Lush green pastures: they are the dream of every horse—and every barn owner. But what does it take to get your grass to grow well, all season long? The short answer to this question is water. Unfortunately, providing the right amount of water in the most efficient way is not simple, and takes some knowledge and experience.
Proper irrigation of pasture grasses is important because either too much or too little water can stress your plants. Grazing plus stress from poor irrigation can leave you with sorry pastures.
Before you can properly irrigate your pasture, you need to know the needs of the particular grasses you are growing. The most commonly grown pasture grasses and legumes for horses include alfalfa, fescue, orchardgrass, bluegrass, timothy and Bermuda. Each of these grasses—or combinations of these grasses—has different irrigation requirements. “It’s important to know the water requirements of the crop you are growing, in addition to the soil textural type and local climate,” says Alan Efetha, irrigated crop water use agrologist for the Alberta Agriculture & Food Department. Any given crop will extract more soil moisture on a windy, hot, clear, and dry day and less on a calm, cool, cloudy, and humid day. “Clay loam soil will hold twice as much water as loamy sand soil (about 8.5 inches per 1 meter root zone as opposed to about 4.5 inches per 1 meter root zone). Understanding your soil’s water-holding capacity enables you to know how much water to put on when you irrigate and how frequent to irrigate.” Irrigation frequency is greater on loamy sand soils than clay loam soils.
How you irrigate your pastures depends on how much acreage you have as well as your time constraints and budget. The climate you live in will play a key role in how much water your pastures need, as well. “The most important point to remember is that pasture needs adequate water for optimum growth,” says Steve Orloff, University of California Cooperative Extension farm advisor in Davis, Calif. “The plant doesn’t care if the water comes from rain or irrigation, but the water must be adequate to meet the plant’s needs.”
Orloff notes that if you short the pasture for water, your yield will be reduced.
“If the field becomes excessively dry, stand loss will occur,” he says. “Most pasture grasses are not as drought-tolerant as other crops, such as alfalfa.”
The actual amount of water to apply varies considerably from location to location. Information on pasture water use, also called evapotranspiration, is available for different areas on the Internet or at your local extension office.
“The key is to meet the needs of the crop through irrigation,” says Orloff. “In order to do this, you must know the amount of water that is applied per irrigation with your irrigation system.”
One way to monitor the water needs of the crop is with soil moisture sensors. These sensors indicate when the soil is becoming too dry and irrigation is warranted. Efetha recommends checking the soil up to one meter in depth to verify moisture content. “Be most concerned about the top 50 percent of this depth,” he says. “Seventy percent of the moisture used by the crop is extracted from the top half of the root zone.”
Terry Smith, GM of Smith Irrigation Equipment in Kensington, Kan., suggests a simple method for calculating how often to irrigate. “The goal for horse pasture irrigation is to supply one inch of water to the pasture every five days from natural rainfall or irrigation,” he says. “If there is no rain, the irrigation system must supply all of the water requirements of the plants.” According to Smith, an easy rule of thumb for the one-inch-per-week requirement is to size the irrigation system using 4 gpm (gallons per minute) per irrigated acre.
“Many irrigation systems operate on less because of available water supply, but the 4 gpm or more per acre rule is optimum,” he says. “A five-acre pasture should have 20 gpm or more to satisfy this requirement.”
Methods of Irrigation
Irrigating a pasture is not as easy as watering a lawn, although in cases of small lots, sprinklers are an option. In most cases, you’ll need a more sophisticated way to get water.
“An irrigation system can consist of anything from a garden hose and one or more sprinklers to a traveling system that operates unattended and shuts off automatically when it is finished,” says Smith. “Irrigation system selection is driven by the available water supply, desired performance, and budget considerations.” The most effective solution for your pasture depends on the site itself. “Drip irrigation is used in some crops, such as high value vegetables and tree crops, but is not economical for pasture irrigation,” Orloff says. “Surface irrigation systems, such as flood irrigation, require the lowest capital investment compared with sprinkler systems, such as hand line, wheel line, or a center pivot.”
Although economical, flood irrigation requires more labor than some sprinkler systems because the operator has to monitor the water flow across the field and shut off the water before it reaches the end of the field, according to Orloff. Also, if the land has too much slope or is undulating, or if the soil is very sandy or variable, flood irrigation is not feasible.
When it comes to ease of use, water reels rate high on the list of irrigation systems, especially for greater acreage. “Larger pastures are more easily irrigated with a traveling irrigation system, like a water reel, because many moves would be required with a single sprinkler,” says Smith. “Water reels can also negotiate difficult terrain and can work around trees and other natural obstructions.” The portability of the water reel also allows use on multiple pastures.
Before investing in an irrigation system, it’s important to make sure you have a reliable water source. A good rule of thumb is 5 to 20 gpm from a well or stream. Consider purchasing a low-volume irrigator, which can conserve water. Remember, too, to test the quality of your irrigation water. Just because you won’t be drinking the water doesn’t mean it doesn’t need to be good quality. Salt or minerals can store up in the soil and affect its fertility. Talk to your local extension agent for advice on optimum levels of salt and minerals in your area. Also, be aware that too much sand or silt in your water can damage your irrigation system.
With a little effort, you’ll be able to provide lush, healthy and well-watered pastures to your horses.