Corn Yield Response to Row Spacing and Seeding Rate

INSIGHTS

• Narrower corn rows allow greater interplant spacing and higher planting populations.
• Planting in 15-inch rows also allows for benefits that follow from quicker canopy cover.
• Yield response to row spacing narrower than 30 inches can be variable from year to year.

Introduction

Corn row spacing can be an important factor that affects yield and profitability. The most common row spacing in corn is 30 inches but increasing seeding rate in 30-inch rows can overcrowd plants and limit water, nutrients, and root growth per plant. Interest in shifting to narrower row spacing as a way of increasing seeding rates and boosting yield potential has grown in recent years. By narrowing row spacing, it’s possible to maintain the distance between individual plants within the rows and keep the same seeding rate. The larger plant-to-plant distance with narrower rows also allows an opportunity for increased seeding rates. Greater distance between plants reduces interplant competition for light, water, and nutrient resources while allowing earlier crop canopy closure. Quicker canopy closure can limit weed growth, help conserve soil moisture and maximize available light for photosynthetic activity.

2024 Agronomy in Action Trial

An Agronomy in Action research trial was established at Slater, IA, to evaluate how hybrids respond to narrower row spacing and increased seeding rates. Four hybrids were evaluated at 15-inch and 30-inch spacings at seeding rates of 32,000, 38,000, and 44,000 plants per acre. 15-inch rows were established using two passes with a 30-inch planter, shifting the second pass 15 inches (Figure 1). When doing so, the first planted set of rows incurred wheel traffic, although this caused little difference in emergence or final stands.

The trial received adequate fertility and above-average rainfall shortly after planting, followed by excessively dry conditions in August and September.

Figure 1. Aerial view showing spatial arrangement of 30-inch corn rows (left) compared to 15-inch rows (right), Slater, IA in 2024.

2024 Results

Graph 1. Historical U.S average soybean grain yield.

Individual hybrids responded similarly to reduced row spacing, therefore responses were averaged across the 4 hybrids and 3 seeding rates. There was no yield increase in narrow row spacing in this trial (Graph 1). However, increasing seeding rates to 38,000 and 44,000 improved yields by 2.3% and 6.9% respectively over the base seeding rate of 32,000 when averaging across hybrids and row spacings.

Individual hybrid response to higher seeding rates varied (Graph 2). G10U97 and G13U96 brands responded significantly to a rate of 44,000 plants per acre but were not responsive to the 38,000 seeding rate. G12U11 and G13U29 brands were less responsive to increased seeding rates, although they did show small incremental yield increases with each seeding rate.

Previous studies that evaluated row spacing have shown there is not always a yield gain with narrower corn rows compared to standard 30-inch row widths.¹ A similar Golden Harvest^® corn row spacing and seeding rate trial carried out at multiple locations in 2020 only had positive responses to 15-inch row spacing in 2 of 4 trial sites. Like seeding rate, the response to row spacing is largely dependent on environmental conditions during the growing season. In prior trials it was observed that responses to narrower row spacing was more consistent when corn was planted at seeding rates greater than a typical 30-inch row spacing seeding rate.

Graph 2. Corn yield of individual hybrids averaged across row spacing.

Row spacing narrower than 30 inches can sometimes increase corn yield by allowing increased planting populations and reducing interplant competition. Narrow row spacing may also improve weed control due to quicker canopy closure, which also maximizes sunlight capture and helps retain more soil moisture. Incorporating narrower row spacing into your operation should be part of a comprehensive management plan that focuses on hybrid selection, seeding rate, fertility, and fungicide application to maximize yield potential. Tire spacing on your current equipment should be considered, as making a switch to narrower row spacing could require the expense of a new planter, spraying equipment, or combine head. Your local Golden Harvest agronomist can help place hybrids with good disease tolerance and stalk strength, and recommend seeding rates that complement narrower row crop systems.

References

¹Licht, M., Parvej, M. and E. Wright. 2019. Corn yield response to row spacing and plant population in Iowa. Crop, Forage, & Turfgrass Management. 5:0032. doi:10.2134/cftm2019.05.0032