INORGANIC NITROGEN LEVELS AND NITRIFICATION POTENTIAL IN LOWBUSH BLUEBERRY SOILS

Abstract

Soil ammonium and nitrate in the top 15 cm of soil were monitored after application of ammonium nitrate and ammonium sulfate to plots at 14 PF (previously fertilized) and 12 NF (never fertilized) lowbush blueberry (Vaccinium angustifolium Ait.) stands representing a range of soil types and management histories. Overall, nitrate values in unfertilized and ammonium sulfate plots were higher at PF than at NF sites, suggesting greater nitrification at PF sites. In laboratory incubation studies, nitrification proceeded immediately in soil from a PF site, but only after a 4-wk lag in that from an adjacent NF site. Nitrification rates were low compared to that in a garden soil (pH 6.6). N-Serve inhibited nitrification in both soils. In ammonium nitrate plots, "excess" N values (N values in fertilized plots minus values in unfertilized plots) were higher for PF than for NF sites, suggesting greater immobilization, plant uptake or loss of N at NF sites. There was no evidence, in laboratory studies, of immobilization of added N by soil from either type of site. Rhizome N concentration increased significantly in response to fertilization at an NF site, but not at a PF site. Key words: Blueberry (lowbush), fertilizer and soil nitrogen