Reduction in Corn Yield Due to High Night Temperatures

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Night Temperatures and Corn Yield

Corn producers are generally aware that high night temperatures can be detrimental to yield; however, the effects on specific plant processes and yield components are not as well understood.
Corn originated in the Central Highlands of Mexico and adapted during its evolution to the predominant climatic conditions of this region, consisting of warm days and cool nights.
Research has shown that above-average night temperatures during reproductive growth can reduce corn yield both through reduced kernel number and kernel weight.

Yield Reductions from Warm Nights

2010 Growing Season

In 2009, many farmers in the Midwestern United States produced record corn grain yields. However, in 2010, even with adequate rainfall, corn grain yields were much lower.
A notable difference between these two growing seasons was night temperatures following pollination.
The average minimum night temperatures during July and August of 2009 were about 5-8º F lower than the average minimum night temperatures in 2010 in the Corn Belt (Figure 1 and Figure 2).

Table showing ave. daily minimum temperatures for Des Moines, IA, in 2009 and 2010. Approximate dates of 10%, 50%, and 90% silking in Iowa in 2009 and 2010. — **Figure 1.** Daily minimum temperatures (7-day moving average) for Des Moines, IA, in 2009 and 2010, and 30-yr average minimum daily temperatures (1981-2010). Approximate dates of 10%, 50%, and 90% silking in Iowa in 2009 and 2010 based on USDA crop progress reports.

Map showing average minimum temperatures experienced in July-August of 2009 and average yields (bu/acre) in Iowa, Illinois, Missouri, Kansas and Nebraska.

Map showing average minimum temperatures experienced in July-August of 2010 and average yields (bu/acre) in Iowa, Illinois, Missouri, Kansas and Nebraska. — **Figure 2.** Average minimum temperatures experienced in July-August of 2009 (top) and 2010 (above) and average yields (bu/acre) in Iowa, Illinois, Missouri, Kansas and Nebraska. Data from NCEI NOAA, USDA NASS.

University of Illinois Study

The first experimental evidence that high night temperatures can have a detrimental effect on corn yield came from an experiment performed at the University of Illinois (Peters et al., 1971).
Corn grown with an average night temperature of 85º F yielded 40% less grain than corn grown with an average night temperature of 62º F (Table 1).

Table 1. Effect of night temperature from silking through physiological maturity on corn yields (Peters et al., 1971).

Table showing effect of night temperature from silking through physiological maturity on corn yields.

Further Research on Temperature Effects

Research has shown a reduction in kernel number associated with high night temperatures (Cantarero et al. 1999).
Results showed that kernel abortion in heated night plots was 8% higher than in the control plots. Ears in the heated plots had an average of 34 kernels per row at harvest, compared to 37 kernels per row in the control plots.
A study by Badu-Apraku et al. (1983) examined the effect of temperature on grain fill after kernel number had already been set.
Results showed that grain yield per plant was significantly affected by temperature regime (Table 2).

Table 2. Effect of temperature on grain fill duration, grain weight per plant and kernel number (Badu-Apraku et al., 1983).

Table showing effect of temperature on grain fill duration, grain weight per plant and kernel number.

Why Do Warm Nights Reduce Yield?

Current research supports two hypotheses that may explain why higher temperatures during the grain filling period reduce grain yield:
- Higher rate of cellular respiration.
- Accelerated phenologicaldevelopment.

Higher Rate of Respiration

The most commonly cited explanation for the detrimental effect of high night temperatures on corn yield is increased expenditure of energy due to a higher rate of cellular respiration at night.
- Cellular respiration consumes carbon assimilated through photosynthesis to maintain and increase plant biomass.
- Higher temperatures produce faster rates of cellular respiration in a corn plant, making less sugar available for deposition as starch in the kernels.
- A lower rate of respiration relative to photosynthesis has generally been viewed as favorable for maximizing agricultural productivity and grain yield.
Although higher night temperatures undoubtedly increase the rate of respiration in corn, research generally suggests that higher rates of night respiration probably do not have a large impact on corn yield.
- In a study that examined the effects of elevated night temperature, night respiration in plant leaves did not significantly differ between heated and control plots (Cantareroet al., 1999).
- In another study, respiration rates were found to be high for newly emerged plants but declined as plants developed (Quin, 1981). Researchers concluded that increased respiration rates associated with high night temperatures likely did not have a major impact on corn yield.

Accelerated Phenological Development

Elevated night temperatures reduce the time required for corn plants to reach physiological maturity.
Shortening the length of time between silk emergence and maturity reduces the number of days that the corn plant is engaged in photosynthesis during grain fill, effectively reducing the amount of energy the corn plant can convert into grain yield.
Following the 2010 growing season, Iowa State University researchers used the Hybrid-Maize model to explore the effects of night temperature on length of grain fill (Elmore, 2010).
The model compared predicted days to maturity based on actual 2010 temperatures vs. daily minimum temperatures from July 15 to Aug 15 replaced with those from the 2009 growing season (labeled as T_minAlt in Table 3).
Results showed that lower night temperatures during the month-long period following silking extended grain fill by a week or more.

Table 3. Simulations conducted with Hybrid-Maize resulting days in reproductive stages and total days to maturity at five Iowa State University Research and Demonstration Farms.

Table listing simulations conducted with Hybrid-Maize resulting days in reproductive stages and total days to maturity at five Iowa State University Research and Demonstration Farms.

Research conducted by Badu-Aprakuet al. (1983) provides further evidence that shortening the days from silk emergence to physiological maturity reduces grain yield.
Results showed that duration of the grain fill period and grain yield per plant were both significantly affected by temperature (Table 2).
Research generally shows that accelerated phenological development is likely the primary mechanism by which high night temperatures can negatively affect corn yield.

References

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.
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.
Elmore, R. 2010. Reduced 2010 corn yield forecasts reflect warm temperatures between silking and dent. Integrated Crop Management. Iowa State University, 9 Oct. 2010.
Peters, D.B., J.W.Pendleton, R.H.Hageman, and C.M. Brown. 1971. Effect of night temperature on grain yield of corn, wheat, and soybeans. Agron. J. 63:809.
Quin, F.M. 1981. Night respiration of a maize crop in the lowland humid tropics. J. of Appl. Ecol. 18:497-506.1