Effect of urea fertilizer on leaching of micronutrient metals and aluminum from forest soil columns

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Abstract
The effects of urea fertilization (0, 112, and 448 kg N/ha) on N transformations, pH, and leaching of Al, Cu, Fe, Zn, and Mn from Ap horizon material of a scarified forest plantation soil were studied in the greenhouse for 15 weeks. Replicated tension lysimeter columns were used, in which seedlings of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and western hemlock (Tsugaheterophylla (Raf.) Sarg.) were grown. Large amounts of the metal elements were released from columns treated with 448 kg N/ha. Amounts released with the 112 kg N/ha treatment were not significantly different (0.05 level) from the controls. Maximum leaching of Cu and Fe occurred soon after urea application, apparently because of mobilization of metal–organic complexes. In contrast, the major Mn and Zn leaching losses occurred later, effected by the increased acidity caused by nitrification. Al leaching showed a pronounced early peak and a large late peak, and apparently was strongly influenced by both mechanisms.