No abstract

Nutrient concentrations in soil solutions near the surface and below the root zone were measured for 8 months after fall application of urea (448 kg N/ha) to four soils under second‐growth forest in southwestern British Columbia. Surface soil solution pH increased due to ureolysis within a few days, while concentrations of some cations were reduced, with Ca and Mg decreasing more than K and Na. Nitrate concentrations peaked at least 3 months after fertilization. With pH decline accompanying nitrification in fertilized plots, concentrations of Ca and Mg increased substantially over concentrations in unfertilized control plots whereas K and Na showed smaller increases. Effects on Ca, Mg, K, and Na are consistent with interpretations based on pH‐dependent cation exchange capacity and Donnan equilibria. Maximum total N, NO3‐N, and Ca concentrations below the root zone were 11.2, 11.0, and 10.0 mg/liter, respectively, and occurred with a recently afforested, coarse‐textured soil which was low in incorporated organic matter and lacked a forest floor.

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.

No abstract

No abstract