Maximizing Sidedress Nitrogen Efficiency in Corn

INSIGHTS

• Additional planter-applied nitrogen (N) sidedressing improved yield by 7.7 Bu/A over the normal preplant rate.
• There was no yield difference between surface and subsurface planter N application.
• N use and yield is maximized when sidedress N application aligns with rapid nutrient uptake.
• Adding a N stabilizer to a sidedress N application was only effective when planter-applied.

Introduction

The annual yield potential of a field is a continuously evolving number dependent on changing weather conditions prior to and during the growing season. Yet nitrogen (N) fertilizer rates selected for specific fields are often identified well before planting and frequently aren’t adjusted to account for favorable or unfavorable conditions that influence N availability and yield potential. When all N is applied preplant, this creates scenarios where N supply may not meet crop demand. Timely nitrogen sidedressing can provide the opportunity to address N shortages. To determine the effectiveness of this approach, the Agronomy in Action (AIA) research team conducted multiple trials to gauge the value of various forms of at-planting or post-N application and identify methods to maximize its effectiveness.

Evaluation of Planter-Applied N Placement

The first trial evaluated placement methods of a supplemental planter-applied N application. While this is not a widely common type of application, it does offer the opportunity to eliminate a potential pass across the field and unlike later sidedress timings, there is no risk of excessive rainfall preventing the application from being made. The trial was designed to determine whether there was an advantage to either applying a sidedress subsurface 2×2×2 placement or surface dribbling. A total of 20 trials were conducted in 2023 and 2024 at eight Agronomy in Action sites with sidedress rates of 40 and 60 lbs N/A as UAN (32-0-0) in 2023 and 2024, respectively. A base preplant N rate was applied evenly across all trials based on individual site yield goals, and incremental N was applied to specified plots during planting.

Planter-applied N sidedressing provided value, as evident by an overall 7.7 Bu/A yield response (Table 1). Additionally, 18 of the 20 sites exhibited positive responses to sidedressed N, with 14 of the 18 responsive sites producing ≥ 5 Bu/A responses. The mechanisms driving these positive responses differed by location. For example, 2024 sites such as Clinton, IL, Malta, IL, and Slater, IA, received well above average precipitation in early May that likely led to preplant N fertilizer loss, and reduced overall N supply. In comparison, 2024 trials at Clay Center, KS, experienced ideal planting conditions and above-average early-season temperatures, which contributed to an increased overall yield potential at the site.

Table 1. Yield response to planter N in 20 AIA research trials, 2023-24.

Different letters indicate statistical differences at P<0.05
Graph 1. Response of yield to planter-applied N placement across 20 AIA research trials, 2023-24.

Another component of this trial was evaluating whether there is an agronomic advantage to subsurface (2×2×2) versus surface dribble planter-applied N. Theoretically, subsurface placement of N reduces the ability for loss via runoff, volatilization, or immobilization by residue in continuous corn and/or no-till situations. Results from this trial found a slight, nonsignificant 2.6 Bu/A advantage to surface dribble over subsurface application (Graph 1). All trials within the experiment were conventionally tilled (except Clay Center, KS, which was no-till) and were either irrigated or received ample rainfall following planting, which may have minimized N loss potential associated with surface application.

Although there was a marginal yield advantage with surface dribble compared to subsurface placement, individual trial-to-trial responses varied greatly. The combination of these responses suggests that there is no definitive agronomic advantage to either planter-applied N placement method. Instead, it should be based on the grower’s preference and used as a complement to, not replacement for, the current starter fertilizer planter setup, if present.

Importance of Sidedress Timing

A second experiment conducted in 2024 at five Agronomy in Action research sites (Clay Center, KS, Clinton, IL, Grundy Center, IA, Janesville, WI, Malta, IL, and Slater, IA) was performed to evaluate the importance of N sidedress timing when N supply from preplant N application is inadequate. The experiment evaluated surface application of 60 lbs/A of N as UAN (32-0-0) at three different timings (planter dribble, Y-drop at V3, and Y-drop at V10). There was an 8.2 Bu/A positive response to planter-applied N applied to the soil surface (Graph 2). There was an incremental 7.1 and 3.2 Bu/A advantage from applying N at V3 and V10 respectively as compared to planter applications. This response coincides with plant N uptake by growth stage, as rapid nutrient uptake by corn begins around V3/V4 and typically peaks between V8 and R1. Since time between application and uptake is the greatest with planter application, it creates the greatest opportunity for potential loss, thus reducing its availability. This experiment also evaluated the value of utilizing an N stabilizer with surface sidedress applications. The selected N stabilizer provided activity against both volatilization (NBPT) and denitrification/leaching (DCD). The greatest value of the N stabilizer was realized with planter-applied N through a 3.7 Bu/A response, though it was not statistically significant (Graph 3). In comparison, there was no agronomic value to using an N stabilizer with the V3 and V10 timings, as no yield response occurred.

Graph 2. Yield response to supplemental N timing (surface application of 60 lbs N/A) at five AIA trials in 2024. Different letters indicate statistical differences at P<0.05.

Graph 3. Yield response to N stabilizer containing DCD & NBPT at three different application timings at five AIA trials in 2024 (surface application of 60 lbs/A of N).

Summary

Nitrogen sidedressing provides an opportunity to reduce the amount of N fertilizer subject to potential loss and reallocating a portion to a period when plant N demand is greatest. It also provides an opportunity to modify or increase the overall N supply when yield potential increases or unexpected loss to the initial N supply occurs. These Agronomy in Action research trials showed that supplemental N application, even when planter-applied, provides agronomic value across a wide range of environments with varying N demands. The results also showed that the efficiency of sidedress N fertilizer is maximized when it occurs during the period of rapid plant N uptake and that a stabilizer was only agronomically valuable with planter-applied N since it reduced its loss potential.