Urea Fertilizer Effects on Dissolved Nutrient Concentrations in Some Forest Soils

Abstract

AbstractNutrient 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.