Corn Development and Dry Down in the Far-Northern Corn Belt

Background and Objectives

Corn development and dry down rates in the far-northern Corn Belt are often predicted using information from the central Corn Belt, since little information is available for this region. As a result, inaccurate predictions are common due to differences in growing environments and hybrid comparative relative maturity (CRM) between regions.
The objectives of this study were to evaluate corn development and dry down rates across several growing environments in the far-northern Corn Belt and determine whether this was influenced by hybrid CRM.

Study Description

Field trials were conducted in northwestern Minnesota and eastern North Dakota at six to eight locations per year from 2015 to 2017.
Two to six Pioneer® brand corn hybrids of differing maturity (73-87 CRM) were evaluated in each trial, with three replications per locations.
Data were collected 10 to 15 times per location from corn emergence until harvest. Corn developmental stage, location of the kernel milk line, and grain moisture content were recorded. Site-specific weather data were used to calculate growing degree units (GDUs) at 86/50 ºF maximum/minimum thresholds.

Chart showing the relationship between corn vegetative (V) stage and cumulative GDUs from planting for 73- to 87-CRM hybrids. — **Figure 1.** Relationship between corn vegetative (V) stage and cumulative GDUs from planting for 73- to 87-CRM hybrids, across hybrids, locations, and years (2015–2017).

Results

There was a linear relationship between cumulative GDUs from planting and corn vegetative stage (Figure 1), and this was consistent among hybrids and years. On average, 59 GDUs were required to advance each vegetative stage during the VE to V18 stages.
The 2011 Iowa State University Extension publication titled “Corn Growth and Development” reports that 108- to 112-CRM hybrids grown in central Iowa require 84 GDUs to advance one vegetative stage during the VE to V10 stages, and 56 GDUs to advance one vegetative stage beyond the V10 stage.
These GDU requirements of 108- to 112-CRM hybrids are similar to those of the 73- to 87-CRM hybrids in this study after the V10 stage, but are greater than those in this study during earlier growth stages (Table 1).
Assuming daily high/low air temperatures of 80/55 ºF, the greater GDU requirements of 108- to 112-CRM hybrids are equivalent to an additional 1.4 days per vegetative stage during the VE to V10 growth period or 14 days total.
There was a linear relationship between cumulative GDUs from planting and progression of the kernel milk line from the crown (Figure 2), which varied by year but did not differ significantly among hybrids. On average, kernel milk line progressed downward by 1% per 4.5, 3.5, and 3.8 GDUs in 2015, 2016, and 2017, respectively.

Table 1. Relationship between cumulative GDUs from planting and corn vegetative (V) stage reported for 108- to 112-CRM hybrids in the 2011 Iowa State University Extension publication “Corn Growth and Development” compared with that for 73- to 87-CRM hybrids in this study.

There was a linear relationship between cumulative GDUs from planting and dry down of grain in the field (Figure 3). As with kernel milk line progression, this differed among years but did not differ significantly among hybrids.
On average, grain moisture declined by one percentage point per 14.4, 7.2, and 13.6 GDUs in 2015, 2016, and 2017, respectively (Figure 3). This is equivalent to a one percentage point decline in grain moisture with each 1.0 day in 2015, 0.5 day in 2016, and 0.9 day in 2017, assuming daily high/low temperatures of 80/50 ºF during the dry-down period.

Conclusions

Results from this study confirm that corn development during the vegetative stages is more rapid until the V10 stage for early-maturity hybrids grown in the far-northern Corn Belt compared to that reported for longer-season hybrids grown in the central Corn Belt.
From the VE to V10 stages, this difference in GDU requirements between hybrid groups was equivalent to 14 days. Beyond the V10 stage, the rate of vegetative development was similar, although the hybrids in this study produced 15 to 18 leaves while hybrids adapted to the central Corn Belt typically produce 19 to 20 leaves.
In this study, there was a linear relationship with GDU accumulation from planting for kernel milk line progression and in-field dry down of grain after physiological maturity. These relationships varied by year, but did not differ significantly among the hybrids tested.
There was also greater variability in the relationship between these variables and cumulative GDUs from planting, in comparison to corn vegetative development, and is attributed to differences in soil moisture content during grain fill and weather conditions during dry down.