Planting is underway, and producers are evaluating soil moisture levels for the growing season’s peak growth potential. In the eastern part of Oklahoma, spring rains are a weekly occurrence, but in the western region, maintaining adequate moisture requires a little more planning.
Maps from Mesonet monitoring stations that show water available to plants indicate that in some Panhandle areas and western Oklahoma, the 4-inch layer of topsoil currently holds moisture levels of 30% or less. When reliable rainfall is not an option, producers turn to irrigation to replenish thirsty soil. About 85% of Oklahoma’s irrigation water originates from groundwater resources, two in particular: the Rush Springs Aquifer and the Ogallala Aquifer that runs throughout the Panhandle and northwest parts of the state.
“While we’re seeing the same trends as previous years in the Rush Springs Aquifer and northwest portion of the Ogallala Aquifer, data from the Panhandle portion of the Ogallala is showing continuous decline,” said Saleh Taghvaeian, Oklahoma State University Extension water resources specialist.
With a water level at 240 feet from the soil surface, the observation well near Texoma suggests a shrinking groundwater capacity to support irrigation, but surface water is limited, too. Taghvaeian said the Lake Altus reservoir, which serves growers within the Lugert-Altus Irrigation District, is at low levels.
“The reservoir storage of Lake Altus is around 37,000 feet, which is the fifth smallest storage reservoir dating back to 1991,” he said. “We hope to get more runoff in May, but the one- to three-month outlook shows the probability of below-normal conditions.”
For those producers preparing for irrigation, OSU Extension recommends completing a comprehensive check of their systems, including the pump, motor or engine, and control and power boxes.
“Always keep safety in mind, and inspect all components such as tires, gear boxes on towers and filters on the drip system,” Taghvaeian said. “Take care of leaks and check nozzles for clogs because the inspections you do now can save you downtime in the middle of the growing season.”
In a year when moisture may be in short supply, Taghvaeian and Jason Warren, OSU Extension soil and water conservation specialist, said excessive irrigation can negatively affect a crop’s root development.
“If we end up with a lazy root system because we’ve provided more water in the beginning, and then conditions get hot and dry, the roots are not there to extract water and nutrients from lower levels of soil,” Taghvaeian said.
Soil moisture sensors can help track root zone water content for irrigation adjustments during the growing season. In a year like 2021, where rainfall and groundwater sources are expected to be limited, Warren said many no-till or strip-till growers in the Panhandle and western Oklahoma are in a good position to conserve moisture.
“No-till is going to reduce the evaporative water loss from the soil surface and also improve the infiltration rate, which allows you to put more water out per application event with your irrigation,” he said.
Increasing the amount of water per application reduces the number of applications, which further reduces evaporation.
With drought threatening parts of Oklahoma in the upcoming months, Warren advised reducing input levels to compensate for the possibility of lower yields. Reducing fertilizer or seeding rates can provide cost savings if water availability is expected to limit yields. Reducing seeding rates for some crops also can delay the development of a full canopy, which can decrease early season water use and help conserve stored soil moisture.
Keeping an eye
Keeping a close eye on inputs, slowing down pivots and delaying irrigation to give a crop time to develop a healthy root system are ways to plan accordingly for a looming drought season. Planting crops that require less water is another strategy to consider. Warren said monitoring soil profiles and recharging them in advance of critical plant growth also can improve an operation’s water efficiency.
“If you’re in a situation where you’ve gotten very little rain since last fall, determine how much water you’ve got in your profile, irrigate in excess of what the crop needs now and then turn off the irrigation to allow for root growth,” Warren said. “This will allow a crop to grow roots deep into the profile so they can use this stored soil moisture in the event that you irrigate when rainfall cannot replace a crop’s water use later in the season.”