As we move into July, the earliest corn will begin to reach maturity within 4-6 weeks. For irrigated corn, the question of when to quit irrigating always comes to mind. We want to maximize yield and water use efficiency, thus not irrigating any more than we have to in order to finish out the crop. Below are a few considerations for when to terminate irrigation in corn.
Generally, we would like to terminate irrigation when the corn has reached full dent (R5) when the milk line in the kernels is approximately 1/2 to 3/4 of the way down the kernel AND there is enough soil moisture to carry the crop to maturity (Black Layer).
The philosophy behind this recommendation is that during the dent growth stage (R5), kernels are still accumulating dry matter; however, as the milk line in the kernels moves down, the plant’s water demand is gradually decreasing. Once the milk line reaches the tip of the kernel, we have made it to black layer (R6), also known as physiological maturity. At this point, irrigation is no longer needed, and the crop will begin to dry down.
With the majority of our irrigated corn production located in the Coastal Plain, it is important to remember that generally our soils have low water holding capacity, so we cannot afford to cut off the water too soon. Below is a figure to help visualize when to terminate irrigation in corn by growth stage.
As always, taking into consideration current soil moisture, weather forecast, and temperatures is recommended. If you have any questions regarding irrigation, scheduling, or termination please reach out to your local agronomy agent.
