Managing Higher Corn Seeding Rates with Narrower Row Spacings

• Like seeding rate, row spacing responses are dependent on the environment.
• Positive yield responses to narrower row spacings are most consistent when seeding rates are above typical 30” row seeding rates for a given environment.
• Hybrids respond differently to changes in row spacing so selecting a hybrid that performs well in narrower rows is key.

Corn grain yield is the product of the number of plants per acre, kernels per plant and weight per kernel. Because kernels per plant and weight per kernel are primarily affected by environmental conditions after initial agronomic management factors are implemented in modern commercial field corn, the yield component factor most under manual control is seeding rate.

Currently, the average corn seeding rate in the U.S. is just under 32,000 seeds/A and has increased by an average of 400 seeds/A/year since the 1960s. As this trend continues, the average U.S. corn seeding rate will reach 38,000 seeds/A in 15 years and 44,000 seeds/A in 30 years. These higher seeding rates reduce the plant-to-plant spacing within the row and the intensifying crowding stress may become yield-limiting. Narrower row spacings can be used to increase plant-to-plant spacing within a row to reduce crowding and subsequently reduce competition among individual plants, allowing the crop to better utilize available light, water and nutrients.

The vast majority of corn is planted in 30” row spacings, with narrow rows generally defined as any row spacing or configuration less than 30". Planting corn in a 15” row creates twice as much distance between plants within a row compared to 30” row spacings at a given seeding rate. For example, at a seeding rate of 38,000 seeds/A, there is 11” between plants when planting in 15” row spacings compared to only 5.5” between plants in 30” row spacings.
 

Previous Findings

• In 2019, The Golden Harvest® Agronomy In Action research team evaluated more than 46 hybrids in 30” and 20” row spacings at various seeding rates across 5 locations. 3 of the 5 locations had a positive yield response to 20” rows, one location had no response and one location had a negative response. On average, across all locations, seeding rates and hybrids there was a 2 bu/A yield advantage to planting 20” rows compared to 30” rows.
• In general, 20” rows tended to perform better at seeding rates greater than 35,000 seeds/A and less than 50,000 seeds/A. When populations were below 35,000 seeds/A, the 30” row spacing tended to yield greater. At 50,000 seeds/A or greater there was little yield difference between the row spacings.
• Hybrid responses to 20” row spacings were variable across locations. Some hybrids tended to have a positive yield response to 20" rows while other hybrids had a negative yield response. 

2020 Narrow Row Corn Trials
In 2020, 4 seeding rates ranging from 35,000 to 50,000 seeds/A were evaluated in 30" and 15" rows across seven hybrids (Figure 1). These trials were established at Clay Center, KS, Clinton, IL, Fairfield, IA, Seward, NE, and Slater, IA(Figure 2). Due to the late season derecho wind events, the Slater location was removed from any data analysis.

Effect of Seeding Rate and Row Spacing on Grain Yield

When averaged across all locations and hybrids, there was a significant interaction between row spacing and seeding rate. At the lowest seeding rate of 35,000 seeds/A, planting 30” rows yielded 5 bu/A greater than planting 15” rows (Graph 1). Lower seeding rates in narrower rows increased in-row plant spacing, likely resulting in a loss of narrow row efficiency for capturing solar radiation. However, 15” rows produced an 8 bu/A yield advantage at 40,000 seeds/A and a 5 bu/A yield advantage at 44,000 seeds/A compared to 30" row spacings (Graph 1). Interestingly, the yield potential of plants grown in a 15” row decreased dramatically at 50,000 seeds/A, whereas plants in a 30” row were not as negatively impacted, resulting in similar yields between row spacings at this seeding rate. Likely, plants experienced enough in-row competition that changes in the between-row environment were not meaningful.

