Simply put, irrigating is taking water from outside the growing season and bringing it into the growing season. That’s how Lyndon Kelley, Michigan State University Extension/Purdue Extension irrigation educator, defined it.

“The question is how much crop per drop can I get?” he asked during his presentation at the most recent Great Lakes Expo.

(The answer, of course, is the ever-ambiguous “It depends.”)

“We want to get the plants to drink at their peak times for the best yield,” Kelley said. A best-case scenario for irrigation efficiency involves the following equation: if one inch of water is applied, there would be no measurable loss to a droplet in the air; 0.1 inch would evaporate from the plant and soil surface and 0.9 inch would infiltrate to the root zone. If no leaching happens, that 0.9 inch is absorbed by the roots and 0.9 inch transpires. This means the application was 90% efficient.

But rarely does the best scenario occur. Things become tougher when water becomes scarcer. And if you see water stress symptoms, it’s already too late to avoid yield loss, Kelley said.

Limited water supply irrigation management is crucial. It can be done by diversifying the crops sharing the water supply between high and low water use; by staggering the planting dates to stagger peak water need times; by planting part of the irrigated area to a sacrifice crop to neglect during extended drought; by starting irrigating early to bank water ahead of time; and/or by staggering forage crop cutting dates to avoid simultaneous peak use.

Where that precious water comes from is important too. Water storage reservoirs are helpful because they allow for the usage of high drain flows in the spring season. However, their storage capacity must include your total need while taking into account evaporative loss and leak loss.

Groundwater sources are also possibilities. They can be manmade or natural. Manmade sources include deep wells, shallow wells, shallow suction wells and horizontal suction wells. There are also surface water sources such as lakes, rivers, streams, drainage ditches and private ponds. Taking advantage of all of them requires some equipment, though.

Kelley noted that a home well is an expensive, undependable and inefficient irrigation water source if it’s run continuously. If you must use your home well, however, isolate the home from it – and remember that backflow protection is required. Install a continuous use pump and consider installing a variable frequency drive.

“If you’re at this point, a dedicated irrigation well may be a good investment,” he said.

In natural bodies of water, a surface pump creates a vacuum to lift water, but issues can include extensive filtration being required for drip systems. Plugged inlets can result in a need for aquatic weed control and rotary self-cleaning screens, and the loss of the vacuum creates a vortex – so users need to maintain more than three feet of water over the inlet or use water guides/flow diverters/floating intakes to keep water at the appropriate level.

With small ponds especially, the recharge capacity is far more important than the volume. A pond’s volume indicates its storage capacity, and many natural ponds will have slow recharge. Additionally, most ponds will have E. coli loads, making them unacceptable for vegetable production.

Natural bodies of water are also subject to riparian rights, where the landowner has rights to the body of water that touches the borders of their property. They may use the water for domestic needs as long as it doesn’t obstruct the natural flow of water for other riparian owners. A riparian may not diminish the rights of other riparian owners – like excessively lowering lake levels through irrigation.

Having enough water for your crops throughout their growing season is a necessity. If your current irrigation supply isn’t quite enough, it may be time to look into additional resources.

by Courtney Llewellyn