Retention and Spatial Distribution of Mineral Nitrogen in the Forest Floor of an Aerially Fertilized Watershed
Abstract:A small, 113 ha forested watershed in New Brunswick was fertilized with 115 kg-N/ha ammonium nitrate (NH4NO3) using fixed-wing aircraft. Eight weeks later, the forest floor of the entire basin was sampled systematically and the NH4- and NO3-N contents of the forest floor were determined. At this time the forest floor had received 36 mm of precipitation, and contained about half of the applied NH4-N fertilizer (i.e., 22.7 kg-N/ha, or 407 ppm), but lateral displacements by runoff of the NH4+-ions following the topographic drainage patterns had not occurred. The nitrate content of the forest floor was more mobile and, therefore, more variable than NH4-N, because the NO3-N contents were 6.4 N-kg/ha (or 96.2 ppm). Lateral NO3-N runoff displacements also occurred because the spatial NO3-N/NH4-N ratio distribution varied about its mean value of 0.36 from 0.0 to 6.0. The fertilizer distribution patterns resulted in positively skewed histograms which could be fitted with a two-parameter gamma distribution model. This model predicts that (i) improvements in fertilizer uniformity should be obtainable by repeated fertilizer applications each involving the entire target area, (ii) the observed spatial fertilizer distribution pattern, within limits, should be independent of the size and shape of the forest floor samples examined for fertilizer content. Forest Sci. 28:613-626.
Keywords: Gamma distribution model
Document Type: Journal Article
Affiliations: Member of the Faculty of Forestry, University of New Brunswick, Fredericton, N.B. E3B 5A3, Canada
Publication date: 1982-09-01
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