For those new to irrigation

Many growers irrigate crops, and those who don’t often wish they did. If a profitable crop is in the ground, it probably pays to initiate irrigation on the farm.

“The goal of irrigation is to supply the water that rainfall doesn’t so that water isn’t the limiting factor for yield,” said Purdue University irrigation educator Lyndon Kelley. At some point, rainfall won’t keep up with what the plant requires. “We use irrigation to do that.”

Irrigation helps farmers achieve a return on their investment in land, equipment and labor. Any crop that takes up 100% of the sunshine that hits the ground will use between 0.27 to 0.32 inches of water on the hottest days, so Kelley suggested building a system to keep up with the hottest days.

Most irrigation water comes from deep wells that produce significant gallons of water per minute. For those currently without a well, it’s a good idea to ask other local growers and well drillers about water availability and recommendations.

Some growers use surface water, which is most often available in summer during the peak growing season. However, contamination issues may play a role in food safety when surface water is used for fresh vegetable irrigation and cooling. For those digging a new pond for irrigation water, ask local excavators if the water source will be reliable.

“If you’re using surface water, you need to be able to get at least three feet below the surface so you don’t create a vortex that sucks air,” said Kelley.

Before making plans, Kelley suggested mapping irrigation ideas on an aerial map of the farm. In some cases, there may be options to share a water source with a neighboring farm through a cost-share or rental agreement. Determine the costs and make sure there is adequate water should the farm expand in the future. Potential water availability is especially important if two growers have agreed to share costs.

“Get multiple bids,” said Kelley. “Get three or four different people to look at your site and come up with their best plan. Somewhere between those plans will be the ideal option.”

Power is a significant expense with irrigation. Three-phase is often the cheapest option. Gas and diesel are other alternatives, but electric motors are about half the cost of diesel engines and are easier to maintain. It’s also easier to add automated controls to electric motors.

“When you make an irrigation investment, make sure you aren’t doing a ‘build it and they will come,’” said Kelley. “Have something lined up with crop or feed contracts.

“Before you make this investment, make sure you’re thinking about the long run and how it will change things. Once you add irrigation, your summers will never be the same – it will be the quickest time of year. With irrigation, you’re doing something all the time. Irrigation is a very equipment-heavy investment, so it doesn’t work well to only use it as an insurance policy. You need to get higher yields every year.”

Kelley urged growers to involve their lender when adding irrigation and realize that once irrigation is added to the farm, it will increase the value of the land greater than the investment of the equipment. That will in turn raise the value of their own land and neighboring land. This is also important if irrigation will be added to rental properties or future property purchases.

Dr. Ron Goldy, vegetable educator emeritus, Michigan State University, said most growers tend to overirrigate. “They have the system, and they use it too well,” he said. “As a result, it wastes water and the expense of putting water on. It also wastes nutrients leached through the soil – especially nitrogen.”

When Goldy took soil samples at one-, two- and three-foot depths at the beginning and end of the season, he found nitrogen pushed down to the three-foot level, which is beyond the root zone for most vegetable crops.

“When you irrigate, you think you’re irrigating the crop,” said Goldy. “In actuality, you are irrigating the soil and the crop picks up water from the soil. You cannot bank water in sand. You can store some water in clay soils, but in sandy soil, it goes right through.”

Know the soil types on the farm and how each reacts to water. One aspect of a soil report is the cation exchange capacity (CEC), which is directly related to soil texture and its ability to retain water and nutrients. Sandy soils are 5 or less; loamy soils are 5 to 10; silt loams are 15 to 25; and clay solids are 20 to 50. Organic soils can be over 100.

“The number tells you how well the soil hangs onto anything you put on it, whether it’s water, herbicides, nutrients,” said Goldy. “Some herbicides state ‘do not use on organic soils’ because organic soil binds the herbicide so tightly that it isn’t free to act on weeds as they germinate.”

A low CEC value indicates that irrigation should be done quickly and for a short period of time. By irrigating quickly, water is dispersed and moves downward. Clay or loam soils should be irrigated slowly but for longer. The goal is for the water to sink down to the roots and not spread out.

“Wherever water goes, that’s where nutrients go,” said Goldy. “If you put out a lot of water, you’re pushing nutrients down below the root zone. The beauty of drip irrigation is you can design your emitter flows (high or low flow) and space the emitters for a much more flexible system when it comes to how fast water goes out.”

Irrigation systems require maintenance, even with automation. “You can automate them so they come on automatically, but we can’t trust that,” said Goldy. “We need real eye contact. Growers also need to check and clean filters no matter what the water source.”

Some growers fertigate, applying nutrients through irrigation. For the least-cost method of basic fertilization, Goldy suggested applying phosphorus, potassium, calcium- magnesium and boron as a pre-plant dry broadcast.

“You can also put on one-third of the nitrogen that way,” said Goldy. “I typically put the other two-thirds of nitrogen through the drip, which varies by crop. For peppers, 75% of the nitrogen should be on the pepper field prior to fruit set.”

For vine crops and tomatoes, it’s best to meter out nutrients. If you put it all on up front, the plants will be large because those crops are good at turning nitrogen into leaves.

The goal with irrigation is moist, not saturated, soil. Goldy sees a tendency for growers to use overhead irrigation at night.

“It’s worst thing you can do,” he said. “It keeps the plant wet from 7 at night until 10 the next morning. That’s a 15-hour wetting period and more than enough time for spores to germinate and infect plants.”

by Sally Colby