Lately I have been having a number of discussions with contractors about Allowed Depletion. It's been getting a lot of buzz in the industry. But what does it really mean and how do we apply it?
Often, when we stand in front of a sprinkler controller, we are trying to decide how often to water and how long to run the valves. We also know it may be 30 days or more before we can come back to change it again. I read a great article by Bruce Carlton several years ago titled, “Wednesday is NOT a Good Reason to Irrigate.” The article teaches a simple principle; don’t water until the soil has had a chance to dry out. This is Allowed Depletion; allow soil moisture to deplete to a managed level before watering again.
A few weeks ago I was with Mark Crookston from Northern Water in Colorado. He was showing me his demonstration garden. He had recently installed a Controller Link that was managing irrigation on a plot of fescue lawn. With his permission I checked the setup and logs. I was blown away. The Irrigation Amount setting was 1.8 inches.
Ok, I admit it, I am a water use efficiency nerd and get excited about weird things. So what is the big deal about a 1.8” irrigation amount setting? This means when the sprinklers run they put down 1.8" of water. Think about it, that is a lot of water. The sprinklers ran for a long time and the water soaked deep into the ground. Some would say he is wasting water. On the contrary, he is saving water. He said that in the summer he could go 10 days between watering. So how did the lawn look? Great, that was the fun part. He said the roots are 21" long. It doesn't get much better than this. He was taking watering deep and less frequently seriously and getting great results.
Now that I am back in the field I am hearing that more people are starting to get the message about air. Roots need to breathe. If they don't get air in the soil they will grow close to the surface to "keep there head above water." When plants are over watered, pore space in the soil is filled with water suffocating roots. Those pore spaces should have both air and water.
As the soil dries out water evaporates. The space once occupied by water is now filled with air. Then, when it rains or we irrigate water comes rushing in and replaces the air. Think of it as a natural respiration cycle; water comes in, air goes out, water evaporates, air comes in. Think about your own breathing habits. Slow deep breathing or rapid quick breaths?
For years horticulturists have been teaching us to water deep and less frequently. This is why.
To teach this principle I often use the gold fish bowl analogy. When you buy your kids a gold fish they have lots of fun for the first couple days. They tap on the glass, stick their fingers in the water, and rearrange the rocks. But the fish ignores them. Kids love to change the water because they can get out the net and catch the fish. But, soon the fun fades away and the poor fish is ignored. A week later you look at the gold fish bowl. The water is cloudy. What are the fish doing? They are swimming right at the top of the water. The fish are on an angle and their mouths are pulsing for air. They are trying to breathe. Plants do the same thing; roots stay shallow in order breath. When we water too much, roots come to the surface to get air.
There is often a misconception. People think their roots are shallow because of soil conditions, most of the time they are shallow because of over watering. Plant fatality is most often because of too much water.
This all sounds good and easy, but is it not easy. If it was easy everyone one would be doing it. Automatic sprinkler systems are set and forgotten and people struggle to know how to manage watering schedules.
Weather Reach climate controlled irrigation products know when to water. They wait for water to evaporate before watering again. This is the right way to water.
Water Managers, our goal is to eliminate waste while sustaining beautiful lawns and landscapes. By identifying and eliminating waste we can conserve water that saves our customers money. May I invite you to explore a thought with me?
We know that ET is short for evapotranspiration; a compound word describing evaporation from the soil and transpiration plants. ET happens; it is part of the water cycle. Remember, water that evaporates from the soil has not helped a plant. The only water plants need is pulled through the plant by transpiration. Once water evaporates, it is gone, it’s out of site. If an irrigation system delivers water that never helps a plant, our customers are paying for water that was wasted. Efficient irrigation gets water to plant roots, so it can transpire.
Let me invite you to look at customer landscapes from a new perspective; look for wasted water. Is there irrigation water that only evaporates and never reaches the plant to transpire? Find that water and you can reduce waste.
There are some obvious places to look. Overspray is quick and easy to find. Sprinkler heads that are out of adjustment or have the wrong nozzle will waste irrigation water. Water pressure is another big factor. When sprinkler system pressure is too high, some of the water coming out of the sprinkler turns to mist. This mist will either evaporate or blow away. In any event, the irrigation system is wasting water and not getting irrigation water to plants.
Mulch insulates the soil by keeping evaporative energy away from the water. We have seen how mulch benefits landscape beds, but stop to think about lawn roots. Beautiful lawns need deep healthy roots. When irrigation is deep, turf acts as a mulch to insulate the soil from evaporative forces.