Agronomic performance of short-season corn hybrids in Illinois

Abstract

Cover crops are increasingly promoted as a strategy for reducing nitrate losses through tile drainage in the upper Midwest (IEPA et al., 2015; IDALS et al., 2013). The literature also highlights several other cover crop benefits, such as reducing soil erosion, suppressing weeds, and increasing soil organic C, which is closely tied to the amount of biomass they produce (Blanco-Canqui et al., 2015; Chudzik et al., 2024; McClelland et al., 2021). In Illinois, cover crop acreage has increased by ∼24% from 2017 to 2022 (0.71 to 0.88 million acres) (USDA-NASS, 2024). However, establishing cover crops remains challenging due to the limited window between cash crop harvest and freezing temperatures.

One potential strategy to this challenge is the use of shorter-season crops, which can be harvested earlier, allowing for earlier cover crop planting and successful establishment before winter. Research in Ohio showed that corn (Zea mays L.) hybrids with relative maturity (RM) ratings of 102 days yielded similarly to 111 days (Lindsey et al., 2015). Baum et al. (2019) also reported no yield differences among 106-, 111-, and 113-day hybrids in southern Iowa. Relatively few studies have evaluated the yield potential of ultra-early (<100-day) hybrids in this region (Lindsey et al., 2020). Therefore, this 2-year field study aimed to compare the agronomic performance of ultra-early and short-season with commonly grown hybrids in Illinois.

Field experiments were conducted in 2023 and 2024 at the University of Illinois Crop Sciences Research Centers in Urbana (40°03′33.3″ N, 88°13′41.9″ W) and Monmouth (40°55′34.4″ N, 90°43′31.0″ W). Trials were on a Drummer silty clay loam (Fine-silty, mixed, superactive, mesic Typic Endoaquoll) at Urbana and Sable silty clay loam (Fine-silty, mixed, superactive, mesic Typic Endoaquoll) at Monmouth (Soil Survey Staff, 2019); both productive soils with >3.5% organic matter. Weather data were collected from site-specific meteorological stations.

Each trial followed a randomized complete block design with four replications. Plots were four 30-inch rows (10 ft) wide by 25-ft long. Treatments included four hybrids with RM of 91 days (DKC41-55RIB, 2295 GDD to black layer), 96 days (DKC46-50RIB, 2405 GDD to black layer), 105 days (DKC105-35RIB, 2605 GDD to black layer), and 111 days (DKC111-33RIB, 2800 GDD to black layer). The 111-day hybrid is hereafter referred to as full-season (commonly grown), and thus the 91- and 96-day hybrids are referred to as ultra-early, and the 105-day hybrid as short-season. Despite the limited number of hybrids tested here, they still provide a baseline for comparing differences in agronomic performance associated with RM.

Corn was grown following soybean (Glycine max L. Merr) in conventional tillage (fall chisel plow followed by field cultivator before planting). Soil pH, P, and K were maintained at adequate levels according to soil tests (Fernández & Hoeft, 2009). Urea ammonium nitrate (28%) was applied pre-plant and incorporated to supply 175 and 185 lbs N acre⁻¹ at Urbana and Monmouth, respectively. Corn was planted at 36,500 seeds acre⁻¹ on May 12, 2023, and May 20, 2024, in Urbana, and May 9, 2023, and April 25, 2024, in Monmouth. Weeds were controlled by applying pre-emergence (Harness Xtra, Bayer) and post-emergence (Armezon PRO, BASF) herbicides at recommended rates, following standard practices in the region.

Corn was hand-harvested from the center of each plot (two rows by 10 ft) on October 8, 2023, and October 18, 2024, at Urbana, and October 11, 2023, and September 25, 2024, at Monmouth. After shelling, grain weight was recorded, and moisture and test weight were measured (Dickey-John, GAC2100). Kernel weight on a dry matter basis (0% moisture) was determined from a subsample of 300 kernels. All yields were adjusted to 15% moisture concentration before yield comparisons.

Analysis of variance was conducted using the PROC GLIMMIX procedure of SAS (SAS Institute) to evaluate the overall effects of corn hybrid maturity on grain yield, grain moisture at harvest, test weight, and kernel weight. Treatment effects were modeled as fixed factors, with year, location nested within year, and block nested within location as random factors. Contrasts were also made to compare ultra-early hybrids (91–96 days) with short-season (105-day) and full-season (111-day) hybrids. Results were considered significant at p ≤ 0.1, and treatment means were compared using Fisher's LSD test with the LSMEANS statement and LINES option.

Growing degree days (GDD, base 50°F, ceiling 86°F) were calculated from planting to September 30 for each site-year (Gilmore & Rogers, 1958). Linear regression models were developed using PROC REG to describe the accumulated GDD throughout the growing season and were used to estimate the dates when corn plants reached black layer (growth stage R6) (Abendroth et al., 2011). To estimate the optimal harvest dates (16%–17% grain moisture), we assumed a 35% grain moisture at R6 and used a constant dry-down rate of 0.69% day⁻¹ in the first 20 days and 0.44% day⁻¹ thereafter, as reported in the literature (Abendroth et al., 2011; Martinez-Feria et al., 2017; Sala et al., 2007). While dry-down rate is influenced by various factors, including environmental conditions (e.g., air temperature, humidity, and wind speed) and hybrid genetics, the above post-maturity drying coefficients explained 83% of the temporal variation across a wide range of genotype-environments (Martinez-Feria et al., 2017). The optimal harvest estimates aimed to minimize grain drying costs and reduce the risk of grain yield and quality losses due to delayed harvest, as well as to determine how much earlier the ultra-early and short-season hybrids could be harvested compared to the full-season hybrid, and allowed for the calculation of cover crop growing season gains from the altered harvest date. The GDD accumulation was calculated using a base temperature of 39°F (Kantar & Porter, 2014; Lindsey et al., 2020).

