Nitrogen-15 evaluation of fertilizer placement at planting for corn production

Numerous studies have been reported to ascertain the benefits of starter fertilization for corn (Zea mays L.) production, but most rely on data collected by measuring early growth or grain yield at harvest. As a more conclusive evaluation, five field trials were conducted using ¹⁵N-labeled urea-ammonium nitrate (UAN) solution (90 kg N ha⁻¹) to compare single and dual subsurface band placement, as well as surface dribble and broadcasting with incorporation. Significant differences in dry matter production and total N uptake occurred between fertilized and unfertilized treatments, but not among the different placements studied. In contrast, fertilizer ¹⁵N uptake efficiency (F¹⁵NUE) tended to be greater for either type of subsurface banding than for the dribble treatment, demonstrating the added sensitivity that can be achieved through isotopic measurements. More importantly, band placement consistently outperformed broadcasting, according to estimates of F¹⁵NUE for total aboveground biomass that ranged from 11% to 46% when UAN was banded and from 7% to 34% for broadcast applications.