Exploring the Viability of Late-Season Split N Application in Corn Production in Eastern South Dakota

Corn [Zea mays L.], yield has increased consistently since the green revolution due in part to a better understanding of crop nutrient demands throughout the growing season. The goal of this research was to investigate the efficacy of late (V10 and V14 growth stages) split N applications in corn compared to pre-plant only N applications. The study was conducted at two locations in eastern South Dakota (Brookings, SD and South Shore, SD) over three years (2018, 2019, and 2020). Pre-plant only N treatments received 135, 180 or 224 kg N ha-1 at planting, as broadcast urea (46-0-0). Split N treatments received 68, 90, or 135 kg N ha-1 at planting as broadcast urea and then received 45, 68, 90, 112, 135, or 156 kg N ha-1 at V10 or V14 as liquid urea-ammonium-nitrate (UAN; 28-0-0) applied with Y-drop units to achieve total N rates of 135, 180 or 224 kg N ha-1. Whole-plant samples were collected at V10, V14, and R6 along with soil samples collected at V10, V14, and post-harvest to determine dry matter accumulation at these growth stages and whole-season N uptake at physiological maturity. At both locations, R6 total dry matter accumulation was not affected by treatments. Grain yield was not affected by the V10 and V14 applied treatments compared to pre-plant only treatments and some fertilizer split N ratios also increased grain yield. Split N application timing or split N application ratio did not increase grain yield across the N rates, or within the same N rate when compared to the pre-plant only treatments. The 200-seed weights of in-season applied treatments were heavier than only pre-plant N treatments. Post-harvest soil samples resulted in residual NO3--N levels being highest in pre-plant 224 kg N ha-1 or V14 applied treatments.