Growing season temperatures averaged 0.6 to 1.6°F warmer than normal at both locations and years (Table 1). Monthly precipitation was generally below normal throughout much of the 2023 season, with growing season rainfall reaching 68% of the average in Urbana and 93% in Monmouth. In 2024, Monmouth again experienced below-normal precipitation throughout the growing season, except for July, when rainfall reached 245% of normal. September was particularly dry, with only 0.7 inches of rainfall compared to the 30-year average of 3.3 inches. Conversely, Urbana received 23.5 inches of rainfall during the 2024 growing season, exceeding the 30-year average of 19.9 inches. However, rainfall in late April and early May delayed planting in Urbana in 2024.

Corn yield significantly increased with increasing RM across the four site-years (Table 2). The ultra-early hybrids (91–96 days) yielded approximately 13% less than the short-season hybrid (105 days) and about 19% less than the full-season hybrid (111 days), primarily due to the lower kernel weights. Despite having a similar kernel weight, the 105-day hybrid had a lower test weight compared to the 111-day hybrid, resulting in a yield that was 7% (17 bu acre⁻¹) less than the 111-day hybrid. As expected, grain moisture at harvest was higher for the 111-day hybrid, followed by the 105-day hybrid, with no significant difference between the 91- and 96-day hybrids. Similar to our findings, Lindsey et al. (2020) reported that ultra-early hybrids (90–95 days) yielded ∼13% (28.7 to 29.7 bu acre⁻¹) less than commonly grown maturity hybrids in Ohio (104–109 days). In contrast, other studies have reported no significant yield differences between short- and full-season hybrids in this region. For instance, Baum et al. (2019) observed similar yields among 106-, 111-, and 113-day hybrids in southern Iowa, while Di Salvo et al. (2021) reported no yield differences between a wide range of 109- and 120-day hybrids in Kentucky.

Table 3 shows the predicted number of days and the associated environmental conditions between optimal harvest dates for each hybrid relative to the 111-day hybrid for each site-year. Our results indicate that corn reached optimal harvest (16–17% moisture) about 23 days earlier for the 91-day hybrid, 18 days for the 96-day hybrid, and 9 days for the 105-day hybrid compared to the 111-day hybrid (Table 3). The earliest harvest timing corresponded to an average of 169 to 575 more GDD and 0.6 to 1.6 inches more precipitation that could be available for cover crops.

The tradeoff between maximizing profitability and allowing adequate time for cover crop establishment was evident under the conditions of our study, where corn yields significantly increased with increasing RM. This highlights the tension between securing higher farm revenue and ensuring sufficient time for effective fall cover crop growth. While ultra-early hybrids can facilitate the establishment and maximize the benefits of cover crops, they generally underperformed agronomically compared to full-season hybrids. For instance, Lindsey et al. (2020) reported that ultra-early hybrids (90–95 days) had partial net returns (accounting for drying costs and test weight premium/discount) that were 6.4%–9.6% ($47.83 to $77.33 acre⁻¹) lower than commonly grown RM hybrids in Ohio (104–109 days).

In our study, yields also declined when switching from 111- to the 105-day hybrid. However, it is important to note that other research in this region found no significant yield differences between short- and full-season hybrids (Baum et al., 2019; Di Salvo et al., 2021; Lindsey et al., 2015), suggesting that some short-season hybrids may be available to facilitate early cover crop seeding without a corn yield tradeoff. This highlights the critical role of hybrid selection as a key management decision when balancing profitability with environmental stewardship. In addition, it is generally accepted that corn kernels are ready for mechanical harvest when moisture falls below 25% (typically between 20% and 25%). Growers aiming to increase the likelihood of successful cover crop establishment may consider harvesting corn at higher moisture levels than those in this study, although this would increase drying costs. To better inform these decisions, further research is needed to evaluate the agronomic and economic performance of a broader range of RM hybrids in Illinois.

For growers interested in cover crops, state and federal cost-share programs can help offset some of the costs associated with cover cropping. For example, financial assistance from several programs ranged from $12 to $92 acre⁻¹ in 2018 (Wallander et al., 2021). More recently, other programs such as the I-COVER have offered higher financial incentives for fields that have never been planted with cover crops or when new techniques or methods are used for earlier establishment (IDOA, 2025). Integrating interseeding or aerial seeding cover crops with planting of short-season hybrids could be another practice for early establishment, provided soil moisture is adequate for seed germination (Preza Fontes et al., 2021; Wilson et al., 2014). However, more research is needed to assess the agronomic and economic viability of these methods in Illinois, as they generally involve higher seeding rates and increased application costs than drilling the seeds after harvest (e.g., high clearance applicator or plane).

Giovani Preza Fontes: Conceptualization; data curation; formal analysis; investigation; methodology; project administration; writing—original draft. Kristin D. Greer: Data curation; investigation; project administration; writing—review and editing.

The authors declare no conflict of interest.