Interactions of High Temperature and Exposure Time Influence Nitrification in a Pine Bark Medium

Pine bark-filled containers periodically fertilized with NH 4 -N were heated from 21C to 28, 34, 40, 46, or 52C for daily exposures of 1, 2, 4, 6, or 24 hours over 20 days. Concentrations of NH 4 -N and NO 3 -N in medium solution extracts were determined every 5 days. Medium solution NH 4 -N concentration was higher at constant (24 hours) exposure to 40C than at lower temperatures or exposure times. There was a similar increase in NH 4 -N concentration for a 2-hour·day –1 exposure to 46C, with further increases in NH 4 -N for longer exposure times. By day 10, NH 4 -N concentration was highest after 1 hour·day –1 exposure to 52C. Decreases in medium solution NO 3 -N concentration generally coincided with the increases in NH 4 -N. These results indicate that container medium thermal periods, similar to those observed in nurseries of the southern United States, may inhibit nitrification, thereby influencing NH 4 -N: NO 3 -N ratios in the medium solution of plants fertilized with predominantly ammoniacal N sources.