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Corn Harvest Timing

 

Harvest Timing Effect on Corn Yield

Background and Rationale
Objectives
Study Description
Results
Conclusions

Background and Rationale

  • When harvest is delayed due to weather or other factors, it is not uncommon to observe lower yields in the portion of the field harvested later than the portion harvested earlier.
  • There are a number of possible reasons why yield may decline with later harvest, including ear drop, stalk lodging, insect feeding, ear rots, and greater harvest loss.
  • Dry matter loss resulting from kernel respiration during grain dry down has also been hypothesized as an explanation for lower yields with later harvest dates, although recent research has failed to detect significant loss in kernel dry matter following physiological maturity.
  • Lower grain moisture at harvest can result in greater shelling at the header; however there is very little recent research to indicate how much this may contribute to lower yields with later harvest dates.

Objectives

  • On-farm trials were conducted in 2018 to document any yield difference when harvesting corn at high moisture (>25%) versus low moisture (less than 20%).
  • A subset of locations were sampled to determine the proportion of observed differences in yield attributable to pre-harvest loss (ear drop) and harvest loss (header + separating loss).

Study Description

  • Trials were conducted at 14 locations in northern Iowa and eastern Nebraska.
  • Fields were selected based upon grower convenience for harvesting at two different timings.
  • A total of 8 different corn hybrids were used across trial locations, ranging from 101 to 118 CRM.
  • Caution was used to prevent as much stalk lodging as possible by leaving extra rows on either side of the harvested strips.
  • Targeted moisture ranges at harvest were >25% and < 20% (referred to as “early harvest” and “late harvest” in the results).
  • One round of corn was harvested at each harvest timing and yield measured by weigh wagon.
  • Pre-harvest and harvest loss were measured at 6 of 14 locations.
    • Pre-harvest loss (ear drop) was sampled by counting the number of ears on the ground prior to harvesting in 1/100 of an acre (or 174 of row in a 30” row spacing)
    • Harvest Loss (header and separating loss) was sampled by counting kernels on the ground (two random locations) after the combine passed in 2 or 3 10 ft2 areas across the header width (Figure 1).

Figure showing sampling area layouts for measuring corn harvest loss (8-row head).

Figure showing sampling area layouts for measuring corn harvest loss (12-row head).

Figure 1. Sampling area layouts for measuring harvest loss.

Results

  • Due to the rapid dry down of grain experienced across much of the Midwest in 2018, grain moistures at early harvest timings were generally below the target range (Table 1).
  • Extended periods of rainy weather resulted in long delays between early and late harvest at some locations (Table 1).

Table 1. Harvest date, grain moisture and yield for early and late harvest timings at each trial location.

Table showing corn harvest date, grain moisture and yield for early and late harvest timings at different plot trial locations.

Table showing corn harvest date, grain moisture and yield for early and late harvest timings at different plot trial locations.

  • Yield differences between early and late harvest varied widely across locations, from a decrease of 22.6 bu/acre to an increase of 2 bu/acre with later harvest. On average, yield was 8.9 bu/acre lower with later harvest (Table 2).
  • Difference in grain moisture between the two harvest timings also varied widely across locations, from 1.2 to 8.0 percentage points (Table 2).
  • Differences in yield between harvest timings showed no correlation with the number of days between early and late harvest or differences in grain moisture (Table 2). In fact, the three locations where yields differed by less than 1% between harvest timings all had greater than a month between the early and late harvest.
  • Differences in yield between harvest timings also did not appear to correspond to hybrid or geography (data not shown).

Table 2. Number of days between early and late harvest and differences in yield and moisture between harvest timings.

Table showing the number of days between early and late corn harvest and differences in yield and moisture between harvest timings.

Harvest Loss

  • At the 6 locations where harvest loss was measured, loss was generally low, averaging 0.62 bu/acre with early harvest and 1.55 bu/acre with late harvest (Table 3).
  • Pre-harvest loss due to ear drop was negligible at all locations (data not shown).
  • Harvest loss tended to increase with lower grain moisture across locations and harvest timings (Figure 2).
  • Measured harvest loss only partially accounted for the differences in yield between harvest timings observed at some locations (Figure 3).
  • However, there was a correlation between the difference in yield between harvest timings and the difference in harvest loss - locations with lower yields at the later harvest timing also tended to have more harvest loss.

Table 3. Yield and harvest loss with early and late harvest at locations where harvest loss was measured, and the differences in both between harvest timings.

Table showing yield and corn harvest loss with early and late harvest at locations where harvest loss was measured.

Table showing grain moisture effect on corn harvest loss.

Figure 2. Grain moisture effect on harvest loss.

Figure showing relationship between difference in corn yield between early and late harvest and difference in harvest loss.

Figure 3. Relationship between difference in yield between early and late harvest and difference in harvest loss.

Conclusions

  • Results of this study showed that corn yield tended to decline with later harvest on average, but it is not clear why and results varied widely among locations.
  • Greater harvest loss only partially accounted for lower yields.
  • The lack of correlation with grain dry down or length of harvest delay tends not to support the hypothesis that reduced yields are due to dry matter loss from kernel respiration.

2018 data are based on average of all comparisons made in over 14 locations through November 8, 2018. Multi-year and multi-location is a better predictor of future performance. Do not use these or any other data from a limited number of trials as a significant factor in product selection.


Authors: Steve Leusink and Mark Jeschke

January 2019

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The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary.

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