WANATAH, Ind. — It sounds pretty basic, but a good irrigation system needs a reliable source of water. In some parts of northern Indiana, that reliable source of water depends on where one lives.

For some, it’s Lake Michigan’s tributaries; for others, it means boring a well, said Lyndon Kelley, an irrigation specialist for both Purdue University and Michigan State University.

When the Great Lakes Compact was approved a few years ago, the key issues were managing water quality and limiting who could use the water. Farmers getting their water from Lake Michigan (or other Great Lakes) and its tributaries were grandfathered in. But anyone setting up an irrigation system today will have to get their water elsewhere.

Kelley explained the Great Lakes Compact came about following two efforts to siphon off water and ship it elsewhere. The first was a venture to send tankers full of fresh water from Lake Superior to Japan, and the second was a plan to fill trucks with water and send them to parched Arizona.

“The Great Lakes Compact was an effort to improve the management of the Great Lakes and head off any diversions of water,” says Kelley.

He talked about Great Lakes water issues and irrigation systems at the “Irrigation Management and the Great Lakes Compact Update” at the Wanatah American Legion on Feb. 14. It was sponsored by the LaPorte County Soil and Water Conservation District.

Limits on the amount of water for daily irrigation are about five million gallons, but Kelley told the 43 farmers at the update none of them would pump that much through their irrigation systems. Part of the reason for that is the improvement in efficiency that’s been designed into today’s irrigation systems.

In the past, he said high pressure pumped thousands of gallons of water through an irrigation pivot, but often much of it would run off the targeted area because the ground couldn’t absorb the water quickly enough. Today’s pivots spray water along a narrower path and in a much more targeted way.

Kelley said that allows less water to be used, even though crops are still receiving as much water as they need to develop.

“Think of your soil as a bank,” said Kelley. “It’s able to store up the water put on for use at a later time. If you look up-close at the soil, it’s like a whole lot of little ponds. The residue in the field helps hold the water there for when it’s needed.”

Kelley said that’s why it’s important for farmers to get out into their fields during irrigation or shortly afterward and look for problem areas where there is too little water or where too much is accumulating. In those instances, Kelley said it’s most likely a problem with a spray nozzle.

“Get out there with a soil probe or a shovel 12 hours after application and check soil’s moisture content,” said Kelley. “You can learn a lot by getting out there and taking a look at four or five random spots in the field.”

He said the key is a uniform application of water and applying only when it’s needed. But getting uniform coverage isn’t easy. Kelley said each nozzle on an irrigation arm has to work perfectly and it’s up to the farmer to make sure that happens.

He explained it’s not uncommon for a 30 percent deviation in spray volume to be noticed from one end of an irrigation arm to the other. If that happens, during an eight-inch application over a year, some areas of a field will get as little as 5.6 inches of water while others could get 10.4 inches.

Kelley said it’s important for farmers to keep in touch with the irrigation experts who installed the system in order to help fix problems like that.

But one variable that’s in the control of the farmer is the kind of power source he or she uses to run the system. Whether it’s electricity or a diesel generator, he said farmers should do their homework.

Based on a 160-acre water supply system, he explained an electric pump costs just under $3,000 a year to operate. With a diesel pump, that cost rises to more than $6,500. While that may seem to make the decision easier, Kelley said farmers need to take into account rising utility and diesel fuel costs, reliability factors and maintenance costs.

Also at the workshop, Purdue soil fertility expert Jim Camberato talked about the impact of irrigation on soil quality. He said the most productive soil has a pH of around 6.5 to 7, but that can be affected by how much water is put onto a field.

“Remember, pH is the foundation of any good soil,” he said. “You can lose more nitrogen in our sandy soil up here in northern Indiana with a good soaking. The key to a good crop is making sure the plants get nitrogen when they need it.”

That’s true of other vital minerals such as boron, magnesium, sulfur and potassium, said Camberato. And each one is affected by irrigation that could leach them out of the soil if too much water is applied.

Camberato suggested farmers do their homework to learn about their soil and apply only what’s needed where it’s needed. And for those using irrigation, he said farmers need to make sure water doesn’t pond on the fields, washing away vital nutrients that could damage plants.