Dark Respiration

One of the topics that has come up in the last few years has been higher nighttime temperatures during the grain fill time. The adage that “warm nights make the corn grow or mature faster” may be more relevant in the vegetative growth stage (VE-V18). However, once corn hits the reproductive growth stage, Tassel/Silking (R1) to Dent (R5), you want the corn plant to cool down at night. When nighttime temperatures do not fall below 72°F, the corn plant does not slow down and will keep on metabolizing sugars at a high rate (we believe this temperature to be closer to 68°F).

This rate of high nighttime metabolism, which is called “dark respiration,” causes kernels to fill faster, reduces the grain fill time and makes the plant mature quicker. In our experience it can also reduce test weight.

For the sake of discussion, remember that a dry or low humidity environment in most instances will have larger temperature fluctuations than an environment with high humidity (it takes less energy to change the temperature in a low humidity environment than in a high humidity environment). With these low humidity conditions, plants recover at night when it cools down. However, when we have high humidity conditions and it starts to cool down at night compared to our daytime temperatures, we experience more dew.

Cooler air cannot hold as much water in the air as warmer air, and as the air temperature drops, the rate of condensation exceeds the rate of evaporation. This causes water droplets to form dew. This is important because a heavy dew can equate to almost 0.1” of moisture, which may assist in keeping the plant alive until the next rain. This dew will also cool the plant to some degree even if the air temperature is warmer, which may, reduce the impact of dark respiration.

Yield losses of 2.0-3.6 bushel per acre have been documented for every increase of 1°F over 72°F during nighttime hours. If a corn plant cannot produce enough energy from their leaves to fill these kernels properly, they may not fill all kernels on the ear, and may start pulling starches from the stalk, or cannibalizing the stalk, to fill the remaining kernels on the ear.

It has been our experience that corn plants that have adequate nutrients are better suited to handle the stress of dark respiration. These healthier plants tend to have better test weight and standability/harvestability.