Corn nitrogen (N) response is influenced by precipitation frequency and intensity. Increased weather variability has prompted growers to pursue improved nitrogen strategies to address economic, social and environmental concerns regarding nitrogen management.
Risks associated with early-applied nitrogen loss have increased interest in delayed nitrogen applications to help synchronize nitrogen availability with corn nitrogen uptake. However, corn nitrogen uptake prior to V6 emphasizes the importance of strategies to meet early nitrogen demands and maintain yield potential until sidedress time.
Recently, a three-year study supported by the Corn Marketing Program of Michigan was conducted investigating corn grain yield and profitability response to nitrogen placement and timing combinations applied at a single nitrogen rate (maximum return to nitrogen). The maximum return to nitrogen rates in Lansing and Richville, Michigan, were 140 and 180 pounds N A-1, respectively. Three nitrogen management strategies were utilized and included:
Starter nitrogen (10-34-0) applied in-furrow (7 pounds N A-1) with sidedress nitrogen (28-0-0) at V4, V10 or a 50/50 split at V4 and V10.
Starter nitrogen (28-0-0) sub-surface banded as 2-by-2 (40 pounds N A-1) with sidedress nitrogen (28-0-0) at V4, V10 or a 50/50 split at V4 and V10.
Broadcast pre-plant incorporated nitrogen with 100 percent urea, 25/75 mix of urea and polymer-coated urea, and poultry litter applied at 1 T A-1 plus sidedress nitrogen (28-0-0) at V10.
Success of sidedress applications can depend on seasonal weather patterns. When April – June rainfall was near normal to deficit, in-furrow applications reduced grain yield up to 22 bushels A-1 when full sidedress was delayed from V4 until V10. Profitability was similarly reduced up to $79 A-1. Reduced nitrogen rates required by the in-furrow placement were not able to maintain yield potential until the V10 sidedress timing when rainfall was below normal.
Similar yield trends (although not statistically different) were observed with the 2-by-2 nitrogen strategy where yield was reduced up to 11 bushels A-1 when full sidedress was delayed from V4 until V10. Unlike the in-furrow strategy, profitability in dry years was not reduced using the 2-by-2 nitrogen strategy. Although the in-furrow or 2-by-2 strategies often achieved similar yields, both increased grain yield up to 18 bushels A-1 compared to pre-plant incorporated nitrogen.
When April – June rainfall was above normal (i.e., wet year), similar yields were achieved when sidedress was delayed from V4 to V10 using the in-furrow or 2-by-2 nitrogen strategy. No yield difference suggested the risk of early applied nitrogen loss (i.e., V4) in wet years was less than the risk of reduced uptake with late applied nitrogen (i.e., V10) in dry years.
In a wet year, poultry litter plus V10 sidedress provided a slowly available nitrogen source and increased yield 17-27 bushels A-1 relative to the in-furrow or 2-by-2 strategies with V4 sidedress. Grower profitability using poultry litter will depend on the cost effectiveness of the litter source.
One point emphasized by the study was the adage “start right to finish well.” Canopy measurements collected at V6 indicated corn yield potential was influenced early in the growing season. Nitrogen management strategies (i.e., pre-plant incorporated, in-furrow, 2-by-2) must sufficiently supply nitrogen until sidedress timing to influence success of the in-season application (see photos).
Except for poultry litter plus V10 sidedress in a wet year, no positive yield or profitability responses were observed when full sidedress was delayed until V10.
To increase corn nitrogen recovery, multi-pass nitrogen application systems are a recommended best management practice in Michigan. In four of six site years, multi-pass nitrogen strategies increased yield 9-30 bushels A-1 as compared to a single one-pass nitrogen application of urea or ESN/urea.
While split-nitrogen applications generally increased yield over a one-pass approach, the in-furrow strategy increased risk due to reduced nitrogen rates and concern for seedling injury. The 2-by-2 strategy allowed for increased starter nitrogen rates and provided a more consistent yield response across site years.
Growers splitting their nitrogen applications will minimize risk when applying sidedress at V4 and may want to consider late vegetative nitrogen sidedress timings as a rescue application for northern corn production regions instead of a standard practice.
In both pictures, corn at V10 received in-furrow starter N (7 lbs. N A-1). Left: Corn received V4 sidedress (total N=140 lbs. A-1). Right: Corn awaiting V10 sidedress and displays signs of N stress (i.e., lower canopy firing) due to in-furrow strategy.