Residual Nitrogen-15 Recovery by Corn as Influenced by Tillage and Fertilization Method
Timmons, D. R. | Cruse, R. M.
Tillage systems that create different surface residue conditions may also affect the recovery of residual fertilizer N during subsequent growing seasons. This study evaluated the recovery of residual labeled N fertilizer in the soil by corn (Zea mays L.) for two tillage systems and two fertilization methods. Five atom % ¹⁵N-enriched 28% urea-ammonium nitrate solution (UAN) at 224 kg N ha⁻¹ was either surface-applied in the fall before any primary tillage or banded (knifed in) just before planting in the spring. Continuous corn was grown with either fall moldboard-plow (MP) or ridge-till (RT) systems. After the initial growing season, the recovery of residual labeled N in the soil by corn was determined for three consecutive growing seasons, and the soil profile was sampled periodically to measure residual ISN in the organic and inorganic pools. One year after labeled UAN application, from 16 to 27% of the initial I5N applied was found in the organic N pool and only 1% as inorganic N[NH₄ + (NO₂ + NO₃)-N]. After four seasons, residual ¹⁵N in the organic N pool ranged from 13 to 24%. Less than 0.5% remained as inorganic N. Regression analyses indicated that about ¹⁵N ha⁻¹ yr⁻¹ became available for both MP and RT systems with banded N, so the amounts were small. Total residual I5N recovery by corn grain plus stover for three seasons ranged from 1.7 to 3.5%, and was greatest for spring-banded fertilizer (p = 0.01). Because the amounts of residual ¹⁵N utilized were too small to affect corn growth, this N source appears to be negligible when considering corn-N needs. Joint contribution: The National Soil Tilth Laboratory, USDA-ARS, and Journal Paper no. 5-13756 of the Iowa Agriculture Home Economics Experiment Station. Project no. 2445.
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