Long-term effects of nitrogen fertilization on nitrogen availability in coastal Douglas-fir forest floors

• Published in: Soil Science Society of America journal Vol. 63; no. 5; pp. 1448 - 1454
• Main Authors: Chappell, H.N, Prescott, C.E, Vesterdal, L
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01.09.1999; Soil Science Society of America; American Society of Agronomy
• Subjects: Agronomy. Soil science and plant productions; biogeochemical cycles; Biological and medical sciences; carbon nitrogen ratio; chemical constituents of plants; fertilized versus unfertilized soils; Fertilizers; forest litter; forest soils; Forests; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; gradients; leaf fall; long term experiments; mineralization; nitrification; Nitrogen; nitrogen content; Nitrogen fertilization; nitrogen fertilizers; nitrogen turnover rate; Nitrogen, phosphorus, potassium fertilizations; nutrient availability; Pseudotsuga menziesii; soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Soils; Oregon; Washington; United States; North America; America; Nitrogen fertilization; Long term test; Soil fertility; Forest soil; Inorganic element; Pseudotsuga menziesii; Coastal zone; Mineralization; Softwood forest tree; Gymnospermae; Secondary forest; Turnover; Nitrogen fertilizer; Litter; Alfisols; Bioavailability; Nitrogen; Long term; Residual effect; Nitrogen cycle; Regional study; Coniferales; Spermatophyta; Inceptisols; Spodosols
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj1999.6351448x

It has been suggested that a long-term increase in N availability could be achieved by repeated N fertilization of forests, and that the increase in N availability would be greatest at initially N-rich sites. The aim of this study was to determine if N availability was elevated 8 to 12 yr after repeated N fertilization, and if the effects of N fertilization were related to the soil N capital. Rates of N cycling in control and fertilized plots of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] were compared by measuring net N mineralization rates in forest floors and by estimating rates of N turnover from the litterfall/forest floor ratio. Litterfall N contents, litter N concentrations, and rates of N turnover increased along the gradient in soil N capital in both control and fertilized stands. Fertilization did not affect litterfall N content, but C/N ratios of litter and forest floors were significantly lower in fertilized stands along the gradient. Turnover rates of N in the forest floors were not higher in fertilized plots than in control plots, nor were rates of net N mineralization affected by fertilization. Net nitrification rates were higher in some of the plots that received 1120 kg N ha(-1) than in control plots. We conclude that N fertilization did not result in a sustained increase in N cycling and N availability analogous to a higher site N capital, and that the effect of N fertilization was not related to the initial soil N capital of these sites.