Night temperatures play an important role in maximizing grain fill potential.- Historical data has shown a 2.8-4.7 bu/A yield decline for every 1° F increase in July and August average night temperatures.
- Both night and day temperatures independently influence yield potential.
Understanding Grain Fill and StressCorn yield potential determination starts almost as soon as the seed is planted, and it continues to evolve throughout the growing season. Pollination is undoubtedly the time period when corn is the most sensitive to yield loss. However, the 60-day period following, known as “grain fill”, and its role in differentiating between an above- or below-average yield, is often overlooked.
Achieving a slow, long and stress-free grain fill period is key to maximizing overall yield potential. During this time, a corn plant primarily directs sugars derived from photosynthesis into kernel development. Additionally, the plant will reallocate small amounts of sugars from other parts of the plant to support grain fill. In times of stress, when the plant is unable to produce enough photosynthate to meet demands, it will prioritize kernel development over maintaining root, lower stalk and overall plant health. It is not uncommon to see plant agronomics impacted, which may result in harvest challenges.
When crop stress occurs close to black layer, it limits the ability of the plant to extend grain fill time, resulting in reduced kernel size and weight. Maintaining good fertility, adequate soil moisture and a disease-free canopy are key factors to extending the grain fill period. Night temperatures throughout July, August and early September are less controllable, but equally important in maximizing grain fill.
Night Temperature Influence on Corn YieldDomestication of corn is believed to have begun in the central highlands of Mexico and continued to evolve with cultivation in the South American Andes Mountains. From early days of domestication in higher elevation areas, maize adapted to warm days and cool nights. Today, producers commonly recognize corn plants’ sensitivity to temperature swings throughout the grain fill stage. Analysis of historical county-level yield, along with minimum daily temperatures (night temperature lows), compiled over the last 64 years illustrates how yield is impacted during years with warmer July-August night temperatures.
On average, IA, IL and IN experienced 2.8 fewer bu/A for every 1° F increase in July and August average minimum temperature (Graph 1a). Sharper yield declines of 4.7 bu/A for every 1° F increase in July and August average minimum temperature were seen in KS and MO (Graph 1b). An increase in night temperature is usually accompanied by higher-than-average daytime temperature as well as drier soil moisture levels. Because of this, it is difficult to look solely at historic temperature responses and separate out the overall influence of nighttime temperatures.
Previous field studies which controlled day and night temperatures at sufficient soil moisture levels provide more insight to understanding the direct impact of temperature. Heat stress occurring prior to silking and 1-2 weeks following can cause kernel abortion.
1 Post-silking heat stress is a critical factor impacting grain size. Delaying heat stress 18 days after silking showed no reduction in kernel count at varying day and night temperatures.
2 The same study did show decreased grain ear weights with increasing nighttime temperatures. Yields were decreased even more if day and night temperatures were increased simultaneously. Elevated daytime temperature had more of a negative impact than high nighttime temperatures, indicating that night and day temperatures independently influence yield. The changes in yield were directly caused by a reduction in kernel size. Smaller kernel size is most likely a result of having a shortened grain fill period. In the study, an increase in temperature shortened grain fill duration by 8 days (night temperature increase), 15 days (day temperature increase) and 18 days (day and night temperature increase).
Potential Reasons Night Temperatures Influence Grain YieldNight temperatures are typically the lowest overall temperature in an entire day. The difference between 65° F and 75° F can seem trivial; most night temperatures feel mild to humans compared to much higher daytime temperatures, but studies have found that corn plants are sensitive to warmer night temperatures. There are 2 common beliefs as to why warmer night temperatures have a negative effect during grain fill:
1. Excessive burning of energy by the plant at night (increased respiration rates)Corn uses photosynthesis during the day to produce and store sugars and starches that support normal plant growth and eventually go into producing a seed. At night, when light for photosynthesis is unavailable, the plant undergoes a separate process referred to as dark respiration. Respiration utilizes a portion of the energy created during the day to maintain growth and development at night. Respiration also uses energy to repair damaged cells and support plant cooling. Higher day and night temperatures result in increased respiration rates. Although increased temperature does speed up respiration rates, previous research suggests it is unlikely that the overall increase is enough to cause significant impacts on corn yield.
1,32. Accelerated growth and developmentPrevious research suggests that accelerated growth and development during grain fill triggered by higher temperatures also reduces the total number of days a plant will have available to conduct photosynthesis. The net reduction in seasonal photosynthesis lessens the amount of sugars the plant can produce and later convert to starch within grain. Controlled studies show yield reductions with increased day and night temperatures confirming that accelerated growth resulted in grain fill periods 8-15 day shorter than normal (Table 1).
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References:
1 Cantarero, M.G., A.G. Cirilo, and F.H. Andrade. 1999. Night temperature at silking affects kernel set in maize. Crop Sci. 39:703-710.
2 Badu-Apraku, B., R.B. Huner, and M. Tollenaar. 1983. Effect of temperature during grain filling on whole plant and grain yield in maize (Zea mays L.) Can. J. Plant Sci. 63:357-363.
3 Quin, F.M. 1981. Night respiration of a maize crop in the lowland humid tropics. J. of Appl. Ecol. 18:497-506.