Douglas-fir soil C and N properties a decade after termination of urea fertilization

• Published in: Canadian journal of forest research Vol. 31; no. 12; pp. 2225 - 2236
• Main Authors: Homann, P.S, Caldwell, B.A, Chappell, H.N, Sollins, P, Swanston, C.W
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.12.2001; National Research Council of Canada; Canadian Science Publishing NRC Research Press
• Subjects: Agronomy. Soil science and plant productions; Ammonium; ammonium compounds; application rate; Biological and medical sciences; Carbohydrates; Carbon; Cations; cellulases; Chemical properties; Coniferous forests; Coniferous trees; Decomposition; degradation; Enzymatic activity; enzyme activity; Evergreen trees; Fertilizers; Forest ecosystems; Forest productivity; Forests; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; ion transport; Land use; Litter; Microbial activity; microorganisms; mineral soils; nitrates; Nitrification; Nitrogen; Nitrogen fertilization; Nitrogen, phosphorus, potassium fertilizations; nutrient availability; Organic matter; phosphoric monoester hydrolases; Pine trees; placement; Pseudotsuga menziesii; R&D; Research & development; Residual soils; Respiration; soil fertility; soil microorganisms; soil organic matter; Soil pH; Soil profiles; Soil properties; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Soils; Urea; Oregon; Washington; United States; North America; America; Nitrogen fertilization; Organic matter; Inorganic fertilizer; Forest soil; Nitrogen; Inorganic element; Carbon; Pseudotsuga menziesii; Urea; Softwood forest tree; Gymnospermae; Coniferales; Spermatophyta; Nitrogen Organic compounds; Nitrogen fertilizer; Coniferous forest
• ISSN: 0045-5067; 1208-6037
• DOI: 10.1139/x01-162

Chemical and microbial soil properties were assessed in paired unfertilized and urea fertilized (>89 g N(.)m-2) plots in 13 second-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands distributed throughout western Washington and Oregon. A decade following the termination of fertilization, fertilized plots averaged 28% higher total N in the O layer than unfertilized plots, 24% higher total N in surface (0-5 cm) mineral soil, and up to four times the amount of extractable ammonium and nitrate. Decreased pH (0.2 pH units) caused by fertilization may have been due to nitrification or enhanced cation uptake. In some soil layers, fertilization decreased cellulase activity and soil respiration but increased wood decomposition. There was no effect of fertilization on concentrations of light and heavy fractions, labile carbohydrates, and phosphatase and xylanase activities. No increase in soil organic C was detected, although variability precluded observing an increase of less than approximately 15%. Lack of a regionwide fertilization influence on soil organic C contrasts with several site-specific forest and agricultural studies that have shown C increases resulting from fertilization. Overall, the results indicate a substantial residual influence on soil N a decade after urea fertilization but much more limited influence on soil C processes and pools.