By Scout Nelson
As crops move into late-season stages, careful irrigation can protect both yield and nitrogen use. Most irrigated corn in Minnesota is near the R2 (blister) stage, while soybeans are progressing through pod fill (R3–R5). These phases are critical for grain development.
Water use to maturity varies by crop:
- Corn at R2 needs 6–7 inches
- Soybeans at R4 need 3–4 inches
- Potatoes during tuber bulking need 4–5 inches
Evapotranspiration remains high in early August but decreases after mid-month. Daily reference ET in central Minnesota averages 0.20 inches, meaning topsoil can dry out quickly in hot, windy conditions.
If soil moisture is low in the top 12–18 inches, light irrigation (0.5–0.75 inch) may help. But before irrigating, use tools like soil probes, moisture sensors, or the U of M Irrigation Management Assistant Tool to check water status.
Overwatering not only delays maturity but can cause yield problems like hollow heart in potatoes. It also increases the risk of nitrate leaching, especially in sandy soils. This happens when excess water pushes leftover nitrogen below the root zone, harming both yield and water quality.
To avoid this, keep soil moisture at 50–60% of available capacity and don’t irrigate before big rains. Late-season nitrogen applications make nitrate loss more likely, so irrigation must be carefully timed.
Growers can use several free tools for smart irrigation:
- Moisture sensors
- Checkbook method
- NDAWN crop water use data
- Open ET
Key reminders:
Check moisture weekly, irrigate only as needed, use the right tools, and avoid irrigating before heavy rain.
To learn more, attend the Field Day at Rosholt Research Farm on August 21, 2025, or register for the Minnesota Irrigator Program. Visit: z.umn.edu/MIP25REG.
Photo Credit:istock-laughingmango
Categories: Minnesota, Crops, Corn, Soybeans, Weather