Fate of 15N-Depleted Ammonium Nitrate Applied to No-Tillage and Conventional Tillage Corn
1984
Kitur, B. K. | Smith, M. S. | Blevins, R. L. | Frye, W. W.
Crop recovery and soil immobilization of fertilizer N under two different tillage systems was observed in a 3-year study. Corn (Zea mays L.) was fertilized with 84 or 168 kg N ha⁻¹ as ¹⁵N-depleted NH₄NO₃. Nitrogen was surface applied as a solution on a Maury silt loam soil (fine , mixed, mesic Typic Paleudalfs). There was no mechanical disturbance of the soil in the no-tillage treatment (NT); conventional tillage (CT) consisted of spring plowing and disking. Grain yields with NT tended to be lower than yields with CT at the low N rate but equal or greater at the high N rate. However, these differences were not statistically significant. In 1980 fertilizer recovery in grain was 21 vs. 38 kg N ha⁻¹ for NT and CT, respectively, at the low N rate. At the high N rate, N recovery by corn grown under NT and CT was not significantly different. Results were similar in 1981. After adding I5N-depleted fertilizer to the same plots for 3 years, 71 to 75% of the fertilizer was accounted for in harvested grain, stover, or soil. Neither tillage nor N rate had a large effect on the fraction of fertilizer N missing and presumed lost by denitrification and leaching. Nitrogen fertilizer remaining in the NT soil was 42% of that applied at the low fertilizer rate and 39% of that applied at the high N rate. In the CT plots apparent immobilization was 28 and 37% for the low and the high N rate, respectively. Approximately one-half of the N apparently immobilized was located in the surface 5 cm of the NT soil, but immobilized N was more uniformly distributed in the top 30 cm of the CT soil. Increased immobilization of N at the surface of the NT soil seems to be the most likely explanation for reduced crop recovery of fertilizer with NT at low N rates.
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