Canadian Forest Service Publications
Mechanisms of response to fertilization. I. Fate of nitrogenous fertilizers. 1991. Marshall, V.G. Pages 51-75 in J.D. Lousier, H. Brix, R. Brockley, R. Carter, and V.G. Marshall, Editors. Improving forest fertilization decision-making in British Columbia, Proceedings: Forest Fertilization Workshop. March 2-3, 1988, Vancouver, BC. BC Ministry of Forests, Victoria, BC.
Issued by: Pacific Forestry Centre
Catalog ID: 4772
Availability: Order paper copy (free)
Nitrogen is deficient in many forest soils in the temperate region. Such deficiencies are often alleviated by the addition of nitrogenous fertilizers, notably urea and ammonium nitrate. These two fertilizers, with contrasting characteristics in their breakdown products, are useful in demonstrating the various pathways that nitrogenous fertilizers might take in a forest ecosystem. The major pathways include losses from the ecosystem, soil immobilization, and plant uptake. Only a small portion of the applied fertilizer (about 5-20%) is initially taken up by the crop tree, and because of tight internal cycling within the soil, the immobilized portion is released extremely slowly. Main sources of loss are erosion (<1%), runoff (<1%), volitilization (about 25% mainly from urea), leaching (8-78%), and biological and chemical denitrification (5-27%). Soil immobilization is usually greater with urea and other ammonium-N fertilizers; nitrate-N fertilizers are subject to greater leaching losses. Since initial plant uptake greatly influences subsequent tree growth, nitrate-N fertilizers give better immediate biological responses, but are not necessarily the best management choice. Factors responsible for the transformation and movement of nitrogenous fertilizers, management options to improve crop-tree uptake and research problems related to fertilizer efficiency are discussed.