The Influence of Nitrification on the Medium Solution and Growth of Holly, Azalea, and Juniper in a Pine Bark Medium

Abstract

Three genera of woody plants were container-grown in a pine bark medium. Pine bark was amended or unamended with nitrapyrin (NI) and fertilized with an NH 4 -N fertilizer. Medium solution NH 4 -N concentrations of bark without NI decreased rapidly for the first 3 to 5 weeks with a concomitant increase in NO 3 -N concentrations. Medium solution pH at 0 NI decreased 0.8 unit during periods of rapid NO 3 -N accumulation. The low medium solution pH of the 0 NI treatment resulted in solution Ca, Mg, and Mn concentrations that were several times greater than at 82 μg of NI. Correspondingly, tissue concentrations of these ions were generally greater at the 0 NI treatment than at the 82 μg NI treatment. In general, there were no differences in shoot dry weight in response to NI treatment. Results indicate that nitrification is important in the nutrition of container-grown plants.