Ammonium Adsorption on a Pine-bark Growing Medium

Pine bark was shown to adsorb 1.5 mg of N/g of bark when NH 4 solutions were leached through the bark. Increasing pH of bark increased adsorbed NH 4 . At pH 3.3, only NH 4 was adsorbed to bark particles when a fertilizer solution containing NH 4 , Ca, K, and Mg was applied. However, adsorption of NH 4 and other cations increased as pH was increased from 3.8 to 5.8. These data indicate that 2 types of sites exist for the adsorption of NH 4 to pine bark. One site is effective at lower pH; the other is active as pH increases. Daily application of 2.5 cm of water containing 50 ppm NH 4 required 20 days for equilibration to occur so as to satisfy all binding sites. Thus, incorporation of NH 4 into a pine-bark medium prior to planting may be advisable to prevent low N levels from occurring in the container solution due to NH 4 binding when plants are first planted and fertilized.