Effects of Time, Temperature, and Nitrogen Source on the Composting of Hardwood Bark for Use as a Plant Growing Medium1

Hardwood bark, amended with either urea (CO(NH 2 ) 2 ) or ammonium nitrate (NH 4 NO 3 ) was composted in 210 liter drums at 10 to 40°C or heated to 55°. In the supplemental heat composted (SHC) bark amended with CO(NH 2 ) 2 , pH increased to 6.8 to 7.4 within the first week. Bark amended with CO(NH 2 ) 2 generated more heat than bark amended with NH 4 NO 3 . Phenolic content decreased (as indicated by the Folin-Ciocalteu (F-C) method), and germination percentage of Lactuca sativa L. cv. Grand Rapids seed in water extracts of bark samples increased with time. Additions of polyvinylpyrrolidone (PVP) to extracts decreased phenolic content and increased the percentage of seed germination. Plant growth assays using Chrysanthemum × morifolium Ramat ‘Bright Golden Anne’ revealed a possible N deficiency in SHC NH 4 NO 3 treated bark. Plants grown in SHC CO(NH 2 ) 2 amended bark did not have as severe a N deficiency. As time of composting increased, naturally composted (NC) bark treated with either N source gave plant growth comparable to that of the control plants grown in a medium of peat:perlite:vermiculite:soil (3:2:2:1 v/v).