders most of the crops dependent on irrigation that originates in groundwater.

About 13 years ago, streams, lakes and marshes in the Sands started to dry up, and some observers blamed the growing number of high-capacity irrigation wells.

The Central Sands region in Wisconsin includes all or part of eight counties: Adams, Marquette, Marathon, Portage, Shawano, Waupaca, Waushara and Wood.

Even though the water level in these fresh waters has improved, the number of high-capacity wells continues to rise, and so the question remains: what is the best route to sustainable irrigation that serves the farm economy and the environment at the same time?

One key question is this: How much water - whether from rain or irrigation - is used by plants, and how much moves deeper, to augment groundwater?

The answer is not obvious, says Mallika Nocco, a recent Ph.D. graduate of UW-Madison's Nelson Institute for Environmental Studies. She has spent eight years studying how much water from rain and irrigation enters the crop before being transferred into the atmosphere, and how much seeps deep into the soil and recharges the groundwater.

Mallika Nocco studied groundwater recharge at the Isherwood farm for six years and now uses data to build a computer model of the Central Sands’ agroecosystem. The model should help predict the impact of irrigation, which is needed for most regional crops.

A complete answer must account for different crops, soils, weather, agricultural practices and markets, says Nocco, who has a joint appointment at the University of Minnesota.

The research continues and the results are not yet published, but the short answer, Nocco says, is this: Expect surprises.

Nocco's hosts in the study are Lynn and Justin Isherwood, who, along with their son Isaac and Justin's brother Gary, plant more than 1,200 acres of corn, sweet peas, soybeans and potatoes southeast of Plover, Wisconsin.

Justin Isherwood, who "was raised right up the road on a dairy farm, and (is) the son, grandson and great grandson of farmers," is concerned with the farm sector and what he calls its ethical relationship to the world.

Lynn and Justin Isherwood are proud survivors of the culling that has reduced the ranks of Wisconsin family farmers.

"You can't grow much here without irrigation, but we're not sure how much is enough, and how to leave the same groundwater resource for the next generation. We have forgotten the role we play in the perpetuation of other species, and of their habitat. It's not just about crops."