Harvest Date Management and Phantom Yield Loss in Corn

• Grain yield loss with delayed harvest is often speculated to be caused by respiration within kernels after maturing.

• Yields declined at 2 of 3 trial sites with delayed harvest, but kernel weight did not decline.

• Harvest should happen when appropriate grain moisture is reached, and decisions should be weighed against economics of drying corn.

There’s a lot to consider when deciding corn harvest date. Delaying harvest and taking advantage of field drying can reduce grain drying costs. However, while grain is field drying, plant health and stalk quality simultaneously begin to deteriorate, increasing potential for harvest losses.

Does Corn Lose Dry Matter When Field Drying?

Table 1.

The notion that field-drying corn will often put fields at a higher risk of yield loss from dropped ears, stalk lodging, mechanical harvest losses or increased disease and insect damage is widely agreed upon. Loss due to a delayed harvest is also believed by many to still occur in the absence of any of the previously mentioned methods, but rather through a loss in kernel dry matter after reaching physiological maturity, often coined as "phantom yield loss." It is believed that during the in-field drydown process, that although kernels have reached physiological maturity and can no longer take up any additional sugars, they continue to undergo respiration which would reduce kernel dry matter. Respiration is a process that all living organisms undergo in which they take in oxygen and in turn release heat and carbon dioxide. The loss in weight is a result of the carbon released within carbon dioxide. Although seeds are considered a living organism which does continue to respire, respiration dramatically slows down after kernels reach 30% moisture¹ and is reduced even more in dry, cooler conditions. Previous studies measuring dry matter loss from 28% moisture grain samples over time, when stored at 50-65°F temperatures, took 50-55 days to lose 1% dry matter. Although fall daily high temperatures can reach much greater than 65°F, the minimum night temperature brings the 24-hour average much closer to 65°F. In the same study, it took 10 days of constant 80°F temperature to observe a 1% dry matter loss, illustrating that respiration loss does increase with rising temperatures. These prior studies would suggest that dry matter loss from a few warm fall days may not be enough to economically offset drying costs associated with harvesting wet grain.

Harvest timing trials have also been conducted with the objective to quantify yield loss and better determine the actual cause of loss. 1 of 6 trials conducted at universities reported either no yield reduction or no grain dry-matter loss (Table 1), although numerous unpublished trials and observations in large scale field comparisons have repeatedly observed similar yield loss as reported by Purdue University 1991-94 trials. On-farm comparisons finding yield losses ranging from 0.5 to 5 bushels for each percent drop in moisture are commonly observed by many in industry. There is often little to no observable harvest losses reported in these same fields, further suggesting potential kernel dry matter loss. However, there can be less obvious reasons causing yield differences. Yield monitors are known to have higher error rates when harvesting high moisture corn which can be worsened if not recalibrating in season as moisture begins to drop. In addition to potential yield monitor error, field losses may be present more than often realized. 2 single kernels per square foot hidden under residue is equivalent to 1 bushel per acre loss. Header losses are found more often as grain moisture drops below 20%.

Figure 1. Hybrid drydown rates at trial locations

Figure 3. Kernel dry weights of individual hybrids compared to harvest moistures at the trial locations

Weekly drops in grain moisture were similar across all trials with some variation in drydown rates among hybrids (Figure 1). Clinton, IL, experienced precipitation later in the harvest season, which temporarily increased grain moisture.

Figure 2. Hybrid yield response to Harvest date

Trials in Slater and Clinton lost an average of 0.3 bushels per day, or an average of ~9 bushels over 30 days, while the trial in Seward showed no significant yield loss (Figure 2). On average, trials showed a 0.6 bushel per acre (bu/ac) loss for each point of moisture removed in the field. This is similar to the 0.9 bu/ac per point of moisture published by Purdue.³

Kernel weight was not found to decrease between the first and last harvest dates in any hybrids at any of the sites (Figure 3). This suggests that although yield decreased over time, the decrease was not due to respiration and loss of kernel dry matter. No lodging or dropped ears were observed in these trials. It is most likely that drier corn experienced greater mechanical loss during harvest than higher-moisture corn. While earlier harvests may capture more yield, this gain should be weighed against the costs of drying grain.

Strategies for building a harvest plan may be different for individual farmers based on total acres needed to harvest, daily per acre harvest capacity, ability to dry grain or drying charges at local elevators. Emphasis should be put on the economics of managing wetter grain and the potential for field loss associated with field drying. There are costs and risks associated with field drying, but kernel biomass reduction caused by respiration are not likely causing it.

References:

¹ Knittle, K.H. and J.S. Burris. 1976. Effect of kernel maturation on subsequent seedling vigor in maize. Crop Sci. 16:851-855.

² Nafziger, E. 1984. Unpublished.

³ Nielsen, R.L., G. Brown, K. Wuethrich, and A. Halter. 1996. Kernel dry weight loss during post-maturity drydown intervals in corn. Purdue University, West Lafayette, IN.

⁴ Elmore, R.W., and W.F. Roeth. 1999. Corn kernel weight and grain yield stability during post-maturity drydown. J. Prod. Agric. 12:300-305.

⁵ Thomison, P.R., R.W. Mullen, P.E. Lipps, T.A.Doerge, and A.B. Geyer. 2011. Corn response to harvest date as affected by plant population and hybrid. Agron. J. 103:1765–1772.

⁶ Licht, M., C. Hurburgh, M. Kots, P. Blake and M. Hanna. 2017. Is there loss of corn dry matter in the field after maturity? In Proceedings of the 29th Annual Integrated Crop Management Conference, Iowa State University, Ames, Iowa.