Manage Water by Rotating Irrigated, Dryland Crops
One way to manage limited irrigation water in the High Plains is to combine irrigation and dryland farming on the same acreage. In recent studies in western parts of Kansas and Texas, researchers alternated irrigation and dryland practices on the same acreage, “to get away from the cycle of fallow, and make maximum use of limited water resources,” says Loyd Stone, soil physicist, Kansas State University.
Citing the findings of those studies, Stone says the average yield improvement in the alternating system was about 10% compared to the overall average for continuous irrigated and dryland crops.
Stone says the irrigation phase provides more residue to the soil, which aids in water storage and protects the soil from wind erosion. It also increases the amount of water available at deeper soil depths, which means that water is available for the subsequent dryland crop, and reduces the need for fallow.
The irrigated and dryland crop partners may vary by irrigation capacity and rotational considerations, such as herbicide carryover. However, an example might be irrigating soybeans or corn, then coming back the following year on the same ground and growing dryland winter wheat, sorghum, or sunflower.
KSU Study: Sunflower Roots Tap Soil Moisture Better Than Sorghum
Sunflower often performs best in dryland conditions, he says, because that crop is most efficient in tapping water at deeper soil depths. Grain sorghum and sunflower both have a reputation for being relatively drought-tolerant crops, but a three-year study conducted near Tribune in the late 1980s showed that sunflower roots go deeper, allowing the plants to take advantage of water further into the soil than sorghum plants. Sunflower roots extended into the soil about 9.9 ft deep, while grain sorghum rooted to about 8.3 ft deep—nearly a 2 ft difference.
In the study near Tribune, both crops were planted in the same field at the same time. In a companion study near Manhattan, for about the first 3 weeks after emergence, daily gain in rooting depth was about the same for both crops. The big difference in rooting depth occurred from 20 to 60 days after emergence, when the sunflower roots went down an average of 1.6” per day; compared to sorghum at 1” per day.
“Because sunflower roots deeper and depletes water deeper in the soil profile, it is an excellent crop in a rotation to utilize water and nutrients, such as nitrate, that have moved deeper in the profile,” Stone says. “Also, rotating irrigated and dryland crops provides increased subsoil water for the dryland crop (sunflower) to utilize what would otherwise be lost.”
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