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

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Abstract
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 rate/split), 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 rate/split) > 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.

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