Can Field Drying Result in Corn Dry Matter Losses?
A “rural legend” has persisted in some circles over the decades that corn left to dry in the field after black layer is susceptible to so-called “mystery” or “phantom” yield loss. The reason for the “mystery” label is because the phenomenon is not ascribed to the most common yield-robbing culprits: dropped ears, lodged stalks, insect feeding, or ear rots. Rather, “kernel respiration” is hypothesized to be the primary cause for the supposed dry matter losses.
The narrative first gained credibility following testimonials in farm publications and a university study in the early 1990s (Nielsen, et al, 1996). Following this, other researchers began to report data from previous studies that had measured grain weight as corn drying progressed. Additional studies were planned and conducted as well, with the express objective of documenting kernel weight changes during field or lab drying. Results of these studies are summarized below.
- An Iowa State University study at 2 locations of 4 hybrids and 6 harvest dates documented no yield reductions as corn field-dried from 35% to 19% (Knittle and Burris, 1976).
- A University of Illinois study tested 4 hybrids and 4 harvest dates. No hybrid showed significant changes in dry weight as moistures decreased from 27% to 18%. (Nafziger, 1984).
- Pioneer researchers measured kernel moistures and dry weights of 8 hybrids at sequential harvest dates in 1983 and 1984 (Cerwick and Cavalieri, 1984). No hybrids showed yield reductions during drydown.
- Pioneer agronomists studied 2 hybrids at 2 locations (Reese and Jones, 1995). Dry weight did not decrease as drydown progressed from black layer to 15% grain moisture.
- In field and lab drydown studies conducted at the University of Nebraska from 1995-1997, a total of 6 hybrids and 9 drying environment/harvest method combinations were examined (Elmore and Roeth, 1996). The study found no evidence of kernel dry matter loss following physiological maturity.
- Importantly, the study included one of the same hybrids tested in the Purdue study, but with conflicting results. The authors concluded that the different results were likely due to different methods in measuring grain moisture; the Nebraska study used oven-dry weights rather than an electronic moisture meter, because meters may be inaccurate at moistures above 25%.
- The authors concluded that their results showing stable grain dry matter following maturity do not support the need for early harvest and the associated energy expense for grain drying.
- In 2002 to 2004, field studies were conducted by Ohio State University researchers at 3 locations to determine effects of 3 harvest date periods and 4 plant densities on 4 corn hybrids differing in maturity and stalk strength (Thomison, et al, 2011). They found no evidence of dry matter losses with harvest delays.
- In 2016 and 2017, Iowa State University conducted replicated studies at 2 locations to determine if corn dry matter loss occurred in the field after maturity (Licht et al, 2017). At each environment, 3 hybrids of differing maturity were planted at 2 planting dates and harvested on 6 (2016) or 7 (2017) separate dates during the post-physiological maturity drydown period.
- In this extensive study in which grain moistures ranged from over 30% down to 15% during drydown, kernel dry matter weight showed no change over progressive harvest dates (Figure 3).
Figure 3.Corn kernel dry matter weights over the post physiological maturity dry down period (Sept. and Oct.) for 2 planting dates and 2 Iowa locations in 2016 and 2017.
Therefore, it appears that yield losses observed in on-farm studies with late compared to early harvest are due to other field loss factors. These factors may not be readily noticeable, but 1 bu/acre is lost with only 2 corn kernels per square foot and these losses can add-up quickly when corn is less than 20% grain moisture (Nafziger, 2018). Combine adjustments to minimize these losses are reviewed in the companion Crop Insights on Measuring and Reducing Corn Field Losses (Butzen, 2018).
Kernel Respiration Effect on Yield
Prior research studies were examined to determine if there was evidence of corn kernel respiration rates high enough to explain large yield losses in the field during drydown. A study conducted at Iowa State University showed that when kernel moisture dropped below 30%, the respiration rate slowed dramatically and was only a fraction of the rate measured at the dent stage (Knittle, and Burris, 1976).
In another study conducted by ag engineers at the USDA, shelled corn samples were evaluated for dry matter losses in storage at six temperatures (Saul and Steele, 1966). Samples were at 28% moisture at the beginning of the storage period. Researchers measured the amount of carbon dioxide given off by the samples over time, and converted this number to dry matter loss (DML). Results are shown in the following table:
Days Required for 1% Dry Matter Reduction in Stored Corn*
*These results represent the undamaged control sample in the study.
Average temperatures in the Midwest U.S. are 55 to 65 degrees F in the last half of September, and 50 to 60 degrees F in the first half of October. At these temperatures in the storage study, 1% dry matter loss would not occur for 25 to 50 days. This level of dry matter loss due to kernel respiration does not warrant early harvest and substantially higher drying costs for wet corn.