Corn nitrogen (N) response is influenced by precipitation frequency and intensity. Increased weather variability has prompted growers to pursue improved N strategies to address economic, social and environmental concerns regarding N management.

Risks associated with early-applied N loss have increased interest in delayed N applications to help synchronize N availability with corn N uptake. However, corn N uptake prior to V6 emphasizes the importance of strategies to meet early N demands and maintain yield potential until sidedress time, says Kurt Steinke, soil science specialist at the Michigan State University.

Recently, a three-year study was conducted that investigated corn grain yield and profitability response to N placement and timing combinations applied at a single N rate (maximum return to N). The maximum return to N rates in Lansing and Richville, Mich., were 140 and 180 pounds N per acre, respectively. Three N management strategies were utilized and included:

• Starter N (10-34-0) applied in-furrow (7 pounds per acre) with sidedress N (28-0-0) at V4, V10 or a 50/50 split at V4 and V10.
• Starter N (28-0-0) sub-surface banded as 2-by-2 (40 pounds per acre) with sidedress N (28-0-0) at V4, V10 or a 50/50 split at V4 and V10.
• Broadcast pre-plant incorporated N with 100% urea, 25/75 mix of urea and polymer-coated urea and poultry litter applied at 1 ton per acre plus sidedress N (28-0-0) at V10.

Success of sidedress applications can depend on seasonal weather patterns. When April through June rainfall was near normal to deficit, in-furrow applications reduced grain yield up to 22 bushels per acre when full sidedress was delayed from V4 until V10. Profitability was similarly reduced up to $79 per acre. Reduced N 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 N strategy where yield was reduced up to 11 bushels per acre 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 N strategy. Although the in-furrow or 2-by-2 strategies often achieved similar yields, both increased grain yield up to 18 bushels per acre compared to pre-plant incorporated N.

When April through 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 N strategy. No yield difference suggested the risk of early applied N loss (i.e., V4) in wet years was less than the risk of reduced uptake with late applied N (i.e., V10) in dry years. In a wet year, poultry litter plus V10 sidedress provided a slowly available N source and increased yield 17-27 bushels per acre 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 N until sidedress timing to influence success of the in-season application. 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 N recovery, multi-pass N application systems are a recommended best management practice in Michigan. In 4 of 6 site years, multi-pass N strategies increased yield 9-30 bushels per acre as compared to a single one-pass N application of urea or ESN/urea.

While split-N applications generally increased yield over a one-pass approach, the in-furrow strategy increased risk due to reduced N rates and concern for seedling injury. The 2-by-2 strategy allowed for increased starter N rates and provided a more consistent yield response across site years.

Growers splitting their N applications will minimize risk when applying sidedress at V4 and may want to consider late vegetative N sidedress timings as a rescue application for northern corn production regions instead of a standard practice.