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

in HortScience
Authors:
Ronald F. WaldenHampton Roads Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University, Virginia Beach, VA 23455-3363

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Robert D. WrightDepartment of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0327

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Pine bark-filled containers periodically fertilized with NH4-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 NH4-N and NO3-N in medium solution extracts were determined every 5 days. Medium solution NH4-N concentration was higher at constant (24 hours) exposure to 40C than at lower temperatures or exposure times. There was a similar increase in NH4-N concentration for a 2-hour·day–1 exposure to 46C, with further increases in NH4-N for longer exposure times. By day 10, NH4-N concentration was highest after 1 hour·day–1 exposure to 52C. Decreases in medium solution NO3-N concentration generally coincided with the increases in NH4-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 NH4-N: NO3-N ratios in the medium solution of plants fertilized with predominantly ammoniacal N sources.

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