Fertilizer Management Effect on Recovery of Labeled Nitrogen by Continuous No-Till

Improved fertilizer N management with respect to placement and timing is especially important in high-residue systems designed to improve N-use efficiency and to speed adoption of erosion controlling tillage practices. By means of point-injection technology, fertilizer solutions now can be applied and soil-incorporated with minimal disturbance of surface residue or existing plants. This study was conducted in large non-weighing lysimeters (with reconstituted soil horizons) to determine the recovery of ¹⁵N -labeled urea-ammonium nitrate (UAN) solution by continuous no-till corn (Zea mays L.) during the initial year of application and two subsequent years for four N management systems. The UAN solution was point-injected in split applications at rates of 125 or 200 kg N ha⁻¹, or knifed-in or surface-banded right after plant emergence at 200 kg N ha⁻¹. For the initial year of ¹⁵N application, the percent recovery of labeled N (NR) in grain was 48, 39,33, and 30% for point-injected (low ratehplit), point-injected (high rate/split), knifed-in, and surface-banded, respectively. The percentage of total grain N derived from labeled N (NF) ranged from 57 to 67% and was in the order of point-injected (high ratehplit) > knifedin > point-injected (low rate/split) > surface-banded. Residual labeled N recovery in grain ranged from 2.3 to 4.6% for the second season and from 0.9 to 1.0% for the third season with no significant differences among application treatments for either season. After five seasons the NR values for labeled N determined in the soil N pool still ranged from 20 to 26%. UAN solution applied in split applications with the point injector was used more efficiently by corn than when knifed-in or surface-banded in a single application, indicating the point-injection/split application system is an option for improved N management in no-till corn. Joint contribution: The National Soil Tilth Laboratory, USDA-ARS, and Journal Paper no. 5-14221 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Project no. 2445.