Nitrification in a pine bark medium in response to a range of applied NH4-N levels (25, 100, and 200 ppm) was studied. Medium solution NH4-N concentrations at the 25 ppm N treatment decreased from 30 ppm at day 1 to 0 ppm at day 40. Ammoniacal-N concentration values decreased from 64 to 6 ppm and from 105 to 20 ppm for the 100- and 200-ppm N treatments, respectively, by day 60. Rapid increases in medium solution NO3-N concentrations coincided with these NH4-N decreases, resulting in low medium solution NH4-N:NO3-N ratios. During the periods of NO3-N increase, medium solution pH decreased 0.3, 0.7, and 1.3 units for the 25-, 100-, and 200-ppm N treatments, respectively. Similarly treated bark without plants was used to determine a NO3-N accumulation rate (NAR). NAR data indicated that the NH4-N supply of the 100- and 200-ppm N treatments exceeded the oxidative capacity of nitrifiers during a 96-hr period.
Graduate research assistant. Present address: Division of Agriculture, Arizona State Univ., Tempe, AZ 85287.
Received for publication 11 Mar. 1986. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.