Simulated current grain accumulating rate

Simulated current grain accumulating rates (in bushels per acre per day) across the three I states. Data from the FACTS project simulations.

Editor’s note: The following was written by Sotirios Archontoulis, Iowa State University assistant professor of integrated cropping systems, and Mark Licht, assistant professor and Extension cropping systems specialist, for the Integrated Crop Management website.

According to the Aug. 19 NASS report, the 2019 corn crop is about two weeks behind normal in terms of reaching dent stage. What are the implications of this delay in grain filling period and end of season yield?

We address this question by examining two key weather variables — solar radiation and temperature.

Solar radiation interception is expected to be 15% lower during the dent phase in 2019 compared to past years. This is because day length, and therefore amount of solar radiation, decreases as we move from August to September.

An unknown factor is the clouds during 2019 dent phase, which may compensate for the decreased radiation energy.

Solar radiation is the main driver for crop photosynthesis, which is strongly related to corn grain accumulation, which for the present week is estimated at 4.5 bushels/acre/day for Iowa. For reference, the maximum grain accumulation rate can be up to 7 bushels/acre/day.

Temperature during the dent phase is also expected to be around 5 degrees lower in 2019 than past years. A two-week delay in the start of dent stage will probably delay corn maturity by three weeks because temperatures begin decreasing from late August to September.

When crops can be expected to reach maturity this year depends on the planting date and hybrid maturity combinations. In general, crops planted before June 1 should not have an issue reaching maturity in Iowa. Historically, the average temperature will be above 50 degrees until Oct. 10 for central Iowa, while the first frost likely would occur after October 20 in central Iowa.

The key issue this year will be the dry-down period for grain moisture to reach 15-20%. While it is expected that with normal fall conditions, even late-planted corn will reach maturity, grain dry down will be slower, resulting in wetter corn at harvest

For the state of Iowa, the 2019 corn yields can be expected to be lower than the past three years because temperature and radiation during the grain filling period is less than would typically be expected due to later than normal planting dates. However, there is a lot of variability across the state for planting date, corn maturity and weather conditions.

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