A recent study found similar results where the greatest yield advantage of narrower row was in the seeding rate range between 44,000 and 50,000 seeds/A.¹ They observed that as seed rate increased, plants focused their energy and resources to producing above-ground biomass at the expense of below-ground biomass. For every additional 6,000 plants/A, the size of the root system decreased 15-18%. However, when switching from a 30" row to a 20" row, the better plant-to-plant spacing resulted in a 22% increase in root mass. They concluded that narrower row spacings helped mitigate crowding stress at greater seeding rates by promoting phenotypic changes that consequently led to greater yields.

There were differences in response to row spacing for each location. Yield response to 15" rows ranged from -5 bu/A to 16 bu/A at 4 locations (Graph 2). 2 out of the 4 locations had a positive yield response to the narrower row spacing while the other 2 locations showed a negative yield response.

The significant interaction between location and row spacing is not surprising, given the typical interaction between location and seeding rate. Both row spacing and seeding rate change the spatial arrangement of plants in a field, which has a major impact on the ability of plants to capture sunlight and acquire nutrients and water. In addition, it effects the movement of air through the canopy which can influence disease development and canopy temperature. The degree of impact on grain yield from these plant spatial arrangement effects depends on the environment.

Hybrid Response to Narrower Rows and Seeding Rate
 
Hybrids responded differently to row spacing and seeding rate:

• In a 30" row, hybrid G03R40-5222 had no yield response to seeding rate until rates exceeded 45,000 seeds/A when yield began to decrease. Alternatively, G03R40-5222 responded positively to increased seeding rates in a 15" row maximizing grain yield at rates between 40,000 – 45,000 seeds/A. There was little to no yield difference between planting G03R40-5222 in 15" rows compared to 30" rows across the different seeding rates.
• Hybrid G13Z50-5222 showed a similar response to seeding rate. However, the yield response to narrower rows was much greater (Figure 3 and Graph 3). When planted in a 15" row compared to a 30" row, G13Z50-5222 yielded 8 and 9 bu/A more at seeding rates of 40,000 and 45,000 seeds/A, respectively.
• Hybrid G10D21-3330 was much more responsive to higher seeding rates than the other hybrids in both a 30" and 15" row spacing (Figure 4 and Graph 3). G10D21-3330 was also responsive to narrower rows at seeding rates of 40,000 and 45,000 seeds/A yielding 5 bu/A greater on average. 

The difference in response between these hybrids demonstrates the importance of selecting the right hybrids to match the management system. Researchers also found that hybrids respond differently to seeding rate and narrower row spacings, attributing the differences to the inherently distinct phenotypic traits of the hybrids.²

Considerations When Planting in Narrower Rows
When planting in narrower rows, it is important to select a hybrid that is responsive to higher seeding rates and narrower rows. A hybrid with excellent agronomic characteristics, such as good stalk strength, standability and a solid root system is beneficial in these more intensive cropping systems.

There tends to be a more consistent response to narrower rows at increased seeding rates for the given environment. For example, in these environments the average seeding rate is around 35,000 seeds/A in a 30” row. Switching to 15” rows while keeping the same seeding rate resulted in a yield decrease. However, by increasing the seeding rate to 40,000 seeds/A in a 15” row there was a yield increase of 8 bu/A compared to the standard practice of planting 35,000 seeds/A in a 30” row. Increased seeding rates when planting in narrower rows can be adjusted accordingly based on the typical seeding rates in 30” rows for the given environment and hybrid. 

At greater seeding rates, crop management becomes even more important. Adequate fertility is critical to setting a higher yield potential and foliar protection is needed to maintain that yield potential throughout the growing season in these more intensive cropping systems. 

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights. 

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References:
1 Bernhard, B. J., and Below, F. E. 2020a. Plant population and row spacing effects on corn: Plant growth, phenology, and grain yield. Agronomy Journal. 112(4): 2456-2465.
2 Bernhard, B. J., and Below, F. E. 2020b. Plant population and row spacing effects on corn: Phenotypic traits of positive yield-responsive hybrids. Agronomy Journal. 112(3): 1589-1699.